PART A

CARBONIUM ION REARRANGEMENTS IN
THE REACTION OF L-AMYL CHLORIDE

WITH ALUMINUM CHLORIDE
PART B

N. M. R. STUDIES OF STEREOISOMERISM
IN SOME CARBOINYL DERIVATIVES

Thesis Ior II“; Degree OI pI‘I. D.
MICHIGAN STATE UNIVERSITY

Floie Marie Vane
1963

“39‘

LIP“'“"
Michigan 5mm
University

 

MICHIGAN STATE UNIVERSITY
EASJ’. LANSING, MICHIGAN

 

ABSTRACT

PART A
CARBONIUM ION REARRANGEMENTS IN THE REACTION OF
i—AMYL CHLORIDE WITH ALUMINUM CHLORIDE
PART B

N.M.R. STUDIES OF STEREOISOMERISM
IN SOME CARBONYL DERIVATIVES

by Floie Marie Vane

PART A: Products from carbonium ion reactions frequently have
been explained by rearrangements of tertiary and secondary carbonium
ions to less stable carbonium ions. In the study of the reaction of
Cu-labeled _t_-amyl chloride with aluminum chloride, a rate of l. 55 was
observed for C-Z # C-3/C-1 €3— C-4 equilibration.1 It was suggested
that 87% of the reaction proceeded through 1 which equilibrates C-Z,
0-3 and 0-1, 04 and 13% through 2 which equilibrates C-l, c-4 only.

<5 <9 <9
C-E-C-C $2: C-C-C-C -.-——- C-C-C-C ‘—-— C-C-C-C (l)
s <9 G.
C-E-C-C # C—g-C+ : C-C-C-C (2)

An alternate explanation for 2 would be a bimolecular reaction (3) which

does not invoke rearrangement to a primary carboniurn ion.

Floie Marie Vane

 

2
(.3 (Ci 9 g”
c-c=c-c c- -c-c 1, c-c- -c
NH C H '
+ a... I a. “;...___.___.L I
c=c':-c«c c-q-c-c (3)
c—E—c-c c4-
é” l
‘9 as
c-c- ~cl4 c c
3.545% I 2’52 cm: c-ézc-c” + c—é-c-c
cuc-c-c
c

Bimolecular paths in the reactions of Luamyl chloride-l-C13 and
L-amyl chloride-Z-Cl3 with aluminum chloride were verified by identifi-
cation (mass spectrometry) of dilabeled L-amyl chloride and hexyl
chlorides in the reaction products. The data support I (3) as the first
intermediate formed by the attack of _t_-amyl cation on a C5 olefin.

This C10 carbonium ion may undergo fast and reversible rearrangements
to other C10 carbonium ions. The C10 unit, which disproportionates into
an olefin and a tertiary carbonium ion, may lead to two C5 units or a

C4 and a C6 unit. Calculations of statistical isotopic distribution suggest
that each L-amyl species has undergone an average of one bimolecular
reaction resulting in complete equilibration of the methyl and partial
equilibration of the non-methyl carbon atoms. No scrambling between
methyl and non-methyl carbon atoms was detected.

The volatile products from the reaction of l. 74 g. of _t_-amyl
chloride with O. 080 g. of aluminum chloride at 00 for five minutes are
68.2% i-amyl chloride, 16. 7% L-butyl chloride, 5. 7% 3-chloro-2-
methylbutane, 4. 2% Z-chloro-Z-methylpentane, l. 5% 3-chloro-3—methy1-
pentane, and 3. 8% of the corresponding hydrocarbons. The percent
recovery of volatile products and the percent _t_-amyl chloride in the
volatile fraction increased with 1) increase in the ratio i-amyl chloride/

aluminum chloride, 2) decrease in temperature, and 3) decrease in

Floie Marie Vane

reaction time. After five minutes the reaction appears to stop. The
apparent termination of the reaction may involve deactivation of the

catalyst by highly unsaturated polymers.

PART B: Problems associated with syn-anti isomers (II, III) of

/Y Y\
N N
'o' I
/ \
R1 R2 R1/ \R2
11 III

Z,4-dinitrophenylhydrazones (DNP‘S), ortho-, meta- and para-nitrophenyl-

 

hydrazones, semicarbazones and thiosemicarbazones were studied by
nuclear magnetic resonance spectroscopy.

Hydrogens, cis and trans to Y usually resonate at different fre-

 

quencies. Assignments offln and an_t_i isomers (syn refers to the isomer
having Y c_i_§_ to the smaller group) were made by comparing the equi-
librium ratios of Z-butanone, Z-pentanone, methyl isopropyl ketone and
methyl L-butyl ketone DNP's.

In methylene bromide and chloroform solutions, aldehydic and
B-hydrogens are deshielded (hydrogens £13 to Y resonate at lower fields
than those t_r_a_ris_) and a-hydrogens are shielded. The isomer chemical
shift differences are 30-45 cps for aldehydic hydrogens and 0-10 cps
for a- and fi-aliphatic hydrogens. Acetaldehyde, benzyl ethyl ketone and
ethyl cyclopropyl ketone DNP's show two resonances for each aromatic
hydrogen of the 2, 4-dinitropheny1 ring.

.Hydrogen bonding of the N-H of the _s_Ln_ isomer of acetaldehyde
DNP to the solvent leads to greater 22:32}: ratios in the better hydrogen-

bonding solvents. In addition two N-H resonances are observed in

Floie Marie Vane

pyridine, dimethyl sulfoxide and dimethylformamide solutions of
acetaldehyde DNP.

Formation of aldehyde DNP's is kinetically controlled and leads
to the syn isomer.

The following long-range spin- spin coupling constants were

observed in DNP's (4): JH1H3 = 0. 7 cps, JH1H4 = O. 2 cps, and JHle =

0.8 cps.
H NO
2 2 ,H1
N02 N I“I5
\
Q N: : <4)
H3 H, R
Reference

 

l. J. D. Roberts, R.-- E. McMahon and J. S. Hine, J. Am. Chem.
Soc., _'_7_Z_, 4237 (1950).

PART A

CARBONIUM ION REARRANGEMENTS IN THE REACTION OF
L—AMYL CHLORIDE WITH ALUMINUM CHLORIDE

PART B

N.M.R. STUDIES OF STEREOISOMERISM
IN SOME CARBONYL DERIVATIVES

BY

Floie Marie Vane

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCT OR OF PHILOSOPHY

Department of Chemistry

1963

ACKNOWLEDGMENTS

The author wishes to express her sincere appreci-
ation to Dr. Gerasimos J. Karabatsos for his guidance
and inspiration during the course of this investigation.

Grateful acknowledgment is given to the Petroleum
Research Fund of the American Chemical Society whose
fellowship program provided personal financial assistance
from January 1961-March 1963.

Appreciation is also extended to John D. Graham
who obtained the n.m. r. spectral data in Part A, and to

Seymour Meyerson of American Oil Company for the mass
spectral analyses.

>{< >:< 3k >:< >:< >1: >:< >:< >:< >:< >§< >:< >:< :3

ii

TABLE OF CONTENTS

Page
PART A

CARBONIUM ION REARRANGEMENTS IN THE REACTION OF
L-AMYL CHLORIDE WITH ALUMINUM CHLORIDE

INTRODUCTION ......... . ......... . . . . . . 1
RESULTS .................... . ....... . 6
.Reactions of t _-Amyl Chloride with Aluminum
Chloride ..... . ..... 6
2. Reactions of Cl3 -Labeled t- -Amyl Chloride with
Aluminum Chloride ....... . . . ......... 11

Analysis oft- -amyl chloride . . . . . . . . . . . 11
Analysis of hexyl and _t_- -butyl chloride . . . . . . . 20

Some calculated distributions of label ....... 24
DISCUSSION ........................... Z7
EXPERIMENTAL ....................... . 32

l. The Reactions of L-Arnyl Chloride with Aluminum
Chloride.... ..... .. ...... 32
2.. Product Analysis ........... . ........ 32
Reaction products of _t_-amyl chloride . . . . . . . 36
Reaction products of _t_-butyl chloride . . . . . . . 36
Reaction products of 3—chloro-3-methy1pentane . . 36
3. Preparations of Reference Compounds. . . . . . . . . 37
4..Syntheses of CB- Labeled Compounds . . . . . . . . . 4O

_t_--Amy1a1coholl-c‘3. ..... 40

t- -Amyl chloride-1--C13 ................ 40

t- -Amyl alcohol- 2- C13. . . . . . . ......... 40

't' Amyl chloride- 2- c:13 ........... . . . . 41

5. Isotope Analysis .......... . . . . . . . . . . 41
SUMMARY ....... . . ................... 42

iii

TABLE OF CONTENTS - Continued Page

PART B

N.M. R. STUDIES OF STEREOISOMERISM
IN SOME CARBONYL DERIVATIVES

 

INTRODUCTION ................... . ..... 45
RESULTS......... .................... 49
1. Chemical Shifts ........ . ........ . . . . 49
2. Isomer Chemical Shift Differences . . . . . . . . . . 65
3. Equilibration and Stability of the Derivatives ..... 74
4. Spin-Spin Coupling Constants ....... . ..... 80
5. Benzene Anisotropy Calculations ........... 80
DISCUSSION . . . . . . . ......... . . . . ...... . 87
l. syn-antilsomerization ................ 87
2. Hydrogen Bonding ................... 90
3. Anisotropy Effects ............ . . . . . . . 90
4. Spin-Spin Coupling ...... . . . . . . . . . . . . . 92
EXPERIMENTAL . . . . . . . ................. 94
1. Nuclear Magnetic Resonance Spectra . . ..... . . 94
2. Solvents ..... . . . ..... . . . . ....... 94
3. Carbonyl Reagents . . . . . . . . ....... . . . . 94
4. Dinitrophenylhydrazones ............ . . . . 95
5. Mononitrophenylhydrazones . . . . . . . . . . . . . . 97
6. Semicarbazones and Thiosemicarbazones ....... 99

7. Equilibration and Fractional Crystallization of
Acetaldehyde 2,4-Dinitropheny1hydrazone ..... 99
SUMMARY........ ........ ..... ..102
REFERENCES ..... . .......... . . ........ 102

iv

TABLE

Ia

Ila

IIIa

IVa

VIa

VIIa

VIIIa

IXa

Xla

XIIa

XIIIa

LIST OF TABLES

PART A

The Reaction Oof i-Amyl Chloride with Aluminum
Chloride at 0 : Effect of Reaction Time .......

The Reaction of L-Amyl Chloride with Aluminum
Chloride for 1. 5 min.: Effect of Temperature. . . .

The Reaction (pf L-Amyl Chloride with Aluminum
Chloride at 0 for l. 5 min.: Effect of Concentration

The Reactions of t- -Butyl Chloride and Methylpentyl
Chlorides with Aluminum Chloride at 00 .......
The Reactions of Propyl + L-Amyl Chlorides, and
Butylo+ _1_:_-Amyl Chlorides with Aluminum Chloride
at 22 ......
The Reactions of C13- Labeled t- -Amyl Chlorides with
Aluminum Chloride at O0 for 5 min. . . . . . . . . .

Partial Mass Spectra of L-Amyl Chlorides ......
Partial Mass Spectra of t_-Amy1 Alcohols. . . . . . .

Label Retention in Selected Ions ...........
Isotopic Composition of L-Amyl Chlorides from
Mass-Spectral Analysis ..... . . . . .

Partial Mass Spectra of Hexyl Chlorides .......

Isotopic Composition of Hexyl Chlorides from Mass-
Spectrometry Analysis . . . . . . . . . . . . . . . .

Comparison of Some Calculated Values of Isotopic
Composition with Experimental Values of Recovered
t_-Arnyl Chlorides from the Reactions of l-Cl3- and
2-C13-Labeled E. -Amy1 Chlorides with Aluminum
Chloride . .

Page

10

12

13
15
16

l7

19

21

23

26

LIST OF TABLES - Continued Page

PART B
Ib Chemical Shifts of Equilibrated Solutions of 2, 4-Di-
nitrophenylhydrazones in Methylene Bromide ..... 50

IIb Chemical Shifts of Formaldehyde 2, 4-Dinitropheny1-
hydrazone in Various Solvents . . . . . . . . . . . . . 55

IIIb Chemical Shifts and anti/syn Ratios of Acetaldehyde
2, 4-Dinitropheny1hydrazone in Various Solvents . . . 56

IVb Chemical Shifts and anti/syn Ratios of 2-Butanone
2,4-Dinitr0pheny1hydrazone in Various Solvents . . . 57

 

Vb Chemical Shifts of 3-Pentanone 2, 4-Dinitropheny1-
hydrazone in Various Solvents . . . . . . . . . . . . 58

VIb Concentration Studies of Some 2, 4-Dinitropheny1-
hYdrazoneS O O O I O O O O O O O O 0 O O O O O O O O O O 59

VIIb Chemical Shifts of para-, meta- and ortho-Nitro-
phenylhydrazones................... 60

VIIIb Chemical Shifts of Semicarbazones ..... . . . . . 66
IXb Chemical Shifts of Thiosemicarbazones ...... . . 68
Xb Isomer Chemical Shift Differences and anti/syn
Ratios of Nitrophenylhydrazones in Methylene
Bromide........... ...... .. ....... 70
XIb Isomer Chemical Shift Differences and anti/syn
Ratios of Semicarbazones and Thiosemicarbazones

inChloroform..................... 72

XIIb Isomer Chemical Shift Differences and anti/syn
Ratios of Semicarbazones in Trifluorbacetic Acid . . 73

XIIIb Time Studies of the Equilibration of Acetaldehyde
2,4-Dinitropheny1hydrazones ..... . . . . . . . . 76

XIVb Spin-Spin Coupling Constants . . . . . ........ 81

vi

LIST OF TABLES - Continued Page

XVb

XVIb

X VIIb

X VIIIb

XIXb

XXb

XXIb

Bond-Lengths and Angles Used in the Anisotropy
Calculations ........ . . ..... . .......

Calculated Shielding Values for cis and trans
Aldehydic and Methyl Protons . . . . . . . . . . . . . 86

 

 

Long-Range Coupling Constants Illustrating the Angle
Dependence of Spin-Spin Coupling ........... 93

Melting Points of 2,4-Dinitrophenylhydrazones . . . . 96

Melting Points of Mononitrophenylhydrazones ..... 98
Melting Points of Semicarbazones and Thiosemi-
carbazones........................100
Fractional Crystallization of Ac etaldehyde 2, 4-Dinitro-

. 101

phenylhydrazone .......... . . . . . . . . .

vii

LIST OF FIGURES

FIGURE Page
PART A

la The v.p. chromatogram of the products from the
reaction of 1. 74 g. of _t_-agnyl chloride with 0. 080 g.
of aluminum chloride at O for 5 min ..... . . . . . 33

2a The v.p. chromatogram of the products from the
reaction of 1. 69 g. of _t_-b161tyl chloride with 0. 087 g.
of aluminum chloride at 0 for 5 min. . . . . ..... 34

3a The v.p. chromatogram of the products from the
reaction of l. 78 g. of 3-chloro-3-rr6ethylpentane with
0. 073 g. of aluminum chloride at 0 for 5 min ..... 35

PART B

lb N.m. r. spectrum of 2-butanone 2, 4-dinitrophenyl-
hydrazone in methylene bromide . . . . . . . ..... 52

2b N.m. r. spectrum of the aromatic and aldehydic
hydrogens of an equilibrated methylene bromide solu-
tion of acetaldehyde 2, 4-dinitropheny1hydrazone. . . . 53

3b N.m. r. spectrum of aromatic and N-H hydrogens of
acetone para-nitrophenylhydrazone in methylene
bromide..... ...... ..............63

4b N.m. r. spectrum of the aromatic hydrogens of
ac etohe ortho-nitrophenylhydrazone in methylene
bromide O O O O O O O O O O O O O O O O O O O O O O O O O 64

 

5b N.m. r. spectra of the methyl peaks of acetaldehyde
2, 4-dinitrophenylhydrazone in methylene bromide:
(A) freshly prepared solution, (B) solution after five
hours, (C) equilibrated solution . . . . . . . . . . . . 75

viii

LIST OF FIGURES - Continued

6b

7b

8b

9b

N.m. r. spectrum of a freshly prepared solution of
benzyl ethyl ketone 2, 4-dinitropheny1hydrazone in

methylene bromide ..... . . . . . . . . . . . . . .

N.m. r. spectrum of an equilibrated solution of

benzyl ethyl ketone 2, 4-dinitropheny1hydrazone in

methylene bromide . . . . . ..... . . . . . . . . .

N.m. r. spectra of (A) formaldehyde 2, 4-dinitro-
phenylhydrazone in methylene bromide and (B) form-
aldehyde 2, 4-dinitrophenylhydrazone exchanged with

DZO in methylene bromide . . . . ..... . . . . . .

N.m. r. spectra of H2 and H4 of (A) acetone 2,4-di-
nitrophenylhydrazone in methylene bromide and
(B) acetone 2, 4-dinitropheny1hydrazone exchanged

with DZO in methylene bromide. . . . . . . . . . . . .

ix

Page

77

78

82

83

PART A

CARBONIUM ION REARRANGEMENTS IN THE REACTION OF
L—AMYL CHLORIDE WITH ALUMINUM CHLORIDE

INTRODUCTION

The action of Lewis acids on organic compounds is a common
method for generating carbonium ions. Investigation of the nature
and proper-ties of these carbonium ions has been the object of many
investigators.

In the study of alkyl halides and isoparaffins in the presence of
aluminum halides, Bartlett, Condon and Schneider1 observed
1) equilibration of the alkyl halide with olefins, 2) addition of alkyl
halides to olefins, 3) rapid halogen-hydrogen exchange between alkyl
halides and alkanes, 4) isomerization and Wagner-Meerwein rearrange-
ments of alkyl halides, and 5) production of products which could not be
explained by simple combinations of starting materials. Pines and
co-workers studied the isomerizations of alkanes with a variety of
catalysts. In addition to Lewis acids, promotors such as acid and
olefins, 2’ 3 oxygen, 4' 5 light, 5' 6 water, 7 or alkyl halides, 8 were
necessary for isomerization. In the condensation of alkyl halides with
ethylene in the presence of Lewis acids, Schmerling9 observed that
the rate increased in the order: primary halides < secondary halides <

10 ll 12
tertiary halides. .Schneider and Kennedy ’ ’

studied the alkyl
fluoride-boron trifluoride induced isomerizations of hydrocarbons.
Often, products were explained by rearrangements of tertiary
and secondary carbonium ions to primary carbonium ions, e. g. , the
isomerization of g-butane to isobutane7 (1a) and methylcyclopentane to
cyclohexane3 (2a). In the reaction of Chi-labeled _t_-amyl chloride with

aluminum chloride, Roberts, McMahon and Hinel3 obtained a rate of

1. 55 for C-2 # C-3/C-l é C-4. Equilibration

c-c-E- e2 E-c-c ea c-¢-c (la)
c

C
+
r e2 ' e 0 (2a)

of C-2 and-C-3 (3a) should proceed twice as fast as equilibration of
C-1 and‘C-4 (4a) if the only path of isomerization was 5a. To explain

the observed value they suggested that 87% of the rearrangement

(.3 <.=
c-c‘4-c-c -\‘=_—\ c—c-c14—c (3a)
(.3 S3
c‘4—c-c-c ea. c-c-c-c“ (4a)
6 G <9 G.
c-q-c-c e2 c-c-Q—c ea c-q-c-c :12 c-c-g-c (5a)

proceeds through 5a and 13% through 6a which effects only C-1, C-4
exchange.

9 c c
c‘4-c-c-c (:2 c“—¢-c+ -..—_-> ago-c“ (6a)
c

Calculations” have shown that the activation energy necessary
for rearrangements of tertiary to primary and secondary to primary
carbonium ions should be at least 33 and 22 kcal. , respectively. These
values warrant examination of alternate mechanisms not involving
primary carbonium ions.

.Disproportionation reactions have been invoked to explain products
. . . 1,9,10,11,12,15
wh1ch were not multiples of starting reactants.

Similarly, reaction of a methylcyclopentyl cation with its olefin, ring

enlargement, and disproportionation (7a) would lead to cyclohexane

without intervention of a primary carbonium ion intermediate. The
isomerization of B-butane to isobutane and the faster C-1, C-4 exchange

in _t_-amyl chloride can also be explained by bi-

:
H:sC>+/>O=C>®+OW
1““? (j “

molecular reactions. Reaction sequence 8a results in C-l :2 C-4
equilibration but not C-1 3 C-3. C10 units, as in 8a, have been pro-
posed to explain formation of _1_;_-buty1 and hexyl chlorides from the
action of aluminum chloride on i- amyl chloride1 and formation of

. . . . l
isobutylene and hexenes from sulfur1c and treatment of 1soamy1enes. 5

c c c
c—ézc-c c- -g- -c c c—c—c-c
F: I Iég c 6 c c
c-S-c-c c 9 C C I- '
14 C14
C14 q
8a)
0“ - - - CH cmc-E- “ H c-$=c-c“ (
lé===ljé£ C C (:5 C a I C LA “‘2‘ +
C- -c-c c-c-c-c
(*3 c <9
c—c—c-c

The purpose of this investigation was to study quantitative and
qualitative effects of temperature, time and concentration upon the
reaction of i-amyl chloride and aluminum chloride. It was hoped that
bimolecular reactions would be verified by identification of dilabeled
products which should result when two Cl3-1abe1ed _t_-amyl species

combine (9a).

 

 

13 C13 (313 (:13
c-c=c-c c-q-c-c ~11 ~c13H c-c—c-c
‘I‘ # l V x V 1‘
c-E-c-c c-c-c-c c- -c-c
13 (I; 3
(9a)
€13 13

RESULTS

1. Reactions of t-Amyl Chloride with Aluminum Chloride

 

The products of the reaction of i-amyl chloride with aluminum
chloride consist of a volatile portion and a brown polymeric residue.
Tables Ia-IIIa summarize the effect of time, temperature and concen-
tration on the recovered products. The qualitative composition of the
products is practically unaffected by time, temperature and concen-
tration. Table Ia indicates that the carbonium ion formed undergoes
many rapid reactions. The reaction appears to stop after five minutes.
Bimolecular reactions decrease, as expected, at low temperatures
(Table Ila). An increase in aluminum chloride concentration greatly
reduces the amount of the volatile fraction collected and decreases
the percentage of _1_;_-amyl chloride in the product.

Additions of 2-methy1-2-butene (1. 8-22%) to the reaction of
_t_-amy1 chloride with aluminum chloride produced little change in the
product composition. Saturation of the t-amyl chloride with hydrogen
chloride or water, or exposure of the aluminum chloride to the atmos-
phere for 10 min. had no effect on the reaction. When the volatile
portion of the reaction products was removed and fresh L-amyl
chloride was reacted with the remaining brown residue, the i—amyl
chloride was recovered quantitatively. The above findings suggest that
the polymer is involved in the deactivation of the aluminum chloride
which causes the apparent termination of the reaction.

If formation of i-butyl and hexyl chlorides occurs by dispro-
portionation of a C10 unit, equimolar amounts of the two are expected.
However, the yield of i-butyl chloride is greater than that of the hexyl
chlorides (Tables 'Ia-Illa). Table IVa contains the product analyses of
the reactions of aluminum chloride with i-butyl chloride, 3-methy1-3-

chloropentane, and mixtures of chlorides. The table reflects the more

6

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Table 11a. The reaction of L-Amyl Chloride with Aluminum Chloridea
for 1. 5 min.: Effect of Temperature

 

Temperature: -610 -350 0o 22C) 500
96 Recovery (volatile fraction) 89 88 72 72 66
06 Composition (wt/wt) of
recovered product
isobutane -- t 0.4 0.9 0.6
isopentane 0.3 0.4 2.7 3.5 2.8
i-butyl chloride 1.3 1.4 16.7 17.2 18.1
2-methylpentane - - - - 0. 6 0 . 6 0. 8
3-methy1pentane -- - - 0. 2 0. 3 0. 2
i-amyl chloride 93.7 91.8 68.2 63.7 61.7
3-chloro-2-methy1butane 4. 7 5 . 7 5. 7 7 . 0 8. 3
2-chloro-2-methy1pentane t 0 . 4 4. 2 4. 7 4. 0
3-chloro-3-methylpentane t 0. 2 1. 5 2. 3 3. 5

 

8'The mole ratio, L-amyl chloride/aluminum chloride, was 28.

1:Only a trace was present (< 0. 2%).

Table IIIa.

The Reaction of L-Amyl Chloride with Aluminum Chloride
at 0 for 1. 5 min.: Effect of Concentration

 

 

_t_-Amyl Cl/A1C13(mole) 190 43 33 26 15

% Recovery (volatile fraction) 97 94 97 76 59

% Composition (wt/wt) of
recovered product
isobutane t t 0. 2 0.9 2.7
isopentane 0.3 0.6 1.7 5.0 6.4
_t_-butyl chloride 0.3 2.6 10.7 19.1 30.8
2--methylpentane -- -- t 0. 5 l. 5
3-methy1pentane -- -- t 0. 4 0. 5
t_-amy1 Chloride 97.7 90.2 77.7 64.1 47.4
3-chloro-2-methy1butane l . 7 5. 9 5. 8 5. 0 3.1
2-chloro-2-methy1pentane t 0. 5 1. 9 3. 7 5. 8
3-chloro-3-methy1pentane t 0. 2 l. 9 1. 3 1.6

 

1:Only a trace was present (< 0. 2%).

.o...

lunar-

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rapid disappearance of i- amyl chloride and hexyl chlorides than t_-buty1
chloride. Condon16 also made this observation and suggested that the
methylpentenes polymerized faster than isobutene.

The absence of is0propy1 and n-propyl chlorides in the reaction
products of L-amyl chloride and their stability under the reaction
conditions (Table Va), indicate that the C10 unit is not disproportionating
into C; and C7 units. Similarly, the absence of 1- and Z-chlorobutane,
which are stable under the reaction conditions, implies that the C10 unit

does not disproportionate to the Z-butyl cation and a C6 olefin.

2. Reactions of Gui-Labeled t-Amyl Chlorides with
Aluminum Chloride

 

 

Analysis of t-amyl chloride. Table Vla summarizes the product

 

composition of the reactions of t-amyl chloride-l-Cl?’ and _t_-amy1
chloride-Z-Cl3 with aluminum chloride at 00 for 5 min.

To verify that the starting Cl3-labeled chlorides had the label only
at the designated carbon, the chlorides and the alcohols from which they
were prepared were analyzed by mass spectrometry and proton n.m. r.

The mass spectrum of a labeled compound can, in principle,
furnish information on the fraction of labeled molecules (isotopic analy-
sis) and the position of labels in the molecules.

The parent ions in the spectra of both L-amyl chloride and L-amyl
alcohol are too small to calculate the isotopic composition. A satis-
factory alternative in the chloride spectrmn, the C5H11+ion, is subject
to interference in the labeled species from C5H10+ and-CSH9+. The
lower appearance potential of C5H10+ eliminated the possibility of remov-
ing the interference. At the same time, Csng-intensity is too low at
ionization voltages below the appearance potential of Can+ to permit
using it as a basis for an isotopic analysis. A satisfactory analysis

+
was derived from the "IO-volt spectrum by assuming that Can , CSHIO

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13

Table VIa. The Reactions of Cl3-La(;beled i-Amyl Chlorides with
Aluminum Chloride at O for 5 min.

 

 

 

Reacting Halide 1.cl3 z-cl3
Wt. of i-amyl chloride (g.) 1. 0 l. O
Wt. of aluminum chloride (g.) 0. 047 0. 047
96 Recovery (volatile fraction) 52 52
70 Composition (wt/wt) of recovered
product
isobutane t t
isopentane 0. 9 l. 2
_t_-butyl chloride 2.1. 6 Z l . O
Z-methylpentane O. 4 0. Z
3-methylpentane 0. Z O. l
L-amyl chloride 62.4 66.6
3-chloro-2-methylbutane 4. l 3. 6
Z-chloro-Z-methylpentane 7 . 4 5 . 3
3-chloro-3-methylpentane 2. 0 1. 5

 

tOnly a trace was present (< 0.1%).

l4

and-C5H9+ are all produced with the same isot0pic distribution. The
intensities of these ions in the_t-amyl alcohol spectrum are consider-
ably lower than in the chloride spectrum; moreover, these peaks

may also include contributions from oxygen-containing ions. Therefore,
isotopic analysis of the labeled alcohols was made by attributing the
peak at mass 59(C3H7O+) to the unlabeled species and that at 60 to the
labeled. - Good agreement of the alcohol analysis with the chlorides

supports and justifies the procedure.

1_Cl3 Z-Cl3
Alcohol, % labeled 43.0 57.6
Chloride, % labeled 43. 0 S7. 7

The mass spectrum of a labeled molecule can be used to locate
the label only if the relevant decomposition paths are known and if
the atoms of the molecule do not lose their identity before decomposition.
Spectra of the l-Cl3- and Z-Cu-labeled species clearly define certain
primary decomposition steps and show that no rearrangement precedes
these steps. Table VIIa contains the partial spectra of t-amyl chloride
unlabeled, l-C13, and Z-C”, corrected for natural abundance of heavy
isotopes andfor the contribution of unlabeled t-amyl chloride. Table
VIIIa contains corresponding data for the t-amyl alcohols. Table IXa
shows derived label-retention values in C4H8X+ and C3H6X+, formed by
respective loss of CH; and Cal-15 from the parent ions. In the chlorides,
C4H8Cl+, C4H7Cl+ and C4,H¢,Cl+ were assumed to have the same retention.
The same assumption was made for C3H6Cl+, C3H5C1+ and C3H4Cl+.

In the alcohols, interference from other ions is evidently very small
and was neglected. Thus, respective intensities at masses 73 and 74
were attributed to unlabeled and labeled C4H30H+, and those at 59 and
60 to unlabeled and labeled C3H6OH+. Evidently, C4H8X+ and C:.,I-16X+

15

Table VIIa. Partial Mass. Spectra of t-Amyl Chlorides

 

 

Relative Intensity

 

 

Mass Ion Unlabeled 1-0” 2-0”
69 c5121.,+ 2.9 0.0 0.0
70 c.4110+ 16.5 2.5 2.6
71 C5Hn+ 100.0 16.3 16.2
72 . .. 0.0 100.0 100.0
75 C3H.,,Cl+ 1.2 0.5 0.0
76 C3H5C1+ 54. 8 1. 2 1. 5
77 C3H601+ 92. 6 57. 8 59. 3
78 . .. 0.1 92.3 98.2
89 c.1001”r 0.4 0.1 0. 0
9o 0414.01+ 1.4 o. 8 0. 2
91 C4H8C1+ 15.8 8.0 1.6
92 . . . 0.1 8.1 16.4
105 C5H10C1+ 0.1 0.1 0. o
106 C5H11Cl+ (parent) 0.1 0.1 0.1
107 . . . . . . 0.2 0.1

 

aUnlabeled ions only are listed.

16

Table VIlIa. - Partial Mass Spectra of _t_-Amyl Alcohols

 

w
Relative Intensity

 

 

Mass Iona Unlabeled 1-63 2 -0“
59 0.1-170’r 100.0 b b
60 . . . 0.0 100.0 100.0
69 0,149+ 0.7 0.0 -- 0 o
70 C5H10+ 1.6 0.5 0.5
71 c514,,+ 6.0 1 l 1.0
72 . . . 0.2 7.0 5.3
73 C4H9O+ 56.2 26.9 0.0
74 . . . 0.0 27.9 57.2
87 csHuo" 0.1 0. 0 0. 0
88 C5H120+(parent) 0. 0 0 . 0 0. l
89 0.0 0.0 0.0

 

a'Unlabeled ions only are listed.

bAssumed zero.

17

Table IXa. -Label Retention in Selected Ions

 

 

 

t-Amyl Chloride t-Amyl Alcohol
Ion 1-013 2.0T“; 1-c13 2--c:TEr
+
0st 51% 100% 51% 100%

C3H6X+ 99 100 100 100

 

18

in the spectra of both the chloride and the alcohol are formed solely
by loss of the original CH3 and Csz groups on the tertiary carbon atom.
The data gave assurance that the starting chlorides contained only the
desired isot0pic species and that the methods of purification and analysis
were acceptable.

The pertinent mass-spectral results on the L-amyl chlorides
recovered from the reactions with aluminum chloride are given in
Table Xa. The data do not distinguish directly between C-3 and C-4;
therefore, these positions are grouped together under %_ label distribu-
tion. To identify individual isotopic species, distinction between-C-3
and'C—4 is necessary. The fact that no label is found in C-Z from the
reaction of the l--Cl3 chloride is strong evidence that no label is present
in C-3, but all of it (34. 6%) is in C-4. Analogously, the finding that
nolabel is in C-l from the reaction of the Z-Cl3 chloride implies that
no label is in c-4, but all of it (50.8%) is in 0.3. . Corroborative
evidence is afforded by proton n.m. r. The spectrum of t-amyl chloride
recovered from the reaction of the l--C13 chloride shows Cl3 satellites
for the gem-dimethyl protons (’1' = 8.47) and the methyl protons (1’: 8. 97)

of the ethyl group (J in both cases is about 130 cps). No excess

c‘3H
label was detected in C-3.
«On the basis of mass-spectral and proton n.m. r. data, the iso-

topic results of _t_-amyl chloride can be summarized as follows:

c c c c c

c‘3-¢-c-c + c-c-c-c —-> c-c-c-c + 013-¢-c-c + c-<,:.-c--c13 +
c1 C1 c1 Cl Cl
43.0% 57.0% 61.0% 24.0% 11.5%

913

c13 g c c13+ c‘3-c-c-c
1 Cl

2 7% 0 8%

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19

 

 

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20

‘3... q 9? 9.. .3
C-C? -C-C + C-g-C-C -—> C-C-C-C + C-C'I -C-C + C- -C -C +

Cl 1 c1 (:1 1
57.7% 42.3% 46.9% 24.1% 24.7%
c
C-C'313-C13-C
1
4.3%

Label retention of the recovered _t_-amyl chlorides agrees with the label
content of starting materials. The data imply that C-1, C-4 and C-2, V
C-3 equilibration has been reached (the small deviations observed are

probably within experimental error)..

Analysis of hexyl and t-butyl chlorides. The presence of the hexyl

 

chlorides in small quantities prevented individual isolation, but evalu-
ation of the isotopic composition of each chloride was possible as a
consequence of their fragmentation patterns. The Q4H8C1f region (parent-
less-ethyl, masses 90 and 91) is hit heavily by 3-chloro-3-methylpentane
andlightly by Z-chloro-Z-methylpentane; conversely, the C3H6C1+ region
(parent-less-propyl, masses 76 and 77) is hit heavily by Z-chloro-Z-
methylpentane and lightly by 3-chloro-3-methylpentane. These differ-
ences are apparent in the partial mass» spectra shown in Table XIa.

By neglecting the contributions of the Z-chloro isomers in the C4HnCl+
region and of the Z-chloro isomer in the C3HnCl+ region, the label
content in the ethyl groups of the 3-chloro isomer and in the propyl group
of the Z-chloro isomer can be estimated. As in the case of the t-amyl
chlorides, the parent peak is very small and the over-all label content

in the molecules was calculated from the Can+ peaks, on the assmnp-
tion again that each C6H13+, . C6H12+ and C6H11+ fragment ion has the same
isotopic enrichment as the original hexyl chloride molecules. Also,

+
the assumptions made in the t-amyl chlorides regarding the C4HnC1 and

21

Table Xla. rPartial Mass Spectra of Hexyl Chlorides

 

 

 

In/e C-C-g-C-C C-g-C-C-C
l 1

105 3.4V 7.8
104 0.7 0.5

91 191.0 5.0

90 122.3 1.4

85 100.0 100.0

84 26.5 68.1

77 3.9 149.6

76 3.2 65.3

 

22

,C3HnCl+ ions were presumed to be valid in the hexyl chlorides. Proton
n.m. r. showed again that the methyl carbons had not equilibrated with
C-2, C-3 or C-4. The hexyl chlorides obtained from the l-Cl3 chloride
had all the label in the methyl groups and none in C-2, C-3 and C-4.
Table XIIa summarizes the pertinent mass-spectral results of the hexyl
chlorides recovered from the 5 min- reaction. In addition to the above
approximations and assumptions, the decomposition of the hexyl
chlorides into hexenes and hydrogen chloride upon standing may cause
the label distribution values to be in serious error.

-Isot0pic results of the hexyl chlorides by mass-spectral and proton

n.m. r. data are summarized as follows:

<9 9 9 <9” 9
c-c-c-c + c‘3-c-C-c -~> c-c-c-c-c + c-c-c-c-c + c-c—c-c—cl3
c1 c1 (:1 c1 (’31
57.0% 43.0% 61.4% 20.9% 12.0%

9 913
-(F-

+ c13 c-c-c” + c13—g-c-c-c
Cl 1
3.9% 1.8%
c c c
c-¢-c-c + 013-g-c-c —->- c-c-g-c—c + c13—c- -C-C + co -c—c
c1 - 1 1 c1 C1
57.0% 43.0% 61.4% 23.4% 9.5%
. C 013
+c‘3'v.c-c':-c-c13 + c-c-c::-c-cl3
c1 CI
2.5% 3.2%

Since C-3 and-C-4 of 2-chloro-2-methylpentane are not distinguishable
by mass spectrometry, evaluation of each individual isotopic species

from the 2--C13 compound is not possible.

‘e-7I>-00¢n<

23

 

 

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24

The over-all label content (44. 3%) in the hexyl chlorides obtained
from the reaction of the l--Cl3 chloride agrees with the starting _’_c_-amy1
chloride (43. 0%). The methyl groups of the hexyl chlorides from the
1.013 chloride have equilibrated (small deviations are probably within
experimental error).

The label content (75. 9%) in the hexyl chlorides obtained from the
reaction of i-amyl chloride-Z-Cn (57. 7%) is lower than what would be
statistically expected (57. 7 x 3/2 = 86.6%). Furthermore, C-2 and C-3
have not attained equilibrium.

Inability to collect _t_-butyl chloride in sufficient purity prevented

their meaningful isotopic analysis.

.Some calculated distributions of label. The degree to which

 

either all carbon atoms in the sample or specific groups of atoms
equilibrate is determined by the rearrangements undergone by the car-
bonium ions. According to the proposed mechanisms a C10 carbonium
ion, as shown in 8a and 9a, is the intermediate involved in the formation
of both dilabeled _t_-amyl chloride and hexyl chlorides.
Formation of these products requires rearrangements of the carbonium
ion before disproportionation; these rearrangements can result either
in complete or partial equilibration of the carbon atoms. The experi-
mental results exclude equilibration of the six methyl carbon atoms
with the four carbon atoms inside the chain; thus, the only equilibrations
possible are those among the six methyl carbon atoms, or those among
the four non-methyl carbon atoms.

Two-separate calculations of label distribution were carried out.

Method A. is based on the assumption that the six methyl carbon atoms,

 

or the four non-methyl carbon atoms, of the C10 unit become statistically
distributed and the C10 unit subsequently disproportionates into two units.
The smaller units recombine and the process is repeated until all methyl

groups, or all non-methyl groups, are statistically distributed throughout

25

all the molecules. Method B is based on the assumption that after the
original statistical distribution and disproportionation, the smaller units
do not recombine further and the reaction stops.

The percentage of dilabeled, monolabeled and unlabeled L—amyl
molecules formed by Method A from 2-chloro--2-methylbutane-2-C13
(57. 7% monolabeled and 42. 3% unlabeled molecules) was calculated by
p2, 2p(l-p) and (1-p)2, respectively, where p is the percent of labeled
carbon atoms (0. 577/2). Similarly, the percentage of trilabeled,
dilabeled, monolabeled and unlabeled t- amyl and _t_«-hexy1 molecules
formed from the same process, was calculated by p3, 3pz(l-p), 3p(1-p)?‘
and (l-p)3, respectively. The percentage of trilabeled, dilabeled, mono-
labeled and unlabeled t_-amyl and _t_-hexy1 molecules formed by Method A
from 2-chloro-2-methylbutane-l-Cl3 (43. 0% monolabeled and 57. 0%
unlabeled molecules) was calculated by p3, 3p2(l-p), 3p(l-p)Z and (1-p)3,
respectively, where p = 0.43/2.

The percentage of dilabeled, monolabeled and unlabeled i-amyl
and t-hexyl molecules formed by Method B from l-C13 and 2-Cl3-1abeled
2-chloro-2-methylbutane was found by Apz, [sz + cp(1-p)] and [DP2 +
Ep(l-p) + F(l-p)z], respectively. The fraction of labeled molecules (p)
is 0.43 for the l-Cl3-labeled L-amyl chloride and 0. 577 for the 2-C13-
labeled _t_-amyl chloride. A, B, and D are the probabilities that a
dilabeled, monolabeled and unlabeled i-amyl or _1_:_-hexyl molecule,
respectively, are formed if two labeled units combine, scramble and
disproportionate. C and E are the probabilities that a monolabeled and
anunlabeled L-amyl or _t_-hexyl molecule, respectively, are formed when
a labeled molecule combines with an unlabeled molecule. F is the prob-
ability of forming an unlabeled molecule when two unlabeled molecules
unite. A + B + D must equal 1; C + E must equal 2;‘ and F is l.

The calculated values are compared in the experimental values

in T able XIIIa .

26

 

 

 

 

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DISCUSSION

The carbonium ions will be represented as free ions, but most
likely they are associated with the tetrachloroaluminate ion. Isotope
effects (C12 versus C”) are small and will be neglected in the discussion.
All rearrangements will be represented as l, Z-Wagner-Meerwein shifts.
l, 3-Shifts, which have been postulated in similar rearrangementsls’ 17
are ignored because the results in the present system are identical with
two 1, 2- shifts. The results afford the following comments and conclu—
sions.

Formation of hydrocarbons in the reactions of aluminum chloride
with _1_;_-buty1, L—amyl and hexyl chlorides must occur by a hydride
transfer from a hydride donor to the carbonium ion (10a). The most
probable source of hydride is a heavy olefin that is eventually converted
to polymer and/or the polymer itself. This highly unsaturated polymer
probably causes the deactivation of the aluminum chloride.

0 c
c-é-c-c + RHv-z‘ c—é-c-c + R+ (10a)

The simplest and most reasonable path leading to 3-chloro-2-

methylbutane is 11a, an intramolecular path that is supported by the

 

c-E-c-c’éuIi c-g-c-c 3193A c-g—c-c (11a)

appearance of the secondary chloride at low temperatures (Table Ia).
Path 12a, similar to 11a, represents the equilibration of Z-chloro-Z-

methylpentane and 3-chloro-3-methylpentane.

27

28

 

c c E - c
c-q-c-c-c $.52 c-c—q-c-c “1351-: 0.3;. -c-c $.24: c-c-c-c-c
(:1

(12a)

Protonated cyclopropanes, as in 13a, do not intervene as inter-
mediates because they would cause methyl and non-methyl scrambling.

(:13

c\ / + ~ C'
c -I—-9 H (a c-c-c--c13 (13a)
/ \c +

c
c-é-cm—c #
C

The occurrence of bimolecular reactions was verified by identi-
fication of dilabeled species in the products. The data are explicable
on the assumption that 1(14a), the first bimolecular intermediate, is

capable of undergoing fast and reversible rearrangements to other C10

C

,c-c‘5-c-c + c-c=c-c $24.. c—gg- (14a)
c-

q-c
c-c-c
c
1

carbonium ions. During these rearrangements the six methyl carbon
atoms attain statistical distribution faster than the four non-methyl
carbon atoms (Table XIIIa). The faster equilibration of methyl carbon
atoms can be seen by inspection of reactions such as 9a which effects
methyl equilibration only and others such as 15a which simultaneously

effect methyl and non-methyl equilibration.

Q 9 (.3 +
c-c‘tc-c ’_V__I_'_I_ ~Et c-c‘3-c-c—c ~iPr c-c-c-c
| <——— \——~—-‘—*‘ ~.———-———-“
c_gl3_c_c C- 13_C C_gl$_ C'l3-C
c

(15a)
C

C i
mCHL :HA C‘é’T'c' ______\ C-é-C-C + C- 132C13-C
C

\

 

 

Z9

Absence of 1- and Z—propyl chlorides, 1- and Z-butyl chlorides,-
and 1-, 2- and 3-penty1 chlorides in the products (Table Ia) indicates
that disproportionation (16a) results in the formation of tertiary

carbonium ions only. Apparently, under the experimental conditions of

l I I \ /' I
442-9-.- ——-> /C=C\ + 4);: (1661)

this work, fission to an olefin and a secondary carbonium ion is more
expensive energetically than rearrangement to a carbonium ion which
undergoes fission to an olefin and a tertiary carbonium ion. Therefore,
Clo carbonium ions may lead to two C5 species or a C4 and a C6 species

as in 17a.

~H/ c-c-c-c \ erH3

9 C 9 9 g
c-C-T-c-C c-g——T+ C-C-|-C
c-c+ c-c—c—c caq-C_c
c c
"A, CH3 JIM/CH3 (Ln/1m
lth c c-c-c
c-c——c-c I
C c | c-c-c-c-c
c-q-c—c-c c-p-c—c c c
| JINCH3
c-c—c 4’ JNV}1
c c c
c W c-c=c-c-c C-C-C
c-c_c-c-c + +
+ c c-c- acuc
c-c-c c

30

"Secondary reactions between C5 and C4 or C5 andJC6 units un—
doubtedly occur to some extent, but their results neither detract nor
add anything significant to the discussion of the L-amyl cation.

Reaction sequences such as 18a must be excluded because the

C 4 c c c - c c
c-c-é-c + c13=<':-c-c Fe c-c-g - cl3 - é-c—c g; c-c-i — $13 - c-c-c
11

(18a)

0
95A c-c-é-gm—g-c—c: c—c-gzcn—c + c-q-c-c

hexyl chlorides obtained from the reaction of i-amyl chloride-l-Cl3
have incorporated negligible amounts of label in C-2, C-3 andC-4.

~ Whitmore and Mosher15 found that 3, 5, 5-trimethyl-Z-heptene (olefin
analog of II in 18a) upon treatment with sulfuric acid leads only to iso-
amylenes.

The relative contributions of bimolecular and unimolecular re-
actions to the over-all isotoPe-position rearrangement in the t-amyl
system can not be assessed with any degree of accuracy for two reasons:
1) complete isotope-position equilibration has been achieved under the
experimental conditions, and 2) the necessary assumption that the non-
methyl carbon atoms equilibrate during each bimolecular reaction is
not true.

_t_-Buty1 chloride, in contrast to _t_-amyl chloride, gives mainly
the Z-chloro—Z, 3-dimethy1butane. All reasonable reaction sequences
‘lead preferentially to the 2, 3-dimethy1buty1 system rather than the 2-
or- 3-methy1penty1 system (19a).

 

 

c c c c; c c
c-c-c + c- -c—v=_= -¢-c-§—c :H‘ Q’CHJ c-c-é-c-c
c
9 (F C.3 +
# C-C=C-C-C + H
C 9 g C C 9 (.5 (.3
c-czc- -c c—c-q-c—c men, ‘ c—é—c—c-c (19a)
+ ..— l ---- | c
c-i-c C—c;c c—c-c
c c
c c c C c c c
“3:25.32 c-c——-<':-c':—c —....._.-—-> c-c=c-c + c-c-c-c
+ ' +
c-¢ c
c

A termolecular reaction would be the most reasonable path for
formation of t_-amyl chloride from _1_;_-butyl chloride and should entail
simultaneous formation of a C7 species. A Unidentified peaks in the
chromatogram (Fig. 2a) of the reaction products could be C7 compounds.

Disproportionation of a C12 unit from the reaction of 3-chloro-
3-methy1pentane and aluminum chloride could lead to L-butyl chloride

and a C8 species, or _t_-amy1 chloride and a C7 species.

EXPERIMENTAL

l. The Reactions of t-Argyl Chloride with Aluminum Chloride

 

In a 25-ml. side-arm flask equipped with a 10 inch glass-spiral
column and distillation head connected to a vacuum system was placed
1. 75 g. (0.016 mole) of -t_-amyl chloride (purified by distillation).

The flask was immersed in an ice bath. ‘ To the magnetically-stirred
L-amyl chloride was added 0. 078 g. (0. 0006 mole) of anhydrous
aluminum chloride (Baker and Adamson, reagent grade). At the end

of 5 min. the reaction was quenched by injection of 73 pl. (0.0006 mole)
of N, N-dimethylaniline. Immediately the ice bath was removed and

the volatile portion of the reaction mixture was pulled under vacuum into
two traps immersed in liquid air. The amount of liquid collected was

1. 26 g. » (72% yield based on weight).

All reactions followed the above procedure with changes in re»
action time, temperature, and reactant concentrations. In many
instances N, N-dimethylaniline was not added; the yield and product

composition were unchanged.

2.. Product Analysis

 

Small amounts (0. 5-1. 5 ul.) of the collected product were injected
into a Perkin-Elmer Vapor Fractometer, Model 154. The columns used
were 5-30% Silicon Oil on Celite and the column temperatures were
about 800. The vapor phase chromatograms of the reaction products of
L-amyl chloride, L-butyl chloride and 3-methy1-3-chloropentane with
aluminum chloride are shown in Figs. 1a, 2a and 3a. The individual
components were identified by comparison of their retention times with

those of authentic samples. Correlation of the area weight of the peaks

32

33

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36

to component weight allowed the quantitative determination of the re-
action components. The error involved (standard deviation) did not

exceed 3; 10%.

Reaction products of t-amjl chloride. Peaks 1, 2, 3, 4, 5, 6, 8

 

and 9 (Fig. 1a) were identified by comparison of the vapor phase
chromatography (v. p. c.) retention times with known compounds.

Attempts to prepare 3-chloro-Z-methy1butane by chlorination of the
alcohol gave a mixture of two chlorides (10:1 ratio) corresponding to
peaks 6(_t_-amy1 chloride) and 7. In some runs the presence of amylenes
could be detected between peaks 2 and 3. Occasionally, a trace of
L-amyl alcohol would appear directly before peak 6. If a sample of the
reaction mixture was passed through the chromatograph at a high
amplitude, an unidentified peak could be seen between peaks 7 and 8,
another after peak 9 and several with very high retention times. The
peak between 7 and 8 did not correspond to the hexyl alcohols, 3—chloro-
pentane, or l-chloro-Z-methylbutane. Isooctane (2, 2,4-trimethy1pentane)
falls on top of peak 7 and 3-chloro-Z, 3-dimethy1butane comes immediately
after peak 8. Isopropyl chloride which would appear after peak 2 and
Z-chlorobutane which would appear between 5 and 6 could not be detected

in the reaction products. n-Propyl chloride falls on peak 3.

- Reaction products of t-butyl chloride. Identification of peaks

 

1, 2, 3, 6, 7, 8 and 9 (Fig. 2a) was made by comparing retention times
with known compounds. The presence of l-chloro-3-methy1pentane
(peak 9) implies the presence of Z-chloro-Z-methylpentane under peak 8.

.Peaks 4 and 5 and two peaks beyond 9 were unidentified.

Reaction products of 3-chloro-3-methllpentane. -Peaks 1 through 9

 

(Fig. 3a) were identified by comparison of their retention times with

known compounds. . Peak 10 and two peaks beyond 10 were not identified.

37

3.. Preparations of Reference Compounds

 

_t_-Amyl chloride, _t_-buty1 chloride, isopropyl chloride, 2-chloro—
butane, n-propyl chloride, 1-chloro-3-methy1butane,i 2-methy1-2-
butene, visobutene, isopentane and isobutane were commercially avail-
able. Z-Methylpentane and 3—methy1pentane were gifts from American
Oil Research-Labs. ,. Whiting, A Indiana.

.Z-Methyl-Z-pentanol. A solution of 28.4 g. A (0. 20 mole) of methyl

 

iodide in 50 ml. of anhydrous ether was added to 5. 2 g. (0. 22 .mole) of
magnesium over a period of 30 min. The solution was refluxed for 30
min. on a steam bath. A solution of 15. 5 g. (0. 18 mole) of 2-pentanone
in 75 m1. of anhydrous ether was added dropwise to the above solution in
an ice bath. The solution was stirred for 2 hrs. and allowed to stand
overnight. .Sixty-five m1. of a cold, saturated ammonium chloride solu-
tion was added to the Grignard complex. The ether layer was separated
and the aqueous layer was washed with ether. The combined ether
layers were washed with cold water and dried overmagnesium sulfate.
The ether was removed and 14. 0 g. (0. 14 mole, 78%) of crude alcohol
was obtained. v.p.c. showed the presence of a slight ether impurity.

The crude alcohol was converted directly into the chloride.

2-Chloro-2-methy1pentane. In a 50-ml. flask connected directly

 

to a distillation head were placed 4. 0 g. (0. 039‘mole) of 2-methyl-2-
pentanol and 7. 0 m1. (0. 080 mole) of cone. hydrochloric acid. The
magnetically stirred mixture was heated with an oil bath and the fraction
boiling from 85-1000 was collected. After the chloride was washed

with-a 10% sodium bicarbonate solutionand with water, it was dried over
magnesium sulfate. The product weighted 2.0 g. (0.017 mole, 42%) and
v.p. c. showed the presence of two small impurities (probably olefins).

_ The chloride was distilled and the fraction boiling at 290/29 mm. was used

for mas s- spectral analysis.

38

3-Methy1-3-pentanol. The Grignard procedure for the preparation

 

of 2-methy1-2-pentanol was repeated using 3apentanone. Identical
amounts were used and a yield of 75% was obtained. . v.p. c. showed a

small ethe r impurity .

3-Chloro-3-methy1pentane. The procedure for the preparation of

 

2-chloro-2-methylpentane was followed using 4. 0 g. (0. 039 mole) of
2-methy1-2-pentanol and 7. 0 ml. (0.080 mole) of cone. hydrochloric
acid. The fraction (2.6 g.,0.022 mole, 55%) boiling between 85 and 95°
was collected. The chloride was distilled and the fraction boiling at

290/28 mm. was collected for massc-spectral analysis.

3—Methy1-2nbutanol. In a 300 m1. threeanecked flask fitted with

 

a stirrer, reflux condenser, and a dropping funnel were placed 0. 73 g.

(0. 020 mole) of lithium aluminum hydride and 125 ml. of anhydrous
ether. In the dropping funnel were placed 5.6 g. (0. 065 mole) of methyl
isopropyl ketone and 20 m1. of anhydrous ether. The solution was added
dropwise over a period of 30 min. and stirring was continued with reflux
for one hour. To the solution was added dropwise 2 ml. of water,
followed by 2 ml. of 10% sodium hydroxide and 1 m1. of water. The solu-
tion was stirred with reflux for one hour. The ether solution was
removed and dried over magnesium sulfate. After removal of the ether,
4. 53 g. (0. 050 mole, 77%) of alcohol remained. Minor ether and ketone

impurities were shown by v. p. c.

3-Chloro-2-methjlbutane. The above mixture of 3-methy1-2-butanol

 

was treated with conc. hydrochloric acid according to the 2-chloro-2-
methylpentane preparation. In addition to the main product (t-amyl
chloride), v.p.c. showed the presence of 3-chloro-2-methy1butane,

unreacted alcohol and methyl isopropyl ketone.

2, 3-Dimethy1-2abutanol. The procedure for the preparation of

 

2nmethy1-2—pentanol was followed using 5. 3 g. (0. 22 mole) of magnesium,

39

28.4 g. (0. 20 mole) of methyl iodide and 17.2 g. (0. 20 mole) of methyl
isopropyl ketone. .After the ether was removed, v.p.c. showed that
themixture‘(24. 5 g.) contained the alcohol (”50%), ether and unre-

acted ketone. Approximate yield was 60%.

Z-Chloro-Z, 3-dimetlglbutane. The above solution of 2, 3—dimethy1-

 

2-butanol, ether and methyl isopropyl ketone was treated with 30. 0 ml.
(0. 34 mole) of conc. hydrochloric acid (see preparation of 2-chloro-2-
-methy1pentane) and the fraction boiling 52-940 was collected. ~ In addition
to the chloride (~40%) v. p. c. showed that the mixture contained ether,

methyl isopropyl ketone and two unidentified low retention compounds.

3-Pentanol. - In a 300-ml. three-necked flask equipped with a

 

stirrer, reflux condenser and a dropping funnel, 3.8 g. (0.10 mole) of
lithium aluminum hydride was added to 15 ml. of anhydrous ether.

To the above mixture 8.6 g. (0. 10 mole) of 3-pentanone in 50 m1. of

~ anhydrous ether was added over a period of 30 min. After stirring for

' 20 min. , the solution, immersed in an ice bath, was hydrolyzed with

35 ml. of 10% sodium hydroxide. After the solution was stirred for

1. 5 hrs. , the ether layer was removed and the aqueous layer was
extracted three times with ether. The combined ether extracts were
washed three times with water and dried over magnesium sulfate. - After
most of the ether was removed, 8. 8 g. of the alcohol-ether mixture was

found by v.p. c. to contain 80% of 3-pentanol (N 0.080 mole/V 80%).

3-Chloropentane. .A mixture of 2. 0 g. of the above-3-pentanol-

 

ether solution and 7. 0 ml. of cone. hydrochloride acid was heated and
the fraction boiling from 75-900 was collected. The presence of 70% of
3-chloropentane,. 30% of the unreacted alcohol and a trace of ether was

shown by v. p. c.

40

4.. Syntheses of Cl3-Labeled‘ Compounds

 

t-Amyl alcohol-1-C13. In a 300-ml. three-necked flask were

 

placed 3.64 g. (0. 15 mole) of magnesium and sufficient. anhydrous ether
tocover the magnesium. A solution of 2. 0 g. (0. 014 mole) of unlabeled
methyl iodide in 7 ml. of anhydrous ether was added through a dropping
funnel to initiate the reaction. 7After the reaction had started, 17. 0 g.
(0.12 mole) of methyl iodide-C13 in-50 m1. of anhydrous ether was added
over a period of 1. 5 hrs. ~ After the solution had refluxed one hour over
a steam bath, 10.4 g. (0. 14 mole) of methyl ethyl ketone in 50 m1. of
anhydrous ether was added over a period of one hour. The Grignard
complex was hydrolyzed with 50 ml. of a saturated ammonium chloride
solution. The ether layer was removed and the aqueous portion was
washed with ether. The combined ether solutions were washed with
water and dried over magnesimn sulfate. - After removal of the ether,
approximately 7. 8 g. (0. 089 mole, 66%) of.1_:_-amy1.alcohol-l-Cl3 was
obtained. ~ The alcohol was purified with a Beckman‘Megachrom before

conversion to the chloride.

t-Amfl. chloride-l-Cl3. A mixture of 6. 8 g- (0.077 mole) of

 

_t_-amyl alcohol-l-Cl3 and 24. 0 ml. 1 (0. 30 .mole) of cone. hydrochloric
acid was heated and the fraction distilling from 65-820 was collected.
Approximately 7. 9 g. (0. 074 mole, 96%) of the chloride was obtained.
The _t_-amy1 chloride-l-C” was purified with a Beckman Megachrom
before mass-spectral analysis and before reaction withaluminum

chloride.

t-Amyl a1cohol-2-C13. The Grignard procedure used for the

 

preparation of the 1--C13 alcohol was followed using 11. 0 g. (0.46 mole)
of magnesium, 65.0 g. (0.46 mole) of methyl iodide and 9.6 g. (0. 11
mole) of methyl pr0pionate-1-Cl3. After removal of the majority of the

ether, 14.4 g. of an ether and alcohol (N 53%,N 0. 087 mole) mixture

41

was obtained. Approximate yield of the crude alcohol was 80 %. The
ether-alcohol mixture was separated with a Beckznan Megachrom

before conversion to the chloride.

t-Amyl chloride-2-013. A solution of 6.2 g. (0.071 mole) of

 

L-amyl alcohol—2.0l3 and 18.0 ml. (0.22 mole) of cone. hydrochloric acid
was distilled and the fraction boiling from 65-820 was collected. The
chloride which weighed 7. 3 g. (0. 069 mole, 98%) contained small amounts
of amylenes as shown by v. p. c. L-Amyl chloride-Z-Cl3 was purified

with a Beckman Megachrom before mass-spectral analysis and reaction

with aluminum chloride .

5 . Is otope Analy sis

 

Analyses of the C13-labeled compounds were p(reformed with a
Consolidated Model 21-103C Mass Spectrometer by Séymour Meyerson
of the Research and Development Department, American Oil. Company,
Whiting, - Indiana.

The n.m. r. spectra were taken with a Model V4300-2 Varian

Associates high resolution n.m. r. spectrometer at 60 Mc.

SUMMARY

Bimolecular paths in the reactions of _t_-amyl chloride-l-Cl3 and
_t_-amyl chloride-Z-C13 with aluminum chloride were verified by
identification (mass spectrometry) of dilabeled L-amyl chloride and
hexyl chlorides in the reaction products. The data support I as the
first intermediate formed by the attack of i-amyl cation on a C5 olefin.

C
c-q-c-c
C-i-C-C
I
This C10 carbonium ion may undergo fast and reversible rearrangements
to other Cm carbonium ions. The C10 unit, which disproportionates into
\an olefin and a tertiary carbonium ion, may lead to two C5 units or a
C4 and a C6 unit. - Calculations of statistical isotopic distribution suggest
that each L-amyl species has undergone an average of one bimolecular
reaction resulting in complete equilibration of the methyl and partial
equilibration of the non-methyl carbon atoms. -No scrambling between
methyl and non-methyl carbon atoms was detected.
< The volatile products from the reaction of 1. 74 g. of _t_-amy1
chloride with 0. 080 g. of aluminum chloride at 00 for 5 min. are 68. 2%
L-amyl chloride, 16. 7% L-butyl chloride, 5. 7% 3-chloro-2-methy1butane,
4. 2% 2-chloro-2-methylpentane, 1. 5% 3-chloro-3-methy1pentane and
3. 8% of the corresponding hydrocarbons. ~ The percent recovery of
volatile products and the percent _1:_- amyl chloride in the volatile fraction

increased with 1) increase in the ratio t_-amyl chloride/almninum

chloride, 2) decrease in temperature, and 3) decrease in reaction time.

42

43

After five minutes the reaction appears to stop. . The apparent termi-
nation of the reaction may involve deactivation of the catalyst by highly

unsaturated polyme r s .

PART B

N.M.R. STUDIES OF STEREOISOMERISM
IN SOME CAR BONYL DERIVATIVES

44

INTRODUCTION

The possibility of stereoisomerism about the carbon—nitrogen
double bond in phenylhydrazones has long been recognized. 18 A survey
of the literature reveals that the majority of the reported isolations
of syn and aiti isomers occurs when there is an o-substituent which is
capable of hydrogen bonding with the N-H group. Geometric isomers
of o-halo 2, 4-dinitropheny1hydrazones (DNP's), a-alkoxy DNP's,’19
o-carbonyl DNP's,20’ 21’ 22 furfural DNPZ3’ 24 and 2-acylpyridine phenyl-
hydrazones25 have been reported. Aromatic DNP's such as those of

26 2 2
acetophenone, benzaldehyde 7 and ethyl benzoyl acetate 8 have been

isolated in syn and anti forms, but examples of aliphatic derivatives are

 

very limited. Gordon29 has observed two bands on a chromatographic
column for 2-butanone DNP. Three forms of acetaldehyde DNP melting
at 168. 50, 156-570 and 1490 were obtained by Bryant. 31 Bryant sug-
gested that the two higher melting forms were the stable and unstable
isomers, while the 1490 form was a mixture of the two. - Ingold and co-
workers32 isolated two forms of acetaldehyde DNP melting at 1460 and
162°. van Duin30 separated aldehyde DNP isomers by chromatography.
The melting point of the major acetaldehyde~DNP was 167--68o and that
of the unstable was 93-40. vLaws and Sidgwick, 33 isolated the isomers
of ac etaldehyde phenylhydrazones.

Various methods have been used to obtain evidence for the existence
of stereoisomers. -Me1ting points are not a reliable criterion because
they are sensitive to impurities. Furthermore, DNP's can exist in dif-
ferent crystalline forms whose melting points may be different. 33’ 34’ 35’ 36

1
Ramirez and Kirby, 9 from differences in the N-H infrared absorb-

tion band and ultraviolet absorption maxima, were able to assign syn and

45

46

.3212 structures to u—halo and a-alkoxy DNP's. Bredereck, 24 with the
aid of dipole moment studies, identified the stabler, higher melting
form of substituted furfural DNP's as the syn-hydrogen isomer.

» Kuhn and-Munzing, 25 through isolation of a 8-aza-indozoliurn salt from
one of the isomers of 2-benzoy1 pyridine phenylhydrazone, were able to

establish the isomeric configurations (1b)

(1 r a . ,1 Q .
\N c/ HCl ?N\ /c/ .931 g/ .
N-N ‘ 7'“ “ N\

' -———-——-—A
r—n—

1x}
0-161 0! Cl' ‘ NH-¢
(1b)

Recently, nuclear magnetic resonance (n.m. r.) spectroscopy has
become a valuable tool in the study of hindered rotation. . The main
areas of study have been hindered rotation about single bonds, about
partial double bonds and about double bonds.

1N.m. r. studies of hindered rotation about single bonds are difficult
becauseone must determine whether the nonequivalence of the hydrogens
should be ascribed to slow rotation, or to rapid rotation in which the
time-averaged environment of each hydrogen, or group of hydrogens,
is different.

Hindered rotation about partial double bonds is exemplified by

38-44 45,46,47

. . . . . 48 .
amides, nitrites and nitrosamines. The two nonequiv-

alent N-CH3 groups of N, N-dimethylacetamide (2b-I) appear as a doublet.

6 -Q\ /H3 R\ R I, 6 .-
cu-N a + 05 + a +o/ ’ (2b)
/ :1 :| El
.’V X, ,CH2 CH2
6 -O "cis" Oé - "trans" CH3 CH3

I II III

47

Doubling of a-hydrogens in the n.m. r. spectra of alkyl nitrites has
been studied at lowvtemperatures. The doubling is again attributed

to partial double bond character which allows the molecules to exist in
sis and trans rotational isomers (Zb-II). Studies of N, N-diethyl
nitrosamine reveal two quartets for the methylene protons and two
triplets for the methyl protons (2b-III).

Relatively high barriers of rotation about double bonds simplify
studies on geometric isomers. - In addition to the well- studied carbon-
carbon double bonds, isomerism of carbon-nitrogen double bonds in
oximes and imines has been investigated. Phillipsqt9 observed two
aldehydic resonances in propionaldoxime and assigned the low field

0
triplet torthe syn form (3b-I, RéCHzCHZCH3). Lustig5 applied n.m. r.

 

OH
OH HO H NM,

/ \ \ //

N N C
I I lcl ll / (3b)
\H R/ HOWJ |
\

syn anti N

I II III

spectroscopy to the study of ketooximes. The isomers of isophorone
(3b-II) and isonicotinaldehyde oximes (3b-III) have been observed by

Slomp and Wecter, 51 and Mosher and co-workers, 52 respectively.

Curtin and Hauser, 53 studying the stereoisomerism of imines, observed
two resonances for the phenyl-methyl and phenyl-methoxy protons in
p-methoxy, p'-nitrobenz0phenone p-tolylimine (4b-I). p-Nitrobenzophenone

methyl imine (4b—II), also, exhibited two methyl resonances.

CH3 Nfcn,

N

\ Q/
Ng;: OCH3

Noz

(4b)

0

I

48

In the n.m. r. spectra of oximes, nitrites and nitrosamines,
but not in amides, the hydrogens in close vicinity of the oxygen were
assigned to the low field resonances.

Application of n.m. r. to other C=N compounds such as DNP's
and semicarbazones (SC's) has been limited. In 1959 Curtin54 used
n.m. r. to distinguish between the DNP's and SC's of aldehydes and of
ketones. .Difference in the n.m. r. spectra of the isomers of ethyl
benzoylacetate DNP allowed Silverstein andShoolery28 to assign the
absolute configuration of each isomer. In their attempts to identify the
isomers by cyclization to pyrazolines, they obtained identical rate
constants for both isomers; therefore, they concluded that isomerization

was much faster than cyclization (5).

c c
/
o-c \c=o 045/ \,c=o
Ilql oCHZCH3 ——> N—N + HOCHZCH3
\NH I NO2
N02 ’ (5)
N02 N02.

The purpose of the present investigation was to extend n. m. r.
studies of C=N isomerism to 2, 4-dinitrophenylhydrazones, the mono-

nitrophenylhydrazones, semicarbazones and thiosemicarbazones.

RESULTS

1. Chemical Shifts

 

2, 4—Dinitrophenylhydrazones (DNP‘s). Table 1b lists the chemical
shifts of aldehyde and ketone DNP's in methylene bromide. The aro—

matic, aldehydic and'N-H hydrogens are numbered as in 6b.

Hz NO;
/H1
N===C
3 H4 \R'(H5!)

In symmetrical DNP‘s (R = R') only one isomer is possible, but
the two groups, R and R‘, are magnetically nonequivalent and usually
resonate at different frequencies. The two possible stereoisomers of
unsymmetrical DNP's are designated as 312 and anti, syn referring to
the isomer which has the 2, 4-dinitropheny1 group -c_is_ to the smaller
group. Assignment of syn-ing structures to the isomers was based on
equilibrium values (Table Xb). When one R is methyl and the other
isopropyl or t-butyl, only one isomer is present. From steric con—
siderations the syn configuration was assigned to these isomers.

On this assumption the minor peaks in the spectra of 2-butanone DNP

(Fig. 1b) and 2-pentanone DNP were assigned to the anti isomer.

 

Isomer compositions of semicarbazones (Tables XIb and XIIb), thio-
semicarbazones (Table le) and aldehyde DNP's (Table Xb) support
this assignment.

Two sets of aromatic hydrogen resonances are observed when one
of the R groups is hydrogen or contains a phenyl or cyclopropyl group.
In addition ethyl cyclopropyl ketone DNP, which was not assigned

49

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syn-anti structures, has two H1 resonance signals. Fig. 2b contains
the partial n.m. r. spectrum of an equilibrated solution of acetaldehyde

DNP. 'Low anti isomer concentrations prevented the observation of

 

two sets of aromatic hydrogens in the n.m. r. spectra of propionaldehyde,
B-butyraldehyde, isobutyraldehyde and phenylacetone DNP's. Although
the presence of a second doublet for the B-CH; of isobutyraldehyde DNP
indicated the presence of 5% of the anti isomer, only one aldehydic
doublet could be observed, because the signal to noise ratio was too low.

The chemical shifts of the alkyl hydrogens, H2, H3, and H; are
fairly consistent, but H1 varies significantly. When the 2,4-dinitrophenyl
group is c_i§ to a group larger than methyl (3-pentanone, diisopropyl
ketone, dibenzyl ketone and benzyl ethyl ketone DNP's), H1 resonates at a
lower field.

‘ Tables IIb, IIIb, IVb and Vb list the chemical shifts of formalde-

hyde, acetaldehyde, Z-butanone and 3-pentanone DNP's, respectively,
in various solvents. Aromatic and alkyl hydrogens are relatively
solvent independent, whereas H1 and H5 are appreciably solvent de-
pendent. Two H1 resonances are observed for acetaldehyde DNP in
dimethyl sulfoxide, dimethylformamide and pyridine.

Table 6b shows the small variation in the chemical shifts of DNP

hydrogens over the available concentration range.

Mononitrcwhenylhydrazones. Table VIIb contains the chemical

 

shifts of pig-nitrophenylhydrazones (p-NP's), meta-nitrophenylhydra-
zones (m-NP's) and ortho-nitrophenylhydrazones (_o_-NP's). The number-
ing corresponds to 7b. Figs. 3b and 4b show the aromatic hydrogens

of acetone p-NP and acetone g-NP, respectively. The aromatic hydrogens

of IFNP'S were complex and were not resolved. Assignment of the

55

Table IIb. Chemical Shiftsa of Formaldehyde 2, 4-Dinitrophenyl-
hydrazone in Various Solvents

 

 

 

Solvent H1 H2 H3 H, 115 H5: Aéf
CHZBrz .1.10 0.93 1.63 2.07 2.73 3.23 30.0
c:Hc13 -1.13 0.85 1.63 2.05 s s s
¢NOZ -1.08 1.10 s s s s s
Dioxane -1.12 1.02 1.67 2.12 2.73 3.30 34.3
Acetone -1.32 1.02 1.60 2.00 2.42 3.17 45.5
DMSOb .1.50 1.13 1.62 2.10 2.37 3.13 48.0
TMUC .1.50 1.10 1.62 2.03 2.23 3.18 57.0
DMFd -1.50 1.10 1.62 s 2.40 3.19 47.5
Pyridine -l. 57 l. 00 s s s s s
TFAe an 0.72 1.53 1.95 3.07 —--- o

 

a‘Internal standard was tetramethylsilane (1’: 10. 00). Numbering corres-
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out

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aromatic hydrogens was made by assuming that the hydrogen at lowest
fields was the hydrogen ortho to the nitro group. Chemical shifts were
calculated using first order approximations. As in DNP's, acetaldehyde

_o_-NP developed a second set of aromatic hydrogens upon equilibration.

Semicarbazones and Thiosemicarbazones. Tables VIIIb and IXb

 

summarize the chemical shifts of SC's and TSC's, respectively. The
N-H and NH; resonances were not calculated. (_3__i_§ and 2213 hydrogens
of TSC's become equivalent in trifluoroacetic acid. Traces of trifluoro-
acetic acid caused the two methyl singlets of acetone TSC in methylene
bromide and chloroform to coalesce. Addition of sulfuric acid to acetone

TSC in methylene bromide broadened the peaks but did not cause them

to coalesce.

2.. - Isomer Chemical Shift Differences

 

Tables Xb,- XIb and XIIb contain the A6 '5 of the nitrophenylhydra-
zones in methylene bromide, the A6 '3 of SC's and TSC's in chloroform,
. and the A6 '8 of TSC's in trifluoroacetic acid, respectively. For con-
venience the values are reported in cps. For the unsymmetrical
derivatives, a positive sign signifies that the hydrogens _c_:_i_s_ to the derivative
group are at higher fields (higher '1’) than the corresponding EELS.
hydrogens. A negative sign indicates the reverse. For example, in the
spectrum of Z-butanone DNP, the minor a-CH3 and fi-CH3 peaks occur
at lower fields than the major peaks. On the assumption that the major

isomer is the syn isomer (2,4-dinitropheny1 group is cis to the methyl),

66

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74

the a-CH3 has a positive A6 . The B-CH3 has a negative A6 , because
it resonates at a lower field when_c_i_s_ to the phenyl group (anti isomer).

Generally, a-hydrogens are shieldedv(positive A6) while aldehydic
and (“l-hydrogens are deshielded (negative A6). fi-Hydrogens of SC's
and Z-butanone DNP in trifluoroacetic acid, B-CH3(CHZ¢) and B-CH3 of
benzyl ethyl ketone DNP and o-CHZ of phenylacetone nitrophenylhydrazones
are exceptions. In trifluoroacetic acid the minor isomer peaks of SC's
of acetophenone and phenylacetone resonate at higher fields than the
major peaks. The methyls of DNP, g-NP and TSC of acetaldehyde are
deshielded in carbonyl solvents (dimethyl sulfoxide, tetramethylurea,
dimethylformamide and dimethyl formamide and acetone). The methyls
of acetaldehyde p-NP and all the Z-butanone derivatives are shielded in
the carbonyl solvents.

A decrease of about 0. 5 cps in A6 '5 of acetone DNP in methylene
bromide, andacetone SC and TSC in chloroform was noted when the

spectra of warmed solutions were compared to those of cooled solutions.

3. Equilibration and Stability of the Derivatives

 

The isomer ratios of some unsymmetrical nitrophenylhydrazones
changed with time to a constant value. ~Most SC's, TSC's and aliphatic
ketone DNP's had equilibrated by the time the spectra were taken.

The n.m. r. of fresh solutions of acetaldehyde, propionaldehyde,
g-butyraldehyde, benzyl ethyl ketone and phenylacetone DNP's showed
the presence of one isomer; upon standing the second isomer (_a_._r_1_1_:_i)
appeared. \ Fig. 5b shows the equilibration of acetaldehyde DNP in

methylene bromide. The anti aromatic and aldehyde resonances appeared

 

simultaneous with the 3.21:; methyl peaks. ~The time required for equili-
bration depended on the solvent, and it decreasedas the melting point of
the crystals decreased (Table XIIIb). Figs. 6b and 7b contain the
partial n.m. r. spectra of benzyl ethyl ketone DNP in a freshly prepared

solution and an equilibrated solution, respectively.

75

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76

Table XIIIb. Time Studies of the Equilibration of Acetaldehyde
Z, 4-Dinitropheny1hydrazones

 

 

 

 

 

 

Nitrobenzene I Pyridine Methylene Bromide
Time anti/s yn Time anti/3E1 ‘ Time anti/m
Acetaldehyde DNP, m.p. = 164-650
0.5 hr. 0/100 0.1 hr. 0/100 0.1 hr. 0/100
11.5 hrs+/100 8.5 hrs. 15/85 8.8 hrs. 19/81
1 day 2 hrs. 4/% 11.3 hrs. 19/81 9.5 hrs. 25/75
3 days 10 hrs. 17/83 1 day 6.7 hrs. 21/79 1 day 7 hrs. 2.8/72
5 days 8 hrs. 19/81 2 days 30/70
11 days 28/72 3 days 10 hrs 34/66

 

Acetaldehyde DNP, m.p. = 145-47°

 

0.2 hr. +/100 0.2 hr. +/100
1.5 hrs. 8/92 2.5 hrs. 11/89
4.0 12.5/87.5 7.5 .28/72

 

 

6.0 20/80 13.0 32/68

 

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79

The equilibration is acid-catalyzed. Some solutions of acetal-
dehyde DNP, which were prepared in the absence of acid, did not
equilibrate after standing at room temperature for 10 days. Addition
of traces of acid to these solutions effected equilibration within
several hours.

When the solvent was removed under reduced pressure from
equilibrated acetaldehyde solutions, the crystals melted over a wider
range and 10-150 lower than the original crystals. When these lower
melting crystals were redissolved, the n.m.r. showed the presence
of 20-25% of the anti isomer.

Attempts to obtain pure fflt} isomer crystals of acetaldehyde
DNP by fractional crystallization from methylene bromide-Li-heptane
solutions resulted in the separation of a mixture (melting point = 87-1050)
which contained 85% 3n_ti_ and 15% 33113. On standing solutions of this
mixture reached the same_a_r_1_t_i_/_S_Ln ratios as the ELI}. isomer.

Acetaldehyde crystals were obtained that melted at 145-460,
157-580, 160-610 and 165-660. The n.m.r. spectra of the latter three
crystals contained one isomer (methyl doublet at 'T’ = 7. 82 in methylene
bromide). The low-melting crystals showed the presence of less than
5% of the 3.213 isomer.

In solution nitrophenylhydrazones did not isomerize to the azo
form; phenylhydrazones have been reported to isomerize.

DNP, _o_-NP, SC and TSC crystals are stable indefinitely, whereas
some m_-NP and p-NP crystals decomposed to a dark oil after standing
for several days. -In general, solutions of all the derivatives were
stable. .Occasionally, decomposition to starting ketones was observed

in trifluoroacetic acid solutions of SC's.

80

4. - Spin-Spin Coupling Constants

 

Table XIVb lists aldehydic, aromatic and N—H coupling constants
(J's) of several nitrophenylhydrazones. The complex spectra of the
aromatic hydrogens of r_n_-NP's were not analyzed.

H1 of DNP's couples strongly with H3 and H5, weakly with H4,
and not at all with Hz and H5“ These couplings disappear upon exchange
with D20 as illustrated in Figs. 8b and 9b. The couplings also disappear
in tetramethylurea, dimethylformamide and trifluoroacetic acid.
Addition of traces of acid and water to dimethyl sulfoxide did not destroy
the coupling. The broadness of H, of formaldehyde DNP in comparison
with H4 of acetone DNP and the broadness of H5: in comparison with H5
of N-deuterated formaldehyde DNP imply that there is a small coupling
(N 0. 2 cps) between H4 and H5“

H1 of _o_-NP's also couples selectively with the whydrogen,
one_p1_et_a hydrogen (H4), and the aldehydic hydrogen of the syn isomer.
Coupling of H1 with aromatic hydrogens is not observed in formaldehyde
p-NP in dimethylsulfoxide, but the H1 does couple with the _<_:_i_§ aldehydic
hydrogen.

5. Benzene Anisotropy Calculations

 

The bond lengths and angles used to calculate the distance of
hydrogens from the phenyl ring are listed in Table XVb. The lettering
corresponds to 8b.

- In the absence of data on bond lengths and angles of DNP's values
were estimated by comparing similar compounds.56 The following
comments are pertinent to the calculations: 1) The most inaccurate
value is that of "e". The only reported N-N bond lengths (1.46 i . 02.8)
are in hydrazine, a, a- and a, B-dimethylhydrazine. 2) For simplifi-

cation angles "ad" and "bd" were assumed to be 12.00 in the syn and anti

 

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84

Table XVb. Bond'Lengths and Angles Used in the Anisotropy

 

 

Calculations

Bond Lengths Bond Angles
a. . .1.08X bc . . .109.5°
b...1.50 bd...120
c...1.10 ad...120
d...1.29 de...112
e...1.45 ef...124
f . . . 1.37

g . . . 1.04

h . . . 1.39

i. . . 1.08

(813)

 

(9b)

 

I II III

 

85

isomers. » This assumption may introduce an error of five degrees
when the 2, 4-dinitropheny1 group is _c_i_§_ toa methyl. 3) A planar
trigonal nitrogen with a N-N-C angle ("ef") of 1240 was assumed.
.The increase of four degrees over 1200 was made by comparison of
trimethylamine (103°) to diethylamine (112°). 4) Hydrogen bonding
of the H1 to the m-nitro group restricts rotation about bond "f".
5) The (averaged) position of the methyl hydrogens was estimated to
be in the center of the triangle formed by the three hydrogens.
6) The distances of H5 and methyl hydrogens along the p and z axes of
the benzene ring were calculated for conformations I and 11 (Fig. 9b),
where the z axis is normal to the plane of the aromatic ring at its
center and the p axis is in the plane of the ring. Conformation III is
sterically impossible when R is methyl. When R is hydrogen, its
distance from H4 is only about 0.8 X .

6 values, obtained from Johnson and Bovey's nuclear shielding
values, 57 are listed in Table XVIb. A positive 6 represents a shielding
effect (shift to higher fields) of the benzene ring on the hydrogens and

a negative 6 , a deshielding effect.

86

Table XVIb. . Calculated Shielding Values for £i_s__ and trans Aldehydic

and Methyl Pr otonsa

 

 

 

R=H R'=H R==CH3 .R'=CH3
Conformation I
’ pm?) 5.13 5.83 5.51 6.53
z" 0 0 0 0 b
(ppm) -0.218 -0. 138 -0. 159 -0.087
Conformation II . .
pd?) 3.63 3.29 5.12 5.87
z " 1.45 3.17 1.30 1.38 b
(ppm) -0.120 -0.154 +0.091 -0.110

 

3‘Values are in ppm.

bValues had to be estimated as Johnson and Bovey's nuclear shielding

table 6

contained values only for p = 095. 56 .

DISCUSSION

1. syn- anti Isomerization

 

The presence of only the 3y_n_ isomer in the n.m. r. spectra of
fresh solutions of aldehyde and some ketone DNP's, and the later
appearance of the _a_n_£i_ isomer, indicate that the crystalline form is the
_s_y_n isomer. The immediate presence of both isomers in aliphatic
DNP, SC and TSC solutions is attributed either to existence of both
isomers in the crystalline form or to rapid _s_Ln-a_r£ equilibration.

The sharp melting point of the original crystals and the lower, wide
melting-point range of the crystals remaining after solvent removal
argue in favor of rapid equilibration.

. .Since the 3.1.12. acetaldehyde DNP‘was found to be more soluble than
the m, it was still possible that the preparation leads to both isomers
but only the ELI} isomer crystallizes out of solution. However, quantita-
tivegyields were obtained from the acid and acid-free preparations of
acetaldehydeDNP. In addition .to the above evidence, the stability of
thew-isomeric recrystallization suggests that formation of the DNP's
is kineticallycontrqlled. 1 The rate-determining step in the acid-
catalyzed formation, of DNP's58 and SC's59 is attack of hydrazine or
semicarbazide on the carbonyl; The second step, whichleads to
products..;.involves the loss of water. If the transition states for the
formation ofthe isomers of acetaldehyde can be visualized as in (10b),
the steric interactions of the CH3 .and R groups in 11 may sufficiently

increase: the. activation energy to prevent formation of the anti isomer.

87

HZOQ H. CH3
/ w— x H
OH: R 1 WHZ (10b)
RNHcHCH3

\ H o——->H -H

2 "‘\ CH

‘ --—-’ .aél 3
’N——C\\

R OHz‘

II

The appearance of. one methyl signal (syn isomer) in the n.m. r. of
the high melting acetaldehyde crystals (157u580, 1604310 and 1655-660)
and only a trace of the anti isomer in the low melting crystals (145-460)

31,32
suggest that the previously reported isomers that melted at

 

146-490, 156-57 and 167-690 were also the 312 isomer. Lowering of
the melting points may be due to traces of impurities or the presence
of small amounts of the 3g} isomer. Although pure 32:} acetaldehyde
DNP was not obtained, the mixture of 85% anti «15% 31E did melt in a

mat: i

. . 3O . .
range close to that obtalned by van Duin for the anti isomer.

 

The greater sensitivity (Table IXb) of TSC's over SC's to tri-
fluoroacetic acid (TFA) may be due to enolization of TSC's, but not
SC's, in TFA. ‘Enolization should be more favorable for the sulfur-
carbon double bond, which is less stable than a carbon-oxygen double
bond. In the enolized form the activation energy of rotation could be
sufficiently lowered by resonance (11b), so that rotation is too fast for

n.m. r. to differentiate between cis and trans hydrogens. Comparison

1 1H 1H +
NH NH TFA = NH /N- =NH
N/ 2' emi‘ N/N 2 N/ Z {:3}
11 1 “r .1
/ \ / \ /—-\
R1 R2 R1 R2 R1 R2
(11b)
SH
N/N*:CNHZ
(Cl
/ \

89

of the chemical shifts of the‘SC's with. TSC's in chloroform and tri-
fluoroacetic acid (Tables VIIIb and IXb) support the above suggestion.
In chloroform the chemical shifts of SC's and TSC's differ by < 0. 1
ppm. In trifluoroacetic acid a—hydrogens of SC's resonate at fields
0. 75 ppm lower than in chloroform, while a-hydrogens of TSC's
resonate at fields 0. 25 ppm higher than in chloroform. The high field
shift of a-hydrogens of TSC's would be expected from the negative
charge placed on the carbonyl carbon in the resonance form of 11b.
- Protonation of the SC must be causing an inductive withdrawal of
electrons which results in the shift of lower fields. Addition of traces
of sulfuric acid to TSC's in methylene bromide, in contrast to trifluoro-
acetic acid, must be protonating the TSC rather than simply promoting
enolization.

N.m. r. differentiates between the cis and gran}? hydrogens of

ketone DNP's in trifluoroacetic acid, but not between the cis and trans

 

hydrogens of aldehyde DNP's (Tables IIuV). Apparently, aldehyde
DNP's isomerize very fast in trifluoroacetic acid.

The observance of the minor isomer peaks of acetophenone and
phenylacetone SC's at high fields (the minor isomer peaks of phenyl-
acetone nitrophenylhydrazones are at low fields) may reflect a solvent
change of Ad's or a change in _a__r_1_t_i/_s_y_n_ ratios. A favorable interaction
between the aromatic ring and a protonated derivative group may in-
crease the stability of the anti isomer (12b).

H+

M
/NHCONHZ

I (12b)

2

O—

CH/a

9O

2 . Hydrog en Bonding

 

Hydrogen bonding of H; of DNP's to the 31:21:) nitro group is
inferred from 1) the low field H1 resonance of DNP's and guNP's
relative to p-NP's in a poor hydrogen-bonding solvent (methylene
bromide), and 2) the greater solvent dependence of H1 in p-NP'S than
in DNP's and 2-NP'S.

The increase of mzaflti ratios and the lower H1 resonance of
acetaldehyde DNP (Table IIIb) with better hydrogen-accepting solvents
imply that H1 is hydrogen bonded, not only to the mnitro group,
but also, to the solvent. The following data imply that steric effects
influence the degree of solvent hydrogen bonding: 1) Hl's of aldehyde
DNP's resonate at lower fields than those of methyl ketone DNP's.

2) The anti H1 of acetaldehyde DNP resonates at higher fields than
the EB H1. 3) H1 resonances of Z-butanone and 3-pentanone DNP's
vary less (0. 2 ppm) with solvent changes than those of acetaldehyde
and formaldehyde DNP's (0. 5 ppm).

Carbonyl solvents (dimethyl sulfoxide, tetramethylurea, acetone
and 'dimethylformamide) shift H1 to lower fields and reverse the
appearance of the methyl peaks of acetaldehyde DNP. Apparently,
these solvents, while hydrogen bonding to H1, either exert a strong
anisotropy effect on the affected hydrogens or greatly alter the con-

formations of the molecule.

3 . Anisotropy Effects

 

The main cause of the nonequivalence between cis and trans

 

hydrogens is not known, because there are many anisotrOpic bonds and
groups present and many conformations available to the molecules.
The phenyl rings of nitrophenylhydrazones and the carbonyls of carba-

zones cannot be the sole causes, because the nonequivalence is also

91

observed in hydrazones, oximes, nitrites, nitrosamines and amides.
No simple correlation of shielding and deshielding effects was observed
in these compounds.60 Hydrogens comparable to the aldehydic hydrogen
of aldehyde derivatives are deshielded in all cases studied except
amides. No uniform effect is found for the a- and B-hydrogens.

Variation of the isomer chemical shift difference (A6 '3) with
the different derivatives and with solvents indicates that the phenyl and
the carbonyl groups are contributing to the anisotropy effect. .Calculations
(Table XVIb) of the nuclear shielding values for hydrogens of conformation
I, assuming that the phenyl ring is the sole contributor to the non-
equivalence, predict a greater deshielding effect on the gihydrogens
than on the m. A6 for the aldehydic hydrogen 3 ~0. 218=-(~0. 138) =
-0.080 ppm. A6 for the a—CH3 = -0.159-(~0. 087) = ~0.072 ppm.
Shielding effects are predicted for the _c__i__s_ aldehydic hydrogen relative
to the m hydrogen (A6 = +0. 201 ppm) and for the gig a-CH3 relative

to the trans in conformation 11. Averaging of conformations l and 11

N02

N03
N02

N
H/ \H l1\II/N

c
/
R/C\R I R' \R H

gives A6 = -0.023 ppm for aldehyde protons and A6 = +0.065 ppm

for methyl protons. Although the signs are in agreement with experi-
mental values (A6 = -O. 5 ppm for aldehydic hydrogens and +0. 05 ppm
for a-hydrogens), the magnitude of A6 for the aldehydic hydrogen is in
error. This may signify that the anisotropic contribution of the phenyl
ring is important for o.- and fl-hydrogens but that another factor, such

as the anisotropy of the nitrogen-nitrogen bond, is important for

92

aldehydic hydrogens. <However, the assumption that a 2,4-dinitro-
phenyl. ring has the same anisotropic effect as benzene and the equal
averaging of conformations I and II may make the correlation of
calculated and experimental shielding values for a-CH3 fortuitous.
The magnitude of A6 's depends upon the difference of the
magnetic environments of the 2.1.2 and t;1;a_1_i_s hydrogens and the rate of
rotation about the C=N bonds. The variation of the A6 '5 of the DNP
SC and TSC of acetone with temperature changes indicate that A6 '3
observed at room temperature are not maximum values. Therefore,
the variation of A6 for different derivatives and in different solvents
may be ascribed to one of, or a combination of the following:
1) conformational differences, 2) anisotropy effects of the associated

solvent molecules, or 3) variation in the rates of isomerization.

4 . Spin-Spin C ouplig

 

The selective coupling of H1 of DNP's and _o_--NP's with one of the
meta hydrogens illustrates the angle dependence of spin-spin coupling.
Hydrogen bonding of H1 to the _o__rtho nitro group places H1 and H3 of

DNP's or H4 of o- -NP's in a t__rans coplanar conformation (13b). Similar

HE“? H.
H5: ——-N<: (13b)
)0: 1:1/ O

.Hsl 4 . 3

transoid couplings have been previously reported and are summarized
in Table XVIIb. Evidently, the hydrogen bond between H1 and a ortho
nitro group is not necessary for'Hl to couple selectively with a c_i_s_

aldehydic hydrogen.

93

Table XVIIb. Long-Range Coupling Constants Illustrating the Angle
Dependence of Spin-Spin Coupling

 

 

 

Compound J(cps) Refer enc e
S
H
6/ \ / 2 J25: f 1.3 6].
H5 N H3 J36: _. 0.5
I
H

3
27‘ \> .
(LT—O
/
P
.E'

0.44io.05 62
H3 0 4 SIM-2120.6 0 05
/\c_—_—_c/ \c/H J.,=i 1.71:0.1 63
Hz 1H JM~—0.8—0.1
R 114
| \ J43: 068 64
R /
H8 ‘

 

 

 

EXPERIMENTAL

1. Nuclear Magnetic Resonance Spectra

All n.m. r. spectra were taken with a Varian A-60 n.m. r.
spectrometer at approximately 350 on undegassed samples. Tetra-
methylsilane was the internal reference standard (assignedT of 10. 00).
Chemical shifts were measured with sweep widths of 1000, 500 and
250 cps. .Spin- spin coupling constants and isomer chemical shift
differences(A 6 's) were obtained from spectra recorded with 100 and
50 cps sweep widths. The internal chemical shift accuracy of a n.m. r.

spectrum is i 0. 02 ppm.

2. . Solvents

Acetone, chloroform, dioxane, dimethylformanide and nitro-
benzene were purified by distillation of commercially available materials.
Dimethyl sulfoxide was obtained from Crown Zellerback. .Pyridine,
,methylene bromide and quinoline were obtained from Matheson Coleman
andiBell. . Dimethyl sulfoxide-d6 and acetone-d6 were purchased from

Merck, .Sharp and Dohme of Canada, limited.

3. Carbonyl Reagents

 

Benzyl ethyl ketone was obtained from. Chemical Intermediates
Research Laboratories, benzylacetone from Aldrich Chemical Co. ,
formaldehyde from- Matheson Coleman and Bell, phenylacetone from
~Perrigo Co. and propiophenone from Eastman Organic Chemicals.
Acetone was purified by the sodium iodide compound.67 All other

ketones and aldehydes were purified by distillation of commercially

94

95

available compounds. Purities were checked by n.m. r. and gas

chromotography.

4. Dinitroghenylhydrazones

 

The majority of the 2, 4-dinitrophenylhydrazones were prepared
according to the method of Shriner, Fuson and Curtin. 68 The diglyme
procedure of H. J. Shine69 was utilizedfor the preparation of the DNP's
of propionaldehyde and E-butyraldehyde which appeared sensitive to
strong acid catalysis. .In some cases the diethyl ether of diethylene
glycol was substituted for the dimethyl ether because of availability.
Acetaldehyde DNP was also prepared using phosphoric acid. 70 The
melting points are listed in Table XVIIIb. The following are typical

preparations.

Acetone DNP. To 1.0 g. (0.005 mole) of 2,4-dinitrophenylhydra-

 

zine (Eastman-Organic Chemicals) was added 5 m1. of conc. sulfuric
acid. Water (N8 ml.) was added dropwise until solution was complete.
- Addition of 25 ml. of 95% ethanol to the solution was followed by
addition of 1.0 g. (0. 017 mole) of acetone in 20 m1. of 95% ethanol.

The solution was allowed to stand at room temperature until crystal-
lization occurred. The yellow crystals were separated by filtration
and were recrystallized twice from water-ethanol solutions. (m.p. =

126-27°)

Propionaldehyde DNP. To a solution of 1.0 g. (0.005 mole) of

 

2,4-dinitrophenylhydrazine in 30 m1. of diglyme was added 1. 0 g. (0.017
mole) of propionaldehyde. . Precipitation was induced by addition of water.
Care was taken not to add excess water because unreacted 2, 4-dinitro-
phenylhydrazine would also precipitate. After filtration the yellow-
orange crystals were recrystallized twice from water-ethanol solutions.

un.p.==150-51°)V

96

Table XVIlIb. Melting-Points of 2,4-Dinitrophenylhydrazonesa

 

 

 

'Reported
7 Observed Melting: Points
DNP Melting Point 'Ref. 71 Ref. 72

Formaldehyde 165—66° 166° 155,167°
Acetaldehyde 145-46, 157-58, 147,168 146, 163. 5-

160-61 4. 5
Propionaldehyde 150-51 154 —--
Isobutyraldehyde 181-83 182 187
B—Butyraldehyde 120 122 123
Acetone 126—27 126 128
2-Butanone 114—15 117 115
3-Pentanone 153-54 156 156
‘Methyl isopropyl ketone 119 117 117
2-Pentanone 143 144 141
Methyl t_-butyl ketone 125-26 125 117
Diisopr0py1 ketone 96 95 94-8
'Phenylacetone 153 156 156
Benzylacetone 127-28 --- ,. 131-32
Benzyl ethyl ketone 133-4 --- 140-41
Dibenzyl ketone 107-8 100 ---
Ethyl cyclopropyl ketone 163 --=- ---

 

8'Melting points were obtained on a melting point block.

97

Acetaldehyde DNP. To a solution of 1.0 g. (0.023 mole) of

 

acetaldehyde in 5 ml. of 95% ethanol was added 20 ml. (0. 005 mole)
of a 0. 25 M phosphoric acid-ethanol solution of 2, 4-dinitrophenylhydra-
zine. The gold crystals were removed by filtration and recrystallized

twice from water-ethanol solution. (m.p.. = 145-460)

5 . Mononitrophenylhydrazone s

 

The procedure of Shriner, . Fuson and-Curtin68 was followed in
the preparation of the p-nitroPhenylhydrazones. , Table XIXb lists the
melting points of the mononitrophenylhydrazones. The following are

typical preparations of ortho-,, meta- and para-nitrophenylhydrazones.

Acetone p-NP. A mixture of 1.0 g. - (0.007 mole) of p-nitrophenyl-

 

hydrazine (Eastman Organic Chemicals), 1. 0 g. (0.017 mole) of acetone
and 10 m1. of 95% ethanol was heated to boiling, and a drop of glacial
acetic acid was added. The dark gold crystals were separated and

recrystallized from a water-ethanol solution. (m.p. = 148. 5-49.50)

\

3-Pentanone o-NP. To a solution of 0.5 g. (0.003 mole) of ortho-

 

nitrophenylhydrazine-hydrochloride (AldricheChemical Co.), 3 ml. of
water and 3 ml. of conc- sulfuric acid was added 10 ml. of 95% ethanol
. and'O. 5 ml). (0. 005 mole) of 3-pentanone. Water was added until the
ELIE-nitrophenylhydrazone precipitated. After heating to dissolve the
precipitate, the solution was cooled. The orange-red crystals were

removed and recrystallized from 95% ethanol. - (m.p. = 57°)

2-‘Butanone m-NP. The procedure for the preparation of 3-

 

pentanone ortho-nitr0pheny1hydrazone was followed using 0. 5 g. (0. 003
mole) of meta-nitrophenylhydrazone-hydrochloride (Aldrich Chemical

Co.) and 0.5 ml. (0.004 mole) of 2-butanone. (m.p. = 97980)

98

.mn .mom tho: mesa-oer oaspmuofid

£003 ops-mom 9:368 .m no 669330 who? 350m man—Hezm

 

 

-- mw-NE -- E-N: -- we esoeeoflsserm
-....- m3 ........ -..... :1...- u...... 983% Heaoumomflfl
«.2 m2 -- -- as S eeoaseeem-m
Am .832: TE: --- £- -- Toe 28683368631562
em-mfi mm; m .3 w-ee 2. $- eeoeeesm-N
3; $13: -- some 2. me 888...
m .mfi 63 ONE 1.. oefi 62 -2 s 6636333...
oz: 68: -- -- -- -- epssepasfisom

.63 .- .30. .63 I .30 .63 I560

mz-e mz-E zm-o

 

mmodoumnpswnacosmonfidocoz mo mwafionm wan—H62. 593% 3an

99

6.. Semicarbazones and Thiosemicarbazones

 

The semicarbazones were prepared according to the procedure of
Shriner,. Fuson and Curtin73 and the thiosemicarbazones according to
Cheronis and Entrikin. 74 For water—insoluble carbonyl compounds a
water-ethanol mixture was used as solvent. Table XXb lists the me1t~

ing points.

Acetone SC. «One ml. (0. 014 mole) of acetone, 1. 0 g. (0.009 mole)
of semicarbazide hydrochloride (MathesonColeman and Bell) and 1. 5 g.
(0. 018 mole) of sodium acetate were dissolved in 10 ml. of water in
a test tube and vigorously shaken. The test tube was placed in a beaker
of boiling water to dissolve the white precipitate. As the solution
cooled white crystals appeared and were collected by filtration. The

. . . o
semicarbazone was recrystallized tw1ce from water. (m.p. = 187 )

Acetone TSC. -To 1.0 g. (0.11 mole) of thiosemicarbazide (Eastman

 

Organic Chemicals) and 1. 0 g. (0. 01? mole) of acetone in a test tube
was added a solution of 2.0 g. (0.024 mole) of sodium acetate in 15 m1.
of water. The solution was warmed for a minute and then allowed to
cool. The white crystals were filtered and recrystallized twice from

water. (m.p.v=179o)

7.. Equilibration and Fractional Crystallization of
Acetaldehyde DNP

‘—

 

 

A solution of acetaldehyde DNP in methylene bromide was heated
on a steam bath (one to two days) until syn-affli- equilibrium was reached.
The progress of equilibration was checked by removing samples and
integrating the methyl signals in the n.m. r. spectrum. - After cooling
_r_1_-heptane was added causing precipitation. The crystals were removed
and more n-heptane was added. ~ The process was repeated until further

addition of Buheptane gave no precipitation. The solvent of the

100

Table XXb. Melting Points of Semicarbazones and Thiosemicarbazonesa

 

 

 

 

Semicarbazones Thiosemicarbazones
Obs. . Lit. Obs. Lit.
Acetaldehyde b 162°C 145-460 14.6"d
Acetone 1870 187C 179 179C1
ZaButanone 148 146C148d 96 -_......
Z~Pentanone 101 IIOC 78 m“...
Methyl isopropyl ketone 111-4 113C, 114-d
3~Pentanone 137~38 139C 86 ..___
Diisopropyl ketone 155-56 160C
Acetophenone 198 198C
Phenylacetone 187 198C

aLMelting points were obtained on a melting point block.

Crystals were not obtained. Solutions were made by extraction from
the oil with methylene bromide.

CLiterature values from Ref. 73.

dLiterature values from Ref. 74, p. 663.

101

heptane-rich solution was removed by evaporation (water aspirator
pressure).

The first crystals were mainly the m isomer while the last
were mainly the 33123. Attempts to purify further the anti- enriched
mixture failed. Table XXIb shows a typical attempt to separate the

isomers.

Table XXIb. Fractional Crystallization of Acetaldehyde Z, 4~Dinitro~

 

 

 

 

phenylhydrazone
Fraction % anti Melting Point
1 2 157-580
2 3-5 154-56
3 21 152-54
4 30 92-94
5 85 89—93

 

Other solvent pairs, such as alcohol-water and ethyl acetate-=-
cyclohexane, failed to produce results as good as those obtained from
methylene bromide-heptane.

Heating of ethanol solutions of acetaldehyde DNP (m isomer),
in the presence or absence of acid, did not effect isomerization.

Isomerization by prolonged heating of acetaldehyde crystals (s12)

resulted in slight decomposition; a small amount of the anti isomer was

 

detected.
Attempts to selectively crystallize the anti isomer by addition of

anti-enriched crystals to equilibrated solutions were unsuccessful.

SUMMARY

The magnetic nonequivalence of hydrogens cis and trans to Y

 

permitted the nuclearmagnetic resonance study of stereoisomerism
N/Y Y\
H |

C , C
\
R-/ \R2 R-/

——2

R2

about the C=N bond in 2., 4-dinitropheny1hydrazones, p_ar__a_-, £1333“
and Ergo-nitrophenylhydrazones, semicarbazones and thiosemi-
carbazones. The chemical shift difference between hydrogens £i_s
and m to Y is 30—45 cps for aldehydic hydrogens, 0=~10 cps for
a-hydrogens and 0-5 cps for fi—hydrogens. Generally, aldehydic
hydrogens and fl-hydrogens are deshielded (hydrogens _c_i3 to Y are
at lower fields), while a-hydrogens are shielded. Solvent effects on
the isomer chemical shift difference are important.
Kinetically-controlled formation of the aldehyde 2, 4-dinitro-
phenylhydrazones leads to the _s_y_n isomer'(Y is 53.5.". to.the smaller R
group) .7 Equilibration occurs with time and it is acid catalyzed.
. Isomer. ratios at equilibrium agree with steric predictions.

-The N-H's of 2, 4-dinitrophenylhydrazones and BEE-nitrophenyl—
hydrazones hydrogen bond to the $9.12 nitro group. Additional hydrogen
bonding between the‘N-H and solvent of acetaldehyde 2, 4-dinitrophenyl—
hydrazone causes a decrease of_a_1_n___t1/_§_Ln_ equilibrium ratios, a low field
shift of N-H resonances, and in some solvents, a reversal in the

appearance of the syn and anti methyl resonances.

102

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@137" ”113

VA 7-”._..._.1.4. - ..M. ..f

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