SOME REACTIONS: of CHLORODIME THYLARSINE and DIMETHYLARSINE by David S

SOME REACTIONS: OF CHLORODIME THYLARSINE AND DIMETHYLARSINE by David S. Dawson

A THESIS. SUBMITTED IN, PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE. DEGREE OF MASTER. OF SCIENCE in the Department of Chemistry

We. accept this thesis as conforming to the required standard

THE, UNIVERSITY. OF BRITISH COLUMBIA.

September 1964 In presenting this thesis-in partial fulfilment of the requirements for an advanced degree at the University of :

British Columbia, I agree that the Library shall make it freely available for reference and study, I further agree that per- . mission for extensive copying of this thesis for scholarly . purposes may be granted by the Head of my Department or by his representatives. It is understood that,copying or publi• cation of this thesis for financial gain shall not be allowed without my written permission*

Department of

The University of British Columbia, Vancouver 8, Canada

Date i

ABSTRACT.

Chiorodimethylarsine is found to add across the triple bond of hexafluorobut-2-yne, forming 2- chloro-3-dimethy 1- arsinohexafluorobut^-2-ene. Arsenic trichloride, dichloromethylarsine and chlorodiphenylarsine do not react,, while chloromethylphenylarsine reacts with great difficulty.. Sim• ilarly, bls(trifluoromethyl)arsine and methylphenylarsine form adduets with the butyne. These reactions are discussed and related to electron availability. The hydrolysis, bromination

and chlorination of the adduct (CR3)2AsCCCF3)=CClCF3 are des• cribed. The reaction of dimethylarsine with dichloromethylara- ine is discussed, and a reaction path suggested. Dimethyl- arsine is found to react with trifluoroacetic acid, its anhy• dride, and acyl chloride, but the products were not all ident• ified. s Perfluorocyclobutene reacts with dimethylarsinomagneslum bromide to give dimethylperfluorocyclobut-l-enylarsine. The cyclobutene does not react with chlorodimethylarsine. iv

ACKNOWLEDGEMENT

I wish to. express, my sincere thanks and appreciation to Dr. W..R. Cullen for his constant guidance throughout the experimental work, and for constructive criticism of the manuacript. ii

TABLE OF CONTENTS:

ABSTRACT i ACKNOWI^LGEMENT iv EXPERIMENTAL. 1 Section I: Reactions Involving Hexafluorobut-2-yne 2 (A) With Chioroarsines . 2 1.. Chior odime thy larsine 2 Synthesis of Chlorodimethylarsine 2 Reaction.of the Arsine with Hexaf luorobut-2r-yne 2 (a) Irradiation-. 2 (b) Heat. 3 2., Other Ghloroarsines 5 Synthesis of Dichloromethy larsine 5 Synthesis, of Chloromethylphenylarsine 6 Reaction-of Chloromethylphenylarsine with Hexa- _ fluorobut-2-yne .... 6 (B) With Secondary Arsines 7 I„ Bis(trifluoromethyl)arsine 7 Synthesis of Bis(trifluoromethyl)arsine 7 Reaction.of. the.Arsine with Hexafluorobut-2i-yne 7 2. Methylphenylarsine ' . . 9 Synthesis of the Arsine 9. Reaction of the Arsine with Hexafluorobut-2-yne 9 Section II; Reactions Involving 2-Chloro^-dimethyl- arsinohexafluorobut-2-ene . . ii (A) Thermal.Stability 11 (B) With Aqueous. Sodium Hydroxide. 11 (0) With Bromine 12: 1.. One Mole Bromine 12 2. Two Moles Bromine 13 (D) With Chlorine 14 (E) Bromination of 2,3-Bis(dimethylarslno)hexa- . fluorobut-2-ene .' 15 Section III: Reactions Involving Dimethylarsine 16 Synthesis of Dimethylarsine ... 16 (A) With Dichlorome thy lar sine 17 (B) With Trifluoroacetyl Chloride 17 (C) With Trifluoroacetic Acid 20 (D) With Trifluoroacetic Anhydride 21 (E.) With Methylmagnesium Bromide 21 Section IV: Reactions. Involving; Perfluorocyclobutene 21 (A) With Dime thy lars inomagne s ium Bromide 21 Synthesis of Dimethylarsinomagnesium Bromide 21 Reaction,of the Bromide>with the Butene 22 (B) With Chlorodimethylarsine. 22 I., Irradiation 22. 2. Heat . . 23 iii

RESULTS AND DISCUSSION. Reactions Involving Hexaf luorobut-2-yne. Reactions Involving 2-Chl orc^ 3-d ime thy lars ino- hexafluorobut-2-ene Reactions) Involving Dime thy lar s ine Reactions Involving Ferfluorocyclobutene B3BLI0GKAPHX INTRODUCTION

It has long been known (1) that arsenic trichloride will add across the triple bond of acetylene, yielding/^ -chloro- vinyldichloroarsine (Lewisite). The reaction is catalyzed by Lewis acids such as aluminum and mercuric chlorides, and pro• duces mainly the trans isomer. Dichlorophenylarsine will also react with acetylene in the presence of aluminum chloride to give several products;, including bisp^-chlorovinyl )phenylars- ine (2).

Cullen and Brierley (3) found that 3,,3,3-trif luoropropyne reacts with chlorodimethylarsine',, under ultra violet irrad•

iation,; to yield lr^imethyIaraino--2,,3,13j3-tetrafluoroprop~2-ene,

rather than the expected (CH3)2A.sCH=CClCT3. .Hexaf luorobut-2-yne has been found to react with the Aa-As bonds of arsenic metal (4) and tetramethyldiarsine (cacodyl) (5), giving compounds containingAsC(CFg) =C(CFg)As units, e.g.

(CH3)2As-As(CH3)2 + CFgCiOQFg » .(CH3)2AsC(CFg)=C(CFg)Aa(CHg)2

This reaction occurs smoothly at. 20°t yielding roughly a 1:1 ratio of cis and trans isomers. The butyne does not react with perfluorocacodyl at 150° (5). It has been found (6), however, that the reaction

(OF3)2AarAsCCF3)2 + CFgC=CCF3 > (CF3)2AsC(CF3)=C(CF3)As(CF3)2 does occur with ultra violet irradiation,, yielding mainly the trans form. . Dimethylarsine and hexaf luorobut-2-yne react at 20° to,

form the adduct (CH )g^se.(CEFg)=GHCE3 (mainly trans) (?). Under the same conditions the arsine combines) with 3,3,3-trif luoro- vi

propyne to generate both XCHg)2&sC(CEg)=CH-g. and CF3CH=CHAs(CH3)2 (cis and trans) (3). In view of these results, it was of interest to conduct further work involving the reactions of hexaf luorobut-2-yne with arsenic compounds. The present investigation was directed primarily, at the reactions of the butyne with As-Cl and As-H bonds.

1. S. J.. GREEN and T. S. PRICE. J. Chem. Soc. 448 (1921). 2. C. K. BANKS,. F. H. KAHLER and C. S, HAMILTON. J. Am. Chem. Soc. 69_, 933 (1947). 3. W. R. CULLEN and P. BRIERLEY. Unpublished observations.

4. C. G..KRESPAN. J. Am. Chem. Soc. 83, 3432; (I96I). ' 5. W. R. .CULLEN and N. KV HOTA. Can. J. Chem. 42, 1123 (1964). 6. W. R. CULLEN, D. S. DAWSON and G. E. STYAN. J. Organometal. Chem. In press. 7. W..R.^. CUL1£N. Unpublished observations. 1

EXPERIMENTAL

Since many of the reactants and products encountered in this work were volatile and often unstable to air or water, conventional high vacuum techniques were employed In their man• ipulations. Unless; otherwise stated, reactions were done in Caxlus tubes. Products exhibiting a reasonable volatility were sep• arated in the vacuum system by trap-to-trap distillation using suitable low temperature baths. Low-volatility products were examined by distillation at reduced pressure, usually in an atmosphere of nitrogen. Product separation was also achieved by means of vapour phase chromatography, using an Aerograph gas chromatograph equipped with a dinonyl phthalate column. Molecular weight determinations of volatile substances were made by Regnault's method. Microanalyses were carried out by Dr. Alfred Bernhardt,; Max Planck Institute, Mulheim, Germany. Infra red spectroscopy was used extensively throughout this investigation for determining purity, identifying known compounds, and ascertaining the structure of new compounds. Most of the spectra were run on a Perkin-Elmer Model 137 (Infracord) double-beam instrument fitted with sodium chloride optics. When greater detail was required, the Perkin-Elmer Model 21 was used. Vapours were contained in a gas cell equipped with sodium chloride windows, liquids were run as films between sodium chloride discs, while solids were incorp• orated into Nujol mulls or potassium bromide pellets. 2

Yarlan H.R.-60 (at 56.4 Mc/s) and A-60 spectrometers were used to obtain the *9F and ^"H nuclear magnetic resonance spectra. Unless otherwise stated, the latter were run relative to internal tetramethylsilane.

Section I: Reactions- Involving Hexafluorobut-2-yne (A) With Chloroarsines

1. Chlorodimethylarsine Synthesis of Chlorodimethylarsine^" Sodium, hyp©phosphite (88 g.) and concentrated hydrochloric acid (300 cc.) yielded a solution of hypophosphorous acid. C275 e.c)» which was used to reduce dimethylarslnic acid (112: g.) in concentrated hydrochloric acid (.200 cc). The crude chloro• dimethylarsine (108 g.) was distilled at atmospheric pressure in a stream, of nitrogen. The fraction boiling at 104-110° was collected (lit. value 107°)2. Reaction of the Arsine with Hexafluorobut-2-yne (a) Irradiation: chlorodimethylarsine (5.0 g.) and hexafluorobut-2-yne (9*5 g.) were irradiated with ultra violet light„ with constant agitation, for two: days, after which time the two colourless phases had become one amber coloured phase. The materials were taken into the vacuum system and a separ• ation was attained using a -78° bath. This yielded unreacted hexafluorobut-2-yne (5.6 g.) and a compound (8.7 g.) which distilled at 79-80° (50 mm.), 131-132;° (83 mm.) and was ident• ified as 2-chloro-3-dimethylarainohexafIuorobut-2-ene. Found: C, 23.98; H, 1.90;; As, 24.63;: Cl, 11.94; F, 37.50 %; M, 280. Calc. for CgHgAsClFg: C, 23.4; H, 1.99; As,, 24.8; Cl, 11.7; 3

F„ 37.8 %; M, 303. Infra red spectrum (liquid film): 2910 vw>

1584 Wj; 1420 vw» 1263 m, 1227 vs, 1187 a, 1156 vs, 1130 sh, 982 w,

1 896 w, 875 w,; 850 w, 780 w cm"*"". The proton, magnetic reson• ance spectrum showed two peaks in the high field region, the smaller at f - 8.44 and the larger as a distorted quartet cen• tred at T=8.69 (J £ 1.5 c.p.s.). The ratio of the areas was approximately 8.3:1. In the downfield region was a very small peak at r =2.54. The magnetic resonance spectrum showed two main bands at +118 and +285 c.p.s., relative to internal benzotrifluoride. These are split into a quartet (high field) and a multiplet (9 peaks),. J for both being 1.4. c.p.s;. Outside these lie two much smaller quartets (J = 15 c.p.s.), centred at +42 and +372 c.p .a. (b) Heat: chlorodimethylarsine (1.8 g.), aluminum chlor• ide (.15 g.) and hexafluorobut-2-yne (7.6 g.) were heated to 140° for 16 hours. Trap-to-trap distillation of the volatile materials yielded hexafluorobut-2-yne (4.0 g.) and a fraction stopping in a -46° bath. This fraction was distilled at atmo• spheric pressure, yielding three cuts: 147-148°, 148-154°, 154-158°. The first (very small) yielded an infra red spect•

:s rum (liquid film) Identical with that of (CH3)2AsC(CF3) GClCF3.. Fractions two (the. large majority of the distillate) and three were identical, as follows (liquid, film):. 3.35 vw, 6.25 m, 7.05 w, 8.05 vs, 8.4 s, 8.6 vs.,, 8.8 s, 10.05 w, 11.1 w, 11.4 m, 11.6 w, 12.4 w, 14.2 m.yu . This material analyzed to be 2-dimethylarsinoheptafluorobut-2-ene.. Found: C,, 24.97j H, 2.04;

As„ 25.97; F, 46.57 %; M, 26g. Calc. for-C^ksF7: C, 25.2; 4

K, 2.10; As, 26.2;; F, 46.5 %; M, 286. The experiment was repeated (20 hrs. at 140°), using 20.3 g. chlorodimethylarsine and 39.4 g. hexaf luorobut-2-yne, in three sealed tubes (no aluminum chloride). The volatile materials were combined in the vacuum system while the small amount remaining was distilled at .67 mm. Unfortunately the temperature rose steadily and essentially uniformly throughout

—noi clear cut boiling ranges could be seen. The two fractions taken had ranges 84-106° and 106-170°. The material remaining in the distilling pot came over at 125-156° (10~3 mm.).

Trap-to-trap distillation of the .volatile materials yielded hexafluorobutr-2-yne (14.8 g.) and a large portion stopping in a -78° bath. This material was distilled at at• mospheric pressure-—four fractions were taken: 101-105°, 110-117° (large), 119-130°, 132-142° (very large). The sec• ond boiled mainly at 115-117°, the fourth at 142°. These two were examined by vapour phase chromatography (column at 132°) and found to contain the same compounds (three major peaks) In. the following approximate ratios: fraction #2, 3.3:3.6:lj fraction #4, 1:8:4. Samples of each of the three major comp• onents were collected, analyzed and subjected to infra red examination. The analysis results:

Component S C % H % As, % Cl % F/ * .26 47.48 1 . .. - 2 20.10 2.99 30.67* * 14.53 31.71 3 23.81 2.08 24.65 11,97 37.99 The third component analyzes to be 2r-chloro-3-dimethylarsino-

hexafluorobut-2-ene. Calc. for C~H~AsClFR; C, 23.8; H, 2.00; * Lack of material prevented further determinationa. ** Obtained by subtracting the sum of the others from 100 %. 5

As, 24.75; Cl, 11.73; F, 37.7 %. The infra red spectra of the three are as follows (liquid films): #1; 3.35 w„ 3.45 w,

6.0 m, 7.0 wr, 7.1 w, 7.2 m, 7.25 s,; 7.6 m, 7.65 s, 7.75 vs, 7.9 vs, broad 8.2: - 9.1 vs., 9.25 w, 9.75 w, 10.3 m, 10.5 w, 10.95 w, 14.55 w^i #2: 2990 w, 2895 w, 1737 w, 1584 m, 1423 m, 1273 s, 1232: vs (broad), 1187 vs (broad), 1151 vs (very broad), 983 m, 895 m, 875 w, 852: m, 829 w, 781 m, 731 vw, 651 s cmT1; #3: 2995 vw (broad), 2905 vw, 1744 vw (broad), 1585 m, 1420 w, 1273 a, 1236 vs (broad), broad 1214 - 1123 vs, 986 m, 896 w, 872 w, 854 m, 782 m, 735 vw, 700 w, 654 s cmT1

2. Other Chloroarsines The results of these experiments are summarized in the table below. Quantitative recovery of the butyne was obtained from all the experiments except the one indicated. Wt. of CFgCECCFg (g.) Reaetant Conditions 28.4 AsClg (10.7 g.) UV irradiation, 2 days 11.2 AsClg. (9.4 g.) Heat (135°), 2 days* 17.9 CHgAaClg (4.8 g.) . UV irradiation, 1 day 12.3 CHgAsCIg (4.7 g.) Heat (105°), 2 days* 10.2 (CgH^gAsCl (4.5 g.) UV irradiation, 2 days

11.3 C6H5(CH3)AsCl (10.0 g.) UV irradiation, 3 days**

Synthesis of Dichlormethylarsine Arsenic trioxide (37 g»), sodium hydroxide (65 g.) and 80% ethanol (750 cc.) were combined;; two liquid phases were formed. Methyl iodide (117 g.) was added and the mixture al• lowed to stand for 20 hours, whereupon the ethanol and unreacted methyl Iodide were distilled off. Excess concentrated hydro• chloric: acid and a little water were added, after which the * AlClg added. ** 8.0 g. butyne recovered 6 mixture was saturated with sulfur dioxide for one hour. The solid product was heated with concentrated hydrochloric acid (i hr,), then distilled at 16 mm. The middle fraction (121- 132°) (31.1 g.) was refluxed with silver chloride (50.g.) until dark colour gone, leaving the colourless dichloromethylarsine and bright yellow silver iodide. The arsine was distil• led at atmospheric pressure, b.p. 130-133° (lit. value 133°)^. The yield was 4.8 g. .4 Synthesis of Chloromethylphenylarsine , Dichlorophenylarsine (181 g.) was synthesized from phenylarsonic acid (168 g.) and concentrated hydrochloric acid (400 c.e.), saturated with sulfur dioxide (i hour)", in the pres• ence of a trace of potassium iodide. The dichlorophenylarsine was converted by aqueous sodium hydroxide and dimethyl sulfate to methylphenylarsonic acid, which was reduced to the chloromethylphenylarsine by sulfur dioxide, in the presence of excess concentrated hydro• chloric acid and a trace of potassium Iodide. The arsine was shaken up with anhydrous calcium chloride and distilled (17 mm.) over silver chloride (b.p. 123-125°) (lit. value 127° at 23 mm.)4. Reaction of Chloromethylphenylarsine with Hexafluorobut-2-yne The recovery of the butyne was not quantitative, ind• icating that some reaction had occurred. The non-volatile product yielded the following infra red spectrum (liquid film):. 2.9 w, 3.5 m (broad), 6.3 vw, 6.75 vw, 7.0 m, 7.15 w, 7.7 vw, 8.15 va, 8.65. vs, 8.75 vs, 9.15 w, 9.3 m, 9.75 vw, 10.0 w, 10.65; vw, 11.0 w, 11.75 m„ 12 .1 vw, 13.2 s, 13.5 vs, 14.4 vsw, 7

(B) With Secondary Arsines

1. Bis(trifluoromethyl) arsine

Synthesis of Bis(trifluoromethy1)arsine (a) Synthesis of tetrakis( trif luorome thy Ddiarsine (perfluorocacodyl): arsenic trichloride (24.6 g.) and tris(trifluoromethyl)arsine (16.8 g.) were heated at 220° (3 days)* Concurrent with this, 24.7 g* AsClg were heated with 16.6 g. (CFg)gAs. The two liquids were immiscible. After two days, there was little difference in volumes of the two phases;, quite a bit of metallic arsenic had deposited on the sides of the tubes. After another day of heating, the only visible difference was an increase in the arsenic deposit. The contents of the vessels were mixed and distilled at. atmospheric pressure, using a dry-ice condenser.. The first fraction, (CTgJgAs, (27.6 g.) distilled at 33-35°; the second,

(CF3)2AsCl, (2.1 g.) at 35-65°; the third, CTgAsClg, (65-100°) was small. The second fraction was shaken, up with mercury (60 g.) for two days and the volatile products, (CF^gAsrA-sXCFg)^ (1.7 g.) taken off. (b.) Synthesis of the arsine: anhydrous hydrogen chloride (4.5g.), mercury (118 g.) and perfluorocacodyl (3.0 g.) were reacted on the shaker (1 week). The presence of a white powder (presumably, mercurous chloride.) in the tube, was evidence that reaction had occurred. Trap-to-trap distillation of the vola• tile materials yielded unreacted hydrogen chloride (4.0 g.), perfluorocacodyl (.1 g.), and bis(trifluoromethyl)arsine (2.9 g.), of known infra red spectrum.

Reaction of the Arsine with Hexaf luorbbut-2-yne

Bis (trif luoromethyl) arsine (2.9 g.) and hexaf luorobut-2-yne 8

(II .0 g.) were combined andallowed to stand at room temperature. After thawing, the mixture formed one phase, a colourless liquid. No apparent change occurred thereafter. After two days the material was (all) taken into the vacuum system;; infra red examination showed that little if any reaction had occurred. The compounds were then heated at 130° (24 hrs.). Examination of the products showed that partial reaction had occurred, but absorption still occurred at the As-H stretching frequency. The material was then heated, for a further three days, but because of a malfunction of the thermostat, the temperature rose: to 210° for part or all of that time. Some yellow-brown solid was produced, but except for this all material went into the vacuum system. Trap-to-trap distillation afforded hexafluorobut-2-yne (8.2; g.),, containing a little silicon tetrafluoride andfluoroform; a small fraction stopping in a -23° bath;; and a fraction stopping in a -46° bath. The -23° frac• tion yielded the following infra red spectrum (liquid f ilm): 5.85 vw, 6.15 vw, 6.25 w, 7.45 m, 7.6 s, broad 7.8. - 9.2 vs, 9.25 vs, 9.4 m, 9.7 vw, 10.05 w, 10.2 vw, 10.65 vw, 10.8 vw, 11.4 w, 11.65 vw, 13.1 w, 13.35 w, 13.6 m, 13.7 w, 13.8 w, 14.1 vw, 14.55 w^ . The -46° fraction (5.0 g.) was distilled at atmospheric pressure, yielding two fractions: 98-99° and 100-101°. Yapour phase chromatography showed each fraction to be virtually the same; after purification by this technique, the compound analyzed to be 2-bis(trifluoromethyDarsino- 1,1,1,4,4,4-hexafluorobut-2-ene. Found* C, 19.31; H, .27;

As, 19.87; F, 60.47 %. Gale, for C6HAsF12: G,, 19.2; H, .27; As, 19.9; F, 60.6 %. Infra red spectrum (second fraction) 9

(vapour, 29 mm.): 3100 vw, 2302 vw, 1793 vw, broad 1728 - 1693 vw, 1649 vw,, 1385 m, 1360 m„ 1331 vs., 1265 vs*, 1215 s*, 1173 va*, 1131 a*, 1099 a*, 1067 m, 1029 m, 1003 w, 949 vw, 887 m, 858 m, 820 vw, 735 a, Tig a cm?1 The proton magnetic spectrum (sample not purified) showed a quartet (J = 7.5 c.p.s.) centred at T = 3.07, and a peak at r = 2:.67. Each peak of the quartet was split into a further approximate quartet (J # 1.5 c.p.s.).

2:. Methylphenylarsine 4 Synthesis of the Arsine Zinc amalgam was prepared by stirring (l£ hrs.) zinc dust (137 g.) in a solution of mercuric chloride (27.5 g.) in water (750 cc), followed by filtering and washing. Chloro• methylphenylarsine (50.5 g.) was reduced, in a nitrogen atmo• sphere, by the amalgam in methanol (250 cc), and concentrated hydrochloric acid (120 cc). The acid was added dropwise (1-| hrs.), followed by stirring for another hour. The mixture was distilled with the exclusion of air into a separatory fun• nel, whence it was transferred into a suitable vessel, into which anhydrous calcium chloride had been placed. The distil• lation was aided considerably near the end by the addition of water to the reaction vessel, apparently because of azeotrope formation. The yield was 37.3 g. methylphenylarsine (unpur- ified). The product would not go into the vacuum system. Reaction of the Arsine with Hexaf luorobut-2-yne Methylphenylarsine (5.6 g.) and hexafluorobut-2-yne (13.3 g.) were reacted at room temperature (a dry-box was used 4£ mm. pressure 10 when putting the arsine into the Carius tube). At room temp• erature the mixture consisted.of two colourless liquid phases, but within a few minutes the lower, phase became yellowish. It became yellower and larger while the vessel became slightly warm. Within half an hour after thawing, the mixture had be• come one phase, a yellow-orange liquid. Within 18 hours amber- coloured crystals had appeared, but no further visible change occurred.

The vessel was opened to the vacuum system; the volatile material was unreacted hexafluorobut-2-yne (7.4 g.). The non• volatile material, which appeared to be a mixture of oil and crystal, was extracted from the tube with a minimum of carbon —3 tetrachloride. The product was distilled at 10 mm., the ... . , \ solvent having first been pumped off at room temperature. Two fractions were taken: 47-49.5° and 53-64°, the second fraction having come over mainly at 54°. An undistillable solid residue, remained behind. Infra red examination indicated that the fractions were identical while proton magnetic res• onance showed in the second fraction a very small amount of impurity at T = 8.5, the "*"H spectra being otherwise identical: two high field peaks, at T = 9.07 (smaller) and the larger as a distorted quartet centred at T = 8.94, the area ratio being 11.1:1; two down field quartets centred at Y = 4.60 (smaller) and T = 3.64 (larger), the area ratios being roughly 11:1. The coupling constant for these was 8.5 c.p.s. Each peak of the larger quartet was split into a quartet, the coupling con• stant being 2 c.p.s. A complex system (aromatic protons) was. centred at T - 3.1. The reference was external tetramethylsilane. 11

This compound analyzed to be 2-methylphenylarsino-l ,1,1,4,4,4- hexafluorobut-2-ene. Found: C, 39.99, H, 2.89;; As, 22.63;

F, 34.73 %, Calc. for G1]LHgAsF6: C, 40.0; H, 2.73;; As, 22.70; F, 34.55 %. Infra red spectrum (first fraction) (liquid film): 3070 w, 2930 vw, 2280 vw, 1641 w, 1582: w, 1485 w, 1438 m, 1363 w, 1330 s, 1283 m, 1255 vs (slightly broad), 1143 vs (broad), 1077 w, 1069 vw, 1023 w, 998 w, 870 w, 850 m, 844 m, 737 s, 721 vw, 693 s, 641 s cm?1 The compound was heated at 140° (3 days). Proton mag• netic resonance revealed that no isomerization had taken place.

Section II: Reactions Involving 2-Chloro-3-dimethylarsinohexaf luorofout-2-ene (A) Thermal Stability

A sample of the compound was heated to 220° (3 days)• A mass of very dark brown solid was observed which appeared to be mostly carbon. Infra red. examination of the volatile mat• erial showed It to be mainly silicon tetrafluoride.

(B) With Aqueous Sodium Hydroxide

The adduct (1.229 g.) was hydrolyzed by excess 10% aqueous sodium hydroxide at 105° (3i hrs.). Trap-to-trap distillation of the products passing through a -78° bath (.118 g.) yielded fluoroform and a trace of hexafIuorobut-2-yne, of known infra red spectra, and a fraction having the following spectrum (vapour, 35 mm.): 6.0 w, broad 6.2 - 6.5 vw, 7.15 vw, 7.35 m, 7.6 vs, 7.9 vs, unresolved 8.3 - 8.9 va, 10.4 s, 11.1 m, 11.6 a, broad 13.2 - 14.3 w^<. The molecular weight of the material passing through the -78° bath was determined twice. The values were 130 and 133. Chloride ion wars found in the aqueous re- 12 malnder, but only traces of fluoride ion could be detected.

1. One Mole Bromine Bromine (.5 g.) and 2-chloro-3-dimethylarsinohexafluoro• but- 2-ene (1.0 g.) In carbon tetrachloride (5 cc.) were reac• ted at room temperature. The bromine was taken up immediately; after three days some flocculent needle-like crystals were observed. The solvent was pumped off, leaving a mass of cream coloured crystals. After a month it was observed that these crystals had liquified;; a second preparation liquified after four days In warm weather. The solid is permanently liquified at 100°. These crystals gave the-following infra red spectrum (KBr pellet): 3040 vw, 2930 vw, 2920 vw, 2330 w,, 1692 vw, 1606 m, 1555 vw, 1538 vw, 1516 vw, 1505 vw, broad 1418 - 1395 w, 1244 vs, 1199 s, 1172 vs., 1140 va, 1000 w, 917 m, 885 w, 875 w, 810 vw, 796 vw, 705 m, 688 vw, 673 m,, 667 w cmT1 The liquid decomposition product analyzed to be 2"-chloro- 3-bromome thy larsinohexaf luorobut- 2-ene. Found.: C, 16.38; H,,0.87; As, 20.35.;: Br, 21.64; Cl, 9.84;; F, 30.91 %. Calc for CgHgAsBrClFg? C, 1.6.3; E, 0.8;; As, 20.2; Br, 21.8;. Cl, 9.66; F, 31.0 %, Infra red spectrum (liquid film): 3.4 vw, 6.25 m, 7.1 vw, 8.1 vs, 8.35 s, 8.6 vs, 10.0 w, 11.35 m, 11.6 w, 12.3 vw, 12.4 vw, 14.2 ny*. Vapour phase chromatography showed that the liquid was one substance; it distilled at 106-115° (70 mm.). The proton magnetic resonance spectrum showed a dist• orted quartet centred at f = 7.95, J ~ 1.5 c.p.s. Two small peaks occurred at T = 7.54 and 2.47. 13 lg The F magnetic resonance spectrum consisted of two quartets (J = 15 c.p.s.) centred at -954 and -1400 c.p.s. rel• ative to external trifluoroacetic acid. Between these lay two much weaker absorptions, the high field one being a quartet (J = 15 c.p.s.) and. the other a distorted quartet. Between and close to these lay two even weaker absorptions,, which under high resolution were observed to be a quartet (.J# 1.4 c.p.s.) and a broad multiplet (low field). Each of these three pairs consis ted.of. approximately equal absorptions. The solid. (.3808 g.,, .824 mmole.) was. heated (li hrs.) in a sealed tube at 100°, after which the material was taken into the vacuum system. The fraction passing through a -78° bath was shown by infra red examination to be methyl bromide (.082 g.,, .863 mmole.). This was confirmed by the molecular weight. Found: 93j, CH^Br requires 95. 2. Two Moles Bromine Bromine (1.5 g.) was reacted with 2-chloro-3-dimethyl- arsinohexafluorobut—2-ene (1.4 g.) in carbon tetrachloride (5 cc.). A light coloured solid was produced immediately but the bromine was not completely taken up. Within four days the solid disappeared, leaving a reddish amber solution, which became very pale yellow in two more days. Most of the mater• ial went into the vacuum system; trap-to-trap distillation yielded methyl bromide (.64 g., 73 %), carbon tetrachloride, and a fraction (-23° bath) having the following infra red spectrum (liquid film): 3.4 vw, 4.25 vw, 6.3 a, 7.15 w, 7.4 vw,, 8.1 vs,, 8.6 vs, 9.3 m, 10.05 m, 10.3 vw, 11.2 vw, 11.4 m, 11.7 w, 12.0 w/, 12.3 m, 13.0 vw, 13.2-m, 14.2 s, 14.35 m, 14

14.55 w, 14.7 w/^» Bromine (.5 g,) and 2-chloro-3-bramomethylarsinohexafluoro• but—2-ene (1.2: g.) in carbon tetrachloride (5 cc.) produced a dark red-brown solution at room temperature; after 18 hours the colour had lightened considerably. When the solution be• came colourless, the material was taken into the vacuum system. Trap-to-trap distillation again yielded methyl bromide (.24 g.» 80 %). The fraction stopping in a —23° bath was combined with the same fraction from the previous bromination and. distilled at 39 mm., yielding two fractions: 92-93° and 98-103°.

(D) With Chlorine.

Chlorine: (.9 g., 1.2.7 mmole.) was reacted with 2-chloro- 3-dime thy larsinohexaf luorobut- 2-ene (4.0 g., 13.2 mmole.) in carbon tetrachloride (3 cc). At room temperature the mixture was a very pale yellow liquid. It was allowed to stand for one week. The volatile materials were taken into the vacuum system, leaving a crystalline white solid. Only a negligible amount passed through a -78° bath; the carbon tetrachloride was dis• carded. The tube was filled with nitrogen and the solid then heated at 50° (1 nr.), which liquified all but a few crystals. The tube was again, heated at 5Q° (22£ hra.),, which liquified the remaining crystals. The volatile products contained no appreciable amount of methyl chloride. A separation was at• tained with a -96° bath, the majority passing through and having the following infra red spectrum (vapour, 72 mm.): 3.3 m, 7.35 w, 7.75 w, 7.9 m, 8.4 s, 8.6 a, broad 9.6 - 10.2 vw,

12.55 m*,; 13.45 s, 13.6 m, 14.0 sjm. The spectrum of the -96°

* Probably due to CC1A. 15 fraction, (vapour, 13 mm.):: 5.55 w, 7.05 w, broad 7.2 - 7.5 w, 7.65 m, 7.9 m,, 8.2 m, 8.6 s, 8.9 m, g.8m,, 12.55 a*^. The non-volatile fraction (liquid f Urn): 3.3 vw, 6.15 m, 7.1 w, 8.0 vs, 8.25 s, 8.55. vs., 9.9 nt, 10.7 m, 11.2 m, 12.25 vw,, 14.0 m, 14.75 w^j.

The non-volatile product was heated in vacuo in a sealed tube at 140° (3 days), and the volatile materials admitted to. the vacuum system, leaving only a very small amount of dark coloured solid. Trap-to-trap distillation yielded three frac• tions. The first, stopping in a —136° bath,, showed a molecular weight of 63 and had the following infra red spectrum (vapour, 74 mm.): 3020 m, 2400 vw, 1610 vw, 1590 w, broad 1490 - 143Q w, 1405 w, 1365 m, 1330 w, 1280 vsD, 1190 vaD, 1155 w, broad 1065 - 985 w, 925 w, 900 mb,. broad 865 - 825 w, 745 a, 735 m, 715 a cm!1 The second, passing through the -136° bath, showed a molecular weight of 91, and had the following spectrum (vapour,.67 mm.): 3020 m, 2510 vw, 2380 w, 2150 vw, 2100 vw, 1975 vw, broad 1860 - 1740 vw, 1610 m, 1580 w, 1400 m, 1360 m, 1285 vsbc, 1195 vsDC, 1150 m, 1110. w, lOOOw, 925 s„ 900 sb„ 840 m, 795 w, 745 m, 730 a, 69O m cmT1 The third fraction stopped in a -78° bath and gave this spectrum (vapour, 13 mm.): 3000w, 1680 vw, 1650 vw, 1600 m, 1345 vw, 1250 vs, 1190 vs, 1025 m, 920 a„ 840.m, 795 w, 725 s, 69Q; m cm?1

(E) Bromination of 2:.3-Bls(dimeth.ylarsino)hexafluorobut-2-ene

Bromine (7.15 g., 44.8 mmole.), carbon tetrachloride

a Probably due to CC14. D Probably due to CTgCsCCFg. c 4 mm. pressure. 16

(20 cc.) and 2,3-bis(dimethylars:mo)hexaf luorobut-2-ene (8.3 g., 22.3 mmole.) were mixed; upon thawing the mixture reacted im• mediately with the: production of some yellowish-white solid. All the bromine waa taken up immediately. The vessel was air lowed to stand (5 days);; no further change was seen.

The products were admitted to the vacuum system, but. a little of the liquid remained in the tube along with the solid. The liquid material was yellow (that in the vessel darkened after exposure to the air for a day). The solid was pale yel• low. Trap-to-trap distillation revealed hexafluorobut-2-yne and a little silicon tetrafluoride among the volatile products, of known infra red spectra. The molecular weight of the frac• tion stopping in a -136° bath, containing most of the butyne, was determined to be 114.. The low volatility fraction yielded the following infra red spectrum (liquid film.).;. 3.4 w, 3*5 w, 4*25 vw, 4*85 vw, 5.55 vw, 6.35 m, 7.1 w, 7.2 m, 8.1 vs, 8.6 vs, 10.35 w, 11.1 w, 11.8 w, 12.05 m, 12.6 w, 13.65 vw, 14.6 ny^ . This fraction was distilled at 35 mm., giving, four fractions: 54-62°, 73-83°, 86-90°, 103-109°. The last two had to be com• bined. The first and part of the second, were bromodimethyl- arsine, of known infra red spectrum. The liquid which did not go into the vacuum system gave the following infra red spectrum (liquid film): 3.4 v, 3.5 w, 4.25 w, 6.15 w, 6.35 m, 7.2 w, 8.1 vs, 8.6 vs, 10.3 w, 10.85 w, 11.8 w, 12.65 w, 13.1 w, 14.6 m^.

Section III: Reactions Involving Dimethylarsine

Synthesis of Dimetfrylarslne • •:_ Chlorodimethylarsine (35 cc) was reduced by zinc and 17 hydrochloric acid, in the presence of ethanolic mercuric chloride, in a nitrogen atmosphere, to dimethylarsine (16.4 g.).

(A) With Dichloromethylarsine

Dimethylarsine (5.5 g.,, 51.9 mmole.). and dichloromethyl• arsine (3.9 g.» 24.2 mmole.) were placed in a Carius tube with a double constriction. Upon warming to room temperature, the reaction produced considerable amounts of an orange-rust solid, and an intense blue-violet mirror on one small part of the tube. A considerable quantity of mobile liquid remained. After one hour, the solid was chocolate-rust colouredjafter four days, a definite chocolate colour. The volatile products were admitted to the vacuum system. A large amount of uncondensable material was present which showed a molecular weight of 2*2, indicating hydrogen. The solid (1.9 g.) was reacted with bromine (7.1 g.) in slight ex• cess in order to convert it to arsenic tribromide and methyl bromide. The arsenic tribromide weighed 6.9 g.; the excess bromine, 0*2 g.;; the recovered methyl bromide, 1.9 g. The methyl bromide and excess bromine were separated by a -96° bath. Chlorodimethylarsine, of known infra red spectrum, was detected in the volatile products of the original reaction; dimethylarsine itself was absent.

(B) With Trifluoroacetvl Chloride Dimethylarsine (.801 g.) and trifluoroacetyl chloride (1.143 g.) were sealed in a Carius tube. When the mixture reached room temperature, it consisted of one phase, a yellow liquid, indicating that reaction had occurred. The materials 18 were all taken into the vacuum system. Trap-to—trap distil• lation yielded hydrogen chloride (.15 g., 55 %), identified by the molecular weight (found: 37.7; HC1 requires 36.5); unreacted trifluoroacetyl chloride (.25 g.), of known infra red spectrum; and a fraction yielding the following spectrum (vap• our, 35 mm.): 2.85 w, 3.25 w, 3.4 m, 3.5 m, 5.55 s, 5.8 s, 7.1 m, 7.4 w, 7.5 m, 7.9 vs, 8.1 vs, 8.4 vs, 8.7 va, 9.0 vs,, 9.75 vw, 10.05 vw, 10.5 w, 11.0 vs, 11.7 m, 11.9 nyu. When this material was exposed to the atmosphere an instantaneous, reaction occurred, forming a brown solid and colourless liquid. This liquid yielded the following infra red spectrum (vapour, 22: mm.): 3060 w, 2990 w, 1810 s, 1420 w, 1360 m, 1340 m, 1270 s, 1240 s, 1190 vs, 1140 vs, 1110 vs, 995 w, 950 vw, 905 m, 830 sh, 825 m, 7g5 m, 770 vw, 725 ah, 720 m, 715 sh, 705 sh, 670 w cm"1 This reaction had been performed with a small excess of trifluoroacetyl chloride. It was repeated, on a larger scale, with a small excess of the arsine, using 4.362: g. trifluoro• acetyl chloride and 3.845 g. dimethylarsine. Upon thawing, the mixture again formed one phase, a yellow liquid; some effer• vescence was noted. As it approached room temperature, the liquid became hazy and dark amber coloured, A few needle- shaped crystals could be seen. After 24 hours the liquid was rust coloured, mobile and opaque. The products were admitted to the vacuum system. Un- condensable material was present, the molecular weight of which was found to be 31.3, suggesting carbon monoxide. This material was discarded through a -lg6° bath and the rest of 19 the volatile products were condensed into the vacuum system. Only a very small amount of material (solid) remained, in the tube. Trap-to-trap distillation yielded, along with traces of fluoroform, silicon, tetrafluoride and carbon dioxide, hy• drogen chloride (.66 g., 55 %), trifluoroacetyl chloride (.25 g.), and two unidentified fractions, one stopping in a -23° bath (1.32 g.), the other in a -46° bath (5.64 g.). The latter yielded the following infra red spectrum (vapour,, 23 mm.): 3.3w, 3.4 w., 3.5 vw, 5.55 s, 5.8 m, 7.05 w, 7.35 w, 7.5 m, 7.9 vs, 8.05 s, 8.4 vs, 8.6 vs., 8.85 va, g.O s, 10.05 w, 11.0 s, 11.55 w, 11.9 w, 12.0 w, 12.9 vw, 13.7 w, broad 14.0 - 14.3 vw, 14.9 w^y. This fraction was a clear yellow liquid which upon exposure to air became colourless with a brown, precipitate. The yellow liquid, was purified on the gas chromatograph, yielding three fractions. The first was very small and was trifluoroacetyl- dimethylarsine, of known infra red spectrum.. The third frac•

tion was much larger and was identified from its spectrum as: being chlorodlmethylarsine. The middle fraction was the lar• gest. Infra red spectrum, (vapour): broad 3.3 - 3.6 w, 5.55 vs, 5.7 w, 7.1 w, 7.35 m, 7.5. s, 7.9 s, 8.1 vs, 8.4 vs, 8.85 vs, g.05 s, 10.05 w, 11.1 m,, 11.5 w, 11.9 w„ 13.0 m, 14.8 m^. The colourless liquid formed by exposure to air was distilled at atmospheric pressure. Three fractions, were taken: 104— 114°, 115-118°, 122-126°. The fraction stopping in a -23° bath (1.32 g.) (m.p. 13-

14°) „ suspected of being cacodyl, was reacted with bromine (I.00 g.) (1:1 mole ratio) in a sealed tube with carbon tetra• chloride (2 c.c). The brWihe~was taken up immediately. " The 20 products, were not all identified,, but the presence of fluorine and oxygen was observed in the infra red spectra. Methyl brom• ide (.27 g.) was also obtained,

(C)With Trifluoroacetic Acid

Dimethylarsine (.783 g., 7.39 mmole.), and trifluoroacetic" acid (.847 g., 7.44 mmole.) were heated at 130° (29 hrs.). Some uncondensable gas was produced;; the remaining material was only very slightly volatile and yielded the following in• fra red spectrum (vapour, 3 mm.): broad 2.9 - 3.35 m, 3.4 m, 3.5 m, 4.3 w, 5.7 s, 6.0 s, 7.1 s, broad 7.8 - 8.1 s, broad 8.2 - 9.1 vs, 9.2 s, 9.4 s, 10.9 m, 11.1 m, 11.9 *m, 12.5 m, 13.85 m, 14.2 ny< • Some of this material (1.40 g.) was heated again at 130° for a further 40 hours. Examination of the prod• ucts revealed some decomposition (to fluorof orm). The mixture (1.33 g.) was then heated at 160° (67 hrs.), which resulted in. the formation of two liquid phases: the upper was clear and very pale yellow while the lower was colourless but slightly hazy. Neither was very volatile. No significant further reac• tion had occurred, other than the formation of more fluoroform, and carbon dioxdde. Two fractions were obtained by trap-to- trap distillation. Their spectra are as follows: stopping in a -23° bath (liquid film): broad 2.8, - 4.0 m, 3.5 w, 4.35 vw, 6.0 s, 7.05 m, 7.85 m, broad 8.3 - 8.55. vs, 8.75 vs, 9.4 m, broad 10.75 - 11.4 w, 12.0 m, 12.5 m, 13.85 ny*; stopping in a -46° bath (liquid film): broad 2.8 - 4.0 s, 6.0 m, 6.15 m, 7.15 w, 7.85 s, 8.5 vs, 8.75 vs, 9.05 s, 9.4 s, 11.95 m, 14.0 HLJA . It is believed that these liquid films picked up water from the atmosphere. 21

(D) With Trifluoroacetic Anhyoride

Dimethylarsine (1.831 g., 17.3 mmole.) and trifluoro• acetic anhydride (.4.158 g., 19.8 mmole.), after being mixed at. -I960, reacted instantly upon thawing, producing a clear yellow liquid. The reaction was noticeably exothermic. The volatile products were taken into the vacuum system (a slight amount of uncondensable material was observed); a considerable amount, however, remained in the tube. This involatile mater• ial had the following infra red spectrum (liquid film): 2.9 w, broad 3*25 - 3.5 w, 4.2 w, 4.6 vw, 5.0 vw, 5.7 m, 6.1 m, 7.1 w, 7.85 w, broad 8.0 - 9.1 s, 10.8 vw, 11.15 w, broad: 12.1 - 12.8 12.5 w, 13.8 w, 14.2; Wy«. Since trap-to-trap distillation did not effect a separation of the volatile products, they were distilled at atmospheric pressure. This procedure proved only partially satisfactory, since the temperature of the material distilling over rose steadily and at an essentially unchanging rate throughout. The upper limits of the boiling ranges of the three fractions taken were 100°, 115°, 160°.

(E.) With Methylmagnesium Bromide

This reaction, and the addition, to the product of perfluorocyclobutene, is discussed under the section dealing with the latter substance.

Section IV: Reactions Involving. Perfluorocyclobutene (A) With Dimethylarsinomagnesium. Bromide

Synthesis of Dimethylarsinomagnesium Bromide , Dimethylarsine (4.3 g.) and methyl magnesium bromide solution* (13 cc), diluted with ethyl ether (10 cc), were * One mole solute in 316 cc solution (solvent: ethyl ether). 22 put Into a large Carius tube via a side constriction which had been fitted onto the side of the tube. This vessel had also been equipped with a double constriction at the top, the outer one of which had been previously sealed off. As the mixture thawed, effervescence was observed. The tube was allowed to stand for three days, after which time a yellow-gray precip• itate had formed.

Reaction of the Bromide with the Butene

The tube was opened to the vacuum system and the uncon— densable material was pumped off without removing the vessel from the liquid nitrogen. Perfluorocyclobutene (11.7 g.) was then added and the tube sealed off. When the mixture had thawed, two liquid phases were noted, the ether being the upper layer.

After standing (20min.), the solid became brown coloured and the tube became slightly warm to the touch. After a further ten minutes the lower phase had become an extremely viscous paste, whereupon the vessel was placed on the shaker (17 hrs.).

Trap-to-trap distillation yielded a low-volatility product

(3.8 g.) plus a very volatile fraction (23.9 g.) containing the ether and excess perfluorocyclobutene. The product, di• me thy lperfluorocyclobut-l-enylarsine, boiled at 127-129° at atmospheric pressure, and yielded the following infra red spectrum (liquid film): 3.3 vw, 3*35 w, 3.45 vw, broad 4.1 -

4.8 vw, 6.0 a, 7.05 m, 7.2 s, 7.9 vs, 8.3 s,. 9.0 vs, 9.95 vw,

10.55 vs, 11.05m, 11.55 m, 12.25 s, 14.65 vw/*.

(B) With.Chlorodimethylarsine

1. Irradiation

Perfluorocyclobutene (10.0 g.) was combined, with chloro- 23

dimethylarsine (4.0 g.) yielding one liquid phase and a little flocculent snow-white precipitate. Ultra violet Irradiation on the shaker (2 days) resulted in an amber liquid and dark brown precipitate. Trap-to-trap distillation yielded perfluoro• cyclobutene (7.7 g.) and a fraction (4.4 g.) stopping in a -78° bath. The infra red spectrum of this fraction was that of un• changed chlorodimethylarsine—no trace of the very strongly absorbing C-F stretching could be detected. 2. Heat Perfluorocyclobutene (7.7 g.) and chlorodimethylarsine (4.4 g.) were heated at 105° (5 days) in the presence of a little aluminum chloride (sublimed into the vessel). After two. days, some crystalline, waxy, caramel-coloured solid could be seen;; after the five days, a considerable amount of amor• phous brown-black solid had formed. Trap-to-trap distillation afforded perfluorocyclobutene (7.6 g.) and a fraction (3.2 g.) whose infra red spectrum indicated that no significant reaction had taken place.. 24

RESULTS. AND DISCUSSION

Section I; Reactions Involving Hexafluorobut-2-yne (A) With Chloroaraines 1 1

Chloroarsines undergo addition reactions with acetylenes, \ • • • 5 the best known of which Is the formation, of Lewisite : AlClo

AsC1

1. Chlorodime thy larsine In the present investigation hexaf luorobut-2-yne was reacted with chlorodimethylarsine under ultra violet irrad• iation, and also at 140° in the dark. These will be discussed separately. (a) Irradiation yields 2-chloro-3-dimethylarsinohexa- fluorobut-2-ene:

(CHgJgAsCl + CF3CSCCE3 (CHg)2AsC(CF3)=CClCF3 (2)

The isomeric distribution of this adduct was studied using nuclear magnetic resonance. The l9F spectrum shows two main bands between two considerably smaller ($5% of total area) quartets (J = 15 c.p.s.). The main bands split under high resolution into a quartet (high field) and a multiplet (nine peaks), J being 1.4 c.p.s. in both cases. The coupling constant of 15 c.p.s. is assigned to the cis isomer; that of 1.4 c.p.s., to the trans . Both cis and trans CFg-CFg coupling should yield quartets; the greater multiplicity observed in the low field band of the trans isomer is believed due to coupling

through space of the CF3 group gem to the methyl groups, with the methyl hydrogens. This same effect should occur in the 25

case of the cis form, and in fact the peaks of the low field cis quartet are broadened, with each peak being split into an approximate sextet. The "^H spectrum shows the methyl peak as a distorted quartet. Since compounds of the type (CHgJgAsRf normally 7 - ' show an unsplit methyl peak , the splitting in this instance

is believed due to CHQ-CFQ through space coupling. The tvro smaller peaks in this spectrum are ascribed to impurity. (b) It is known thataluminum chloride catalyzes the formation of ^-cnlorovlnyldichloroarsine (Lewisite) from arsenic trichloride and acetylene, as do some other Friedel-Craft salts such as mercuric chloride^ and it was thought that aluminum chloride would catalyze reaction between chlorodimethylarsine and hexaf luorobut-2-yne:

A „ _ +

(CHgJgAsCl + AlClg A1C14 + (GHgigAs (3)

CF3C=CCF3 + (CHgJgAs* —> GFg-Cs ^C-CFg —> CFg-C^C-CFg (4)

CH^CH, ^CH3)2AS +

AlCl" + CF3-C=C-CF3 (CH3)2AsC(CF3)=GClCF3 + AlClg (5) (CHg^s +

Steric considerations would appear to favour the trans con• figuration. The expected product, 2-chloro-3-dimethylar&inohexa- fluorobut-2-ene, is indeed formed, but it is accompanied by the formation of 3-dimethylarsinoheptafluorobut-2-ene. A third product is observed in the least volatile portion of the reaction mixture; this compound gives an infra red spect• rum very similar to that of 2-chloro-3-dimethylarsinohexa- 26 fluorobut-2-ene, the differences occurring in the C=C and C-Cl stretching regions. The shift of the C=C frequency to higher energy may Indicate an increase in the electronegativ• ity of ethylenic substituents. A suggested structure is

(CKg) gA.sC(CFg) =CFCF2C1. It is believed that the carbonium ion arrived at In the previous mechanism may experience a 1,2—shift before abstracting a chloride ion:

(CH3)2AsC(CF3)=CCF3 > (0EQ)2ks0(CFQ)^CFCJ2 (6)

(CHg)2 As C(CT3) = CFCF2 + AlCl^ > (CHQ) gAsC (.GFg.) =CFCT2C1 + AlClg

In conjunction with the above investigation, chlorodimeth• ylarsine and hexafluorobut-2-yne were heated (on a much larger scale) in the absence of aluminum chloride. The reaction pro• ceeds smoothly and again the product is (CHgigAsCCCFg^CClCFg predominantly. The failure of 3-dimethylarsinoheptafluorobut- 2-ene to form in appreciable quantity suggests that its; form• ation depends upon the aluminum chloride, perhaps involving AlCIgF. Aluminum chloride is known to bring about the follow- 8 ing fluorine replacement reaction :

ASCI3 * CT2=CT2 A1Gls> cy-or^g CM

The same very low volatility product formed in the pres• ence of aluminum chloride is observed in the absence of the salt. This substance is believed to be l-chloro-3-dimethylarsinohexaf luorobut-2-ene. The volatile products on examination by vapour phase chromatography showed three major components. The first was a fluorocarbon, containing hydrogen and a double, bond. The second and third yielded nearly identical infra red spectra 27 and were thought to be the two^ geometrical isomers of 2-chloro— 3-dimethylarsinohexaf luorobut—2-ene, but analysis shows only that the third fraction is this adduct. The analysis of the middle fraction, is exceedingly difficult to interpret;, all attempts to correlate the figures to a molecule of reasonable structure have failed.

It is of interest that chlorodimethylarsine and hexafluorobut-2-yne do react smoothly on heating without the aid of a Frledel-Craft catalyst. It is believed that the reaction is initiated by the auto'-ionization of the arsine:

2 (GH3)2&sCl : " (CHgJ^sClg + (CHg)-^* (g)

The reaction then proceeds as indicated in the previous mech• anism, with the (CHgJgA-sClg ion functioning in the same way as AlCl^. The ease of reaction in. the absence of aluminum chloride suggests that the auto-ionization is quite pronounced.

2. Other Chloroarsines Hexafluorobut-2-yne does not react with arsenic trichlor• ide, dlchloromethylarsine, chlorodiphenylarsine, or chloro• methylphenylarsine*, under the conditions of heating and/or Irradiation selected. In view of the ready reaction of the butyne with chlorodimethylarsine, on both heating and irrad• iation, it Is clear that the addition of As-Cl across the triple bond is very dependent upon the electronegativity of the substituents on the arsenic atom. Although steric hindrance may play a part in, the case of the aromatic arsines, it certainly is not a factor with the other two. The butyne, whether in

* Partial, reaction with this arsine, see experimental. 28 the ground or excited state, will show only limited availa• bility of the acetylenic electrons, because of the trifluoro• methyl groups. As mentioned earlier, arsenic trichloride does., react with acetylene itself.., Thus this addition reaction is; dependent, upon electron availability * both acetylenic and ars• enic lone pair electrons being pertinent. On going from dlehloromethylarsine to chlorodiphenylarsine, the lone pair availability should be appreciably increased. However in this molecule, steric hindrance could be quite pronounced. Another factor may be delocalization of the lone pair into the aromatic systems:

"As < > etc. (10) Cl Cl It is believed that this effect is small, because of the known reluctance of the arsenic atom to form a double bond. * Substitution of a phenyl group by a methyl both increases. the lone pair availability and decreases the steric hindrance and any lone pair delocalization. These effects are in fact sufficient to allow the molecule to react very slowly with the butyne. This same very slow reaction shows that substitution of a methyl group in chlorodimethylarsine by a phenyl greatly inhibits reaction.

(B) With Secondary Arsines

1. BisCtrif luoramethyl)arsine Hexafluorobut-2-yne and bis(trifluoromethyl)arsine on , heating react with difficulty as follows:

(CFgJ^sH + CF3C=CCF3, -^-» (CjTg)2AsC-(GF3)=CHCF-g (II) 29

At room temperature the reaction (CHgigAsH + GTgCsCCEg —(GHgigAsCtCTg^CHCFg (12) proceeds instantaneously, producing mainly the trans isomer0'. The much smaller tendency of the perfluoro analogue to react with the butyne suggests that the reaction me. chanism involves the arsenic lone pair,, these electrons being less available when electronegative substituents are placed on the arsenic atom. The proton magnetic resonance spectrum, reveals the pres• ence of only one isomer (i.e. only one quartet) and that this isomer is trans (each peak is split into a further quartet)• However since the reaction mixture reached 210° it cannot be stated that the cis isomer does not form at 130°. The peak at T= 2*67 is believed due to impurity.. It is suggested that the addition of secondary arsines to hexafluorobut-2-yne proceeds via attack of the arsenic lone pair on an acetylenic carbon atom, resulting in the fol• lowing zwitterion intermediate:

3 ^ « 3

*2 If the proton then shifts to the negative carbon atom, the product is cis. If, however, this intermediate abstracts a proton from another arsine molecule, the product would be predominantly if not completely trans.

2. Methylphenylarsine Under ordinary conditions the reaction 30

CH3(CgH5)AsH + CFgCECCFg > CH3(CgH5)AsC(CF3)=CHCF3 (13) proceeds; smoothly, but slowly (i hour), which is convincing evidence that the addition of the arsenic hydrides, as well as the chlorides, to the triple bond depends upon the avail• ability of the arsenic lone pair. The substitution of one of the electron-donating methyl groups of dimethylarsine by a phenyl should cause an appreciable decrease in the availabil•

ity of the loneo pair. From electronegativity considerations alone, this effect should be small compared with the substitu• tion of both methyl groups by trifluoromethyIs. The observed results are indeed consistent with these statements. Again, the reactivity of the methylphenyl-arsine may be lowered by sterlc hindrance and resonance derealization of the lone pair.

The *H spectra of the product reveal the presence of both isomers: an 11:1 ratio of trans to cis. Thus if the proposed mechanism, in this case involving the intermediate

CF3-C^-CT3

^3: is correct, this reaction involves mainly intermolecular proton transfer rather than intramolecular, since the latter process would yield the cis isomer. The same argument may be submitted in the ease of dimethylarsine. In fact, since dimethylarsine and hexafluorobut^2-yne do not react in the gas phase0, , it would appear that the intermediate is short lived and dissociates; very quickly in the absence of an im- 31 mediate collision with a proton source, such as could be provided in the liquid phase. From this it would follow that the intramolecular proton transfer,, in this case at least, offers no* contribution. Therefore it is suggested that the roughly 9% cis-2-methylphenylarsino-l,l,l,4,4,4-hexaflucre*- but-2-ene which was obtained resulted not from intramolecular proton transfer but rather from attack from the sterically hindered cis direction.

Section IIg Reactions Involving 2-Chloro-3-dimeth.ylaraino- hexafluorobut—2-ene > (A) Thermal Stability

The compound Is completely decomposed after three days at 220°. The very dark brown solid which is produced appears to be mainly carbon, the volatiles being primarily silicon tetrafluoride•

(B) With Aqueous Sodium Hydroxide

It was expected that hydrolysis of (CHgJgAaCCCFgXJClCFg would cleave the arsenic-fluorocarbon bond, and that the vol•

atile product would be 2-chloro-l,l,l,4,t4,4-hexafluprobut^2-ene. The infra red spectrum of the volatile material is highly suggestive of the expected chloro-olef in, in particular a presumed G=G stretching absorption (6.0^), ana three peaks at 10.4, 11.15 and 11.65^. The latter peak also occurs in the spectrum of the unbydrolyzed adduct and is believed due to C-Cl stretch-. The production of hexafluorobut-2-yne is not unexpected, since the chloro-olefin could be expected to lose a molecule 32

of hydrogen chloride in the highly basic environment. The butyne being present In only trace amounts is understandable, since it has been found by separate experiment that the comp• ound Itself undergoes hydrolysis to fluoroform under these conditions.. The low yield of volatile material (100% chloro- olefin = .806 g.) is probably due to continued hydrolysis, leading to carbonate and trifluoroacetate ions, in addition to chloride. Carbonate formation would entail production of fluoroform, which is in fact observed.

CO With Bromine

1. One Mole Bromine The adduct readily reacts with one mole of bromine. Infra red examination of the solid product revealed the cont• inued presence of a double bond, indicating that the arsenic atom had been oxidized to the pentavalent state:

(CH3)^sC(CF3) ^(CHg)2AsBr'^C(CF3)=CClCF3 (14)

This is not surprising in view of the three electronegative groups attached to the two ethylenic carbons. The ff electrons linking these two atoms should be considerably less available for the formation of new bonds, than those in a normal double bond. It seems likely also that there would be an appreciable steric barrier to bromination of the double bond.

This solid product slowly liquifies on standing at 20°, yielding methyl bromide and the bromomethylarsino compound:

^(CH3)2AsBr^C(CF3)=CClCF3 —» (.CHgAsBr)C(CF3)=CClCFg + CHgBr 05)

The same reaction occurs much faster at 100°.

19 The F spectrum of (CHqAsBr)CL(CF3)=CClCF3 shows two large 33 quartets (J = 15 c.p.s.) J a much, weaker quartet (J =15 c.p.s.) and distorted quartet (low field) between thesej and a quartet (J £ 1.4 c.p.s.) and broad multiplet (low field) between and close to these, the latter pair being considerably weaker still. Since a splitting of 15 c.p.s. is associated with the cis form , it is seen that this isomer is predominant. The inter• mediate absorptions are believed due to impurity, probably cIs-2-chloro-3-dibromoarsinohexafluorobut-2-ene. The weak bands represent the trans bromomethylarsino compound, which is present to the extent of less, than 5%. As would be expected from consideration of the spectrum of the . dimethylarsino adduct, the large low field quartet is broadened, as in fact are all the low field bands. Again, this down field broadening is ascribed to CFg-GHg coupling. It is seen that bromination of the predominantly trans dimethylarsino adduct yields mainly the cis bromomethylarsino compound. This isomerization is not yet understood; it appears., however, that the same phenomenon occurs upon bromination of 2-dimethylarsino-l,l,l,4,4,4-hexafluorobut-2-ene10. The H spectrum shows the methyl peak as a distorted triplet. As in the case of the dimethylarsino compound, this splitting is believed due to CHg-CEg coupling through space. Two smaller peaks also appear in this spectrum, but again they are likely due to impurity. 2. Two Moles Bromine On reaction of the adduct with two moles of bromine, one mole is taken up quickly, but the second reacts much more slowly. Two possible routes are: 34

JBr«AsCCGP«)=CClGFo + 2 CH^Br (16) CCHo)JlsC-((JPo)=CClC5Po + 2 Br,.—/1 ^ . ,d 05 d d ^ d d CHgAsBr Cl CFg^C-i-CFg + CHgBr (17) Br Br Infra red examination of theproducts, and the yield of methyl bromide, indicate that (16) occurs. Thus the double bond in this adduct Is inert to bromine under ordinary conditions. The reaction which does, occur probably goes through the fol• lowing stages:

(CHQ)2AsC(CT3)=CClCF3 * Brg ^GH3)^aBr^C(C5F3)«CClCSF^J (18)

slow ^OT3)2AsBr2^C(CIF3)=CClCF^ > (CHgAsBr)C(CF3)=CC1CF3 + CHgBr Q9)

Slow (CHgAsBr)C(CF3)=CClCF3 + Br2 > Br^sC(CFg)=CClCF3 + CHgBr (20)

Further evidence is offered by the following reaction: 2-chloro—3-bromQmetbylarsinohexafluorobut-2-ene plus one mole bromine generate methyl bromide and probably 2-chloro-3-dibromoarsinohexafluorobut-2-ene, the latter being also produced by the reaction of the dimethylarsino adduct directly with two moles of bromine:

CCHJLsBrOC(GFQ)=CClGF« + Br0 d d + . . V^Br9AsCCGF„)=CClGFo (2) CHqBr (21)

(CH3)2AsC(CF3)=CClCF3 +. 2Br2 • Unexpectedly the bromine is not taken up immediately but rather very slowly. Thus the pentavalent species. (CHgAsEr^Cp^^JGlCEg is not readily achieved, if at all (arsenic tribromide will ,not take up bromine). Another possibility is that the bromine cleaves off the methyl group to give methyl bromide and the dibromoarsino compound. The C-H. stretching absorption in the distillate of the low volatility material* is believed due to •Obtained by combining the low volatility products from the bromination of the bromomethylarsino compound, and the bromination (2 moles) of the dimethylarsino adduct. 35 dibromamethylarsine, which would, mean that the arsenic-olefin bond is cleaved by the bromine to a certain extent,

(D) With Chlorine

The dimethylarsino adduct and chlorine react to produce

a white solid, which was thought to be jjCH3)^sCl^C(CF3)=CClCF3, and which might have been expected to decompose on heating in the following manner:

jjCH3)2As(lQc.(CF3)=CClCF3 (CHgAsCl)C(CF3) =CC1CF3 + CHgCl (22)

However, although heating produces a liquid (non-volatile) that does not solidify, it does not result in any significant amount of methyl chloride. This liquid on heating to 140° again gives no methyl chloride. The resulting liquid, however, does go into the vacuum system. Infra red examination, of the two liquids shows that they are similar but not identical, and are both olef inic

(E) Br ominat ion of 2,3-Bis (dime thy lars ino) hexaf luorobut-2-ene

In conjunction with the halogenation of {CH^AsCCCFg^CClCFg, it was of interest to react the bls(dimethylarsino) compound with two moles of bromine, in particular to determine whether the double bond would again resist bromination and whether the products would be methyl bromide and 2,3-bis(bromomethylarsino)- hexafluorobut-2-ene. The infra red spectrum of the very low volatility material shows an absorption at 6.35^, assigned to the double bond of the bis(bromomethylarsino) species, and a weaker absorption at 6.15^ , believed due to. the bis(dibromoarsino) compound. The very volatile material consisted of methyl bromide, hexafluorobut-2-yne and—traces of silicon 36 tetrafluoride. Brcmodimethylarsine is also a product. The most startling result of this reaction is the form• ation of hexafluorobut-2-yne. The immediate uptake of the bromine indicates that the initial product is the wholly pentavalent arsenical, which is expected, but the production of hexafluorobut-2-yne and brcmiodimethylarsine means that the arsenic-olefin bond breaks upon decomposition of the inter• mediate, as well as arsenic-methyl bonds. It is significant that the decomposition yields the butyne rather than 2,3-dibromo- hexafluorobut-2-ene or 2-bromo-3-bromomethylarsinohexafluorobut- 2-ene. If the decomposition of the pentavalent compound occurs via a radical mechanism, then it is quite likely that the un• paired electron at the olefinic carbon atom becomes delocalized into the double bond, thereby causing elimination of the arsenic atom (with unpaired electron) from the other unsaturated carbon. This would give a triple bond. This scheme entails the release of bromine, which would then immediately be taken up in either of two ways:

Br2 + (CHgJgAsBr —» QcHgJgAsBrg —> CHgAsBr2 + CHgBr (23)

, 2 Br2 + (CHgAsBr)C(Ci g)=C(CF3) (CHgAsBr) >

jjt CHgAsBrg) C( CFg) =C (CFg) (CHgAsBrg)j >

Br2AsC(CFg)=C(CFg)AsBr2+ 2CHgBr or CEgC^CCFg + 2CHgAsBr^ + Br2 (24)

No attempt was made to separate the hexafluorobut-2-yne and methyl bromide for weighing purposes, since their boiling points differ by only 25°. The value of 114 found for the apparent molecular weight of the mixture indicates a very nearly 1:2 mole ratio respectively, the calculated value for 37

this ratio being 117.

Section III; Reactions Involving Dimethylarsine (A) With Dichloromethylarsine

Dimethylarsine is known to react with chlorodimethyl- .11 arsine :

(CHgJgAsGl .+ RAs;(CH3)2 > (CHgi^a-AstCHg^ + HC1 (25)

It was predicted that dimethylarsine would react with dichloromethylarsine, and it was of particular interest to determine whether the triarsine (IV) is formed:

HG1 + HAs(CIJg)2 ^ C^gla^e^^^a (26)

GHgAsClg + RAs(CHg)2~~^~R^l~T7cH^^ (III) Reaction occurs at 20° giving a chocolate brown solid, plus chlorodimethylarsine and hydrogen chloride. Hydrogen is also generated but the reason for this is not fully understood. The appearance of the solid is similar to that of the polymer

(GHgAa)n (V). Reaction of the solid with excess bromine was used as a. means of analysis and the calculated values tabulated below clearly indicate that it is the polymer (CHgAs)^:

Reactant Wt. Br2 Wt. Product (g.) (1.9 g.) Used (g.) CHgBr ASBTg Ill 5.3 2.0 5.2 TV 7.1 3.0 6.0 V 6.75 2.0 6.65 found 6.9 1.9 6.9 The path for the reaction

n CHgAsCl2 + n (CHg)2AsH ^(CHgAs)n •+ n (CHgJgAsCl + nHGL (27)

may be represented schematically as follows: 38

(CHgAa)n + HC1« -HOI, HGL- (CHgJgAsH + CHgA-sClg^i^ (•C^)^As(CH3)Ca.^=±-(C!H3)^sGl + HAs(CHg)Cl

7 CCHgJgAsHp^^ /(GHg)2AsH; -HCl^^ j-HCl

(CHQ) ^s-AsCCTU-AsXCH.J„ (CH„)0As-As(CHQ)H d ^ d d ^ ^ (CHgJgAsCl; -HC1 6 Z • - 3

The first step in the reaction of dimethylarsine with dichloro- nrethy lars ine is probably the formation of chlorotrimethyldiarsine (III). Since (25) is an equilibrium reaction11, it follows that hydrogen chloride will cleave the arsenic-arsenic bond in (III),. even If only to a small extent. Moreover, in view of the high polarity of the H-Cl bond, the slight polarity of the As-As bond in (III) (due to the chlorine atom) should result in the cleavage products being mainly chlorodimethylarsine and chloro- methylarsine, rather than the starting materials. The latter compound would react with itself to produce the polymer (V) and hydrogen chloride, or with dimethylarsine or chlorodimeth• ylarsine. If with chlorodimethylarsine, then (III) would result.; if with dimethylarsine, the product would be trimethyldiarsine, which would react with chlorodimethylarsine to form the triarsine (IV). Of course (III) should react to a greater extent with dimethylarsine than with hydrogen chloride, the products being hydrogen chloride and (TV), but again this should be an equil• ibrium reaction, thus leading eventually to complete conversion to chlorodimethylarsine, hydrogen chloride and (V).

(B) With Trifluoroacetyl Chloride

It was predicted that dimethylarsine and trifluoroacetyl

V 39

cMori.de would react, with elimination of hydrogen chloride:

CFgCOCl + HAs(CRg)2 > CFgCOAs(CRg)2 + HCl (28)

The reaction is in fact much more complex, yielding chloro• dimethylarsine, hydrogen, chloride and two unidentified sub• stances. With slight excess acyl chloride, the infra red spectrum of the medium volatility material shows two absorp• tions in the double bond region, one of which (5.8^) corres• ponds with that of trif luoroacetyldimethylarsine. With slight excess arsine, a very similar spectrum is obtained, one dif• ference being that the, 5*55^ absorption is stronger than at 5.8^ „ Instead of weaker. The latter liquid contains in fact very little of the acetyl-arsine, consisting mainly of chloro• dimethylarsine and an unidentified substance. The low volatility product from the excess arsine exper• iment was believed to be cacodyl, because the products from the excess acyl chloride reaction react violently with air. Cac• odyl andbromine in 1:1 mole ratio simply yield two moles bromo- dimetbylarsine; bromination of this material however produces several products, Including methyl bromide andeither bromo- or chlorodimethylarsine. But since some of the product material contains fluorine, and the unbrominated material melts at 13- 12 14°, the latter is not cacodyl (f.p. -6°) It is clear that the reaction between dimethylarsine and trifluoroacetyl chloride is fairly complicated. Since the carbonyl carbon of the latter carries an appreciable pos• itive charge, It should, be vulnerable to nucleophilic attack such as could be produced by the highly available arsenic lone pair. Such attack could cause direct elimination of. chloride ion from the carbon atom, whereafter proton loss from the arsenic atom would yield the acetyl-arsine. Another mani• festation of s uch attack, might be the formation of the inter• mediate Cl:.

GE3-J"Z— *f(GB3y2 (YI) 0" H followed by intra- or intermolecular proton transfer to the oxygen atom. Since oxygen, is considerably more electroneg• ative than chlorine, this mechanism might compete favourably with chloride; elimination. The resulting alcohol should, however, react readily with the acyl chloride: Cl Q 0 Cl I H II I

CF3-(J-0H + C1-C-CF3 —» CFg-C-Q-C-CF3 +. HCl (29)

ka{CE2)2 As(CHo)0

(VII) D * The large fraction of unidentified product (medium volatility) gives a spectrum highly suggestive of the CFg-g-O-G^ group (in particular the peaks at 5.55, 7.35 and 7.5^< ); it seems, doubtful, however, that (VII) could pass through a -23° bath. The formation of carbon monoxide and fluorof orm may be due to decomposition of the alcohol, which probably would also yield chlorodimethylarsine. The arsenic lone pair might also attack the oxygen atom, of trifluoroacetyl chloride. This atom should be somewhat

electron deficient because of the Cl and CF3 groups. Moreover, since there is. essentially no polarity in the As-H bond, there should be no electrostatic driving force for these two groups to add across the carbonyl in a particular way. The resulting

"ether"', CF3-CHCl-0As(CH3)2, may be the low volatility product. 41

Trifluoroacetyl chloride might be expected to: cleave the G-As bond: Cl 0 0 Cl I % II .11 I CF3-CH-0As(CH3)2 + CFg-C-Cl —» CFg-C-O-CH-CFg + (CHgJgAsCl (30) (YIII) The ester (YIII) could be expected to behave as did the large unidentified fraction.as regards volatility and Infra red ab• sorption. Chlorodimethylarsine is in fact a major product, and its presence is an explanation for the absence of dimeth• ylarsine and the presence of trifluoroacetyl chloride in the products even though the former was in excess, since these two arsines react to form cacodyl. Yet another possibility is the reduction of the. acyl chloride by dimethylarsine to 2,2,2-.trifluoroethanol, followed by reaction, of this alcohol with another mole of. the chloride: 0 ' 0 CFg-C-Cl * CFgCHgOH —» CFg-C-OCHgCFg + HCl (31) (IX) The ester (IX) also could, be expected to behave as did the large unidentified, fraction; in fact, the intensity of the C-H absorption in the infra red spectrum makes (IX) more at• tractive than (YIII).

It was anticipated that dimethylarsine and trifluoroacetic acid, would react in this way:

CFgCOOH + HAs(CHg)2 ——-> CFgC0QAs(CH3)2 + Hg, (32) (X) The actual reaction path is exceedingly difficult to ascertain. The main reaction product (very low volatility) shows, a strong double bond absorption (presumably C=0) at 6.Cy/ • The "ester** CX) absorbs at 5.7^ . Addition of dimethylarsine across the carbonyl bond would, not result in a compound, with a double bond other than the aeetyl-arsine CTQGCAsCGHgig, which absorbs, at 5*8^ • This substance Is not produced.to any appreciable degree. Another possibility is the formation of the onium compound 0 H

+ CF3-G-a" As(GH3)2 (XX) H although this seems unlikely because the material was liquid. However, trifluoroacetic acid is a strong acid, and it is known that dimethylarsine is considerably more basic than other . 13 ' arsines

(D) With Trifluoroacetic Anhydride

Bimethylarsine reacts readily with trifluoroacetic an• hydride, but as was the case with t rifluoroacetic acid, the reaction is; not simple. It appears that the first step is as follows:

"(CH^gAsH + (CF3C0)20 > CFgCQA&CCHg)2 + CFgCOOH (33)

The remainder of the arsine reacts with the trifluoroacetic acid as well as remaining anhydride. This scheme is supported by the presence in the products both of trifluoroacetic acid and the same substance of very low volatility produced by the dimethylarsine-trifluoroacetic acid, reaction. The presence of unreacted anhydride is also observed, but the infra red spectra do not definitely-confirm the presence of the acetyl- arsine. This may be due to the failure to obtain a good sep• aration of the products.

(E) With Methylmagnesium Bromide

This reaction, and the addition, to the product of per• fluorocyclobutene, are discussed In the. section dealing..with the latter substance.

Section IV; Reactions Involving Perfluorocyclobutene (A) With Bimethylarsinomagnesium Bromide

Synthesis of Bimethvlarsinomagnesium Bromide This compound was-prepared from dimethylarsine and-methylmagnesium bromide: (CHgJgAsH + CHgMgBr > (CHgJgAsMgBr + CH^ (34)

Since it was to be used in. a reaction, and had to be kept out of contact with the atmosphere,, the effervescence during its synthesis and the presence of uncondensable material in the products (methane) was deemed sufficient evidence that dimethylarsinomagnesium bromide had formed. Reaction of the Bromide with the Butene Bimethylarsinomagnesium bromide and perfluorocyclobutene react to form dime thy lperfluorocyclobut-1-enylarsine:

(CHgigAsMgBr +. CF=CF-CF2-CF2 —> (CHg) gAsC^CF-CFg-GFg + MgBrF (35)

The considerable vulnerability of perfluorocyclobutene to nu• de ophilic attack—it is attacked by amines and mer cap tans14— suggests that the reaction occurs via attack of the arsenic lone pair onto an olefinic carbon atom. This should result

in immediate loss of fluoride ion from this atom, followed by elimination of MgBr* from the arsenic atom. OA

(B) With CMorodimethylarsine

1. Irradiation Perfluorocyclobutene andchlorodimethylarsine do not react on irradiating even though the mixture forma one liq• uid, phase, while the arsine reacts smoothly with hexafluoro>- but-2-yne in spite of the two being immiscible. This suggests that either the cyclobutene molecule is not excited at all by the radiation, or that the lifetime of the excited state is so s hort that the probability of it colliding with another molecule is very low. Since no trace of the strongly absor• bing C-F stretching bands is observed in the infra red spec• trum, the former circumstance is preferred, especially since the reactants are miscible. This complete lack of reaction would also appear to rule out failure of the diradical to react for some other reason, such as steric hindrance. 2. Heat No significant reaction occurs between chlorodimethyl• arsine and perfiuorocyclobutene, even in the presence of alum• inum chloride, whereas hexaf luorobut-2-yne combines readily with the arsine. It is believed that the reactive species is (CHgigAs*, the anions being AlCT^' or (CHgJgAsClg, or both. If this is so, then it remains to account for this cation reacting with the butyne but not the cyclobutene, even though one liquid, phase is achieved (only) in the latter instance. Steric hind• rance probably plays a small part, in that the cation cannot approach the unsaturated bond from all directions, as is the case with the acetylene. The main factor however appears to 45 be the much decreased vulnerability of the butene to electro- philic attack, as compared with the butyne, owing to. the pres<- ence of a fluorine atom on each of the unsaturated carbon atoms. This is substantiated by the known great reactivity of perfluorocyclobutene toward nucleophiles, as previously men• tioned. 46

BIBLIOGRAPHY

1. G. W.. RAIZISS and J. L. GAYRON. Organic arsenical compounds. The Chemical Catalog Co., Inc., New York. 1923. p. 54. 2. Ibid. p.55. 3. Ibid. p.41. 4.. E. J. CRAGOE, Jr.,, R. J. ANDRES, R. F. COLES, B. ELPERN, •'• J. F. MORGAN and C. S. HMXLTGN. J. Am.. Chem. Soc 69, 925 (1947). 5. S. J. GREEN and T. S. PRICE. J. Chem. Soc. 448 (1921). 6. P.. M. TREICHEL, E. PITCHER and F.. G. A. STONE... Inorg. Chem. 1, 511 (.1962). 7. W. R. CULLEN., D. S. DAWSON and G. E. STYAN. J. Organometal. Chem. In press. 8. A. B. BRUKER, T. G. SPIRIDONOVA and L. Z.. SOBOROYSKII. J. Gen. Chem. (U.S.S.R.) 2Q, 347 (1958). 9. W. R. CULLEN. Unpublished observations. 10. W. R. CULLEN, D.. S, DAWSON and G... E.. STYAN. Unpublished observations. 11. W. R. CULLEN.. Can. J. Chem. 41, 322 (1963). 12. G... W. RAIZISS and J. L. GAYRON.. Op. cit. p.63. 13. Ibid. p.46. 14. W. R. CULLEN and P. S. DHALTWAL. Unpublished observations.