1!:

”9“

‘23

!

xmrm

$9.313er

5‘

 

~ ~»~ .
’.= ‘~},‘f r

;_':’€':ZL‘~

.9} 'J A 5}
\ -§<_ 1, ‘F

, 51‘ .4“. v ..I '

. u

.z 459’: _

 

- '4‘ E.»
.: w“

P v “:1;
I' . ‘1'.
~ {-6. 21,9.- ' ‘ gm
1; 1.33.“. -5»,

'u ,

J;
1‘
..
.
i‘
1

1*,

3%.:

a
.,v. a“

4: ‘
7‘- grant». 1
,0 ‘.< '11». ,
.‘. h...
‘ r.’ '

1

513‘!»
.Juu a:
“saw, a '

,..~,- “'11:“...‘fl 9:;

"an“

"I" .
~21...»ny
“3

ug-

 

‘370 Jr

.,. 0:1,-

1%}

l

 

 

llllllllllllIll!IllUllllllllllllllilllllllllllllllllllllllll

300790 3184

This is to certify that the

thesis entitled

Hydrogen Exchange in Ketone-Semipinacol
Radical System: Kinetics and Mechanism

presented by

Yuanda Zhang

has been accepted towards fulfillment
of the requirements for

Master Chemistry

degree in

 

 

 

Uajor prsgss'or
Date/1,035.!Ja:
F

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

[4'
\

[i— ‘T W
LIBRARY
Michigan State

i University

x iJ

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or beiore date due.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

iii—7
___JL_JI___|
EFT

—7

M80 I: An Affirmative Action/Equal Opportunity Institution
chS-DJ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HYDROGEN EXCHANGE IN KETONE-SEMIPINACOL RADICAL SYSTEM:
KINETICS AND MECHANISM

BY YUANDA ZHANG

A THESIS

SUBMITTED TO
MICHIGAN STATE UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE
DEPARTMENT OF CHEMISTRY
1989

b050775

ABSTRACT

HYDROGEN EXCHANGE IN KETONE-SEMIPINACOL RADICAL SYSTEM:
KINETCS AND MECHANISM

BY
YUANDA ZHANG

El | l I' I | | l . I
The rate constants for the photoreduction of ketones by pinacol and
pinacol-d2 were measured to determine the isotope effect in the hydrogen

abstraction step. No significant isotope effect was detected.

II I l . l I _ . . l I. I I

After irradiation of a mixture of two ketones in the presence of 2-
propanol, the ratio of steady state semipinacol radical was obtained by
analysis of pinacols resulted from the radical combination. Several
equilibrium constants of degenerate hydrogen exchange from semi-

pinacol radical to ketone was calculated.

From the initial interaction of excited state ketone with aromatic

alcohol, the overall radical quantum yield was quantitatively measured,
and the maximum quantum yield and kd/k, were obtained.

The rate constants of hydrogen exchange in ketone-semipinacol
system were measured by a steady-state approximation method. The
contribution of such rate constants to the overall competitive reactions
was estimated. The substituent effect and steric effect for hydrogen

exchange in ketone-semipinacol system were compared.

Copyright by
YUANDA ZHANG
1989

I would like to dedicate this thesis to my family,
for their support and patient understanding, for

their constant encouragement and love.

ACKNOWLEDGEMENTS

I wish to thank professor Peter J. Wagner for his guidance in
conducting this research and for sharing his knowledge and experience
with me. I would also like to thank the members of the Wagner research
group for many informative discussions.

I would like to thank the Department of Chemistry at Michigan
State University for its financial support and use of its facilities, I would
like to express my gratitude to the National Science Foundation for their
support through research assistantships from Professor Peter J. Wagner's

research grants.

iv

TABLE OF CONTENTS

 

Pam

INTRODUCTION ....................................... - _ .................... 1

Bimolecular Hydrogen Abstraction Reaction in Ketone

Photochemistry .......................................................................................... 1
Early Mechanism studies .......................................................................... 12
RESULTS ......................................................................................................... 20
Quantum yield ........................................................................................... 20
Photoreduction of ketones by pinacols ................................................ 20
Measurement of equilibrium constants .................................................. 24
Photoreduction in ketone-semipinacol radical system ........................ 28
DISCUSSION ..................................................................................................... 38
Photoreduction of ketones by pinacols ................................................... 38
Fate of radicals ............................................................................................ 39
Photoredox in ketone-semipinacol system ............................................ 44
CONCLUSION ................................................................................................. 56
Suggestion for further investigation ....................................................... 57
EXPERIMENTAL ............................................................................................. 58
mneticc and calculation ............................................................................ 58

Calculation the ratio of rate constant for triplet decay over

hydrogen abstraction and maximum quantum yield for

hydrogen exchange ...................................................................................... 58
Correction of light absorption .................................................................................. 58
Calculation of quantum yield .......................................................................... 59
Solvents .............................................................................................................. 61
lntemal standards ............................................................................................. 62
Hydrogen donors ............................................................................................. 63
Reactants ............................................................................................................ 66
Identification of photoproducts ........................................................................ 69
TECHNIQUES ........................................................................................................... 74
Glassware ........................................................................................................... 74
Preparation of samples ..................................................................................... 74
Degassing procedure ....................................................................................... 75
Irradiation procedure .......................................................................................... 75
Analysis ................................................................................................................. 76
Spectroscopic measurement ............................................................................ 77
REFERENCES .............................................................................................................. 78
APPENDIX .................................................................................................................... 83
ABSTRACT ..................................................................................................................... i

LIST OF TABLES .......................................................................................................... viii

LIST OF FIGURES ....................................................................................................... xii
LIST OF SCHEMES ..................................................................................................... xiv
ABBRB/IATIONS .......................................................................................................... xv

vii

LIST OF TABLES

Table Page
1. Quantum yields and rate constants for photolysis of
acetophenone, propiophenone and isobutyrophenone in
2-propanol— benzene solvent .............................................................. 7
2. Quantum yields for 2,4-dimetnyI-3-heptanone formation
and kinetic data for acetophenone, propiophenone and
isobutyrophenone with 2M 2,4—dimetnyl-3-heptanol in
benzene ................................................................................................... 8
3. Competitive hydrogen abstraction ...................................................... 9
4. Reactivities of substituted acetophenone with 2-butanol
(di-t-butyl peroxide induced at 125° C) .............................................. 10
5. Results for photoreduction of various ketones by
acetophenone pinacol and acetophenone pinacol-d2 ................... 21
6. (1 ).Radical ratio of irradiation different ketones with 1M
2-propanol in benzene ........................................................................... 25
6. (2). Calculation of equilibrium constants in hydrogen
exchange reaction ..................................................................................... 26
7. Results of photoredox reaction for ketones (varied concentration)

and phenyl alcohol (0.2M) in degassed benzene .............................. 28

viii

8. Results of photoreduction for 0.05M ketone with varied

concentration of phenyl alcohol in degassed benzene ............................. 30

9. Results for photoreduction of various ketones by acetophenone

10.

11.

12.
13.

14.
15.

16.

17.

18.

pinacol and acetophenone pinacol-d2 ......................................................... 38
Calculated equilibrium constants of triplet energy transfer
between dfferent ketones .............................................................................. 40
Estimation of original formed radical ratio in the measurement of
equilibrium constants for hydrogen exchange ........................................... 41
Estimated rate constants of combination reactions ................................... 46
Sum of the quantum yields from disproportionation and
combination reactions ..................................................................................... 48
Disproportionation over combination ratios for radical pairs ................... 51
The ratio of rate constants for disproportionation over
combination reactions ...................................................................................... 52
Results for the photoreduction of 0.1 M propiophenone
by acetophenone pinacol and acetophenone pinacol-d2 ........................ 84
Result for photoreduction of 0.1M p—methoxylacetophenone
by acetophenone pinacol ............................................................................... 85
Radical ratio for reaction of acetopenone and propiophenone

with isopropanol (1 M) in benzene ................................................................ 86

ix

19.

20.

21.

22.

23.

24.

25.

26.

27.

Radical ratio for reaction of acetopenone and propiophenone

with isopropanol (1 M) in benzene ................................................................ 87
Radical ratio for reaction of 0.1M acetopenone and 0.2 M
propiophenone with varied concentrations of isopropanol
in benzene ......................................................................................................... 88
Radical ratio for reaction of acetopenone and

p-chloroacetophenone with isopropanol (1 M) in benzene ....................... 89
Radical ratio for reaction of acetopenone and

p-methylacetophenone with isopropanol (1 M) in benzene ..................... 90
Radical ratio for reaction of acetopenone with different

ketones and 1M isopropanol in benzene ..................................................... 91
Quantum yields for acetophenone formation as a function

of propiophenone concentration in benzene ............................................... 93
Quantum yields and radical ratio for reaction of propiophenone

with 0.2 M 1-phenylethanol in benzene ....................................................... 94
Quantum yields of acetophenone as a function of 1-phenylethanol
concentration with 0.05 M isobutyrophenone in benzene ....................... 95
Quantum yields for acetophenone formation as a function

of isobutyrophenone concentration in benzene ......................................... 96

28.

29.

31.

32.

33.

Quantum yields and radical ratio for reaction of

isobutyrophenone with 0.2M 1-phenylethanol in benzene ................ 97
Quantum yields of acetophenone formation a function of
1-phenylethanol concentration with 0.05M

p-methylacetophenone in benzene ........................................................ 98

. Quantum yields for acetopenone formation as a

function of p-methylacetophenone concentration in benzene ........... 99
Quantum yields and radical ratio for reaction of

p—methylacetophenone with 0.2M 1-phenylethanol in benzene ....... 100
Quantum yields of p-chloroacetophenone formation as a

function of 1-(4'—chlorophenyl) ethanol concentration

with 0.05M acetophenone in benzene ..................................................... 101
Quantum yields of p-chloroacetophenone formation as a

function of acetophenone concentration in benzene ............................ 102

34. Quantum yields and radical ratio for reaction of

acetophenone with 0.2 M 1-(4'-chlorophenyl) ethanol

in benzene ...................................................................................................... 103

35. 60 response factors ....................................................................................... 104

xi

LIST OF FIGURES

Fig u re P a g e
1. n,x*andrr,1r* excited state ......................................................................... 6
2. Primary products of photoreduction ............................................................ 15
3. Hydrogen exchange with starting ketone ................................................... 15
4. Schuster' mechanism ..................................................................................... 15
5. Hydrogen-bonded complexes of the ketone-semipinacol

interaction ........................................................................................................... 17

6. Reaction of 0.1M propiophenone with acetophenone pinacol
and acetophenone pinacol-d2 in benzene ................................................. 22
7. Reaction of 0.1 M p-methoxyacetophenone with acetophenone
pinacol in benzene ........................................................................................... 23
8. Quantum yields for acetophenone formation as a function of
propiophenone concentration with 0.2M 1-phenylethanol in
benzene ............................................................................................................. 31
9. Quantum yields for acetophenone formation as function of
1-phenylethanol concentration with 0.05M isobutyrophenone

in benzene ......................................................................................................... 32

xii

10. Quantum yields for acetophenone formation as a function of
isobutyrophenone concentration with 0.2M 1-phenylethanol in
benzene ............................................................................................................... 33
11. Quantum yields for acetophenone formation as function of
1-phenylethanol concentration with 0.05M
p-methylacetophenone in benzene ............................................................... 34
12. Quantum yields for acetophenone formation as a function of
p-methylacetophenone concentration with 0.2M 1-phenylethanol
in benzene .......................................................................................................... 35
13. Quantum yields for acetophenone formation as function of
1-(4'-chlorophenyl) ethanol concentration with
0.05M acetophenone in benzene ................................................................... 36
14. Quantum yields for p-chloroacetophenone formation as a
function of acetophenone concentration with 0.2M

1—(4'-chlorophenyl )ethanol in benzene ........................................................ 37

xiii

LIST OF SCHEMES

Scheme Page
1. Mechanism of photoredox in ketone-semipinacol system ................ 2

2. The correlation between structures and abbreviations for

Scheme 1 ..................................................................................................... 3
3. Hammond's mechanism of photoreduction ........................................... 12
4. Equilibrium between two semi-pinacol radicals .................................... 39

xiv

AP

PP
MOAP
isBP
MOOAP
CIAP
(AH)2
(PH)2
(CIAH)2

(BH)2

(MeAH)2

AH2
PHz
CIAH2
isBH2
MeAH2

ABBREVIATIONS

Acetophenone
Propiophenone
p-Methylacetophenone
lsobutyrophenone
p-Methoxyacetophenone
p-Chloroacetophenone
2,3-Diphenyl-2,3-butanediol, acetophenone pinacol
2,3-Diphenyl—3,4-hexadiol, propiophenone pinacol
2,3-Bis(4~chlorophenyI)-2,3-butanediol
p-Chloroacetophenone pinacol
2,5-Dimethyl-3,4-diphenyl-3,4-hexadiol
lsobutyrophenone pinacol
2,3-Bis(4-methyl)-2,3-butanediol
p-Methylacetophenone pinacol
1 -phenylethanol
1 -Phenylpropanol
1-(4'-Chlorophenyl) ethanol
2-Methyl-1 -phenylpropanol
1-(4'-methylphenyl) ethanol

XV

INTRODUCTION

The photoreduction of ketones by alcohols has been an important
subject in photochemistry for about a century and generally considered as
one of the best understood organic photochemical reactions. Since the
appearance of a number of comprehensive review articlesil}, this area has
undergone much expansion. A series of important and exciting research,
including investigation of kinetic parameters and mechanism, has
appeared. In addition, a new development in probing hydrogen exchange in
ketone-semipinacol radical system has been reported.{2}

The research presented and discussed in this thesis is bimolecular
hydrogen abstraction reaction focusing on the measurement of kinetic
parameters by one of the important steps for hydrogen exchange in the

ketone-semipinacol radical system.

HI I III Ell I. B I. . III
W Ketone photochemistry is one of the most intensively
studied areas in organic photochemistry. The study of carbonyl compounds
has helped our understanding of very fundamental questions.

Photoexcited ketones undergo characteristic hydrogen abstraction
from compounds having active hydrogens. These include both bimolecular

and intramolecular reactions. For the bimolecular reaction, the products

are formed by the coupling and disproportionation of two radicals produced

in the initial hydrogen abstraction step; hydrogen exchange from semi-

pinacol radical to ground state ketone. Scheme 1. gives the mechanism for

this reaction:

 

 

 

 

 

"V I n: kisc 3 .
1. K =_.k.—d'1—.r K K
2. 3K._.k3_2._p K
3 * km
3. K + AH2 > 'KH + 'AH
kex
4. K + AH ;k : A + .m
kdis
5- 'KH+-KH : K+ KH2
k - I
6. 'AH + -AH ““3 e A + AH2

 

 

k 3" i
7. 'KH+ -AH di , KH2+ A +K+AH2

 

 

 

k
8- -KH+ 'l<H °" = [K2H2]
k
9. 'AH+ -AH °a > [A2H2]
kcm
10. -KH+ -AH = [KHAH]

Scheme 1: Mechanism of photoredox in ketone-semipinacol radical system

K AHz -KH -AH A

I” 5" °"
ArfiR Ar'CR' Ar . R AF'QlR' ArfiR'

KHZ K2H2 A2H2
EH OH
Ar NHHAT Ari—$1" Ar' 'iH—(EAr'

Scheme 2: The correlation between structures and abbreviations for

Scheme 1.

The experiments presented in this thesis attempted to measure the
rate constants of hydrogen exchange reactions occurred during the
irradiation of ketone with alcohol in degassed benzene. The comparison of
these rate constants with other competitive rate constants would give us
a better understanding of the actual processes occurring in the old
photoredox reaction.

There are five factors expected to influence the reaction: the
strength of the bond being broken, the strength of the bond being formed;
P018" or

charge-transfer effects on the energy of the transition state relative to
the energy of the reagents; steric effects on the approach of the substrate;
solvent effects on the reagent, substrate, and transition state.

Each of these effects has an influence on the rate constant for
the abstraction of a hydrogen atom by an excited state of a carbonyl
compound. During the course of research involving the photoreduction of
ketones, a wide variety of reactions have been reported. The reactions
closely related to the research presented in this thesis are summarized
below.

The rate constants of hydrogen abstraction are strongly affected by
C-H bond strength. The triplet carbonyl reactions are corresponding to the

following step:

8R2.CO. + H'R ——".' Rz'b'OH + . R (1 )
11H :- D(R-H) - { ET - E, + E(O-H)}

where E, :- E(C=O) - E(C-O) is the carbonyl ”rt-bond energy”. The term {ET-
E,‘ + E(O-H)} represents the strength of the forming bond.l3} Previtali and

Scaianol4l carried out a bond-energy-bond-order calculation for hydrogen
abstraction by triplet benzophenone and acetcphenone. They took En and
E(O-H) to be the same for both carbonyl groups. They also indicated that

the best available interpretation of equation (1) was that of considering

the 3n, x‘ state of carbonyl compounds as a biradical, where the oxygen
atom behaved as a true free radical center. A resonance stabilization of
the carbonyl with a benzene ring lowers the C-0 x-bond energy because the
semi-pinacol radical is resonance stabilized.

The 3n, u‘ state of carbonyl compound is radical- like and has a
reactivity very similar to that observed with t-butoxy radicals.l5l The
energy of hydrogen abstraction by triplet benzophenone can be obtained

from the following thermochemical cycle:

(C6H5)20=O —> (c.H.),¢_6 + 69 kcal/mol (2)
(C3H5)2CHOH ——> (csHs).c=o + H2 + 9 kcaI/mol (3)

H, —> 2H' + 104 kcal/mol (4)

H- + (C.H.),<'>—on —> (c.H.).CH0H - 78 kcal/mol (5)

 

(C.H5)2(')—0H—> (06H5)2¢_b + H. + 104 kcal/mol (6)

Where equation (2) is the triplet excitation energy of bezophenone
known from spectroscopic data,{61 equation (3) and (4) are available from
standard thermochemical tables. The energy of equation (5) has been
estimated by Gibian according to several resultsi7i. The accepted value of
energetics for t-butoxy radicals is 104 kcal/mollB} which gives the same

value for bezophenone triplet, uncertain by at least 5-10 kcaI/mol.

The activation energy for abstraction of an unactivated secondary
hydrogen is 3-3.5 kcaI/mole; the activation entropy dependents on the
system.l3-9l This activation energy is also comparable. to the t-butoxy
radicals.

Most phenyl ketones have two low-lying triplets, an n, 1r' and a 1m“
triplet, whose energy levels are affected by the ring substituentsJIOI The
n, x’“ triplet comes from excitation of a nonbonding electron of the
carbonyl group to a n-antibonding orbital, creating an electron deficient
oxygen. The chemical behavior of the n, 1r’“ triplet state is similar to an
alkoxyl radical, and hydrogen abstraction is the predominant reaction for
the n, 1r’“ triplet state.llll In a n, it’“ triplet, excitation of a re electron
to arr-antibonding orbital makes the oxygen atom slightly electron rich
(Figure 1.), slowing down the hydrogen abstraction and making the 1:, 1p
triplet much less reactive than the n, n‘ triplet. In general, electron
withdrawing substituents stabilize the n, it" triplets relative to the wt"
triplets and electron donating groups lower the rut" triplet energy

levels.{‘21

0'
. + "'""
n, 1t‘ 1t, n‘

Figure 1. n, n' and n, n* excited state

Ring substituents have significant effect for the observed rate in
the reactions. 4-Methylbenzophenone shows a 1.5 fold decrease in the rate
constant of hydrogen abstraction, while 4-trifluoromethylbenzophenone,
which n, x‘ lowest triplets are easily photoreduced by 2-propanol,113l
shows 1.8 fold increase in the rate of hydrogen abstraction, as compared to
benzophenone. The photoreduction of 4-trifluoromethylacetophenone (n, 1?
lowest triplet state) shows a 6 fold increase in the rate of hydrogen
abstraction, but 4-methylacetophenone (1c, rc" lowest triplet state) has a
10 fold decrease in reactivity, with reference to acetophenone.{14l

Lewisi15} et al. have examined the steric effects in the
bimolecular hydrogen abstraction from 2-propanol by aryl-alkyI-ketone
triplet from 2-propanol and found that the rate constant for acetophenone
photoreduction decreased with increasing a-methyl substitution. The
results are given in Table 1:

Table 1: Quantum yields and rate constants for photolysis of
acetophenone 1, propiophenone 2. and isobutyrophenone 3. in 2-propanol-

benzene solvent.

Ketone (bpinacol (Dbenzhydrol Kr M'IS'1X105 Kd X 105 S'1
1 0.37 0.007 6.8 3.4
2 0.19 0.033 4.4 3.2

3, 0.071 0.049 0.9 3.4

From Table 1, the quantum yields of pinacol formation and the
rate constant for hydrogen abstraction (Kr) decrease with increasing a-
substitution. There is no corresponding increase in rate constant for
triplet decay (Kd), therefore the authors concluded that the decrease in
reactivity is due to the structural effect: increased steric hindrance at a
position makes abstraction of a hydrogen from 2-propanol more difficult,
and the steric effects can play an important role in determining the rate
of hydrogen abstraction reaction.

Lewislls} also reported further evidence for a steric requirement
for hydrogen abstraction by employing 2,4-dimethyl-3-heptanol as a
hydrogen donor given in Table 2.

Table 2: Quantum yields for 2,4-dimethyl-3-heptanone
formation and kinetic data for acetcphenone 1. propiophenone L and

isobutyrophenone 3, with 2M 2,4-dimethyl-3-heptanol in benzene:

Ketone <I> KrM'IS'1X105
1 0.185 2.8
2 0.130 2.5

3. 0.055 0.6

Table 2 reflect a substantial decrease in reactivity when compared
with the 2-propanol results in Table 1.

M. Y. Moss, et al.I17l have reported that relative reactivity of
bimolecular hydrogen abstraction by triplet benzophenone depends on the
size of the secondary alcohols. They mixed benzophenone (0.5-3.0 moles)
with two pure alcohols (6-26 moles each), after irradiation for 12-30
hours, mole ratios of the two generated ketones were followed by GLC
analysis using predetermined calibration curves. The results of the

competition for hydrogen abstraction are shown in Table 3:

Table 3: Competitive Hydrogen Abstraction

S | I I B I I. B I. 'I
2-Pr0panol 1 .00
Methyl-t-butylcarbinol 0.9 .+_ 0.02
3-Heptanol 0.67 :t. 0.02
Methylisobutylcarbinol 0.39 :1; 0.01
Methylneopentylcarbinol 0.18 :l: 0.01
Diisobutylcarbinol 0.074 3; 0.001

The results indicated that the reactivity of hydrogen abstraction

decreases as steric hindrance and chain-branching increases.

10

Neckers and Huyseril3l reported the relative reactivities for

peroxide-induced reductions of substituted acetophenone given in Table 4:

Table 4: Reactivities of substituted acetophenone with 2-
butanol (Di-t-butyl peroxide induced at 125° C)
Substituent k/ko
p-Cl 3.01
H 1.00
p-Me 0.59

k/ko - log( AolA) / log( BOIB)

where k/ko is the relative reactivity ratio, A0 and Bo are
quantities of the substituted acetophenone and acetophenone before
reaction, A and B are the quantities of the two ketones after reaction.
From Table 4, an electron releasing group, para methyl substituent,
decreases the reactivity of the carbonyl of acetophenone toward reaction
with the 1-hydroxyalkyl radical, whereas electron withdrawing para chloro
substituent increases the reactivity.

The different rate constants for hydrogen abstraction reaction in
solvents of different polarity suggest a change in reactivity with the

polarity of media. Gramain et al.{19i reported that the rate constant for

11

hydrogen abstraction by acetophenone from 2-propanol was 4.8 X 106 M45-1
in carbon tetrachloride as solvent. In the case of the acetophenone-2-
propanol system, the second order rate constants were 19 X 105 M-Is-1 in
benzene and 7 X 105 M-ls-1 in neat 2-propanol. {20. 10(8)} In the xanthone—2-
propanol system, the rate constants for hydrogen abstraction were 1.1X108
M491 in CCI4.4.1X105 M-IS-1 in 1:1 CCl4-2-propanol, 2.1X105M-IS'1 in neat
2-propanol.1211 Wagner 1221 has indicated that the carbonyl oxygen became
electron deficient in n, n“ triplet, the polar solvents generally make the
hydrogen bonding unstable, even though the solvent effects can be
observed, there must be reverse hydrogen transfer by polar solvents and
reduced the rate constants for the bimolecular hydrogen abstraction

reaction.

12

WW Hydrogen abstraction by an n, it"
triplet ketone was first reported by Ciamician and Silber.123i They
reported that the action of sunlight on a mixture of benzophenone and
ethanol formed a precipitate identified as benzpinacol. This initial report
led to interests in the mechanistic aspects and the measurement of
relative rate constants.

G. S. Hammond et al.{24l studied the photoreduction of bezophenone
and deduced the analysis method to calculate the ratio of rate constants
for triplet decay over hydrogen abstraction. They accounted for the

mechanism shown in scheme 3:

 

 

 

K L1Ke Kisc ~3K*
T v

3 Kd

Ki __.3_. K
3 Kt

K" + 3H2 : KH- + BH-

(1

KH- + BH' : (KH)2+(KHBH)+(BH)2+KH2+B
KH- + BH- "0‘ ; K+ 8-12

 

Scheme 3: Hammond's mechanism of photoreduction

13

1. The efficiency of triplet formation is:

k
fee

k k
lsc+ d1

2. The efficiency of intermediate formation is :
krIBHzl
k. [3H2] + ks

3. The efficiency of the intermediate going to product is c

 

(Disc-

 

The overall quantum yield is a product of these three efficiencies:

kr [BH2]
‘3” krlBH21+kd2

 

<D=or® )

By inverting the equation for CD , a linear plot of 1/0 versus 1/[BH2]

can be obtained.

-1 -1 k
CD 40:01») (WWI) (7)

The slope of the plot is kd/(o (D isckr): and the intercept is 1/ot (D isc-

In Hammond's equation, the intercept equals one.

£1 slope (8)
k. intercept

14

The value of maximum quantum yield was obtained from infinite

concentration of substrate which is reciprocal of the intercept.

(bmex " “(Disc (9)

Flash photolysis and ESR techniques are excellent methods for
the study of hydrogen abstraction reaction, but the kinetics of the
hydrogen exchange between ketone-semipinacol radical can not be
detected directly by the flash technique, because the degeneracy of the
reaction prevents measurement by absorption or ESR spectroscopy. M.
F. Quinn et al.125} reported the results of a flash photolysis study of
benzophenone in ethanol. They suggested the mechanism including
combination and disproportionation products. They can not detect if
some of the disproportionation products should come from ketone-
semipinacol radical interaction.

There are some early research126l reported when bezophenone
irradiated with 2-propanol, cyclohexanol and benzyl alcohol yielding
acetone, cyclohexanone and benzaldehyde.

Weizmani27l reported an investigation of the photoreductions of
acetophenone with butanol, acetophenone with cyclohexanol,
cyclohexanone with cyclohexanol, and acetone with butanol. The
products were pinacols from the starting ketone and another ketone or
aldehyde corresponding to the starting alcohol. They concluded that the

first step of irradiation is the activation of the carbonyl compound,

15

leading to a diradical form. This form react with the carbinol, splitting
the C—H* bond and giving two radicals (Figure 2). They

indicated that the two radicals were subsequently

R1\C 0 R3 R1 R3\c
' ’ / —0'r ‘0'
H"

Figure 2: Primary products of photoreduction

stabilized by symmetrical or unsymmetrical dimerization or by a second
oxidation-reduction process.

Franzenl23i first reported that hydrogen exchange with starting
ketone removes most of semi-pinacol radical produced from the starting

alcohol before it can react with another radical (Figure 3).

(CsHsiznq'OH 1 (C6H5)2“C-O

C H 12Ca-O
( 6 5)2 (CeHsizuCE-OH
(06H5)2“CH-OH hv (CeHsizug-OH (CeHs)21ZC-0H
+ —_-> + -——> +
(C5H5)2‘ZC-O (CsHs)2‘29-0H (CeH5)2IZC-OH
(061192195014

Figure 3: Hydrogen exchange with starting ketone.

16

Schusterl29l demonstrated that the primary photochemistry
gives a triplet radical pair which do not couple directly, but escape from
solvent cage followed by a series of hydrogen transfer reaction with

ground state ketone or labeled benzhydrol (Figure 4).

 

 

 

h *
PH#200 —x—.» 1PH#2CO 3PH#2CO*
3PH#ZCO* + PHZCI-O-I 3PH#250H + PHzCOH

 

3PH#260H + PHzCOl-l -—> PH#2COH + PHzCOl-l
PH#2COH + PH#zco ——> PH#200 + PH#2COH
911.com szco PH2CO + PH#2COH

2 PH#2COH

 

 

PH#2C(OH)C(OH)PH#2

Figure 4: Schuster's mechanism. (# represents some

positional or isotopic label)

Warashina et al.i3°} observed the kinetic behaviors of electron
spin resonance spectra during photolysis of benzophenone in ethanol,
with and without sodium methoxide. The diphenylhydroxymethyl radicals
and hydroxyethyl radicals revealed by ESR gave a firm evidence of
hydrogen abstraction of excited bezophenone from ethanol, in the
presence of sodium methoxide, and the diphenylhydroxymethyl radicals
being transformed into bezophenone ketyl anions. The observed

concentration of diphenylhydroxymethyl radical and bezophenone ketyl

17

anion formed during the photolysis of ben20phenone in ethanol was
plotted as a function of sodium methoxide concentration, giving the rate
constant of benzpinacol formation at the value of 3 X107 mol-i-L-S-l.

G. O. Schenck et al.i3li studied the mechanism of the
ketone-semipinacol interaction by electron spin resonance spectra. They
irradiated benzene solution of benzhydrol with high concentration of
benzophenone and found that the ketone-semipinacol radical interaction
was due to hydrogen-bonded complexes of type II. (Figure 5.) They

excluded the mechanism of ketyl anion formation by Warashina.

Ph Ph Ph

\ \ “

-c—o--- H -c—o H---

Ph/ h Pl/ h

Figure 5: Hydrogen bonded complexes of ketone-ketyl interaction

J. N. Pittsi32} et al. studied the photoreduction of benzophenone in
ISOpI‘OpyI alcohol. They observed quantum yields close to unity for
benzopinacol and acetone, but no cross pinacol was formed. They
assumed that the dimethylketyl radical of acetone transfered hydrogen
to benzophenone to form the more stable free radical of benzhydrol. This
step was much faster relative to the combination reaction because of

the strong reducing nature of the dimethylketyl radical of acetone.

18

Neckers and Huyserl18l demonstrated the mechanism reported by
J. N. Pitts. They studied the decomposition of di—t-butyl peroxide in a
solution of acetophenone in 2-butanol, reducing acetophenone to
acetophenone pinacol and oxidizing 2-butanol to 2-butanone. They
examined the products stoichiometrically and found the amount of 2-
butanone formed is in excess of the expected amount of peroxide used.
From this result, they assumed that the excess of 2-butanone came from
the interaction of 1-hydroxyalkyl radicals with the aromatic ketone
producing benzhydrol radicals which proceed to disproportionation and
combination reactions.

Clossl33} et al. have studied the benzaldehyde proton signals by
CIDNP spectra and suggested that bezoin is formed by cage collapse and
the escaping free radicals are polarized oppositely to cage product, in
which the hydrobenzyl radical transfers a hydrogen atom to benzaldehyde
to give polarized benzaldehyde and unpclarized hydroxybenzyl radicals.
The later step is similar to the hydrogen transfer as suggested by J. N.
Pitts.

C. Steel etalfi’l studied the photoreduction of bezophenone
by 2-propanol in acetonitrile, focusing on the rate constant for hydrogen
transfer from semi-pinacol radical of acetone to benzophenone (K) by
measuring the quantum yields of benzopinacol (K2H2), using numerical
methods and some literature data. They used the approximate equation

(10) at steady state:

19

 

zom-r k [K1
- 1/2 1/2 (10)
(1' 0m)": kdis I

They neglected the self and crossing disproportionation reaction of steps
5 and 7 in Scheme 1. In equation (10), I is the rate of light absorption
(Einstein/Ls) by benzophenone and they used literature value kdis- 2 X
109 M"S"l34l, and found k9,, - 2 X 104 M"S". They used the Newton-

Raphson methodi35} to get the semi-benzopinacol radical value X. Using

¢K2H2 = (1' OK) kck [XV/1

they set a at the value of 0.01, the kck, in acetonitrile, was 1.05 X 108 M-
1S-1i36}, and obtained model curves. By comparing the model curves with
the experimental data, they reported the rate constant for the hydrogen

transfer from semi-acetopinacol radical to bezophenone is ( 3.5 :I; 1.5 ) X
104 M" S" at 298 K.

20

RESULTS

Quantumarield

Quantum yield was determined by parallel irradiation at 313 nm
of degassed sample solutions and an actinometer in a merry-go-round
apparatus at 25° C. The sample contained ketone and the hydrogen donor.
The solvent was degassed benzene. The actinometer was a 0.1 M solution
of valerophenone in benzene.l37l Percentage of conversion was kept as
low as possible, usually around 10%, linear plots were obtained in the
1/<D region of 1-6 or larger for all ketones and alcohols. The ratios of

product to standard were obtained by HPLC or GC analysis.

El | I I. i I I I . I

The quantum yields of the photoreduction for ketones by pinacol
and pinacol-d2( 70% deuterated ) have been measured to see the isotope
effect. The solution was prepared in various concentrations of pinacol
and 0.1M ketone in degassed benzene. All samples were irradiated in
parallel at 313 nm for the same amount of time which assured that each
sample absorbed the same intensity of light. Analyses were performed on
HPLC. The reaction shows no isotope effect in the hydrogen abstraction
step. Table-5 gives the slope and intercept of plotting. The

measurements were shown in Table 16, 17 and plotted in Figure 6,7.

21

Table 5: Results for photoreduction of various ketones by acetophenone
pinacol and acetophenone pinacol-d2:

 

 

Reactants Slope Intercept
PP/[AH]2 0.76 3.0.041 19 t, 2.7
PP/[AD]2 0.96 10.033 22 1:. 2.0

MeOAP/[AH]2 0.86 30.048 10 :t 2.9

 

22

 

140

120‘

100-

o Column2
O Column4

1/Quantum yields of AP
8

 

 

2° ' l r I ' T I I '
o 20 40 so so 100 120

1/[acetophenonepinacol M] (column2)

1/Iacetoohenonepinacol-d Ml (column 4)

 

1 V

Figure 6: Reaction of 0.1M propiophenone with acetophenone pinacol
(column 2) and acetcphenone pinacol-d2 (column 4) in benzene:

23

 

 

 

 

 

100
p
l.
D.
< 30 '
o.—
O
'2
Q
'5. so -
E
3
u
C
‘3 4o
2'
1-
20 ,__0 l 1 1 1
0 20 40 60 80 100

1/[acetophenone pinacol M ]

Figure 7: Reaction of 0.1M p-methoxyacetophenone with

acetophenone pinacol in benzene:

24

II IIE'I'I' C II

After irradiation of a mixture of two ketones ( high concentration
0.05-0.5 M and equal amount) with 2-propanol (1 M) in degassed benzene
at 313 nm, two semi-pinacol radicals were produced from two starting
ketones. Three types of pinacol can occur by self and crossing
combination reactions. Analyses were performed on a Varian 1400 gas
chromatograph with the flame ionization detector and column DB-10 at
175° C.

The calculation of radical ratio from analysis of combination

products is given by equation (11):

w 2[A2H2] + [AHKl-l]

(1 1 )
[-KH] 2[K2H2] + [AHKH]

 

All pinacol products were identified by preparative irradiation of
ketone with 2-propanol. After recrystalization, the spectra of
preparative pinacol products were compared with authentic data. The
result, obtained by analysis of pinacols from irradiation, was compared
with preparative products by GC. The SF value of cross pinacol was
obtained by dividing the sum of the SF value from two pure pinacols. The
experimental data are listed in Table 18 to 23. The summarization of

radical ratio is listed in Table 6:

Table 6-1 :

2-pr0panol in benzene:

25

Radical ratio of irradiation

different ketones with 1M

 

 

 

AP (M) 0.1 0.2 0.3
PP (M) 0.1 0.2 0.3
(AH)2(M) 0.0033 0.0026 0.0024
(AHPH)(M) 0.0020 0.0014 0.0010
(PH)2(M) 0.00024 0.00019 0.00018
-AH/-PH 3.4 3.6 3.6
AP (M) 0.10 0.15 0.2 0.30
CIAP (M) 0.05 0.05 0.1 0.10
[AH]2(M) 0.00011 0 00022 0.00013 0.00019
[AHCIAH](M) 0.00053 0.00069 0.00063 0.00058
[CIAH]2(M) 0.00068 0.00046 0.00074 0.00046
-ClAH/-AH 2.5 1.4 2.4 1.6

 

confinue

26

 

 

AP (M) 0.05 0.05 0.10 0.10
MeAP (M) 0.10 0.15 0.20 0.30
(AH)2(M) 0.00040 0.00027 0.00038 0.00022
(MeAHAH)(M) 0.00063 0.00052 0.00063 0.00042
(MeAH)2(M) 0.00021 0.00021 0.000092 0.00018
-AH/-MeAH 1.4 1.1 1.6 1.1
AP (M) 0.05 0.05 0.10 0.10
isBP(M) 0.10 0.15 0.20 0.30
(AH)2(M) 0.00018 0.00013 0.00019 0.00013
(isBHAH)(M) 0.00076 0.00096 0.00086 0.00091
(isBH)2(M) 0.00063 0.00011 0.00063 0.00012
-AHl-isBH 4.9 3.0 4.6 3.1

 

The value of equilibrium constants for hydrogen exchange can be

calculated by equation (12):

_ k _ [Kll-AHI
K° fix [All-KH] (12)

27

 

 

Table 6-2: Calculation of equilibrium constants in hydrogen exchange

reaction.

Reactants Direction K9
AP/PP AH-IPH- 3.5:1
APfIsBP AH-IisBH- 9:1
AP/MeAP AH-lMeAH- 3:1
AP/CIAP AH-ICIAH-

1:5

28

EIII'II-"ll'll
In the hydrogen exchange reactions, the samples were prepared in
various concentrations of ketone and 0.2 M phenyl alcohol in degassed
benzene, and irradiated in parallel for the same length of time at 313
nm. Analyses were performed on both varian 1400 and 3400 gas
chromatographs, column 08-10 for pinacols, column DB-210 for exchange
and disproportionation products. In all cases, all exchange products gave
plots of [ketone quantum yields)" versus [hydrogen donor]". The
experimental data are listed on Table 24, 27, 30, 33, and plotted in
Figure 8, 10, 12 and 14, the slope and intercept are listed in Table 7.

Table-7: Results of photoredox reaction for ketones (varied

concentration) and phenyl alcohol (0.2 M ) in degassed benzene:

 

 

Reactants slope intercept
PP/AH2 0.043 5.5
isBP/AHZ 0.024 7.1
MeAP/AHZ 0.046 8.3
AP/CIAHZ 0.050 5.1

 

The calculated rate constants for hydrogen exchange are listed

29

as follows by using equation (13):

intercept
Re“ slope (kclao-KH+-AH)1/2 (13)

 

The value of kc is 2 X 109 M"s"l381, the light absorbances are from Table

24, 27, 30, 32; quantum yield for radicals is an average value from
Table-13:

In PP/AH2 system, radical -AH exchange with PP:

 

5.5 _
kex- 0 043 ( 2 X109X1.3 X106X 0.23)"2 . 3,1 X103M"s"

In isBP/AH2 system, radical -AH exchange with isBP:

 

7.1 _
k...- (2 X10"X1.1 X10 6x 0.19)"2 - 6,0 x 103 (II-15.1
0.024

In MeAP/AH2 system, radical -AH exchange with MeAP:

 

8.3 .
2.3 (2 X109X1.5 x106x 0.18)"2 = 4.1 X103M'1s"
0.046

In AP/CIAHZ system, radical -ClAH exchange with AP:

5.1
0.050

k .3

-ex

 

(2 X109 x 0.74 X10"3 x 0.20)"2 - 1.7 x 103M"s"

30

because

K°__ku_ [AP] fClAI-II - 0.2

k-” [CIAP] {-AH]

The value of kg, for radical -AH exchange with CIAP should be
9X103M"s1.

Several complementary experiments were accomplished to evaluate
the extent of maximum quantum yields for hydrogen exchange reaction
and the ratio of rate constants for triplet decay over hydrogen
abstraction. In this study, varied concentrations of phenyl alcohol (0.1
to 1 M) were irradiated with certain concentration of ketone (0.05 M) in
degassed benzene at 313 nm. The experimental results were listed on
Table 26,29, 32 and plotted in Figure 9,11,13, the slope and intercept

were listed in Table 8.

Table-8: Results of photoreduction for 0.05 M ketone with varied

concentration of phenyl alcohol in degassed benzene:

 

 

Reactants slope intercept
isBP/AH2 0.57 2.6
MeAP/AH2 0.60 4.2

AP/CIAH2 0.64 2.6

 

31

 

 

 

 

14

o

C

o

C

2 12-

a

o

e-n 1

8

1° 10+

to.

O 1

8

E 8"

> 1

E

3 6-

C

(U

3

2'

1- 4 . fi _

0 100 200

1/[pr0pi0phen0ne M]

Figure 8: Quantum yields for acetophenone formation as a function of
propiophenone concentration with 0.2M 1-phenylethanol in

benzene.

32

 

 

 

 

 

9

O
C I
8
o 8'
.r:
O- .
1% 7

b
o
I“ l
'0—
o 6-
a)
'2
.9
>4 5'
E
3
c 4'
(U
3
g 3 l l l 4
,_

0 2 4 6 8 10

1/[1-phenylethan0l M ]

Figure 9: Quantum yields for acetophenone formation as a function of

1-phenylethan0l concentration with 0.05M isobutyrophenone in benzene.

33

 

 

 

 

11
0
C
O
5
.C 10"
Q.
g
at
o.-
O 9.1
.9
>5
E
3
2'
F
7 . I .
0 100 200

1/[is0butyr0phen0ne M]

Figure 10: Quantum yields for acetophenone formation as a function
of isobutyrophenone concentration with 0.2M 1-phenylethan0l

in benzene.

34

 

11

1/quantum yields of acetophenone

 

 

 

 

1/[1-Phenylethan0l M]

Figure 11: Quantum yields for acetophenone formation as a function
of 1-phenylethan0l concentration with 0.05 M

p-methylacetophenone in benzene.

35

 

 

 

 

18
o
C
O 1
C
2 16 -
O.
o
4...
o
o
°° 14 «
o.—
O
8
E 12 1
>4
E ' °
2 10 1
C
to
3 d
o-
\
P 8 v I I
o 100 200

1/[p-methylacetophen0ne M]

Figure 12: Quantum yields for acetophenone formation as a function
of p-methylacetophenone concentration with 0.2M

1-phenylethan0l in benzene.

1/quantum yields of acetophenone

Figure 13:

36

 

10

 

 

 

1/[ 1-(4'-chl0r0phenyl) ethanol M]

Quantum yields for acetophenone formation as a function
of 1-(4'-chl0r0phenyl) ethanol concentration with

0.05M acetophenone in benzene.

37

 

 

 

 

g 12

6

.c:

8

g 10 '1

2 .

.9

.c

3 9‘

oo—

0

3 1

9. 34

E

3

E

(U

3

E 4 . 1 .
'- 0 100 200

1/[acet0phen0ne M]

Figure 14: Quantum yields for p-chloroacetophenone formation as a
function of acetophenone concentration with 0.2M

1-(4'-chlorophenyl) ethanol in benzene.

38

Discussion

Wis A comparison was made

between undeuterated pinacol and deuterated pinacol. From the ratio of
rate constants for triplet decay over hydrogen abstraction, it can be
found that the hydroxy proton has no effect on the efficiency of the
reaction. The pinacol-d2 was 65% deuterated. The product acetophenone
and its quantum yield are calculated in Table 16, 17. In all cases, all
products gave linear plots of (D "1 vs [AH]2". The slopes of the double
reciprocal plots for the pinacols are shown in Figure 6 and Figure 7.
Dividing the slope of the intercept gives kd/k,. The experimental results

are listed in Table 9. In comparing the kd/k, of these reactions, it shows

no isotope effect.

Table-9: Results for photoreduction of various ketones by
acetophenone pinacol and acetophenone pinacol-d2:

 

 

Reactants CD max Kd/k,
PP/[AH]2 0.053 0.040
PP/[AD]2 0.044 0.043

MeOAP/[AH]2 0.105 0.082

 

39

For the electron-donating group substituted ketone p-
methoxyacetcphenone, the reaction slows down, meaning the electron-
donating group makes most molecules easily undergo a 1:, x‘ reaction and

slows down the n.1r* reaction.

Magical: To understand the tendency of hydrogen
exchange from semi-pinacol radical to ground state ketone, four groups
(propiophenone and acetophenone; isobutyrophenone and acetophenone; p-
methylacetophenone and acetophenone; p-chloroacetophenone and
acetophenone) equilibrium constants of degenerate hydrogen
exchange at a certain steady state have been measured. The

mechanism of equilibrium is illustrated in Scheme 4:

 

 

 

 

 

 

 

A hV : 3A.
K hV : 3K.
. k5:
K + 3A s P A + 3K'
k-et
. k
3 _uA_.
A 2-pr0pan0l AH
. km
3 : e
K 2-pr0panol KH
A + KI-l . '°" 5 K 1. -AH
k' OX

confinue

40

 

 

 

kck

-KH+ “KI-l : [K2H2]
kca.

'AH+ 'AH > [Asz]
kcm

'KH+ 'AH = [KHAH]

Scheme 4: equilibrium between two semi-pinacol radicals.

From different triplet energy of ketones, the equilibrium

constant for triplet energy transfer can be deduced by equation (14).

11 6° - - RT In KET (14)

Table-10: Calculated equilibrium constants of triplet energy transfer

between different ketones.

 

 

 

 

ketone, ET ketonez ET K573
kcal/mol kcal/mol
AP 74.1b PP 74.5° 2.0
AP 74.1 '3 BP 74.7d 2.8
AP 74.1° MeAP 72.8° 0.11
AP 74.1b CIAP 72.1' 0.034

 

(a). In the equilibrium, take ketone, as product, ketonez as a starting
material. (b). references {39). (c). references {40}. (d). references {41}.

(f). references {42}.

41

In the measurement of equilibrium constants, the rate constant of
triplet decay for ketones is kd - 3 1 1 X 105 s-IIIBI. The rate constants of

hydrogen abstraction are on the order of 105 M"s" {15}, the rate constant
of triplet energy transfer is km - 109 s"l43l, and the triplet energy of
ketones should be very close. From the above data, the energy transfer is
a fast step. The triplet decay and hydrogen abstraction steps are major
competitive pathways. From the two competitive pathways, the

originally formed radical ratio can be estimated.

Table-11: Estimation of originally formed radical ratio in the

measurement of equilibrium constants for hydrogen exchange:

 

 

 

ketones kdx105 kHTX105 radical pair Ker ratioa ratiob
s" M"s"
AP 3.40 6.8°
33%d 67%
PP 3.2c 4.4°
42% 58% AH-IPH- 2.0 2.4 : 1 3.5 : 1
isBP 34° 09°
79% 21% AH-lisBH- 2.8 8.9 : 1 9 : 1
MeAP 3.0° 0.98f
75% 25% AH-IMeAH- 0.11 1 : 3.4 3 : 1
CIAP 3.0° 1.6f

65% 35% AH-ICIAH- 0.034 1 :15 1 :5

 

42

Footnote of Table-11:

(a). The starting ketones are of equal amount. The estimated radical
ratio equals the ratio of percentage for hydrogen abstraction multiplied
by KET.

(b). The ratios were measured from experiment.

(6). From references {15}.

(d). The percentages show the competition between kd and km.

(6). From references {16}, the rate constant of triplet decay is taken as
same as acetophenone.

(f). The rate constant of hydrogen abstraction was estimated from

relative rate constant of substituted valerophenone from references

{10(8)}-

In equilibrium reaction, the concentration of ketones is 0.1-0.3M.
The rate constant of triplet decay for ketones is kd - 3 1 1 X 105 s-1l16l,
the rate of triplet decay is on the order of 104 Ms". The rate constant of
triplet energy transfer is kat - 109 s"l43l, the rate of triplet energy
transfer is on the order of 108 Ms". The rate constants of hydrogen
abstraction are on the order of 105 M"s"ll5l, the concentration of
hydrogen donor 2-propanol is 1M, the rate of hydrogen abstraction is on
the order of 104 Ms". As indicated from the above data, triplet energy
transfer is a fast step, before triplet decay and hydrogen abstraction
steps, the equilibrium of triplet energy transfer is established.

Within the experimental error, except for the radical pair of

43

AH-IMeAH-, all other estimated radical ratios are the same or very close
to the ratios measured from experiments. The rate constants of
hydrogen exchange from this research are on the order of 103M"s". In
the case of radical pair AH-lMeAH-, it is possible that the radical of
MeAH- is consumed in the exchange reaction, so that the measured ratio
is 10 times larger than the estimated ratio.

The value of the equilibrium constant for hydrogen exchange from
experiment can be obtained by using equation (12).

The values of equilibrium constants were obtained by measuring of
the radical combination product pinacols using equation (11). For the
coupling products of radicals, a portion of them are cross-coupled
product and another portion of them is self-coupling product. Because
the differences of relative triplet energy between excited ketones, and
the varied rate of reactions for hydrogen abstraction, and hydrogen

exchange , actual semi-pinacol radicals were formed in unequal amounts.

WWW From the

mechanism in Scheme 1, the rate constant of hydrogen exchange from

semi-pinacol radical to ground state ketone can be deduced.

1. The efficiency of intermediate formation is :

k .1 (N12)
kdz '9' km (AHZ)

 

'Q-KH

2. The efficiency of product ketone (A) formed from exchange is:

11,... (K)(-AH)- k-..(A)tKH)+ kdis'éAHV +kdis'( -KH ll-AH)

 

kex (KX'AH)’ k-exIAN'KH) + ll(ca ('AH) + kcrn( 'KH )(' AH)+ kdis' (“'02 +kdi3'( 'N‘I )('AH)

In order to simplify analysis, it is helpful to make some
approximations.

At the beginning, there was no exchange product ketone (A) and
the starting ketone concentration was relatively high (K - 0.005-0.1M ).
The forward reaction was a major pathway. The conversion was kept
lower than 10%, the final concentrations of ketone (A) were 0.0007-
0.002M, so the backward exchange reaction k- ,x can be ignored.

Wagner has reported that the disproportionation for radical pairs
is just 2.5%l44l for acetophenone, because most (-AH) radicals undergo
the combination and exchange reactions. For the (-AH) radical, ignoring

self disproportionation item k.,i$.(-AH)2 and crossing disproportionation

ilef

C8

75"

I}

45

item kdI,-(-AH)(-KH) should not have a large effect on the overall

calculation.

After approximations, the efficiency of ketone formed from
hydrogen exchange should be:

kex (K)
kox (K) + kcaI 'AH) 1' kcm ('KH)

The overall quantum yield of ketone from exchange is:

kex(K)

o -0 xo.
A "° K" k..(K)+ kca(.AH)+Rcm(.KH)

 

k..<-AH) + kcml-KH)
k..( K) 1 ‘1 5’

 

-1 .1 -1
0A u®IscX®.KH[ 1+

At steady state:

. -138
Ia‘DtAH); kca(-AH )2, kca- 2 x 109M1s I I.

['KH]

{-AH} '
_ products of [KH] from diproportionation and combination
products of {-AH] from combination

 

I CD I (D
kck - 4L2): ’ kcm' a (KHAH) ’
(~KH) (-KH WW I

46

The estimated rate constants for combination reactions are listed as

following:

Table-12: Estimated rate constants of combination reactions:

 

 

ketone (M) PP 0.0060 (M) isBP0.071(M) MeAP0.071(M)
AP0.0079(M)

IaX10'7E/LS 7.7 7.1 10 4.9

o «H. 0.0028 0.013 0.0032 -
0W), 0.0076 0.012 0.0098 0.051
0 (KHIZ 0.023 0.048 0.039 -

0 (KW, 0.036 0.050 0.036 0.038
[-AH]X10-9 1.7 2.1 2.2 3.5

2 1.7 2.1 2.1 0.27
[~KH]X10-9 2.9 4.5 4.6 0.95
kckM"s"X109 2.1 1.7 1.8 -
kcmM-Is-1X109 5.6 3.7 3.6 5.6

 

From Table-12, within experimental error, the rate constants of

combination seem to be on the same order.

approximation:

k0,- kcm - k0,, - kc- 2 X109 M"s"

Then equation (15 ) becomes:

It is possible to make an

47

kc [I'AHl + I-KHH
kex( K)

-1 -1 -1
CDA = (Disc'cD'KH{1+

 

(16)

 

(.AH +.KH)-{ IaleH2+2X(®IAH);' 900112 +9018100)] I""’
C

lam-Kl-IwAH 1’2
=1 k )
C

At steady state, the sum of radicals should be constant. It can be
verified by radical products from disproportionation and combination

reactions in Table-13.

48

Table-13: Sum of the quantum yields from disproportionation

and combination reactions: *

 

 

 

 

PP(M) 0.0060 0.017 0.025 0.05 0.10 0.15
5...-..17'1. """" {I2} """" {.23 """"" 6'2; """ 5'2; “.1...
lsBP(M) 0 0071 0 10 0 016 0 025 0.05
8;... """ (322' """" 0' AWN}; """"" ééi'mmlil'f
MeAP(M) 0.0051 0.0071 0.010 0.016 0.025 0.051
5'.;..'....""J{. """ 0' 3'7 """ A}; """" é}; """" A 1; """" 0 a.
AP(M) 0.0079 0.010 0.013 0.016 0.025 0.051 0.10

3...}...[fljé """ l; .1. """ A}; """ o I; """ iiimlééw'i...

 

* ¢'AH+'KH II (DKHZ + 2 X [ ¢(AH)2 + ¢(KH)2 + (DIKHAHil

49

From Table-13, within experimental error, the quantum yields of all

radicals are constant, so the equation (16 ) becomes:

.1 -1 -1 (kcIa ‘9 'KH+'AH)'I2
0 : m . . @- 1 +
A 101
{ k...( K >

 

.1 -1
The intercept = (Disc- CD. KH

-1 -1
(D isc ' 0' K" ( kc111 ‘13 -KH+-AH)'/2

 

 

The slope -
kex
k intercept 1,2
ex - s'ope ( kcIa ® 'KH+'AH)

This experiment using the steady state radical concentration for
reaction provided a method to calculate the rate constant for hydrogen
exchange from semi-pinacol radical to ground state ketone.

Recently, Steel and Cohen reported a similar studyi2l, they neglected
the (~KH) self disproportionation, crossing disproportionation and crossing
combination reactions, and deduced two approximate equations and all
rate constants in their equations using literature data. In the first
equation, they measured the benzopinacol quantum yields, comparing
experimental data with the calculated model curves, and reported k9, must
lie between 3 X 104 M"s" and 5 X 104 M"s". In the second equation, they

measured the benzopinacol and mixed pinacol quantum yields, and obtained

50

kmt - ( 2.5 ,+_ 0.5 ) X 104 M"s". From both methods, they finally reported
kex-(3.5;)-_1.5)X104M"s".

Quantum yields for the hydrogen exchange, disproportionation, and
combination products were determined in four groups of the
photoreduction reactions: propiophenone by 1-phenylethanol;
isobutyrophenone by 1-phenylethanol; p-methylacetophenone by 1-
phenylethanol; and acetophenone by 1-(4'-chlorophenyl) ethanol. In these
studies, the starting ketone began with a relatively low concentration of
0.005M and varied through a large range to 0.1M, the alcohol concentration
was kept constant and relatively high (0.2M). According to the mechanism
drawn in scheme 1, the products were: (1). alcohol corresponding to
disproportionation of semi-pinacol radical from two-electron reduction of
starting ketone; (2). ketone corresponding to hydrogen exchange from
semi-pinacol radical by two-electron oxidization of the starting alcohol,
(3). pinacols formed from the self coupling or cross coupling of two
semi-pinacol radicals. In all cases, all exchange products gave plots of
ketone’s <0" versus [hydrogen donorj" ( Table 24, 27, 30 and 33, Figure 8,
10, 12 and 14).

In the ketone-semipinacol photoredox reaction, there are
three competitive reactions: hydrogen transfer from semi-pinacol
radicals to ketone, disproportionation reaction, and combination reaction.
In this research, the quantum yields of disproportionation reaction were

low from 0.00002-0.07. The hydrogen exchange reaction and radical

51

combination reaction seem to be the major competitive reactions.

LewisllSI has reported the disproportionation/combination
ratios for radical pairs of bimolecular hydrogen abstraction by triplet aryl
alkyl ketones. (Table-14)

Table-14: Disproportionation/Combination Ratios for Radical Pairs

Radical pair kdis/kco m

H
0.02

H
Ila“! 0.17
P ' CHa
i
_ CH(CH3)2 0.69

From Table-14, the relative rate constant of disproportionation
reaction increases by increasing the size of the a-methyl substitution,

which is consistent with the observation in this research.
The calculated ratio of rate constant for disproportionation over

combination are listed in Table-15 by using equation (18)

kdis/kcom - ‘1’an /( 2 X ‘D(KH)2 + ‘D(KHAH)) (18)

52

Table-15: The ratio of rate constants for disproportionation

over combination reactions: *

 

 

 

 

PP(M) 0.0060 0.017 0.025 0.05 0.10 0.15
...,L...'Jo'a. """ 66;; """ g...“".57“... """ it}.
isBP(M) 0.0071 0.10 0.016 0.025 0.05
....i... """ 0 .13.; """" 3.11;; """"" 3.21;. """"" if}; """"" A .1.
MeAP(M) 0.0051 0.0071 0.010 0.016 0.025 0.051
..../L...""o'.£.;. """ 0 .32; """ 6.2.2.} """" 0' .QQQWIQQQWJJQQ

AP(M) 0.0079 0.010 0.013 0.016 0.025 0.051 0.10
....I.;,I"".""""'I """" .' """ A A}; """ 0 '..}};""}.'..}J;"".{.;;;

 

* Data are from Table 25, 28, 31, 34.

53

For the ketone that has or substituted groups, like isobutyrophenone,
there is a significant steric effect. The quantum yields of combination
reaction were lower than propiophenone. The quantum yields of
disproportionation reaction were higher than propiophenone. The hydrogen

transfer reaction was preferred and the rate constant of hydrogen
exchange doubles that of propiophenone. The para-position electron
withdrawing group like halogens can conjugate with the carbonyl group
and cause electron density to move away from oxygen. This inductive
effect should stabilize n,1r* state and its electron-donating resonance
effect should stabilize the 1:, x‘ transition. In the case of p-
chloroacetophenone, there is a reversed equilibrium radical ratio. The
reaction should be controlled so that the competitive absorption of light
by produced ketone can be minimized. Almost no disproportionation
product from starting ketone and self combination products from starting
alcohol can be measured. The hydrogen exchange became the dominant
pathway.

In the case of electron donating substitutes, (like p-
methylacetophenone), the electron density moves from benzene ring to the
carbonyl group. This substitution stabilizes the 1:, n‘ triplet transition,
so that the electron rich carbonyl group would not react like an
electrophilic radical. The quantum yields of both combination and
disproportionation were lower than that of propiophenone. The rate

constant of exchange from semi-pinacol radical to ketone was 1.3 times

that of propiophenone.

The rate constants of hydrogen exchange obtained in this research
are on the order of 103 M" S". These rate constants are slower than the
rate constant of hydrogen exchange in benzophenone system measured by

Steel et al.12l. It is not surprising, since the benzophenone has more
bulky semi-pinacol radical, the rate constant of combination is 1 X 103
M"S"l36I which is twenty times slower than the rate constant 2 X 109
M"S‘"133} of combination reaction for acetophenone. Therefore, it is
possible that the rate constant of the hydrogen exchange in benzophenone
system is faster than that in aryl alkyl ketone system.

Weineri45} et al. have demonstrated that the products from
crossing combination and disproportionation reactions were the products
arising from solvent cage. All other products were produced from free
radicals escaped from solvent cage. From the product distribution in
Tables 25, 28, 31, 34, the cage products were 20-30% of the total radical
products. The hydrogen exchange product was approximately 70% of total
escaped products. This information indicated that most radicals products
came from cage escaped free radicals, and because of the hydrogen
bonding effect, the hydrogen exchange product was the major product of
cage escaped products. Since the products of the cage reaction must be
formed in their ground state, one electron must flip its spin. From these
data, it is possible to estimate a value for thermally generated free

radicals which formed in singlet radical pairs.

55

Several complementary experiments have been done by using
certain amounts of ketone and varing amounts of alcohol to relate the fate
of radical from photoreduction reaction. The ratio of rate constant for
triplet decay over the rate constant of hydrogen abstraction and maximum

quantum yields of acetcphenone from hydrogen exchange were obtained.

56

CONCLUSION

The results of the research reported in this thesis have several

conclusions regarding the photoreduction reaction. The main points are the

steric effect and the substituent effect in the hydrogen exchange
reacfion.

The tendency of photoreduction for different ketones by alcohol
has been understood by comparing the equilibrium constants of degenerate
hydrogen exchange from semi-pinacol radicals to ground state ketone. At
equilibrium, the radicals from electron-withdrawing group substituted
and less bulky alkyl aryl ketone have higher ratios.

From the initial interaction of excited ketone with aromatic
alcohol, the maximum quantum yield of the product from hydrogen
exchange indicates that ketones with electron donating substituted ketone
have less reactivity.

The rate constants of hydrogen exchange in ketone-semipinacol
system have led to a greater understanding of the photoredox processes.
It has clarified that the degenerate hydrogen exchange is an important
individual step in the initial interaction of semi-pinacol radical with
ground state ketone in the photoredox reaction. It has provided an
independent method to calculate the kinetic parameters and a
comprehensive experiment to separate the complicated aspects of the

reacfion.

57

S I'Itll'l'l'

The hydrogen exchange is caused by the interaction of hydrogen
bonding between semi-pinacol radical and ground state ketone. The
solvent polarity should have a strong effect on the competitive reactions
of exchange, combination, and disproportionation. The solvent can be
changed from benzene to acetonitrile, pyridine, or neat alcohol such as 2-
propanol. These solvent effects are unprecedented and should be
investigated further. The study of temperature dependencei46} and the pH
dependenceW} will help to explain the activation energy and the life time
of radicals.

In the photoreduction of ketone by pinacols, the rate constants
should be measured for ketones substituted with elecron-withdrawing
groups (such as CF3). Electron-donating groups (such as OCH3) can be
compared with the unsubstituted ketone by using 99% deuterated versus
undeuterated pinacols. The substitutuent and isotope effect would assist
in the understanding of the mechanism of hydrogen abstraction and the

extent of the charge transfer reaction.

58

EXPERIMENTAL

W To understand excited state reactivity,

it is necessary to make quantitative measurements of quantum yields and

rate constants.

..H. 1: '3. .; H .1 . 3.... .

.0 00:. .0 .010. ..0 ...... .. 0 .. .. :0 0 .0 00:. :‘ ...0:
From Figure 9, using equations (8), and (9), the value of rate

constant for triplet decay over hydrogen exchange and maximum quantum

yield can be obtained as following:

Kd/K, - 0.57/2.6 - 0.22
(hm, - 1/intercept - 1/2.5 - 0.40

C I. [I'll | I.

At low concentration of reactant, when A<2, the light
absorption was corrected as the followingzl48l
Io - the intensity of the radiation energy striking on the
sample
I - the intensity of the radiation energy transmitted from the

sample

59

T - I/Io - transmittance
A - log( Io/I ) - absorbance (optical density)
Ta - 1- T - 1-10-A - fraction of light absorbed

IaTa- the actual light absorbed after correction

0 I I I. I Q I . II _

The amount of light absorbed (Ia in Einstein/liter) was
determined by valerophenone actinometer. A benzene solution containing
0.10M valerophenonei37} as a standard was irradiated in parallel with the
samples to be analyzed. The acetophenone concentration was calculated

using the following equation:

acetophenone - (SF X standard X peak area of acetophenone)/(peak area

of standard)

where SF is the standardization factor determined from the relative
HPLC or CO peak area of the two compounds with known concentrations.
From the concentration of acetophenone and the quantum yield of
acetophenone formation (0 ap' 0.33 in benzene for 0.1M valerophenone), the

amount of light absorbed can be calculated.

Ia- light absorbed - acetcphenone/ (0.33)

60

The concentration of the photoproducts of the reaction in the
equation were determined using a standard and their standardization
factors. Dividing these concentrations by the light absorbed results in the

quantum yield for the product.

(D - quantum yield - [productlea

Sample calculation:
Actinometer: 0.10M valerophenone
0.003M undecane (C11), SF - 1.72
area of acetophenone/area of dodecane - 0.469
[acetophenone] - (SF X [012] X area of AP)! area of 012
[acetophenone] - 1.72 X 0.0110 X 0.469 - 0.00887M
Ia - light absorbed - 0.00887/0.33 - 0.0269 E/L
CD - quantum yield - [productlea :- 0.33 for acetophnone
Sample: 0.050 M PP,
0.00456M dodecane (012)
0.10M 1-phenylethanol
SF . 1.82 for acetophenone (AP) over dodecane (Cm)
area of AP/area of dodecane - 0.205
[AP] - (SF X [C12] X area of AP)/area of C12
[AP] - 1.82 X 0.00456 X 0.205 - 0.00170 M
(D AP . [AP]/Ia - 0.00170/ 0.0269 - 0.063

61

3.0119015

Benzene; (Baker) was purified by stirring over concentrated
sulfuric acid .The sulfuric acid was changed every twenty-four hours until
it remained clear . The benzene was then washed several times with
water, several times with saturated sodium bicarbonate solution, and
finally two times with water. The benzene was pro-dried with sodium
sulfate and distilled from phosphorus pentoxide through a column packed
with glass helices. The first 10% and the last 20% were discarded.
(bP-80°C)

Henna; (J.T.Baker) was purified by washing with concentrated
sulfuric acid in a method similar to benzene, dried by magnesium sulfate
and distilled over calcium hydride. The first and the last 10-20% were

discarded.

62

IntemaLStandaIds

The internal standards were purified by various members of Dr.

P. J.Wagner research group as follows:

um (C1,): (Aldrich) was purified in the same method as

benzene and distilled under reduced pressure.

mugging (C12): (Phillips) was purified in the same manner as

benzene and distilled under reduced pressure.

W (Cm): (Aldrich) was purified in the same manner as

undecane.

22W (0516): (Aldrich) was Purified

in the same manner as undecane.

W (017): (Chemical Samples Co.) was purified in the

same manner as undecane.

W (018): (Chemical Samples Co.) was washed with

concentrated sulfuric acid and recrystallized from ethanol.

Madman (019): (Chemical Samples Co.) was recrystalized

from ethanol.

8W3;

Amhennnujnagnl; was formed by preparative irradiation of 10ml
acetophenone with 200ml 2-propanol in a 250 ml photochemical immersion
well at 313nm for 48 hours. After removal of the solvent from the
irradiation product, the solid residue was recrystallized several times from
petroleum ether. ( MP - 122°C ) Spectra were compared with authentic
data.l49l The reported melting point is 125°Cl49l. 1H-NMR (250 Hz, CDCI3): 8
- 1.5 (s, 6H, 2CH3), 8 - 2.6 (s, 2H, 20H) (was exchanged by D20), 8 - 7.21 (m,
10H, Phenyl). MS: 121 (M+/2), 111 . IR: 3500 cm-1 (OH), 3300 cm-1, 1270

cm-1.

MW; To an oven dried 3-neck round bottom

flask, flushed with argon, was added acetophenone pinacol. Benzene was
distilled from sodium metal directly into the reaction flask. Butyllithium (4
equivalents) was injected. After stirring for 30 minutes in an ice bath, D20
was added (10 equivalents). The organic layer was isolated and the solvent
was removed to give a solid product. The solid was dissolved in dry hexane by
refluxing, and a crystalline product , containing 65% deuterium , was
obtained upon cooling. The low amount of deuterium incorporation was
probably due to low quality 020 .
The pinacol of low percentage deuteration was recrystallized in dry

hexane, then dissolved in a 5 : 1 mixture of ethanol-d and D20, the solvent was
removed and the solid was dissolved in ethanol-d, 020 again, the crystal was

dried by diffusion pump vacuum. The 99% deuterium pinacol-d2 was obtained.

NMR spectrum showed no OH peak, and IR spectrum showed 99% OD peak at
2200 cm-1, only 1% at 3500 cm-1.

W was prepared by stirring 5ml acetophenone with
29 H4AlLi and 25ml dried ether in a 50ml round bottom flask for 24 hours.

After removed of solvent, it was isolated by silica gel column. This
procedure was repeated several times. G. C. analysis indicated that it was
100% pure, and it was finally distilled at reduced pressure. (BP
50°C/1mmHg) Spectra were compared with authentic data.i5°l 1H-NMR (250
M2, CDCI3): 8 - 1.45 (d, 3H, CH3), 8 - 1.89 (s, 1H, CH) (was exchanged by DZO),
8 - 4.81 (q, 1H, CH), 8 - 7.21 (s, 5H, Phenyl). The reported melting point is
204°C/745mml50}.

WISH Grignard reagent was synthesized
by dropping 10 ml distilled methyl iodide (baker) into 3 gram magnesium

metal covered by 100 ml dried ether. The whole system was protected under
argon. Then 10 gram dried 4-chlorobenzaldehyde dissolved in 30 ml dried
other were dropped in. The system was quenched in the usual manner.
Because the system was in acidic condition, some elimition occurredi52} and
there were always some p-chloroacetophenone being detected. The p-
chloroacetophenone was reducted by aluminium isopropoxide.l53} 27 g (1mol)
aluminium foil were placed in a 1-liter flask containing 300ml (3.9mol) 2-

propanol dried by calcium oxide and 0.4 g of mercury chloride. The solution

65

was stirred and refluxed until all metal had reacted. The excess 2-propanol
was distilled to a 250 ml receiving flask until the temperature of distillate
rose above 90°C, and then aluminium isopropoxide was distilled at 140-
150°C/12mmHg. 5 Gram of 1-(4'-chlorophenyl)ethanol was stirred with 50ml
aluminium isopropoxide for 24 hours. After removing solvent, final
purification was accomplished by distillation under reduced pressure.(BP
55°C/1.1mmHg) Spectra were compared with authentic data.{54} 1H-NMR (250
M2, CDCla): 8 - 1.31 (d, 3H, CH3), 8 - 3.56 (s, 1H, CH) (was exchanged by D20),
8 - 4.64 (q, 1H, CH), 8 - 7.18 (s, 5H, Phenyl). The reported melting point is
121°C/15mm154l.

66

Reactants

W was prepared by Freidel-Crafts acylation of benzene.
109 valeric acid were placed in a three neck round bottom flask; 14 g
redistilled thionyl chloride were dropped in the flask and refluxed for 40
mins. The valeryl chloride was isolated by distillation, bp 125-128°C. A
500 ml three necked flask with a reflux condenser was equipped with a
mechanical stirrer and a dropping funnel; the top of the condenser was
connected to a trap for absorbing the hydrogen chloride. 69 (0.045mol)
anhydrous aluminium chloride and 100 ml benzene were placed in the flask
with a cooling water bath; 59 valeryl chloride were added during 30 min. The
mixture was refluxed for 2 hours before being cooled and poured to 200ml
ice-water. The organic layer in a separatory tunnel was washed with water,
then saturated NaHCOa, and then dried with magnesium sulfate. After work-
up, the crude product was dried and distilled under reduced pressure. (BP :-
105-11000 l2mm).

Agntgnhnnnng; was purified by Dr. P. J. Wagner research group.

aninnhnnnng; (MC and B) was passed through alumina and then
purified by distillation under reduced pressure. (BP 55-58°C/7mm). Spectra
were compared with authentic data.l55} 1H-NMR (250 M2, CDCI3): 8 - 1.18

(t, 3H, CH3), 5 - 2.94 (9. 2H, CH2). 8 - 7.47 (m, 3H, Phenyl), 8 - 7.92 (m, 2H,
Phenyl). The reported melting point is 218°C155}.

67

AW (Eastman Kodak) was purified by fractional

distillation through 1-foot column packed with glass helices. One of the
impurities, acetophenone was totally removed, and another impurity, 2'-
methylacetophenone was reduced to 0.5 percent. The product was collected
at 415°C / 2mmHg. Spectra were compared with authentic data.l55} 1H-NMR
(250 M2, 00013): 8 - 2.32 (s, 3H, Phenyl CH3), 8 - 2.42 (s, 3H, carbonyl CH3),
8 - 7.09 (m, 2H, Phenyl), 8 - 7.69 (m, 2H, Phenyl).

i-ztltmycmmatttxliammhanmm (Aldrich) was Purified by
distillation, hot water was used in the condenser to prevent the compound
from condensing in the distillation head. (BP 78-80°C/8mm).

Spectra were compared with authentic data.157l 1H-NMR (250 Mz, CDCla):

8 - 2.62 (s, 3H, CH3), 8 - 7.71 (m, 2H, Phenyl), 8 - 8.08 (m, 2H, Phenyl).

W was synthesized By Dr. Boli Zhou and purified by
distillation under reduced pressure. ( BP 54 °C /0.9mmHg). Spectra were

compared with authentic data.{58I 1H-NMR (250 M2, c0013):
8 - 1.18 (d, 6H, 2CH3). 8 - 3.47 (h, 1H, CH), 8 - 7.33 (m, 3H, Phenyl), 8 - 7.85
(m, 2H, Phenyl). The reported melting point is 91.5-93.5°C /7mm {58}.

Wanna; was prepared by Freidel-Crafts acylation of

anisole by acetic anhydride. A 500 ml three necked flask with a reflux
condenser were equipped with a mechanical stirrer unit and a dropping funnel;
the top of the condenser was connected to a trap for absorbing the hydrogen
chloride. 6 9 (0.045mol) Anhydrous aluminium chloride and 5.4 ml (0.05mol)
of anisole with 200ml CCL4 were placed in the flask with a cooling water
bath, the mixture was stirred and refluxed, 5.1g (4.7ml, 0.05mol) of
redistilled acetic anhydride were added during 30 min, then refluxed for 2
hours. After cooling the reaction mixture was poured to 200ml ice-water and
50ml concentrated hydrochloric acid. The organic layer was separated in a
separatory funnel, washed with water, then with saturated NaHCOa, and dried
with magnesium sulfate. After removing solvent, the crude product was
crystallized several times from petroleum ether. (MP - 35-37°C) .

Spectra were compared with authentic data.l59l 1H-NMR (250 M2, CDCI3):

8 - 2.56 (s, 3H, CH3), 8 - 3.88 (s, 3H, OCH3 ), 8 - 6.98 (m, 2H, Phenyl), 8 - 7.97
(m, 2H, Phenyl).

69

III'I'I' [II II

W was formed by preparative irradiation of 10ml

propiophenone with 200ml of 2-propanol in a 250 ml photochemical
immersion well at 313nm for 48 hours. After removal of the solvent from the
irradiation product, the solid residue was recrystallized several times from
petroleum ether. ( MP - 130-13200 )

Spectra were compared with authentic data.16°I 1H-NMR (250 M2, CDCI3):

8 =- 0.6 (t, 6H, ZCH3), 8 - 1.58 (qd, 2H, CH2), 8 - 2.08 (s, 2H, CH), 8 - 2.30 ( qd,
2H, CH2). 8 - 7.2 (s, 5H, Phenyl). The reported melting point is 133-1340C161l

- ' - - - ' - was formed by preparative
irradiation of 2ml p-chloroacetophenone with 2ml 2-propanol in a pyrex test
tube, sealed by a rubber stopper, deoxygenated with a steam of dry nitrogen
passing through the solution by two needles (one entry, one out) for 20
minutes, then irradiated at 313nm for 48 hours. After removal of the solvent
from the irradiation product, the solid residue was recrystallized several
times from petroleum ether. ( MP - 182-184°C )

1H-NMR (250 M2, c0c13)162): 8 - 1.54 (s, 6H, 2CH300H),
8 - 2.2 (s, 2H, 20H) (was exchanged by D20), 8 - 7.1 (m, 8H, Phenyl).
MS: 135 ( M/2, 155), 111 . IR: 3500 cm-1 (OH), 3000 cm-1, 1500 cm-1, 1100

cm-1, 1000 cm-1.

70

- ' - - ’ - - ' ' was formed by
preparative irradiation of 2ml isobutyrophenone with 2ml 2-propanol in a
pyrex test tube, sealed by a rubber stopper, deoxygenated with a steam of dry
nitrogen passing through the solution by two needles (one entry, one out) for
20 minutes, then irradiated at 313nm for 48 hours. After removal of the
solvent from the irradiation product, the solid residue was recrystallized
several times from petroleum ether.
1H-NMR (250 M2, CDCI3)l63I: 8 - 0.34-0.37 (d, .1 - 6.7 Hz; Me),
8 - 1.20-1.23 (d, J - 6.4 Hz; Me), 8 - 1.69-1.85 (sept, J - 6.6 Hz; CH),
8 - 2.8 (s, OH) (was exchanged by 020), 7.2-7.4 (m, Phenyl).

13C-NMR: (250 Mz, CDCI3) 8 - 18,20 (Me), 35 ( CH ), 84 (COH), 126,
126.5, 127.5, 143, (Phenyl).

MS: 149 ( M/2, 100), 105, IR: 3600 cm-1, 3500 cm-1 (OH); 3000 cm-1,
1500 cm-1, 1000 cm-1, 750 cm-1.

MP -118-120°C, the reported melting point is 11842000154}

- ' - - - ' ' was formed by preparative
irradiation of 2ml p-methylacetophenone with 2ml 2-propanol in a pyrex test
tube, sealed by rubber stopper, deoxygenated with a steam of dry nitrogen
passing through the solution by two needles (one entry, one out) for 20

minutes, then

71

irradiated at 313nm for 48 hours. After removal of the solvent from the
irradiation product, the solid residue was recrystallized several times from
petroleum ether.

1H-NMR (250 Mz, CDCI3) (651: 8 - 1.53 (s, 6H, 2CH300H), 8 - 2.32 (s,
6H, 2CH3), 8 - 2.1 (s, 2H 20H), (was exchanged by D20), 8 - 7.0-7.2 (m, 8H,
Phenyl). MS: 135 ( M/2, 85), 121(10) , IR: 3500 cm-1 (OH), 3000 cm-1, 1500
cm-1. 1100 cm-1, 900 cm-1. MP - 130-132°C.

- - - ' was synthesized from reducing
isobutyrophenone by H4AlLi. 100ml dried other were placed in a three necked
round bottom flask with a stirrer unit, condenser and dropping funnel. 39
lithium aluminium hydride were introduced to the flask, 10ml
isobutyrophenone in a 30ml dried other were added by the dropping funnel. The
mixture was stirred for 2 hours before 20ml water were dropwise added in a
ice-water bath. After the water layer was separated, the ethereal solution
was dried by magnesium sulfate and evaporated, the residue was distilled
under reduced pressure. (BP 50° C/2mmHg). Spectra were compared with
authentic data.166l 1H-NMR (250 M2, CDCI3): 8 - 1.25 (d, 6H, 20H3), 8 - 3.41
(d, 1H, CH), 8 - 4.38 (d, 1H, CH), 8 - 7.30 (m, 5H, Phenyl). MS: 150 ( M+), IR:
3600 cm-1, 3500 cm-1 (OH), 3000 cm-1, 1500 cm-1, 1000 cm-1. BP - 222-
224°C.

72

- '- ° was synthesized from reducing p-
methylacetophenone by H4AILi. 100ml dried other were placed in a three
necked round bottom flask with a stirrer unit, condenser, and dropping funnel.
3g lithium aluminium hydride were introduced to the flask, 10ml p-
methylacetophenone in a 30ml dried ether were added by the dropping funnel.
After stirring for 2 hours, 20ml water were dropwise added in a ice-water
bath. After the water layer was separated, the ethereal solution was dried by
magnesium sulfate and evaporated, the residue was distilled under reduced
pressure. (BP 45° C/1.7mmHg). Spectra were compared with authentic
data.l57}

1H-NMR (250 M2, coma): 5 - 1.27 (d, 3H, CH3), 5 - 2.26 (s, 3H,
CH3), 8 - 3.76 (s, 1H, OH), 8 - 4.60 (q, 1H, CH), 8 - 6.98 (s, 2H, Phenyl), 8 - 7.10
(s, 2H, Phenyl). MS: 136 ( M+), IR: 3600 cm-1, 3500 cm-1 (OH), 3000 cm-1,
1500 cm-1, 1000 cm-1. BP - 180° C/20mmHgl67} .

W was prepared by Freidel-Crafts acylation of

chlorobenzene by acetic anhydride. A 500 ml three necked flask with a reflux
condenser were equipped with a mechanical stirrer unit and a dropping funnel,
the top of the condenser was connected to a trap for absorbing the hydrogen

chloride. 6 g (0.045mol) aluminium chloride anhydrous and 5.6 ml (0.05mol)
of chlorobenzene with 200ml CCL4 were placed in the flask and

73

the mixture was stirred and refluxed, 5.1g (4.7ml, 0.05mol) of redistilled
acetic anhydride were added during 30 min, then refluxed for 2 hours. The
mixture was cooled and poured into 200ml ice-water and 50ml concentrated
hydrochloric acid. The organic layer was separated in a separatory funnel,
washed with water, then with saturated NaHCOa, and dried with magnesium
sulfate. After removing solvent, the crude product was distilled under
reduced pressure. (BP 48° C/1mmHg). Spectra were compared with authentic
data.l68} 1H-NMR (250 M2, CDCIa): 8 - 2.49 (s, 3H, CH3), 8 - 7.31 (m, 2H,
Phenyl), 8 - 7.80 (m, 2H, Phenyl).

Wag]; was obtained from reducing propiophenone
by H4AlLi. 100ml dried ether were placed in a three necked round bottom

flask with a stirrer unit, condenser and dropping funnel. 3g lithium aluminium
hydride were introduced to the flask, 10ml propiophenone in 30ml dried ether
were added by the dropping funnel. After stirring for 2 hours, 20ml water
were dropwise added under cooling in a ice-water bath. After the water layer
separated, the ethereal solution was dried by magnesium sulfate and removed.
The residue was distilled under reduced pressure.

(BP 45° C/1.7mmHg). Spectra were compared with authentic data.{°9l

1H-NMR (250 Mz, cocua): a - 0.9 (t, 3H, CH3), 5 -1.7(q,2H, CH2),8 .-
2.0 (s, 1H, CH), 8 - 4.5 (t, 1H, CH), 8 - 7.2 (s, 5H, Phenyl).

74

Techniques

filamam
All solutions were prepared with class A volumetric flasks and
pipets. The volumetric ware was cleaned by soaking in hot soap water and
boiling. This was followed by rinsing and soaking in hot distilled water, while
changing water several times over a period of at least three days. Pyrex
culture tubes used for irradiation were cleaned in the same manner. Syringes
used for transfering solutions from volumetric flasks to culture tubes were
cleaned in a manner similar to the volumetric ware. All glassware was
dried in an oven at 140°C used only for analytical glassware to avoid
contamination.
The Pyrex culture tubes (13X100mm) were drawn out by heating
near the top so that a narrow constriction (approximately 3X50mm) was

formed 30mm from the top of the tube.

BrenazatimLoLSamnles

Solutions were made by weighing samples directly into
volumetric flasks and diluting to the mark or pipetting from a stock solution ,
made in the above manner, into volumetric flasks and then being diluted. The
latter method was used when a number of solutions were needed with the
same component, such as an internal standard. A 2.8 ml aliquot of these
solutions were then added to the constricted culture tubes by means of a 5cc

syringe.

75

Wan—Ema

The tubes prepared above were then attached to a vacuum line with
diffusion pump capable of 10-4 Torr by means of size 00 one-hole rubber
stoppers fitted to a manifold containing twelve stopcocks. The solutions
were frozen in liquid nitrogen and the stopcocks opened. After pumping on the
samples for 15 minutes the stopcocks were closed and the solutions allowed
to warm to room temperature until completely thawed. The freeze-pump-
thaw cycle was repeated four more times, after which the tubes were sealed

using a torch while the samples were frozen.

| I' I' E I

All quantum yields were measured by parallel irradiation of
samples and actinometer on a merry-go-round apparatus. The light source
was a Hanovia medium-pressure mercury lamp with 313nm region isolated by
means of a chemical filter . The chemical filter was a 0.0002M potassium
chromate solution buffered by 1% potassium carbonate. The entire apparatus,
merry-go-round and light source with filter, was immersed in a constant
temperature bath at room temperature.

Preparative irradiation were performed in a photochemical
immersion well. The light was filtered by a pyrex sleeve surrounding the
lamp. The well had a capacity of 150 ml of solution and was fitted with a
condenser to prevent loss of solvent. A stream of dry nitrogen was passed

through the solution by a frit at the bottom of the well. For small amount

76

preparative irradiation, was using a pyrex test tube, sealed by a rubber
stopper. The stream of dry nitrogen was passed through the solution by two
needles (one entry, another one out) for 20 minutes, then irradiated by a

filtered light in a immersion well.

Analxsis

Analysis was done by HPLC made of a Beckman 332 Gradient Liquid
Chromatography System, equipped with a Du Pont 860 Instruments Column
Compartment, Beckman Modal 110A pump, Perkin-Elmer Spectrophotometric
LC-75 Ultraviolet-Visible Detector. The HPLC system was connected to a HP
Hewlett Packard 6080 Integrating recorder. An Altex UltraspThere Si
Absorption Phase Column was used. The flow rate was 1.0 , solvent ratio
were 92% hexane , 8% ethyl acetate. The gas chromatography was Varian
model 1440 and 3400 gas chromatography, employing flame ionization
detectors. Model 1440 Gas chromatography was connected to either Hewlett-
Packard 3393 A, or 3392 A Integrating recorder.

Two types of columns have been used for gas chromatography.

Column # 1- Magabore DB-1, 15 meter in length
Column # 2- Magabore DB-210, 15 meter in length

For AHZ' PHZ, AP, PP, 8H2, MHZ, column was DB-210, temperature 60°C 10
minutes, then 170°C 3 minutes; for PCIAP, column was DB-210, temperature
60°C 8 minutes, 95°C 8 minutes,then 170°C 3 minutes; for pinacols, column

was DB-1, temperature was 175°C.

77

Wants

1H NMR spectra were recorded on either a Varian T-60 or a Bruker
WM-250 Fourier Transform Spectrometer.

Infrared spectra were recorded on a Niclet lR/442 Spectrometer.

Ultraviolet-visible spectra were recorded on a Shimadzu UV-
160 Spectrometer.

Mass spectra were recorded on a Finigan 4000 GC/MS.

78

References

-L

. (a) P. J. Wagner, “Chemistry of Excited Triplet Organic
Compounds“, Wu 1976 £5 1
(b) Scaiano, J. C., J._Ehoto.ct1em. 81 1973/74 2, 81
2. Colin Steel and Saul G. Cohen, Wham. 1988 22 6574
Giering, L., Berger, M., Steel, 0., W 1974 26 953

4. C. M. Previtali and J. C. Scaiano, W41, 1972
1667, 1672

5. C. Walling and M. J. Gibian, W 1965 82 3361
6. W. Herkstroeter, A. A. Lamola and G. S. Hammod, W
1964 86 4537

7. (a) C. Walling, ”Free Radicals in Solution" John Wiley and Sons, Inc, New
York, N. Y., 1957, Chapter 2

(b) G. L. Esteban, J. A. Karr, and A. F. Trotman-Dickenson, mm
1963 3873

P. Gray and A. Williams, M 1959 52 239

9. Lewis, F. D., Jonhnson, R. W., kory, D. R., W 1974
2.6 6100

10. (a) P. J. Wagner, A. E. Kampainen, and H. N. Schott, MW
1973 25, 5604

(b) P. J. Wagner, and A. E. Kampainen, mm 1968
9.0. 5896

11. P. J. Wagner, W19“ 1 168

79

12. P. J. Wagner, and E. Siebert, mm 1981 1Q: 7329
13. N. C. Yang, R. Dusenberg, Wham. 1969 1 159

14. N. C. Yang, R. Dusenberg, W 1968 20 5899

15. F. D. Lewis, J. G. Magyar, Mam. 1972 22 2102

16. F. D. Lewis, W 1970 15 1373

17. D. E. Pearson, M. Y. Moss W 1967 .12 3791
18. E. S. Huyser and D. C. Neckers, LAW 1963 81 3641
19. Jeandrau, J. P.; Gramain, J. C.; Lamaire, J.; W

1979 186; J._Qhem._Bes._MinioLim 1979 2240
20. Lutz, H.; Duval, M. C.; Breheret, E.; Lindqvist, L. m

1972 Z6_ 821
21. Scaiano, J. 0., WWW 1Q2 5902
22. P. J. Wagner, M 1967 18 1753
23. (a) G.Ciamician and P.Silber, W 1900 13 2911
(b) G.Ciamician and P.Silber, m 1900 .31 1530
24. G. S. Hammond, W. M. Moore, ”MM 1959 81 6334

25. P. Colman, A. Dunne, M. F. Quinn, W5. 1976
22 2605

26. W. D. Cohen, W5, 1920 :12 243

27. Ch. Weizman, E. Bergman, Y. Hirshberg, W 1938
50 1530

28. V. Franzen, MW 1960 £11 1

29. D. I. Schuster, P. B. Karp, AW 1980 12 333

30. H. Yoshia and T. Warashina, W 1971 11 2950

80

31. G. O. Schenck, G. Behrens and E. Roselius, W 1970
5185

32. J. N. Pitts, R. L. Letsinger, R. P. Taylor, J. M. Paterson G. Recktenwald
and R. B. Martin, MW 1959 81 1068

33. G. L. Class and D. R. Paulson, Wham 1970 22 7229

34. Paul, H., Segaud, C. Wm 1980 12 637

35. McCracken, D. D.; Dorn, W. S. Numerical Methods and Fortran
Programming; Wiley: New York, 1964: PP 144.

36. Naguib, Y. M. A.; Cohen, S. G.; Steel. C. W 1985
101 128

37. P. J. Wagner, P. A. Kelso and R. G. Zeep, mm 1972 14
7480

38. P. J. Wagner unpublished work.

39. N. C. Yang, D. S. McClure, S. L. Murov, J. J. Houser, Ruth Dusenbery,
W196? 8.2 539

40. S. L. Murov, Ph. D. Thesis, Univ. of Chicago, 1966

41. J. N. Pitts, D. R. Burley, J. C. Mani and A. D. Broadbent, W
1968 9.0 5900

42. D. R. Arnoold, “Advances in Photochemistry”, Vol. 6, Wiley, New York,
1968, p. 301.

43. P. J. Wagner, Irene E. Kochevar, and A. E. Kamppainen, MW
1972 21. 7489

44. P. J. Wagner and A. E. Puchalski, W 1980 102 7138

81

45. (a) B. M. Monroe, S. A. Weiner and G. S. Hammond, W

46.
47.
48.

49.
50.
51.
52.
53.
. The Sadtler standard spectra, NMR 2615
55.
56.
57.
58.
59.
60.
61.
62.
63.

1968 2Q 1913

(b) B. M. Monroe, S. A. Weiner, W 1969 91 450
E. A. Lissi, J. C. Scaiano, et al., W 1983 105 1856

R. A. Caldwell, et al., LAW 1985 1QZ 5166
Robert B. Fischer and Dennis G. Peters, ”Quantitative Chemical

Analysis“ W. B. Saunders Company, Philadelphia London Toronto 1968
H. Agahigian, W1963,1L 194

The Aldrich library of NMR spectra p. 921-0.

Lester. A. Brooks, LAW 1944, £5. 1295

Dar'eva and Miklukhin, 4.320420%]. 1959 22, 620 (USSR)

Hanai, W (Japan) 1944 52, 1208

The Sadtler standard spectra, NMR 34

The Sadtler standard spectra, NMR 10188

The Sadtler standard spectra, NMR 13807

The Sadtler standard spectra, NMR 10447

The Sadtler standard spectra, NMR 10243

Dieter. Sebach ME. 1977 1LQLQL 2316

W. A. Mosher, N. D. Heindel, W 1963 23, 2145

Angelo. Clerici and Ombreta. Porta, mm 1985 M12. 80
Peter. Weyerstalh. mm 1982 115 3697

64
65
66
67
68
69

82

. A. Claus, man 15 474

. Angelo. Clerici and Ombretta. Porta, Wham. 1985 m 80
. Rolf. H. Prager._Au§1,_J._thm._1977 fiQLLL 151

. The Sadtler standard spectra, NMR 2629, Grating IR 4714

. The Sadtler standard spectra, NMR 18007, Grating IR 272

. The Aldrich library of NMR spectra p. 923-3

83

APPENDIX

This section contains the raw experimental data from which the
results were obtained. The concentrations of reactants and standards are
listed. The product to standard peak ratios were obtained from gas
chromatographic analysis. The G. C. conditions are given in each table.

The valerophenone actinometry was measured on column DB-1 at 75°

The product yields, given as concentrations, are calculated from the
peak area ratios and the appropriate response factors, which are also listed.
A sample calculation is included in the kinetics and calculation section.
From the product yields and the amount of light absorbed by the samples, as
determined by valerophenone actinometry, the quantum yields were
determined. The quantum yields, the radical ratio, the amount of light
absorbed, the ratio of peak area from analysis, and the G. C. response factor

are listed here.

Table-16: Results for the photoreduction of 0.1 M propiophenone with
acetcphenone pinacol [AH]2 and acetophenone pinacol-d2 [AD]2, measured by

HPLC, flow rate1.0, solvent ratio: 92% hexane with 8% ethyl acetate,
irradiation 3 hours, Ia - 0.31 E/L, SFAPNP- 1.2,

Actinometer: 0.11M valerophenone, 0.0044M y-phenylbuteronitrile

[AH]2(M) Ami-P" [AP1<M) «up
0.010 0.060 0.0033 0.011
0.014 0.77 0.0042 0.013
0.021 1.1 0.0059 0.019
0.10 2.0 0.011 0.036
[AD]2(M)

0.010 0.47 0.0026 0.0083
0.014 0.64 0.0035 0.011
0.020 0.79 0.0043 0.014
0.040 1.2 0.0067 0.022
0.10 1.8 0.0096 0.031

* peak area ratio

85

Table-17: Results for the photoreduction of 0.1 M p-methoxyacetophenone

with acetophenone pinacol [AH]2, measured by HPLC, flow rate1.0, solvent

ratio: 92% hexane with 8% ethyl acetate, irradiation 4.5 hours,
Ia I 0.90 E/L, SFAP/‘y-P‘ 1.2,

Actinometer: o.10M valerophenone, 0.0054M y-phenylbuteronitrile(y-P)

[AH]2(M) AP/y—P“ [AP] (bAp
0.010 1.42 0.0094 0.010
0.022 3.3 0.022 0.024
0.040 4.1 0.027 0.030
0.10 6.7 0.045 0.050

* peak area ratio

86

Table-18: Radical ratio in the reaction of acetophenone (AP) and
propiophenone (PP) with 2-propanol (1 M ) in benzene:
column DB-1 temperature 165°C, C19 - 0.0012M, Ia a 0.020 E/L

SF(AH)2/Cle ' 1-41 SF(AHPH)/C19 " 13: SI:(PH)2/C19 " 1'1
SPAM;11 - 1.7, irradiation 4 hours

 

AP (M) 0.05 0.1 0.5
PP (M) 0.05 0.1 0.5
(AH)2/C19* 2.1 2.4 0.91
(AHPH)/C19* 1.4 1.5 0.85
(PH)2/C19* 0.38 0.24 0.10
(AH)2(M) 0.0045 0.0040 0.0015
(AHPH)(M) 0.0022 0.0023 0.0013
(PH)2(M) 0.00050 0.00031 0.00014
damz 0.18 0.20 0.075
¢(AHPH, 0.11 0.12 0.055
0(pH,2 0.025 0.015 0.0065
~AHl-PH 2.9 3.4 2.8

 

* peak area ratio
VP - 0.11(M), C11 = 0.0013(M), AP/C“ = 3.3, 3.2, 2.4, 2.4.

87

Table 19: Radical ratio in reaction of acetophenone and
propiophenone with 2-propanol (1M ) in benzene,
column DB-1 temperature 165°C, C13 - 0.00099M, I,1 a 0.021 E/L

SF(AH)2/C18 " 12: SF(AHPH)2/018 ' 1-1» SF(PH)2/c18 " 10»
SFAWC11 - 1.7, irradiation 5 hours.

 

AP (M) 0.1 0.2 0.3
PP (M) 0.1 0.2 0.3
(AH)2/C,3* 2.8 2.2 2.0
(AHPH)/C,8* 1.8 1.3 1.1
(PPH)2/C,3* 0.29 0.21 0.19
(AH)2(M) 0.0033 0.0026 0.0024
(AHPH)(M) 0.0020 0.0014 0.0010
(PH)2(M) 0.00024 0.00019 0.00018
chum, 0.16 0.12 0.11
chomp“, 0.0093 0.068 0.064
¢,p,,,2 0.013 0.0093 0.0088
-AHflPH 34 36 36

 

VP - 0.11(M), c,, - 0.015(M), AP/c,1 =- 0.27, 0.29,
0,, - 0.014(M), AP/c,, - 0.28, 0.27.

* peak area ratio

88

The radical ratio of two ketones with different concentrations of
2-propanol was measured to ensure no effect for radical ratio from
varied concentrations of hydrogen donor.

Table-20: Radical ratio in reaction of (0.1M) acetophenone and
(0.2M) propiophenone with different concentrations of 2-propanol in

benzene: column DB-1 temperature 165°C, C13 - 0.0011M, Ia - 0.012 E/L

SF(AH)2/C18 ' 121 SF(AHPH)2/C18 I 1.1, SF(PH)2/C18 I 1.0, SFAP/Cll = 1.7,
irradiation 5 hr.

 

2-Prop (M) 1 0 1 5 21
(AH)2/C,8* 0.70 0.73 0.77
(AHPH)/C,8* 0.90 0.94 0.99
(PH)2/C18* 0.28 0.30 0.31
(AH)2(M) 0.00092 0.00096 0.0010
(AHPH)(M) 0.0011 0.0011 0.0012
(PH)2(M) 0.00029 0.00031 0.00032
(Dwm 0.072 0.076 0.080
chm“, 0.0848 0.0884 0.0926
<0,p,,,2 0.024 0.025 0.026
-AH/-P H 1.74 1.74 1.74

 

VP - 0.11(M), c,, = 0.016(M), AP/c,, = 0.14, 0.14, 0.13, 0.14.

* peak area ratio

89

 

Table-21: Radical ration for reaction of acetophenone and p-
chloroacetophenone with (1M) 2-propanol in benzene:
Column DB-1, temperature 175°C, C18 - 0.00055M, Ia =- 0.015 E/L
SF(AH)2IC18 ' 1-2- SF(CIAHAH)2/C18 ' 13» SF(CIAH)2/018 ' 1.4.
SFAP/C11 - 1.7, irradiation 5.5 hr.
AP (M) 0.05 0.10 0.15 0.2 0.24
CIAP (M) 0.05 0.10 0.15 0.2 0.24
(AH)2/C, 8* 0.062 0.033 0.031 0.026 0.023
(ClAHAH)/C,8* 0.65 0.67 0.67 0.61 0.57
(CIAH)2/C,8* 1.4 1.5 1.5 1.4 1.3
(AH)2(M) 0.000041 0.000022 0.000020 0.000017 0.000015
(ClAHAH)(M) 0.00046 0.00047 0.00047 0.00044 0.00040
(CIAH)2(M) 0.0011 0.0012 0.0012 0.0011 0.0010
(D(APH)2 0.0027 0.0015 0.0014 0.0011 0.0010
¢(CIAHAH) 0.033 0.031 0.031 0.029 0.0027
‘D(c1AH)2 0.067 0.08 0.08 0.073 0.067
-ClAH/-AH 4.3 5.6 5.6 5.5 5.5

 

VP - 0.1(M), c,, .. 0.0017(M), AP/c,, - 0.51, 0.52, 0.52, 0.51.

* peak area ratio

90

Table-22: Radical Ratio for reaction of acetophenone and p-

methylacetophenone with 1M 2-propanol in benzene,
Column DB—1, temperature 170°C, C13 - 0.00034M,

 

SF(AH)2/C18 = 12» SF(AHMH)2IC18 ' 1-3: SF(MH)2/C18 = 1-4-
AP (M) 0.05 0.10 0.15 0.25 0.45
MeAP (M) 0.05 0.10 0.15 I 0.25 0.45
011196,; 3217 """""" 1 '1} """"" 1 I; """" 6'87
(MeAHAH)/C,8* 2.0 0.95 0.99 0.91 0.48
(MeAH)2/C,8* 0.13 0.043 0.054 0.056 0.033
(APH)2(M) 0.0013 0.00065 0.00067 0.00051 0.00031
(MBAHAHXM) 0.00088 0.00041 0.00043 0.00043 0.00025
(MBAH)2(M) 0.000062 0.000020 0.000026 0.000027 0.000016

-AH/-MeAH 3.4

3.8 3.6 2.9 3.0

 

* peak area ratio

91

Table-23: Radical Ratio in reaction of acetophenone with different
ketones and 1M 2-propanol in benzene, irradiation 5.5 hr,
Column DB-1,Temperature 170°C, C13 - 0.00044M, SFAPK;11 - 1.7,
SF(AH)2/C18 = 1-2- SF(AHMH)2/Ct8 ' 13: SF(MH)2/C18 ' 1-4: SF(CIAHAH)2/C18 =

12. SF(CIAH)2/C18 = 1-4. SF(BHAH)2/018 ' 1-15: SF(isBH)2/Ct8 = 1-1»

 

AP (M) 0.10 0.15 0.2 0.30
CIAP (M) 0.05 0.05 0.1 0.10
M276; """" .TéJMMmglé """""" 6.2; """"" . 67""
(ClAHAH)/C,8* 1.0 1.3 1.2 1.1
(CIAH)2/C, 3* 1.1 0.75 1.2 0.74
[AH]2(M) 0.0001 1 0.00022 0.00013 0.00019
[AHCIAH](M) 0.00053 0.00069 0.00063 0.00058
[CIAH]2(M) 0.00068 0.00046 0.00074 0.00046
~ClAH/-AH (k9) 2.5 1.4 2.4 1.6

confinue

92

 

 

AP (M) 0.05 0.05 0.10 0.10

MeAP (M) 0.10 0.15 0.20 0.30
(AH)2/C,3* 0.79 0.53 0.75 0.43
(MeAHAH)/C, 3* 1.1 0.91 1.1 0.80
(MeAH)2/C,8* 0.34 0.34 0.15 0.30
(AH)2(M) 0.00040 0.00027 0.00038 0.00022
(MeAHAH)(M) 0.00063 0.00052 0.00063 0.00042
(MeAH)2(M) 0.00021 0.00021 0.000092 0.00018
-AH/-MeAH (kg) 1.4 1.1 1.6 1.1

AP (M) 0.05 0.05 0.10 0.10
isBP(M) 0.10 0.15 0.20 0.30
(AH)2/C,8* 3.5 2.5 3.6 2.5
(isBHAH)/C,8* 1.5 1.9 1.7 1.8
(isBH)2/C,3* 0.13 0.23 0.14 0.24
(AH)2(M) 0.00018 0.00013 0.00019 0.00013
(isBHAH)(M) 0.00076 0.00096 0.00086 0.00091
(isBH)2(M) 0.000063 0.00011 0.00068 0.00012
-AH/-isBH (kg) 4.9 3.0 4.6 3.1

 

* peak area ratio

93

Table-24: Quantum yields for acetophenone (AP) formation as a
function of propiophenone concentration in benzene: Ial - 0.0161 E/L,
lrr. 3.5 hous, Column DB-210,Temperature 60°C, 10 min, 170°C, 5 min,
SFNWC11 - 1.7, SFAM;12 - 1.8, C,2 = 0.0016M, (AH2) - 0.2 M.
Before irradiation, the sample containing 2X10'4M acetophenone, the

calculation was done by subtracting starting AP from each sample.

 

PP(M) 0.0060 0.017 0.025 0.050 0.10 0.15

A 0.40 0.95 1.34 >2 >2 >2

T a@ 0.60 0.89 0.95 1 1 1
IaTa 0.0097 0.014 0.015 0.016 0.016 0.016
AP/C 12* 0.36 0.70 0.81 0.97 1.03 1.0
AP(M) 0.00077 0.0018 0.0021 0.0026 0.0027 0.0028
A°/AP 20% 10% 9% 7% 7% 7%
(DAP 0.080 0.13 0.14 0.16 0.17 0.17

 

VP - 0.10(M), c,, = 0.0017(M), AP/c,, = 0.57, 0.58, 0.57.

* peak area ratio , @ percentage of light absorbed

94

Table-25: Quantum yield and radical ratio for reaction of
propiophenone with 0.2M 1-phenylethanol in benzene:
Column DB-210,Temperature 60°C, 10 min, 170°C, 5 min,for AP and PH2,
Column DB-1, Temperature 175°C, for pinacols,
C12 - 0.0016M, 0,3 - 0.00080M, SFAP/Clz - 1.8, SFpH2,C,2 - 2.3,

SF(AH)2/C18 '12. 3F(AHPH)/C1e '1-1. SF(PH)2/C18 ‘1-0» SFAP/Cll =1-7-

 

PP(M) 0.00601 0.0170 0.0251 0.0501 0.100 0.150

PHz/cm' 0.012 0.034 0.053 0.068 0.085 0.070

PH2(M) 0.000044 0.00013 0.00020 0.00025 0.00031 0.00026

<0sz 0.0028 0.012 0.013 0.016 0.020 0.017
<I>AP 0.079 0.12 0.14 0.16 0.17 0.17
(AH)2/C,3* 0.13 0.11 0.038 0.019 - -
(AH Pl-l)/C,8* 0.49 0.69 0.67 0.56 0.36 0.27
(PH)2/C,8* 0.51 1.2 1.6 2.2 2.3 2.2

(AH)2(M) 0.00013 0.00011 0.000036 0.000018 - -
(AHPH)(M) 0.00043 0.00061 0.00059 0.00049 0.00032 0.00024
(PH)2(M) 0.00038 0.00090 0.0012 0.0016 0.0017 0.0016
chum“, 0.0076 0.0062 0.0022 0.0011 _ -
(D‘AHPH) 0.036 0.035 0.034 0.029 0.018 0.014
c,,-MPH) 0.023 0.057 0.073 0.10 0.11 0.10

 

* peak area ratio

95

Table-26: Quantum yields of acetophenone as afunction
of 1-phenylethanol concentration with 0.05 M isobutyrophenone in
benzene:

Column DB-210,Temperature 60°C, 10 min, 170°C, 5 min, irradiation 8 hr,
C12 - 0.0024M, SFAFVC12 = 1.8, SFAp/Cll = 1.7, Ia= 0.022E/L

 

(AH2)(M) AP/Cm' AP(M) (PAP
1.00 1 7
1 .70 0.0073 0.33
0.33 1.2
1.2 0.0050 0.23
0.20 0.94
0.92 0.0040 0.18
0.13 0.77
0.78 0.0033 0.15
0.11 0.64
0.63 0.0027 0.12

 

VP = 0.1, c,, = 0.00071, AP/C,, = 5.8, 5.9, 5.8, 5.9.

* peak area ratio

function of isobutyrophenone concentration in benzene:

Column DB-210:

Table-27: Quantum yields for acetophenone (AP) formation as a

Temperature :

60°C, 10 min,

(AH2) = 0.2 M

170°C, 5 min,
C12 - 0.0011M, SEN/C12 .. 1.8, sap/c,, - 1.7, irradiation 3.5 hr, Ia=

 

0.014E/L

isBP(M) 0.0071 0.010 0.016 0.025 0.050

L. """"" A... """"" A... """"" A .6; """"" J.;. """"" 8""
Ta@ 0.67 0.77 0.89 0.97 1

Tax, 0.0090 0.011 0.012 0.013 0.014
AP/C,2* 0.43 0.55 0.69 0.83 0.91
AP(M) 0.00086 0.0011 0.0014 0.0017 0.0018
0),. 0.096 0.11 0.12 0.13 0.14

 

VP = 0.1, c,, = 0.0033, AP/c,, = 0.77, 0.79, 0.78, 0.78.

* peak area ratio, @ percentage of light absorbed

Table-28:

Quantum yield

97

and

radical ratio

isobutyrophenone with 0.2M 1-phenylethanol in benzene:
Column DB-210,Temperature 60°C, 10 min, 170°C, 5 min,for AP and 8H2,

Column DB-1,

Temperature 175°C, for pinacols,

I, =- 0.014E/L
0,2 = 0.0011M, 0,8 = 0.00039M, SPAM12 .. 1.8, SFBH,,C,2 = 1.5,

SF(AH)2/C18 = 12. SF(AHBH)/Cta = 1-15. 3F(iseH)2/C18 = 1-1-

for reaction of

 

0.025

0.050

isBP(M) 0.0071
BH2/C,2 0.11
BH2(M) 0.00018
(D3142 0.013
(DAp 0.096
(AH)2/C18* 0.24

(AHBH)/C,8* 1.0
(iSBH)2/C18* 10

(AH)2 (M) 0.00011
(AHBH)(M) 0.00045
(isBH)2(M) 0.00043
(Dawn) 0.012
$001311) 0.050
(b(BHBH) 0.048

0.0100 0.016
0.12 0.11
0.00024 0.00022
0.014 0.014
0.097 0.12
0.24 0.079
1 .1 1 .1
1 .3 1.7
0.0001 1 0.000036
0.00049 0.00049
0.00056 0.00073
0.010 0.0030
0.045 0.041
0.051 0.061

0.17
0.00028
0.021
0.13
0.12
0.96

1.9
0.000053
0.00043

0.00082

0.0041

0.033
0.063

0.16

0.00026
0.019
0.14
0.30
2.0
0.00013
0.00086

0.0096
0.061

 

* peak area ratio

98

Table-29: Quantum yields of acetophenone as a function of
1-phenylethanol concentration with 0.05 M p-methylacetophenone in

benzene:
Column DB—210,Temperature 60°C, 10 min, 170°C, 5 min, Ia =0.022 E/L

C12 8 0.0041M, SFAP/Clz = 1.8, SFAP/C11 = 1.7, irradiation 8 hrs

 

(AH2) AP/C,2* AP <0”,
- ( M) ------------------------------------ (M) -----------------------
0.10 0.30

0.29 0.0022 0.099
0.13 0.34

0.33 0.0025 0.11
0.20 0.42

0.41 0.0031 0.14
0.33 0.50

0.48 0.0036 0.17
1.0 0.61

0.60 0.0045 0.21

 

VP .. 0.1, c,, .. 0.00077, AP/c,, = 5.7, 5.4, 5.5, 5.3.

* peak area ratio,

99

Table-30:

function of p-methylacetophenone concentration in benzene: (AH2) :- 0.2 M

Quantum yields for acetophenone (AP) formation as a

Column DB-210,Temperature 60°C, 10 min, 170°C, 4 min,
C12 3 0.0031M, SFAP/Clz - 1.8, SFAP/Cll - 1.7, irradiation 4 hr, Ia =0.022

E/L

 

MeAP A Ta@ Tax, AP/C,2" AP

- ( M ) --------------------------------------------------------- ( M ) - - -
0.0051 0.38 0.58 0.013 0.13 0.00072
0.0071 0.54 0.71 0.015 0.18 0.0010
0.010 0.76 0.83 0.018 0.25 0.0014
0.016 1.2 0.94 0.020 0.34 0.0019
0.025 1 .8 0.98 0.021 0.38 0.0021
0.051 >2 1 0.022 0.41 0.0023

 

VP - 0.1, c,, - 0.0016, AP/c,, - 2.7, 2.6, 2.7, 2.7.

* peak area ratio, @percentage of light absorbed

100

Table-31: Quantum yield and radical ratio for reaction of
p-methylacetophenone with 0.2M 1-phenylethanol in benzene:
Column DB-210,Temperature 60°C, 10 min, 170°C, 4 min,for AP and MHZ,
Column DB-1, Temperature 175°C, for pinacols,

0,2 - 0.0031M, c,,, = 0.00032M, SFAP,C,, -1.8, SFMH2,C,2 = 1.4,

SF(AH)2/018 - 12. SF(AHMH)/Cta - 13. SF(MH)2/C18 = 1-4

 

MeAP(M) 0.0051 0.0071 0.010 0.016 0.025 0.051

I, 0.013 0.015 0.018 0.020 0.021 0.022
MHz/012* 0.0073 0.012 0.017 0.024 0.032 0.035
MH2(M) 0.000030 0.000050 0.00007 0.00010 0.00013 0.00015
<I>MH2 0.0024 0.0032 0.0038 0.0050 0.0063 0.0067
<I> AP 0.057 0.067 0.079 0.092 0.099 0.1 1
(AH)2/C,3* 0.45 0.34 0.26 0.39 - -
(AHMH)/C,8* 1.8 1.3 0.59 0.78 0.55 0.38
(MH)2/C,8* 0.70 1.3 2.2 3.4 3.7 4.5

(AH)2(M) 0.00017 0.00013 0.00010 0.00015 - -
(AHMH)(M) 0.00069 0.00054 0.00025 0.00032 0.00023 0.00016

(M H)2(M) 0.00031 0.00058 0.00099 0.0015 0.0017 0.0020
¢(AH)2 0.013 0.0098 0.0053 0.0048 - -
<I>(AHMH) 0.053 0.036 0.014 0.016 0.011 0.0073
<I>(MHMH) 0.024 0.039 0.055 0.076 0.079 0.092

 

* peak area ratio

101

Table-32: Quantum yields of p-chloroacetOphenone formation as
a function of 1-(4'-chlorophenyl) ethanol concentration with 0.05 M
acetophenone in benzene: Column DB-210,Temperature 60°C,4 min,
Temperature 95°C, 8 min, 170°C, 3 min, C17 - 0.0079M, SFCIAWCI, :- 2.2,
SFAP/011 = 1.7, irradiation 8.5 hr, Ia - 0.0135 E/L

 

CIAH2 CIAP/017* CIAP chow,
- ( M) ------------------------------------ ( M) ------------------------
0.1 0.089
0.086 0.0015 0.11
0.13 0.11
0.10 0.0018 0.14
0.2 0.14
0.14 0.0023 0.17
0.33 0.18
0.18 0.0030 0.22
1.0 0.23
0.23 0.0040 0.29

 

VP = 0.1, c,, = 0.0013, AP/c,, - 2.0, 2.1, 1.9, 2.0.

* peak area ratio

102

Table-33: Quantum yields for p-chloroacetophenone (CIAP) formation

as a function of acetophenone concentration in benzene:

(CIAHZ) = 0.2 M,

Ia - 0.0146 E/L Column DB-210,Temperature 60°C,8 min, Temperature

95°C, 8 min, 170°C, 3 min, C17 - 0.0078M, SFCIAp/Cl7 - 2.2, SFAPK;11 - 1.7,

irradiation 5.5 hr.

 

(AP) A Ta@ Tax, CIAP/C,7* CIAP
- ( M) ---------------------------------------------------------- ( M ) - -
0.0071 0.50 0.68 0.0099 0.046 0.00078
0.010 0.68 0.79 0.012 0.068 0.0011
0.013 0.84 0.85 0.013 0.082 0.0014
0.016 1.0 0.91 0.014 0.095 0.0016
0.025 1.4 0.96 0.014 0.12 0.0020
0.051 >2 1 0.015 0.15 0.0025
0.10 >2 1 0.015 0.15 0.0026

 

VP = 0.1, c,, = 0.0016, AP/c,1 = 1.7, 1.8, 1.9, 1.8.

* peak area ratio, @ percentage of light absorbed

103

Table-34: Quantum yield and radical ratio for reaction of

acetophenone with 0.2M 1-(4'-chlorophenyl) ethanol in benzene:
Column DB-210, for CIAP and AH2, Column DB-1, for pinacols,

0,6. - 0.0035M, c,7 - 0.0079M, c,8 - 0.00053M, SFC.AP,C,., - 2.2,
SFAHz/C16' - 2-1. SF(AH)2/C18 '1-2. SF(AHCIAH)/C18 '1-2. SF(CIAH)2/Cte - 1-4

 

AP(M) 0.0079 0.010 0.013 0.016 0.025 0.051 0.10

Ia 0.0099 0.012 0.012 0.013 0.014 0.015 0.015
AH2/Cb,6* - - - 0.0033 0.0051 0.0074 0.011
AH2(M) - - - 0.000024,0.000037,0.000054,0.000081
(PAH, - - - 0.0019 0.0027 0.0037 0.0054
chomp 0.084 0.98 0.11 0.12 0.14 0.17 0.18

(AH)2/C,3* 0.82 0.88 1.0 1.4 1.8 2.4 3.0
(AHCIAH)/C18* 0.59 0.60 0.52 0.57 0.51 0.38 0.25

(AH)2(M) 0.00052 0.00056 0.00064 0.00089 0.0011 0.0015 0.0019

(AHCIAH)(M)0.00038,0.00038 0.00033 0.00036 0.00032 0.00024,0.00016
cm“), 0.051 0.047 0.049 0.065 0.079 0.10 0.13

(DMHCMH) 0.038 0.032 0.028 0.028 0.023 0.016 0.011

 

*peak area ratio

104

Table-35: GC Response Factors

 

Compounds Standard Condition SF
acetophenone 9-butyrophenyl-
acetonitrile HPLC 1 .2
dodecane(C,2) # 2- 60°C 1.8
undecane(C11) # 1- 75°C 1.7
1-phenylpropanol dodecane (C12) # 2- 60°C 2.4

1-phenylethanol 2,2,4,4,6,8,8-heptamethyl-

nonane (C161) # 2- 60°C 2.1

isobutyrobenzyl alcohol dodecane (C12) # 2- 60°C 1.5

p-chloroacetophenone Heptandecane(C,7) # 2— 95°C 2.2
1-(4'-methy|phenyl)

ethanol dodecane (C, 2) # 2— 60°C 1.4

acetophenone pinacol octadecane(C,3) #1- 175°C 1.2

nonadecane(C,9) #1- 175°C 1.4

conflnue

propiophenone pinacol

CIAP pinacol

MeAP pinacol

isBP pinacol

105

octadecane(C, 8)

nonadecane(C, 9)

octadecane(C, 3)

octadecane(C,3)

octadecane (C18)

#1- 175°C

#1- 175°C

#1- 175°C

#1- 175°C

#1- 175°C

1.0

1.1

1.4

1.4

1.1

”ililliliillliilli