PERFLUORINATED COMPOUNDS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By

ROBERT RAYMOND BROWN, B. S., M. S.

The Ohio State University 1955

Approved by

Adviser Department of Chemistry ACKNOWLEDGMENT

The author expresses his sincere gratitude to Dr. Albert L. Henne for his encouragement and helpful guidance in this research. He also wishes to express appreciation for the counsel of Dr. Harvey V. Moyer

during the latter phase of this work.

11 TABLE OF CONTENTS

PAGE

INTRODUCTION 1

HISTORICAL 5

EXPERIMENTAL 6

Reactions of Perfluoro-n-propylzinc Iodide 6

Preparation of C^FjZnl 6

Attempted reaction of C^FyZnl with 7

C3FjCOOC2Hj

Attempted reaction of C^F^Znl with CFgCOQC^H^ 1 8

Reaction of C^F^Znl with acetophenone 10

Attempted reaction of C^FyZnl with benzaldehyde 12

Reaction of C^F^Znl with acetic anhydride 12

Metal interchange with magnesium 13

Chain doubling reaction of C^Fyl with zinc 13

Preparation of C^FyZnBr 15

Synthesis of Hexafluoroacetone 17

Esterification of CF^COOH 17

Preparation of CF3-C(OH)CH3 18

ch3

Dehydration of CF3-C(OH)CH3 .19

ch3

Preparation of CF3-CH-CH3 20

CH3

Chlorination of CF3-CH-CH3 (I) 23

c h 3 ill iv

PAGE

Dehydrohalogenation 26

Fluorination 29

Chlorination of CF3-CH-CH3 (il) 35

Dehydrohalogenation 37

Chlorination of CF0-CH-CH0 (ill) k2 I 0 ch3

Dehalogenation of CF^-CCl-CCl^ ^7

CH3

Attempted dehydrohalogenation of CF^-CH-CCl^ b8

CHC12

with sodium carbonate

Dehydrohalogenation of CFo-CH-CClo with KOH and 1 chci2

isopropyl alcohol

Dehydrohalogenation of CF^-CH-CClo 50 1 CC1- 3 Fluorination 50

Attempted ozonolysis of CFo-C=CHCl and CF-d-C=CC12 51 1 1 CF3 cf3

Oxidation of CF3-C=CHC1 and CF-^-CzCCl^ to CF3-CO-CF3 52

cf3 cf3 V

PAGE

Attempted Bromination of CF^-CHg-CF^ 57

Preparation of CF^-CHg-CF^ 58

Attempted ’bromination of CF^-CHg-CF^ with N-bromo- 58

succinimide in glacial acetic acid

Attempted bromination of CF^-CHg-CF^ with N-bromo- 59

succinimide in nitrobenzene

Attempted bromination of CF^-CHg-CF^ with bromine 59

and aluminum bromide

PHYSICAL CONSTANTS OF NEW COMPOUNDS 62

SUMMARY 63

GENERAL CONCLUSIONS 66

BIBLIOGRAPHY 68 INTRODUCTION

Purpose. It is the purpose of this research problem to improve the synthesis of hexafluoroacetone reported by Henne, Shepard and

Young (l) , and to investigate other reaction sequences that anight lead to this perfluorinated ketone.

Scope of Dissertation. One way to synthesize hexafluoroacetone and other perfluorinated ketones could be the condensation of perfluoro- alkyl-metal halides with perfluorinated esters, acyl halides or acid

anhydrides. Henne and Francis (2), for example, reported that ethyl perfluorobutyrate condensed with perfluoro-n-propylmagnesium iodide to

give 20 per cent of the perfluorinated ketone, C2F7COC3F7, t>ut no

tertiary alcohol. The same ketone was isolated in 2 per cent yield

from the simultaneous addition of methyllithium and ethyl heptafluoro-

butyrate to heptafluoro-l-iodopropane in ether, together with a 37 per

cent yield of tris-perfluoropropyl-carbinol (3). In both cases there

was no mention of trifluoroacetone, but only its higher homolog, which

might be due to the general feeling that CF3 derivatives do not act

entirely as higher homologs. The scope of the present work, therefore,

includes an investigation of perfluoro-n-propylzinc iodide and its be­

haviour toward ethyl perfluoro-n-butyrate, isoamyl perfluoroacetate,

acetophenone, benzaldehyde, and acetic anhydride.

The synthesis of hexafluoroacetone reported by Henne, Shepard and

Young (l) involved the following steps:

* Order of citation is in order of appearance.

-1- INTRODUCTION

Purpose. It is the purpose of this research problem to improve the synthesis of hexafluoroacetone reported by Henne, Shepard and

Young (l) , and to investigate other reaction sequences that might lead to this perfluorinated ketone.

Scope of Dissertation. One way to synthesize hexafluoroacetone and other perfluorinated ketones could be the condensation of perfluoro- alkyl-metal halides with perfluorinated esters, acyl halides or acid anhydrides. Henne and Francis (2), for example, reported that ethyl perfluorobutyrate condensed with perfluoro-n-propylmagnesium iodide to give 20 per cent of the perfluorinated ketone, C2F7COC3F7, but no tertiary alcohol. The same ketone was isolated in 2 per cent yield from the simultaneous addition of methyllithium and ethyl heptafluoro- butyrate to heptafluoro-l-iodopropane in ether, together with a 37 per cent yield of tris-perfluoropropyl-carbinol (3). In both cases there was no mention of trifluoroacetone, but only its higher homolog, which might be due to the general feeling that CF3 derivatives do not act entirely as higher homologs. The scope of the present work, therefore, includes an investigation of perfluoro-n-propylzinc iodide and its be­ haviour toward ethyl perfluoro-n-butyrate, isoamyl perfluoroacetate, acetophenone, benzaldehyde, and acetic anhydride.

The synthesis of hexafluoroacetone reported by Henne, Shepard and

Young (l) involved the following steps:

* Order of citation is in order of appearance.

-1- - 2 -

Cl2 KOH Clo CH3-C=CHC1 > CH2G1-CC1-CHC12 ------> CHgCl-CsCClg * I » alcohol I c h 3 c h 3 c h 3

KOH SbF, CH2C1-CC1-CC13 > CHCl-C-CClo CHCl=C-CFo l alcohol I I c h 3 c h 3 c h 3

SbFo KOH or CH2C1-CC1-CC13 ------> CH^Cl-CCl-CFo > CHCl=C-CFo ' SbF3Cl2 > alcohol I J g h 3 c h 3 c h 3

C2H5OH (1) CH3MgGl ?H3 Po0_ or CFqCOOH - - ■■■ - > CFqCOOCpHr ______— — v CFo-C-OH £2^ > H + (2) Aqueous 1 WH^Cl CH3

CIq KOH CF3-C=CH2 ---- > c f 3-c c i -c e 2c i ------> c f 3-c =c h c i I » alcohol 1 CH3 c h 3 c h 3

cig KOH then CF3-C=CHC1 ------* CF3-CC1-CHC12 ______> CFo-CrCClg • 1 alcohol I c h 3 c h 3 c h 3

HF Cl2 KOH ------> CF3-CH-CF0 » c f 3-c h -c c i 3 ------> c f 3-c =c c i 2 SbF3Cl2 I 1 ~ alcohol « CH3 CF3 CF-.

KMuO^ -> CFq-CO-CF-:

Each of these steps gave a very good yield, and the last oxida­ tion was reported to give 60 per cent of the desired ketone. The present investigation includes attempts to improve this synthesis by de­ veloping shorter sequences and by improving the yield of the last oxidation. 3 -

The proposed outline of reactions is:

CH- CH3OH (1) CH3MgBr 1 HgO CF3COOH CP3COOCH3 -* CFo-C-OH H + (2) E* ** 1 CHo

Cl. CP3-C=CH2 -» CF3-CH-CH3 t CHo CH-

base allylic either -> CF3-CH-CCI3 -> CFo-C=CHCl J « fluorination CHCI2 CClo base allylic or CF3-CH-CCI3 -> CF3-C=CC12 > 1 fluorination CC10 CC1-,

CFo-C=CHCl ■3 i CFq CF3-CO-CF3

CFo-C=CC12 '3 I CFq

A third and very novel approach to making hexafluoroacetone would be the bromination of hexafluoropropane, CF3-CH2-CF3, to dibromo- hexafluoropropane, CF3-CBrg-CF3> a compound which should readily form a semicarbazone or a 2, lt-dinitrophenylhydrazone from which hexafluoro­ acetone might be recovered by hydrolysis.

Hexafluoropropane has been made by the sequence:

HF Zn HF CF3-CClrCCl2 * CF3-CHC1-CF2C1 cf3-ch=cf2 SbF^Clg

CF3-CH2-CF3 (k, 5 ) This seemed to be a feasible method ■worthy of exploration since this same general procedure had been applied successfully to

CF3-CO-CH2-CF3 in the preparation of CF^-CO-CBrg-CF^ and its convers­ ion to CFo-C---- C-CFo (6). 3 II II 3 N N I I WH NH HISTORICAL

Hexafluoroacetone was first prepared by Fukuhura and Bigelow (7 ) who passed a mixture of fluorine gas and acetone vapors diluted with nitrogen over copper gauze heated to 65° - 90° C. The yield of hexa­ fluoroacetone was five to ten per cent. The other products were carbon tetrafluoride, CF^j trifluoroacetyl fluoride, CF3COF; and monofluoro- acetone, CHgF-CO-CHy Henne, Shepard and Young (l) reported the perman­ ganate oxidation of CF3-C=CCl2 to give 60 per cent hexafluoroacetone. c f 3 A direct fluorination method which involved passing gases over silver fluoride was employed by McBee (8) to get the perfluorinated ketone from acetone. Other investigators (9, 10) have reported the permanganate oxidation of perfluoroisobutene in yields up to 31 Per cent. Hazel- dine (ll) oxidized CF^-C^CHBr to get 55 per cent hexafluoroacetone, and CF3 also prepared it by reacting CF3MgI with CF3C0C1 or CF^CR to give claimed yields of K9 crc* 33 per cent respectively (12).

- 5 - EXPERIMENTAL

Reactions of Perfluoro-n-propylzinc Iodide

Discussion. The preparation of C^FyZnl in dioxane solution was first described by Miller (13). This was the first example of a perfluoroalkylzinc halide. Metallic zinc and C3F7I reacted readily in gently heated dioxane solutions. The resulting alkylzinc iodide was

stable at the boiling point of dioxane but, when heated to 150°, produced

CjFg and a small amount of what was believed to be perfluoro-di-n- propylzinc. Addition of water to C^F^Znl formed C^F^H readily and at a measurable rate. As indicated by this reaction the chemical reactivity of the perfluoroalkylzinc compounds lies between that of the fairly unre­ active perfluoroalkylmercury compounds (ik) and that of the unstable perfluoroalkylmagnesium compounds (15). These properties suggest that

the zinc compounds might be useful synthetic intermediates.

This thesis presents a preliminary study of C^F^nl and its

reactivity with C3F7COOC2H5, CF^COOC^H^jl^ acetophenone, benzaldehyde,

and acetic anhydride in the belief that the study might lead to a

practical synthesis of perfluoro ketones.

Experimental.

Preparation of C^FyZnl. This reagent was prepared several times

and the best procedure was found to be essentially that reported by

Miller (13)- A typical example is described.

A 250-ml. round bottom three-neck flask was fitted with a dropping

funnel, a mechanical stirrer, and a cold water condenser leading to a

Dry Ice trap. Granular zinc or zinc dust (7 .2 g., 0.11 mole) and pure

dry dioxane (20 g.) were placed in the flask. The stirrer was started

and the flask was warmed to 90° by means of an oil bath. Heptafluoro-n-

- 6- - 7 - propyl iodide (30 g., 0.101 mole) dissolved in dioxane (1+0 g.) was added from the dropping funnel at such a rate that the C^Fyl, h.p. 1+0°, refluxed gently. The total time for addition was about one hour.

External heating was applied one half hour longer until refluxing stopped.

Percentage yields of 65 to 80 per cent of C^FyZnl were verified by adding water to an aliquot of the dioxane solution and measuring the volume of C^FyH evolved.

The CgFyl which was used in this reaction was first synthesized from silver heptafluorobutyrate and iodine by conventional procedure

(l6, IT), but was later purchased from the Caribou Chemical Co.

Attempted reaction of C^FyZnl with C^FyCOOCgHc;. The reaction was carried out in a 300-ml. round bottom three-neck flask provided with a dropping funnel; mechanical stirrer with a rubber hose seal, and a water cooled reflux condenser which led to a Dry Ice trap. Perfluoro- n-propyl iodide (66 g., 0.22 mole) and granular zinc (13 g., 0.20 mole) reacted in dry dioxane to give approximately 0.15 mole of C^FyZnl. The excess of C3F7I was recovered in the Dry Ice trap. Ethyl heptafluoro- n-but'yrate, b.p. 95° (31-5 g-, 0.13 mole), was added dropwise to the dioxane solution of C^FyZnl without observable indications of reaction.

The mixture was refluxed for six days; during this time about one gram of low boiling material was collected in the trap. This was probably

CgF^ which would be expected from a slight decomposition of the C^FyZnl.

Water (1+0 g.) was then added to the reaction mixture followed by

1+0 ml. of 25 per cent sulfuric acid. Approximately 2 g. of low boiling liquid regarded as G^FyH was collected in the trap. The presence of dioxane maintained a one phase system. Because of excessive decomposition during distillation, it was extremely difficult to work up the reaction - 8 - products and get a satisfactory material balance. None of the desired product, C^FyCOC^F-y, b.p. 75° (2), was isolated.

A more thorough examination of the fractions which were isolated was not made because it seemed to present more difficulties than a slightly altered repetition of the experiment. The alterations were:

(1) Use a higher boiling ester.

(2) Prepare the C^FyZnl in dioxane as usual, and then effect a solvent interchange by adding excess ester and distilling off the dioxane.

Attempted reaction of C^FyZnl with CFqCQOCqHi^. Isoamyltrifluoro- acetate, b. p. 119° (228 g., 1.2^ moles), was added to a prepared dioxane solution of C^FyZnl (0.11 mole) in a 300-ml. round bottom three-neck flask fitted with a dropping funnel, mercury sealed mechanical

stirrer, and a water cooled reflux condenser trailed by two Dry Ice traps.

A large amount of white precipitate indicating the insolubility of

C^FyZnl in the ester formed immediately. There was no evidence of an

exothermic reaction during addition of the ester.

The dropping funnel was replaced by a Claisen distilling head which was trailed by a downward water cooled condenser, a flask to act

as a receiver, and a Dry Ice trap. The other two holes of the flask

were plugged with ground glass stoppers. An oil bath temperature at

lkO° which was applied to the reaction flask failed to remove any of the

dioxane but 3 g. of C^Fg was collected in the trap. After connecting

another Dry Ice trap to the system a slight vacuum was applied. With

the oil bath temperature at 110°, 225 S- of material, were distilled from

the flask. This material was fractionated. - 9 - Grams B.p. (l atm.)

128 90 - 114 dioxane and ester

80 111 - 118 ester

17 residue ester

The ester was returned to the flask, and with the oil bath at

130° the mixture was refluxed for 48 hours. Approximately 2 g. of C3F6 was collected in the trap during this period of heating.

The precipitate was dissolved by adding ^1-5 ml. of water and then

1+5 ml. of 25 per cent sulfuric acid. There was no CgFyH formed during

the hydrolysis. Free iodine which was formed during the reaction was

reduced with RagSgO^- The water layer was extracted with ether and this

extract was added to the organic layer. This layer was fractionated.

Fraction Grams B.p. (l atm.)

1 10 30 - 32 l . 3k9 0 .7 6 8 5

2 6l 32-36 1 - 3^9 0 .7 4 7 7

3 55 (top layer) ? (20 mm.) 1-369 1 .0 2 k

8 (lower) 1-359 1 .0 2 2

1 + 8 9 ? (20 mm.) 1 .1 2 2

Residue 12

Fractions 3 a^d 1+ were combined and distilled from ^2^5’

Fraction Grams B-p. (l atm.)

1 16 33 - ll1*

2 101 Ilk - 119

3 7 ? (20 mm.)

Residue 28 tar

Physical properties (18) of CF3COC3F7, the expected product, are

b.p. 30 - 33?. None of the above fractions as shown by low density and 10 failure to give a positive test with 2,k-DNPH or semicafbazide seemed

to contain this product.

The aqueous layer from the reaction was also distilled but a

series of density measurements did not detect organic material.

Reaction of C-gFyZnI with acetophenone. (l) This experiment

followed the same procedure as for CF^COOC^H-j^. Working up the mixture

did not reveal any organic product.

(2) A repetition of this experiment with substitution of steam

distillation for the mechanical phase separation produced a very small

yield of an organic liquid which gave a positive test for fluorine after

sodium fusion. Acetophenone (127 g-, 1 .0 6 moles) was added to a dioxane

solution (52 ml.) of about 0 .0 7 mole of C^FyZnl. The dioxane was

distilled off as usual and the remaining mixture was heated for 21 hours

in an oil bath at 95 - 130°. Ten grams of water was added to the

mixture, followed by 17 g. of 50 per cent sulfuric acid. No material

was collected in the trap. More water (75 ml.) was added and the

mixture was steam distilled into a flask which was trailed by two Dry

Ice traps. The organic distillate was dried over sodium sulfate and

then fractionated.

Fraction Grams B.P. (100 mm.) n ^ D 1 ^•5 30 - 13k 1 .U850

2 98.0 13^ 1.5280

Residue 12.0 1.5260

Trap 1 8.5 i.kooo

Trap 2 0 .5 1.3750 - 11 -

Fraction 1 and the trap material were combined and gave two layers.

Grams n-'30 Fluorine test D Top layer 3*5 1.3830 Negative

Lower 10.0 1.UU90 Positive

The lower layer was fractionated with the following results:

Fraction Grams B.p. (82 mm.) n^® Fluorine test D 1 2.5 110 - 127 1 .1*950 Positive

2 0.6 127 1.5275 negative

Residue 0.9 1.5260 Negative

Trap 1.0 1.3865 negative

Fractionation of the first fraction (2.5 g.) gave:

Fraction Grams B.p. (82 mm.) n ^ Fluorine test

1 0.5 117 - 122 1.1*330 Positive

2 1.5 122 - 125 l.l)-980 Positive

Residue 0 .0

Trap 0.5 1.3985

Fractions 1 and 2 represent the yield of product, presumably c 3ft -c (o h )c6h 5.

c h 3

(3) A third attempt with acetophenone working with twice the amounts of 'the preceding run produced a product with similar boiling point in approximately the same yield. For example, fractionation of the organic steam distillate gave the following results: - 12 - OQ Fraction Grams B.p. (85 mm.) n Fluorine test D 1 11.5 37-50 Top layer Positive 1.426

Lower Negative 1-399 2 12.5 50 - 128 1.489 Positive

3 38.0 128 - 129 1-529 Negative

4 30.0 129 - 130 1-5295 Negative

Residue 5-0 1.525 Positive

Trap 1-5

Attempts to prepare a phenyl- and «• -naphthylurethan and a

3,5-dinitrobenzoate of this fluorinated product were unsuccessful.

Attempted reaction of CgFyZnl with benzaldehyde. The same general procedure was followed in this reaction. Obvious side reactions complicated the experiment, hence further investigation of this reaction was abandoned.

Reaction of C^FyZnl with acetic anhydride, (l) Acetic anhydride

(100 g ., 1 mole) was added to a previously prepared dioxane solution

(50 g. ) of approximately 0.07 mole of C^F^nl which still contained Zn and C^Fyl. The dioxane was distilled off and produced a lower layer of

1.5 g. which was believed to be CgF^- This could have been formed by a chain doubling reaction of C^Fyl with Zn. This compound had not been seen in the previous experiments with ethyl perfluoro-n-butyrate, isoamyl perfluoroacetate, or acetophenone.

The reaction mixture was then heated for 64 hours at 100 - 125° by means of an oil bath. Steam distillation gave 1 .2 g. of organic material which gave a positive sodium fusion test for fluorine. Attempts to prepare an alcohol or ketone derivative were unsuccessful. - 13 -

(2) Metal Interchange with magnesium. Magnesium was employed to effect a metal interchange with C3F7Z.nl to determine whether the resuilting C^FjMgl would react more efficiently with the acetic anhydride.

Acetic anhydride was added to a dioxane solution of C^F^Znl and the dioxane was then removed in the usual manner. When magnesium turnings were added to the mixture a very vigorous exothermic reaction occurred which resulted in the decomposition of the organometallic halide and formation of C^Fg. Stirring for one hour at room temperature caused the mixture to set to a pasty mass. After heating for two hours at

100 - 120° steam distillation gave one gram of organic liquid.

(3 ) The above experiment was repeated with provisions to regulate the metal interchange more carefully. The dioxane was not removed

in this case. Cooling with ice water when the Mg was added to the

C^F^Znl caused the interchange to occur smoothly with none of the usual CF3-CF=CF2 collecting in the trap. The preceding general procedure was then followed to give 0.95 g* of organic liquid. Attempts to prepare derivatives of the organic product from three runs with acetic

anhydride were unsuccessful.

Chain doubling reaction of C3F7I with zinc (19)- In the reaction

of C^FyZnl with acetic anhydride there was evidence of CgFpi^ formation.

This could have occurred when unreacted C3F7I condensed with itself

in the presence of unreacted zinc and acetic anhydride. In an experi­ ment to determine whether such a condensation occurred CgFpi^ was

obtained in 7^ per cent yield by treating C^F^I with Zn in acetic anhy­

dride. The preference of the C3F7I to undergo dehalogenation with

condensation rather than to form C3F7ZnI was demonstrated by the high

yield of CgF^ and the absence of C^F^H after hydrolysis. - I ll- -

Perfluoro-n-propyl iodide (Ho g., 0.135 mole), granular zinc

(9-3 g*, 0.1^2 mole), acetic anhydride (28 g., 0.28 mole), and methylene chloride (67 g.) were mixed in a 300-ml. flask provided with a sealed stirrer and a wafer cooled reflux condenser trailed by two

Dry Ice traps. Stirring at room temperature caused a slight cloudiness, but with external heating applied to cause refluxing at ^0 - a white precipitate began to form. In 2 b hours the precipitate was so thick that it interfered with stirring, and the reaction was worked up.

While cooling in an ice-bath, water* (20 ml.) was added dropwise.

It dissolved the precipitate and caused the formation of three layers.

There was no gas evolved. The empty Dry Ice trap showed that CF2“CF-CP2 had not been formed during the zinc attack, nor CF2-CF2-CF2H during the hydrolysis. The top layer (8l g.) contained acetic acid, water, acetic anhydride, and zinc iodide; the middle layer (^b g.) was methylene chloride with about 1+ per cent of unused iodide; the bottom layer (17 g.) was the doubled up molecule, CgF-^, quite pure. As 5-5 g. of zinc was recovered, the aggregate weights showed a loss of 6.6 g. of material, attributed to mechanical handling. There was no indication of a ketonic material which would have resulted from the action of the organometallic halide on the solvent.

The top and middle layers were returned to the flask and neutralized with sodium carbonate. The organic layer was obtained from the aqueous layer, and proved to be a clean mixture of methylene chloride with ij- per cent of unused C^Fyl as determined by a graphic plot of refractive index.

The bottom layer was dried over sodium sulfate and distilled; it came over entirely at 57 °, the correct boiling point for CgF^. The - 15 - refractive index of 1.25 was too low to be read on the available instrument; the density was measured at I .6707 at 25° (lit. 1.6995 at 20°).

The conversion from the iodide was jk per cent, and as 3*4 per cent of iodide was recovered, the net yield was 77 per cent. A

computation based on the amount of zinc that had been consumed showed

that an additional 12 per cent might have been formed and lost.

Preparation of CgFyZnBr. Perfluoro-n-propylzinc bromide was pre­ pared in 26 - 29 per cent yield by heating C^F^Br with Zn and dioxane in

a sealed tube. A mixture of C^FyBr (6.2 g., 0.025 mole), granular Zn

(3.2079 g., 0.049 mole), and dioxane (24 g.) were heated in a sealed

glass tube at 50° for about 6 hours. The excess C^F^Br (b.p. 15°) was

distilled off. The residual Zn weighed 2.7879 g- which indicated a

conversion to C^F^ZnBr of 26 per cent. By adding water to an aliquot of

the dioxane solution the amount of evolved gas computed as C^FyH indicated

a conversion of 29 per cent.

Perfluoro-n-propyl bromide was prepared by a previously reported

sequence of reactions. This synthesis involved the following steps:

C^FyCOOH J 21 > C3F7COOC2H5 C3F7COIJH2 C3F7Br

Perfluoro-n-propylzinc bromide was not investigated further. - 16 -

Conclusions

The experimental investigation of C^F^Znl and its reactivity with certain carbonyl compounds showed that this proposal was an impracticable method for making perfluorinated ketones. Although there were indications of a reaction with acetophenone and acetic anhydride, the yields were quite low and the identity of these organic products was not established.

Furthermore, there was no indication of reaction with oxygenated per- fluoro compounds; and in order to get perfluoro ketones, this would be a necessity. The use of the expensive reagent, C^F^I, also made this study unprofitable when one considered the unlikelihood of working out a successful synthesis by this procedure. Consequently, this phase of research was abandoned for a more promising approach to the problem. - IT -

Synthesis of Hexafluoroacetone

The synthesis of hexafluoroacetone described by Henne, Shepard and Young (l) involved the potassium permanganate oxidation of

CFo-C=CCl2 in 60 per cent yield. The necessary olefin was obtained 0 I c f 3 from CF-,-C(Cl)CHpCl in a sequence of steps, each of which gave 90 - 95 1 I * c h 3 per cent yield when the unreacted reagents were reworked. The

CF3-C(Cl)CH2Cl was obtained practically quantitatively from CF^COOH;

c h 3 and was also obtainable from CHo-C=CHCl. Although the yields were good I c h 3 for the reaction steps leading to CFn-C-CClp, these steps were too I c f 3 numerous and the final oxidation to CF3-CO-CF3 was not developed to an optimum yield.

The present work improved the synthesis of CFp-C=CClP, and developed 5 I cf3 a procedure for the synthesis of CFp-C-CHCl, a new compound. The oxida- 3 I c f 3 tion step was developed to a yield of 80 per cent with an additional

7 per cent recovery of starting olefin.

Esterification of CF3C00H . Shepard (2 2) prepared CF^-CCOHjCH^ by

c h 3 the reaction of CF^OOCpH^ with CH3MgCl. This gave the azeotrope of the desired tertiary alcohol with CpH^OH which upon reaction with Pp0^ - 18 - gave CfL^CHg as well as CF^-C^Hg- Although the CE^CHg did not com-

ch3 plicate the isolation of the CFo-C-CHp, the presence of the C2H1-OH in

ch3 azeotrope required an extra amount of PgO^. In order to prepare the pure tertiary alcohol and avoid the azeotrope formation, the methyl ester was prepared to he used in place of the ethyl ester.

Experimental. Pure methyl trifluoroacetate was obtained in 90 per cent yield by mixing one mole of CF3COOH and two moles of absolute

CH^OH in a flask equipped with a reflux condenser and pouring 1.5 moles

of concentrated sulfuric acid in small portions through the condenser as fast as the exothermic reaction would permit. After cooling, the top

layer of nearly pure ester was decanted and distilled from PgOtj (t».p. ^3°)*

Preparation of CF,-C(QIl)CH3 .

c h 3

Experimental. Trifluoromethyldimethylcarbinol was prepared several

times by the Grignard reaction of CF^COOCH^ and CH3MgBr. For example,

a 5 -liter 3-neck round bottom flask was fitted with a water cooled

reflux condenser and sealed mechanical stirrer. Magnesium turnings

(153 g-, 6.3 moles) were added to the flask and the apparatus was then

flame dried and swept with dry nitrogen. After initiation of the reaction with small amounts of methyl bromide and ether, two and one half liters

of anhydrous ether were introduced followed by methyl bromide, in

slight molar excess, dissolved in $00 ml. of anhydrous ether. This was

added at a rate to keep the reaction going and in sufficient quantity

to consume most of the magnesium. - 19 -

A solution of CP^COOCH^ (384 g*, 3 moles) in 384 ml. of anhydrous ether was added dropwise at a rate which kept the ether refluxing rapidly. External heating was applied for an additional two hours.

Hydrolysis was effected by dilute hydrochloric acid. The top ethereal layer was decanted and together with an ether extract of the aqueous layer was fractionated to give the CF^-CCoeQ cH^ (b.p. 78 - 82°).

ch3

The yields of several runs were in excess of 95 per cent.

CHo > Dehydration of CFq --C(OH)CH^. Shepard reported that the P20^ dehydration of the CF3-C(OH)CH3 and C2HcjOH azeotrope proceeded in almost

ch3 quantitative yield and that the reaction required external heating for about eighteen hours before all of the product was formed (22).

Experimental. In the present work it was observed in two attempts to dehydrate this azeotrope that the heating had to be applied for four days before the product began to form. Two more days of heating were required before all of the olefin had distilled over. This olefin boiled at 6 - 7°. Because of excessive foaming, the mixture could be heated only -under observation; and therefore the actual total heating period was about 50 - 60 hours.

The dehydration of pure CF^-CKoiOCH.^ was accomplished by the

ch3

same technique. The tertiary alcohol (55 & g*> 434 moles) was added drop- wise to P205 (550 g., 3*87 moles) in a 3-liter flask which was equipped with a dropping funnel, sealed mechanical stirrer, and water cooled reflux condenser trailed by a receiver cooled in Dry Ice and acetone. Mdition of the alcohol caused evolution of heat and much foaming.

The mixture was heated in an oil hath at 130° for a total of ho hours before all of the olefin had been collected in the receiver. Two separate runs gave yields of 92 and 9^ per cent of the olefin (b.p. 6 -

7°) plus some recovered starting material.

Coworkers in this laboratory later showed that this tertiary alcohol could be dehydrated much more rapidly by a 30 per cent HgSO^ -

70 per cent mixture.

CH, I Preparation of CF^-CH-CH^. The synthesis of hexafluoroacetone as previously described (l) had involved the chlorination of CFo-CrCHg to 1 c h 3

CF^-CfClJCHgCl. As the next step the present investigation deviated

c h 3 from this sequence by hydrogenating CF^-CrCf^ to CF^-CH-CH^; a new com-

c h 3 c h 3 pound. It was proposed to chlorinate this trifluoroisobutene structure in an attempt to get chlorinated compounds with the tertiary hydrogen still intact. The presence of the tertiary hydrogen would permit several possible sequences for obtaining CF3-CO-CF3. For example, - 21 -

base SbF- (0) (2) CF3-CH-CCI3 ----- > CFo-C-CClo CF.-C-CFo i J ii 3 11 CHgCl ch2 CH2

or base CF3-CO-CF3

HF base cf3-c=cci2 -» CFo-CH-CF. CFo-C-CFq J » - 11 3 CHgCl CH2C1

or \ Glc

I base CF3-CH-CF3

CCIq CCL-

(0) CF3-CO-CF3 base SbF- (3) CF3-CH-CCI3 > cf3-c-cci3 CF^-C-CF., ii 3 11 J CHC1, CHC1 CHC1

or * CF3-CO-CF3

Vbase HF base (0) -» cf3-c=cci2 — » CF3-CH-CF- cf3-c-cf3 II CHC1- CHC12 CHC1

-> CFoCO-CF-

base SbF0 (0) (U) CF3-CH-CC13 > cf3-c=cci2 ± » CF3-C=CC12 CF3-CO-CF3 ~3 I CC13 wCC1' ^3 CF-^ 3

It is known that the chlorination of CF3~CH2 -CH3 (23), for ex­ ample, gave 20 per cent CF3-CHCI-CH3,- 65 per cent CF^CHg-CHgCl, and 15 per cent CF^CHg-CHClg. This result demonstrates the directive effect of the trifluoromethyl group and indicates that the same effect would be present in CFo-CH-CHo, but perhaps to a different degree because of 1 CHo - 22 - the additional methyl group. On the basis of a purely random chlori­ nation, however, the odds are 6 to 1 in the isobutane structure and only

3 to 2 in the propane structure for not getting any chlorination on the carbon adjacent to the trifluoromethyl group. This fact alone was sufficient reason to believe that the tertiary hydrogen in CF^-CH-CH^

ch3 would remain essentially intact during chlorination and the directing effect as an added favorable factor made the odds excellent. Consequently, this approach presents several feasible methods for making hexafluoro- acetone.

The only saturated chlorinated derivatives of CF^-CH-CH^ which had

been reported previously were CF^-CCl-CH^Cl (l), CF3-CCl-CHCl2 (l) and i i CH3 CH3

CF3-CC1-CC13 (2k). Therefore, CF3-CH-CH3 and its chlorinated products

CH3 ch3 with the tertiary hydrogen still intact would have to be isolated and properly identified in order to proceed with any degree of certainty.

Experimental. Hydrogen added to CF3-C=CH2 quantitatively and

ch3 rapidly at room temperature in the presence of absolute ethanol and catalytic amounts of platinum oxide. The reaction was carried out in a two and one half liter steel bomb equipped with the conventional pres­ sure gauge and outlet valve. Platinum oxide (l g.) was added to the bomb along with 180 g. of absolute ethanol. The bomb was then fitted with the gauge and valve, cooled in Dry Ice and acetone, and evacuated.

Trifluoroisobutene (130 g., 1.18 moles) was introduced followed by - 23 - hydrogen to give a pressure of about k-0 p.s.i. and the bomb was rocked in a mechanical shaker. The pressure dropped rapidly as the bomb warmed to room temperature. More hydrogen was added in successive in­ crements until the theoretical amount had been absorbed and no further reaction occurred as indicated by the stationary pressure reading. The product distilled steadily at 8 - 9°•

In order to establish the actual formation of the paraffin analog, the boiling point difference was determined for the olefin and the hydrogenation product. An Engler distillation of each in the same appa­ ratus at 7^5 mm. gave a boiling point of 5 -8° for the olefin and 8 A ° for the saturated analog.

Analysis for F in CF3-CH-CH3, calc. 5 0 .8 5 , found 50.88.

ch3

ch3 Chlorination of CF^-CH-CH^ (i). After consideration of the

various reaction sequences leading from chlorinated products of

CF^-CH-CH^ to CF^-CO-CF^, it was believed that either the h, 5> or 6

ch3

chlorine level should preferably be investigated. The approach to this

problem then would involve the following steps:

(1) The successful chlorination of CF3-CH-CH3 directly to the desired t CH, 3 level.

(2) The separation of the b, 5; and 6 chlorine level compounds, a step

which might later be found to be superfluous.

(3 ) The successful dehydrohalogenation of at least one level.

(h) Fluorination of the resulting olefin to get 6 fluorine atoms in the - 2k - molecule either by (a) hydrogen fluoride to get a saturated molecule which would have to be dehydrohalogenated, or chlorinated and then dehydrohalogenated to get a desirable olefin, or (b) antimony trifluo­ ride to get allylic fluorination to a desirable olefin.

In order to develop successfully this proposed outline of research, it proved necessary to go through this sequence with three successive batches of CF^-CH-CHy Each of these three series of research resulted

ch3 in additional information,'and the third series brought the investi­ gation to a conclusion with improved yields for each of the steps.

Experimental. The apparatus for this chlorination is illustrated below.

Dry Ice trap

Cl2

Sulfuric Trap at Chlorination Trap in Water to acid room tube with Dry Ice- absorb bubbler temp. ultraviolet acetone HC1 radiation bath - 25 -

Trifluoroisobutane (327 g., 2.92 moles) was chlorinated to give a total of 591 grams of product. The rate of chlorination was con­ trolled by immersing the chlorination tube in a water bath which could be either cooled or heated. Chlorination was begun at the boiling point of the starting material, 8 - 9°, and completed by gradually raising the temperature of the bath to about 30°• This required a total of 32 hours.

The increase in weight by 26k grams would raise the chlorine level to about 2.6 chlorine atoms per molecule. Titration of the evolved HC1 was in good agreement with the calculated amount of evolved

HC1. Fractionation of the chlorinated products showed a peak at 92 - 93° with a broad range of peaks at 120 - 1^0°. Rather than attempt to

isolate any of these products into more clearly cut fractions it seemed more desirable to continue the chlorination to the higher chlorinated products. This would minimize the number of possible compounds and make the various identifications less difficult. For example,

CF3-CCI-CCI3 has a boiling point of 1^+9°; therefore the compounds

ch3

CF?-CH-CC13, CFo-CH-CClo and CF3-CH-CCI3 should boil higher than 1^9°. 1 1 1 CHgCl CHC12 CCI3

The fractions which boiled at 130° or higher in this fractiona­ tion (260 g.) were combined and rechlorinated to give a total of 336-5 g-

(n^ 1.I670). This chlorination required 62 hours with the temperature

of the bath being gradually raised from 30° to 100°. See Table I for fractionation of this product.

The fractions from the first chlorination which boiled below

130° (310 g*) were combined and rechlorinated to give a total of g- - 26 -

This chlorination required 70 hours with the temperature of the hath

"being increased gradually from 20° to 100°. The product contained

considerable solid material at room temperature. It was roughly

fractionated by distillation from a distilling flask. See Table II for

the results of this fractionation.

Dehydrohalogenati on.

Experimental. All of the fractions listed in Tables I and II were used in experiments to effect a sticcessful dehydrohalogenation.

All of the attempted dehydrohalogenations were done by adding an excess

of KOH in isopropyl alcohol dropwise to a solution of the chlorinated

compound in isopropyl alcohol. The mixture was stirred rapidly and the

internal temperature was maintained below 10° during addition of the

base.

Fractions 1 and 2 (Table i) and fraction 1 (Table Ii) produced

only a solid product by treatment with the base. This product was

mostly starting material and, in addition, probably contained some

dimer. The product was not investigated further.

Fractions 3> 5, and 6 (1^6 g., Table I) were treated separ­

ately with KOH in isopropyl alcohol to give 117 g. of products. These

products were removed from the reaction mixtures by addition of an

excess of water and decantation of the lower layer. They were combined,

dried over CaCl2 , and fractionated to give: - 2 7 - * Fraction Grams B.p. (64 mm.) n^® *20 ARp 4 1 20.0 84-89 1.4540 1.6700 1.24

2 15-0 89-94 1.4576 1.6796 1.24

3 8.5 9 k-100 1.4625 1.7009 1.21

4 18.0 100-105 1.4720 1.7443 1.14

5 31.0 105-110 1.4750 1.7660 1.06

Residue 7-5 1.4750 1.7948 0.84

Fractions 2., 3, and 57 S- of fraction 4 (170 g., Table II)

■were combined and treated with KOH and isopropyl alcohol to give

142 g. of dried product. Fractionation gave: „20 * Fraction Grams B.p. (7 mm*) ARji

1 16.0 40-42.5 1.4490 1.6649 1.18

2 13.5 42.5-45.5 1.4512 1.6599

3 16.0 45-5-48.5 1.4548 1.6549

4 10.5 48.5-52.0 1.4586 1.6655

5 14.0 52-55 1.4633 1.6918

6 32.0 55-58 1.4678 1.7302 1.12

7 15.5 58-61 1.4682 1.7504

Residue 2.5

In all of these dehydrohalogenations the aqueous-alcohol which formed on addition of excess water was slightly acid. Since the base was present in excess there were probably side reactions which reduced the yield of the desired olefins.

* Computed on the basis of 4 Cl atoms. - 28 -

TABLE I

2“5 Fraction Grams B.p. (20 mm d, ■' Cl atoms per molecule •> $ Analysis G Mol Wt

1 19 75-78 1.4495

2 114 78-85 1* *1-535 1.7200

3 bb 85-93 1.4620 l.?488 4.8

4 21 93-96 1.4675

5 39 96-102 1.4715 1-7923 4.7

6 b2 102 1.4782 1.8221 5-1

Residue 45

32i+

TABLE II

Fraction Grams B.p. P(mm. ) Cl atoms per molecule Analysis

1 192 (Thermometer coated with solid)

2 14 75 10

3 102 74.79 9

4 88 77-81 8 4.7

Residue 14

4l0 - 29 -

Fluorination. The calculated atomic refraction for fluorine in these dehydrohalogenated compounds indicated that they were essen­ tially ^ Cl olefins with perhaps some 5 Cl olefins. There was probably some unreacted starting material in these fractions. The possible structures for these olefins would be CF3-C=CHC1, CFo-C=CCl2 i i CC13 CHC12 and CF^-CsCClg. These are unreported compounds.

CC13

It has been shown that CF^-ClCClg and CH^-CHrCC^ can be con-

ch3 verted respectively to CF3-CH-CF3 (l) and CH3-CH2-CF3 (25, 26) by

ch3 using excess HF and small amounts of SbF3Cl2 - Also, CCl^CClsCClg and CC13-CC1=CHC1 can be changed to CF3-CC1=CC12 and CF3-CC1=CHC1 respectively by excess SbF2 (25). Either of these two general proce­ dures of fluorination could be applied to the three dehydrohalogenated compounds, thus: SbF, CFo-C=CHCl -» CFo-C=CHCl 3 1 1 CC1, CF-

HF cf3-c=cci2 -» cf3-ch-cf3 I chci2 CHClo

SbF: CF3-C:CC12 cf3-c=cci2 1 CClo or CF

HF ^ cf3-ch-cf3 1 CC1:-3 - 30 -

Since the allylic fluorination by SbF^ would give the more desirable products, this method was attempted first. As fluorination would depress boiling points, the appearance of desirable compounds would be readily detected and their separation easily achieved.

Experimental. A sample of crude olefin (31 g-, h.p. 105-110°

64 mm., n2^ 1.4750) was added to SbF^ (24 g.) in a 250-ml three neck round bottom flask. The flask was equipped with a thermometer and a water cooled reflux condenser which was trailed by an ice water trap and a Dry Ice trap. After heating the flask for two hours with an oil bath at 150°, there was no apparent reaction. After further heating the mixture suddenly began refluxing and the internal temperature dropped rapidly from 185° to l4o°. The temperature continued to drop slowly to 100° over a period of four hours. Further heating for 15 hours caused no further decrease in the internal temperature. Steam distillation of the reaction mixture gave 15-5 g- of crude organic product. This was dried over CaCl^ and fractionated to give: 20 *20 Fraction Grams B.p. (744 mm*) 4 1 0.7 80.0-82.5 1.3588 1.6427

2 0.7 82.5-87.5 1.3620 1.6473

3 2.0 87.5-93.0 1.3685 1.6548

k 3-0 93-103 1.3810 1 .6548

5 3-7 103-105 1.3920 1.6725

6 1.0 105-110 1.4265 1.7135

Residue 3-0

The drop in boiling point and index of refraction showed that fluorination had occurred but in poor yield for any hexafluoro pro­ ducts . - 31 -

Several more fluorlnations were attempted under slightly more drastic conditions. In the following rims the reaction mixture was placed in a steel bomb equipped with the conventional gauge and valve. The bomb was usually heated in an oil bath at about 100° to

130° for a period of 12 hours or more and then bled while being heated by a free flame. Since the starting material in each of these runs was composed of crude samples, no exact percentage yield could be calculated. It was known, however, that if any hexafluoro product would be produced the boiling point would drop toward 75°> the boiling point of CF^-CrCClg’ The other two desirable hexafluoro compounds,

cf3

CF -C=CHC1 and CF_-CzCH , would boil lower than 75° and- also would be 3 , 3 t « cf3 cf3 possible products. The latter compound, however, would be present in only a small amount since the dehydrohalogenation products were shown by atomic refraction measurements to consist mainly of t chlorine ole­ fins and therefore would not include CF^-CriCE^* Consequently a rough 1 cci3 yield was calculated for the hexafluoro products (b.p. 75° °r lower) by estimating the molecular weight of the starting material. As a very rough approximation the remainder of the fluorinated products was assumed to consist mostly of the pentafluoro compounds (b.p. higher than 80°). For example:

(l) A mixture of 33 g* of crude olefin samples and 10 g. of mostly pentafluoro samples from the flask fluorination was treated with

SbF^ containing 4 3 per cent SbF3Cl2 in a bomb to give 15 g. of dry - 32 - organic product. This material was fractionated.

Fraction Grams B.p. n ^ D 1 1.3 65 - 68 1 .3^35

2 3*7 68-73 1-3^75

3 6.5 73 - 75 1.3500

Residue 2-7 1.3920

Assuming the gram molecular weight of starting material to be approximately 260, the starting mixture of O .165 mole produced about

0.051 mole of hexafluorinated compounds (31 per cent) and about

0.011 mole of pentafluorinated compounds (6.7 per cent). The loss was 63 per cent.

(2) Seventy-eight grams of crude olefin samples were treated with SbF^ containing 20 per cent SbF^C^ to give ^3 g. of product.

Fractionation gave:

Fraction Grams B.p. ng°

1 1-7 56-58 1.3262 1.5296

2 3 A 58-62 1 . 33*10 1.5^27

3 9 .0 62-73 1.3395 1.5776

2 .3 73-76 1.3*1-72 1.5968

5- 2 .6 76-80 1.3533 1.5988

Residue 21.0 1.3870

Approximately 32 per cent to hexafluoro cpds.

33 per cent to pentafluoro cpds.

35 per cent loss

(3 ) Ninety grams of crude olefin samples were treated with

SbFg containing 30 per cent SbF^C^ to give 58 g- of product. - 33 -

Fractionation gave:

Fraction Grams B.p. n20 df° D *4 1 *4.2 56-58 1.3200 1.523*4

2 *4.6 58-62 1.3300 1.5366

3 10.0 62-73 1.3375 1.5659

k *4.2 73-76 1.3500 1.6018

5 *4.1 76-80 1.3510 1.612*4

Residue 28.0 1.3905

Approximately 39 per cent to hexafluoro cpds.

38 per cent to pentafluoro cpds.

23 per cent loss

(it-) Pentafluoro samples (*4-7.5 g.) from previous fluorinations were treated with SbF^ containing *40 per cent SbF^CL^ to give 32 g. of product. Fractionation gave: 20 iction Grams B.p. *20 gd *4 1 2.2 7*4.5-77 1.3*482 1.5862

2 9-0 77-80 1-3512 1.6063

3 2.5 80-111 1.3585 1.6155

*4 7.0 111-120 1.3839 I.6169

Residue 9-5 1.14089

Approximately 30 per cent to hexafluoro cpds.

35 per cent to pentafluoro cpds.

35 per cent loss 3^ -

A summary of results for these four runs shows:

Run Per cent 6 Fluorine 5 Fluorine Loss SbF3Cl2 Mole ratio of

Atoms Atoms SbF2 to starting

material

(1 ) 31 6.7 62.3 ^3 1.70

(2 ) 32 33 35 20 1.50

(3) 39 38 23 30 1-55 W 30 35 35 4o 1.50 In order to get better separation of the fluorinated olefins, the fractions from the second and third fluorinations were refractionated to give: \ 20 Fraction Grams B.p. (743 mm.) n fl2 0 arf D 4 1 4.5 45.5-46 1.3130 1.5112 1.18 for CFc 2 12.0 46-46.5 1.3130

3 4.0 46.5-70 1-3352

4 9-0 70-73 1.3494

5 6.5 73-74.5 1-3515 1.6318 1.25 for CF- Residue 5-5 1-3732

.Analytical data: Calculated Found

Fraction 1, Cl F Cl F CF3 CF3C=CHCL 17.86 57-^3 1 7 .^3 57.52

Fraction 5> cf3 CF3C=CC12 30.44 48.94 30;21 46.47

Although the fluorine analysis for fraction 5 was slightly low, none of the other possible fluorinated products either at the 6 F level or lower would have both a Cl and F content close to the values - 35 -

calculated for CF^CrCClg- The observed physical properties of

CF3 Fraction 5 also compared favorably with the literature values i o 20 ?0 b.p. 7^-5 ) n-p 1*3517> dj^ 1 .6429. Therefore this product was pre­

sumed to be CF,C=CC1 . 2 CF3

The analytical data and ARp indicated that Fraction 1 was

CF~CrCHCl, a new compound. This was later verified by oxidation to

CFoCOCF, (page 52). ?H3 Chlorination of CF^-CH-CHg (ii)•

Experimental. A second batch of the trifluoroisobutane (305 g.j

2.73 moles) was chlorinated by the usual procedure to give a total

of 717 g- (n^O I.A505)• This weight was equivalent to approximately

Cl atoms per molecule. The chlorination required 1^0 hours with

the temperature of the bath being increased gradually from -15° to

100°.

This material was roughly fractioned from a two-neck flask which

was fitted with a thermometer dipping below the surface of the liquid

and which was trailed by a Dry Ice receiver and trap leading to a

vacuum pump. This method was used in place of a packed column since

it was less difficult to distill the high melting material. See

Table III for the results of this fractionation. - 3 6 -

TABLE III

action Grams B.p. (9 mm.) n ^ Cl atoms Physical state G Mol Analysis 25° 0 Wt

1 150 50-52 solid 4.16 solid --

2 137 52-60 solid solid —

3 l4l 60-69 1.4462 liquid semi-solid —

4 90 69-73 1.4550 4.46 liquid liquid

5 45 74-78 1.4588 liquid liquid

6 42 78-90 1.4660 liquid semi-solid --

7 27 90-110 1.4730 liquid solid

Residue 33 viscous and sticky 582 (di­ mer

AC 7 Material on walls of tube between flask and receiver

Trap 23

695

The second and third fractions (278 g.) which were slightly above an average of 4 Cl atoms per molecule were combined and rechlorinated to give 325.5 g. of product. This material was treated in parts with

KOH in isopropyl alcohol to give 278 g. of crude organic liquid. The liquid was dried over CaCl2 to give 2J0 g. which were fractionated:

Fraction Grams B.p. P(mm.) vFJ n^° dh° D D ^ 1 93-5 55-70 28-32 1.4420 Solid at 25°

2 56.O 60-73 20 1.4463 1.4488 1.61*38 Liquid at 0°

3 5^.0 73-93 20 1.4549 1.4575 1.6402 Liquid at 0°

Residue 7*0 1.4655 Liquid at 0°

Trap 36.0 1.4050 1.4090 1.1925

246.5 (Low boiling material must have been lost through the - 37 - trap.)

Dehydrohalogenation.

Experimental. Fraction 1 was retreated with base but gave only solid product. This product had a boiling point of l45-l60° and a melting point of 95-100° (very difficult to purify). A molecular weight determination gave 249- These properties compare with those reported for CF3CCICCI3 (b.p. 149°, m.p. Il6°, g. mol. wt. 249.9).

L 3

The presence of this compound in the four-chlorine product would explain why this product had been resistant to dehydrohalogenation

(page 26). Young (24), for example, showed that attempts to dehydro- halogenate CFoCClCFoCl were unsuccessful and produced excessive decom- 1 ch3 position. However, CF0CHCCI0 with the tertiary hydrogen still intact 0 | cf3 was shown to split out HC1 successfully with KOH in isopropyl alcohol

(1).

Undoubtedly there had to be either CF3CHCCI3 or CF3CHCHCI2 or both ch2ci" chci2 present, but these structures should be more susceptible to further chlorination than CF0CCICCI0 (page 45). Consequently, if the chlori- jch3 nation were carried far enough, the four-chlorine product should consist almost wholly of CFoCClCClv ^ch3 - 38 -

Fractions 2 and 3 (page 36) were fractionated to give: ,20 action Grams B.p. (744 ram.) 4 ° di* 1 6 130-152 1.4345 1.5837

2 15 152-157 1 .^38^ 1.6079

3 12 157-162 1 A 392 1.6165

4 9 162-167 1.4418 1.6241

5 14 167-177 1.4478 1.6302

6 18 177-182 1.4481 1.6933

7 20 182-183 1.4701 1.7454

Residue 12 1.4690 1.7433

106

Refractionationl of fractions 2 , 3, 4, and 5 (* 20 ,20 action Grams B.p. (744 ran*) di» 1 2.7 145-150 1.4298

2 5*7 150-153 1.4348 1.6120

3 10.5 153-156 1.4360 1.6179

4 6.5 156-159 1.4370 1.6120

5 4-5 159-162 1.4360

6 2.2 162-165 1.4338

2.0 165-168

7 1.8 168-171 1.4405

1.8 171-174

3.0 174-177

Re sidue 6.0 1.4648

Refractionation of fractions 6 , 7, and R (page 38, b.p. 177-183°) gave: - 39 -

Fraction \ 20 ,20 Grams B.p. (745 mm.) n£ d4 1 2.0 167-173 1.4583

13-5 173.178

2 4.8 178-180 1.4680

3 4-7 180-181 1.4705 1.7499

4 5-5 181-182 1.4705 1.7499

5 2.4 182-183 1.4700 1.7554

6 2.2 183-184 1.4690

Residue 11.0

The above two refractionations indicated that tl principal peaks:

B.p.

153-156 1.4360

180-182 1.4705

Refractionations of these fractions until there change in the index of refraction gave:

B.p n20 20 D dl» 181-182 1.4705 1.7499

154-154.5 1-4528 1.6457

Since these two compounds were isolated from the product of a dehydrohalogenation reaction, they were believed to be olefins. The predicted olefins would be CFqC=CHCl or CF~C=CCl2 , and CF_C=CCl2 * o, u, 3| CC13 CHClg CC13

Analytical data indicated that the two fractions were probably these compounds: - ko -

Sample Percentage chlorine Probably

B.p. 15^15^.5 Calc. 57-22 Found 55-5^ CF3C=CHC1 or CF3C=CC12

CCI3 chci2

B.p. 181-182 Calc. 62.79 Found 62.11 CF3C=CC12 CCI3

Since these olefins were presumably formed by treating CF 3 CHCCI3

CCI 3 and CF3CHCCI3 with base, an attempt was made to isolate these saturated

CHClg compounds. Refractionations of the higher boiling fractions from the chlorination reaction (page 36) gave a compound with the following properties:

B.p. njp dj^ Percentage Cl

186° 1.1+590 1.7^55 62.39 Calc, for CF^HCCI^

CHC12

62.37 Found

A higher boiling compound, over 210°, was a solid at fairly warm temperatures and was not purified. This was presumed to be

CF3CHCCI3 .

CCI3 - Ill -

Conclusions

Although the final proof of structure for the above isolated compounds lay in the final step of oxidizing to CF3COCF3, the evidence thus far was fairly conclusive.

The results of experimentation with two batches of trifluoro- isobutane indicated that:

(1) CF3CHCH3 could be chlorinated to CF3CHCC13 and CF^HCCly These

ch3 chci2 cci3 five and six-chlorine compounds had apparently reacted with KOH in isopropyl alcohol to give the corresponding olefins.

(2) An appreciable quantity of CF3CC1CC13, estimated at UO per cent,

ch3 was formed and would not split out HC1 when treated with KOH in iso­ propyl alcohol.

(3) The remaining 60 per cent of material was presumed to be mostly five-, and six-chlorine compounds with some four-chlorine compound each with the tertiary hydrogen still intact; this remained to be proved, however. If this conclusion proves to be an accurate estimation of the chlorinated products, it leads to a procedure where the four- chlorine compound can be used in Shepard's sequences (l) while the five- and six-chlorine compounds can be used as recommended in this thesis.

(i+) The chlorinated products of trifluoroisobutane which contained 5 and 6 Cl atoms could be distilled at atmospheric pressure without any noticeable decomposition.

(5) A small amount of material dimerized during the chlorination. - k2 -

C H 3 Chlorination of CFg-CH-CHg (ill). Further experimentation with a third hatch of trifluoroisohutane would attempt to:

(1) Determine the exact amount of tertiary H in CFoCHCHo which °ch3 remains intact during chlorination to higher levels.

(2) Determine more exact percentage yields in the dehydrohalogenation and allylic fluorination steps and attempt to improve these yields.

(3 ) Oxidize CF^CrCHCl to CF3COCF3 and. develop the reaction to optimum yield.

Experimental. A third hatch of 2-trifluoromethylpropane (261 g.) was chlorinated hy the usual procedure to give a total of 518 g. The temperature of the acetone hath was gradually raised from -15° ^0 ahout

25° during this phase of the chlorination which required about 2b hours. The product was then transferred to a one liter quartz flask.

The flask was fitted with a Dry Ice reflux condenser trailed hy a Dry

Ice trap. Chlorine was introduced into the flask in sequence through a sulfuric acid bubbler, trap at room temperature, and sintered glass tube dipping below the surface of the liquid. A much more intense source of ultraviolet radiation was used for this second phase of the chlorination. While chlorine was bubbled through the solution the temperature of the external water bath was gradually raised from 25° to 100° and after 63 hours gave 6bk g. of product (n^° 1.Uk8 8 ). This material still contained dissolved HC1 and chlorine which were removed by fractionation through a 12 plate glass helices-packed column: - 43 2° Fraction Grams B.p. (758 mm.)

1 29 70-li|-9 (mostly 70) l. *1-330

2 160 1*1-9-153 Solid heated to prevent 3 85 153-155 Solid freezing of these fractions. 4 33 155-158 1.^350

5 59 158-182 (mostly 16*!-) 1.4390

, 6 169 182-191 1.4550

Residue 86 1.4835

In order to determine more accurately the percentage of tertiary chlorine compounds in these fractions, the properties of previously reported compounds (24) are listed for comparison:

B.p. M.p. n20 dg° ch3 D CFjCClCHgCl 93-5 1.3782 1.3899

?H3 c f 3c c i c h c i 2 123.7 1 . i+08i+ 1.5201

c h 3 CF3CC1CG13 1^8 -ll+9 1 1 5 .6-116.4

Fraction 1 was none of these compounds. Other possibilities for compounds in this boiling range of approximately 70° would be

CF3-CC1-CH3 and CF^CH-CKLpCl, unreported compounds. It was not proved

CH,,3 CH- which of these two structures actually represented fraction 1, however the physical properties of the corresponding propane compounds (2 5 ) were utilized to show that the more probable structure was CF^H-CHgCl.

CH- - ith -

B.p. B.p. difference B.p. B.p. difference c f 3-ch2-c h 3 - 13° cf3-c h -c h 3 8°

^ 3 ° C H 3 iJ-3° ?

CF3-CHC1-CH3 30° CF3-CC1-CH3 51°' ?

15° CH3 15° ?

CF3-CH2-CH2C1 ^5° CF3-CH-CH2C1 66° ?

ch3

By applying the boiling point differences of the propane com­ pounds to predict the boiling points of the isobutane compounds, it can be seen that a predicted boiling point of 66° for CF3-CH-CH2C1 makes

c h 3 it the more probable structure of Fraction 1.

Fractions 2 and 3 appeared to be CF3-CC1-CC13.

c h 3

Fraction k was probably a mixture of CF3-CC1-CC13 and CF3CHCC13.

c h 3 CH2C1 ,, o Fraction 5 with a boiling point close to 164 was undoubtedly

CF3-CH-CC13. Its boiling point indicates a ^ chlorine compound; and

CHgCl since it was not CF3-CC1-CC13, which is a solid, it is fairly certain

c h 3 that the tertiary H was still present.

In order to establish the absence of any tertiary chlorine in the higher boiling fractions the following reasoning was considered:

If there were any five- and six-chlorine compounds with tertiary Cl, they probably would have been formed by the further chlori- - k$ - nation of CF^CCICC^ since the formation of CF^-CCl-CHClg would he

CH3 CHgCl improbable and the atomic chlorination of CFoCHCClo* CFoCHCClo> or ■3CH2C1'5 JCHCl2

CF0CHCCI0 to compounds with tertiary Cl would be very unlikely due to cci3 the acidity of the tertiary H. It would be expected that the chlori­ nated products with the tertiary H intact could lose HC1 and then add chlorine. This chemical change did not appear to be occurring, however, since the chlorinated product, CF3-CH-CCI3 , had been distilled at

chci2 atmospheric pressure with no loss in weight (page to).

Therefore CF0CCICCI0 (l80 g., b.p. 1^8-151°) was exposed to 3 chlorination in the usual apparatus (page 2k) at 90-100°. After a total of 23 hours there was no increase in weight and fractionation recovered only the starting material.

This chlorination was repeated with 151 g. of starting material in a quartz flask with more intense ultraviolet radiation (page b2)•

After 6k hours of chlorination the product weighed 198.5 g« Fraction­ ation gave the following results. , , . 20 Fraction Grams B.p. (7^5 mm*)

1 lto.O 1^9-165 Solid

2 31.5 165-198 1.^595

3 7.0 198-205 1A750

Residue l8.0

Apparently chlorination did take place to form higher chlori­ nated products, but the chlorination was very sluggish. This indicated - k6 - that there could be some of the five- and six-chlorine tertiary chlorine compounds in the higher boiling fractions from the chlori­ nation of trifluoroisobutane.

To check this further, the residue from a previous dehydrohalo- genation of five- and six-chlorine compounds was retreated with KOH in isopropyl alcohol. This gave additional amounts of olefin. For example, a residue of 15 g- (b.p. over 188°) was treated with base.

Addition of excess water gave a lower layer which when dried over

CaClg weighed 11.0 g. Fractionation gave: 20 Fraction Grams B.p. n^

1 3.5 150-155 1.^165

2 k.5 155-185 1A530

Residue 2.5 1 .1+660

The resistance of CF^CClCClo to chlorination and the reaction of CH3 dehydrohalogenated residues to give more olefin established that there was no appreciable amount of tertiary chlorine compounds in the higher boiling fractions.

Therefore fractions 6 and R (page ^3) were essentially five and six-chlorine compounds with the tertiary H still intact. Fraction 6

(b.p. 182-191°, n ^ 1 A 55O) was undoubtedly composed of mostly

CFo-CH-CClo (b.p. 186°, n?° 1.^590). It was not known what percentage J chci2 of fraction R was CF^-CH-CClg but there was also undoubtedly some

« i 3 polymeric material and possibly some of the seven-chlorine product.

A previous chlorination of trifluoroisobutane and fractionation of the - 1+7 -

products (Table III) showed that about 4.7 per cent by weight of the

products was dimeric material. It was presumed therefore that about

the same amount was formed in this chlorination and that about 29 g.

of the residue (86 g.) was dimer. Calculation of the number of .

moles of material in each fraction (page 43) showed.that fractions

2 , 3; and one half of 4 comprised 1+3-2 per cent of. the total product.

Consequently, this method for the proposed synthesis of hexafluoro-

acetone could utilize approximately 53 per cent of the chlorinated

products, but lower fractions can be used according to Shepard's

scheme as follows. ch3 Dehalogenation of CF3-CCI-CCI3 . Since essentially 1+3 per cent

of these chlorinated products would be CF3CCICCI3 , an alternate method ch3

was proposed to utilize this by-product. Shepard (22) and Young (24)

showed that: SbF3Cl2 Zn HF CF 3 CCICCI3 ------v CFoCClCFpCl v CF-C-CFp > CF3 CHCF3 CH3 JCII3 CH3 ch3

and that: HF H CFpC=CClp -----> CF 3 CCF3 CHs CH3

Aq improved sequence would be possible if CF3CCICCI3 could be dehalo- 3 genated to give CF-,C=CClp. CH 3 J CHp 1 / \ Experimental. Fifty grams of CF2-CCI-CCI3 (0.2 mole) was mixed with 100 ml. of absolute methanol and added dropwise to a vigorously

stirred mixture of zinc dust (16 g., 0.25 mole) and 20 ml. of absolute

methanol. The reaction was vigorous and, with no external heating,

gave 28 g. of dried organic product. Fractionation gave: - 1+8 -

Grams B.p. n20 D 2.2 56-8U 1.3850

22.1 81+-88 1.3960

1.6 88 1-3965

1.6 residue 1.1+085 20 The literature values for CF3C=CC12 are: b.p. t55.4-~, n^ 1.391+7 . ch3

If it is assumed that 26 g. of product were formed, the yield was

73 per cent. Since this was a trial run, the yield could probably be improved.

This makes possible the proposed sequence which utilizes the recovered CF-,CC1CC1,: 3i 3 ch3

CH- CHo CEU CC1, CF 3 1 Zn J HF 1 Cl 2 1 J KOH i CF 3 CC1CC13 ----> CF 3 C=CC12 ----» CF 3 CHCF3 1 CF 3 CHCF3 > CF3 C=CC12

CHCloI Attempted dehydrohalogenation of CF3-CH-CC13 with sodium carbo­ nate . Previous dehydrohalogenations had been accomplished by KOH in

isopropyl alcohol. The products which were formed by splitting out

HC1 were presumably CF^-C=CHC1 and CF~-C=CC12. Both of these contain 1 3 , CCI3 CC13 active allylic chlorine atoms and contact with a strong base was considered to be undesirable.

Experimental. A sample of CF3~CH-CC13 (30 0.105 mole,

CHC12 b.p. 182-191°) was mixed with a 50-50 per cent by volume aqueous-iso- propyl alcohol solution of :Wa2C03 (ll+ g., 0.132 mole). This was o stirred vigorously while heating to 70 with an oil bath. After one - k9 - hour there was still no evolution of COg. The starting material was recovered. chci2 i Dehydrohalogenation of CF^-CH-CCl^ with KOH in isopropyl alcohol.

Experimental. A 500 ml. round bottom 3-neck flask was equipped with a magnetic stirrer and fitted with a dropping funnel, thermometer dipping into the solution, and a water cooled reflux condenser. Potas­ sium hydroxide (27 g. 85 per cent pure, O.^t-10 mole) dissolved in

300 ml. of isopropyl alcohol was added dropwise to a solution of

CFg-CH-CClj (101 g., 0.355 mole, b.p. 182-191°) in 100 ml. of isopropyl

CHClg alcohol. During addition of the base to the chlorinated compound the mixture was stirred vigorously and the temperature of the solution was kept below 10° by an external cooling bath of Dry Ice and acetone.

The time of addition was about one hour and the mixture was stirred for an additional 15 minutes. Excess water was added to dissolve the KC1 and to form a lower organic layer. The organic layer was washed twice with water to remove the alcohol and then dried over CaClg to give 78 S* °f product. Fractionation gave:

Fraction Grams B.p. (7^0 mm.) n^° Probable Product

1 ^.5 67-82 I.3850 alcohol

2 1.2 82-90 I.U075 intermediate

3 ^7-5 1^5-160 (mostly I.U518 CF C=CHC1 15^) 3 Residue 22.0 Solid CFo-CH-CCl2- ° CHClo

Trap empty

75-2 - 50 -

If the crude material was pure, the conversion to product was

5*+ per cent.

In order to improve this yield by reducing the amount of residual

solid, the same experiment was repeated with 63 g. (0.221 mole) of

CF 3 CHCCI 3 and only 60 per cent of the required amount of KOH. This chci2 gave 1+8 per cent of the desired olefin and 1+7 per cent of organic

residue. Of this residue there was 1+6 per cent of recovered starting material and 5^ per cent of dimer. Reworking the residue would give

a total yield of 70 per cent. CCI3 Dehydrohalogenation of CF3-CH-CCI3 . CCI 3 Experimental. The six-chlorine compound, CF3 -CH-CCI3 , which was

a solid was never isolated in the pure form. Experiments with crude

samples of the compound, contaminated with dimer and possibly the

seven-chlorine compound, Indicated that the ease of dehydrohalogena­

tion was essentially the same as for the five-chlorine compound.

Fluorination. Previous successful allylic fluorinations of crude

samples of CF^C-CCl^ and CF C=CHC1 (page 3 1 ) were conducted in a CCI3 CC13 stationary steel bomb which was heated alternately by an oil bath and

a free flame. In an attempt to improve this fluorination a different

procedure was followed which involved rocking the bomb while it was

held in an electrically heated jacket.

Experimental♦ A 1+50-ml. steel bomb was loaded with SbF^ (179 S-,

O .56 mole) containing 20 per cent SbF3Cl2 , CF C=CHC1 (78 g*, 0.315 'CCI 3

mole), and CFoC=CCl2 (15 g., 0.053 mole approximate). The bomb was CCI3 - 51 - fitted with a conventional 600 p.s.i. gauge and outlet valve, and then rocked in a mechanical shaker for 20 hours. During this time the temperature of the electrically heated jacket was maintained at

100°. The pressure rose from 122 p.s.i. after one half hour to

158 p.s.i. at the completion of the reaction. The bomb was then heated with a free flame, with the pressure at 20-40 p.s.i., while it was bled through a flask containing ice water trailed by a drying tower of CaClg and two Dry Ice traps. This gave an organic layer of

50 g. The traps were empty. By adding water to the bomb and steam- distilling the residue, an additional 9-5 g. was obtained. The crude organic material was washed with water and dried over calcium chloride to give 55-5 g* of product. Fractionation gave: PO Fraction Grams B.p. (740 mm.) n^ Moles

1 4i.o UU-h-7 1.3130 CFoCrCHCl 0.207 jcf3

2 3-0 ^7-78 1.3515 CF3C=CC12 0.013 cf3

Residue 10.5 1.3960 Pentafluoro cpds. 0.049

Yield: 59*0 per cent 6 Fluorine atoms.

13-3 per cent 5 Fluorine atoms.

A slightly higher reaction temperature or a longer reaction , period would undoubtedly give a conversion of approx. 70 per cent. CF3 cf3 Attempted ozonolysis of CF3~C=CHC1 and CF^-C^Clg. 20 Experimental. Six grams of a sample (b.p. 70-73* 1-3494) containing mostly CF-^CClg with some CF^C=CHC1 was dissolved in jcf3 cf3

12.4 g. of pentane. Ozone was bubbled through the solution at -78° until it acquired the characteristic blue color for ozone. Since this - 52 color persisted for several hours, the mixture was treated with

Raney nickel and pentane but showed no signs of reaction. Working up the reaction mixture did not produce any of the desired CF^COCP^- cf3 cf3 Oxidation of CF3 -C=CHC1 and CF3~C=CClp.

Experimental. Several of these oxidation reactions were per­ formed. The best of these is reported as follows:

Grams Moles

CF C=CHC1 8.0 0 .0 *K)3 Total 0.0M*6 mole " 3 CF-CrCClo 1.0 0.00*4-3 3 ■ ^ CF3 KMnO^ 12.3 0.0779

HgSO^ 11.5 0.1235

Water 25.0

The above ingredients were added to a 250-ml. 3-neck flask which was trailed in sequence by a cold water reflux condenser, two Dry Ice traps, and an inverted graduated cylinder immersed in water to measure approximately the volume of evolved gas. Vigorous stirring was accomplished by a magnetic stirrer. The mixture was stirred for

200 minutes with external cooling to keep the internal temperature well below reflux temperature (about *4-5°)• The rate of the reaction was followed as indicated by the volume of evolved gas measured against the time:

Minutes 18 36 55 65 73 81 95 105 1*40 200

Vol. ml. 100 230 310 *4-10 510 610 710 810 850 855

After completion of the reaction, the first trap contained 3.0 g. of

CF?C=CHC1 measured as 1.3130) and some chlorine which was distilled 6 f3 - 53 - off. This left a total of 0.0295 mole of starting olefins which had been available for oxidation. The excess permanganate was discharged by sulfur dioxide and the mixture was then continuously extracted with ether for six hours. The ether extract was distilled to remove most of the ether leaving about 6 g. of liquid which precipitated a solid at room temperature. This solid was probably the hydrate of hexafluoroacetone. This ether solution of the hydrate was added drop- wise to PgOc; (30 g. ) which was contained in a flask trailed by a water condenser and two Dry Ice traps. It was necessary to have a dry atmosphere in the apparatus and to avoid the rapid addition of the hydrate solution; otherwise, crystals of hexafluoroacetone-hydrate collected in the reflux condenser. After addition of the material to the the first trap contained the liquid hexafluoroacetone and a

small amount of ether which formed a top layer. The ketone was distil­ led off to give 3.9 g. of product. This formed a semicarbazone m.p. l*t-5-l*i-90 (literature m.p. l*t-9°> dec. 153°) • Recrystallization of the derivative confirmed the reported melting point.

(3 .9 /1 6 6 ) 100 Percentage conversion ------= 79-6 0.0295

[(3 .9/1 6 6 ) + (3 .0 /1 9 8 .5 )] 100 Total yield

In an attempt to account for the missing 13*5 per cent an investiga­ tion of the material in the aqueous residue did not reveal any unextracted organic material. The loss could have been purely mechan­

ical; or possibly, some unreacted starting material was extracted by the ether and was lost when added to the P2O5 ; or, one could assume - 5b - complete oxidation of the available starting olefins, with subsequent decomposition of the ketone to CF^COOH and CF^H. In the latter case

855 ml. of evolved gas, corrected for temperature and pressure, is equivalent to 0.0357 mole. Complete oxidation of the starting olefins would give 0.0295 mole of COg or CO and the difference between

0.0357 mole and 0.0295 mole which is 0.0062 mole could be CF^H. It may not have been coincidence that 0.0062 mole represented 13*9 Per cent of the total starting olefins. This would give a material bal­ ance of 1 0 0 . per cent. An infra red spectrum of the evolved gas showed the characteristic absorption for COg and possibly a trace of fluoroform. The presence of fluoroform was not definitely established, however.

Repetition of this experiment with a larger quantity of

CF^CrCHCl (i+0 g.) confirmed the 79 pe^ cent conversion to CF^COCF^. cf3 The product boiled -26° to -25° and gave an infra red spectrum which was identical with the known spectrum for hexafluoroacetone. It was also observed in this experiment that the ratio of KMnOi^ to starting material, as used in the procedure on page 5 2 , was not quite sufficient in the event that all of the starting material would be available for oxidation.

Analysis of the semicarbazone showed it to be the monohydrate:

Per cent C H N F 0 Calc. 19.93 2.09 17.^3 ^7-29 for (CFgJ^sMHHCNHe'HaO

Found 20.03 2.0b 1 7 A 3 b8.bh - 55 -

Conclusions

The investigation of three separate batches of 2-trifluoro- methylpropane led to the following results:

(1) The chlorination of 2-trifluoromethylpropane gives i+3 per cent of product containing tertiary chlorine. Practically all of this can be isolated as CFoCClC01o . Furthermore, this tetrachloro- 36h 3 3 compound can be dehalogenated in 73 per cent yield or better to give

CF^CrCClp. This compound was utilized by Shepard to prepare hexa- jch3 fluoroacetone; hence, this compound can be used as more starting material for obtaining the ketone.

(2) Dehydrohalogenation of the five-chlorine compound can be effected with KOH in isopropyl alcohol to produce CF3-C=CHC1 in 70 per 6c i 3 cent yield by reworking the residue. CG13 (3) The allylic fluorination of CF^CsCHCl can be made to proceed in yields of 70 per cent to CF3 -C=CHC1. c f 3 (U) Oxidation of CF3C=CKC1 to CFoCOCFo in 80 per cent yield with •3c f 3 J

7 per cent recovered starting material confirmed the intermediate structures of CFoCrCHCl and CFoCzCHCl. cci3 c f 3

(5) Dehydrohalogenation of crude mixtures of the six-chlorine compound produced CF3C=CC12 - This was established by the subsequent cci3 allylic fluorination to CFoCrrCClg available for oxidation to CF -CO-CFo c f 3 3 - 56 -

WAVE NUMBERS IN CM-' I.R. STECIROrHOIOMEIER Moo 2500 2000 1500 1400 1200 H i d PRISM 100

MOEX

Qea <>11 (ft co J

* 'FROM R o tc rt R . Tirowi CMS. CMS. CHEM ms. SOLV.

VOL. C.G C.C SOUO C m r AiidiUm. IU&. CAMORIOeS, MASS, UAA. 2 43 6 6 7 8 imm WAVE LENGTH IN MICRONS

WAVE NUMBERS IN CM-' . 1100 1000 900 800 625 100

44 8 9 10 II 12 13 14 15 16 WAVE LENGTH IN MICRONS

Figure 1 Infrared Spectrum of Hexafluoroacetone - 57 -

Attempted Bromination of CF^-CHp-CFg

Discussion. The preparation of hexafluoroacetone by hydrolysis of the bromine atoms in CFg-CBrg-CF^ would be a very novel synthesis and would be preferred to any known procedure for its simplicity.

4 The proposed method would depend on the successful bromination of

CFg-CI^-CFg to give CF^-CB^-CF^ which should react readily with

2,^-dinitrophenylhydrazine to give the N-derivative of hexafluoroace­ tone. Possibly CF^-CBrg-CF^ could be hydrolyzed directly to the hydrate of the ketone.

The first step then would be to brominate CF^-CHg-CF^ and it was believed that the use of a positive brominating agent might be success­ ful. For example, Schmitz (27) reported that CFg-CO-CH^-CO-CF^ did not react with bromine - at best, very slowly; whereas Avonda (6 ) was successful in this bromination to form CF2“CO-CBr2 -CO-CF2 by the use of N-bromosuccinimide in carbon tetrachloride. Furthermore Avonda was able to brominate CF^-CO-CH^-CF^ to its dibromo derivative by

N-bromosuccinimide in nitrobenzene - the less polar solvent, carbon tetrachloride, was unsatisfactory in this case. This requirement of a positive brominating agent for these two compounds should be even more necessary in the bromination of CF^-CE^-CF-^. In the latter com­ pound both carbonyl groups are removed and the adjacent trifluoro- methyl groups exerting a strong electronegative effect should make the hydrogen atoms very protonic.

Avonda (6 ) had successfully prepared CF -C C-CFo Ih 9h NOo' NO- - 58 - from CFg-CO-CBrg-CF^ and 2, 4-dinitrophenylhydrazine. The immediate

objective in this work was to prepare CF^-CB^-CF^ and convert it to

a phenylhydrazone of CF^-CO-CFg.

Experimental.

Preparation of CFg-CHp-CFg. Hexafluoropropane was prepared by

a previously reported sequence of reactions (^, 5 )*

HF Zn HF CFo-CC1 =CC12 ------» CFo-CHCl-CFpCl > CF,-CH-:CF2 ----- > J SbF3Cl2

CF3-CH2-CF3

Attempted bromination of CFg-CHp-CFg with N-bromosuccinimide in

glacial acetic acid. N-bromosuccinimide (19•5 B-, 1.1 mole) and

75 ml. of glacial acetic acid were added to a 250-ml. flask equipped with a thermometer, magnetic stirrer, and a Dry Ice reflux condenser

trailed by a Dry Ice trap. Hexafluoropropane (b.p. -0.7°; 1-5 g->

0 .0^9 mole) was bled into the system while the flask was cooled with

a Dry Ice-acetone solution. The mixture was then stirred at room

temperature for 3 hours while being exposed to ultraviolet radiation.

A slight orange tint developed in the solution but there was no

refluxing. Stirring for an additional two hours with an oil bath at

90°, at which temperature the N.B.S. was completely dissolved, caused more decomposition and fairly rapid refluxing. During this period of

heating the internal temperature did not vary appreciably from about

60° and there was no apparent change in the rate of refluxing. The

trap was empty.

Fractionation of the mixture gave essentially all of the starting

CF^CHgCF^, an intermediate cut of about 13 g- b.p. 105-115°^ and - 59 - finally acetic acid. The material with b.p. 105-115° had a refractive index of I.368O at 20° as compared to 1.3692 for the acetic acid. It did not freeze at 0° and reacted vigorously with water. It would not form a derivative with semicarbazide or 2 ,k-dinitrophenylhydrazine.

This fraction was presumed to be mostly acetic acid with some acetyl bromide.

Attempted bromination of CF^-CHg-CF^ with n-bromosuccinimide in nitrobenzene. The same procedure and apparatus were used in this experiment except for substituting nitrobenzene in place of acetic acid. Stirring the mixture in an oil bath at 110° for 5 hours gave a rapid rate of reflux with the internal temperature staying at about

60°. There was little decomposition and the trap remained empty.

Fractionation recovered starting material and nitrobenzene. The solid residue was filtered off and was found to be heavier than CCl^. This indicated the absence of succinimide which would have been formed if bromination had occurred.

Attempted bromination of CFg-CHg-CF-^ with bromine and aluminum bromide:

Grams Moles

6.0 0 .0!+

Bromine 2.0 0.025

Aluminum bromide 0 .00k

The aluminum bromide was prepared by adding an excess of bromine dropwise to alluminum foil contained in a 250-ml. 3-neck flask. The flask was equipped with a water reflux condenser trailed by a Dry

Ice reflux condenser and Dry Ice trap. Hexafluoropropane was bled into the flask in the usual manner. Stirring by a magnetic stirrer for - 60 - one hour with the temperature of the external bath at 50° gave no trace of evolved HBr. The starting material was recovered. - 6i -

Conclusions

This preliminary investigation of the susceptibility of

CF^CI^CFg to bromination showed that more strenuous conditions would be required. It is recommended that a sealed tube reaction be tried since this would permit a higher reaction temperature. It is also possible that because of a probably shorter C-H bond distance that atomic brominating agents employed at high temperatures would be preferable to the more positive brominating agents. o O o O O CO•*1 CO*1 CO CO*1 CO 5 o O O o o Q O a o 5j " O II O ll M M w w O H O H O O o CO O W CO o Co K H O w O M O ro H CO H ro H Co HSCL OSAT O NW COMPOUNDS NEW OF CONSTANTSPHYSICAL

H -P* on on H •P" M • CO i 03 on H H CT\ 03 to i on * p- *T“r— ■p-

T) On -3 -d -3 -3 -3 ro •p- -F" •F" -p- -F 2 co on on -P- On

H H H H Co •P* -F" V i tP ro H -3 on on o CO O ro VO O on CO O

H*•H H H on -a- oo ■-3 i -p- ro H --p* -F* -P- O H vo on vn ro VO -d on

H H H o H ro £: VO 03 vo -P av SUMMARY

A study of C^FyZnl showed it to he very unreactive toward such compounds as ethyl perfluoro-n-butyrate, isoamyl perfluoroacetate, benzaldehyde, acetophenone, and acetic anhydride. There was some indication of reaction with acetophenone and acetic anhydride but to such a small degree that this would be an impracticable method for obtaining fluorinated ketones. The reaction with benzaldehyde pro­ duced obvious side products and the reaction with the oxygenated perfluoro compounds gave no indication of any product.

The preparation of trifluoroisobutane and its chlorinated analogs led to new sequences for synthesizing hexafluoroacetone. For example,

c h 3o h (l) CHqMgBr c f 3-c o o h -> CFq-COOCH. CFq-C( OH)CH' *

Hg d 2 --- » CF3-CH-CH3

CF3-CC1-CC1-CClq3

CF3-CH-CCl3 >

CHgCl chci2

Cl,•2 (C) * CF3-CH-CC13 ->

CC1 3

- 63 - - 6k -

Zn (A) » CF^-CrrCClg----- ^ etc. by Shepard's method (22) to i CH 3 CF3-CO-CF3

KOH SbFq tS&SSfl. CF3 - f CHC1 ■■aJ cl > ®3-?--°H01 a2-ao h °1 C013 3 2 0P3

KMnO[j_ -» CF3-CO-CF3

KOH SbF3 (C) > CF.,-C:CC12 > CFo-CrCClo isopropyl 3 , sbFgClg J 1 alcohol CC1^ - CF^

KMnOh -> cf3~co-cf3

In the above sequences of reactions the chlorination of trifluoro­ isobutane gave approximately i+3 per cent of the compound with tertiary chlorine, CF3-CC1-CC13, which was very resistant to further chlorina-

ch3 tion and about 53 per cent of a mixture of the five and six-chlorine compounds. There was about a k per cent loss in high molecular weight residues. A good yield was obtained in each of the reaction steps and the final oxidation step in sequence B was developed to an optimum conversion of 80 per cent with a 7 Per cent recovery of start­ ing olefin.

Another method was proposed for the synthesis of hexafluoro- acetone which involved the hydrolysis of the bromine atoms in

CF^CBrg-CFy However, attempts to prepare CF3-CBr2-CF3 by bromination - 65 - of CF^-C^-CF^ were unsuccessful. The resistance of CF3-CH2-CF3 to bromination was demonstrated by its failure to react with N-bromosuc­ cinimide in either glacial acetic acid or nitrobenzene and bromine in the presence of aluminum bromide. GENERAL CONCLUSIONS

1 . Perfluoro-n-propylzinc iodide is very unreactive toward such compounds as ethyl perfluoro-n-butyrate, isoamyl perfluoro- acetate, benzaldehyde, acetophenone, and acetic anhydride.

2. Hydrogen in the presence of platinum catalyst adds quanti­ tatively to CF^-CB^CE^* ^ i ch3

3 . The chlorination of CF^-CH-CH^ gives approximately ^3 per

c h 3 cent substitution in the tertiary position whereas the chlorination of CF3 -CH2 -CH3 had given only 20 per cent substitution on the central carbon. The additional methyl group in the former structure apparent­ ly opposes somewhat the directive influence of the trifluoromethyl group.

h. The pentachloro compound, CF3-CH-CCI3, can be dehydrohalo- l CHC12 genated in about JO per cent yield by using only one half the theoret­ ical amount of base and then reworking the residue. The product appeared to be predominantly CF3-C=CHC1 with no evidence of CF^-CsCClg* 1 1 CC13 chci2

5- The allylic fluorination of CFo-C=CHCl to CF~-C=CfICl can be 1 ^ 1 CCI3 CF^ accomplished in 70 per cent yield which is comparable to the allylic fluorination of CH0-C=CHC1 to CH,-C=CHC1. 3 , 3 , cci3 c f 3

The same reaction was accomplished with crude samples of

- 66 - - 67 -

CFg-C=CCl2 however the exact percentage yield is not known.

CCI3

6 . The acid permanganate oxidation of CFo-C=CHCl gives 80 per ** 1 CF3 cent conversion to CF^-CO-CF^ in contrast to a previously reported

60 per cent conversion for the oxidation of CF^-C^CC^-

gf3

7* Hexafluoropropane, CF^-CHg-CF^, is extremely resistant to bromination by positive brominating agents. BIBLIOGRAPHY

1 . A. L. Henne, J. W. Shepard and E. J. Young, J. An. Chem. Soc., 72, 3577 (1950). 2. A. L. Henne and W. C. Francis, J. Am. Chem. Soc., 75, 992 (1953)- 3- 0. R. Pierce, E. T. McBee and G. F. Judd, J. Am. Chem. Soc., 76 , 777 (195*0* 7. E. T. McBee, A. Truchan and R. 0. Bolt, J. Am. Chem. Soc., 70, 2023 (1978). 5- A. L. Henne and T. P. Waalkes, J. Am. Chem. Soc., 68, 796 (19 76). 6. F. P. Avonda, Ph.D. Dissertation, The Ohio State University, 1953. 7- N. Fukuhara and L. A. Bigelow, J. Am. Chem. Soc., 63, 788 (l97l). 8. E. T. McBee and W. B. Ligett, U.S. Patent 2,6l7,129 1952; C.A., if7 , 8769. 9- T. J. Brice, J. D. LaZerte, L. J. Hals and W. H. Pearlson, J. Am. Chem. Soc., 75, 2698 (1953). 1 0 . W. H. Pearlson and L. J. Hals, U.S. Patent 2 ,617,836 1952; C.A., 77, 8770. 1 1 . R. N. Hazeldine, J. Chem. Soc., 3 5 6 5 (1953)- 1 2 . R. IT. Hazeldine, J. Chem. Soc.., 1273 (1957). 13- W. T. Miller, Abstracts of Papers, 122nd Meeting, Am. Chem. Soc., Atlantic City, Sept. 1952. 1 7. H. J. Emeleus and R. W. Hazeldine, J. Chem. Soc., 2978 (19^9)- 15- A. L. Henne and W. C. Francis, J. Am. Chem. Soc., 73, 3518 (1951). 1 6 . A. L. Henne and W. G. Finnegan, J Am. Chem. Soc., 72, 3806 (1950). 17- M. Hauptschein and A. V. Grosse, J. Am. Chem. Soc., 73, 276l (1951). ~ 1 8 . 0. R. Pierce and M. Levine, J. Am. Chem. Soc., 75, 1257 (195 3) - 19- A. L. Henne, J. Am. Chem. Soc., 75, 5750 (1953)* 2 0 . R. N. Hazeldine, J. Chem. Soc., 2789 (1950). 2 1 . B\ R. Husted and W. L. Kohlhase, J. Am. Chem. Soc., j6f 5l7l (1957). 22 . J. W. Shepard, Ph.D. Dissertation, The Ohio State University, 1978. 23- D. D. Krehbiel, Ph.D. Dissertation, The Ohio State University, 1957. 27. E. J.. Young, Ph.D. Dissertation, The Ohio State University, 1977- 25. A. M. Whaley, Ph.D. Dissertation, The Ohio State University, 1971. 2 6 . A. L. Henne and A. M. Whaley, J. Am. Chem. Soc., 67, 1157 (1972). 27. J. V. Schmitz, Ph.D. Dissertation, The Ohio State University, 1979.

68 - AUTOBIOGRAPHY

I, Robert Raymond Brown, was born in Akron, Ohio, June 30;

1922. I received my secondary education in the public schools of

Akron, Ohio, and began my undergraduate training at the University of Akron in 19^+0. This training was interrupted by three years service in the United States Infantry during World War II. After returning to the University of Akron in 1

Bachelor of Science in 19^7• For the next three years I was employed in the Research Laboratory of The Firestone Tire and Rubber Company in Akron, Ohio. During this same period I attended night school at the University of Akron and in 1950 received the degree Master of

Science. I enrolled in the Graduate School of The Ohio State

University in 1950 where I served as a teaching assistant for two years while completing the requirements for the degree Doctor of

Philosophy.

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