Title: Migratory aptitudes in the elimination-rearrangement reactions of 1, 1-diaryl-2-bromoethylenes
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Permanent Link: http://ufdc.ufl.edu/UF00097965/00001
 Material Information
Title: Migratory aptitudes in the elimination-rearrangement reactions of 1, 1-diaryl-2-bromoethylenes
Physical Description: v, 66 l. : illus. ; 28 cm.
Language: English
Creator: Damico, Ralph Anthony, 1935-
Publisher: s.n.
Place of Publication: Gainesville
Publication Date: 1962
Copyright Date: 1962
Subject: Ethylene dibromide   ( lcsh )
Chemistry thesis Ph.D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: l. 63-65.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00097965
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000423943
oclc - 11035136
notis - ACH2348


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Migratory Aptitudes in the Elimination- Rearrangement

Reactions of 1, 1-Diaryl-2-Bromoethylenes




February, 1962


The author wishes to express his gratitude to the faculty

members of the Chemistry Department, especially those persons who

served on his graduate committee, and to his student associates

for their many helpful suggestions and advice.

He is especially indebted to Dr. W. M. Jones, Chairman of

the author's supervisory committee, for his advice, assistance and


The author also wishes to thank Miss Jan Brockett for typing

and drawing the figures of this dissertation, and Texaco, Inc., for

their financial assistance.









A. Syntheses and Reactions

B. Spectra . . . .

C. Kinetic Methods . .

D. Dipole Moments . . .

RESULTS . . . . .


SU Y . . . . .

REFERENCES . . . . .


. . . . . . . 1

. . . . . . . 4

. . . . . . . 13

. . . . . . . 23

. . . . . . . 27

. . . . . . . 31

. . . . . . . 43

. . . . . . 62

. . . . . . . 63

. . . . . . . . . . . 66








Table Page

1. Data for the calculation of cis-l-p-chlorophenyl-1-
phenyl-2-brmnoethylene in trans-l-p-chlorophenyl-1
phenyl-2-brmnoethylene . . . . . . . . 9

2. Absorption Maxima of Compounds Used in Kinetic Measure-
ments . . . . . . . . . . . . 19

3. Extinction Coefficient Determination for 1-p-Methoxy-
phenyl-2-phenylacetylene . . . . . . . . 20

4. Extinction Coefficient Determination for trans-l-p-
Methoxyphenyl-l-phenyl-2-broaoethylene . . . .. 20

5. Extinction Coefficient Determination for cis-l-p-
Methoxyphenyl-l-phenyl-2-bromoethylene . . . . 21

6. Extinction Coefficient Determination for 1-p-Chloro-
phenyl-2-phenylacetylene . . . . . . . . 21

7. Extinction Coefficient Determination for Diphenylacety-
lene . . . . . . . . . . . . . 22

8. Quantitative Analysis of 1,1-Diphenyl-2-brcnoethylene
and Diphenylacetylene Mixtures by Vapor-phase Chraooto-
graphy . . . . . . . . . . . . 26

9. Data for the Determination of Dipole Moments of cis-
and trans-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene . 32

10. Kinetic Data for the Reaction of trans-l-p-Methoxy-
phenyl-l-phenyl-2-bromoethylene with 0.20 M Potassium-
t-butoxide at 950 . . . . . . . . . 37

11. Summary of Kinetic Data for the Reactions of 1,1-
Diaryl-2-bromoethylenes (EH) with Potassium-t-butoxide
(KB) at 950 . . . . . . . . . . 38

12. Average Rate Constants of the Reactions of 1-Phenyl-
1-p-substituted Phenyl-2-bramoethylenes with 0.20 M
Potassium-t-butoxide . . . . . . . . . 52


Figure Page

1. Determination of o0 for cis- and trans-1-p-
Methoxyphenyl-1-phenyl-2-bromoethylene . . . 33

2. Determination of 6/ for cis- and trans-i-p-
Methoxyphenyl-1-phenyl-2-bromoethylene . . . 34

3. Reaction of trans- and cis-1-j-Methoxyphenyl
1-phenyl-2-bromoethylene with 0.197 M Potas-
sium-t-butoxide at 950 . . . . . . .. 40

4. Comparison of Rate Constants of 1,1-Diaryl-2-
bromoethylenes at 0.20 M Potassium-t-butoxide . 41



The elimination and rearrangement reactions of 1,1-diaryl-2-

haloethylenes with strong bases to yield diarylacetylenes (tolans)

was first reported by Fritsch [l1, Buttenberg [2 and Wiechell [3 .

\ /
C = C + B~ -- AR -C=C- AR + BH + X-
/ \

They used ethanolic solutions of sodium ethoxide at 180-200o

to promote reactions. More recently, potassium amide in liquid am-

monia [4,5 butyl- and phenyl-lithium in ether 6,7 and potassium-

t-butoxide in t-butyl alcohol [8,9] have been used to produce high

yields of tolans. Due to the general base initiation, the first step

in the reaction is believed to be the abstraction of a proton to form

the diaryl vinyl anion.

\ / \
C =C + B -*- C ==C- + BH
/ \ / \

Curtin and Flynn [7] have proposed this to be the rate deter-

mining step in their system in which they used butyl-lithium as the

base, while Pritchard and Bothner-By [9] have shown it to be a rapid

equilibrium reaction under their conditions with potassium-t-butoxide.

The rearrangement step has been shown to be stereospecific.

In the reaction of cis- and trans-l-p-bromophenyl-l-phenyl-2-bromoethy-

lene with potassium-t-butoxide, the group trans to the leaving bromide

ion migrates preferentially [8]. Cis- and trans-l-p-chlorophenyl-1-

phenyl-2-bromnoethylene rearranges similarly when promoted by butyl-

lithium [10|. These results exclude the possibility of a carbene

being involved in the major reaction and strongly suggest a geometri-

cally stable vinyl carbanion as an intermediate in the reaction.


c =-C: C =C-
/ / \
Ar AR Br
Carbene Carbanion

The effect of the leaving halogen on the rate of the reaction

is known [8]. The purpose of our work was to make a kinetic study

of the migratory aptitudes of phenyls containing various substituents.

For this purpose the cis and trans isomers of 1-2-methoxyphenyl-l-

phenyl-2-bromoethylene (cis- and trans-I), 1-p-chlorophenyl-l-phenyl-

2-bromoethylene (cis- and trans-II) and 1,1-diphenyl-2-bromoethylene

(III) were prepared. Dipole moment studies were also undertaken to

determine the configurations of the high and low melting isomers of


Potassium-t-butoxide-t-butyl alcohol was chosen as our reac-

tion medium for several reasons. Proton transfer is known to be a

rapid step under these conditions [91 leading to the presumption that

substituted phenyl groups will change the rate of the reaction as

compared to phenyl groups. Few, if any, side reactions occur with

this base and relatively simple analysis of products can be obtained.



A. Syntheses and Reactions


This compound was prepared by adapting the method used by

Nielson and McEwen 1n] in the preparation of a similar compound.

Twenty-four grams (1 mole) of magnesium was placed in a three-necked

one-liter flask equipped with a reflux condenser and a stirrer.

Seventy-eight grams (0.5 mole) of dry, freshly distilled bromoben-

zene in 200 ml. of dry ether was added dropwise over a two-hour

period. The reaction started with stirring after a few milliliters

of bromobenzene had been added. The reaction mixture was then re-

fluxed for one hour, cooled, and 50 g. (0.32 mole) of p-methoxy-

acetophenone in 50 ml. of dry ether added over one hour. After re-

fluxing for one hour the reaction mixture was hydrolyzed with 30 g.

(0.565 mole) of ammonium chloride in 60 ml. of water. The organic

and aqueous layers were separated and the aqueous layer extracted with

ether. The organic layers were combined. The ether was removed by

distillation and 100 ml. of 20 percent sulfuric acid was added to the

cooled mixture. After refluxing for one hour the organic layer was

separated. Yellow crystals appeared upon cooling the organic layer.

Recrystallization from 95 percent ethanol* gave 40.8 g. (0.178 mole,

*Ninety-five percent ethanol will be called ethanol in this text.

55.5 percent) of white crystals, melting point* 74-76o (lit. [12] 750).

Repeating this experiment under essentially the same conditions af-

forded a yield of 53 percent.

cis- and trans-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene (cis- and


Thirteen grams (0.064 mole) of 1-p-methoxyphenyl-l-phenyl-

ethylene was brominated with 10.5 g. (0.065 mole) of I-ronine in 50 ml.

of carbon disulfide. The addition took forty-five minutes and was

allowed to reflux with no aid. Hydrogen bromide was liberated after

about 20 ml. of the bromine solution had been added. The mixture

was then refluxed overnight. Carbon disulfide was removed by distil-

lation and the residual oil dissolved in ethanol. White crystalline

needles were obtained upon cooling. These were removed and the solu-

tion set aside for one week, during which time more crystals came out

of solution. A total of 4.45 g. (0.015 mole, 23.4 percent) of the

trans** isomer was obtained. These were recrystallized from ethanol,

m.p. 81-82o (lit [12] 82.50)

The resultant filtrate, from which the trans isomer had been

removed, was passed through a 1 x 30 cm. column of alumina eluting

with ethanol. Twenty milliliter samples were collected and allowed

to evaporate at room temperature. Yellow oil and white crystalline

flakes came out of solution and were separated by filtering.

*All melting points and boiling points are uncorrected.
**The trans configuration was assigned by Stoermer and Simon 12
and confirmed by dipole moment measurement (see discussion) by the author.

Recrystallizing the white crystals from ethanol gave 1.05 g. (0.0036

mole, 5.5 percent) of cis isomer, m.p. 55-560 (lit. [12] 520).


1,1-diphenylethylene was prepared according to the method of

Allen and Converse [13].


The bromination of 1,1-diphenylethylene was performed using

the procedure of E. Hepp [14 .

The product was recrystallized from methanol to yield very

white crystalline flakes, m.p. 42-430 (lit. [14] 400).


This compound was prepared using a modification of Curtin's

[10] procedure. Seventy-two grams (3 moles) of magnesium was placed

in a dry two-liter three-necked flask. Approximately 143 g. (1.5

moles) of methyl bromide in 500 ml. of dry ether was added over three

hours. The reaction was allowed to reflux without external heating.

At the end of this time an ether suspension of 150 g. (0.695 mole)

of p-chlorobenzophenone was added in small portions. The reaction

was refluxed for two hours and then hydrolyzed with 53.5 g. (1 mole)

of ainonium chloride in 200 ml. of water. After separating the

layers and washing the organic layer with water, the ether was re-

moved by distillation and the resultant carbinol was dehydrated with

200 ml. of 20 percent sulfuric acid. After separating the organic

and aqueous layers the organic layer was dried and the remaining oil

fractionated under reduced pressure through a 6-in. column packed with

glass helicies. One hundred grams (0.45 mole, 66.5 percent) of 1-p-

chlorophenyl-l-phenylethylene, b.p. 151-158o (5-8mm.) lit. [10j b.p.

153-158o (10 mm.), was obtained.

cis- and trans-l-r-Chlorophenyl-l-phenyl-2-bromoethylene (cis- and


Fifty grams (0.232 mole) of 1-r-chlorophenyl-l-phenyl-ethylene

was brominated with 44.2 g. (0.245 mole, 6 percent excess) of bromine

in 200 ml. of carbon tetrachloride at room temperature. The mixture

was refluxed for eighteen hours to eliminate hydrogen bromide. After

stripping off the carbon tetrachloride more hydrogen bromide was

evolved during the distillation of the mixture. The resultant oil

was then refluxed with 14 g. (0.25 mole) of potassium hydroxide

dissolved in 100 ml. of absolute alcohol. After refluxing for one

hour, water was added and two layers separated. The water layer was

extracted with ether and the organic layers combined and dried with

anhydrous sodium sulfate. The ether was removed on a steam-bath

and the remaining oil fractionated through a 6-in. column packed

with glass helices. The middle fraction was collected, b.p. 149-155o

(1-1.3 mn.), to yield a total of 49 g. (0.167 mole, 72 percent) of

colorless liquid. On standing at room temperature white crystals

formed. These were removed and the filtrate allowed to remain one

week in the refrigerator. The crystalline product was recrystallized

from ethanol, m.p. 88-89O (lit. [10] 88-890), and has the cis con-

figuration as assigned by Bergmann 15].

The remaining filtrate was then redistilled and a slightly

yellow oil collected, b.p. 155-157o (1-1.3 mm). Infrared spectra in-

dicated this product had not more than 30 percent of cis-II as an im-

purity (Table 1). This was made on the basis of the absorption at

723 ca71 where the cis isomer has a strong absorption. Attempts to

crystallize the oil from pentane both before and after passage through

an alumina column proved fruitless (lit. [15 m.p. 43-44o).

Analysis: Calculated for C14H10BrCl: C,57.27; H, 3.43.

Found: C, 57.45; H, 3.29


Diphenylacetylene was prepared according to the method de-

scribed in Organic Syntheses [16].


This compound was obtained impure using a modification of the

method of Orekhoff and Tiffeneau 17 .

To an ether solution of benzyl magnesium chloride, prepared

from 22.4 g. (0.18 mole) of benzyl chloride and 3.4 g. (0.14 mole)

of magnesium, 14 g. (0.10 mole) of p-methoxybenzaldehyde was added

over thirty minutes. The solution was refluxed for one hour, cooled,

and hydrolyzed with 40 ml. of saturated ammonium chloride solution.

The ether and water layers were separated, the water layer extracted

with ether and the organic layers combined. The ether was allowed

to evaporate and the residual oil was then dehydrated with 50 ml. of



Concentration of
cis-II in

Optical Density
(723 cm.-1)

Cell Width


1.14 x 10-1

9.00 x 10-2

7.89 x 10-2

1.85 x 10-la

a impure trans-II isomer.

Extinction Coefficient = EAvg.= 44.1

Maximum Amount of cis-II in trans-II

+ 2.0 liters/mole-cm.

= 0.120/(42.1)(0.0518) = 0.0551

Maximum Percent of cis-II in trans-II = (0.0551/0.185)(100) = 29.8












30 percent sulfuric acid. After refluxing for fifteen hours the

mixture was poured into ice water and pale yellow crystals separated.

These were recrystalized from ethanol, m.p. 125-130o (lit. 17]

137-1380). This product was assumed to be 1-k-methoxyphenyl-2-


Six grams (0.028 mole) of this product was brominated with

4.5 g. (0.028 mole) of bromine in 100 ml. of chloroform for forty-

five minutes at room temperature. After the addition was completed

the chloroform was removed on a steam-bath and a red solid resulted.

A total of 7 g. (0.19 mole, 67.7 percent) of 1-p-methoxyphenyl-2-

phenyl-1, 2 dibromoethane was obtained, m.p. 170-1750 (lit. 17]


In order to effect the elimination of two moles of hydrogen

bromide from this compound a variety of bases were used. Two and

one-half grams (6.7 moles) of the dibromo compound was refluxed

for five hours with 1.85 g. (13.4 mmoles) of potassium carbonate

in 75 ml. of water. The reaction mixture was then cooled and a reddish-

ycllow oil separated. The oil was dissolved in ether. After drying

with anhydrous sodium sulfate the ether was removed and ethanol added

to crystallize the oil. A small amount of yellow-red solid separated,

m.p. ) 1800 (lit. [17] 89-90o).

Potassium hydroxide in absolute ethanol, sodium hydroxide

melt, and potassium hydroxide melt were tried to obtain the 89-90o

product. In all cases a reddish colored oil was recovered. Adding

ethanol resulted in two solids, a yellow solid soluble in hot ethanol

and a red solid insoluble in hot ethanol. The yellow solid had a

melting range from 60 to 1000, with most of the solid melting about

60. The infrared spectrum of this compound was identical to the

spectrum of the product (m.p. 57-58o) obtained from the reaction of

trans-l-2-methoxyphenyl-l-phenyl-2-bromoethylene (trans-I) with po-

tassium-t-butoxide (described later) except for the absorptions at

965, 895, and 859 c-1. Absorptions 965 and 859 cm.-1 correspond to

two peaks observed in the infrared spectrum of l-k-methoxyphenyl-2-

phenylethylene. Vapor-phase chromatography, using a Perkin-Elmer

Model 154B, showed two peaks for the yellow solid. These peaks had

the identical retention times as the peak observed from the product

of the potassium-t-butoxide with trans-I reaction and the peak of

1-p-methoxyphenyl-2-phenyethylene. Analysis of the product obtained

from the potassium-t-butoxide reaction agreed with the formula of

1-k-methoxyphenyl-2-phenylacetylene. From this it is concluded that

the yellow solid is mainly a mixture of 1-L-methoxyphenyl-2-phenylacety-

lene and 1-k-methoxyphenyl-l-phonylethylene. Attempts to separate

these components were unsuccessful.

The red solid melted above 1800. No further identification

was attempted.

mgo- and dJ-Stilbene Dibromide

These compounds were prepared from trans-and cis-stilbene and

pyridinium bromiOd perbromide as described by Fieser [18 .


Three and six-tenths grams (0.105 mole) of meso-stilbene di-

bromide was added to 0.59 g. (0.0105 mole) of potassium hydroxide

dissolved in 10 ml. of absolute ethanol. After refluxing for one

hour the mixture was cooled, excess water added, and then extracted

with two 25 ml. portions of ether. The ether solution was dried over

anhydrous sodium sulfate and evaporated under dry nitrogen. A red

oil resulted which solidified at 160 (lit. [19] 190) in an ice-bath.

trans-Monobromost i lbene

Eight-tenths of a gram (2.3 moles) of dl-stilbene dibromide

was added to 0.13 g. (2.3 mmoles) of potassium hydroxide in 5 ml.

of absolute ethanol. The reaction was treated in the same way as in

the preparation of cis-monobromostilbene. A light yellow oil was

recovered and solidified by dissolving in ethanol and cooling in a

dry ice-acetone bath. White crystals, m.p. 29-30o (lit. [i9] 320),

were obtained.

t-Butyl Alcohol

t-Butyl alcohol was purified by refluxing with a small amount

of sodium for one hour and then distilling through a 3-ft. column

packed with stainless steel sponge. The fraction, with a boiling

range of 82-82.50, was collected for use.

Potassium-t-butoxide in t-Butyl Alcohol

Potassium metal, cut under white mineral oil and dipped once

in dry pentane, was added to t-butyl alcohol and allowed to dissolve

under dry nitrogen. Concentrations of the solutions were measured

by titrating aliquots added to water against standard hydrochloric

acid solution using phenolphthalein as the indicator.

Reaction of 1,1-Diphenyl-2-bromoethylene (III) with Potassium-

t-butoxide (I)

One gram (3.9 =moles) of 1,1-diphenyl-2-bromoethylene (III)

was dissolved in 50 ml. of dry t-butyl alcohol and 240 mg. (6.1

mmoles) of potassium was added. The reaction was refluxed for

seventy-two hours and then quenched by adding nitric acid until the

mixture was neutral. Water was added until an oil separated. The

oil was dissolved in ethanol to yield 440 mg. (2.5 mmoles, 64 percent)

of diphenylacetylene, m.p. 57-58o (lit. [16] 60-610). An authentic

sample of diphenylacetylene mixed with this compound gave no depres-

sion in melting point. The infrared spectra of both samples were


Reaction of 1,1-Diphenyl-2-branoethylene (III) with Potassium-t-

butoxide (II)

This reaction was carried out in exactly the same manner as

reaction I except that the reaction time was twenty-four hours. Ap-

proximately 650 ag. of oil were recovered. Vapor-phase chromatography

using a 6-ft. Tide column at a temperature of 1900 and a pressure of

10 lbs./sq.in. showed two peaks, retention times 2.7 and 4.7 minutes.

Under identical conditions a mixture of III and diphenylacetylene

also exhibited two peaks, retention times 2.7 and 4.8 minutes. Pre-

pared trans-monobromostilbene indicated one peak with a retention

time of 7.9 minutes. Cis-monobromostilbene also showed one peak with

a retention time of 3.8 minutes. A mixture of cis-monobromostilbene

and III gave only one broad peak. A broad peak was also observed with

the reaction mixture and the cis-isomer at approximately the same re-

tention time. Attempts to resolve these broad peaks were unsuccessful.

The infrared spectrum of the reaction mixture was identical to an

infrared obtained from a mixture of III and diphenylacetylene. Cis-

monobromostilbene had several peaks (2900, 1360, 1190, 1095, 890, and

792 cm-1) which did not appear in the infrared spectrum of the reaction


Reaction of 1-p-Methoxyphenyl-l-phenyl-2-bromoethylene (I) and Potas-


One gram (3.5 mmoles) of trans-I was dissolved in 25 ml. of a

0.40 M (10 mmoles) solution of potassium-t-butoxide in t-butyl alcohol.

The reaction mixture was refluxed for six days. After neutralizing

with hydrochloric acid and extracting with ether, 500 mg. (2.4 mmoles,

69 percent) of yellow-white crystals (m.p. 53-580) resulted on evapora-

tion of the ether extract. These were recrystalized from ethanol to

give a white crystalline product, m.p. 57-58o (lit. [17] 89-90o).

Similar results were obtained with the cis-I isomer.

Analysis: Calculated for C154120: C, 86.54; H, 5.75

Found: C, 86.56; H, 5.82.

Reaction of 1-p-Chlorophenyl-l-phenyl-2-bromoethylene (II) with


Fifty-four hundredths of a gram (1.84 mmoles) of cis-l-2-

chlorophenyl-l-phenyl-2-bromoethylene (cis-II) was refluxed for

sixty-nine hours with a large excess of potassium-t-butoxide in

20 ml. of t-butyl alcohol. Following this, water was added to the

reaction mixture until it became cloudy. After placing the mixture

in a refrigerator for two days, 240 mg. (1.1 moles, 61.5 percent)

of 1-p-chlorophenyl-2-phenylacetylene was recovered. Recrystalliza-

tion from ethanol gave a pure product, m.p. 81-830 (lit. 10 82-830),

as evidenced by one peak recorded by vapor-phase chromatography.

Reaction of 1-y-Methoxyphenyl-l-phenyl-2-bramoethylene (I) with

Sodium Ethoxide

Two hundred and thirty milligrams (0.79 mmole) of trans-I was

refluxed for forth-eight hours with 100 mg. (4.35 mmoles) of sodium

in 15 ml. of absolute ethanol. Water was added to quench the reac-

tion and crystals separated which were identical with the starting

material as evidenced by the melting point, 79-810, and a mixed

melting point. Cis-I gave similar results.

Reaction of trans-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene (trans-I)

with Potassium-t-amylate

Two hundred milligrams (0.69 nanole) of trans-I was treated with

150 mg. (3.94 mmoles) of potassium in 20 ml. of t-amyl alcohol for

sixty-one hours at reflux temperature. Water was added to the reaction

mixture and white crystals separated, m.p. 45-90o. These were not

characterized further.

Reaction of trans-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene (trans-I)

with Potassium-t-butoxide in Diglyme

Five hundred milligrams (1.73 =moles) of trans-I was treated

with 300 mg. (2.68 mmoles) of potassium-t-butoxide in diglyme solvent

for ninety-six hours at reflux temperature. The addition of water

resulted in an oil which was separated from the other liquid and dis-

solved in ethanol. White crystals separated, m.p. 45-900, and were

not characterized further.

Reaction of trans-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene (trans-I)

with Potassium Amide in Liquid Ammonia

One and one-tenth grams (3.8 mmoles) of trans-I was dissvoled

in 40 ml. of dry ether and added dropwise to 1.0 g. (18.2 mmoles) of

potassium amide in 150 ml. of liquid ammonia. After the addition, the

solution was allowed to evaporate overnight. Water and ether were

added to the residue and a reddish-white solid was obtained from the

ether layer. Recrystallization from ethanol yielded a white solid,

m.p. 48-500. The infrared spectrum showed the presence of C C --

at 2225 cm.-1. Vapor-phase chromatography showed one peak at the same

retention time as an authentic sample of 1-2-methoxyphenyl-2-phenylacety-

lene run under identical conditions.

Reaction of cis-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene with

Phenyl-lithium in Ether

Two hundred milligrams (0.69 mole) of cis-I was treated with

10 ml. of 0.23 N (2.3 moles) of phenyl-lithium in dry ether for two

hours at reflux temperature. After the removal of ether, water and

hydrochloric acid were added to the residual oil. Yellow-white

crystals separated, m.p. 500. Vapor-phase chromatography indicated

this was starting material.

Attempted Rearrangement of trans-l-p-Methoxyphenyl-l-phenyl-2-bromo-

ethylene (trans-I) to cis-l-p-Methoxyphenyl-l-phenyl-2-bromoethylene

with Ultraviolet Light

Three hundred milligrams (1.04 mmoles) of trans-I was dissolved

in 20 ml. of ethanol and placed under an ultraviolet lamp for eight

hours. Water was added and yellow-white crystals separated, m.p.

76-78o. The crystals were redissolved in ethanol and placed under

the lamp for an additional fifteen hours. The solution was treated

as before. A solid, m.p. 75-780, and oil were recovered. Some impure

crystals were obtained from the oil, m.p, 70-80o. To the mother li-

quor, after the separation of solid and oil, ether was added, separated

from the water layer, dried with anhydrous sodium sulfate and evaporated

almost to dryness. Ethanol was added and some crystals were recovered,

m.p. 79-81.

B. Spectra

1. Ultraviolet Absorption Spectra

Ultraviolet absorption spectra were employed to determine the

concentrations of starting materials and products used in the kinetic

measurements. Ninety-five percent ethanol was used as our solvent.

A scan of the spectra from 340 mp to 220 mp by the use of the Beckman

DK-2 Spectrophotometer indicated the maximum absorptions for our

materials. The extinction coefficients for each of the maxima needed

for our concentration calculations were determined utilizing the Beck-

man Model DU. Table 2 summarizes the maxima observed for each of our

compounds used in kinetic measurements. In cases where there are

several maxima the largest two are given.

Data for the calculation of the extinction coefficients of

tolans formed from the reactions as well as some of the starting

materials are summarized in Tables 3, 4, 5, 6, and 7.

2. Visible Absorption Spectra

It was desirable to follow the formation of bromide ion in

the kinetic measurements. Since the concentration of starting mater-

ial was approximately 10-3 M an accurate method of determining bro-

mide ion was desirable. Accordingly, the method used by Goldman and

Byles was tried [20]. The principle of the method was the oxidation

of bromide ion with chloramine T reagent and the bromination of phen-

ol red in a buffer solution. A color comparison of brominated com-

pound versus distilled water was made with a Beckman DU Spectrophoto-

meter at 590 mp. The brominated compound should appear reddish to








cis- 1--chlorophenyl-1-phenyl-2-bromoethylene

trans- 1--chlorophenyl-1-phenyl-2-brNooethylene



Maxima (mp)

306 287

268 248

269 254

302 284

259 235

not determined
due to impurities

296.5 279




Concentration in
moles/liter x 105

Optical Density
(306 mp)

Extinction Coefficient
x 10-4

1.73 0.351 2.02

3.46 0.698 2.02

4.34 0.865 1.98

i.00 0.20b 2.06

0.10 0.021 2.01

2.00 0.404 2.02

E = Extinction coefficientAvg. = 2.02 + 0.007 x 104 (306 mp)



Concentration in
moles/liter x 104

Optical Density
(306 mp)

Extinction Coefficient
x 10-3





Extinction CoefficientAvg. = 1.98 +





0.015 x 103 (306 mp)







Concentration in Optical Density Extinction Coefficient
moles/liter x 104 (306 mp) x 10-3

1.22 0.139 1.14

2.44 0.267 1.09

3.63 0.422 1.16

2.61 0.296 1.14

1.31 0.154 1.16

E = Extinction CoefficientAvg. = 1.14 + 0.01 x 103 (306 mp)



Concentration in Optical Density Extinction Coefficient
moles/liter x 105 (302 my) x 10-4

0.764 0.190 2.48

1.53 0.409 2.68

0.580 0.153 2.64

0.725 0.182 2.52

E = Extinction CoefficientAvg. = 2.58 + 0.03 x 104 (302 mp)



Concentration in
moles/liter x 105





Optical Density
(296.5 mp)





Extinction Coefficient
x 10-4





E = Extinction CoefficientA = 2.48 + 0.015 x 104 (296.5 mp)
Avg. -

violet, depending upon its concentration. By constructing a calibra-

tion curve of bromide ion concentration from 0.1 to 1.0 mg./1. versus

optical density at 590 mp a sharp differentiation within + 1 percent

can be made between varying quantities of bromide.

C. Kinetic Methods

1. Ultraviolet Absorption Method

Essentially the kinetic method described by Pritchard and

Bothner-By [9] was used. The reactions of 1,1-diaryl-2-bromoethy-

lenes with potassium-t-butoxide in t-butyl alcohol were carried out

as follows.

Standard base was prepared as previously described. Glassware

used was washed twice with acetone, once with tap water, then with

distilled water, and then dried in an oven at 1350.

Weighed amounts of 1,1-diaryl-2-bromoethylenes were accurately

diluted to a standard volume with t-butyl alcohol. Twenty-five milli-

liter samples were added to a 50 ml. volumetric flask and standard

base was added until the total volume was 50 ml. The contents of the

flask were thoroughly mixed and added to a 50 ml. buret. Five milli-

liter samples were then added to 10 ml. ampoules, previously flushed

with dry nitrogen, using a needle on the tip of the buret in order to

obtain a fine stream of liquid. The ampoules were capped with medi-

cine dropper tops, after flushing again with dry nitrogen, and placed

in an ice-bath. The tubes were then sealed, preheated in a water bath

for 20 seconds at ca. 950 and immediately transferred to a constant

temperature mineral oil bath, which was maintained at a temperature

of 950 + 0.020. The purpose of preheating the frozen tubes was to

eliminate the large drop in temperature in the mineral oil bath which

would result from adding the tubes directly. Zero time was taken

when the tubes were placed in the bath. Ampoules were withdrawn at

intervals and quenched by placing in an ice-bath. While frozen the

tubes were opened and distilled water added to convert any potassium-

t-butoxide remaining to potassium hydroxide. The tubes were then

allowed to warm to room temperature and the solution transferred to

a volumetric flask. The tubes were rinsed once with ethanol and once

with distilled water. After accurately diluting with ethanol to a

standard volume at room temperature the ultraviolet spectra were run

versus ethanol as a blank.

Optical densities were measured at wave lengths corresponding

to maxima of tolans. These were selected because starting olefins

either absorbed very little or did not absorb at all at these wave


Concentrations were calculated from Beer's Law, assuming the

formation of product is equal to the disappearance of starting material.

The general equation A = abc, was used, where

A = absorbance or optical density of the solution,

a = molar extinction coefficient of the solute,

b = thickness of the cell containing the solution, and

c = concentration of the solution in moles/liter.

For the reactions of trans- and cis-l-p-methoxyphenyl-l-phenyl-2-

bremoethylene (I), which absorbed slightly at the maximum of

1-p-methoxyphenyl-2-phenylacetylene, the following modified equation

was used:

ATotal = aTbcT + aEHbcEH,

where Total refers to l-p-methoxyphenyl-2-phenylacetylene (tolan)

and cis- or trans-I. T represents p-methoxytolan and EH refers to

cis- or trans-I.

Knowing the concentration of starting material the relation

cT + cEH = constant was used to substitute in the equation and de-

termine the concentration of product or starting material during the


A plot of -log cEg versus time gave a straight line, indica-

tive of a first-order reaction. Values of k were calculated by the

method of least squares [21 .

2. Vapor-phase Chromatography

Quantitative analyses of mixtures of 1,1-diphenyl-2-broBoethy-

lene and diphenylacetylene were made in the anticipation of following

the rate of the reactions by the use of vapor-phase chromatography.

Samples were accurately weighed, dissolved in chloroform and injected

into a vapor-phase fractometer, Perkin-Elmer Model 154. A 6-ft. Tide

column at temperature ca. 1800 and a pressure of 25 lbs./sq.in. (helium)

was used to separate the mixtures. The areas under, the curves for

each component were measured by constructing triangles over the curves

and calculating the areas of the triangles. Table 8 sunmarizes the

results obtained. This method of analyses was not used in the kinetic




Mole percent of Mole percent of
1, 1-Diphenyl-2-bromoethy lene Diphenylacetylene

Calculated 77.4 60.6 41.9 22.6 39.4 58.1

Measured 78.5 59.2 44.1 21.5 40.8 55.9

D. Dipole Moments

1. Apparatus

Dipole moments were obtained by measuring the dielectric con-

stant of dilute solutions in benzene, a nonpolar solvent. The dielec-

tric constant D was determined by measuring the ratio of the capacity

of a condenser with the substance between the plates of a cell compared

to the capacity of the condenser with a vacuum between the plates of

a cell.

Capacities of the cell were measured by balancing a General

Radio Company type 716-C capacitance bridge containing the measuring

cell (unknown capacitor) and a precision capacitor (balancing capa-

citor). These measurements were made at frequencies of 90 and 70 kilo-

cycles obtained by a General Radio Company oscillator type 1302-A.

Null or balance points were found by observing the smallest sine wave

on a Tektronix type 541-A oscilloscope. A J.C. Balsbaugh 2TN50 cell

was used for measurements. The volume of liquid used in this cell

was ca.15 ml. The cell was immersed in a water bath held at 250 +

0.020. Since the temperature of the room was ca. 240 little heating

was necessary to maintain the temperature. It was found that shield-

ing the thermoregulator, stirring motor and heater from the cell with

a 10" x 10" x 1/8" piece of copper metal removed any interference ob-

served on the oscilliscope.

Readings of capacitance were made after the solutions had

10 minutes to reach equilibrium. Five readings were taken at each


Refractive indices of the solutions were measured with an

Abbe refractometer held at 250 + 0.020.

Densities of the solutions were determined with a 5 ml. pycno-

meter calibrated with distilled water. The pycnometer was filled at

ca. 200 and immersed in a constant temperature bath, 250 + 0.020, for

ten minutes. After removing, it was carefully dried and weighed.

Densities were not corrected for the buoyancy of air.

Solutions were made up by weighing both solute and benzene

for the first sample and then accurately diluting this sample with

volumetric pipets in a room at ca. 200 to obtain the other solutions.

Five solutions were prepared for each compound. These ranged from

0.015 to 0.002 mole fraction of solute (x2).

2. Materials

Pure benzene previously prepared for dielectric studies was

used, n250 = 1.4982, d250 = 0.8736.

Spectral grade carbon tetrachloride was used.

The purest available samples of cis- and trans-l-p-methoxyphenyl-

1-phenyl-2-bromoethylene were used.

3. Calculations

a. Molar Refraction

Molar refractions of the solutions were calculated according

to the equation

n2 1 XIMI + x2M2
R12 =n- + 2 d12 '

where R12 is the molar refraction of the mixture, n is the refractive

index, x1 and x2 are the mole fractions of solvent and solute respec-

tively, and M1 and M2 are the molecular weights of solvent and solute.

d12 is the density of the solution.

The values of R12 were determined from the equation

R12 = x1R1 + x2R2,

where R1 and R2 are the molar refractions of solvent and solute, re-


b. Dielectric Constant

The total capacitance of a cell is made up of the capacitance

of the cell leads CL and the capacitance of the cell when filled

sith a substance DCo. When the capacitance of the cell is measured

with air (D = 1.000), and with benzene of a known dielectric constant

(D = 2.273 at 25) [22] the cell constants may be determined and used

in the measurement of the dielectric constant of an unknown material.

The following standardization was made:

Capacity with air in cell = 143.35 mmf. = Co + CL

Capacity with benzene in cell 177.6 mmf. = 2.273Co + CL

(mmf. = micromicrofarads).

From these two equations,

1.273Co = 34.25

Co = 26.90 Baf.

CL = 116.45 mmf.

To check the standardization pure carbon tetrachloride was

placed in the cell and its dielectric constant calculated.

Capacity with CC14 in cell = 176.4 mmf.

176.4 = [(D)(26.90)] + 116.45

DCCI4 = 2.228 (lit. [22] = 2.227)

c. Dipole Moment

The dipole moment p was calculated using

p = 0.01281 x 10-18 (P2oo R2)T 1/2

where R2 is the molar refraction of the solute,

temperature and P2oo is the polarization of the

dilution. P2oo was determined by the method of

using the equation

where the

slopes of

the equation

T is the absolute

solute at infinite

Hendestrand [23]

(DI 1)(M2 N4i) + 3M1D1
P2oo = (DI + 2)dI dl(DI + 2)2

symbols have the usual significance. 8 and ao are the

the lines obtained from the following equations:

D12 = D1(1 ax2)

dl2 = dl(1 + x2)

D12 and dl2 are the dielectric constants and densities of the solu-

tions. These slopes were calculated by the method of least squares.



Dipole Moments

The dipole moments of the cis and trans isomers of 1-p-

methoxyphenyl-l-phenyl-2-bromoethylene were measured. The trans

configuration was assigned to the higher melting isomer and the cis

configuration to the lower melting isomer on the basis of the ob-

served moments as compared to the calculated moments. These results

are summarized in Table 9. Figures 1 and 2 were used to determine

ca and 0 used in the calculation of the dipole moments. 0c and

are the slopes of the lines in Figures 1 and 2, as determined by

the method of least squares [21].


Five compounds were prepared for kinetic measurements. These

were the cis and trans isomers of 1-p-methoxyphenyl-l-phenyl-2-bromo-

ethylene (cis- and trans-I), the cis and trans isomers of 1-p-chloro-

phenyl-l-phenyl-2-bromoethylene (cis- and trans-II) and 1,1-diphenyl-

2-bromoethylene (III). All were obtained pure, except trans-II which

was contaminated with a maximum of 30 percent of cis-11 as calculated

quantitatively by infrared spectra.

Cis- and trans-monobromostilbene, products of possible in-

termediates in the reaction of 1,1-diphenyl-2-bromoethylene, were

also prepared.


m 9w (7 0
a) to 0n
co CO t- t-

N coN


0 (0 r-



Bo -




0000 1

e r-4 0 0
* .




9 5





o 0
*0 *
8 I


0 0
.. 34

0 7)0

0 0
C; C

F-4 0
co 0n
f- t-
* *

N Ml
i0 1
* *

yr-4 in tl-c
CO t*1tf
co 0o 0)
* 0 .


G6 o
* *


CO r-4
* *w
M *

10 CO4

cl m
* *

<* *r
cq C4

* *
0 0

C0 (0
4n t

0 0


r-4 NO CV) qwP







rI I


O !

4 4


S 1

01 0
\ 8 a
0 1

\- CD )

\ I \ C
\u;So \ J;o s

0 891-

0.887 J


0.879 -


0.871 -

x = cis

. = trans

2 .4 .6 .8 1.0 1.2 /4 /.6 /. 8
Mole Fraction of Solute x 102

Figure 2. Determination of 0 for cis- and trans-I-p-methoxyphenyl-l-phenyl-2-bromoothylene.

Products from the reactions of 1,1-diphonyl olefin (III) and

cis and trans-p-methoxy compounds (I) with potassium-t-butoxide were

synthesized by an alternate route. They were diphenylacetylene and

1-p-methoxyphenyl-2-phenylacetylene (obtained impure).

Product Analysis

All results indicate that the reactions of the bromoethylenes

with potassium-t-butoxide give mainly diphenyl and substituted diphenyl-

acetylenes (tolans). Thus, spectroscopic analysis indicated at least

85 percent of the reaction yielded tolans for all of the starting bromo-

ethylenes (e.g. see Table 10). Furthermore, the reaction of 1,1-diphenyl-

olefin (III) with excess base gave a 64 percent yield of diphenylacety-

lene, after recrystallization. Trans- and cis-k-methoxy compounds (I),

when reacted with'potassium-t-butoxide, yielded 69 and 62 percent re-

spectively, of essentially pure tolans.

A careful analysis of the crude reaction mixture, resulting

from the incomplete reaction of 1,1-diphenyl olefin (III) with potas-

sium-t-butoxide, indicated it consisted only of starting material and

diphenylacetylene. This mixture was analyzed by:

1. Comparing the vapor-phase chromatograms of the reaction

mixture and a mixture of 1,1-diphenyl olefin (III) and diphenylacety-


2. Preparing cis- and trans-monobromostilbene, two possible

products from intermediates in the reaction of 1,1-diphenyl olefin

(III) with base, and comparing their vapor-phase chromatograms and

infrared spectra to those of the reaction mixture.

3. Comparing the infrared spectrum of the reaction mixture

to the spectra of the starting material and diphenylacetylene.


Since spectroscopic evidence indicates that all of the olefins

gave over 85 percent of the tolan, the reaction may reasonably be

described by

djt -dt kobs.CEH*

where CT and CEH are molar concentrations of tolan and bromoethylene

derivatives, respectively, and kobs. is the observed rate constant for

the reaction. A plot of -log CEH versus t (time) gave a straight line

representative of a first-order reaction in all cases. Values of k

were calculated from the slope of the lines by the method of least

squares [21]. Table 10 indicates the typical data used in the kinetic


The kinetic results of the five compounds studied are summarized

in Table 11. The same base concentration (ca. 0.20 M) was used in all

cases to eliminate any differences in the rate constants resulting from

the base term inherent in these constants and to minimize differences

in salt effects between compounds. Three runs were made for each com-

pound except 1,1-diphenyl-2-bromoethylene, whose rate constant was

previously reported under very similar conditions [7]. A concentra-

tion of ca. 1.0 x 10-3 M of starting material was used. In cases

where this varied the pseudo-first-order rate constant remained essen-

tially the same.



Optical Density
(306 mu)








Concentration of tr -I
in moles/liter x 103







a 1 ml. of sample to 9 ml. of solvent. All
of sample to 49 ml. of solvent.

others were diluted 1 ml.

b Measured initial concentrations were within 5 percent of those cal-
culated by weighing of samples and diluting to standard volume.

Sample No.











of KB in

of EH in
x 103





















a tra-1-P-chlorophenyl-l-phexyl-2-bromoethylene was contaminated
with a maximum of 30 percent of cis-l-p-chlorophenyl-l-phenyl-2-

bA kobs. of 0.85 x 10-3 (min.-1) at 0.212 M KB agrees w11 with a
reported kobs. of 0.73 x 10-3 (min.-1) at 0.215 M KB l91.


x 103

A characteristic plot of -log CEH versus time (minutes) is shown

in Figure 3.

It is desirable to compare the rate constants of the bromoethy-

lenes with each other. For that purpose Figure 4 was drawn. Since the

rate constants are independent of the concentration of bromoethylenes,

the average rate constants of each compound are used to determine the

average slopes of the lines in Figure 4. The base concentration of

0.20 M was used. The calculated rate constants of 1.62, 1.06, 0.45,

1.04, 0.82 x 10-3 for trans- and cis-p-methoxy compounds (I), trans-

and cis-E-chloro compounds (II) and 1,1-diphenyl olefin (III), respec-

tively, were used. A distinct difference of slopes, except between cis-

k-methoxy-I and cis-j-chloro-II, can be observed in each case.

Reactions with Other Bases

A few bases, other than potassium-t-butoxide in t-butyl alcohol

were tried to effect the rearrangement. Treatment of cis- or trans-

1-p-methoxy compounds (I) with sodium ethoxide in ethanol and phenyl-

lithium in ether gave no 4-methoxytolan. Potassium amide, in liquid

ammonia, was successful while potassium-t-amylate in t-amyl alcohol

and potassium-t-butoxide in diglyme (diethylene glycol dimethyl ether)

gave dubious results.

Miscellaneous Experiments

Attempted rearrangement of trans---methoxy-I to cis-p-methoxy-I

under ultraviolet radiation was unsuccessful.




x a cis

* = trans

80 JZO O

240 280 320

Time (minutes)

Reaction of trans- and cis-1-p-methoxyphenyl-l-phenyl-2-branoethylene (I) with 0.197 M
Potassium t-butoxide at 950.




Figure 3.


3. I1





120 18o 240 300
time (minutes)

Comparison of rate constants of 1,1-diaryl-2-bramoethylenes at 0.20M potassium-t-butoxide.



Figure 4.


A quantitative method of calculating the percent of 1,1-diphenyl-

2-bracoethylene and diphenylacetylene by vapor-phase chromatography

was developed and found to be accurate within + 1 mole percent.



Dipole Moments

In order to interpret the relative reaction rate constants

and properly discuss reaction mechanisms the proper geometric con-

figuration of the isomers of 1-p-methoxyphenyl-l-phenyl-2-bromoethy-

lene (UI2- and trans-I) and of the isomers of 1-r-chlorophenyl-l-phenyl-

2-bromoethylene (gcs- and tras-II) must be known. Usually the best

way to assign these configurations is by dipole moment measurements.

This has been done for cis- and trans-II and the higher melting isomer

was found to have the cis configuration (bromine and 2-chlorophenyl

cis) [15].

Stoermer and Simon [12], who first prepared the cis- and trans-

p-methoxy compounds (I), assigned the trans configuration to the higher

melting isomer. Their assignment was based on two assumptions:

1. The one isomer of 1-phenyl-l-o-hydroxyphenyl-2-bromoethy-

lene, which reacts with base to yield 2-phenylbenzofuran, necessarily

has the cis configuration.

O /H /0

O Br


2. Since this isomer was lower melting, the trans configura-

tion could be assigned to all the higher melting isomers of 1,1-diaryl-

2-bromoethylenes with a substituent in one of the benzene rings. These

assumptions are not valid in all cases, as evidenced by the cis-p-

chloro compound (II) being the higher melting isomer of the isomers

of cis- and trans-p-chloro compounds. Thus, a determination of the

dipole moments of the cis and trans-p-methoxy compounds (I) was under-


Theoretical dipole moments were calculated upon the following


1. The carbon-bromine bond moment is 1.38 debye units, the

value assigned by Smyth [24].

2. The bond moment of the vinyl hydrogen is taken as zero

because Gent [25] has stated the carbon-hydrogen bond moment is ca.

zero in ethylene.

3. The moment of the p-methoxyphenyl group is 1.25 debye

units, the same as that reported for anisole [26]. The moment

angle of the mothoxy group is 780 from the line of attachment to

the benzene nucleus and at a direction into the benzene ring [27 .


A further assumption made here is the free rotation of the methoxy-

methyl group around the carbon-oxygen bond resulting in the rotation

of the methoxy-moment around the line of attachment to the benzene


4. All other moments in the molecule are zero.

5. The bond angles are not distorted from their normal values.

Using these assumptions the dipole moments of the cis- and

trans-p-methoxy compounds (I) were calculated by the law of cosines.

In the case of trans-I the moment of the methoxy group is always

780 from the carbon-bromine moment. In the cis isomer the angle be-

tween the methoxy moment and the carbon-bromine moment varies from a

minimum of 420 to a maximum of 1620 when the methoxy moment rotates.

t'he calculated value of cis-1 is taken as the average of the maximum

and minimum values. The calculated dipole moment of the trans-p-

methoxy compound (I) is 2.05 debye units, while the calculated value

of the cis-p-methoxy compound (I) is 1.45 debye units, an average of

a maximum value of 2.46 and a minimum value of 0.43 debye units.

The observed dipole moments of the trans- and cis-p-methoxy compounds

(I) are 2.65 (820 isomer) and 2.18 (530 isomer) debye units, respec-

tively. The observed values are approximately 0.6-0.7 debye units

higher than the calculated values, but the difference between the

moments observed of the cis- and trans-p-methoxy compounds (I) is

essentially that calculated. On this basis the isomer with the high-

est dipole moment is assigned the trans configuration. This is the

same as that originally given by Stoermer and Simon [12].

Migratory Aptitudes and Reaction Mechanisms

The tendency for various groups to rearrange or migrate in

the elimination rearrangement reaction of 1,1-diaryl-2-bromoethylenes

is called the migratory aptitude of the groups. One reasonable approach

to measuring this tendency is to examine the rates of the elimination-

rearrangement reaction of various substituted phenyl groups on the vinyl

bromide. However, inherent in such a study is the problem of the effect

of the substituent group on the acidity of the vinyl hydrogen. In view

of the known stereospecificity of this reaction, it was thought that

this problem could be obviated by examining the relative rates of re-

arrangements of the cis and trans isomers in which only one of the phenyl

rings contained the substituent under consideration. Thus, the cis and

trans isomers of 1-L-methoxyphenyl-l-phenyl-2-bromoethylene (cis- and

trans-I), 1-p-chlorophenyl-l-phenyl-2-bromoethylene (cis- and trans-II)

and 1,1-diphenyl-2-bromoethylene (III) were prepared. In these five

different compounds we have an electron-donating group (-OCH3) on the

migrating phenyl, an electron withdrawing group (-C1) on the migrating

phenyl and what we could call our neutral or reference group (-H). In

a pair of isomers, if the trans group is migrating with its electrons

the electron-donating group would be expected to increase the rate of

the reaction. If, on the other hand, the phenyl is migrating without

its electrons, the electron-donating group would be expected to retard

the reaction whereas the electron withdrawing group would be expected

to increase the rate. This study of migratory aptitudes can be com-

pared to the known migratory aptitudes in the pinacol rearrangements.

R' R'
R-C -C-R


R-C -C-R
0 R'
R' -C--C --R
0 R

In the pinacol rearrangement it was found that the migratory apti-

tudes for a phenyl migrating are as follows [28]:

p OCH3 > p alkyl >p H >p Cl

The general reaction mechanism (8,9 for the reaction of

1,1-diaryl-2-bromoethylenes with potassium-t-butoxide may be written

as follows:

C = C

+ B- C = C"
/ \

+ BH


AR--C C--AR + Br-

AR = aryl group

Because of the wide variety of strong bases 1-10] which can

initiate the rearrangement a reasonable first step in the reaction is

the abstraction of the vinyl proton to form anion V. By the use of

deuterated solvent Pritchard and Bothner-By (9] have exchanged the

C =C-_

4_ _71111_0

vinyl hydrogen of IV with a deuterium atom. They have calculated

the exchange reaction to be at least a hundred times faster than the

conversion to diphenylacetylene at the same temperature. Moreover,

the rates for the rearrangement reactions are considerably faster in

deuterated solvent than they are in t-butyl alcohol. From this in-

formation it is plausible that the reaction mechanism involves rever-

sible carbanion (V) formation. If the formation of carbanion V were

irreversible, so that its formation would be the rate-determining

step, the reaction of deuterated substrate would proceed more slowly

than that of undeuterated substrate (IV). Further evidence that the

abstraction of a proton is not the rate-determining step, using po-

tassium-t-butoxide as the base, is the difference in rate constants

of the cis and trans isomers observed by the author. In my opinion,

the cis- and trans-p-methoxy compounds (I), for example, should be

identical as far as the abstraction of the vinyl proton is concerned,

yet they have rate constants of 1.06 and 1.62 x 10-3 (min.-1), re-

spectively. The most reasonable explanation of these rate constants

is that the migration is involved in the rate-determining step, rather

than occurring after it. On the other hand, Curtin and Flynn (7) have

demonstrated that in the formation of diphenylacetylene, 1,1-diphenyl-

2-bromoethylene-2-d reacts at an appreciably slower rate with butyl-

lithium than does 1,1-diphenyl-2-brmaoethylene. This would indicate

that the breaking of the carbon-hydrogen bond is the rate-determining

step when butyl-lithium is used as a base. However, under these con-

ditions, the first step of the reaction is most probably not reversible.

The second step, or rate-determining step of the reaction, us-

ing potassium-t-butoxide as the base, is the migration of the group

trans to the bromine atom. Implicit in this system is the configura-

tional stability of anion V. The fact that the trans group migrates

and anion V was stable was demonstrated by Bothner-By [81 and by Cur-

tin, al. [101. Bothner-By prepared the cis and trans isomers of

l-p-bromophenyl-l-phenyl-2-bromioothylene-1-14C and converted them to

labeled 4-bromotolans using potassium-t-butoxide in refluxing t-

butyl alcohol (ca. 330). By oxidizing the tolans, radioactive benzoic

and p-bromobenzoic acids were obtained. From this he found the cis

isomer to rearrange with 88 percent migration of the phenyl group

while the trans isomer rearranged with 92 percent migration of the

p-bromophenyl group. Curtin, et al., found similar results with cis

and trans p-chloro compounds using butyl-lithium to initiate the re-

action at -350.

It might be well to point out now the similarity between this

rearrangement and the Beckmann rearrangement [29]. The Beckmann re-

arrangement involves migration between doubly-bonded carbon and

nitrogen with the migration of the group trans to the leaving -OH or

-OR group.

R OX 0 X
\ / II I
C = N acid or heat R-- C --N --R'
X = H or R group,

R', R = alkyl or aryl


Moreover, the nitrogen atom is isoelectronic with carbanion V. There

are, of course, differences in the reactions, the most obvious being

the initial reaction with strong base in our rearrangement while the

Beckmann is initiated with acids or heat.

There remains unanswered the important questions of migratory

aptitudes and of the detailed reaction mechanism of the second step

of our reaction. The three most reasonable mechanisms for the migra-

tion step are:

1. The slow migration of the trans aryl group without its

electrons followed by a fast loss of bromide ion:


C =-C slow fCa=C fast AR- C =-C -AR' + Br-
/ \ / \


2. The same as mechanism 1 except that the first step is fast

and the second slow.

It was important to consider these two mechanisms because the

rearrangement of phenyl groups without their electrons to carbanions

has been postulated by Zimmerman and co-workers [30 .

3. The slow rearrangement of the trans group with its electron

accompanied by the displacement of bromide ion.


C= C- slow AR C C-AR' + Br-
/ Br

The values of the average rate constants, a measure of migra-

tory aptitudes in our reactions, are summarized in Table 12.

It can be seen, from a comparison of the rate constants of the

cis- and trans- p-methoxy compounds (I), that the migrating group

donating electrons into our system speeds up the reaction over the

migrating neutral or reference group. Conversely, the cis- and

trans-2-chloro compounds (II) indicate that the migrating group with-

drawing electrons slows down the reaction compared to the migrating

reference group. Normally, this type of information could be taken

as evidence that a group is migrating with its electrons [28,29 .

Thus, mechanism 1 would appear unlikely because the slow migration

without electrons would predict the opposite orders. For example,

Zimmerman and Zweig [30] have shown that a p-tolyl group migrates

slower than a phenyl group in the rearrangement reactions of 1-chloro-

2-phenyl-2-p-tolylpropane with lithium. This is consistent with an

electron-donating group (-CH3) retarding the rate of rearrangement

compared to a phenyl group when the groups are rearranging without

their electrons. Any effect of the various substituted phenyl

groups on anion VI would not affect the rate of the reaction since

this anion is formed after the rate-determining step. However, in

mechanism 2 the stability or instability of anion VI would certainly

be expected to affect the rate of the reaction since this anion is

formed before the slow step of the reaction. For example, anion

VI-a of the cis-p-chloro compound (II) would be expected to be more



Compounds k x 103(min.-1)

trans-l-p-methoxyphenyl- l-phenyl 1-2-
bromoethylene 1.62

bromoethylene 1.06

bromoethylene 0.45

bromoethylene 1.04



stable than anion V1-b of the trans-p-chloro compound (II) due to

the electron-withdrawing effect of the p-chloro group.


/ /0
/ \ / \
Br Br

VI-a VI-b

y = -Cl or -OCH3

Conversely, anion VI-a of the cis-p-methoxy compound (I)

would be less stable than anion VI-b of the trans-p-methoxy com-

pound (I) due to the destabilization of the cis-I anion by the

p-methoxy group. Thus, from an examination of the relative rates

of reaction of the cis-trans pairs of isomers it is seen that the

results can be made equally consistent with either mechanism 2 (rapid

equilibration of the two anions followed by slow loss of bromide) or

mechanism 3 (migration of the phenyl with its electrons). Further-

more, a more careful comparison, not only of the relative rates of

the cis-trans pairs, but also of the relative rates of various com-

pounds, leads to the same conclusions; although, admittedly, some of

the assumptions required to rationalize the results with mechanism 2

are rather unlikely. However, in the discussion to follow, it is seen

that mechanism 2 becomes a very unlikely possibility.

As was pointed out earlier, Bothner-By [91 succeeded in trap-
ping anion V with deuterium.

+ t BuOD ',

C = C

+ t BuO-

It is certainly reasonable that anion VI, in which the carbanion

electrons have the possibility of being conjugated with a phenyl

or substituted phenyl group, would be at least as stable, and probab-

ly more stable, than anion V. Therefore, if present, anion VI or

VI' should react with solvent by an analogous reaction to that of

anion V to give VII, VII', or both

C== C


[- = = -





+ t BuOH C = C





C = C
/ \
H Br


Possible Conjugation

C = -C

A reaction of 1,1-diphenyl-2-bromoethylene (III) with potassium-

t-butoxide was, therefore, allowed to proceed to partial completion

and the crude mixture, after neutralization, was carefully analyzed

for trans- and cis-monobromostilbene, the products of anions VI and

VI'. By the use of vapor-phase chromatography, infrared spectra

and a comparison with authentic samples it was shown that the re-

action mixture resulting from the partial reaction of the 1,1-diphenyl

olefin (III) with base consisted only of starting material and diphenyl-

acetylene. There was no detectable trace of the bromostilbenes. These

results tend to exclude mechanism 2 as being operative.

The third mechanism involves the slow rearrangement of the

trans group with its electrons. The rate constants for the cis and

trans isomers are consistent with this mechanism. The trans-p-methoxy

compound (I) would be expected to react faster than the cis-p-methoxy

compound (I) because the migrating group is p-methoxyphenyl in trans-I

and phenyl in cis-I. According to mechanism 3, the p-methoxy group,

being an electron-donating group, increases the rate of the rearrange-

ment compared to the rate of rearrangement of a phenyl group. Con

versely, the cis-p-chloro compound (II) reacts faster than the trans-

2-chloro compound (II) because a p-chlorophenyl group is migrating

in trans-It, retarding the rate of the reaction.

Phenyl is the migrating group in the cis-p-methoxy compound (I)

and in the cis-p-chloro compound (II). The differences in rate con-

stants between the cis isomers and 1,1-diphenyl olefin (III) is rea-

sonably due to the effects of the stationary substituted phenyl groups.

Probably the most important of these effects is the acidity of the

vinyl hydrogen abstracted in the first step of the reaction.

Roberts and co-workers [31] have measured the rates of deuterium-

proton exchange of o-, m-, and p-deuterated fluorobenzene, benzo-

trifluoride and anisole. In such reactions the combined inductive

and field effects of the substituents on the benzene ring appear

to be of major importance and the electromeric effects of minor im-

portance. They have shown that fluorine, although four carbon atoms

from the deuterium atom, increases the rate of the removal of deuterium

two hundred times over that of the unsubstituted deuterobenzene. The

methoxy group had little effect on the acidity of the deuterium atom.

In view of this paper we can be fairly certain that the chlorine atom

of the cis-p-chloro compound (II), having the same type of effect as

the fluorine atom, would increase, at least to some degree, the acid-

ity of the vinyl hydrogen over that of the acidity of the vinyl hy-

drogen of 1,1-diphenyl olefin (III). It is reasonable, therefore, to

say that the cis-p-chloro compound (1) reacts faster than the 1,1-di-

phenyl olefin (III) due to the greater acidity of the vinyl hydrogen.

The cis-p-methoxy compound (I) also reacts faster than 1,1-

diphenyl olefin (III). Since Roberts, et al. ,31], have shown that

the methoxy group has little effect on the acidity of the deuterium

atom it is difficult to rationalize cis-I reacting faster than III.

One possible explanation of this increase is the possible stabiliza-

tion of the incipient carbon-carbon triple bond by the p-methoxyphenyl

group. Probably occurring simultaneously with the migration of the

trans aryl group is the formation of the carbon-carbon triple bond.

Since the p-methoxyphenyl group is conjugated with the vinyl group

it probably has some effect on the formation of the triple bond.

Depuy and Leary [32] have shown that in the pyrolytic elimination

reactions of some acetates of substituted 1, 3-diphenyl-2-propanols

the reaction is controlled by the stability of the olefin formed.

In these cases, the olefin formed conjugated with a p-methoxy phenyl

group predominated by a factor of ca. three over that of an olefin

formed conjugated to a phenyl group. These results would indicate

that the p-methoxyphenyl group stabilizes the incipient double bond

compared to a phenyl group. The fact that the cis-p-methoxy compound

(I) reacts faster than 1,1-diphenyl olefin (III) could be explained,

therefore, by the greater stability of the triple bond being formed

in the reaction of the cis-p-methoxy compound (I). The trans-p-

methoxy compound (I) reacts faster than 1,1-diphenyl olefin (III) due

to the p-methoxyphenyl group aiding in the rearrangement with elec-

trons. Conversely, the trans-p-chloro compound (II) retards the rate

of the reaction compared to 1,1-diphenyl olefin (III) because the

p-chlorophenyl group destabilizes the rearrangement of the trans group

with its electrons. Comparing the rate constants of the cis and trans

isomers to each other is consistent with mechanism 3. In view of

this and the reasonable rationalization of the relative rate constants

of the cis and trans isomers to 1,1-diphenyl-2-bromoethylene, mechanism

3 is certainly the most probable.

There remains the question of just what is the driving force

of the rearrangement, or why do groups rearrange with their electrons

to an electron-rich site? In the Beckmann rearrangement the polarity

of the N-OX bond is thought to influence the rearrangement [29]. The

more powerfully the OX group attracts electrons the faster the rear-

rangement. This could conceivably give rise to a partial breaking of

the N-OX bond, leaving a vacant orbital to which the trans group could

migrate. There is no evidence that there is any actual dissociation

into free ions. This would result in a nitrogen sextet intermediate

sometimes postulated for the Beckmann rearrangement [33].

C =N:

This intermediate is unreasonable due to the stereospecificity of

the rearrangement.

It is then conceivable that the partial breaking of the

carbon-bromine bond and the probable rehybridization to give a vacant

p orbital, into which the trans group could migrate, would be the

driving force of the rearrangement. There are many cases of ioniza-

tion of a halide resulting from the formation of a carbanion. The

most common of these are the well known carbene reactions [34-36.

In particular, the reaction of chloroform with sodium hydroxide

involves an initial rapid proton transfer and then a slow loss of

chloride ion from the resulting carbanion [34 .

CHC13 + OH" "-- ~CC13 + H20

CC13 low :CC12 + Cl"

The fact that the chloride ion does not ionize until the carbanion

is formed might explain why the rearrangement is initiated by the

removal of the vinyl proton. Once the vinyl carbanion is formed the

bromide atom can ionize, at least to some degree, causing the forma-

tion of the vacant p orbital necessary for the rearrangement. An ex-

treme case of this might be depicted as such:


/C = C-


This poses the problem of why, in the Beckmann rearrangement,

the rate constant of the p-methoxyphenyl group migrating is so much

greater than that of the phenyl group migrating, while in our rearrange-

ment it is not? For instance, R. Huisgen and co-workers [37] have found

trans-2-methoxyacetophenone oxime to react ca. 150 times faster than

acetophenone oxine, yet trans-l-methoxy compound I reacts only 1.6 times

as fast as cis-p-methoxy compound I. Even though the nitrogen atom in

the Beckmann rearrangement is isoelectronic with the carbanion in

our rearrangement the fact remains that the nitrogen atom is neutral

and the carbon has a negative charge. If the driving force of the

reaction is the partial breaking of the C-Br bond, this would still

leave some negative charge on the carbon atom while the partial break-

ing of the N-OX bond would leave the nitrogen atom partially positive.

This difference in charge on the migrating terminus affecting the

rates of reaction is reflected in other rearrangements where the group

is migrating with its electrons. For instance, the rate constant for

the migrating p-methoxyphenyl in the symmetrical pinacol rearrangement

is five hundred times greater than the migrating phenyl group [28].

In this rearrangement the group is believed to migrate to a positively

charged terminus. In the Lossen and Hofmann rearrangements the phenyl

or substituted phenyl groups are migrating to a negatively charged ni-

trogen atam. Hauser, et al. [38], have indicated the migrating p-me-

thoxyphenyl group to be ca. six times as fast as the migrating phenyl

group in the Lossen rearrangement while in the Hofmann rearrangement

they found it to be approximately ten times as fast. This comparison

of charge on migrating terminus would tend to predict a small differ-

ence in rate between p-methoxyphenyl and phenyl due to a group migrat-

ing with its electrons to an electron-rich site.

The p-chlorophenyl group, on the other hand, does not affect

the rates of rearrangement to a radical degree [28,29,39 Chapman

and Fidler [39] have shown that the picryl ether of p-chlorobenzophenone-


-oxime reacts 1/5 as rapidly as the picryl ether of benzophenone

under the same conditions. The fact that the trans-2-chloro compound

(II) reacts 1/2 as rapidly as 1,1-diphenyl olefin (III) is not sur-

prising from this comparison.



A kinetic study of the migratory aptitude, or tendency

of a group to rearrange, was made on the cis and trans isomers of

a series of 1-phenyl-l-2-substituted phenyl-2-broaoethylenes. The

kinetics of the reactions of the bromoethylenes with base was fol-

lowed by measuring the ultraviolet absorption spectra of the pro-

ducts obtained. Rate constants for the rearrangement of the bromo-

ethylenes showed that an electron-donating group on the migrating

phenyl increases the rate of the reaction compared to a phenyl

group. Conversely, an electron withdrawing group on a migrating

phenyl retards the rate of the reaction. Kinetic results also in-

dicated that the cis-bromoethylenes reacted faster than 1,1-diphenyl-


Three mechanisms have been considered for the reactions and

the most reasonable consists of a rapid equilibrium involving the re-

action of the bromoethylene with base followed by a slow rearrange-

ment of the phenyl or substituted phenyl group with its electrons.

A comparison of the elimination-rearrangement reaction to

the Beckmann, Pinacol, Lossen and Hofmann rearrangements is made,

and the differences between the elimination-rearrangement reaction

and the others is rationalized.


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18. L. F. Fieser, "Experiments in Organic Chemistry," D. C. Heath and
Company, Boston, 1955, pp. 180, 185.

10. P. Rumpf and M. Gillois, Bul. Soc. Chim., 1348 (1955).

20. E. Goldman and D. Byles, Jour. AWWA, 55, 1051 (1959).

21. W. J. Youden, "Statistical Methods for Chemists," John Wiley
and Sons, Inc., New York, 1951, p. 42.

22. J. Timmermans, "Physico-Chemical Constants of Pure Organic
Compounds," Elsevier Publishing Co., Inc., New York, 1950.

23. G. Indastand, Z. Physik. Chem., B2, 428 (1929).

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Book Company, Inc., Now York, 1955, p. 244.

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26. C. P. Smyth, "Dielectric Behavior and Structure," McGraw-Hill
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27. L. F. Sutton, Proc. Roy. Soc. (London), 133A, 668 (1931).

28. (a) W. E. Bachmann and J. W. Ferguson, J. Am. Chem. Soc., 56,
2081 (1934).

(b) W. E. Bachmann and 11. R. Steinberger, ibid., 56, 170 (1934).

29. B. Jones, Chem. Revs., 35, 335 (1944).

30. (a) H. E. Zimmerman and A. Zweig, J. Am. Chem. Soc., 83, 1196

(b) H. E. Zimmerman and F. J. Smentowski, ibid,, 79, 5455 (1957).

31. G. E. Hall, R. Piccolini and J. D. Roberts, ibid., 77, 4540 (1955).

32. C. IH. Depuy and R. E. Leary, ibid., 79, 3705 (1957).

33. G. H. Wheland, "Advanced Organic Chemistry," 2nd Ed., John Wiley
and Sons, Inc., New York, 1949, p. 483.

34. (a) J. Hine, J. Am. Chem. Soc., 72, 2438 (1950).

(b) J. Hine, ibid., 76, 2688 (1954).

35. P. S. Skell and A. Y. Garner, ibid., 78, 5430 (1956).

36. D. Y. Curtin and W. HI. Richardson, ibid., 81, 4719 (1959).

37. R. Huisgen, J. Witte, H. Walz and W. Jira, Ann., 604, 191 (1957).


38. (a) W. B. Renfrow, Jr., and C. R. Hauser, J. Am. Chem. Soc., 59,
2308 (1937).

(b) W. B. Renfrow, Jr., and C. R. Hauser, J. Am. Chem. Soc., 59,
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Ralph Anthony Damico, Jr., was born in Chester, Pennsylvania,

on July 2, 1935. In June, 1957, he received the degree of Bachelor

of Science in Chemistry from Saint Joseph's College, Philadelphia,

Pennsylvania, and enrolled in the graduate school of the University

of Florida. During his graduate study at the University of Florida

he has held a graduate assistantship, a teaching assistantship and

a Texaco research fellowship in the Chemistry Department.

Mr. Damico is married to the former Darrina Dee Turner. He

is a member of the American Chemical Society and of Gamma Sigma

Epsilon fraternity.

This dissertation was prepared under the direction of the

chairman of the candidate's supervisory committee and has been ap-

proved by all members of that committee. It was submitted to the

Dean of the College of Arts and Sciences and to the Graduate Council,

and was approved as partial fulfillment of the requirements for the

degree of Doctor of Philosophy.

February 3, 1962

Dean, College of Arts an

Dean, Graduate School

Supervisory Ceunittee:


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