STUDIES ON THE MECHANISM OF AROMATIC ALKY NATIONS
PAR T A:

THE PREPARATION AND P R O PE R TI ES OF
2,6-DI- TERTIARY-BUTYLPHENOL

P A R T B:

KINETIC STUDIES OF THE ALKYLATION OF
PHENOLS WITH TERTIARY HALIDES

P A R T C:

THE MECHANISM OF THE INHIBITION OF
PHENOL ALKYLATIONS BY OXYGENATED
COMPOUNDS

By
F r a n k A. C a s s i s , J r .

AN ABSTRACT
Submitted to the School of G ra du ate Studies of Michigan
State College of A g r ic u l t u re and Applied Science
in p a r t i a l fulfillm en t of the r e q u i r e m e n t s
for the degr ee of
DOCTOR OF PHILOSOPHY

D e p a r t m e n t of C h e m i s t r y

Year

Approved

1953

F R A N K A. C A S S I S , J R .

ABSTRACT

A kinetic study of the u ncatalyzed alkylation of phenol was f i r s t
r e p o r t e d in 1949 (1).

The p r e s e n t in v est ig ati on i s c o n c e rn e d with

f u r t h e r elucidation of the m e c h a n i s m of this
following e x p e r i m e n t a l ap p ro ach es:

r eaction , using the

(a) a study of the effect of

l a r g e ortho alkyl groups on the p r o p e r t i e s and p a r a r e a c t iv i t y of
the phenol molecule; (b) a detailed kinetic a n a l y si s of the alkylation
of phenol with triph en y lm e th y l chloride in dilute solution and in an
i n e r t solvent; and (c) an investigation of the kin e tic s and m e c h a n ­
i s m of the r e p o r t e d inhibition of phenol alkylations by oxygenated
compounds (1, 2).
2 , 6 - Di-t-butylphenol was p r e p a r e d by the alkylation of p - b r o m o phenol with an e x c e s s of isobutylene, followed by redu ctive d e b r o m i n a tion with Raney N ick el -A lu m in um alloy in alkaline solution.

This

phenol p o s e s s e d a s t e r i c a l l y h in d e re d phenolic hydroxyl group, the
p r e s e n c e of which was d e m o n s t r a t e d by its complete insolubility in
Cla is e n solution, and by the position of the i n f r a r e d hydroxyl a b s o r p ­
tion band a t 2 . 7 6 |j l .

The r a t e s of p a r a b r o m i n atio n and diazonium

coupling f o r this compound w e re found to be negligible when c o m ­
p a r e d to those f o r 2,6-xylenol.

This is a t t r ib u t e d to the g r e a t e r

s t e r i c inhibition of the c u s t o m a r y p a r a activating r es o n a n c e of a

F R A N K A. CASSIS, J R .

ABSTRACT

hydroxyl group by the bulky t e r t i a r y butyl g ro ups .

A tte mp ted n i t r a ­

tions of 2 , 6 -d i- t- b u ty lp h e n o l r e s u l t e d in e i t h e r cleavage of a t e r t i a r y
butyl group to give 2 , - 4 - d i n i t r o - 6 - t-butylphenol, or, u nder m i l d e r
conditions, oxidative coupling to 3, 3', 5,5 ' - t e t r a - t-buty ld iph en oq uino ne.
Relative r a t e s of p a r a t e r t i a r y butylation at 50° w e re d e t e r ­
m i n ed f o r phenol, o - c r e s o l , m - c r e s o l , £ - c r e s o l , o_-t-butylphenol,
2,6-xylenol, and 2 , 6 -d i-t -b ut ylp hen ol .

The r e a c t i o n was c a r r i e d out

using the phenol to be alkylated in l a r g e e x c e s s , and was followed
by a bs or bing the evolved hydrogen chloride in sodium b ic a r b o n a te
tubes followed by Volhard an al ysi s f o r the chloride ion.

The a l k y l a ­

tion r a t e d e c r e a s e d m a r k e d l y as the size a n d / o r n u m b e r of ortho
su bst it ue nts was i n c r e a s e d .

This in dicate s th at the f o r m a t i o n of the

r e a c t i o n t r a n s i t i o n state und er the conditions employed is l e s s favore
when the phenolic hydroxyl group is s t e r i c a l l y hindered.
A p r e c i s e kinetic study of the alkylation of phenol and o_-cresol
with trip h en y lm e th y l chloride was made in oy dichlorobenzene at 88° .
The r e a c t i o n was r e ad ily followed by m e a s u r i n g the i n c r e a s e in p r e s
s u r e of evolved hydrogen chloride at v a r i o u s t im e i n t e r v a l s in a
c o n s t a n t -v o l u m e

s yst em .

F R A N K A. CASSIS, J R .

ABSTRACT

It was found that the r e a c t i o n was a u t o - c a t a l y z e d by the product,
hydrogen chloride.

When this m a t e r i a l was in t ro d u c ed initially, o v e r ­

all t h i r d o r d e r k in e tic s w e r e o bs er ve d, the r e a c t i o n being f i r s t o r d e r
e ac h in phenol, t r i ty l ch lorid e, and the hydrogen ch lorid e.

A m ath ­

e m a t i c a l a n a l y s i s of the a u t o - c a t a l y z e d r e a c t i o n s d e m o n s t r a t e d that
the alkylation r a t e was

s a t i s f a c t o r i l y e x p r e s s e d by the t w o - t e r m

equation:

= k^fphenol^halide] + k^[phenol][halide][hydrogen chloride]
The v alu es of k
expression.

0

and k

I

w e re d e t e r m i n e d g r a p h ic a l ly f r o m the above

These c ons tan ts w e r e u s ed to obtain ca lc ula te d values

of the r e a c t i o n p r e s s u r e

at v a r i o u s t i m e s , which w e re in ex ce llen t

a g r e e m e n t with the e x p e r i m e n t a l values o v e r the e n t i r e

r eaction .

The

k^ value was o b s e r v e d to d e c r e a s e m a r k e d l y in going f r o m phenol
to o_-cresolj how ever, the k^ value f o r the l a t t e r a p p r o a c h e s that
obtained f o r the u n s u b st it ute d phenol.
sition state r e q u i r e s m a x i m u m

This in di ca te s tha t the t r a n ­

s t e r i c f r e e d o m of the hydroxyl group

f o r the u ncat aly ze d p o r t i o n of the alkylation.
A. c a r b o n i u m ion m e c h a n i s m involving p r e l i m i n a r y solvation of
the halide by the phenolic hydroxyl group, o r by the hydrogen chloride

4
F R A N K A. C A S S I S ,.J R .

ABSTRACT

when p r e s e n t , was shown to be c o n s i s t e n t with all the o b s e r v e d
f ac ts .

The p o s s i b i l i ty of phenyl t r i ty l e t h e r as an i n t e r m e d i a t e ,

followed by acid cata ly ze d r e a r r a n g e m e n t to the alkylated phenol
was shown to be untenable.
A. p r e c i s e kinetic study was also made of the in hibitory effect
of varying amounts of dioxane and t e t r a h y d r o p y r a n on the alkylation
of phenol by t-butyl chloride at 50°.

This inhibition is a p p a re n tly

due to the f o r m a t io n of oxonium type complexes between the e t h e r
added and the hydroxyl group of the phenol, which d e c r e a s e s the
amount of phenol available f o r p a r t i c ip a t i o n in the alkylation p r o c e s s .
A. c o m p a r i s o n of the o b s e r v e d r ea c t io n half t i m e s and those
c a l cu la t e d f o r a 2:1 phenol-dioxane com plex w e re in e xc e l le n t a g r e e ­
ment.

Accordingly, the mono-functional t e t r a h y d r o p y r a n was o b s e r v e d

to give only half as m u c h inhibition p e r mole as that obtained f o r
diox an e.

Refe r ence s

1.

H. H a r t and J. H. Simons, J. Am. Chem. Soc., 71, 345 (1949).

2.

J. J. Bordeaux, M.S.

Thesis, Michigan State College (1949).

STUDIES ON THE MECHANISM OF AROMATIC ALKYLATIONS
PAR T A:

P AR T B:

P A R T C:

THE PREPARATION AND P RO PE R TI ES OF
2,6-D I-T ERTIA RY -B UTY LP HEN OL
-a*
KINETIC STUDIES OF THE ALKYLATION OF
PHENOLS WITH TERTIARY HALIDES
THE MECHANISM OF THE INHIBITION OF
PHENOL ALKY LA TION S BY OXYGENATED
COMPOUNDS

By
FRANK A. CASSIS, JR.

A THESIS
Submitted to the School of G r ad uate Studies of Michigan
State College of A g r i c u l tu r e and Applied Science
in p a r t i a l f ulf illm en t of the r e q u i r e m e n t s
f o r the d eg ree of

DOCTOR OF PHILOSOPHY

D e p a r t m e n t of C h e m i s t r y

1953

ProQuest Number: 10008471

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ACKNOWLEDGMENTS

The author would like to e x p r e s s his s i n c e r e a pp r e c i a ti o n to
Doctor H a r old H a r t f o r his aid, guidance, and i n t e r e s t throughout the
c o u r s e of this inv estig atio n and during the p r e p a r a t i o n of this m a n u ­
script.
He also w i s h e s to e x p r e s s his g ratitu de to the R e s e a r c h C o r ­
p o r a t i o n of New York f o r a F r e d e r i c G a r d n e r C o t t re l l r e s e a r c h g r a n t
which financed the m a j o r i t y of this work,

and to his wife, Betty, f o r

h e r p a t ie n t aid and e n c o u r a g e m e n t during the completion of this t h e s i s .

ii

359314

TABLE OF

CONTENTS

P age
INTRODUCTION
HISTORICAL
P A R T A:

P AR T B:

1

................................................................................................

THE PREPARATION AND P RO PE R TI ES OF
2,6-D I-T ER TIA R Y -B U TY LPH EN O L

22

Experimental

23

D i s c u s s i o n ..............................................................................

36

KINETIC STUDIES OF THE ALKYLATION
OF PHENOLS WITH TERTIARY HALIDES . .

46

Experimental

47

R es ults and Calculations
D i sc us si on

.

.

M e c h a n i s m ..................
P ART C:

63
86
92

THE MECHANISM OF THE INHIBITION OF
PHENOL ALKY LA TIONS BY OXYGENATED
COMPOUNDS ..............................................................................

100

Experimental

101

R es ult s and Calculations

10 4

D i sc u s si o n . .

116

S U M M A R Y ..................

121

BIBLIOGRAPHY

123

TABLES AND ILLUSTRATIONS

PAR T A
Figure

P ag e
1.

F i g u r e 2.

Figure

Figure

Table

3.

4.

1.

U l t r a v i o l e t A bsorption S p e c t r a of
H ind er ed P h e n o l s .............................................................
U l t r a v i o l e t A bsorption S p e c t r u m of
3, 3',5,5 T e t ra - t- b u t y l - p - d i p h e n o q u i n o n e

,

32

33

I n f r a r e d Absorption S p e c t ru m of
2, 6 - Di- t-butylphenol ...................................................

34

I n f r a r e d A bsorp tion S p e c t ru m of
2,6-D i-t-butylcyclohexanone

35

Effect of Alkylation Method on Yield
of 2 , 6 - D i - t- b u t y l - 4 - h a l o p h e n o l ...............................

37

PART B
Figure

1.

F i g u r e 2.
Table

1.

Table 2.

Figure

3.

A p par atu s f o r the M e a s u r e m e n t of
Relative Reaction Rates
. .....................................
The R a t e - D e t e r m i n i n g A p p a r atu s

50
51

Relative R ates of Alkylation of
Substituted P h e n o ls with
t -B u ty l C h l o r i d e .................................................................
Kinetic Studies of the Alkylation of
P h en o ls with Triphenyl methyl Chloride
. . . . . . .
in o^-Dichlorobenzene at 88°
P r e s s u r e v e r s u s Time C u rv es f o r
Some Alkylation E x p e r i m e n t s
..............................

iv

64

66

67

P age
F i g u r e 4.

F i g u r e 5.

F i g u r e 6.

F i g u r e 7.

Figure

8.

F i g u r e 9-

Figure

10.

Application of Kinetic Data to a
T h i r d - O r d e r Rate Equation ...............

70

Application of Kinetic Data to a
S e c o n d - O r d e r Rate Law
.....................

73

C o m p a r i s o n of C a lcu lated Rate
Curve f r o m A p pr ox im ated Constants
and O b s e r v e d Rate Curve ............................

74

A dherence of A uto -C a ta ly ze d Reaction
to a T w o - T e r m Rate E q u a t i o n .....................

79

C o m p a r i s o n of Calculated Curve f r o m
P r e c i s e Rate Constants and E x p e r i ­
m e ntal Rate C u r v e ...........................................

81

A dherence of C atalyzed Alkylation
to a T h i r d - O r d e r Rate L a w ......................

83

V ariatio n of Rate Constants with
Log of P henol C oncen trati on
. . . .

85

PART C
Figure

Table

1.

1.

F i g u r e 2.

Table 2.

P r e s s u r e v e r s u s Time Cu rves
f o r Some Inhibition E x p e r i m e n t s

105

Kinetic Data f o r the Alkylation of
P h e no l in the P r e s e n c e of
Oxygenated Compounds .........................

106

Adherence of Inhibition Data to a
F i r s t - O r d e r Rate Law
.......................................

109

S u m m a r y of C alcu lated and O b s e r v e d
H a l f - T i m e s f o r the Various Alkyla­
tion E x p e r i m e n t s ..............................................

Ill

3.

Y a r i a t i o n of Reaction H a l f - T i m e s
with Mol Ratio of Dioxane to Phenol

F i g u r e 4.

V a r ia tio n of Reaction H a l f - T i m e s
with Mol Ratio of T e t r a h y d r o p y r a n
to Phenol
............................................................

Figure

TO MY MOTHER

vii

INTRODUCTION

The alkylation of the a r o m a t i c nucleus has long been an i m ­
p o r ta n t p r o c e s s to the organic c hem is t.

Although s e v e r a l m e c h a n i s m

of alkylation have been p o s tu la t e d over the p a s t h a lf -c e n tu r y , t h e r e
have been only a r e l a t iv e l y few kinetic studies of the r ea ct io n .
The u ncatalyzed alkylation of phenol with t e r t i a r y halides,
d i s c o v e r e d in 1927 (1), conveniently p r o v id e s an ideal s y s t e m f o r a
kinetic study of the m e c h a n i s m of the alkylation p r o c e s s .

Such an

investig atio n was underta ken by H a r t and Simons in 1949 (2).

On

the b a s i s of t h e i r e x p e r i m e n t a l evidence th ese i n v e s t ig a t o r s indicated
the i m p r o ba bili ty of a high e n e r g y or simple ionic i n t e r m e d i a t e , and
p r o p o s e d i n s te a d what was t e r m e d as
fect."

" th e a m p h o t er ic m e d iu m e f ­

This effect depends in e s s e n c e on the a m p h o te ric p r o p e r ­

ti es of phenol f o r a o n e - s t e p condensed phase r e a c t io n quite s i m i l a r
in theory to the t e r m o l e c u l a r m e c h a n i s m s of L o w r y (3), which have
been m o r e f i r m l y e s t a b l i s h e d r e c e n t l y by Swain (4, 5).
The kinetic data obtained by H a r t and Simons did not, however
e n t i r e l y disqualify the p o s si b i li ty of a c ar bo niu m ion m e c h a n i s m f o r
the alkylation reac tio n .

In view of the i n c r e a s i n g evidence favoring

a c ar bo ni um ion i n t e r m e d i a t e in this and many oth er organic

reac­

tions, it was obvious th at additional e x p e r i m e n t a l evidence was n e c ­
e s s a r y in o r d e r to e s t a b l i s h a m e c h a n i s m f o r the alkylation r e a c ­
tion that was c o n s i s t e n t with all the known f a c ts .
This

study is t h e r e f o r e c o n ce rn e d with a f u r t h e r elucidation

of the m e c h a n i s m of this re a c t io n by thr ee e x p e r i m e n t a l a p p r o a c h e s .
First,

it a p p e a r e d d e s i r a b l e to synthesize phenols with l a r g e

alkyl groups in the ortho positions,

such as 2 , 6 - di- t-b utylp heno l, and

to study the effect of such groups on the r a t e of alkylation in the
p a r a position.

If the m e c h a n i s m w ere of the S^.1 type, then in an

equivalent o r identical solvent the r ate of alkylation should not be
g r e a t l y affected by the p r e s e n c e of l a r g e alkyl groups ortho to the
hydroxyl.

On the o t h e r hand,

should the r ea c t io n involve a c o n c e r t e d

m e c h a n i s m , p a r t i c u l a r l y one r e q u ir in g coordination of the phenol with
the halogen of the alkyl halide in the t r a n s i t i o n state (2), one would
expect a d e c r e a s e in the r a t e of p a r a alkylation due to s t e r i c hin­
d r a n ce of the hydroxyl group by the bulky ortho sub stituents.

Sev­

e r a l r e c e n t investigations have d e m o n s t r a t e d the la r g e s t e r i c effect
of such s ub stitu en ts on the r e a c t iv i t y and s p e c t r u m of the phenolic
hydroxyl group (6, 7, 8) .

In all these c a s e s , however, th e r e was a

sub st it ue nt p r e s e n t in the p a r a as well as the ortho position, t h e re b y
making a study of a r o m a t i c

substitution r e a c t i o n s i m p o s s i b l e .

Second, an ex am ination of the kinetic data r e p o r t e d by K a r t
and Simons indicated the need f or a kinetic an al ysi s of this
in dilute solution, and in an i n e r t solvent.

r eaction

This would p e r m i t the

d e t e rm i n a t io n of the p r e c i s e r a t e o r d e r with r e s p e c t to phenol, and
avoid v a r i o u s explanations that a r e n e c e s s a r y when the phenol is
p r e s e n t in e x c e s s as the r e ac tio n solvent.
Third, in p a r t i a l s u ppo rt of t h e i r c o n c e r t e d m e c h a n i s m H a r t
and Simons d e m o n s t r a t e d the inhibitory effect of dioxane on the a l k y l ­
ation of phenol.

Bo rd eau x (9) l a t e r showed that this inhibition was

p rob ab ly due to the f o r m a t i o n of a 1:1 oxonium complex between
phenol and dioxane of the type
CH -C H

/

\

\

/

O

o - - - - H-°^

CH2 -CH2

If the p r e s e n c e of an unhindered hydroxyl group is r e q u i r e d in the
tr a n s i t i o n state of the alkylation reac tio n, such a com plex would i n ­
deed account f o r the l a r g e inhibition observed.
In view of the b i- f un ctio nallity of dioxane, how ever, it was of
i n t e r e s t to in ve stigate the s t o ic h i o m e t ry and m e c h a n i s m of this i n ­
hibition in m o r e detail.

A r e - e x a m i n a t i o n of the kinetic method

u sed by B o r d ea ux c r e a t e d some doubt as to the a c c u r a c y of the

s t o i c h i o m e t r i c d e t e rm i n at io n , and indicated that m o r e p r e c i s e kinetic
data f o r the inhibition of phenol alkylations by dioxane w e re needed
in o r d e r to f i r m l y e s t a b l i s h the n a tu r e of the p os tu la te d oxonium
complex.

In addition, it s e e m e d advisable to ver ify the g e n e r a l it y

of the inhibition by extending this work to other oxygenated compounds.
The th r e e ap pr oa ch e s e n u m e r a t e d above have all been s a t i s ­
f a c t o r i l y completed.

F o r the sake of c l a r i t y in d e s cr ib in g the studies

c a r r i e d out and the b e a r i n g that they have on the alkylation m e c h a n ­
ism , this th e s i s has been developed in t hr ee e x p e r i m e n t a l

sections.

However, it should be pointed out that e ac h p a r t is an outgrowth of
the one p re ce di ng it, thus giving a s e r i e s of stepping stones leading
u lt i m a t e l y to an i n t e r p r e t a t i o n of the m e c h a n i s m of the u ncatalyzed
alkylation of phenol.

HIS TORICAL

A.

P r e p a r a t i o n and P r o p e r t i e s of H indered Pheno ls

The p r e p a r a t i o n of alkylated phenols is quite commonly a c c o m ­
p li sh e d through the well-known F r i e d e l and C r a f ts r e a c t i o n using
such c a t a ly s t s as aluminum chloride,
and o t h e r s .

sulfuric acid,

zinc chloride,

In m o s t c a s e s , however, the p r e p o n d e r a n c e of p ro du ct

is the p a r a s ubstituted phenol.

This o rien tatio n is even m o r e

strik­

ing when the alkylation is c a r r i e d out with t e r t i a r y halides or a l co ­
hols.
of

Indeed, H a r t has r ec e n t l y d e s c r ib e d , f o r example, a p r e p a r a t i o n
t-butylphenol in 90-95% yields by this method (10), and s e v e r a l

workers

(1,

12) have r e p o r t e d p rev io u s to this that the d i r e c t a lk y l­

ation of phenol was not s a t i s f a c t o r y f o r the s y n th es is of o - t - b u t y l p hen ol.
In 1934, how ever, Chichibabin (13) r e p o r t e d the sy nth es is of
s e v e r a l ortho alkyl phenols in good yields f r o m alcohols, phenols,
and a p ho sp h or ic acid ca ta ly st.

Although the alkylation of phenol

it se lf was not d e s c r i b e d by Chichibabin, p r e d o m i n a n t ortho s u b s t i t u ­
tion was r e p o r t e d f o r the benzylation and t e r t i a r y butylation of o_c re sol.

This unique o r ie n ta ti o n effect a t tr ib u t e d to the use of p ho sp hor ic

acid was r e - i n v e s t i g a t e d by H a r t and Haglund (14) in 1950 and the
6 - t - b u t y l - o - c r e s o l r e p o r t e d by Chichibabin was

shown to be the 4-

iso me r ,
Recently (15) the synthesis of o_-t-butylphenol was r e p o r t e d
in 70 p e r c e n t yields using the s ch em e which is outlined below:
OH

OH
(CH,)
3 3 Raney Ni-Al alloy^
Aqueous NaOH

Isobutylene^
H2S° 4
’
X

OH
-C-(CH )
3 3

-V '

X

+ NaX.

The r a n e y N ick el -A lu m in um alloy r eduction of the halogenated
intermediate,

c a r r i e d out in alkaline solution, p r ev e n t e d the r e a r r a n g e ­

m e n t of the o -t-buty lph en ol to the p a r a i s o m e r .
2, 6- D i-t-butylphenol has been r e p o r t e d by P a r d e e and Weinr i c h (16), and Stillson and Sawyer (17), the l a t t e r a ut ho rs being the
only ones to indicate its method of s yn thesis.

The p r o c e d u r e u sed was

quite s i m i l a r to that d e s c r i b e d above f or the o-t-butylphenol, except
that the reduction step was c a r r i e d out using p o t a s s i u m and liquid
am m on ia.

No indication of yield was given.

It mig ht be well to mention h e r e
the p r o p e r t i e s of h in d e r e d phenols.
2,4,6-tri-t-butylphenol

in

some p r e v io u s

studies on

Following t h e i r s y n th es is of

1945, Stillson, Sawyer, and Hunt (8) i n v e s ­

tig ate d the p r o p e r t i e s of this compound.

This phenol was found to be

insoluble in aqueous and alcoholic alkali and showed no c u s t o m a r y
phenol co lo ra tio n with e i t h e r aqueous or alcoholic f e r r i c ch lorid e.
T r e a t m e n t of the phenol, however, with a solution of phosphomolybdic
acid and am m o n iu m hydroxide yielded a deep blue color.

This te st ,

f i r s t developed by P l a tk o v s k a y a and Vatkina (18) in 1937, will det ec t
as li ttl e as one p a r t h i n d e r e d phenol in 8,500 p a r t s of alcohol.

All

a t te m p ts to p r e p a r e a deriva tive utilizing the c u s t o m a r y re ac tio ns of
the hydroxyl group failed, except f o r the f o r m a t i o n of a c r y s t a l li n e
benzoate by refluxing a hexane solution of the sodium salt of the
phenol (form ed in liquid a m m o n i a solution) with benzoyl chloride.
Shortly following the introduction of the c l a s s of compounds
known as the h in d e r e d phenols, Coggeshall (6) conducted a study
of th e se m a t e r i a l s in o r d e r to d e t e r m i n e the effect of ortho s u b s t i ­
tuents on the i n t e r m o l e c u l a r hydrogen bonding of phenols.

This p h e ­

nomenon is r ea d i ly r ec og ni ze d in the i n f r a r e d due to the f o r m a t io n of
an abs or pti on band at 3 . 0 [jl c h a r a c t e r i s t i c of hydroxyl g roups in such
c om plexes.

In dilute solution in n o n - p o l a r solvents, w here t h e r e is

little chance f o r hydrogen bonding to occur, only an ab so rp ti on band
a t 2.75|x is obtained which is c h a r a c t e r i s t i c of the u n p e r tu r b e d h y ­
droxyl group.

Consequently, a wave shift of 0 . 2 5 |jl is obtained f o r

phenol in going f r o m dilute to c o n c e n t r a t e d solution.

Cogge shall

p o s tu l a t ed that l a r g e alkyl gro up s ortho to the hydroxyl would s t e r ic a lly m i n im i z e i n t e r m o l e c u l a r hydrogen bonding and thereu po n r e ­
duce this wave shift, with the magnitude of the reduction being a
m e a s u r e of the hydroxyl hindrance by the ortho substituents p r e s e n t .
Various alky lated phenols w ere studied and divided into the following
c l a s s e s by v ir tue of the wave shift exhibited;
1.

Unhindered phenols.
Ex am ples :

2.

p - c r e s o l , 2 , 6 - d i m e t h y l - 4 -t-butylphenol

P a r t i a l l y hin de re d phenols.
Ex am p le s:

3.

Wave shift > 0 . 1 5p

2-methyl-4,6-di-t-butylphenol
2 - t-bu ty l - 4 -methylphenol

H in der ed phenols.
Example s :

Wave shift > 0.0 4p but < 0 . 15 |jl

Wave shift < 0. 0 4^

2, 6 - d i - t - b u t y l - 4 - methylphenol
2 , 6 - d i - s e c - b u t y l - 4 -methylphenol

The u l t r a v i o l e t a bs or pti on s p e c t r u m of o-t-butylphenol r e p o r t e d
by H a r t (15) is v e r y s i m i l a r to that of phenol, with m a x i m a of a l m o s t
identical extinction coefficients at 271 and 278m|a.

This was c o m p a r e d

to the s p e c t r u m of p - t- bu ty lp h en o l which is n e a r l y identical to that of
the ortho i s o m e r , ex ce pt that the e n t i r e s p e c t r u m is shifted by 6 mp
t ow a rd the r e d (peaks at 277 and 283 m p ) .

The s p e c t r u m of p - c r e s o l

as r e p o r t e d by Wolf and H erold (19) shows a s i m i l a r shift tow ard
the lo n g e r wavelengths, w h e r e a s iq-cresol has its m a x i m a at a l m o s t

identical wavelengths as phenol.
alkyl substituent,

This s p e c t r a l shift due to a p a r a

r e g a r d l e s s of its size, has been used as a c r i ­

t e r i o n f or s t r u c t u r e a s s i g n m e n t studies of alkylated phenols

(14),

Before concluding, it should be pointed out that all the p r e ­
vious in ve st ig ati on s have d e m o n s t r a t e d the effect of ortho s ubstituents
on the r e a c t i v i t y of the hydroxyl group and do not show what effect,
if any, the se

s ubstituents have on the usual ring activation by the

p o l a r hydroxyl group.

F o r this r eas on , a study of the s p e c t r a and

p a r a r e a c t iv i t y of a compound such as 2 , 6 - di-t -b ut ylph en ol would be
quite valuable and i n t e r es t in g .

B.

The M e ch an is m of A r o m a ti c Alkylation

A r o m a t i c n u c l e a r substitution has been divided into f r e e r a d i c a l
and ionic m e c h a n i s m s , with the l a t t e r subdivided into e l e c tr o p h il ic and
nucleophilic

r ea c t io n s .

The ionic e l ec tr op h il ic

substitutions have long

been the c e n t e r of attention, f o r in this c l a s s have b een p la c ed such
i m p o r t a n t r e a c t i o n s as nit ratio n, halogenation, acylation,

sulfonation,

and the r e ac tio n und er c o n s id e r a t io n h e r e , the F r i e d e l - C rafts a l k y l a ­
tion p r o c e s s .
Although few kinetic studies have b een made of the m e c h a n i s m
of a r o m a t i c alkylation, ionic i n t e r m e d i a t e s ,

such as those usually

10
a s s o c i a t e d with halogenation and n it ra tio n , have been f a v o r e d by many
investigators.

The g e n e r a l m e c h a n i s m f or the al uminum chloride

ca ta ly ze d alkylation c o n s i s ts of the f o r m a t i o n of a c ar bo ni um ion,
followed by e l e ct ro p h i l ic attack on the a r o m a t i c nucleus.
R-X*.
+
*.

A1C1„^ ^

R-X: A1C1

-

O
R® + [ :X-A1C1 ]

R

..
+

©

[-'X-A1C1 ]

+

HX

+

A1C1

C on sid era bl e evidence has been obtained to explain the f u n c ­
tion of the c a t a l y s t in this r e ac tio n , as is shown in the f i r s t equation
above.

Although a solution of aluminum halide in benzene o r of

ethyl chlo ride in benzene shows negligible conductivity, it has been
shown that a solution of all th r e e conducts an e l e c t r i c a l c u r r e n t
with m i g r a t i o n of aluminum to the anode c o m p a r t m e n t (20).

More

r e c e n t evidence in fa vo r of p r e l i m i n a r y carbo niu m ion f o r m a t i o n was
obtained th rou gh r ead y in terchang e of halogen in the p r e s e n c e of
a lu min um b r o m i d e .

Thus, when benzyl chlo ride, and aluminum

b r o m i d e w e r e m ix ed in benzene solution, the offgas f r o m the r e ac tio n

11
contained 25.67 p e r c e n t HC1, and 74.33 p e r c e n t HBr.

..

On the b a s i s

0

of f o r m a t i o n of the ion [ : C l - A l B r ], the values of 25 and 75 p e r c e n t
would be exp ec ted (21).
racem izes

Also, the f ac t that oQ-phenylethy 1 chloride

rapidly in the p r e s e n c e of aluminum chlo ride and oth e r

Friedel-C rafts

c a t a l y s t s is b e s t explained by the f o r m a t i o n of the

p l a n a r c a r b o n i u m ion (22).
T h e re has been a g r e a t deal of doubt concerning the s u b s e ­
quent steps of the alkylation r e ac tio n b eca use of the r e p o r t e d f o r m a ­
tion of b e n z e n e - a l u m i n u m chloride complexes (2 3).

By employing

g alliu m t r i c h l o r i d e as the alkylation catalys t, Ulich and Heyne (2 4)
have obtained, however, the e qu ilib riu m constant for the f o r m a t i o n
of the c a t a l y s t - h a l i d e complex, and have shown that the r ate of a l ­
kylation is d i r e c t l y p ro p o r t i o n a l to the c once ntr atio n of this complex
and of the a r o m a t i c h ydr ocarb o n.

It was concluded, t h e r e f o r e , that

a f u r t h e r activating function of the c a t a l y s t was negligible.
Since the function of the c a t a l y s t in this r ea c t io n c o n s i s t s in
the g e n e r a t io n of c a rb o n i u m ions f r o m the alkyl halide, it would be
exp ec te d that o th e r s t ar tin g m a t e r i a l s and rea ge nt s leading to c a r ­
bonium ions should be capable of effecting alkylation.

Indeed, P r i c e

(25) h as s u m m a r i z e d the use of olefins, alcohols, e t h e r s , and e s t e r s
f o r s t a r t i n g m a t e r i a l s in the p r e s e n c e of such c a t a l y s t s as bo ron
t r i f l u o r i d e , hydrogen fluoride,

and sulfuric acid.

12
P e r h a p s a b r i e f mention should be made at this point of the
school of thought concerning the ionic i n t e r m e d i a t e p r o p o s e d f or
e l e c t r o p h i l ic a r o m a t i c

substitution.

Dewar (26) suggests that the

e l e c t r o p h i l i c s p e cie s r e a c t s with the a r o m a t i c m olecule through the
f o r m a t i o n of a -fT'-complex.

S everal types of e x p e r i m e n t a l data have

shown the suitability of th ese ■'fT'-electrons f o r such dative bond f o r ­
mation.

Thus, Andrews and K e ef er (27) have attr ib ute d the solubility

of a r o m a t i c h y d r oc ar bo ns in aqueous s i l v e r n i t r a t e to the f o r m a t io n
of com plex es

such as A.r-Ag^ and Ar-A g^^^, while a s i m i l a r e x p l a n a ­

tion f o r the solubility of HC1-A1C1^ m i x t u r e s in benzene was made
by Brown and B r a d y (28).

In a r e c e n t extensive study of such c o m ­

p le x es , however, Brown and c o - w o r k e r s

(29) have p o s tu la te d the

e x is te nc e of a r o m a t i c c ar bo ni um s alt s of the type
Ar is C^H^), which can s e rv e as a highly p o l a r
m e d iu m f o r the f o r m a t i o n and r ea c t io n of ionic i n t e r m e d i a t e s in the
Friedel-C rafts

r ea ct io n.

These car bo ni um ion s a lt s (tr-complexes)

w e re found f o r benzene, toluene, m -x yl en e, and m e s i ty le n e and a r e
i l l u s t r a t e d by the following example:

13

©H
CH

CH.

H-C-H
II

+ HCl + A1C1

A1C1 o

4

©

V

H H

H H

In this connection it is of i n t e r e s t to note that a s im ple l i n e a r r e l a ­
tionship was shown to e x i s t between the s tability of such g~-complexes
and the r a te of a r o m a t i c

substitution (30).

No such r ela tio ns hip is

known to e x i st between substitution r a t e s and the stability of the
1r - co m p lex es orig in ally p r o p o s e d by Dewar (26).
At the sam e time, Brown and c o - w o r k e r s (29) extended t h e i r
inv estig atio n of the A1C1-HC1 c a t a l y s t to include its r ela tio ns hip with
alkyl ha lid es , which a r e g e n e r a l ly used as substituting agents in the
Friedel-C rafts

r eaction.

D e te rm i n ati on of the m o l e c u l a r weight of

aluminum b r o m i d e in methyl b r o m id e solution f r o m v ar io us vap or
p r e s s u r e m e a s u r e m e n t s indicated that these components e x i st e d as
a 1:1 complex.

It was t h e r e f o r e concluded that the initial phase in

the c u s t o m a r y a r o m a t i c alkylation r e ac tio n is the f o r m a t io n of a
c a t a l y s t - a l k y l halide complex, followed by ionization as a p os si ble ,
but not e s s e n t i a l ,

second stage.

(1) RX

+

> (RX: MX^)

MX

(2) (RX:MX3)

->

R® MX ®
4

14
It n a t u r a l l y follows that the ionization step would be expected to i n ­
c r e a s e in i m p o r t a n c e when going f r o m a p r i m a r y to a t e r t i a r y alkyl
halide.
With the cationic m e c h a n i s m of a r o m a t ic

substitution well

e s t a b l i s h e d by the e a r l y "forties, Simons and c o - w o r k e r s (31,

32) p r e ­

sented so me challenging kinetic studies on the hydrogen fluoride
c ata ly ze d alkylation of toluene with t-butyl chloride.

These p a p e r s

show th at although an ionic i n t e r m e d i a t e will explain the type of
r e a c t i o n r a t e c u r v e s obtained, the r eactio n p r o c e e d s at too r apid a
r ate to allow f o r the e n e rg y r e q u i r e m e n t s of such an i n t e r m e d i a t e .
On the b a s i s of e x p e r i m e n t a l o bs e rv a ti o n s, Simons (31) p r o p o s e d a
t h i r d - o r d e r m e c h a n i s m which he t e r m e d the
effect."

" a m p h o t e r i c m e dium

This m e c h a n i s m involved simultaneous bond-making and

b on d - b re ak i n g in the t r a n s i t i o n state, to avoid the n e c e s s i t y of a
high e n e r g y ionic i n t e r m e d i a t e .

It should be pointed out h e r e that

such e x p e r i m e n t a l o b s e r v a ti o n s as the f act that the hydrogen fluoride
ca ta ly ze d alkylation of benzene with d - s e c -butyl alcohol yields

sec-

butyl benzene with 99.5 p e r c e n t r ac e m i z a ti o n , while in a c c o r d with
the cationic m e c h a n i s m , would be difficult to explain on the b a s i s
of the c o n c e r t e d m e c h a n i s m s ugges ted by Simons (36). ’

15
The r a t e of the r e ac tio n studied by Simons and c o - w o r k e r s
was highly dependent on the p r e s s u r e of the hydrogen fluoride c a t ­
alyst.

Since the kinetic activity of this c a t a l y s t in the r e ac tio n

m i x tu r e was not known, n o r its v a ri a n c e with t e m p e r a t u r e changes,
it was not p r a c t i c a l to study the r ate o v er a t e m p e r a t u r e range in
o r d e r to d e t e r m i n e the activation e n e r g i e s .

In addition to this, these

r e a c t i o n s involved a m a t e r i a l that was c o r r o s i v e to g la s s,

and t h e r e ­

f o re r e q u i r e d a m e t a l r e a c t i o n s yst em .
With the d i s c o v e r y by van Alphen in 1927 that phenols could
be al kylated in the p a r a position with t e r t i a r y alkyl halides in the
absence of any added c a t a l y s t s (1) followed by the work of Bennett
and Reynolds (33) and Simons and H a r t (34), a re ac tio n was supplied
which o ffer ed ideal conditions f o r kinetic study of the alkylation
mechanism.

The l a t t e r w o r k e r s found that the alkylation with t-butyl

chloride was a homogeneous, quantitative rea ct io n that p r o c e e d s at
a m easurable

r ate at convenient t e m p e r a t u r e s .

c a r r i e d out in an evac uated g la s s

If the rea ct io n w ere

s yst em , it could r e ad ily be f o l ­

lowed by m e a n s of the i n c r e a s e in p r e s s u r e

due to the evolution of

hydrogen chloride gas.
H a r t and Simons r e p o r t e d a kinetic an al ysi s of the r eactio n
in 1949 (2).

The alkylations w ere c a r r i e d out on phenol, p - c r e s o l ,

16
and anisole using t-buty l chloride as the halide.

The i m p o r t a n t e x ­

p e r i m e n t a l o b s e r v a t i o n s f r o m this work can be e n u m e r a t e d as f o l ­
lows:
1.

The r e a c t i o n exhibited a high o r d e r r a t e dependency upon

phenol c on ce ntr atio n.
2.

Initial hydrogen chloride p r e s s u r e had little o r no effect

on the r e a c t i o n r a t e .
3.

C a lculated e n e r g i e s of activation w e re quite low, a p p r o x ­

i m a te ly 14-17 k. c a l . / m o l e .
4.

Anisole f ailed to r e a c t un der cor re sp on d in g r ea c t io n c o n ­

5.

The r e a c t i o n was a l m o s t completely inhibited by the a d ­

ditions .

dition of p-dioxane in diluent amounts.
The l a s t two r e s u l t s indicated the i m p o rta nc e of the hydroxyl
group in the t r a n s i t i o n state of the reactio n.

The actual role of

the dioxane in the inhibition was not d e t e r m i n e d by H a r t and Simons.
B o r d e a u x (9) l a t e r c a r r i e d out a kinetic study of the alkylation
of phenol using varyin g amounts of dioxane as a diluent.

On the

b a s i s of a s e r i e s of calculations B or deau x showed that the inhibition
was p r o b ab ly due to the f o r m a t i o n of a 1:1 oxonium complex between
phenol and dioxane.

T h e re is no doubt of the m e r i t of the suggestion

17
of such co m p lex es f o r explaining the m e c h a n i s m of the inhibition, as
dioxane is b a s i c and the f o r m a tio n of oxonium s a lt s of this m a t e r i a l
has b een d e m o n s t r a t e d p r e v i o u s l y by B a r t l e t t and Dauben (35).

A

close e xa m ination of the kinetic method u sed by Bordeaux, however,
creates

some doubt as to the a c c u r a c y of the s to i c h i o m e t r ic d e t e r ­

mination, and indicates the need f o r m o r e p r e c i s e kinetic data in
o r d e r to e s t a b l i s h the role of oxygenated m a t e r i a l s in the alkylation
reaction .
On the b a s i s of the e x p e r i m e n t a l r e s u l t s e n u m e r a t e d above,
H a r t and Simons (Z) c o n s i d e r e d th ree m e c h a n i s m s , all of which could
s a t i s f a c t o r i l y account f o r the r a te data obtained.
The p o s s i b i l it y of the f o r m a t io n of an unstable phenyl alkyl
e th er , followed by r e a r r a n g e m e n t of this e t h e r in the p r e s e n c e of the
g e n e r a t e d hydrogen chloride, was d i sc ar de d ,

since the r eaction showed

no c a t a l y s i s o r a u t o - c a t a l y s i s by hydrogen ch lo ri de.

A second p o s s i ­

bility involved the p r e l i m i n a r y f o r m a t io n of a f r e e o r solvated c a r ­
bonium ion, followed by e le c t ro p h i l ic attack at the p a r a position of
the phenol.

Such a m e c h a n i s m was not favored,

since it was pointed

out th at cal cu lat io n s s i m i l a r to those of P e a r l s o n and Simons (31)
gave a m i n i m u m e n e r g y r e q u i r e m e n t s of Z8 k.cal. p e r mole f o r the
f o r m a t i o n of a solvated t-bu tyl c a r bo n iu m ion, in phenol at 45°.

The

e x p e r i m e n t a l l y d e t e r m i n e d activation e n e r g i e s were

14-17 k.cal. p e r

m ole.
The t h i r d m e c h a n i s m which was p r o p o s e d by these i n v e s t i g a t o r s , and which, has been mentioned b ef or e, was t e r m e d the ^ a m p h o t e r i c m e d iu m e f f e c t . "

This m e c h an is m , e s p ec ia lly suited to the

e n u m e r a t e d o b s e r v a ti o n s , involves a o n e - s t e p condensed phase r e a c ­
tion which m a k e s use of the a m p h o t er ic p r o p e r t i e s of phenol.

Thus,

it c o n s is ts of p o l y m o l e c u l a r attack on the chlorine of the alkyl halide,
and on the p a r a hydrogen of phenol, as is shown s c h e m a t ic a l ly below.
O-H

-H

C l- B u

The solid lin es indicate the bonds p r i o r to reaction, and the dotted
lines indicate the bond shifts when r e a c t io n o c c u r s .

The chief point

h e r e is the concept of s im ultan eo us b r eakag e and f o r m a t i o n of bonds
with no r e q u i r e m e n t f o r a high e n e r g y i n t e r m e d i a t e capable of i n d e ­
pendent e x i s t e n c e .

This m e c h a n i s m finds support in that it is s i m ­

i l a r to the suggestion of a c i d - b a s e c a t a ly s i s by Lowry (3), and the
t e r m o l e c u l a r m e c h a n i s m s p r o p o s e d r ec e n t l y by Swain (4, 5).
Price

(36) has c r i t i c i z e d the i nf er en ce of Simons and co- wor ke

tha t f r e e ca rb o n c at ion s, such as those p o s tu la te d as i n t e r m e d i a t e s in

19
the F r i e d e l - C r a f t s

r e action , cannot exist.

He points to the i n d i s ­

putable evidence of Hughes and Ingold (37), of H a m m e t t (38), and of
B a r t l e t t (39), f o r the t r a n s i e n t ex istence of the trip heny lm eth yl cation
in many nucleophilic d i s p l a c e m e n t r e a c t i o n s .

Swain (4), however,

has shown quite conclusively that trip heny lm eth yl halid es , and even
methyl h al id es (5), can undergo d i s p l a c e m e n t in benzene solution,
r eq u i r i n g in the r a t e - d e t e r m i n i n g

step both pull on the leaving group

and at tack on carbon; i.e ., by a " c o n c e r t e d " p ush-p ull, or t e r m o l e c ular p ro c e s s.

Even though benzene was the only solvent used,

th e r e is no a p p a r e n t r e a s o n why such m e c h a n i s m s should be l e s s
c o n c e r t e d in alcohol o r even w a t e r solution (40).
Following a study of the f o r m at io n of triphen ylm eth yl e t h e r s
with phenol and methyl alcohol, Swain pointed out that although kinetic
o r d e r has been u s ed m o r e than any other evidence as a c r i t e r i o n
f o r deciding which m e c h a n i s m is operating in a p a r t i c u l a r ca s e, it
does not depend on m e c h a n i s m alone, but r a t h e r on the degree of
p a r t i c i p a t i o n of the solvent (5).

Thus, trip hen ylm ethy l chlo ride in

w a t e r gives f i r s t o r d e r kin e tic s (both attack on carbon and solvation
of chlorine by the solvent); benzyl chloride with m e r c u r i c n i t r a t e
in w a t e r solution gives second o r d e r kin etics (attack on car bo n by
solvent and solvation of chlorine by phenol, and no p a r ti c ip a t io n by

20
solvent).

T h e r e f o r e , Swain p r e f e r s to say that all d i s p la c em e n t s i n ­

volving tri p h en y lm e t h y l, t-butyl, benzyl, and methyl halides in benzene
solution o c c u r by one m e c h a n i s m , a t e r m o l e c u l a r one, r e g a r d l e s s of
the kinetic o r d e r obs erv ed .
It m i gh t be well to point out, befo re concluding this s urv ey ,
that all through the h i s t o r y of the th e ory of a r o m a t i c substitution,
r e a c t i o n s involving the phenol molecule have o ffered some u nex plain­
able r e s u l t s on the b a s i s of conventional e l ec tr op h il ic substitution.
F o r e xam p le, when iodine monochloride is u s ed as a chlorinating
agent, iodine r a t h e r than chlorine is intro du ced into the benzene ring
as a r e s u l t of the unequal c h ar g e d is tr ibu tio n between the d i s s i m i l a r
halogen atoms:

[ :A
+S

:ci:]
-S

Although some chlo rin atio n occa si on ally o c c u r s even with iodine monoch lo ride, M i l i t z e r has shown (41), and it is not c l e a r why, that iodine
m ono bro mid e acts ex cl usi ve ly as a b ro m in atin g agent f o r phenol.
S im i la r l y , although the k in e tic s of halogenation of benzene is c o n s i s ­
tent with the c a r b o n i u m ion m e c h a n i s m , P a i n t e r and Soper (42), and
r e c e n t l y B e r l i n e r (4 3) have indicated f r o m iodination k in etics that
the halogenation of phenols is a different, m o r e complex p r o c e s s .

21
In addition, although the r e a c tio n s of for mal deh yd e and a r o m a t i c s s upposedly p r o c e e d by at tack of a p r o to n a te d f o rm ald eh yd e
cation, 0 CH^-OH (36), the well-known condensation of formaldeh yde
and phenols p r e s u m a b l y involves a differen t m e c h a n i sm , deriving its
driving fS rc e f r o m something o th e r than the e l ec tr op h il ic n a t u r e of
the f o r m a l d e h y d e - p r o t o n com plex (36).

P AR T A

THE PREPARATION AND P RO PE R TIE S OF
2 ,6 -DI-TERTIARY -BUTYLPHENOL

22

Expe r i m e n t a l

4 - B r o m o -2, 6 -d i- t- b u ty lp h e n o l
c

Br-('

-( c h 3) 3

yOH
c

-(c h 3) 3

A m i x t u r e of p -b ro m op h en o l (86.5 g., 0.5 mole),

200 ml. of

benzene, and 4 m l . of 98 p e r c e n t sulfuric acid was t r e a t e d at 65±5°
f o r ten h o u r s with two m o l e s of isobutylene in an alkylation v e s s e l
s i m i l a r to tha t u s e d by Stillson, Sawyer, and Hunt (8).

After e x t r a c ­

tion with 20 p e r c e n t alkali to remov e the u n r e a c t e d p-bro moph en ol
o r any m ono alkylated pro duct, the benzene solution was washed with
w a t e r until n e u t r a l to l i tm u s , d r i e d o v er anhydrous
and the solvent r e m o v e d at r edu ced p r e s s u r e .

sodium sulfate,

Any t-butylbenzene

f o r m e d by alkylation of the solvent was also r em ove d at this point.
The r e s id u e was f r a c t i o n a l l y d isti lle d in a n it ro g en a t m o s p h e r e
through a V i g r eu x column.

The d is ti lla te , b.p.

126-128

at 4 m m . ,

yielded white c r y s t a l s on cooling, which, r e c r y s t a l l i z e d f r o m aqueous
ethanol, m e l t e d a t 83-83.5°.
Anal.

The yield was 51 g. (35.6%).

Calcd. f o r C ^ H ^ O B r :

B r, 27.95 and 27.75 p e r c e n t .

B r , 28.03 p e r c e n t .

Found:

When |)-xylene was u s ed as the solvent, alkylation of the s o l ­
vent was m i n im i z ed , and the d i- al k y la te d p r o d u c t was obtained in a
yield of 47 p e r c e n t .

At 70° in the absen ce of a solvent, and with

the isobutylene u n d e r ZOO p . s . i . in a steel bomb, 2 3 p e r c e n t of the
d e s i r e d p r o d u c t was obtained.
In e a c h ca se , n e u t r a l iz a t io n of the initial alkali e x t r a c t , and
f r a c t i o n a l d isti lla tio n of the organic l a y e r yielded 20 to 25 p e r c e n t
of 4 - b r o m o - 2 - t-butylphenol, b.p. 129-131° at 6 m m .

4 -Chloro - 2 , 6-di -t-butylphenol
C-(CH )
C l-

-OH
C-(CH )

A m i x t u r e of p -c hlo ro p he n ol (64 g., 0.5 mole) and 100 g. of
85 p e r c e n t sulfuric acid was t r e a t e d at 70±5° f or th r e e h o ur s with
1.5 m o l e s of t- bu tyl alcohol in a th r e e - n e c k e d , o n e - l i t e r f la s k equipp
with a s t i r r e r and t h e r m o m e t e r .

F ifty g r a m s of 98 p e r c e n t sulfuric

aci d was added r ap id ly at the end of each of the f i r s t two hours, in
o r d e r to m a in ta in the acid c on ce ntr ation .

A fter s t i r r i n g f o r an a d ­

ditional h ou r, the s yrupy r e d solution was p o u r e d onto c r a c k e d ice
and the p r o d u c t e x t r a c t e d with benzene.

The benzene

solution was

25
then w a sh ed with b ic a r b o n a t e and e x t r a c t e d with C la is en solution.
The b en ze ne l a y e r was d r i e d o v e r anhydrous p o t a s s i u m carbonate
and the

solvent r e m o v e d at r edu ced p r e s s u r e .

The r e s id u e was

f r a c t i o n a l l y d is t i ll e d through a Vigreux column.

The d isti lla te , b.p.

111-115° at 5 m m . , yielded white c r y s t a l s on cooling, which,
c r y s t a l l i z e d f r o m ligroin, m e l t e d at 75-76°.

re -

The yield was 29 g.

(2 4%).
Anal.
Cl,

Calcd. f o r C

H OC1:
14 21

Cl, 14.76 p e r c e n t .
^

Found:

14.61 and 14.70 p e r c e n t .
The C la is en solution e x t r a c t yielded about 5 p e r c e n t of 4-

c h l o r o - 2 -t-bu ty lph en ol a f t e r n e u t ra liz a tio n .
was followed with p - b ro m o ph en ol ,

When the above p r o c e d u r e

5 p e r c e n t of 4 - b r o m o - 2 -t-butylphenol

was r e c o v e r e d f r o m the alkali e x t r a c t , but the benzene solution
yielded no 4 - b r o m o - 2 , 6 - d i - t - b u t y l p h e n o l ; only p o l y m e r i c r e s i d u e s
w ere obtained.

2, 6- D i- t-b u ty lp he no l

C -<CH 3) 3
A m i x t u r e of 4 - b r o m o - 2 , 6 - d i - t - b u t y l p h e n o l (10 g., 0.0 35 mole),
50 ml. of 95 p e r c e n t ethanol and 30 g. of Raney n ic k e l - a lu m i n u m

26
alloy in a o n e - l i t e r f l a s k equipped with a reflux c on d e n s e r was tr e a t e d ,
o v e r a p e r i o d of t h i r t y minu tes with 300 ml. of 10 p e r c e n t aqueous
sodium hydroxide.

The m i x t u r e was refluxed f o r an additional hour,

f i l te r e d , and the nickel wash ed with 10 p e r c e n t alkali followed by
benzene.

The aqueous l a y e r was then cooled and p o ur ed into 250

ml. of c o n c e n t r a t e d h y d r o ch lo r ic acid.

A fter e xt ra c t io n with benzene,

combination of the washings and drying o ver anhydrous sodium,
fate, the solvent was s tr ip p e d using a Vigreux column.

sul­

The r es id ue

yielded 6.7 g. (93%) of 2 , 6 - d i- t-bu ty lph en ol, b.p. 94-98° at 5-6 mm.
The p r o d u c t of the alkali r eduction was a c o l o r l e s s liquid,
while the s a m e p r o d u c t r e p o r t e d by Stillson and Sawyer (17) was
c l a i m e d to be a yellow solid, m.p.

38-39 .

The p ro du ct was t h e r e ­

f o r e s u bjected to i n f r a r e d an al ysi s as a t e s t of p u r i t y and s t r u c t u r e .
The s p e c t r u m

showed the p r e s e n c e of the hin de re d hydroxyl at about

2.7 6 [ j l but also ind icate d the p r e s e n c e of a small amount of an a l i ­
phatic car bo ny l compound.

This im p u r it y was susp ected of being

2 ,6 - d i- t- b u ty lc y c l o h ex a n o n e , which has been is o la te d as the m a j o r
p r o d u c t f r o m the r eduction of 4 - b r o m o - 2 , 6 - d i-t-bu ty lp henol by h y d r o ­
gen in the p r e s e n c e of p al lad iu m chloride on c h a r c o a l (44).
The liquid r e a c t i o n p r o d u c t was, t h e r e f o r e , f u r t h e r f r a c t i o n ­
ated in an a t t e m p t to e l im i n ate the carbonyl im pu rity .

When the

27
f r a c t i o n a t e d p r o d u c t was

solidified in d ry ice and f i l t e r e d im m ed iatel y,

a white solid was obtained, which gave white p r i s m s f r o m 95 p e r c e n t
ethanol; m.p.

o
37-37.5 .

A sample of the 2 ,6 - di-t-b utylcy clo hexano ne

(supplied to us by R. H. Rosenwald, U n i v e r s a l Oil P r o d u c t s Company)
gave a me ltin g point of 38-38.5 ; when mixed with a small amount of
the c r y s t a l l i n e phenol, i m m e d i a t e liquefaction o c c u r r e d at roo m t e m ­
perature .
Anal.
Found:

Calcd. f o r C

H O:
14 22

C, 81.5 p er ce nt ;

C, 81.6 and 81.45 p e r c e n t ; H,

H, 10.68 p e r c e n t .
1

10.80 and 10.75 p e r c e n t .

P o t a s s i u m in Liquid A mmonia Reduction

In a o n e - l i t e r , tw o-necked flask,

400 g. of liquid am m o nia was

condensed on 10 g. (0.035 mole) of 4 - b r o m o - 2 , 6 - d i - t - b u t y l p h e n o l .
P o t a s s i u m m e t a l was in tr od u ce d (mixture continuously s tir red )
the solution took on a p e r m a n e n t blue co lo r.

until

Ammonium chloride

was added to d e s t r o y the u n r e a c t e d p o t a s s i u m and the a m mo nia was
allowed to e v a p o r a t e overnight.

The r es id u e was dis so lved in p e ­

t r o l e u m e t h e r , w ash ed with w a t e r until n e u t ra l to li tm us and d rie d
o v er anhydrous sodium sulfate.
pressure

The solvent was re m o v e d at reduced

and the r e s i d u e f r a c t i o n a t e d through a Vigreux column.

The pro du ct, b.p. 94-98° at 5-6 m m . , weighed 3.5 g. (48.6%).

28
T e s t s f o r the H in der ed Phenol

The 2 , 6 - di- t-b u ty lp he no l obtained f r o m both methods of r e d u c ­
tion yielded a deep blue colo r when t r e a t e d with phosphomolybdic acid
and a m m o n i u m hydroxide (18).

The p r o d u c t was insoluble in 20 p e r ­

cent sodium hydroxide, and showed no co lo r change when t r e a t e d
with alcoholic f e r r i c

Nitration:

chloride solution.

4,6 -D in itro -2 -t-butylphenol

n°

ON-<\

\\

2

//—OH
A
c

-( c h 3) 3

To 1 g. of 2 , 6 - d i- t-b u ty lp he no l was cautiously added 5 ml. of
a 1:1 m i x t u r e of c o n c e n t r a t e d n i t r ic and gla cial acetic acids.

The

solution was w a r m e d f o r one minute, then p o u re d onto c r a c k e d ice.
A f te r f i l t r a t i o n and r e c r y s t a l l i z a t i o n f r o m dilute methanol, yellow
p l a te s w e re obtained, m .p .

124-125°.

o
4 , 6 - d i n i t r o - 2 -t-butylphenol is 124 .)
p i c r i c acid,

(The l i t e r a t u r e value [46] fo r
A mixed melting point with

o
85-100 , p r o v e d that only one alkyl group underwent

cleavage during the n it ra tio n .
Anal.
N,

Calcd. f o r C lrtH . ^ O cN_:
IU I J D £

11.82 and 11.73 p e r c e n t .

N,

11.66 p e r c e n t .

Found:

29
A t te mp ted N i tr a t i o n Without Cleavage

To 1.03 g. (0.005 mole) of 2 , 6 -d i- t-b ut ylp h en ol was added a
solution of 0.315 g. (0.005 mole) of c o n c e n t r a te d n i t r i c acid in 2 ml.
of gla c ia l ace tic acid, and the t e m p e r a t u r e was held below 0°.
s e v e r a l m i n u t e s , the m i x t u r e was p o u r e d onto c r a c k e d ice.

After

The

r e d d i s h - b r o w n oil was wash ed by decantation with w a t e r and sodium
b i c a r b o n a t e , then d i ss o lv e d in 95 p e r c e n t ethanol.
w a te r , c r y s t a l s

On dilution with

s e p a r a t e d which on re c r y s t a l l iz a t io n f r o m aqueous

ethanol gave d a r k r e d n e e d l es , m.p. 245-247°.
Anal.

——>

Found:

Calcd. f o r C

2o

H

40

O :
2

C, 83.2 p er ce nt ; H, 9.85 p e r c e n t .

C, 82.5 and 82.7 p e rc en t ; H, 9.69 and 9.65 p e r c e n t .
This p r o d u c t was identified as

3, 3',5,5 1- te tr a - t- b u t y l d i p h e n o -

quinone on the b a s i s of the above a na ly si s, coupled with a subsequent
study in this l a b o r a t o r y by W. J . D e t ro i t on the p r o p e r t i e s and
s p e c t r a of s e v e r a l sub st it ute d diphenoquinones (45).

Acid R e a r r a n g e m e n t

The w a r m solution of five drops of 98 p e r c e n t sulfuric acid
in one m l . of 2 , 6 -d i- t-b u ty lp h en o l was f u r t h e r heated f o r s e v e r a l
m in u te s , then p o u r e d into cold w a t e r .
up in p e t r o l e u m e t h e r ,

The org an ic p r o d u ct was taken

and the l a t t e r washed with 10 p e r c e n t aqueous

30
alkali to e x t r a c t any r e a r r a n g e d pro du ct.

Acidification, followed by

e x t r a c t i o n with l i g r o in and ev ap o ra tio n of the solvent yielded c r y s t a l s
which, r e c r y s t a l l i z e d f r o m lig roin , m e l t e d at 55-55.5°; m ixed with
an authentic sample of 2 , 4 -d i-t-b uty lph en ol, 55-56°.

Relative R at es of B ro m i na ti on and Coupling

T r e a t m e n t of 2 , 6 - di- t-bu tylph en ol with b ro m i ne in carbon
t e t r a c h l o r i d e solution showed no lo ss in b ro m in e co lo r o ver a p e r i o d
of t h i rt y m i n u te s .

S i m i l a r t r e a t m e n t using 2,6-xylenol as the phenol

gave d ec ol or atio n of the b r o m in e solution in l e s s than one minute.
To a cold solution of. 1 g. of 2,6-xylenoi in 20 ml. of 5 p e r ­
cent sodium hydroxide, was added an e x c e s s of diazotized aniline.
A f t e r a few m in utes the solution was f i l t e r e d f r e e of small amounts
of r e s in o u s m a t e r i a l ,
acid.

and the f i l t r a t e was n e u t r a l i z e d with acetic

A fte r f i l t r a t i o n and r e c r y s t a l l i z a t i o n f r o m ligroin, yellow

p l a t e s w e r e obtained, m . p . 94.5-95.5°.

The melting point r e p o r t e d

,o
f o r 4 - p h e n y l a z o - 2 , 6-xylenol is 95-96 .
A t te mp ted coupling with 2 , 6 -di-t-b ut ylp hen ol in alcoholic
sodium hydroxide un der the s a m e conditions r e s u l t e d in quantitative
r e c o v e r y of the s t a r t i n g m a t e r i a l .

31
A bso rp tio n S p e c t r a

The u l t r a v i o l e t a b s or pti on s p e c t r a shown in F i g u r e s

1 and 2

w e re d e t e r m i n e d with a B eckm a n s p e c t r o p h o t o m e t e r (Model DU), using
1-cm. q u a r t z ce lls .

The cyclohexane solvent (for the phenols) was

f r e e d of benzene by p a s s a g e through a ctivated s i l i c a gel, followed
by f r ac t io n a ti o n .
quinone.

Absolute alcohol was u sed as solvent f o r the

The 2 , 6 - d i - t - b u t y l - 4 - m e t h y l p h e n o l was obtained f r o m the

K o pp er s Company, P i t t s b u r g h , Penn sy lvania, and was p u r if ie d by
d is ti lla tio n (146° at 20 mm*) and r e c r y s t a l l i z a t i o n f r o m ligroin, m.p.
69-70°.
The i n f r a r e d abs or pti on s p e c t r a (F ig u re s

3 and 4) w ere o b ­

tained through the g e n e r o s i t y of Dr. G. B. B. M. Sutherland and Dr.
W. R. Vaughan, U n i v er s it y of Michigan, Ann A r b o r.

2200

32

FIGURE I
2 , 6 -D i-t-b u ty lp h en o l

2000

2 ,6 -D i-t-b u ty l-p -creso l
( 2 . 3 6 x 1 0 ~ 4 4* .T

1800

1600

1400

200

1000

800

600

400

200

220

230

240

250

260

270

Wave L e n g th (m*/)

280

290

300

Log

g

33

360

400
Wave L e n g t h

440

480

520

(m^y)

FIGURE 2 *
The U l t r a v i o l e t A b s o r p t io n S p ectru m
3 , 3 ' , 5 , 5 1~ t e t r a - t - b u t y l - j ^ - d i p h e n o q u i n o n e .

of

% Transmission

34

too

100

90

90

80

80

80

70

70

70

60

60

60

50

50

50

40

40

30

20

100

100

100

100

90

90

90

90

80

80

80

80

70

70

70

60

60

60

50

50

60

60

40

40

40

40

40

30

30

30

20

20

20

100

70

30

20

Wave Length (p)
2

3

4

5

6

9
7
8
FIGURE?. Infrared Absorption Spectrum of 2,6-Di-t-butylphenol

10

20

35

V* Transmission

100

100

100

100

100

100

100

90

90

80

80

80

90

90

90/

90

80

80

80

. 3(

70

70

70

70

TO

TO

60

60

60

60

60

60

50

50

50

50

50

50

40

40

40

40

40

40

30

30

30

30

30

30

20

20

20

20

20

20

Wave Length (//)
2

3

4

6

8

FIGURE fcInfrared Absorption Spectrum of 2,6-Di-t-butylcyclohexanone

10

40

20

3.6
D is c us si on

The following sch eme

represents

the s e r i e s of r ea ct io ns by

m e an s of which 2 , 6 -d i- t-b ut ylp h en o l was s yn thes iz ed in this work:
OH

OH
Isobutylene
H SO
2
4

X

X

Raney Ni-A.l alloy
Aqueous NaOH and
Ethyl Alcohol
(CH ) -C
3

OH

c

-( c h 3) 3
+ NaX

This p r o c e d u r e is e s s e n t i a l l y the sam e as that outlined by H a r t (15)
f o r the p r e p a r a t i o n of o-t-butylphenol.
C o n s id er ab le difficulty in the alkylation step was encountered
in attempting to introduce the second t-butyl group.

This difficulty

undoubtedly a r i s e s b e c a u s e of the high s t e r i c r e q u i r e m e n t s of the
two t- bu ty l g r o u p s .

A study of the alkylation step was th e r e f o re

made, and the r e s u l t s a re

s u m m a r i z e d in Table

1.

E x p e r i m e n t 2 (Table I) p r od uc ed the h ighest yield of the d e ­
s i r e d p r o d u c t.

C o ns id era bl e quantities of t-butylbenzene were o b ­

t a in ed in E x p e r i m e n t 1 due to p r e f e r e n t i a l alkylation of the solvent
a f t e r in tr odu ction of the f i r s t t-butyl group.

The fo rm at io n of such

37
TABLE

1

E F F E C T OF ALKY LA TION METHOD ON YIELD OF
2,6-DI- T -B U T Y L - 4-HALOPHENOL

Reagents
Expt.
P hen ol

Alkyl ating
Agent

Solvent

Catalyst

Temp.
(° C.)

MonoDiAlkyl- AlkylTime ated
ated
(hrs.) P r o d - P r o d ­
uct
uct
<%)
(%)

p - b ro mophenol

i so b u­
tylene

ben­
zene

98%
H SO
2
4

65±
5

10

29

35.6

-b ro mo phenol

isobu­
tylene

E- x y ­
lene

98%

65=t
5

10

18

47

£-bromophenol

isobu­
tylene J’c

none

70

25

23

E"
chlorophenol

t-buty l
alcohol

85%
H SO
u
Tt

75

5

24

p-bromophenol

t- butyl
alcohol

85%

75

H2S° 4
98%H SO
2
4

H2S° 4

* U n d e r 200 p . s . i . in steel bomb.

none

38
a b y - p r o d u c t was m i n i m i z e d by using p -xy len e as the solvent.

A t­

te m p t s to i n c r e a s e the yield of d i- a l k y la t e d p r o d u c t in E x p e r i m e n t
3, by c a r r y i n g out the r ea c t io n under p r e s s u r e in a steel bomb and
in the abs ence of a solvent, f ailed b eca use of i n c r e a s e d for mat io n
of p o l y m e r i c r e s i d u e s .

The o th e r alkylation method ( Exp er im en ts

4 and 5), although producing a f a i r amount of d e s i r e d p rod uct with
-chlorophenol yielded only p o l y m e r i c m a t e r i a l s when the b r o m o i s o m e r was used.
The r eduction of the halogen in t e rm e d i a t e was c a r r i e d out
using Raney N i ck el -A l um i nu m alloy and aqueous alkali according to
the p r o c e d u r e of Papa, Schwenk, and c o - w o r k e r s (47), and the phenol
was s olu bilized by the addition of ethyl alcohol to the r eaction m i x ­
t u re .

This reduction method afforded a s u p e r i o r yield (93%) to the

p r o c e d u r e of Stillson and Sawyer (17), who used p o t a s s i u m and liquid
a m mon ia.

Although the p r o d u c t r e p o r t e d by these w o r k e r s was a

solid, m.p.
liquids.

38-39°, both m ethods of reduction afforded us c o l o r l e s s

At that ti m e , we w e re in fo rm ed by Dr. R. H. Rosenwald

of the U n i v e r s a l Oil P r o d u c t s Company, that his group had succeeded
in p r e p a r i n g what was thought to be c r y s t a l li n e 2,6 —
di—
t—
butylphenol,
m.p.

38-38.5°, by the reduction of 2,6 - di- t-b u t y l -p-bro mop heno l with

hyd rog en in the p r e s e n c e of p allad iu m on charcoal.

When our phenol

failed to c r y s t a l l i z e a f t e r the addition of a sample of Dr. Rosenw ald's
product, both m a t e r i a l s w e re

subjected to u l t ra vio le t an aly sis .

While

o u r m a t e r i a l gave the c h a r a c t e r i s t i c phenol s p e c t ru m (see F i g u r e

1),

the solid p r o d u c t f u r n i s h e d us by Dr. Rosenwald gave no absorption
in this region.

This p r o d u c t was subsequently shown to be 2 , 6 - d i - t -

butylcyclohexanone (44).

It is known that phenols can be converted

to the c o r r e s p o n d i n g cyclohexanones by p a r t i a l hydrogenation.

How­

e ver , the m i l d conditions (room t e m p e r a t u r e and 50 atm.) used by
Rosenwald, which effected such a con vers io n a r e quite s u r p r i s i n g
and c e r t a i n l y b e a r f u r t h e r investigation.

F o r example, Whitaker (48)

has r e p o r t e d the p r e p a r a t i o n of s e v e r a l alkyl cyclohexanones by
hydrogenation with Adams platinum ca ta ly st.

2, 6 - D i - t - b u t y l - 4 - m e t h y l -

phenol r e q u i r e d a t e m p e r a t u r e of 200° at 150 atm. p r e s s u r e f or
c onv er sion to the co r r es p o n d in g cyclohexanone.

It might also be

pointed out that f u r t h e r hydrogenation to the cyclohexanol was i m ­
p o s s ib le with such a m ol ec ule due to the s t e r i c p ro te c tio n of the
carbonyl by the t -a l k y l groups.
In view of these o b s e r v a ti o n s , the i n f r a r e d absorption s p e c t r u m
of our p r o d u c t was obtained, and a slight con ce ntration of the a l i ­
phatic carbonyl group was detected by virtue of the c h a r a c t e r i s t i c
a b s o r p ti o n band at 5.8p (for example, see F i g u r e 4 for the i n f r a r e d

40
s p e c t r u m of the p u r e carbonyl compound).

Chem ical se pa ra tio n of

such an i m p u r i ty being a l m o s t im p o ss ib le due to the l a r g e s t e r i c
h ind ranc e of the t- buty l g rou ps, the phenol was car ef ully fra ct io n ate d
and, a f t e r f r e e z i n g in d ry ice and im m e d i a te vacuum f il tr ati on , a f ­
fo rded a solid which gave white p r i s m s f r o m ethanol, m.p.

37-38°.

The i n f r a r e d s p e c t r u m of this pro du ct (Figure 3, e x p e ri m e n t a l s e c ­
tion)

showed no a b s o r p ti o n band at 5.8|jl.
A study was also made of the r e ac tio ns and p r o p e r t i e s of

2 , 6 - d i- t- b u ty lp h e n o l and s e v e r a l points of this study a r e worthy of
discussion here.
When the phenol was n i t r a t e d with con ce n tra te d n i t r ic acid in
g la cial acetic acid (1:1) at room t e m p e r a t u r e , a yellow solid, i de n ­
tified as 4 , 6 - d i n i t r o - 2 -t-butylphenol was isolated.

This pro duct is

identical with th at obtained by Ipatieff, P i n e s and F r i e d m a n (46)
f r o m the n i t r a t i o n of 2 , 4 - d i - t - b u t y l p h e n o l .

In the l a t t e r case, the

4 - t- bu ty l group was c leaved f r o m the ring, w h e r e a s in the p r e s e n t
in sta n ce one of the 2 - t-b utyl groups was cleaved.

This r e s u l t is

also in a c c o r d with the r e p o r t by Stevens (49) of the dealkylation
of ortho alkyl phenols during distillation in acidic media, and the
r e a r r a n g e m e n t of o-t-bu ty lp heno l to the p a r a i s o m e r in the p r e s e n c e
of s ulfuric acid, r e p o r t e d by H a r t (15).

O u r p ro d u c t also underwent

41
r e a r r a n g e m e n t , to 2 ,4 - d i- t -b u t y l p h e n o l , under the conditions d e s c r ib e d
by the l a t t e r i n v e s t i g a t o r .
An a t t e m p t at n i t r a t io n without cleavage, using a 1:6 n itr ic
to acetic acid m i x t u r e at 0° yielded small quantities of dark r ed
n ee dl es , m . p . 245-247 , which contained no nitrogen.

The analysis

of this compound a g r e e d with that calculated f o r 3 , 3',5,5 ' - t e t r a - t butyl-p-diphenoquinone.

S i m i l a r oxidation p rod ucts have been is ola ted

in a n u m b e r of n i t r a t io n s of substituted phenols as well as f r o m other
phenol oxidations.

As f u r t h e r proof of s t r u c t u r e , the absorption

s p e c t r u m of th is compound is shown in F i g u r e 2.

The m a j o r peak

in the s p e c t r u m , at 418 mp, is s i m i l a r to that r e p o r t e d by Valyashko
and S h c he rb ak (50) f or diphenoquinone, but shifted slightly tow ard a
lon ger wave length.

D e tr o it and H a r t (51) have r ecently r e p o rt e d

the p r e p a r a t i o n and s p e c t r a of diphenoquinone and s e v er a l alkylated
de riv ativ e s .
S e v e r a l p r e l i m i n a r y e x p e r i m e n t s w ere c a r r i e d out to c om par e
the r e l a t iv e p a r a r e a c t i v i t y of this highly h in d e r e d phenol with 2,6dimethylphenol, which by the s ta n d a r d s set up by Coggeshall (6) b a s ed
on the i n f r a r e d s p e c t r u m , would be c l a s s e d as an unhindered phenol.
The l a r g e d ifferenc e in the ' s t e r i c effect of the methyl and t e r t i a r y
butyl groups is also exe m p lif ie d by the solubility beh av io r of the

42
two compounds.

W h e r e a s 2 , 6 -dimethylphenol is soluble in 20 p e r c e n t

sodium h ydroxide, the d i - t - b u t y l d eriv ativ e is completely insoluble
even in alcoholic p o t a s s i u m hydroxide ( C l a i se n 's

solution).

In the

f i r s t e x p e r i m e n t it was found that the dimethylphenol rapidly d e c o l ­
o r iz e d a solution of b r o m i n e in car bo n t e t r a c h l o r i d e while the d i - t butylphenol showed no b ro m i n atio n a f t e r a much lo ng er p e r i o d of
reactio n.

More conclusive evidence of d e c r e a s e d rea ct iv it y at the

p a r a p ositio n in the m o r e h ind red phenol was obtained by the diazonium coupling reac tio n .

The 4 - ph en yla z o-2, 6 -dimethylphenol was

obtained f r o m the dimethylphenol and diazotized aniline quite easily,
while s e v e r a l a t te m p t s with the 2 , 6- d i- t-bu tylp heno l gave p r a c t i c a l l y
quantitative r e c o v e r y of the s ta rt in g m a t e r i a l .
An explanation of the above r e s u l t s using known e l e c t r i c a l
effects of alkyl g ro up s a p p e a r s untenable.

The introduction of ortho

alkyl g roups can affect ring activity by virtue of t h e i r inductive and
hyperconjugative effects.

B e r l i n e r (52) c a r r i e d out a study of the

r ela tiv e e l e c t r o n i c effects of the methyl and t e r t i a r y butyl groups
by m e a s u r i n g the r a t e s of b r o m i n a t io n of toluene and t-butylbenzene
in 85 p e r c e n t ace tic acid.

The r e s u l t s of this work show that toluene

is b r o m i n a t e d five t im e s f a s t e r than the t-butyl deriv ativ e.

This

d if fer en ce w as a t t r ib u t e d to the l a rg e d e g re e of hyperconjugation that

43
is p o s s i b le in the methyl group, which supposedly o v e rc o m e s the
g r e a t e r inductive effect of the t-bu ty l group.

In a r e c e n t book on

hyper conjugation, however, B a k e r (5 3) has d is c l o s e d the r e c e n t kinetic
studies of Conn, Hughes, and Jon es f o r the n i t ra t io n of a s e r i e s of
alkyl b e n z e n e s.

Although these studies v er if y the o v e r - a l l r e s u l t s

obtained by B e r l i n e r f o r c o m p a ra tiv e activity of toluene and t-butyl benzene, these w o r k e r s a r e carefu l to point out that the p ro po rtion
of i s o m e r i d e s f o r m e d in the r e ac tio n shed a different light on the
explanation of the r a t e i n c r e a s e in going f r o m t-butylbenzene to
toluene.

Thus, the following r ela tiv e r a t e s of r ea c t io n w ere obtained:
Ring Substituent

Me

Et

i-P r

t- Bu

H

Relative Rate

100

97

87

73

6.8

However, the p r o p o r t i o n of i s o m e r i d e s d e t e r m i n e d gave p a r t i a l rate
f a c t o r s of the following magnitude:
Ring Substituent
Me
t-Bu

% Ortho
54.6
12.3

Consequently, even though the o v e r - a l l

% Meta

% Para

3.2
8.7

42.2
79.0

rate of n i t ra t io n of toluene

was f a s t e r than t-bu ty lb en zene , the a p pa re nt activation of the positions
m e t a and p a r a to the alkyl groups is much g r e a t e r in the l a t t e r c o m ­
pound, and m u s t be a t t r ib u t e d to the g r e a t e r inductive effect of the
t- bu ty l group,

since t h e r e a r e no c(^-hydrogens available in this group

44
f o r h yper conjugation.

B a k e r , t h e r e f o r e , points out that the d e t e r ­

mining f a c t o r in the o v e r - a l l r a t e s is the ortho substitution, which
is m uch s lo w e r in t-bu tylb en zene b e ca u se of the l a r g e r

s t e ri c effect

of the t- buty l group.
On the b a s i s of these studies one would expect a g r e a t e r
p a r a activation in 2 , 6 - d i- t-b u ty lp he no l than in the dimethyl derivative
b eca use of the l a r g e r inductive effect of the t-butyl group.

The fact

that this is not the c a s e , ind icate s that an a ltern ativ e m e c h a n i s m
m u s t be sought.

S te ri c hindrance of the hydroxyl group in the

phenol m o le cu le , by the l a r g e t-butyl groups, could p re ve nt co p l an ­
a r i t y between this group and the benzene ring, th e re b y reducing the
e l e c t r o n d ensity at the p a r a po sition by virtue of a s t e r i c inhibition
of the usual hydroxyl r e s o n an c e.

This would account fo r the lack

of b r o m i n a t io n and diazo coupling which was o b s er ve d f or the h i n ­
d e re d 2, 6 - d i- t-b u ty lp he no l.
Both the u l t r a v i o l e t and i n f r a r e d a bs or ptio n s p e c t r a of the
2 , 6 - d i -t -b ut ylp h en ol w e re d e te rm i n ed .

The f o r m e r is given in F ig ur e

1 with that of 2 , 6 - d i - t - b u t y l - 4 - m e t h y l p h e n o l f o r c om par is on .

The

m a j o r p eak s at 271 and 278 mp a r e identical with those of phenol
and o t h e r ortho al kylated phenols, and indicate the absence of any
alkyl group in the p a r a position.

45
The i n f r a r e d a b s o r p t i o n s p e c t r u m is shown in F i g u r e

3.

The

hydroxyl a b s o r p t i o n band o c c u r r i n g at 2.76 p. is indicative of a highly
h in d e re d hydroxyl gro up , since Coggeshall (6) has

shown that an u n ­

h in d e re d hydroxyl, in c o n c e n t r a t e d solution, will exhibit c h a r a c t e r i s t i c
abs orption at 3.0 p wavelength due to p ro b ab le a s s o c ia t io n o r i n t e r m o l e c u l a r h ydrog en bonding.

In 2 , 6 - di- t-bu ty lp hen ol, all i n t e r m o l e c -

ula r h ydrogen bonding is a p p ar en tly prev en ted .

PART B

KINETIC STUDIES OF THE ALKY LA TION OF PHENOLS
WITH TERTIARY HALIDES

46

47
Expe r i m e n t a l

I.

Materials

The phenol was J.

T. B a k e r Chemical Company m a t e r i a l , and

was p u r i f i e d by d is ti lla tio n at a t m o s p h e r i c p r e s s u r e with a small
amount of benzene to r em ove the w a ter.

The f ra c t io n boiling 175 to

183° at a t m o s p h e r i c p r e s s u r e was f u r t h e r f ra c t io n a te d in a Vigreux
column, the m a t e r i a l boiling f r o m

180 to 182° being retained.

The

phenol was then d e g a s s e d and f u r t h e r p u rif ie d f o r kinetic s am p les
in an a p p a r a t u s

s i m i l a r to the one d e s c r i b e d by H a r t and Simons (2).

The de ga ss in g was a c c o m p l is h ed by a l te r n a te f reezing , evacuation,
and thawing.

The a p p a r a t u s design then enabled distillation at 20

mm. in a n i t ro g e n a t m o s p h e r e ,

such that a 50 ml. f o r e - c u t could

be d i s c a r d e d b ef or e collection of the phenol u sed in the kinetic m e a ­
surements.

The phenol was

s t o r e d in a d e s i c c a t o r under a nitrogen

a t m o s p h e r e until r e a d y f o r use.
The t-b uty l chlo ride was E a s t m a n Kodak white label m a t e r i a l .
This was d r i e d o v e r p o t a s s i u m carbon ate (anhydrous), and f r a c t i o n ­
ated in a n i t ro g e n s t r e a m ,

retaining the sample which boiled c o n ­

stantly at 52° at a t m o s p h e r i c p r e s s u r e and had a r e f r a c t i v e index
of n

20

D

1.3851.

The halide was then p laced in a small distilling system,

48
d e g a s s e d accord ing to s t a n d a r d techniques, and dis ti lle d and collected
in a n i t ro g e n a t m o s p h e r e .
The tri ph en yl methyl chloride ( h e r e a f t e r r e f e r r e d to as trityl
chloride) was M ath ies on C hem ical Company p r a c t i c a l g rad e.

This

m a t e r i a l was t r e a t e d twice in benzene solution with decolorizing
c h a r c o a l , followed by r e c r y s t a l l i z a t i o n f r o m benzene -pentane s o l u ­
tion.

The faintly yellow tinted c r y s t a l s w ere f i l t e r e d rapidly, dried,

and s t o r e d in a vacuum d e s i c c a t o r o ver m i n e r a l oil.

The d ried

c r y s t a l s w e r e as c o a r s e as g r an u la te d s ug ar and had a melting
point of 110-111°.

All o per at io ns in this p u rif ication w e r e designed

to exclude a t m o s p h e r i c m o i s t u r e .
The p - d i c h l o r o b e n z e n e was f r a c t i o n a t e d through a Vigreux
column with a s m a l l amount of benzene to r em ov e t r a c e s of w a te r.
The f r a c t i o n boiling 180-181° at a t m o s p h e r i c p r e s s u r e was re ta in ed
and s t o r e d in a n it ro g e n a t m o s p h e r e .
The o th e r phenols used in the r ela tiv e r ate studies were all
car ef ul ly f r a c t i o n a t e d and s t o r e d under n itrog en until used.

In a d d i ­

tion to f ra ct io n a ti o n , the 2,6-xylenol (Edcan L a b o r a t o r i e s ) was r e c r y s t a l l i z e d f r o m p e t r o l e u m e t h e r , m.p.

49°.

The p u rif icatio n of

the 2 , 6 - d i - t -b u t y l p h en o l was d e s c r i b e d in P a r t I of this th e si s.

49
II.

A p p a r a tu s

A..

Relative R at es of Alkylation

The a p p a r a t u s u s e d is shown in F i g u r e

I.

It c on s is te d of a

125 m l . r e a c t i o n f la s k , A, with a n it ro g en bub ble r extending to the
bottom of the f las k.

The f l a s k was s ea le d to a co nd en ser at B,

which was f itted at the top with a 14/35 m ale ground g l a ss joint, C.
The c o n d e n s e r was a t ta ch e d to a tube, D, with a t h r e e - w a y stopcock,
E, whose outlets w e r e fit ted with 14/35 male ground g l a s s joints, F,
to which sodium b ic a r b o n a te tubes w ere connected.

The sodium b i ­

c ar bo nat e tubes w e r e connected to a d ry ice t r a p by me ans of a
r u b b e r joint, G.

The r ea c t io n f l a s k was shaken manually at i n t e r ­

vals, and a continuous s t r e a m of dry n it ro g en gas was bubbled
through the r e a c t i o n m i x tu re during the c o u r s e of the reaction.

The

r e a c t i o n f l a s k was s u b m e r g e d in a co nstant t e m p e r a t u r e bath m a i n ­
tained at 50.0±0.1° during the e x p e r i m e n t s .

B.

Quantitative Kinetic M e a s u r e m e n t s

A s c h e m a t i c d i a g r a m of the r ate ap p ar at us is shown in F ig u r e
2 with p ho tog raph s of v ar io u s p a r t s of the s y s t e m appearing on follow­
ing p ag es .

50

Ng

D

\ ^ -G

FI GURE 1*
Apparatus
Rates of R ea ctio n .

for

th e Measurement

of

R elative

51

e

e>

0=dy=:
<IR

LUCM
AL

53

54

55
A w e l l - d e t a i l e d p i c t u r e of the r eactio n flask is shown in the
f i r s t photograph.

It c o n s i s t e d of a 125 ml. F l o r e n c e flask,

at the neck to a m e r c u r y seal

sealed

14/35 male ground g lass joint.

The

r ea c t io n v e s s e l contained two exit tubes joined to the f las ks ju s t
below the b a s e of the neck.
via two 4 -ml.

Each of these tubes was connected

stopcocks to a 15-inch,

15 mm . (O.D.) piece of glass

tubing, s e a l e d at the end with a 24/40 female ground gla ss joint.
These tubes t h e r e b y f u r n is h e d the ampoule c h a m b e r s f r o m which the
phenol and halide solutions were admitted to the reaction flask.

The

re a g e n t am poules were varying lengths of 12 m m . g l a ss tubing that
were s e a l e d off with 1 - 1 /2 inch c a p i l l a r y tip, which would slide into
the b ore of the top stopcock when the ampoules w ere placed in the
addition c h a m b e r s .

The top of the c h a m b e r s could be closed off

with 24/40 m a le plugs,

so that the rea ct io n s y s t e m could be c o m ­

p le tely evacuated.
The r e a c t i o n flas k was connected to the r e s t of the s yst em
through the 24/40 m e r c u r y seal joint (B).
tions w e r e

Since some of the r e a c ­

studied at e lev ated t e m p e r a t u r e s , a co nd en se r (C) was

used to p r e v e n t the dis ti lla tio n of the r e a c t a n t s to c oo ler p a r t s of
the s y s t e m .

The r e m a i n d e r of the r eaction side of the differential

m a n o m e t e r (D) c o n s i s t e d of 1 m m . c a p i l l a r y tubing with lines to a
vacuum and d r y n i t ro g e n s ou rce.

56
The outside of the differen tial m a n o m e t e r contained an e l e c t r i c
r e s t point signalling device (E) which c o n s i s t e d of both a light and
b u z z e r f o r indicating completion of the circ uit.

The r e s t of the

s y s t e m contained a o n e - l i t e r b uffer volume (F), a c a l ib r a t e d m a n o m e t e r
(G), and li ne s to the vacuum and dry nitrogen s o u r c e s .

The nitrogen

inlet contained a fine in v e r te d c a p i ll a ry to p e r m i t the i n c r e a s e in
p r e s s u r e on the outside of the d ifferential m a n o m e t e r by v e ry small
increm ents.
The n it ro g en so u rc e was a c o m m e r c i a l cylinder.

The n i t r o ­

gen was d r i e d by p a s s i n g it through a tube of phosphorus pentoxide
and the p r e s s u r e was r eg ula ted by m e a n s of a m e r c u r y blowout valve
set at a pp r o x im a t e ly 100 mm. above a t m o s p h e r ic p r e s s u r e .

A Cenco

Hy-Vac pump in s e r i e s with a m e r c u r y v ap or pump provided the
so ur ce of vacuum.
The r e a c t i o n f la s k was s u b m e rg e d in a constant t e m p e r a t u r e
bath of ethylene glycol, such that 90 p e r c e n t of the reaction s y s t e m
was t h e r m o s tatted at 88±0.01°.

E x c e lle nt s t i r r i n g was obtained in

the r e a c t i o n m i x t u r e by a g la ss c o v e r e d magnetic s t i r r i n g b a r
se ale d in the r ea ct io n flask.

C on sid er able ca re had to be taken,

however, in o r d e r to p r o t e c t the magnetic s t i r r i n g m o t o r which was
p l a c e d in the hot glycol bath.

A method that finally p r oved effective

57
was to e n ca se the r u b b e r e l e c t r i c a l lead to the m oto r in a copper
tube that was f a s t e n e d to the m o t o r case through an a ir ti g h t b r a s s
fitting.

The bottom of the case was m e ta l sealed, and the en tir e o ut­

fit coated with glyptal r e s i n and c o v e re d with h ar d - s ur faced black
fr ict io n tape.

The r e ac tio n flask, when clamped in the bath,

rested

l e s s than o n e- ha lf inch above the s t i r r i n g motor.

III.

Method of M e as u r in g Rate and Operation P r o c e d u r e

A.

Relative Rates of Alkylation

The p e r c e n t a g e of alkylation during a definite time interval
was d e t e r m i n e d by collecting the evolved hydrogen chloride in a
sodium c ar b o n a te tube and d et er min in g the chloride content by the
Vo lhard method.
The m i x t u r e of the t-butyl chloride and substituted phenol
was allowed to r e a c t , with a slow s t r e a m of dry nitrogen bubbling
through the m i x t u r e .

A. c o n s is t e n t r ate of agitation and nitrog en flow

was m a i n t a in e d throughout the m e a s u r e m e n t s .

At the end of the

defined t im e int er va l, the sodium carbonate tube was removed, its
contents d i ss o lv e d in w a t e r, and an alic[uot was acidified with n it ric
acid and an aly zed f o r chloride by the V olhard method.

58
When n i tro b en ze ne was used as the solvent, a blank e x p e r i ­
m e n t (in which the phenol was omitted)

showed no dehydrohalogenation

of the t-butyl chl ori de und er the conditions of the e xp er im en t.

A

qualitative t e s t made in each of the e x p e r i m e n t s also showed that
little if any isobutylene was c ollected in the dry ice trap, during the
c o u r s e of r e a c t io n .

B.

The Alkylation of Phenol with Trityl Chloride

(1)

P r e p a r a t i o n of Samples.

Since sm all t r a c e s of w a te r

would l e a d to i n c o r r e c t data due to the generation of hydrogen chloride
by h y d r o l y s i s of the halide, e x t r e m e c a r e was e x e r c i s e d in the handling
of all r e a g e n ts in o r d e r to exclude m o i s t u r e .
The ampoule, d e s c r i b e d in the section on app aratus, was drawn
out slightly to f o r m a c o n s t ri c ti o n n e a r the top, and then weighed with
a stopper.

The p u r i f i e d phenol was then pipetted in, the tube filled

with dry n i t ro g e n and r e- weig hed.

The p re v io u s ly d e ga s se d solvent

was then added, the m i x t u r e f r o ze n , and the ampoule s ealed under
vacuum.

The weight of o -d ic hl or ob en ze ne was then obtained by d i f ­

f e r e n c e when the two halves of the ampoule w ere weighed.
The t r i t y l ch lorid e was made up by weight in o_-dichlorobenzene
solution.

A s pecified amount was added to a weighed ampoule, the

59
m i x tu re f r o z en , and the ampoule s eale d under v3.cu.um,

The two

halves of the ampoule w e re then weighed, giving the weight of the
solution s am pl e by difference.
When hydrogen chloride was added to t e s t for acid c a ta ly s is ,
the phenol ampoule was a ttach ed to a hydrogen chloride g e n e r a t o r
and the d r i e d gas bubbled through the m i x tu re for s e v e r a l minutes,
before the ampoule was sealed.

(2)

M easurement P ro ced u re.

The method of following the

rate of the r e a c t i o n was to add a known weight of alkyl halide to a
known weight of phenol in a t h e r m o s t a t t e d v e s s el, and then m e a s u r e
the i n c r e a s e in p r e s s u r e due to the evolution of hydrogen chloride
gas in a co ns ta nt volume sy stem .
When making m e a s u r e m e n t s , the phenol solution was added
to the r ea c t io n v e s s e l and t e m p e r a t u r e and p r e s s u r e equilibrium
were r a p id l y e s ta b l i s h e d .

The t e r t i a r y halide was then admitted

and time v e r s u s p r e s s u r e

read in gs w e re made.

The reactio n was

followed in m o s t c a s e s until 85 to 100 p e r c e n t complete.
Thus, the am pou les w e r e p la c ed in the c h a m b e r s of the r e a c ­
tion f l a s k so that the c a p i l l a r y tip extended into the b o re of the top
stopcock, and the c h a m b e r s w ere closed off to the a t m o s p h e re .
e n t ir e s y s t e m was then evacuated,

The

sparked, and checked for leaks.

60
M e r c u r y w as then a d m itt e d to the differential m a n o m e t e r until c on ­
t a c t with the u p p e r tungsten le ad was made.

Both sides of the s y s t em

were then filled with d r y nitrogen and twice r e - e v a c u a t e d in o r d e r
to in s u r e the p r e s e n c e of v e r y little oxygen in the system, and t h e r e ­
fo re, v e r y little oxidation of the phenol during the co u r s e of the r e ­
action.

With the s y s t e m evac uated the phenol solution was admitted

to the r e a c t i o n v e s s e l by turning the stopcock gently in o r d e r to b r e a k
the c a p i l l a r y tip.

The tube was then gently f lam ed and the lower

stopcock c lo s ed so th at the c h a m b e r a r e a would not be included in
the r e a c ti o n s y s t e m volume.

( E ar ly work showed that two stopcocks

were n e c e s s a r y f o r this p r o c e d u r e , as small p i e ce s of g la s s often
p r e v e n t e d the closing of the stopcock used to c r a c k the cap illa ry tip.)
A f te r a p p r o x i m a t e ly t h ir ty minutes the halide solution was a d ­
m i tte d in the sam e m a n n e r as d e s c r i b e d above.

The stopwatch was

s t a r t e d as soon as the stopcock was opened admitting the halide,
and in all e x p e r i m e n t s this stopcock was opened f o r a p e r i o d of only
th i r t y seconds.
Readings w e re begun in e v e r y case as quickly as p os si ble.
The n i t r o g e n was b le d in to the outside of the differential m a n o m e t e r
in s mal l i n c r e m e n t s and read in g s w e re taken on the 1,m a k e 11 of c o n ­
t a ct with the u p p e r tungsten lead.

Readings were taken as frequently

61
as p o s s ib le

( every few minutes) ■at the beginning of the r eaction and

l e s s f r e q u en t l y as the r e a c t i o n p r oceede d.
A f te r the completion of a run, the halide addition tube was
r i n s e d with hot aqueous ethanol.

The w a t e r caused h yd roly sis of any

tr ity l chloride that r e m a i n e d behind in the addition tube.

These r i n s ­

ings w e r e t h e r e f o r e analyzed f o r chloride by the Volhard p r o c e d u r e ,
and th e s e d e t e r m i n a t i o n s

showed that l e s s than 0.1 p e r c e n t of the

halide r e m a i n e d behind.
The r e a c t i o n v e s s e l was then thoroughly cleaned, d rie d and
r e - j o i n e d to the s y s t e m f o r the subsequent run.

IV.

The N a tu re of the Alkylations

The r e a c t i o n between t-butyl chloride and phenol, used in the
r ela tiv e r a t e

studies was d e m o n s t r a t e d to be e s s e n t i a l l y quantitative,

yielding p - t- b u ty lp h e n o l with no dehydrohalogenation.
When n it ro b en zen e was u s ed as a solvent, E x p e r i m e n t s

8 to

10, Table 1, a blank e x p e r i m e n t in which phenol was omitted, showed
no dehydrohalogenation under r e a c t io n conditions.
T ri ty l c hlorid e was found to r e a c t with phenol in the same
m a n n e r , giving p - tr it y l p h e n o l .

A fte r completion of E x p e r i m e n t 4,

Table 2, the r e a c t i o n m i x t u r e was cooled and a white solid s e p a r a t e d

62
rapidly.

The p r e c i p i t a t e was f i l te r e d , and r e c r y s t a l l i z e d f ro m hot

benzene; m.p. 280-281
(4).

.

L i t e r a t u r e value f o r p - tr ity lp h e n o l is 282°

Following the completion of E x p e r i m e n t 5, Table 2, the same

p r o c e d u r e was u s ed to s e p a r a t e the p r odu ct of the o - c r e s o l t r i t y l
chloride r e a c t io n .
solid, m.p.

185-186°.

Anal.
Found:

R e c r y s t a l l i z a t i o n f r o m hot benzene gave a white

Calcd. f o r

2 6^22^*

89-12 p er cent; H, 6.33 p e rc en t.

C, 89.32 p e r c e n t ; H, 6.48 p e r c e n t .
The melting point of this p r o d u ct is the same as that r e p o r te d

by Iddles and c o - w o r k e r s

(54) f o r the alkylation of o - c r e s o l with

tr ity l c a rb in o l in the p r e s e n c e of a s u l f u r i c - g l a c i a l acetic acid c a t ­
alyst.

At the s a m e time and in two subsequent publications (55, 5 6),

Iddles v e r i f i e d the a s s i g n e d s t r u c t u r e ( p - t r i t y l - o - e r e s o l ) by a s e r i e s
of independent sy nth eses which elim i na te d the possibility of ortho
orientation f o r the incoming tri ty l group, o r side chain alkylation
of the methyl group.
A blank e x p e r i m e n t involving the heating of tr ity l chloride in
o -d ic h lo r o b en z en e solvent at 90 , showed no hydrogen chloride e v o ­
lution o v e r a p e r i o d of 24 h o u r s .

This indicated that no solvent

alkylation had o c c u r r e d , and that the solvent would not i n t e r f e r e
with the r a t e d e t e r m i n a t i o n s .

63
R e s ult s and Calculations

I.

Relative Rates of Alkylation

The e x p e r i m e n t s which w ere c a r r i e d out a r e s u m m a r i z e d in
Table

1.

The data obtained f r o m the Volhard an aly se s were in the

f o r m of m o l e s of hydrogen chloride evolved in a given time interval,
t.

Since this was equivalent to the m o le s of alkyl halide which had

r e a c t ed , the p e r c e n t a g e of alkylation f o r time t (last column,

Table

1) could be c a lc u la te d as follows:

. ...
.
m o l e s evolved HC1
% alkylation = -———-------—---- r*r* x 10 0
initial m o l e s of t-butyl chloride
Two and s o m e t i m e s even th r e e check runs were made on each e x ­
p e r i m e n t , and as can be seen f r o m the tabulations the r e s u l t s were
quite r ep r o d u ci b le in spite of the crude r a t e - d e t e r m i n i n g method used.

II.

Alkylations with Triphenylmethyl Chloride

A..

Data

Due to the r a t e - d e t e r m i n i n g method d e s c r i b e d in the e x p e r i ­
mental section, a hund red or m o r e time v e r s u s p r e s s u r e readings
w e re ob tain ed in each e x p e r i m e n t .

N um er ou s kinetic m e a s u r e m e n t s

w ere c a r r i e d out; consequently, a complete tabulation of the data

64
TABLE

1

RELATIVE RATES OF ALKYLATION OF SUBSTITUTED PHENOLS
WITH t-B UTY L CHLORIDE

Moles
of
Expt.
t-Bu
Cl

Substituent
on
Phenol

Moles
of
Ph en ol

Solvent

Moles
of
Solvent

Total
Reac tion
Time
( h r s .)

_
Temp,
*

Alkylation
(%)

0.01

none

0. 1

50

41 ±2

0.005

2-tbutyl

0.05

50

2.3

0.01

2
m ethyl

0.1

50

2. 7±
0.2

0.01

2,6- di­
methyl

0. 1

50

1 A±
0.2

0.005

2,6- dit- buty l

0.05

50

0.0

0.01

4methyl

0. 1

50

2 .2±
0.1

0.01

3methyl

0. 1

50

2 2 ±2

0.1

none

0.1

N i tr obenzene

0.25

24
48

75

9±1
14±1

9

0.1

2,6- dit-butyl

0.1

N i tr obenzene

0.25

24
48

75

0,8
1.3

10

0.1

2,6-di0.1
t- bu ty l
with 0.1
mole phenol

N i tr o benzene

0.25

48

75

13.7

7

-

A v er age of t h r e e r un s .

Average of two runs

65
f r o m e ac h individual e x p e r i m e n t would be prohibitive.

A summary

of the e s s e n t i a l r e s u l t s obtained f r o m nine of the e x p e ri m e n ts is
given in Table 2.
Time v e r s u s p r e s s u r e plots were made f o r each run, and
s e v e r a l of these a r e i l l u s t r a t e d in F i g u r e

3.

These cur ves

show

the c o n s i s t e n c y of the m e a s u r e m e n t s in any one e xp er im en t, and for
the sake of c l a r i t y in the drawings only one e xp er im e n ta l point out
of e v e r y ten i s included.
E x p e r i m e n t s 8 and 9, Table 2, r e p r e s e n t two runs c a r r i e d
out with phenol and t-butyl chloride, under the same conditions used
by H a r t and Simons (2).

Since the r e s u l t s obtained in these runs

w ere in a g r e e m e n t with those p r e v io u s l y repo rte d, it was a s s u m e d
t ha t the r a t e - d e t e r m i n i n g a p p ar at u s was functioning p rop erly .

B.

T r e a t m e n t of Data

The e x p e r i m e n t a l plots of p r e s s u r e v e r s u s time (Figure 3)
gave

MS M shaped c u r v e s in all runs except n um b e r 7.

In this run,

the phenol ampoule was s a t u r a t e d with anhydrous hydrogen chloride
before being a d m itt ed to the rea ct io n v e s se l.

Since the ’’induction

p e r i o d ’’ was e l im i n a t e d in this re ac tio n (see F i g u r e

3, curve n u m b e r

7), it was r e a s o n a b l e to a s s u m e that an i n c r e a s e in r eaction rate

66
TABLE 2
KINETIC STUDIES OF THE ALKYLATION OF PHENOLS
WITH TRIPHENYLMETHYL CHLORIDE IN
o-DICHLOROBENZENE AT 88°
M o la r ity
Expt. P hen ol
(M/L)

M o la ri ty
Halide
(M/L)

( P° >
(mm.)

Pf
(mm.)

k
(1 mole-1
m i n - 1)

kl
...(1 m o l e - 2
m i n - 1)

1

0. 315(P)

0.631

88.2

5 42.2

0.20 37

0.001744

2*

0 . 6lO(P)
0.610(F)

0.629
0.629

71.5
73.8

525.5
529.0

0.4296
0.4389
Appr.k =
0.2786°

0.005381
0.0054305
Appr.k =
0.005812

3

0.9132(F)

0.6105

87.4

657.0

0.78623

0.0081475

4

1.184(F)

0.5935

126.2

670.5

1.0869
Appr.k =
0.6814°

0.013125
Appr.k =
0.012950

5

1.184(C)

0.5921

101.5

757.5

0.3327

0.010353

6

1.368(C)

0.3571

162.0

435.0

0.3552

0.010114

7 **

1.368(C)

0.3571

279-1

553.4

0.01112(B)

107.8

506.2

8

10.55(F)

0.009779
0.01241
5 ^

9

10.61(F)

0.009881(B) 104.5

499.7

min.)

0.01357
5 i / l 2 min.)

* Check runs m ad e at this concentration.
' ^ H y d r o g e n chloride added initially.
P = phenol.
C = o - e r e sol.
B r e p r e s e n t s the n u m b e r of m o le s of t-butyl chloride added
to the phenol (in p la ce of t r i t y l chloride).

67

700

600

Pressure,

M illim eters

500

400

300

200

100

0

100

200

300
Time,

FI GURE 3 .
Pressure
and 7 , T a b le 2.

vs.

400

500

600

700

M inutes

Time C u r v e s

for

Experim ents

4,

5,

68
was b r o ug h t about in all the o th e r e x p e r i m e n t s following the f o r m a ­
tion of a sufficient c on c e n t r a ti o n of hydrogen chloride in the reactio n.

OH
C-C l

+

OH + HC1

Working with this hy pothesis the following equation was applied in an
at te m p t to d e s c r i b e the r e a c t i o n rate:
d p /d t =

[phenol] [halide] [HCl]

(1)

Using Ma M as the initial phenol concentration, and 1’b M as the initial
halide co n ce ntr ati on , the above t e r m s would be r e p r e s e n t e d f r o m the
e x p e r i m e n t a l data a t any time during the r ea c t io n as:
[phenol] = a - [(p - p )/(p - p )]a
o
i
o
[halide] = b - [(p - PQ)/(Pf * PQ)]b
[HCl] = P - PD
where p r e p r e s e n t s the ins ta ntaneous p r e s s u r e ,

p

pressure

solvent, phenol,

(a total of the v a po r p r e s s u r e s of the

halide), and p

the initial reaction
and

the final e q u i li b r iu m p r e s s u r e .

Substituting the above in equation (1) we

get

d p /d t =■ k [a - (p - p )/(p - P ) a ][t> - (p - P ) / (Pf - P ) b Kp ~ P ]
1
O
t O
o
x
o
which can b e s im p lif ie d by expanding and collecting t e r m s to:

d p / d t = k^ab[(p^ - p )/( pf - pQ)]2 [p . p ]

(2)

or
[dp/ (p - p) {p - p )] = [k a b/(p - p )2]dt
1
o
l
i
o
Inte gr atio n of the l a t t e r gives
[l/(P£

P q) 1 [ U / ( p f - pi] + [ l / ( Pf - Po)]ln [(p

- p o) /( pf - p 07j

=

[k ab /(p - p ) ]t + C[p - p ]
JI
o
t o

(3)

Evaluation of the c ons tan t of in tegr ati on is im p oss ible h er e, however,
b e ca u se on setting t = 0 and p = p , the equation b eco m es
o
[l/(p

I

)T|

- p ) ] j [ l / ( P f - P )] + [ l / ( p f - P )]ln[(p
- p )/(p - p
= C,
OL _ _ f
O
f
O
O
O
f
Q i

which is in d e t e r m i n a t e due to the n a t u r e of the log t e r m .
By multiplying equation (3) through by (p
can be

f

- p ), however, it
o

r e v i s e d to the f o r m of an e q u a tio n r e p r e s e n t i n g a s t r a i g h t line

[T l/(p f - P)] + [2.30 3 / (pf - PQ)]log[(p

- PQ)/(Pf - P)TJ =

[ k 1a b / ( p f - PQ)]t + c tPf - PQ]2
T h e r e fo r e , using Y to r e p r e s e n t the le ft side of the equation, a plot
of Y v e r s u s t should yield a s t r a i g h t line when the ex per im en ta l data
a r e applied to the equation.
shown in F i g u r e

4.

A plot of this type f o r E x p e r i m e n t 4 is

It is r e a d i l y s een that the equation holds e x c e p ­

tionally well f o r the l a t t e r p a r t of the reaction, but gives no s t r a i g h t line r el a t io n s h i p during the f i r s t 150 m in utes of reaction.

70

10

*

to

X

-2

“4
-5
-6
00

300

200
Time

F I GU R E 4 .
Experim ent

A pp lication
4.

of

,

Data

400

500

M inutes
to Third

Order R ate E q u a t io n ,

71
Since the l a t t e r p a r t of the re a c tio n was r e p r e s e n te d so well
by equation (1), it b e c a m e a p p a r e n t th a t the in itia l ra te might be
d e s c r ib e d b y the sam e equation m inus the HCl te r m , which of co u rse
would be of in s ig n ific a n t m agnitude n e a r the beginning of the reactio n .
Thus,
d p /d t = k [phenol][halide]
o

(4)

T r a n s c r ib in g th is to the e x p e r im e n ta l un its, expanding, and collecting
t e r m s as w as done in the p re v io u s c a s e , we get
d p /d t = k ab[(p
o
f

- p ) /( p , - p )]2
f
o

o r,
[dp/(pf - p )2] = [kQa b /(p f - PQ) 2]dt
Upon in te g r a tio n one then obtains
[ l / ( p f - P)1 = [kQa b /(p f - P q)2 ]1 + C

^

Thus, when t = 0, p = p , the in te g ra tio n constant, C, b eco m es equal
o
to [ l / ( p

f

- p )]•
o

Substituting th is value f o r C in equation (5), we ob-

tain the e x p r e s s io n
[X/(pf - P)] = [kQa b /(p f - PQ) 2]t + U /( P f " PQ)]
which once ag ain is the f o r m equation f o r a s tr a ig h t line.

(6)
C o n se­

quently, a p lo t of [ l / ( p £ - p)] v e r s u s [t] should give a s tr a ig h t- lin e
r e la tio n s h ip when applied to the e x p e r im e n ta l data, if the in itial ra te
is s a t i s f a c t o r i l y r e p r e s e n t e d by equation (4).

Such a p lo t is shown

72
fo r E x p e r im e n t 4 in F ig u r e 5.

Once again the m a rk e d deviation fro m

a s tr a i g h t line is seen; it is r e a d ily ap p aren t, how ever, that the d e ­
viation does not begin till a f te r the f i r s t 125 m inutes of reactio n .
F r o m the fo reg o in g r e s u l t s , th e re f o re , it is re a so n a b le to a ssu m e
th a t a co m b in atio n of equations (1) and (4) m ight well d e s c rib e the
e n tir e r e a c tio n r a t e .

Thus,

d p /d t - k Q[phenol][halide] + k [phenol][halide][HCl]

(7)

The e v alu atio n of the r a te co nstan ts in the above equation was a t ­
te m p te d b y c o n s id e rin g the two p a r t s of equation (7) s e p arately , and
using the two g r a p h ic a l m ethods which have ju s t been d escrib e d .
Each r a t e co n s ta n t was d e riv e d f r o m the slope of the s tra ig h t-lin e
p o rtio n of the d e riv a tiv e c u rv e s , exem plified by F ig u r e s 4 and 5.

This

was done f o r s e v e r a l ru n s, and the valu es obtained ap p ea r in Table 2,
d esig n ated as the a p p ro x im a te d values of

and k^.

In o r d e r to te s t

the a c c u r a c y of the co n stan ts ev alu ated in this m an n er, a calcu lated
curve f o r E x p e r im e n t 2 was p r e p a r e d fr o m equation (9) resu ltin g
f r o m the in te g r a tio n of equation (7), which follows.

The solid

curve in F ig u r e 6 r e p r e s e n t s th is calcu lated cu rv e, while the dotted
line shows a s i m i l a r p lo t of the e x p e rim e n ta l data f o r co m p ariso n .
Since the e x p e r im e n ta l points show co n sid era b le deviation fro m the
c a lc u la te d c u rv e , it i s obvious th at the d e te r m in e d v alu es of the

73

45

40

35

30

25

20

o

I—
I

K

a

o

50

100

50

200

250

300

350

T im e, M i n u t e s
FIGURE 5 .
A p p l i c a t i o n o f D a t a t o S e c o n d Order R a t e Law,
E xp erim ent 4.

74

-o

Pressure,

M illim eters

300

100

1000

2000

3000

Time , M i n u t e s
FIGURE 6 .
C o m p a r i s o n o f C a l c u l a t e d Curve from A p p r o x i ­
m a ted R a t e C o n s t a n t s and O b s e r v e d Curve f r o m E x p e r i m e n t 2.

75
ra te c o n s ta n ts a r e in e r r o r .

Consequently, the application of th ese

co n stan ts, o btained by tr e a tin g the beginning and end of the re a c tio n
s e p a r a te ly as p ro v id e d by equations (1) and (4), gives a th e o re tic a l
ra te cu rv e of the sam e shape as th at o b serv ed , but does not r e ­
produce the o b s e r v e d curve as a c c u r a te ly as one m ight like.
tic u la r , the v alu es of k

o

In p a r ­

s e e m to be quite a b it off, as seen fro m

Table 2.
E quation (7) was th e r e f o r e ev alu ated in the following m anner:
T r a n s c r ib in g to the e x p e r im e n ta l te rm s as d e s c rib e d p rev io u sly , we
get
+

ki E ■C(p ■ po)/(pf ■ po)]3 E ■[<p ■ po>/(pf ■ po>3 E ■p3
Expanding and co llectin g t e r m s ,

dp /dt = k ab[(p

- p)/(pf -

2
P Q) ]

+ k t ab[(pf - p ) / ( p f -

2
P q >]

[p -

P Q]

d p /d t = ab[(p X - p ) / ( p I, - P O )] [kO + k X (p - p vJ )]

dp /dt = [ a b / (p f - P0) 2 ][Pf - P]2 tk 0 + k ! (P ‘ Po)]
Equation (8) can now be tr a n s f o r m e d to an in teg rab le fo rm ,
2
2,
[dp/ (pf - p) {kQ - k 1Po + kjp)] = [ab /(p £ - Pq) ]dt
Upon in te g r a tio n of the above we then g et

(8)

It w a | quite obvious at this point that the in te g ra te d fo rm
was too co m plex f o r a re a s o n a b le evaluation of the reactio n c o n ­
s ta n ts .

A ttention was th e r e f o r e tu rn e d to the u n in teg rated fo rm

(equation 8).

If this equation is r e a r r a n g e d as follows,

[(dp/dt) / (p - p )Z] = [{k ab) / (p - p
±
i
l
o

)2][p - p ] + [(abk ) / (p
o
o
f o

-

p)2](10)

we once again have the m a th e m a tic a l e x p r e s s io n fo r a s tr a ig h t line.
2
Thus, if [(dp/dt) (p - p) ] w e re p lo tted a g ain st [p - p ], the r e s u lt
f
o

should be a s tr a i g h t line f o r

all the ex p e rim e n ta l data if equation

(10) s a ti s f a c to r il y r e p r e s e n t s

the

re a c tio n .

In such a case, the te rm

2
[(k. ab) / (p - p ) ] would r e p r e s e n t the slope of this line, and
1
f
o
2
[(abk )/(p - p ) ] would be equal to the value of the in te rc e p t,
o f
o
f r o m which then k

o

and k

1

could be evaluated.

The d e te r m in a tio n of (dp/dt) f o r the MY U t e r m of equation
(10) was c a r r i e d out a c c o rd in g to the method d e s c rib e d by H a r t and
Sim ons (2).

A. p lo t of the e x p e rim e n ta l data was f i r s t made on la rg e

g ra p h p a p e r , and a spline was u se d to draw a sm ooth curve through
th e se p o in ts.

N o r m a ls to the r a te c u r v e s w e re then drawn with a

77
plane f i r s t - s u r f ace m i r r o r held in a sm all fra m e at rig h t angles
to the plane of the c u rv e .

The n o r m a l was e s ta b lis h e d when the

curve and its im age a p p e a re d to give no p e rc e p tib le b r e a k .

The

slope of the r a te cu rv e, [dp/dt], was then d e te rm in e d as the n e g a ­
tive r e c i p r o c a l of the slope of the n o rm a l.

About fifteen to twenty

slopes w e re d e te r m in e d f o r each curve, at r e g u la r tim e in te rv a ls
throughout the r e a c tio n .
The v alu e of p* was d e te rm in e d by ex tra p o latio n of the r e a c ­
tion cu rv e to z e ro tim e.

Since the re a c tio n curve was quite flat

n e a r the beginning of the re a c tio n ,
with c o n s id e ra b le a c c u r a c y .

this d e te rm in a tio n could be made

The value of p was found ex p erim en ta lly
\
f

in all the ru n s , with the exception of the v e r y slow phenol alkylation s.
In th e se ru n s it was found th a t the data n e a r the end of the re a c tio n
gave a l i n e a r p lo t of [dp/dt] v e r s u s p.
e x tra p o la tio n of th is line to [dp/dt] = 0.

T h e re fo re , p

was found b y

This l i n e a r it y was ju stified

by the s u b stitu tio n of some actu al data, obtained n e a r the end of the
re a c tio n s , in equation (10).

When this was done at s e v e ra l p r e s s u r e s ,

it was found th a t the r e a c tio n r a te , [dp/dt], divided by the in s ta n ta n e ­
ous p r e s s u r e gave v a lu e s th a t changed p ro p o rtio n a lly with the change
in p r e s s u r e .
squares

(57).

The b e s t p lo t was d e te rm in e d b y the method of l e a s t
The a c c u r a c y of the v alu es of pf by this method was

78
checked in s e v e r a l r e a c tio n s by c o m p a ris o n with the e x p e rim e n ta lly
d e te r m in e d p^, v a lu e s.

The d ifferen c e was of the o r d e r of one p e r ­

cent.
The v alu es of " a 11 and " b 11 r e p r e s e n tin g the in itia l co n cen ­
tr a tio n of the phenol and halide, w e re d e te rm in e d by using both
e x p e r im e n ta lly m e a s u r e d d e n s itie s , and available data f r o m the l i t ­
e r a t u r e f o r the d e n s itie s of the phenols u s e d in each ex p erim en t.
The d e n s ity of the h a lid e - s o lv e n t com bination was d e te rm in e d at the
r e a c tio n t e m p e r a t u r e in the u su al m a n n e r and the volume of solution
was c a lc u la te d .

The volum e of the phenol at the re a c tio n te m p e r a ­

tu r e was c a lc u la te d f r o m the l i t e r a t u r e d en s itie s , its solution in the
halide - solv en t m ix tu r e being a s s u m e d to be p e r f e c t.

Since the

solutions w e re dilute, this assu m p tio n p ro b ab ly did not introduce
an a p p re c ia b le e r r o r .

Once the total r e a c tio n volume was c a l c u ­

la te d the m o l a r i t i e s of the phenol and halide could be d e te rm in e d in
the u su al way.
Having d e te r m in e d the n e c e s s a r y values f o r testin g the a p 2
p lic a b ility of equation (10), p lo ts of [(dp/dt)/(p^_ - p) ] v e r s u s [p - p^]
w ere m ade and a r e i l l u s t r a t e d in F ig u r e 7.
ta in ed o v e r the e n t ir e alky latio n re a c tio n .

S traig h t lin es w ere ob­
The b e s t s tr a ig h t line

w as d e te r m in e d in e a c h c a s e b y the method of l e a s t s q u a r e s , which

79

80

dp/dt

70

20

0

100

200
-

FI GURE 7 .

Adherence

of

300

p Q, M i l l i m e t e r s

A uto-C atalyzed

R eaction

tc

Equation

10.

80
a u to m a tic a lly y ields the v alu es f o r the slope and in te rc e p t.
ues of k^ and k , co lu m n s 6 and 1 ,

The v a l ­

Table 2 , could then be calculated.

The a c c u r a c y of the c o n sta n ts d e te rm in e d in this way is illu s tr a t e d
in F ig u r e 8, which shows the c lo se n e ss of the fit of the calculated
curve ( p r e p a r e d f r o m equation 9) and the e x p e rim e n ta l points.
r e s u l t s f o r E x p e r im e n ts

The

1 through 6 w e re th e re f o re d e te rm in e d by

this p r o c e d u r e , and a r e tab u lated in Table 2.
The m a th e m a tic a l ap p ro a ch to E x p e rim e n t 7 was v a r ie d
slightly since anhydrous hydrogen chloride was added before the
r e a c ta n ts w e re m ixed in the re a c tio n v e s s e l.

Since the ra te curve

f o r this r e a c tio n shows no induction p e rio d (see F ig u re

3), the f i r s t

t e r m of equation (7) can be d is c a r d e d and the re a c tio n d e s c rib e d by
d p /d t = k^ |a~ - [(p - p Q) /(p f - p^3) £ | [ b - [<P - P o)/(P f - P 0)]b||p - p j j

(ID

This equation d if f e r s f r o m equation (2) only by v irtue of the p ^ 1 te rm ,
which r e p r e s e n t s the z e ro p r e s s u r e o b se rv e d in E x p e rim e n t 6.

Since

the l a t t e r ru n is e x a c tly the sam e as E x p e rim e n t 7, save f o r the
added hy d ro g en c h lo rid e in E x p e r im e n t 7, the [p - P *] t e r m

rep re­

sen ts the a c id c o n c e n tra tio n as a sum of the hydrogen ch lo rid e
added [p - p fl p lu s th at which is f o r m e d during the alkylation [p - p ].
o
R e a r r a n g in g (11), we get

81

800

700

Pressure,

M illim eters

600

500

400

300

200

100

0

100

200

300

400
Tine

500

600

700

, M inutes

FI GURE 8 .
C o m p a r iso n o f C a l c u l a t e d Curve
E x p e r im e n t a l D a ta from E x p erim en t 5.

from

E q u a t i on

9 and

800

82
[(d p /d t)/(p

- p) ] = [(k ab)/(p
1

l

- p )2][p - p ']
i

o

which is the eq uation of a s tr a i g h t line having a zero

(12)

o

in te rc e p t.

This p lo t is shown in F ig u r e 9, and the lin e a r ity shows the ap p lic a ­
b il ity of equation (11) to the alkylation when hydrogen chloride is
p r e s e n t in su fficien t c o n c e n tra tio n a t the beginning of the reactio n .
The slope of this line was thus equal to [(k ab)/(p - p )^] fro m
1
f
o
which the k^ value, shown in Table 2, is obtained.
Since s e v e r a l alk ylatio n s w ere m ade at varying phenol co n ­
c e n tr a tio n s , the r e s u l t s can be u sed in an atte m p t to d eterm in e the
k inetic o r d e r of the re a c tio n with r e s p e c t to phenol.
in Table 2, the k

o

and k

1

As can be seen

r a te co n stan t values show a m a rk e d change

with change in phenol co n ce n tratio n .

This would be e x p r e s s e d

m a th e m a tic a lly thus,
r
,n
k = [phenolj

w here n r e p r e s e n t s the exponential r a te dependence on the phenol
co n ce n tra tio n .

C onverting fr o m exponential fo r m to log fo rm ,
log k = n log[phenol]

we a r r i v e a t an e x p r e s s io n f o r a s tr a ig h t line, having a slope of n.
If the r e a c tio n showed a f i r s t - o r d e r dependence on phenol
c o n c e n tra tio n , th e o r e tic a lly , the ra te co n stan t would show no change
with v a ry in g phenol co n c e n tra tio n , and thus the slope of the above

dp/dt

83

s

150

250
P -

FI GURE 9 .
Order R ate

Adherence
Law.

450

350
P 0r> M i l l i m e t e r s

o f .C atalyzed A lk y la tio n

to

Third

84
p lo t would be z e r o .

T h e r e fo r e , the kinetic o r d e r with r e s p e c t to

phenol m u s t be d e te r m in e d f r o m such a plot as the slope plus one,
o r [n + 1].

G rap h s of log k^ and log k^ v e r s u s log of the phenol

c o n c e n tra tio n a r e

shown in F ig u r e

d is c u s s e d in the sectio n to follow.

10, and th e i r significance will be

85

-

6. 0 -0.60

Ko, m = 1.23
-5.0-

-4 .0 -0 .4 0

.40

-3 .0 -

-0.30

-

-

-

6.0

-5.0

-4.0

-3.0

-

2.0

0.20

1. 0 -

1.0

Log P h e n o l C o n c e n t r a t i o n x 1 0
FIGURE 1 0 .
V ariation
Phenol C o n ce n tr a tio n .

o f R a t e C o n s t a n t s With Log o f

+ 1.0

86
D iscu ssio n

The alkylation of phenol and v a rio u s alkylated phenols was
c a r r i e d out using both t-b u ty l c h lo rid e and tr ity l chloride as the
alkylating ag en ts.

In ea c h case the o v e r - a ll re a c tio n s can be d e ­

s c r ib e d by the following equations:

H° - ( \

H°

y

/>

>7

+ t-R C l

+ t RC1

R

\ -OH

HCl

Q

/> - ° H

HCl

R

The r e s u l t s a r e
p e r im e n ts

^ t-R -/

s u m m a r iz e d in Table 1 in the p re v io u s section.

Ex­

1 through 7 w e re c a r r i e d out with the phenol to be alkylated

p r e s e n t in la r g e e x c e s s ; consequently, the r e a c tio n m edium could
h a r d ly be c o n s id e r e d as eq uivalent f ro m one e x p e rim e n t to another.
The la r g e r a te d e c r e a s e o b s e rv e d in going fro m un su b stitu ted phenol
to the highly h in d e re d 2 ,6 -d i-t-b u ty lp h e n o l m a y th e re f o re be the r e ­
sult of s e v e r a l f a c t o r s .

Substitution in the ortho positions should

d e c r e a s e the e ffic ie n c y of phenols f o r solvating carb o n iu m ions a n d /o r
in co o rd in a tin g the halogen of the t-b u ty l ch lo rid e.

That the effect

is p r e d o m in a n tly s t e r i c is in d icate d by the g r e a t e r r e a c tiv ity of
2 ,6 -d im eth y lp h e u o l as c o m p a re d with the d i- t- b u ty l d eriv ativ e.

The

87
opposite r e s u l t would have been p r e d ic te d on the b a s is of the r e l a ­
tive a c tiv a tio n of the p a r a p o sitio n due to the inductive effect of the
alkyl g ro u p s.
M eta and p a r a e r e sol (E x p erim en ts 6 and 7) both alkylate
ortho to the hydroxyl and consequently r e p r e s e n t co m p arab le r e a c ­
tions.

The so lv en t p r o p e r t i e s of th ese two m o lecu les a r e v e r y s i m ­

i l a r (58); th u s, the la rg e en h an cem en t of alkylation ra te fo r m - c r e s o l
o v e r the p a r a i s o m e r is a s c r ib e d h e re to the in c r e a s e d e le c tro n
density at the 6-p o sitio n cau sed by the inductive a n d / o r hyperconjugative e ffect of the m ethyl group.
It b e c a m e obvious at this point in o u r study, that in o r d e r
to avoid a m u ltip lic ity of explanations cau sed b y high phenol co n ce n ­
tr a tio n s in the r e a c tio n m edium , the k in e tic s m u st be studied in dilute
solution and in an i n e r t solvent.

The alkylation d e c r e a s e s in rate

quite r a p id ly when solvents such as p -x y lene, et c e te r a , a r e used.
In r e la tiv e r a te E x p e r im e n ts

8 to 10, an a tte m p t was made to use

n itro b e n zen e, but h e r e again the ra te was exceedingly slow, even at
75° C.

These e x p e r im e n ts do, how ever, r e p r e s e n t d eterm in atio n s

in m o r e dilute solution, and once again the m a rk e d d e c r e a s e in rate
f o r the 2, 6 -d i-t-b u ty lp h e n o l is o b s e rv e d .

88
In o r d e r to o v erco m e the ra te d e c r e a s e when an i n e r t solvent
is em ployed, we tu rn e d o ur attention to h ig h e r-b o ilin g halides,

so that

the r e a c tio n ra te could be in c r e a s e d by elevating the te m p e r a tu r e .
T rity l ch lo rid e m ade p o s s ib le a d ete rm in a tio n of m o r e p r e c i s e a lk y l­
ation k in e tic s m dilute solution (see Table 2 of the p rev io u s section),
and in addition e lim in a te d the p o s s ib ility of dehydrohalogenation of
the t e r t i a r y c h lo rid e.

Ortho dichlorobenzene was se le c te d fo r the

r e a c tio n solvent, as it o ffered an i n e r t m ed iu m of a m o d e ra te ly p o la r
n a tu re (E — 7.8).
The alky latio ns of phenol w ere c a r r i e d out at s e v e ra l phenol
c o n c e n tra tio n s in o r d e r to d e te rm in e the o r d e r of the reactio n with
r e s p e c t to phenol.

At the lo w e r c o n ce n tratio n s, when the instantaneous

p r e s s u r e was p lo tted a g a in s t the re a c tio n tim e,
w ere obtained.

n S M shaped cu rv es

The a p p a re n t induction p e r io d was not r e a d ily n o ti c e ­

able a t the h ig h e r co n c e n tra tio n s of phenol, but was even m o re evident
in the alk y latio n of o - c r e s o l .
Since the m e a s u r e m e n ts w ere made in an a l l- g la s s reactio n
s y s te m and a t an e le v a te d t e m p e r a tu r e , the p o s s ib ility of a p p a ra tu s
le akage w as f i r s t in v e stig a te d as an explanation fo r the type of
c u r v e s obtained.

R eaction 6 was th e re f o re c a r r i e d out at a reduced

halide c o n c e n tra tio n so th a t the final s y s te m p r e s s u r e would be well

89
below a tm o s p h e r ic p r e s s u r e , u n le ss leakage o c c u rre d .

Tlie reactio n

curve le v e le d off and held a t 435 m m . p r e s s u r e .
The only o th e r lo g ical explanation f o r the induction p e rio d
was th a t the r e a c tio n was a u to -c a ta ly z e d b y the hydrogen chloride
f o r m e d fu rin g the alkylation.

Reaction 7 was th e re fo re c a r r i e d out

using the sa m e c o n c e n tra tio n s and conditions of Reaction 6, except
th at an h y d ro u s h y drogen ch lorid e was added to the c r e s o l ampoule
befo re it was b ro k e n in the re a c tio n sy stem .
the e x p e r im e n ta l cu rv e (F igure

As can be seen fro m

3), the induction p e rio d was c o m ­

p le te ly e lim in a te d u n d er th ese conditions, indicating that it was,
indeed, the hyd ro g en ch lo rid e which was resp o n s ib le f o r the auto c a ta ly sis.
The e x p e r im e n ta l data obtained in E x p e rim e n t 7 a re r e p r e ­
sen ted

s a t i s f a c t o r i l y by the t h i r d - o r d e r equation,
d p /d t = k ^ [ c r e s o l] [ tr ity l chloride][HCl]

Once the ro le of the h y drogen ch lo rid e was u n d ersto o d

in the

tion, it w as r e a d ily seen th a t the o th e r experim ental curves

reac­
should

be fitte d by a t w o - te r m equation, a r r a n g e d so th at one t e r m would
in c r e a s e and a n o th e r t e r m
p ro c e e d e d .

Thus, the

d e c r e a s e in im p o rtan ce as the re a c tio n

n S M shaped c u rv e s , f o r all the o th e r alkylation

e x p e r im e n ts , we ire defined by the e x p re s s io n ,

90
d p /d t =

[phenol][halide] + k [phenol][halide][HCl]

w here k^ is a s e c o n d - o r d e r ra te co n stan t and k^ the th i r d - o r d e r
r a te c o n s ta n t d is c u s s e d above.
E x am in atio n of th e se ra te co n stan ts, Table 2, r e v e a ls , however,
th a t they v a r y c o n s is te n tly with change in phenol co n cen tratio n (i.e.,
f r o m one run to an o th er, although they a r e co n stan t f o r any given
run).

A lo g -lo g p lo t of phenol co n cen tratio n v e r s u s the ra te c o n ­

stan ts k^ and k^ gives a slope in both c a s e s of slightly g r e a t e r than
1.00 (F ig u re

10), which would le ad to a re a c tio n o r d e r of a p p ro x i­

mately 2 w ith r e s p e c t to phenol.

This would a p p e a r to be in c o n s is ­

te n t with the r a te - d e te r m i n in g equations.

One m u s t co n sid er, how­

e v e r, th a t the c o n c e n tra tio n of phenol (0.315 M to 1.184 M) is still
too g r e a t f o r r e a l ly ideal kinetic m e a s u r e m e n ts .

It th e re fo re a p ­

p e a r s re a s o n a b le to a s s u m e th at the change in phenol co n cen tratio n
is g r e a t enough to cause a change in solvent c h a r a c te r , which in
tu r n would account f o r the v a r ia tio n in the re a c tio n ra te co nstants.
It is i n t e r e s tin g to note the la r g e d e c r e a s e in k^ when o - e r e s o l
is u s e d in the e x p e r im e n ts in p lace of phenol.

If E x p erim en ts 4 and

5 a r e c o m p a re d , w h ere the a r o m a tic co n cen tratio n s a r e equivalent,
we see th a t the in itia l re a c tio n ra te f o r the q - c r e s o l alkylation is
ju s t about 1/3 th at of phenol.

The k^ value fo r the c r e s o l, however,

91
i s n e a r l y a s g r e a t as th a t f o r the phenol alkylation, which would lead
one to b eliev e th a t the h ydrogen ch lo rid e, following its fo rm a tio n in
the re a c tio n , a s s u m e s a role in the alkylation m e ch an ism which
w as p e r f o r m e d in itia lly b y the o - c r e s o l , and som ew hat l e s s efficien tly
than b y the u n s u b stitu te d phenol.

92
M ech an ism

B efore fo rm u la tin g a m e c h a n is m fo r the re a c tio n under co n ­
s id e r a tio n , it will be well at this point to c o r r e l a te the facts p r e ­
sented in p a s t in v e stig atio n s with those re su ltin g fro m o ur kinetic
stu d ie s co n ce rn in g the effect of hydrogen chloride on the alkylation
r e a c tio n .
In 1927 van Alphen (1) showed that phenyl tr ity l and o - c r e s y l
t r i ty l e t h e r s could be t r a n s f o r m e d b y hydrogen chloride to p a r a
alk y late d p h en o ls.

B ased on this evidence, th is w o rk e r concluded

th at the alk y lation of phenol with t e r t i a r y halid es p ro ceed e d by way
of an e t h e r in te r m e d ia te , which, being unstable in the p r e s e n c e of
hydrogen c h lo rid e , un d erw en t r e a r r a n g e m e n t to the alkylated phenol.
The k in e tic stu d ies of H a rt and Simons (2), however, in d i­
c a te d th at when alkylation was c a r r i e d out in an e x c e ss of phenol
as the solvent, it was n e i th e r a u to -c a ta ly z e d by the p roduct, hydrogen
ch lo rid e, n o r c a ta ly z e d by added hydrogen ch lo rid e.
We have found th a t when the re a c tio n is c a r r i e d out in dilute
solution, the r e a c tio n ra te is slow enough to o b serv e a u to -c a ta ly s is
by the h yd ro g en c h lo rid e f o r m e d during the re actio n .

This a p p a re n t

induction p e r io d is e lim in a te d when hydrogen chloride is added
in itia lly to the re a c tio n m ix tu r e , and the re a c tio n is found to be

93
f i r s t - o r d e r with r e s p e c t to hydrogen ch lo rid e.

It th e re fo re a p p e a rs

th a t when the alk y latio n is c a r r i e d out in ex ce ss phenol, as was done
hy H a r t and S im o n s , the re a c tio n is too rap id to give evidence of the
a u to -c ataly sis.

F u r t h e r m o r e , the s t i r r i n g technique u se d in the

p r e s e n t w ork was s u p e r i o r to th at em ployed by H a rt and Simons,
and p e r m i t t e d p r e c i s e

r a te m e a s u r e m e n ts within one o r two m inutes

a f te r the beginning of the re a c tio n .

This is im p o rta n t in detecting

auto - c a t a ly s is .
In connection with th is d is c o v e ry one should also c o n sid er
the k in etic stu d ies of Swain (4, 5) on the re a c tio n of tr ity l chloride
with phenol in benzene solution.

The re a c tio n p ro d u c t in this case

was found to be phenyl tr ity l e th e r , but the r a te - d e te r m in in g method
em ployed in th is w ork r e q u ir e d th at the hydrogen chloride produced
in the r e a c tio n be consum ed b y py rid in e p r e s e n t in the reactio n
m edium .

Although this study a p p e a rs to add su pp o rt to van A lphen's

p o stu la tio n th a t the e t h e r is f i r s t fo rm e d in the alkylation of phenol,
followed by h y d ro g en ch lo rid e r e a r r a n g e m e n t, it is e n tire ly possible
th at the n a tu re of the r e a c tio n is com pletely changed by the p re s e n c e
of p y rid in e in the r e a c tio n m edium .
On the b a s i s of th e se co n sid e ra tio n s and the facts p r e s e n te d
in the d is c u s s io n sectio n , th e r e ap p ear to be two g en eral, and

94
e s s e n ti a lly d iffe re n t m e c h a n is m s that m ight well explain the facts
o b s e rv e d , and thus d e s c r ib e the alkylation of phenol by t e r t i a r y
h a lid e s in dilute solution.
The f i r s t of th e se would involve the p r e li m in a r y fo rm atio n
of the phenyl t r i t y l e t h e r as an unstable in te rm e d ia te , followed by
the r e a r r a n g e m e n t of this e th e r in the p re s e n c e of the g en erated
h ydrogen ch lo rid e to f o r m the

tr ity l phenol.

On the b a s is of some

r e c e n t e x p e r im e n ts with the tr ity l e t h e r of o - c r e s o l (59), this m e c h ­
a n is m does not a p p e a r tenable f o r the alkylation reaction.

Thus,

when a 0.5 m o l a r solution of tr ity l q - c r e s y l e th e r in benzene was
t r e a t e d w ith d ry hydrogen chloride fo r ten m inutes at 60 , a 90 p e r
cent y ie ld of o - c r e s o l was is o la te d fro m a 10 p e r cent alk ali e x ­
t r a c t of the r e a c tio n m ix tu re .

F r o m the alk ali-in so lu b le m a te r ia l a

70 p e r cen t r e c o v e r y of tr i ty l carb in o l, which is the expected h y ­
d r o ly s is p r o d u c t of tr ity l ch lo rid e, w as m ade.

The re a c tio n between

the e t h e r and hy d ro g en ch lo rid e, th e r e f o r e , is a v e r y ra p id cleavage,
and not a r e a r r a n g e m e n t .

Since the s ta rtin g m a te r ia l s used in the

alkylation a r e the p r i m a r y p ro d u c ts of the e th e r cleavage, it follows
th a t the a lk y la te d phenol is f o r m e d d ir e c tly and not b y way of the
e th e r .

95
In the lig h t of th e s e fa c ts it is of i n t e r e s t to note the actual
d ata r e p o r t e d b y Swain (4) f o r the k in e tic s of fo rm atio n of the phenyl
tr ity l e t h e r .

With a phenol m o la r ity of 0.056 in benzene solution at

25°, Swain d e te r m in e d a t h i r d - o r d e r ra te co n stan t of 0.004 ± 0.002
2
-1
S. 'm ole

. -1
-mm.

.

By c o m p a ris o n , at o u r low est reactio n concentration

(phenol m o l a r i t y = 0.315) in o -d ich lo ro b en zen e a t 88°, the reactio n
ra te as e x e m p lifie d by the t h i r d - o r d e r ra te constant is only 0.001744
2
1 - 1
JL -mole
-min.
-

.

The fo rm a tio n of the e th e r under the conditions

u sed by Swain, th e r e f o r e , a p p e a rs to be a much f a s t e r conversion
than the alk y latio n re a c tio n , which once again indicates that the r e ­
action u n d e r stu d y is c o m p le te ly changed in n atu re by the p re s e n c e
of p y rid in e in the r e a c tio n m ix tu re .
A second and p r e f e r r e d m e c h a n ism , which is c o n s is te n t with
all the d a ta o b tained in this study, involves the p r i m a r y ionization
of the t e r t i a r y halide to f o rm a f r e e or solvated carbonium ion,
which then a tta c k s the p a r a p o sitio n of the phenol to fo rm £ - t r i t y l phenol.

Such a m e c h a n is m is d e s c r ib e d b y the following sequence,

w here R is the trip h e n y l m ethyl group:

t_R<^

^

/ / ~ OH

S l °- - ->

t - R

- /

^"°H+ ^

with the e le c tr o p h ilic a tta c k at the p a r a position constituting the r a te d e te rm in in g step.

It is re a s o n a b le that this be the slow step b ecause

the t e r t i a r y carb o n iu m ion is the m o s t e a s ily fo rm e d of carbonium
ions, and is in tu r n the m o s t u n re a c tiv e following its fo rm atio n, due
to the s tab ilizin g e ffect of re so n a n c e .
As to the con trib u tion by hydrogen chloride in the alkylation,
it is quite lik e ly that it would fa c ilita te the ra p id fo rm atio n of the
carb o n iu m ion f o r its attack on the phenol m olecule.

G rayson and

Brow n (60) have r e c e n tly shown th at the alkylation of benzene with
a p r i m a r y halide p r o c e e d s by a t h i r d - o r d e r m e ch an ism involving
the alkyl halide, AlCl^, and the a r o m a tic component.

The r a te -

d e term in in g step in th is r e a c tio n is d e s c rib e d as a nucleophilic a t­
tack by benzene on a h alid e-A lC l^ complex.
fast
R -C l

[R -C l : A1C13]

A1C13

+

^

^

<■----[R-Cl : A1C13]

SlQ^> R- ^

^

+ Hcl + A1C1 3

97
The couple [R -C l : A lC g ] is l e a s t ionic when R is p r im a r y , and
m o s t ionic when R is t e r t i a r y .
F o r the th ir d .- o rd e r m e c h a n is m we can th e re f o re w rite the
m e c h a n is tic equations,

+

2HC1

f r o m which the following ra te law can be derived:
V = [(k 1)(k2)(H C l)(0 3-C -C l)(phenol)]/[(k_

+ k 2){phenol)]

When k 1 is la r g e as c o m p a re d to k , which m u s t be the case h ere
“1
c*
(the e q u ilib riu m c o n ce n tratio n of the carbo n iu m ion has to be v e ry
sm all), then the e x p r e s s io n re d u c e s to the t h i r d - o r d e r ra te law,
V = [(k1)(k2)(H C l)(0 3-C -C l)(p h e n o l)]/[k _ 1]

= [(k 3)(H C l)(0 3-C -C l)(phenol)]

When the h ydrogen ch lo rid e is not p r e s e n t in itially in the reactio n
m ix tu re , the s o lv o ly sis of the t e r t i a r y halide is undoubtedly u n d e r ­
taken by the phenol p r e s e n t, which is known to have a high affinity
f o r halogen.

This e ffe c t is r e a liz e d in the k^ v alu es (Table 2) f o r

98
c o m p a ra tiv e

ru n s of phenol and o - c r e s o l .

The l a t t e r is le s s effective

a t solvating c a rb o n iu m ions, and th e r e f o r e gives a slow er rate of
re actio n .

H ow ever, as soon as the hydrogen chloride is fo rm ed , the

k^ v alu es f o r o^-cresol alkylation a pp ro ach that of phenol as the o - c r e s o l
is r e p la c e d by hydrogen chloride i*t the solvolysis step.
B e fo re concluding,

some m ention should be made as to the

re la tio n s h ip of this p r o p o s e d m e c h a n is m to the " a m p h o te ric medium
e f f e c t " of H a r t and Sim ons (2), and the te r m o le c u l a r m e ch an ism s
of Swain (4).

Indeed, Swain has pointed out (5) th a t th e re is no sig ­

n ifican t d iffe re n c e b etw een a t e r m o le c u l a r re a c tio n and one involving
p r e li m in a r y ,

r e v e r s i b l e fo rm a tio n of a p o la r com plex o r solvated ion

of two r e a c t a n t s , followed by a slow re a c tio n with the third.

Since

such an i n t e r p r e ta t io n is s ta tis tic a lly le s s p robable in dilute solution,
it a p p e a rs m o r e u seful at p r e s e n t to su b sc rib e to the g en eral con­
cept of the d is p la c e m e n t re a c tio n accep ted by m o st in v e stig a to rs .

In

the case of the w o rk of H a r t and Simons (2), how ever, such a t e r m o ­
l e c u l a r m e c h a n is m is highly p ro b ab le since the re a c tio n was c a r r i e d
out in phenol as a solvent.

We have shown the im p o rtance of the

phenol m o lecu le f o r solvation of the halide when no o th e r c a ta ly s t
is p r e s e n t , and in view of the a cc ep ted am p h o teric p r o p e r ti e s of
phenol, th e r e is no doubt th a t a c o n c e rte d m e ch an ism , of the type

99
p ro p o s e d by H a r t and Sim ons (2), p ro v id es an a ttr a c tiv e a lte rn a tiv e
when the r e a c tio n conditions fa v o r a m e ch an ism of r e la tiv e ly low
e n erg y r e q u ir e m e n ts .

PART C

THE MECHANISM OF THE INHIBITION OF PHENOL ALKYLATIONS
BY OXYGENATED COMPOUNDS

100

101
Expe rim e n ta l

L

Mate r i a l s

The phenol and t-b u ty l chloride u sed in this investigation were
p u rifie d by the sam e m ethod as th at d e s c r ib e d in P a r t B.
The dioxane, an E a s tm a n Kodak pro d u ct, was p u rified by the
m ethod d e s c r ib e d by F i e s e r (6 l).

One l i t e r of dioxane was refluxed

with 14 m l. of c o n c e n tra te d h y d ro ch lo ric acid fo r twelve hours.

The

m ix tu re was then cooled and s a tu r a te d with p o ta ss iu m hydroxide
p e lle ts .

The l a y e r s w ere s e p a ra te d , and the dioxane was tr e a te d

with f r e s h p o ta s s iu m hydroxide, decanted, and refluxed with sodium
f o r tw e n ty -fo u r h o u r s .

F r e s h sodium was added at definite in te rv a ls

until the m e ta llic s u rfa c e re m a in e d b rig h t.

The dioxane was then

d is tille d f r o m the sodium , s to r e d o v e r sodium and in a nitrogen a t ­
m o s p h e re u n til r e a d y f o r use.
The te tr a h y d r o p y r a n was p r e p a r e d fr o m duPont dihydropyran
by c a ta ly tic h y d ro g en atio n .

To 8 g. of Raney nickel c a ta ly s t in a

r u b b e r - s t o p p e r e d hydro g en atio n bottle was added 50.5 g. (0 . 6 mole)
of dihydrop.yran.

The bottle was shaken u n der f o r ty pounds hydrogen

p r e s s u r e f o r t h i r ty m in u te s , the c a ta ly s t allowed to s e ttle , and the

102
p ro d u c t d eca n ted off f o r d is tilla tio n .

The f r a c tio n a te d te tra h y d ro p y ra n ,

b.p. 85-86 , w as s to r e d u n d er n itro g e n until read y fo r use.

II.

P r e p a r a t i o n of Sam ples

Since the a p p a ra tu s u s e d was the sam e as that d e s c rib e d in
P a r t B, the s a m p le s w e re p r e p a r e d in much the same m a n n er.

A fter

the phenol was added to the am poule, sto p p ered and weighed, the
oxygenated compound was added, the m ix tu re fro z e n in d ry ice and
the am poule s e a le d u n d e r vacuum.

The weight of the oxygenated

compound was then o btained f r o m the total weight by difference.
The t e r t i a r y halide sa m p le s w ere p r e p a r e d in the same m a n n er,
using s ta n d a r d techniques f o r deg assin g and sealing off the sam p les.
C are was tak en to keep oxygen and t r a c e s of m o istu re fro m the
s a m p le s .

III.

Me a s u r e m e n t P r o c e dure

The r a te of r e a c tio n was followed in the same m a n n e r as
d e s c r ib e d in P a r t B f o r the quantitative k in e tics m e a s u re m e n ts .
Follow ing e a c h run the halide addition tube was rin s e d with
95 p e r cen t ethanol, and the rin s in g s analyzed f o r chloride by the
V olhard p r o c e d u r e , allowing fifteen m in u tes f o r re a c tio n of s ilv e r

103
n it r a te w ith the o rg a n ic halid e.

The weight of alkyl halide in the

am poule was then c o r r e c t e d f o r the am ount which rem a in ed behind.
This c o r r e c t i o n was u s u a lly l e s s than one p e rc e n t.

104
R e s u lts and C alculations

L

D ata

As w as p o in ted out p re v io u s ly , the ex p erim en ta l technique and
ra te —
d e te rm in in g m eth o d u sed h e r e is e s s e n tia lly the sam e as that
d e s c r ib e d m D a r t B of this th e s is .

Anywhere fro m 100 to as many

as 2 0 0 t i m e - v e r s u s - p r e s s u r e read in g s w ere obtained f o r each run,
and s p a c e p r e v e n ts th e i r tabulation.
d ata a r e

shown in F ig u r e

However, s e v e r a l plots of these

1, and th ese c u rv e s will point out the

c o n s is te n c y of the m e a s u r e m e n ts in any one ex p erim ent.

Only one

out of e v e r y ten p oints is shown on th ese cu rv es fo r the sake of
c l a r i t y in the p lo ts.

II.

T r e a tm e n t of Data

A s u m m a r y of the e s s e n ti a l data and r e s u lts is shown in Table
1.

The e x p e r im e n ta lly d e te r m in e d f i r s t - o r d e r ra te constants (k) and

the re a c tio n half tim e s

(t

. ) a r e given in columns 8 and 9, re sp ec-

1/ Z

tively, and w e re d e te r m in e d by the following p ro c e d u r e .
The u n c a ta ly z e d alkylation of phenol in the p re s e n c e of ex ce ss
phenol w as deterjrained to be f i r s t - o r d e r with r e s p e c t to the t e r t i a r y
h alid e.
equation.

Thus, the r e a c tio n is r e p r e s e n t e d m a th e m a tic a lly by the

500
105

Pressure,

M illim eters

400

200

0

Time,
FI GURE 1 ,
3 , and 5,

Pressure
T a b le 1.

300

200

100

vs.

M inutes

Time C u r v es

for

Experim ents

1,

106
TABLE

1

KINETIC DATA FOR THE ALKYLATION O F P H E N O L IN THE
P R E S E N C E OF OXYGENATED COMPOUNDS

E x p t.

t - B u Cl
M ole s

Phenol
Mole s

O x y g en ate
Mole s

( 1)

(2 )

(3)

(4)

-

0.01112

0.2156

0.009881

0.2165

0.009150

0.2120

0.006082

0.01071

0.2166

0 .0 1 347 D

0.01050

0.2123

0.02405 D

0.01167

0.2 223

0.0 3722 D

0 .0 1 1 2 9

0.2164

0.01221

0.01129

0.2091

0.02422 P

0.01 140

0.2142

0.0 3472 P

0 .0 1 1575

0.21 33

0.0 3248 X

10

* T h ese v a lu e s w e r e c a l c u la t e d on the b a s i s
o x y g en ate a c t s only as a d ilu en t.
M ean ing of s y m b o ls used:
D — 1 , 4 - d io x an e.
P = te tra h y d ro p y r a n .
X = p_-“xylene .

D

P

th a t the a d d e d

107
TABLE

M o la rity *
P henol

1 (Continued)

Pf

Po

k

(5)

(6)

(7)

(8)

10.55

506.2

107.8

0.01241

55.2

10. 61

499.7

104.5

0.01357

53.1

10.28

401.2

98.1

0.007158

96.7

9-9,0

419.4

100.8

0.00 3884

178.6

9.46

413.2

95.0

0.001515

457.8

9.08

501.4

100.2

0.0004637

9.86

434.3

1 06 , 1

0.005828

1 19. 0

9.38

432.0

103.6

0.002580

268.8

9.06

390,0

132.0

0.001561

423.7

9.00

375.1

97.8

0.00 4742

146.1

t l /2
(9)

1497.3

108
d c / d t = kc
w h ere c is the h alid e co n ce n tratio n .
In te g ra tin g ,
In c = k t + co n stan t
th e r e f o r e ,
log c = (k/2.30 3)t + constant
Since the halide c o n c e n tra tio n in o u r m e a s u r e m e n ts is r e p r e s e n te d
by the t e r m

(pf - p), the equation is r e v is e d to read:
(p£ “ p) = (k/2.30 3)t + co n stan t

w here p r e p r e s e n t s the in stan tan eo u s total p r e s s u r e , p^ the final
e q u ilib riu m p r e s s u r e , t the tim e, and k the f i r s t - o r d e r velocity
constant.

Thus, when log(p^ - p) is plotted a g a in st tim e, a s tra ig h t

line should be obtained, the slope of which is equal to (k/2.30 3).
This p lo t f o r some of the e x p e rim e n ts is shown in F ig u re 2.

It is

re a d ily seen how w ell the s tr a ig h t- lin e relatio n sh ip held throughout
the e x p e r im e n ts .
The r a te c o n sta n ts (k) w ere then obtained fro m th ese graphs
as the p r o d u c t of the slope and 2.30 3.

The values of

in m o st

c a s e s w e re d e te r m in e d e x p e rim e n ta lly by allowing the re a c tio n to
go to com pletion.
the

In the c a s e of the v e r y slow re a c tio n s , however,

value w as d e te r m in e d by e x tra p o la tio n of the s tr a ig h t line

109

3.0

2.8

2.6

2.4

2.2

2.0

oQ

o

1.60

Time,
FI GURE 2 .
R a t e Law.

Adherence

300

200

00
of

M inutes

Observed Data

to

F irst

Order

110
o b tained by plo ttin g (dp/dt) v e r s u s p to (d p/d t = 0).
shown in colum n 7, Table

The p

o

value

1, r e p r e s e n ts the v ap o r p r e s s u r e of the

t e r t i a r y h alid e, p lu s th a t of phenol and the oxygenated m a te r ia l used,
and w as found by e x tra p o la tio n of the p r e s s u r e - tim e cu rv es to zero
tim e.

With th e se data av ailab le, it was then p o ssib le to calculate

the v alu es of

§^ven *n column 9, Table 1.

It was then n e c e s s a r y to calcu late the half tim e s , t

1/2

, which

one would ex p ec t under v ary in g assu m p tio n s concerning the actual
role of the oxygenated m a t e r i a l in the alkylation reaction.

This

was done in the following m an n er:
B o rd eau x and H a r t (9) d e riv e d the equation
,n
[ ( tl / 2) / ( t l / 2 ° )] = [M /M]I
in w hich t

L/c,

0 r e p r e s e n ts ' the re a c tio n half tim e when no oxygenated

m a t e r i a l is p r e s e n t ,

tim e fo r the reactio n un d er o b s e r ­

vation, M° the m o la r ity of phenol in the re a c tio n with no oxygenated
m a te r ia l , M the phenol m o la r ity in the re a c tio n being studied, and n
is the o r d e r of the re a c tio n with r e s p e c t to phenol.
F rom

Table 1, the r e f e r e n c e values a r e

54.0, and M° - 10.57 a t 50°.

seen to be

~

The c alcu lated t ^ 2 values a r e shown

in Table 2, and have the following significance:

Ill
TABLE 2
SUMMARY OF CALCULATED AND OBSERVED HALF-TIM ES FOR
THE VARIOUS ALKYLATION EXPERIMENTS*

^
Expt.

V2
obs.
(min.)

Mole Ratio
\ / ' Z\
(mm.)

h LZ\
(mm.)

(mm.)

(oxygenated
compound/
phenol)

I

55.2

2

53.1

3

96.7

65.5

78.7

95.4

0.02868

4

178.6

84.7

118.2

174.3

0.06205

5

457.8

10 3.1

217.6

497.7

0.11320

6

1497.3

134.0

461.3

1654.7

0.16751

7

119.0

85.9

118.4

165.7

0.05635

8

268.8

111.3

247.6

557.4

0.11598

9

42 3.7

137.2

400.2

1433.4

0.16198

10

146.1

144.5

0.15252

>!< The sym bols ^ y / Z ^ 3 ^1 / 2^* an(^ *d/2C a re <
^e^^ne<^ orL P

112,

112
The v alu es of

(c0 ! 111*111 3, Table 2) w ere calcu lated a s ­

suming th a t the oxygenated m a t e r i a l s e r v e s only to d e c r e a s e the
phenol c o n c e n tra tio n by dilution of the reactio n m ix tu re.

F o r exam ­

ple, d ata f r o m E x p e rim e n t 5 a r e considered:
6
[ (11 / 2, a ) / 5 4 .iP] = [10.57/9-46] ; t ^ y^ a - 103.1 m inutes
The o r d e r n was taken as 6 b eca u se H a rt and Simons (2) pointed out
th a t the a p p a r e n t re a c tio n o r d e r with r e s p e c t to phenol was sixth.
The v alu es of t

. b (column 4, Table 2) w ere calcu lated with

1/2

the a s s u m p tio n that eac h mole of added oxygenated compound com ­
bined with one m ole of phenol, and thus d e c r e a s e d the available
phenol f o r alkylation.

Using the sam e E x p e rim e n t as above, t

. b
1/ ^

is found to be:
[(t^ /^ b )/5 4 .0 ] = [10.57/8.36]^;
The v alu es of t

1/2

~

m inutes

c (column 5, Table 2) w ere obtained in the

sam e m a n n e r f r o m the assu m p tio n that each mole of oxygenated
m a t e r i a l co m b in ed with two m o les of phenol, to d e c re a s e the phenol
c o n c e n tra tio n f o r alkylation even f u r th e r .

E x p erim en t 5 is used

again as an ex am p le.

6

[ ( t i / 2 c ) / 54.°] = [10.57/7.29] ; t 1 /2 c = 497.7 m inutes
In the c a s e of the e x p e r im e n ts involving fetra h y d ro p y ra n as
the oxygenated m a te r ia l ,

the l a t t e r assu m p tio n is omitted, of co u rse,

113
since only one oxygen atom is p r e s e n t fo r com plex fo rm atio n with
the phenol m o lecu le .
F ig u res

3 and 4 show plots of th ese calculated half tim es

a g a in st the oxygenate-phenol c o n ce n tratio n ratio, as co m p ared to the
sam e c u r v e s fo r the e x p e rim e n ta l half tim es {column 2, Table 2).

114

800

600

/ t I OBS.

400

i— !

-P

200

0.00

0.025

0.050

0.075

0.100

0.125

0.150

Mol R a t i o
FIGURE 3„
to Phenol.

H alf-Tim e Values

vs.

Mol R a t i o

of Gioxane

0.175

115

800

700

600

500

400
OBS
CM

300

f-I

-P

200

00

0

.05

0.15

0.10
Mo l R a t i o

FI GURE 4 .
H alf-Tim e V alues
T e tr a h jd r a p y r a jn t o P h e n o l .

vs.

Mol R a t i o

of

116
D iscus sion

The m e c h a n is m p o stu la te d by H a r t and Simons (2) fo r the
u n cataly ze d alkylation of phenol with t e r t i a r y halides was b a s e d upon
s e v e r a l e x p e r im e n ta l o b s e rv a tio n s .

-Arnong these was the com plete

inhibition of the re a c tio n by the addition of ap p ro x im ately 21 mol
p e r c e n t of 1,4-dioxane.

In view of the fa c t that o ther diluents of

eq u iv alen t d ie le c t r i c c o n s ta n t had no such m a rk e d effect on the r e ­
action r a te , it was suggested that the dioxane inhibition was due to
a h y drogen bonding effect which red u ced the available hydroxyl groups
fo r p a r tic ip a tio n in a c o n c e rte d reaction.
In an e ffo rt to f ir m ly e s ta b lis h the role of the dioxane in the
r e actio n , B o rd ea u x (9) conducted a kin etic investigation of the r e a c ­
tion using v ary in g am ounts of dioxane.

Once again the re s u lts in d i­

c ated th a t the inhibition was too g r e a t to be due to a dilution effect,
and it was su g g e s te d th a t the dioxane fo rm e d a 1:1 oxonium-type
com plex with the hydroxyl group of the phenol.

This suggestion is

su p p o rted by the w o rk of B a r t l e t t and Dauben (35), which showed that
dioxane was b a s ic enough to fo r m oxonium compounds with acidic
s u b s ta n c e s

such as phenol.

In view of the r a t h e r cru d e ex p e rim e n ta l technique used by
B ordeaux, how ever, i t was f e l t th a t m o re p r e c i s e quantitative

117
m e a s u r e m e n ts of the s to ic h io m e try of the inhibition would be of
value.

With the aid of a ra te m e a su rin g a p p a ra tu s such as that

d e s c r ib e d in P a r t II, it was p o ssib le in this investigation to make
3- m o r e a c c u r a te

study of the effect of oxygenated compounds on the

alkylation r a t e .
It was pointed out by H a rt and Simons (2) that the uncatalyzed
re a c tio n p ro c e e d e d by v irtu e of the p r e s e n c e of a la rg e e x c e ss of
phenol.

As was seen f r o m th e ir kinetic data, any significant d e c re a se

in phenol co n c e n tra tio n r e s u lte d in a la rg e d e c r e a s e in reactio n rate .
T h e r e fo r e , the addition of any in e r t m a te r ia l would be expected to
cause a r a te d e c r e a s e .

The r e s u lt s tabulated in Table 1 verify this,

but the d e c r e a s e o b s e rv e d is f a r g r e a t e r than would be expected fo r
only dilution of the re a c tio n m ix tu re (column 3, Table 2).

F or ex­

am ple, c o n s id e r E x p e rim e n t 4, in which dioxane was used as the
in h ib ito r.

The e x p e r im e n ta lly d e te rm in e d half tim e was 178.6

m in u tes; the c a lc u la te d half tim e fo r dioxane dilution is 84.7 m inutes,
while the half tim e b a s e d on the assu m p tio n th at one mole of phenol
is co m p lex ed p e r m ole of dioxane is

118.2 m inutes.

When the half

tim e was c a lc u la te d f o r the a ssu m p tio n that each mole of dioxane
co m p lex ed two m o les of phenol, it was found to be 174.3 m inutes.
The l a t t e r value c o r r e s p o n d s quite well to the e x p erim en ta lly

118
determ ined, value in E x p e r im e n t 4, and it can be seen that the other
dioxane E x p e r im e n t 3 through 6 coincide m the same m an n er.
c o r r e l a t i o n i s i l l u s t r a t e d in F ig u r e

This

3, w here it is seen that the ex ­

p e r im e n ta l half tim e cu rv e follows quite clo sely the calcu lated curve
fo r a 2:1 oxonium com plex between phenol and dioxane.
If an inhibition of this type is g e n e ra l and if the r e s u lts ob\
tained above a r e f a ir l y a c c u ra te , then it follows that an oxygenated
m a t e r i a l s i m i l a r to dioxane, but having only one available oxygen for
oxonium fo rm a tio n , should inhibit the reactio n by the fo rm atio n of a
1:1 oxonium com plex.

T e tra h y d ro p y ra n was chosen^for this work

b e ca u se the ring size is the same as in dioxane except that one
dioxane oxygen is re p la c e d by a m ethylene group.
to 9, Table

E x p erim en ts 7

1, and F ig u re 4 show th at this reasoning is substantiated.

The r e s u l t s of this study add additional evidence to the p o s tu ­
lation by H a r t and Simons (2) and in P a r t s A. and B of this th e sis
that the u n c a ta ly z e d alkylation of phenol p ro c e e d s by a m echanism
involving the a v a ila b ility of the phenolic hydroxyl group, and that
the effective c o n c e n tra tio n of phenol is d e c r e a s e d by the form ation
of co m p lex es

such as:

and

V

/° 'H

E x p e r im e n t 10 was c a r r i e d out using p^-xylene in place of
the oxygenated m a t e r i a l .

C om paring this ex p e rim e n t with E x p erim en ts

6 and 9, w h ere c o m p arab le am ounts of oxygenated m a te r ia l w ere
added, it is

seen th a t the o b s e rv e d half time is much low er in the

xylene e x p e rim e n t, w here the ra te d e c r e a s e is cau sed only by
dilution.
A no th er p o s s ib le explanation of the inhibition studied h e re ,
which h as not been m entioned, is that the addition of an oxygenated
m a terial

such as dioxane m ight cause in c r e a s e d solubility of the

evolved hydrogen ch lo rid e in the phenol-dioxane m ix tu re s .

Since

the r a te w as followed by the in c r e a s e in hydrogen chloride p r e s s u r e ,
this could give the effect of a p p a re n t inhibition.

This p o ssib ility

was e lim in a te d by H a r t and Simons (2), who c a r r i e d out two e x p e r i­
m e n ts with a c o n s ta n t m ol ra tio of dioxane to phenol.

In the f i r s t

e x p e r im e n t the r e a c tio n was conducted in the usual m ann er and no
alky latio n o c c u r r e d .

In the second ex p erim en t, the re a c ta n ts w ere

f i r s t s a tu r a t e d with h y drogen ch lo rid e and then the reactio n c a r r i e d

120
out as b e f o r e .

Once again the r e s u l t was the same; th ere was c o m ­

p lete inhibition of the re a c tio n .

Since hydrogen chloride was not

evolved even when the re a c tio n m edium was alre ad y s a tu ra te d with
the g as, it was concluded th a t the inhibition was not an a rtifa c t.

SUMMARY

^ -D i-t-b u ty lp h e n o l, a compound exhibiting maximum s te r ic
h in d ra n c e of the hydroxyl group, was syn th esized by the method of ~
H a r t (15) in 44 p e r c e n t y ie ld s.

This compound was c h a r a c te r iz e d

by its a lk a li in so lu b ility, sen sitiv ity to the phosphomolybdic te s t for
h in d e re d p h en o ls, and its c h a r a c t e r i s t i c u ltrav io le t and in f r a r e d
ab s o rp tio n s p e c tr a .
The action of su lfu ric acid cau sed this phenol to r e a r r a n g e
to 2 ,4 -d i-t-b u ty lp h e n o l, while n itra tio n at 25° to 35° in glacial acetic
a c id (1:1) gave cleavage of a t-b u ty l group to yield 4 ,6 - d i n i t r o - 2 - t butylphenol.

U nder m ild e r n itra tin g conditions the phenol was

oxidized to 3, S '^ B '- te tr a - t- b u ty ld ip h e n o q u in o n e .
2 , 6 -D i-t-b u ty lp h e n o l gave negligible r a te s of p a r a brom ination,
diazonium coupling, and alkylation when co m p ared to 2 , 6 -xylenol.
This is a ttr ib u te d to s te r i c inhibition of the usual hydroxyl resonance
with the a r o m a tic rin g , by the bulky t-butyl groups.
R elative r a t e s of p a r a t-b u ty latio n of s e v e ra l phenols w ere
d e te r m in e d a t 50°, using the phenol to be alkylated as the reaction
solvent.

The alk y latio n r a te was found to d e c re a s e with an in c re a s e

121

122
in size a n d / o r

n u m b e r of ortho alkyl groups.

The o b serv e d rate

d e c r e a s e , u n d e r the r e a c tio n conditions employed, could, r e s u lt fro m
several facto rs,

all of which, how ever, could be a ttrib u te d to s te ric

h in d ra n c e of the hydroxyl group by the bulky ortho substituents.
P r e c i s e kin e tic studies of the alkylation of phenol and o - c r e s o l
w ere m ade in o -d ich lo ro b en zen e a t 8 8 °, using triphenyl methyl ch lo rid e.
The r e a c tio n was found to be auto cataly zed by hydrogen chloride
f o r m e d during the alkylation, and t h i r d - o r d e r kin etics w ere obtained
when the hydrogen ch lo rid e gas was p r e s e n t initially in the reaction.
A k in e tic study of the inhibition of this re a c tio n by dioxane
and te tr a h y d r o p y r a n was c a r r i e d out at 50° in ex ce ss phenol.

E vi­

dence w as p r e s e n te d to show that phenol f o r m s 2:1 and 1:1 com plexes,
re s p e c tiv e ly , with th e se m a t e r i a l s , thus d ec re a sin g the phenol a v a il­
able f o r alkylation.
A c a rb o n iu m m e c h a n is m involving p r e li m in a r y solvation of
the halide by the phenol o r hydrogen ch lo rid e, followed by a r a te d e te rm in in g e le c tr o p h ic attack by the carbonium ion on the phenol,
is p r o p o s e d to account f o r the facts o b serv ed h ere and in s e v eral
p re v io u s in v e s tig a tio n s .

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