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2000

The Dehydrochlorination Mechanism of the Internal Allylic The Dehydrochlorination Mechanism of the Internal Allylic

Chloride Structure in Poly(Vinyl Chloride) Chloride Structure in Poly(Vinyl Chloride)

Lynda B. Payne College of William & Mary - Arts & Sciences

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Recommended Citation Recommended Citation Payne, Lynda B., "The Dehydrochlorination Mechanism of the Internal Allylic Chloride Structure in Poly(Vinyl Chloride)" (2000). Dissertations, Theses, and Masters Projects. Paper 1539626253. https://dx.doi.org/doi:10.21220/s2-x2cs-0908

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THE DEHYDROCHLORINATION MECHANISM OF THE INTERNAL ALLYLIC CHLORIDE STRUCTURE IN POLY(VINYL CHLORIDE)

A Thesis

Presented to

The Faculty of the Department of Chemistry

The College of William and Mary in Virginia

In Partial Fulfillment

Of the Requirements for the Degree of

Master of Arts

by

Lynda B. Payne

August, 2000

APPROVAL SHEET

This thesis is submitted in partial fulfillment of

the requirements for the degree of

Master of Arts

Author'

Approved, August 2000

ChristopherfJ. Abedt

Robert D. Pike

TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS iv

LIST OF TABLES v

LIST OF FIGURES vi

ABSTRACT viii

INTRODUCTION 2

Synthesis of PVC 3

Properties of PVC 5

Additives 6

Thermal Degradation of PVC 7

Possible Structural Defects 9

Mechanism of the Thermal Dehydrochlorination of PVC 12

EXPERIMENTAL 23

Instrumentation 23

Materials 24

Experimental Procedures 25

RESULTS 29

Model Compound for the Internal Allylic Structure in PVC. 29

Models for the Possible Thermal Dehydrochlorination Products of 4. 35

DISCUSSION AND CONCLUSIONS 39

REFERENCES 71

iii

ACKNOWLEDGMENTS

The writer wishes to express her appreciation to Professor William H. Starnes, Jr.,

whose support and guidance for the duration of this project have been extremely helpful.

She also wishes to thank Vadim Zaikov, Xianlong Ge, Ying Li, and Bin Du for their

assistance in the laboratory. Finally, she is indebted to the Department of Chemistry at

the College of William and Mary for the experiences and opportunities that she has

gained as a result of her education.

IV

LIST OF TABLES

Table Page

1. Dehydrochlorination Rate Constants for Some Models 20

2. GC Parameters 23

v

LIST OF FIGURES

Figure Page

1. Synthesis of PVC 3

2. Formation of an internal allylic chloride structure in PVC 8

3. Dichlorobutyl-branch structure formation 10

4. Long-branch structure formation 11

5. Formation of the ketochloroallylic structure in PVC 11

6. Alternative mechanism for the formation of the internal chloroallylic structure 12

7. lon-pair mechanism for the dehydrochlorination of PVC 13

8. Proposed six-center dehydrochlorination mechanism for PVC 14

9. Thermal degradation and rearrangement of £r<ms,-6-chloro-4-decene 15

10. Thermal degradation experiment on /traw5-9-chloro-6-tridecene 15

11. Kinetic plots for the thermal degradation of ?ra«^-6-chloro-4-deceneand /r£ms-9-chloro-6-tridecene at 170 °C 16

12. Dehydrochlorination of frYws-6(4)-chloro-4(5)-tetradecenes at 150 °C 17

13. 1,2 Dehydrochlorination of 2-chloro-1 -ethylidenecyclohexanes 21

14. Six-center 1,4 dehydrochlorination of cz'.s-2-chloro-l- ethylidenecyclohexane. 21

15. Synthesis of 2-chloro-1 -ethylidenecyclohexanes 29

16. Formation of hydrazine 31

17. Synthesis of 2-ethylidenecyclohexanols 32

18. Synthesis of 2-chloro-1-ethylidenecyclohexanes 34

19. Synthesis of 3-ethylidenecyclohexenes 35

vi

20. Synthesis of 1-vinylcyclohexene 36

21. Side product formed during reaction of Grignard reagent and cyclohexanone 37

22. Formation of 3-ethylidenecyclohexenes through a 1,2 dehydrochlorination mechanism 39

23. Formation of 1-vinylcyclohexene through a six-center 1,4 dehydrochlorination mechanism 40

1 -1. GC/MS analysis of 1 -acetylcyclohexene oxide (2) 41

1-2. Impurity in compound 2 42

2-1 - 2-5. GC/MS analysis of Wharton transposition product after 48 h 43-47

3-1 - 3-2. GC/MS analysis of 2-ethylidenecyclohexanol purified by columnchromatography 48-49

3-3. !H NMR spectrum of 2-ethylidenecyclohexanols 50

133-4. C NMR spectrum of 2-ethylidenecyclohexanols 51

4-1 - 4-5. GC/MS analysis of products from 2-chloro-1-ethylidenecyclohexanesynthesis 52-56

4-6. 13C NMR spectrum of 2-chloro-1-ethylidenecyclohexane product mixture 57

5-1 - 5-2. GC/MS analysis of diene products from thermal dehydrochlorination 58-59

5-3. Initial-rate kinetic plot for the thermal dehydrochlorination of the allylicchlorides at 170 °C 60

5-4. Crude first-order kinetic plot for the thermal dehydrochlorination of the allylic chlorides at 170 °C 60

6-1. GC/MS analysis of the isomerization product of 4-vinylcyclohexene 61

7-1 - 7.2. GC/MS analysis of the products from the synthesis of1-vinylcyclohexanol 62-63

7-3. NMR spectrum of 1-vinylcyclohexanol 64

7-4. 13C NMR spectrum of 1-vinylcyclohexanol 65

8-1 - 8.5. GC/MS analysis of dehydration products of 1-vinylcyclohexanol 66-70

vii

ABSTRACT

Poly(vinyl chloride) (PVC) is a thermally unstable material that rapidly loses

hydrogen chloride upon heating to temperatures at or above 150 °C. The loss of HC1

may occur at a number of possible structural defects within the polymer. The mechanism

for the thermal dehydrochlorination at a chloroallylic defect is thought by many workers

to be a 1,2 elimination involving an ion pair or a highly polarized four-center transition

state. Another proposed mechanism for the dehydrochlorination involves the

rearrangement at the chloroallylic structure into a cis-allylic configuration that

subsequently loses HC1 through a six-center concerted process. In the research described

here, 2-chloro-1-ethylidenecyclohexane (actually, a mixture of isomers) was prepared by

a three-step route and subjected to thermal dehydrochlorination at 170 °C. The rate of

this reaction was found to be in line with expectations for sec-allylic chloride moieties

such as those in PVC, and the dehydrochlorintion was found to form cis- and trans-3-

ethylidenecyclohexene, rather than 1 -vinylcyclohexene. These results are shown to argue

strongly against a concerted six-center process for the thermal loss of HC1.

THE DEHYDROCHLORINATION MECHANISM FOR THE INTERNAL ALLYLIC

CHLORIDE STRUCTURE IN POLY(VINYL CHLORIDE)

2

I. INTRODUCTION

Poly(vinyl chloride) (PVC) is one of the oldest and most important

commercially produced plastics in the world. With production beginning in the

1930’s in the United States, the average annual use of PVC has greatly increased, and

we are now likely to encounter PVC in several 'aspects of our lives every day. It has

been estimated that the annual world consumption of PVC in 1996 totaled 23 million

tons.1 The usefulness of the polymer is still being expanded, and its production is

likely to continue rising in the future.

For several years, PVC has been subjected to extensive research. Many issues

are being investigated, such as the degradation processes of the polymer, its thermally

labile sites, environmental issues, etc. The main intent of this thesis is to assess some

continuing discrepancies in the literature regarding the thermal dehydrochlorination

mechanism of an allylic chloride structural defect in PVC. First, an overview of the

structural characteristics of the polymer and some of the research speculations will be

explored, in order to give the reader insight into two different mechanisms that have

been proposed for the thermal dehydrochlorination of an internal allylic chloride

group.

Synthesis of PVC

Poly(vinyl chloride) is made up of repeating monomer units o f vinyl chloride.

Subjecting vinyl chloride to a free-radical source leads to the formation of the polymer

(Figure 1).

Cl ClI free-radical source I

nC¥L2=CU ---------------------------► -(CH2-CH)„-

Figure 1. Synthesis of PVC.

Several different processes, such as emulsion, suspension, and mass# 2

polymerization are used for the manufacture of this material. Formation by suspension

polymerization is currently the most common method, producing up to 75% of the

world’s supply of PVC.3

Polymerization follows a generalized mechanism involving initiation,

propagation, and termination. During initiation, radicals are produced in pairs from

the decomposition of an initiator (I) (eq 1).

I ---- ► 21 • (1)

The initiator radicals subsequently add to the monomer (M), vinyl chloride (eq 2).

!• + M -------► P (2)

Propagation involves the continual addition of monomer molecules to P* radicals,

resulting in chain growth (eq 3).

+ M Pn+1* (3)

The addition of monomer usually occurs in a head-to-tail manner in order to maintain the

thermodynamic stability of the growing free radical. However, occasional head-to-head

addition of monomer is possible. Addition in that manner results in the formation of a

high-energy structure which rearranges by a 1,2 chlorine atom shift and then undergoes

the abstraction of a chlorine atom by vinyl chloride.4 The latter reaction results in chain

transfer to the monomer, a process that is very important for controlling the molecular

weight of the polymer during polymerization. In order to increase the molecular weight,

the monomer concentration should be kept high.

Propagation will continue until two radicals interact with each other and terminate

polymerization by coupling or disproportionation. Coupling reactions occur when two

radicals combine to form a bond between the two radical-containing atoms (eq 4).

Termination via coupling leads to a large increase in the molecular weight of the

polymer.

p ; + p * — ► pn+m (4)

Disproportionation occurs when an atom (usually hydrogen) is abstracted from

one radical species by another radical (eq 5). A saturated group is formed at the end of

5one polymer chain, and a double bond is formed between the two carbons at the end of

the other polymer molecule.

Pn* + P^ ---- ► Pn(+H) + P m(-H) (5)

Properties of PVC

Poly(vinyl chloride) has several advantageous properties. It is regarded as one

of the most durable plastics produced. This polymer is insoluble in most solvents and

resistant to corrosion and weathering, properties that allow it to be excellent for use in

building construction materials.1

A feature that is of great importance and is very admirable to consumers is the

long “lifespan” of these polymers. Unless they are used at high temperatures, these

materials remain stable for extended lengths of time. In addition to having good

stability, they are inexpensive to manufacture, and the polymer, itself, requires little

maintenance, making it cost-effective. The extent to which PVC has been thermally

degraded can be tested by using an instrumented drop weight impact test on PVC

samples that have been aged at temperatures above their glass-transition temperature.5

This test is useful for estimating the length of time the polymer retains its useful

properties and for determining the overall extent of degradation after long-term aging.

Materials in landfills are commonly burned for disposal. Burning materials

containing PVC has caused growing concern environmentally because of the corrosive

and toxic hydrogen chloride gas that is given off. However, this polymer is essentially

resistant to fire when it does not contain plasticizers. Because of this property, PVC

can be used as a protective covering for materials that bum easily.1

When PVC is heated in air to temperatures where it does bum, benzene is

formed from the polyene sequences and bums with a smoky flame. The conjugated

polyene stmcture can be modified (usually by crosslinking) in order to prevent

benzene formation. Polyene formation is discussed briefly in the following section of

this chapter.

One disadvantage among the properties of this polymer is its thermal

instability. There are several speculations on the cause of this instability, and several

attempts, many of them successful, have been made to solve this problem.

Additives

During the production and end use of most polymers, additives are necessary for

stabilization, lubrication, plasticization, etc., in order for the polymers to retain their

desirable characteristics. The use of stabilizers in the processing of PVC can slow the

production of hydrogen chloride from the thermal degradation. Plasticizers, in addition

to giving the polymer its flexibility, prevent embrittlement and cracking of the polymer.

Plasticizers will soften the polymer to aid in the formation of a pliable material during the

manufacture of PVC.

The weatherability of PVC is an important consideration to manufacturers

because of the common use of this polymer as a construction material. The presence of

oxygen results in the formation of hydroperoxide groups that affect the stability of the

polymer and its duration of use. Most polymers will degrade in the outdoor environment

7at rates that are dependent on their chemical structure. Within several weeks, the

polymers tend to become brittle without the addition of stabilizers or antioxidants after

the polymerization.6 Ultraviolet (UV) absorbers are additives that are frequently used to

prevent color formation resulting, in part, from the photodegradation of PVC. In the UV

absorption spectrum of PVC, a band appears at 250 nm.7 Pure PVC does not have

structures that are expected to absorb at this wavelength. The most obvious structures in

PVC giving rise to this band are polyene sequences. These sequences are now

considered to be the main photoinitiators in PVC absorbing at 250 nm.7 Ultraviolet

absorbers can be added to polymers such as PVC and are capable of absorbing photons

and then dissipating their energy by radiationless decay to the polymer matrix.7

Additionally, additives that react with the polyene chromophores can prevent or reduce

the color formation in the polymer by shortening polyene length.8

Thermal Degradation of PVC

Unstabilized PVCTmdergoes nonoxidative thermal degradation when it is

heated to temperatures at or above 100 °C. The initiators of this degradation and thus

the main contributors to the thermal instability are thought to be primarily the

structural defects within the PVC. The formation of these defects may occur during

the polymerization process and/or during heating of the polymer.

Regardless of the site of initiation, once dehydrochlorination begins, the loss of

one molecule of hydrogen chloride generates an allylic chloride structure, which is a

thermally unstable site within the polymer. The hydrogen chloride has an

autocatalytic effect on degradation that results in the sequential elimination of HC1

without the loss of monomer and thus leads to the formation of polyene sequences.

-«HC1

v

-(CH=CH)-„+1

Figure 2. Formation of an internal allylic chloride structure and a polyene sequence in PVC.

Polyene sequence formation is favorable because of the additional resonance

stabilization that this process involves. The longer the polyene sequences, the faster the

rate of dehydrochlorination. The tacticity of the polymer is also a factor in determining

the amount of HC1 that is generated during the degradation. The isotactic configuration

liberates HC1 with the most facility.9,10

The polymer is initially colorless. However, polyene growth adds color to it at

less than 0.1-0.2 weight % of HC1 loss.7 The color transition proceeds from colorless to

yellow to black, depending on the number of double bonds present.

The dehydrochlorination will terminate along the polyene sequence once it

contains anywhere from 5 to 25 conjugated double bonds.8 A structural defect within the

polymer may be encountered that leads to termination, or the dehydrochlorination may

oundergo an interruption reaction where the process is randomly stopped.

9

Possible Structural Defects

There are differences in opinion as to the cause of the initiation of the thermal

dehydrochlorination. The relatively unstable structural irregularities in the polymer are

known to be very low in abundance. These irregularities contain easily removable tertiary

or allylic chlorine atoms.9

The microstructure of PVC resin and the polymerization mechanism have been

investigated by 13C NMR, but have given researchers little additional information

regarding the process of degradation. If the 13C spectrum of the polymer itself were

examined, many peaks due to structural defects would be hidden by the complex

resonances of the ordinary monomer units, which occur in different tactic sequences. As

discussed by Starnes,11 in order to solve this problem, tri-«-butyltin hydride can be used

in the presence of a free-radical source in order to replace all of the chlorines with

hydrogens. The 13C spectrum of the resultant polymeric product can then be used to

determine the carbon skeleton. To determine the placement of the chlorines in the

original polymer, tri-rc-butyltin deuteride is used in the same way to replace the chlorines

with deuteriums. The resonances of the deuterated carbons and the carbons to which

those carbons are attached will be shifted upfield.10

As indicated above, most researchers agree that the main initiators of

dehydrochlorination are structural defects containing labile chlorines. These structures

are formed during the polymerization process in different manners. Keeping the

monomer concentration high will decrease their abundance.4 Figure 3 illustrates the

formation of a dichlorobutyl branch.9

10Cl

p p p H2-CH-CH2-CH2-C1

-CH2-C-CH2-C-CH2-CH -c h 2-c * VC

H Cl

Cl

etc. f:h 2-c h -c h 2-c h 2-ci

-c h 2-c -c h 2-

ci

Figure 3. Dichlorobutyl-branch structure formation.

In the formation of this branch structure, an intramolecular “backbiting” reaction

takes place within the propagating radical. Vinyl chloride adds to the new radical to

produce a tertiary chloride, which is thermally unstable. The formation rate of the

dichlorobutyl branch is not affected as the concentration of monomer decreases.

However, this decrease will reduce the rate of normal propagation and thereby increase

12the number of dichlorobutyl branches in the polymer per unit mass.

Another labile structure leading to the initiation of dehydrochlorination is the

long-branch structure. The formation of this defect is shown in Figure 4.9 The

propagating polymeric radical, P., abstracts a chloromethylene hydrogen from a polymer

molecule to form a new radical that will add monomer.

11f fP • + -c h 2c h c h 2- -c h 2c c h 2-

C1

VC c h 2c h c h 2-

-c h 2c c h 2-

C1

Figure 4. Long-branch structure formation.

For the purpose of studying the degradation mechanism of PVC, resins have been

prepared that contain larger than normal concentrations of tertiary and allylic chlorines.

When compared to the degradation rate of normally synthesized PVC, the rates for these

resins were found to be significantly greater during the initial stages of degradation. Onceo

the structural defects were exhausted, the rates slowed to that of normal PVC.

Other possible structures leading to the initiation of degradation are the

ketochloroallylic structure, -CO-CH=CH-CHCl-, and the internal chloroallylic (IA)

7 9structure. ’ The formation of the ketonic structure would be most likely to occur by air

oxidation of the latter one, as shown in Figure 5. However, conclusive evidence for the

presence of the ketonic structure is lacking.10

CH2(CH=CH)nCH

Figure 5. Formation of the ketochloroallylic structure in PVC.

12In addition to the process shown in Figure 2, formation of the IA structure is

known to occur during polymerization by the mechanism in Figure 6.9’10

P* + -CH2 i- PH + -CHoCHCHCH- ̂ •

Cl Cl

VCCl

CICHjCHC] + -CH3CH=CHCH-iFigure 6. Alternative mechanism for the formation of the internal chloroallylic structure.

Several other structural defects are known to be present within the polymer, but

to an ordinary (head-to-tail) propagating polymer radical has not been found to affect the

quantitatively rearranges to radicals that are more stable. Thus, the head-to-head

structure has not been found in the polymer.

Mechanism of the Thermal Dehydrochlorination of PVC

As we have previously seen, there have been several opinions as to the causes of

the rapid thermal degradation of PVC, some of which have been upheld by investigative

research and others that still are speculative. The sources of thermal instability now are

reasonably well understood, but the degradation mechanism itself still is controversial.

An ongoing controversy that is related to this mechanism involves work by W. H.

Starnes, Jr. of the College of William and Mary and R. Bacaloglu and M. Fisch of the CK'

they are not expected to increase the instability.9 The head-to-head addition of monomer

overall thermal stability.10,11 The head-to-head radical that results from this process

13Witco Corporation. As concluded by Starnes et al., PVC undergoes a thermal

dehydrochlorination reaction involving either ion pairs or a four-center transition state

with highly polarized C-Cl bonds.13 The mechanism of the reaction involving ion pairs is

shown in Figure 7.

ci c r-CH2-(CH=CH)„-CHCH2- ■ -CH2-(CH=CH)„-CHCH2- ------- ►

Cl

HC1 + -CH2-(CH=CH)„+i-CHCH2- - - etc.

Figure 7. Ion-pair mechanism for the dehydrochlorination of PVC.

Bacaloglu and Fisch have studied the degradation and stabilization of PVC for

several years. Their publications give insight into their perspectives on the degradation

process and on new methods of stabilization. As discussed in a paper dealing primarily

with kinetics, they have proposed that PVC will undergo dehydrochlorination by a

mechanism in which an internal alkene or polyene structure rearranges via HC1 catalysis

at its homochloroallylic end. The resulting structure, which contains an isolated cis

double bond, then loses HC1 in a six-center concerted process.8 They believe that this

structure is very reactive and that the corresponding trans arrangement does not lose HC1

at all because it is thermally stable. They also claim that the degradation does not involve

the loss of F1C1 through the mechanism in Figure 7. Their initially proposed reaction

mechanism is shown below in Figure 8.

Cl14

Cl

HC1

-HC1

n+1

Figure 8. Proposed six-center dehydrochlorination mechanism for PVC.

Stames et al., tested this mechanism for dehydrochlorination. They synthesized

model compounds for chloroallylic and homochloroallylic structures with one double

bond, in order to compare their thermal stabilities.13 The two compounds were heated

under argon at 170 °C. After only a few minutes, the compound rLra«1s-6-chloro-4-decene

was still present along with a rearranged product, Jraw^-chloro-S-decene (Figure 9), and

a mixture of dienes formed by dehydrochlorination.

Cl15

Cl170 °C

+ dienes

Figure 9. Thermal degradation and rearrangement of 6-chloro-4-decene.

The compound nvms-9-chloro-6-tridecene, did not react, however, after

heating for 24 hours (Figure 10).

Cl

170 °C

no reaction

Figure 10. Thermal degradation experiment on ^wj-9-chloro-6-tridecene.

Degradation experiments also were performed with mixtures of the two

compounds, so that they would be subjected to the same concentration of HC1. This

16procedure caused no significant changes in results. The individual degradation rates

of these models can be visualized from Figure l l . 13

0.0

ID

X I- 1.0

0 100 200 300 400t ime, min

Figure 11. Kinetic plots for the thermal degradation of rra«5-6-chloro-4-decene (•) and ^ra^-9-chloro-6-tridecene (V) at 170 °C.13

In a recently published paper, Bacaloglu and Fisch addressed these results and

acknowledged that the dehydrochlorination of the allylic chloride is a faster process than

the isomerization and subsequent dehydrochlorination of the homoallylic chloride.14

Thus, they concluded that their mechanism in Figure 8 had been ruled out.

In the same paper, Bacaloglu and Fisch provided information regarding the

dehydrochlorination of a cw-allylic intermediate.14 The compounds trcins-6(4)-chloro-

4(5)-tetradecenes were synthesized with the cis isomer making up as little as 4-5% of the

product mixture. Upon heating at 150 °C, a temperature at which PVC

dehydrochlorinates rapidly, HC1 was eliminated, and trans.trans- and cis,trans-4,6-

Con

cent

ratio

n m

ol/k

g17

tetradecadienes were formed. The concentration of the cis isomer of the starting material

increased during the first thirty minutes and then decayed exponentially. Figure 12

shows the concentrations of the four compounds under steady-state conditions.14

4.0" trans-6(4)-chloro-4(5)-tetradecenes

3.5trans-trans-4,6-tetradecadiene

3.0

2.5

2.0cis~trans-4,6-tetradeeadiene

1.5

1.0cis~6(4)-chloro-4(5)-tetradecenes

0.5

0.03002502001500 10050

Time min.

Figure 12. Dehydrochlorination of /r<3«^-6(4)-chloro-4(5)-tetradecenes at 150 °C.14

From these results, the authors concluded that the starting chlorides lose HC1

exclusively via the cw-allylic chloride in a six-center transition state via a 1,4

elimination.14 The cis compound was now suggested to result, however, from the 1,3

rearrangement of chlorine at the chloroallylic end. Other reaction schemes were

considered, but this mechanism was thought to be the most likely scenario.

18In further attempts to investigate the possibility of dehydrochlorination via a four-

center transition state or an ion pair, we have performed several experiments. Model

compounds that correlate with the thermally unstable structural defects in PVC have been

prepared previously in order to compare their degradation rates.9 A model for the

product of a six-center dehydrochlorination, as proposed by Bacaloglu and Fisch, has

been made, and a model has now been synthesized for the expected product of a 1,2

dehydrochlorination in the same system. This system consists of a new allylic chloride,

which was synthesized and dehydrochlorinated in order to determine both the product(s)

and the rate of its degradation.

For obvious reasons, the rate constants for the degradation of individual

structural defects in actual PVC samples are very difficult to determine. The reactivity

difference between the cis and trans structures of PVC can, however, be related to the

reactivities of model compounds. Such model compounds were synthesized earlier in

order to obtain their dehydrochlorination rate constants and to learn whether internal

allylic, terminal allylic, or tertiary chloride is the main destabilizing contributor. The

compounds used for that study are illustrated below and numbered according to the

corresponding numbering sequence in the literature.10

14

R = ft-Pr; R ’ = ?z-Bu

Table 1 contains the dehydrochlorination rate constants of these models in two

different solvents. Decreasing the argon flow rate increases the steady-state

concentration of HC1. Thus the allylic chlorides 10 and 11 are shown to be much

more susceptible to HC1 catalysis than the tertiary chloride. From this table we also

see that there is not much reactivity difference between the cis and trans isomers of the

allylic chlorides. This result does not support Bacaloglu and Fisch’s theory that a cis-

allylic chloride is much more reactive than the corresponding trans structure.

Table 1. Dehydrochlorination Rate Constants for Some Models.102 0

ka x 105, (min) 1

model ^ a 2C6H4 Ph2CO

9 780*1100 5800950c

10 3120*600 3300

29OF11 2000 4900

860c12 6 2113 7 2214 2 20

a At 170i0.5°C with an argon flow rate of 0.14 mL/s unless noted otherwise; reproducibilities were <(±7%). b Argon flow, «;0.14 mL/s (too slow for accurate measurement). c Argon flow, 1.3 mU s.

Our present research on the mechanism of the thermal dehydrochlorination of

PVC was concerned with the synthesis o f the model compounds 3-

ethylidenecyclohexene, 1-vinylcyclohexene, and 2-chloro-l-ethylidenecyclohexane.

These compounds were useful for exploring the mechanism of thermal HC1 loss from

PVC containing internal allylic chlorides as structural defects.

2-Chloro-l-ethylidenecyclohexane (a mixture of cis and trans isomers) was

synthesized to model internal allylic chloride structures in PVC. When these compounds

undergo thermal dehydrochlorination, the 1,2 dehydrochlorination mechanism(s) would

lead to the formation of 3-ethylidenecyclohexenes (Figure 13).

2 1

- HC1

Figure 13. 1,2 Dehydrochlorination of 2-chloro-1 -ethylidenecyclohexanes.

On the other hand, the six-center dehydrochlorination mechanism could occur

only with the cis isomer and would lead to the formation of 1-vinylcyclohexene (Figure

14).

HC1

Figure 14. Six-center 1,4 dehydrochlorination of czs-2-chloro-l-ethylidenecyclohexane.

However, allylic rearrangement of the starting mixture of chlorides by a 1,3

chloro shift, followed by 1,2 dehydrochlorination, would also produce 1-

vinylcyclohexene. Moreover, the latter compound conceivably could undergo HC1-

catalyzed isomerization into the 3-ethylidenecyclohexenes. Therefore, conclusive

evidence against the occurrence of six-center dehydrochlorination would consist of (a)

observation of the reaction in Figure 13 and (b) a conclusive demonstration of the failure

22of 1-vinylcyclohexene to rearrange to 3-ethylidenecyclohexenes under the

dehydrochlorination conditions.

This thesis presents evidence that argues strongly against the concerted six-center

dehydrochlorination of 2-chloro-l-ethylidenecyclohexanes. This evidence, together with

the data in Table 1, argues strongly against the new mechanism of Bacaloglu and Fisch.14

Not only has it been found that trans-allylic chlorides are not thermally stable, inv

opposition to what those workers14 have concluded, but also the isomerization from trans

to cis chlorides has been shown to cause only small changes in the rates of degradation.

The new experimental results that do not support concerted six-center

dehydrochlorination are reported and discussed in subsequent chapters.

II. EXPERIMENTAL

A. Instrumentation

1. Nuclear Magnetic Resonance (NMR)

The NMR spectra were obtained at normal probe temperature through the use of

an Gemini NMR 400 instrument. The chemical shifts are reported in ppm (6) with

TMS (Me4 Si) as an internal reference (6 = 0.00 ppm). The solvent used was

chloroform-<i.

2. Gas Chromatography/Mass Spectroscopy (GC/MS)

The GC/MS data were acquired with a Hewlett-Packard 5890 Series II GC

instrument used in conjunction with a 5971A Mass Selective Detector. This apparatus

was equipped with an HP-1 capillary column (crosslinked methyl siloxane, with

dimensions of 12.5 m x 0.2 mm x 0.33 m). Helium was used as a carrier gas. The GC

parameters are listed in Table 2.

Table 2. GC Parameters.

Injector temperature 250 °C

Detector temperature 250 °C

Initial temperature O o o

Final temperature 300 °C

Rate 20 °C/min to 300 °C

23

243. Dehydrochlorination Rates

Samples were titrated with 0.01 M NaOH, using a Metrohm 702 SM Titrino

apparatus in order to maintain a constant pH value of 4.30. Samples were

thermostated at 170 + 2°C, and the evolved HC1 was swept into deionized water by

using an argon flow of 9-10 mL/min.

4. Evaporations

A Buchi Rotavapor was used under aspirator vacuum for the rotary evaporation of

ethereal product fractions.

B. Materials

Aldrich was the supplier of 1-acetylcyclohexene (97%), cerium(III) chloride

heptahydrate (99.9%), A-chlorosuccinimide (98+%), cyclohexanone (99.8%), 1,2-

dichlorobenzene (99%), anhydrous DMSO (99.8%), hydrazine monohydrochloride

(98+%), hydrogen peroxide (30 wt % solution in water), KOABu (95%), anhydrous

methyl sulfide (99+%), oxalic acid dihydrate (99%), sodium borohydride (99%), sodium

ethoxide (21 wt % solution in ethanol), triethylamine (99.5%), 4-vinylcyclohexene

(99%), and 1.0 M vinylmagnesium bromide solution in THF. Fisher supplied Reagent

Grade acetaldehyde, acetonitrile, anhydrous magnesium sulfate, chromatographic silica

gel (Catalog No. S744-1), potassium bisulfate, ethyl acetate, hexanes, and 4 A molecular

sieves.

25C. Experimental Procedures

Details of compound characterization appear in the Results chapter.

1. Synthesis of 1-Acetylcyclohexene Oxide15

1-Acetylcyclohexene (49.6 g, 0.4 mol) and a 30% aqueous solution of

hydrogen peroxide (37 mL, 1.2 mol) in 400 mL of methanol were combined and

stirred in an ice bath between 2-5 °C. A 6-M sodium hydroxide solution (33.3 mL, 0.2

mol) was then added dropwise to the mixture in such a manner that the temperature

did not rise above 30 °C. The solution was stirred for three additional hours to ensure

completion of the reaction. Then the reaction was quenched with 400 mL of deionized

water and extracted with two 400-mL portions of ether. After the combined ethereal

extracts had been dried over anhydrous MgSCL, the ether was removed at room

temperature by rotary evaporation under aspirator vacuum. Presence and purity of the

desired product were established by GC/MS data. The epoxide was purified by

vacuum distillation at ~5 torr; bp 82 ± 5 °C (lit.16 bp 86-87 °C at 12 torr); yield, 44.8 g

(80%); purity, 95-100%.

2. Synthesis of 2-Ethylidenecyclohexanol16

Hydrazine monohydrochloride (0.14 g, 2 mmol) and triethylamine (0.30 g, 3

mmol) in 2 mL of acetonitrile (dried over 4A molecular sieves) were ultrasonicated in

a Fisher Scientific FS9 Ultrasonicator for 2 h at room temperature. 1 -

Acetylcyclohexene oxide (0.09 g, 0.65 mmol) in 1 mL of dry acetonitrile then was

added, and the mixture was stirred at room temperature under N 2 for 40-52 h. The

progress of the reaction was monitored by GC/MS. When all o f the epoxide had

26reacted, the reaction was terminated by quenching with a saturated sodium chloride

solution (15 mL). The mixture was extracted with two 15-mL portions of ether. Then

anhydrous magnesium sulfate was used to dry the combined ethereal layers and the

ether was removed by rotary evaporation under aspirator vacuum. The crude allylic

alcohol was isolated by chromatography on a 300-mL, 350-mm silica gel column

(eluent, hexane- A cO Et: 8-2). Presence and purity of the desired product was

determined by GC/MS and NMR data; yield, 0.03 g (35%); purity, 97%.

3. Synthesis of 2-ChIoro-l-ethyIidenecyclohexane17

A solution of A-chlorosuccinimide (0.29 g, 2.2 mmol) in anhydrous methylene

chloride (10 mL) was cooled to 0 °C in an ice bath under argon. Methyl sulfide (0.15

g, 2.4 mmol) was added dropwise to this solution with stirring. The reaction mixture

was cooled to -20 °C prior to the addition of 2-ethylidenecyclohexanol (0.25 g, 2.0

mmol) in methylene chloride (1 mL). After the addition, the reaction mixture was

warmed to 0 °C and stirred for an additional hour. The mixture was then poured into

an ice-cold sodium chloride solution (10 mL) and extracted with two 4-mL portions of

ether. The combined organic layers were washed with two 4-mL portions of cold

sodium chloride solution and dried over magnesium sulfate; then the ether was

removed by rotary evaporation under aspirator vacuum. The presence of the desired

product was established by GC/MS and NMR data; yield, 0.20 g (71%); purity (60%).

4. Thermal Dehydrochlorination of 2-Chloro-l-ethylidenecyclohexane

2-Chloro-l-ethylidenecyclohexane (0.14 g, 1 mmol) was added to 1,2-

dichlorobenzene (1.1 mL, 10 mmol), and the solution was heated at 170 ± 2 °C. An

27argon stream (9-10 mL/min) was used to sweep the evolved hydrogen chloride into

deionized water where it was titrated with a 0.01 M solution of NaOH. The base was

introduced via the Metrohm 702 SM Titrino apparatus in order to maintain a constant

pH of 4.30. The products of this reaction were analyzed by GC/MS.

185. Synthesis of 3-Ethyhdenecyclohexene

4-Vinylcyclohexene (20.0 g, 0.19 mol) and 0.7 M potassium /-butoxide in

dimethyl sulfoxide (125 mL) were combined and heated to 100 °C with stirring for 75

h. The progress of the reaction was monitored by GC/MS. The resulting solution was

quenched with water (100 mL), extracted with two 100-mL portions of ether, and

dried over magnesium sulfate. The presence and purity of the expected product was

verified by GC/MS data; yield, 6.9 g (35%); purity, 99%.

6. Synthesis of 1-Vinylcyclohexanol19

1-Vinylcyclohexanol was formed by allowing cyclohexanone to react with

vinylmagnesium bromide in the presence of cerium chloride, a catalyst for the

reaction.19 The cerium chloride (0.56 g, 1.50 mmol) was finely ground into a powder

and placed in a flask that then was sealed under vacuum. For two hours the catalyst

was heated at 100± 5 °C under vacuum at ~5 torr. Then the temperature was increased

to 140 °C under vacuum for two more hours. The flask was filled with argon and

immersed in an ice bath between 2-5 °C. Tetrahydrofuran (5 mL), freshly distilled

from sodium/benzophenone, was added, and the suspension was vigorously stirred at

ambient temperature overnight. The flask was cooled to -78 °C; 0.20 mL (1.50

mmol) of a 1.0-M solution of vinylmagnesium bromide in THF was added with

28stirring; the mixture was kept at -78 °C for 1.5 h. Cyclohexanone (0.15 g, 1.0 mmol)

was added and allowed to react for one hour, while maintaining a temperature o f -78

°C. At this point, the reaction mixture was checked by GC/MS for presence of the

alcohol and subsequently treated with 10 mL of 10% acetic acid solution in water.

The cooling bath was removed, and the mixture was stirred for 30 min. Then it was

extracted with two 25-mL portions of ether, and the ether solution was washed in

succession with 10 mL of 10% sodium chloride solution and 10 mL of 10% sodium

bicarbonate solution. The ethereal solution was dried over anhydrous magnesium

sulfate and subjected to rotary evaporation. The presence of the expected product was

verified by GC/MS and NMR data, and the alcohol was isolated by vacuum

distillation at ~5 torr; bp 63 ± 2 °C (lit.20 bp 61 °C at 13 torr); yield, 0.09 g (57%);

purity, 97%.

7. Synthesis of l-Vinylcyclohexene20

The isolated alcohol (1.7 g, 13 mmol) synthesized in the above way was

combined with 5 wt % of anhydrous potassium bisulfate (0.09 g, 0.66 mmol), and the

mixture was heated at 100 °C and stirred for three hours. It then was filtered; the solid

was washed with ether (10 mL); and the washings were combined with the original

filtrate. Rotary evaporation was used to remove the ether, and the product was

analyzed by GC/MS; yield, 1.20 g (71%); purity, 61%.

III. RESULTS

Model Compound for the Internal Allylic Structure in PVC

Two possible synthetic routes leading to a model compound (4) for the internal

allylic structure in PVC are shown in Figure 15.

O

2

OH

4

Figure 15. Synthesis of 2-chloro-l-ethylidenecyclohexanes.

29

30One route required the preliminary synthesis of 2-ethylidenecyclohexanone (l).21

The carbonyl group of this compound was to be reduced to a hydroxyl group in order to

form 3. Cyclohexanone and sodium ethoxide (21 wt % in ethyl alcohol) were combined

with stirring and cooling to 0 °C. A solution of acetaldehyde in cyclohexanone was then

added slowly, and the mixture was stirred for an additional 45 minutes. Addition of

water and treatment with oxalic acid dihydrate, followed by a conventional aqueous

workup, gave a product mixture that was subjected to vacuum distillation in a spinning

band micro still with a nominal separation efficiency of 150 theoretical plates. Vacuum

distillation was the method of separation used by Van-Catledge et al., and the yield they

91reported for 1 was 26%. An easier and more effective method of separation may be

column chromatography, but this method was never tried. Despite considerable

difficulties encountered with the distillation, we eventually isolated the compound in very

low yields with a purity of 95% and then reduced it to compound 3 having a purity of

81%.

99The method used for the reduction was as follows. Compound 1 (1 mmol) and

cerium(III) chloride heptahydrate (1 mmol) were dissolved in methanol. Sodium

borohydride (1 mmol) was added with stirring, which was continued for 1 hour.

(Cerium(III) chloride heptahydrate was used to form a complex reagent to prevent the

formation of alkoxyborohydrides from the methanol and NaBFL*.) After neutralization

with dilute aqueous HC1 and a standard aqueous workup, crude 3 (identified by GC/MS)

was obtained in low yield. Because of the small amount of alcohol formed, the

conversion of this product into 4 was not attempted. Following several unsuccessful

31attempts to prepare a useful amount of purified 1, an alternative method of synthesis was

chosen.

The second method for the synthesis of 3 required the preparation of 1 -

acetylcyclohexene oxide (2), which was subsequently converted into the desired alcohol.

The synthesis of 2 was patterned after a similar synthesis published in Organic

Syntheses.15 The results were checked by GC/MS analysis (Figures 1-1 and 1-2). The

retention time of 2 was 3.44 min, and after vacuum distillation, a purity of 95-100% was

obtained. The mass spectrum of this compound is shown in Figure 1-1. It shows M+# =

140, as required. Figure 1-2 shows the mass spectrum of a minor impurity typically

present and difficult to separate from the epoxide. The retention time of this impurity is

3.71 min and it apparently has M+* =156 (very weak). It appears that the impurity may

have resulted from the base-promoted addition of methanol to the alkene double bond of

1 -acetylcyclohexene.

After purification, 2 was converted into 3 by a process known as the Wharton

transposition, which enables the formation of allylic alcohols from acyl epoxides, via

a,p-epoxyhydrazones.16 This reaction requires anhydrous hydrazine, which was formed

by the ultrasonication of triethylamine and hydrazine monohydrochloride. The

ultrasonication helps to establish the equilibrium shown in Figure 16, which is shifted to

the right by using an excess of triethylamine. The suggested mechanism of the Wharton

transposition is shown in Figure 17.

H2NNH3 Cl + Et3N H2N-NH2 + Et3NH+Cl"

Figure 16. Formation of hydrazine.

32

L2 I N - lN r i2

-NH

+ HoO

N-NH- N=NH

Et,N

OH

N=NH

OH

Et,N

OHNo

Figure 17. Synthesis of 2-ethylidenecyclohexanols.

The results of this reaction were determined by GC/MS analysis, which showed

that the purity of the crude alcohol product (3) was never greater than 50%. The GC/MS

results after 48 h of reaction are shown in Figures 2-1 through 2-5. In the mass spectra,

the two peaks with retention times of 0.37 and 0.40 min are due to residual hydrazine and

acetonitrile. Compound 3 (M+#= 126) occurs as two stereoisomers with very similar

mass spectra (Figures 2-1 and 2-2) and retention times of 2.91 and 3.05 min. The

component with a retention time of 3.22 min and M+,= 124 is apparently an isomer of 1-

33acetylcyclohexene. Figures 2-4 and 2-5 show the mass spectra o f two other unidentified

by-products that had retention times of 5.05 and 9.41 min.

Isolation of 3 was performed by using column chromatography. The column was

packed with silica gel, and an 8:2 (v/v) mixture of hexane:ethyl acetate was used as the

eluent. The GC/MS results for the purified alcohol stereoisomers are shown in Figures 3-

1 and 3-2. The retention times of 0.47 and 0.62 in these figures are for the components of

residual eluent. Figures 3-3 and 3-4 show the *H and 13C NMR spectra, which are in

very good agreement with the spectra reported for 3 in the literature.16,23 Distorted

singlets (actually triplets) present in the lH spectrum at 4.1 and 4.8 ppm correspond to the

CHOH proton of the trans and cis isomers, respectively. Additional absorption occurs

between 1.2 and 2.6 ppm, owing to the presence of residual eluent. The unassigned

13peaks in the C spectrum are thought to be due in part to residual eluent and partly to

multiplicity resulting from the presence of the chiral CHOH carbon.

Compound 3 was converted into chloride 4 via a method utilized by Corey et al.,17

in which the replacement of the hydroxyl group by chlorine is done under neutral

conditions (see Figure 18). The alcohol reacts with the complex formed from N-

chlorosuccinimide and methyl sulfide in order to produce 4.

34

-C1 + CH.SCH +

OH

+ (CH3)2SOOS(CH3)2

Figure 18. Synthesis of 2-chloro-l-ethylidenecyclohexanes.

The presence of 4 was verified by GC/MS (Figures 4-1 through 4-5) and NMR

analysis (Figure 4-6). The M+* values of this product are 144 and 146 in a ratio of 3:1,

respectively. Three isomers of the compound sometimes appeared in the gas

chromatograph. Two are believed to be the stereoisomers of 4, while the other is

considered to be the product of an allylic rearrangement. The retention times of the three

isomers are 3.18, 3.29, and 3.33 minutes. It is not yet entirely clear which of these

compounds is which.

Dehydrochlorinated product isomers (dienes) appeared in the GC/MS traces as

well. It was uncertain whether the thermally unstable chlorides degraded after injection

into the GC/MS apparatus or simply upon exposure to atmospheric conditions. The

degradation products had retention times of 1.97 and 2.07 min and the expected M+*

value of 108. Their mass spectra are shown in Figures 4-1 and 4-2.

351 7Figure 4-6 shows the C NMR results. This spectrum strongly suggests the

absence of significant amounts of dehydrochlorination products from the original mixture

of allylic chlorides.

The mixture of chlorides was thermally dehydrochlorinated at 170 ± 2 °C.

After 50 minutes, the extent of dehydrochlorination was calculated to be 72.6%, and

two isomeric dienes were formed. Figures 5-1 and 5-2 show their mass spectra. The

rate constant for the initial stage of dehydrochlorination was estimated to be ca. 4.3 x

10" /min from the slope of the plot in Figure 5-3. Figure 5-4 shows a plot of [In a/(a-

x)] vs. time, where a = the initial amount of 4, and x = the total amount of NaOH used

in the titration. This crude first-order plot gave a rate constant of ca. 2.3 x 10"2/min.

Both rate constants are similar to values reported previously for 10 and 11 in o-

dichlorobenzene (see Table 1).

Models for the Possible Thermal Dehydrochlorination Products of 4

The base-catalyzed isomerization of 4-vinylcyclohexene in the presence of 0.7 M

potassium f-butoxide in DMSO was conducted in order to synthesize the cis and trans

1 Xisomers of 5.

DMSO

Figure 19. Synthesis of 3-ethylidenecyclohexenes.

36After the reaction, the product mixture usually contained up to 97% of compound

5. As noted in the published procedure,18 purification of 5 was attempted by fractional

distillation under atmospheric pressure. However, when this purification method was

tried, the purity of 5 decreased. Heating promoted the formation of by-products and

resulted in poor separation. The GC/MS results for the product formed prior to

distillation are shown in Figure 6-1.

The synthesis of diene 7 first required the preparation of 1-vinylcyclohexanol,

(6). This compound was then dehydrated to form 7.

O

1. CH2=CHMgBr

6

H

Figure 20. Synthesis of 1-vinylcyclohexene.

The first attempt at the formation of the alcohol was unsuccessful for producing a

large yield of product. Under nitrogen, vinylmagnesium bromide was added dropwise to

cyclohexanone. During the addition, the temperature was kept at or below 35 °C.

Stirring was continued for 30 minutes upon completion of the addition, and the mixture

then was refluxed for one hour. A saturated solution of ammonium chloride was slowly

added. Ether was used to extract the organic layer, which was subsequently dried over

magnesium sulfate and subjected to rotary evaporation in order to remove the ether.

Analysis by GC/MS showed that cyclohexanone comprised a large part of the residue.

37Vacuum distillation through a Vigreux column was attempted, and when this method of

separation did not succeed, the spinning band microstill was used. The results of the

separation still were poor. The major difficulty was the unsatisfactory separation of the

1-vinylcyclohexanol from the cyclohexanone.

The second method used for the synthesis of 6 involved the reaction of

cyclohexanone with vinylmagnesium bromide in the presence of cerium(III) chloride.

From the experimental results published by Imamoto et al., it is seen that when the

reaction was performed without cerium chloride, a 30% yield was obtained for the

alcohol addition product and a 35% yield for the ketol product shown in Figure 2 1.19

OH

Figure 21. Side product formed during reaction of Grignard reagent and cyclohexanone.

When cerium(III) chloride was used in the reaction, the yield of 6 increased to 80%, and

no ketol product was formed.19 This reaction must be performed at very low

temperatures (-78 °C was used by us). At 0 °C, vinylic Grignard reagents will

decompose upon interaction with cerium(III) chloride.19

The GC/MS results for the synthesis of compound 6 are shown in Figures 7-1 and

7-2. Figure 7-1 shows the mass spectrum of a minor by-product, which has a retention

time of 1.51 min. The retention time of 1-vinyl-1-cyclohexanol (M+’= 126) is 2.25 min,

38as shown in Figure 7-2. The 'H NMR spectrum of this alcohol, shown in Figure 7-3, has

a peak between 3.3 and 3.5 ppm resulting from the proton of the hydroxyl group. Peaks

present at 5.0, 5.2, and 6.0 ppm are due to the protons of the vinyl group. Figure 7-4 is

the I3C NMR spectrum.

After fractional vacuum distillation of the reaction products, the isolated portion

of 6 was dehydrated to compound 7 upon addition of potassium bisulfate. The GC/MS

results for the product mixture are shown in Figures 8-1 through 8-5. Compound 7 has a

retention time of 1.72 min and its mass spectrum (Figure 8-1) differs considerably from

the dehydrochlorination product spectra shown in Figures 5-1 and 5-2. The 13C NMR

spectrum (not shown) of the product mixture was complex but, significantly, did not

contain any resonances near 12 ppm, which is the region where the methyl peak of cis-

and trans-5 would have appeared.

IV. DISCUSSION AND CONCLUSIONS

2-Ethylidenecyclohexanol was prepared and converted into 2-chloro-1 -

ethylidenecyclohexane (4). This compound (actually an isomer mixture), which models

the internal chloroallylic structure in PVC, was synthesized in order to measure its rate of

dehydrochlorination and to determine whether its major degradation product consists of

3-ethylidenecyclohexenes or 1-vinylcyclohexene. The products expected via the 1,2 loss

of HC1 are 3-ethylidenecyclohexenes (5), as shown in Figure 22.

4

Figure 22. Formation of 3-ethylidenecyclohexenes through a 1,2 dehydrochlorination mechanism.

If the reaction were to proceed through the six-center 1,4 process that Bacaloglu &

Fisch14 would expect, the dehydrochlorination product would be 1-vinylcyclohexene (7),

as illustrated in Figure 23.

39

40

7

Figure 23. Formation of 1-vinylcyclohexene through a six-center 1,4 dehydrochlorination mechanism.

The gas chromatogram of compound 5 obtained from the isomerization of 4-

vinylcyclohexene shows that 5 has a retention time that is extremely close to the retention

times of the dienes formed by dehydrochlorination. Those two isomers have retention

times of 1.96 and 2.07 min, while the retention time of the isomerization product is 2.00

min. Thus the dehydrochlorination appears to have occurred via the 1,2 mechanism

shown in Figure 22. Dehydrochlorination through the 1,4 mechanism shown in Figure 23

does not appear to have occurred to any significant extent. If HC1 had been lost through

that mechanism, a diene peak for 7 with a retention time of 1.72 min and a mass spectrum

like that of Figure 8-1 would have been observed. Acid-catalyzed isomerization of 7

into 5, under the dehydrochlorination conditions, has not yet been ruled out by

experimentation. However, this isomerization would have had to occur quantitatively in

order to account for the apparently exclusive formation of 5 from 4.

All of the evidence now available strongly suggests, therefore, that the new six-

center mechanism14 for the dehydrochlorination of secondary allylic chlorides is

inoperative.

- HC1

Abundance

1 -4 e+07 -

1 .2 e + 0 7 -

le+ 07 -

8000000 -

6000000

4000000 -

2 0 0 0 00 0 -

Time ->

'Abundance

3.'4 4TIC: PVCS5.D

3 . 7 1

2 . 0 0 4 .0 0 6 . 0 0 8 . 0 0

S can 412 (3 .4 22 min)

1 0 . 0 0 1 2 . 0 0

2 20 000 0

2 0 0 0 00 0

1800000 -

1600000 -

1400000

1 2 0 0 0 0 039

1000000 -

800000 - I

600000 -j 27 5569

1094 0 0 0 0 0

2 0 0 0 0 0 -

140137| 1 54159

•l/Z 20 30 50- > 60 70

Figure 1-1. GC/MS analysis of 1-acetylcyclohexene oxide (2).

42

• 1 . 4e+07

le+07

8000000

6000000

4000000

2000 00 0

12 . 0 01 0 . 0 00000002 . 0 0(Time' ->

(AbundanceminScan

60000.

50000

40000

7130000

20000

124 •

1 0 0 0 0

25263 28930025020 01501 0 050- >

Figure 1-2. Impurity in compound 2.

43

TIC: PVC39.Dabundance 550000 i 22

500000 - p - 37

450000 -

'400000 -

5 .05350000 -

300000 40

250000

200000

150000

1 00 00 0

50000

1 2 . 0 01 0 . 0 08 . 0 06 . 0 04 . 00prime ->

Abundance S can 348 (2 .9 0 9 ruin)2f7 39

1000

10000

9000

558000

7000'OH

6000

69500083

4000 93111

3000126

2000 -

1000

180160140120100804020

Figure 2-1. GC/MS analysis of Wharton transposition product after 48 h.

44

TIC: PVC39.DAbundance 550000 -t 22

500000 -jO-37

450000 -

400000

5 .0 5350000

300000

250000

20 00 0 0 -

150000 -

3 .521 0 0 0 0 0 -

— >11|>»\ il> »50000 -

1 2 . 0 01 0 . 0 08 . 0 06 . 0 04 . 002 . 0 0

S can 366 (3 .0 5 6 min)(Abundance2!7

10000

9000

800097

7000 55OH

6000

83500069

400079

1113000

1262000

1 0 0 0 -1 170133 142 153

180160140120100806020M/Z ->

Figure 2-2. GC/MS analysis of Wharton transposition product after 48 h.

45

TIC: PVC39.DAbundance 550000 i 22

500000 I0 *37

450000

‘ 400000

5 .0 5350000

300000

250000

200000

150000

3.52100000

50000

1 2 . 0 01 0 . 0 0006 . 0 04 .002 . 0 0

Scan 386 (3 .2 2 0 m in)Abundance4'3

90000

80000

70000

60000

50000

4000079

30000 109

53 12420000

1000018391 97 136144

180160140120100806020M/Z ->

Figure 2-3. GC/MS analysis of Wharton transposition product after 48 h.

46

TIC: PVC39.D22

500000 - 9 - 31

450000 -

400000

5 .0 5350000

300000 40

250000 -

200000

1 5 0 0 0 0 -

3 .52100000 -

50000

12.0010.00.006.004 .002.00r im e ->S can 610 ( 5 .0 5 9 m iniAbundance

6000 -

5000 1

1381094000 -

23

573000 -[69

2000 - 12091

1000 -183 I 94

1806014120100806020->

Figure 2-4. GC/MS analysis of Wharton transposition product after 48 h.

47

TIC: PVC3922

500000 -]0 - 37

450000

•400000

5 .0 5350000

300000 40

250000

200000

150000

3 .52100000

50000

12.0010.008 .006.004 .0 02.00Time ->Scan 1140 (9 .4 0 6 min)fUsundance

9000

8000

7000 -

6000 -

5000 -

4000 -

215 22991300028

1602000 -

174107 146120 2431000 -2 5 $ 67

260100 120 140 160 180 200 22080604020M/Z ->

Figure 2-5. GC/MS analysis of Wharton transposition product after 48 h.

PVC05TICAbundance26

1 .6e+07 -

1. 4e+07 -

le+07 -

8000000 -

6000000

4000000

2000000

. 6210.008.006.004 .002.00Time ->

s ^ n r r -<3 . 1 0 9 min)(Abundance

800000

70000039

55600000

'OH500000

400000 27 111

300000 126

200000

100000 -19014 4152 H&B

180160140120100806020

Figure 3-1. GC/MS analysis of 2-ethylidenecyclohexanol purified by columnchromatography.

49

TIC: PVC05.D26

le+07 -

8000000 -

6000000 -

4000000 -

2000000 - 0 .4 7

0 .6 2 12.0010.008.006.004 .00

Scan 389 (3 .2 5 6 mini

2.00

1600000

1400000

391200000 55OH

1000000

83 11169800000126

600000 - 79

400000 -

200000 -185193131913 155 169

18012010080604020M/2 ->

Figure 3-2. GC/MS analysis of 2-ethylidenecyclohexanol purified by columnchromatography.

50

Figu

re

3-3.

NM

R sp

ectru

m of

2-et

hylid

enec

yclo

hexa

nols.

51

«oFi

gure

3-

4.

C sp

ectru

m of

2-et

hylid

enec

yclo

hexa

nols.

52

Abundancele+07-f

SOOOOOO -

8000000 •

7000000

6000000

5000000 -

4000000

3000000

/Time ->

3 .2 9TIC: PVC0 6.D

2.0'

1.3-3 . 8

■ 3 33

! 1 J. -A2.00 4 .00 6.00 8 .00 io Too ■12.00

jAbundartce S can 233 (1 .9 7 0 min)

400000

350000 -

300000 -

250000

200000 -

150000 -

108100000

50000 -

2 95 3 KB 34 0129 152350pi /Z -> 50 100 300200150 250

Figure 4-1. GC/MS analysis of products from 2-chloro-l-ethylidenecyclohexanesynthesis.

53

Abundance TIC: PVC06.Dle+ 07 - 3 .29

9C00000 2 .07 j

8000000

7C00000I 1

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202215 250 266 235 30014149 175h/z -> 50 100 200 250150 300

Figure 4-2. GC/MS analysis of products from 2-chloro-l-ethylidenecyclohexanesynthesis.

54

P r.dance le + 0 7 -j

TIC; PVC0 6.D

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180000 -

160000 -

39140000 -

120000 -

100000 -

80000 -

9160000 -I

40000 144

20000 ■2 281 306 32834220317 246

M/Z 50 300250100 200150->

Figure 4-3. GC/MS analysis of products from 2-chloro-l-ethylidenecyclohexanesynthesis.

55

Puzundancele+07 h

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7000000

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33

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350000 -

300000 -

250000 -

200000

150000

100000

50000

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Figure 4-4. GC/MS analysis o f products from 2-chloro-l-ethylidenecycIohexanesynthesis.

56

Abundancele+07A

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160000 -

67140000 -

120000 -

39100000 -

30000

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40000

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Figure 4-5. GC/MS analysis o f products from 2-chloro-l-ethylidenecyclohexanesynthesis.

57

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58

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Figure 5-1. GC/MS analysis of diene products from thermal dehydrochlorination.

59

TIC: PVC07.DAbundance

le+ 07

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2000000

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80000 -

70000 -

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40000 - 108

30000 -

20000 -

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35030025020015010050

Figure 5-2. GC/MS analysis of diene products from thermal dehydrochlorination.

60

Time (min)

Figure 5-3. Initial-rate kinetic plot for the thermal dehydrochlorination of the allylic chlorides at 170 °C.

140

120

100

^ 80 4

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T.v'-.y = 2.2805x + 25.4191 t : -> R2 = 0.9233 1

r,-* -mmmesm

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40

20

10 15 20 25 30

Time (min)

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Figure 5-4. Crude first-order kinetic plot for the thermal dehydrochlorination of theallylic chlorides at 170 °C.

Abundance 500000 - 00

450000

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30000

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Figure 6-1. GC/MS analysis o f the isomerization product of 4 -vinylcyclohexene.

62

TIC: PVC28.D2 .2 5

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18000 -42

16000 -

14000 -

55120C0

10000 -

000 -

6000 -

4000 - 8269

2000 -184190112 125 137

18016014012010080604020M/2

Figure 7-1. GC/MS analysis o f the products from the synthesis o f 1-vinylcyclohexanol.

63

TIC: PVC^a.DLbundance 2400000 i 25

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250000 -

200000 - 27

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Figure 7-2. GC/MS analysis of the products from the synthesis of 1-vinylcyclohexanol.

64

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66

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80000

70000

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50000 - 51

4000091

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Figure 8-1. GC/MS analysis o f dehydration products o f 1-vinylcyclohexanol.

67

TIC: PVC32.D72

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40000 -

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30000

25000

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Figure 8-2. GC/MS analysis of dehydration products o f 1-vmylcyclohexanol.

68

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2 0 0 0 ■

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Figure 8-3. GC/MS analysis o f dehydration products of 1-vinylcyclohexanol.

----------:---------------------------- TIC: PVC32.DAbundance

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700000 -

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Figure 8-4. GC/MS analysis o f dehydration products of 1-vinylcyclohexanol.

70

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71REFERENCES

(1) Chlorine Chemistry Council. PVC in Building & Construction. Available: http://www.c3.org/library/pvcbuild.html

(2) Alger, M. S. M. Polymer Science Dictionary; Elsevier Applied Science: London, 1989; p 386.

(3) Choi, K. Y.; Kwag, B. G.; Park, S. Y.; Cheong, C. H. In Handbook o f Radical Vinyl Polymerization; Mishra, M. K.; Yagci, Y., Eds.; Marcel Dekker: New York, 1989; Chapter 12.

(4) Starnes, W. H., Jr.; Zaikov, V. G.; Chung, H. T.; Wojciechowski, B. J.; Tran, H. V.; Saylor, K. Macromolecules 1998, 31 1508.

(5) Elleithy, R. H.; Abu-Ali, A. J. o f Vinyl Addit. Technol. 1999, J , 200.

(6) Scott, G. Polymers and the Environment; Royal Society of Chemistry: Cambridge, 1999; p 53.

(7) Minsker, K. S.; Kolesov, S. V.; Zaikov, G. E. Degradation and Stabilization o f Vinyl Chloride Based Polymers', 1988.

(8) Bacaloglu, R.; Fisch, M. Polym. Degrad. Stab. 1994, 45, 301.

(9) Starnes, W. H., Jr., In Polymeric Materials Encyclopedia’, Salamone, J. C., Ed.;CRC Press: Boca Raton, 1996; Vol. 9, p 7042.

(10) Starnes, W. H., Jr.; Girois, S. Polym. Yearbook 1995,12, 105.

(11) Starnes, W. H., Jr.; Presented at the Society of Plastics Engineers Regional Technical Conference, New Brunswick, NJ, October 1995.

(12) Starnes, W. H., Jr.; Wojciechowski, B. J.; Chung, H.; Benedikt, G. M.; Park, G. S.; Saremi, A. H. Macromolecules 1995, 28, 945.

(13) Starnes, W. H., Jr.; Wallach, J. A.; Yao, H. Macromolecules 1996, 29, 7631.

(14) Bacaloglu, R.; Fisch, M. J. Vinyl Addit. Technol. 1999, 5, 205.

(15) Wasson, R.; House, H. O. In Organic Syntheses', Rabjohn, N., Ed.; John Wiley & Sons: New York, 1963; Vol. 4, p 552.

(16) Dupuy, C.; Luche, J. L. Tetrahedron 1989, 45, 3437.

72(17) Corey, E. J.; Kim, C. U.; Takeda, M. Tetrahedron Lett. 1972, 42, 4339.

(18) Bank, S.; Rowe, C. A., Jr.; Schriesheim, A.; Naslund, L. A. J. Org. Chem. 1968, 33, 221 .

(19) Imamoto, T.; Takiyama, N.; Nakamura, K.; Hatajima, T.; Kamiya, Y. J. Am. Chem. Soc. 1989, 777,4392.

(20) Suga, K.; Watanabe, S.; Kamma, K. Can. J. Chem. 1967, 45, 945.

(21) Van-Catledge, F. A.; Boerth, D. W.; Kao, J. J. Org. Chem. 1982, 47, 4096.

(22) Gemal, A. L.; Luche, J. L. J. Am. Chem. Soc. 1981,103, 5454.

(23) Birtwistle, D. H.; Brown, J. M.; Foxton, M. W. Tetrahedron Lett. 1986, 27, 4367.

73VITA

Lynda Beth Payne

The author was bom in Virginia Beach, Virginia on September 15, 1976. She

received her high school diploma from First Colonial High School in June 1994. She

attended Virginia Tech for her undergraduate education and received the Bachelor of

Science degree in Biology in May 1998. She then enrolled in the Master o f Arts program

in Chemistry at the College of William and Mary in August 1998, and completed this

program under the guidance of Dr. William H. Stames, Jr.