Vinylic disulphide

Thiocamphor, under similar conditions, furnishes a vinylic disulphide as the major product (70%), which slowly undergoes a hetero-Cope rearrangement. ... 

The photoinitiation of vinyl polymerization by organic compounds (carbonyl, azo, peroxide, disulphide compounds, etc.) or inorganic salts (e.g., metal halides and their ion pairs, etc.) will not be discussed here, since these type of photoinitiators are beyond the scope of the present chapter. 

This product is best obtained by heating dehydroquininc with about five times its weight of arsenic trichloride in an oil-bath at 130" to 135" for three hours, in the absence of a solvent. It may also be prepared by digesting the previous compound with aqueous ammonium carbonate. It darkens at 199° to 200° C., sinters at about 204° C., and melts at 207 to 209° C. it is easily soluble in alcohols and pyridine, very sparingly soluble in chloroform and acetone, and insoluble in ether, ethyl acetate, aromatic hydrocarbons, and carbon disulphide. Its salts arc not crystalline. The fact that it forms a benzoyl derivative shows the presence of a free hydroxyl group, and consequently the attachment of the arsenic to the vinyl group. 

Chemicals which can damage (a) the liver, include carbon tetrachloride, paracetamol, bromobenzene, isoniazid, vinyl chloride, ethionine, galactosamine, halothane, dimethylnitrosamine (b) the kidney, include hexachlorobutadiene, cadmium and mercuric salts, chloroform, ethylene glycol, aminoglycosides, phenacetin (c) the lung, include paraquat, ipomeanol, asbestos, monocrotaline, sulphur dioxide, ozone, naphthalene (d) the nervous system, include MPTP, hexane, organophosphorus compounds, 6-hydroxydopamine, isoniazid (e) the testes, include cadmium, cyclophosphamide, phthalates, ethanemethane sulphonate, 1,3-dinitrobenzene (f) the heart, include allylamine, adriamycin, cobalt, hydralazine, carbon disulphide (g) the blood, include nitrobenzene, aniline, phenylhydrazine, dapsone. 

The role of sulphur-containing compounds in photopolymerization appears to have attracted some interest. Bis(j -methylpyridazinyl)-3,3 -disulphide has been found to initiate the photopolymerization of styrene but inhibits the thermal polymerization. The role of thiyl radicals (PhS-) in photoinitiated polymerization of vinyl monomers by aromatic thio-compounds has been postulated by several workers. In one study, flash photolysis was used to identify the nature of the radical. Sulphur-containing monomers such as 4-methyl-2-(vinylthio)thiazole and thiocyclanes have been photopolymerized and copolymerized with other vinyl monomers. Luca et al. have devised a mathematical model for the photopolymerization of 2,3-dimethylbutadiene and thiourea. 

Recognition of the role of sulphoxides in the inhibition chain has resulted in several studies of the autoxidation of mono- and disulphides (see later). In addition to the work by Hargrave [84], Bateman et al. [88— 90] have studied the oxidation of monosulphides, unsaturated monosulphides and cyclo-hex-2-enyl methyl sulphide. Allylic and vinylic sulphides were found to be much more reactive than saturated sulphides, although the methylene group, rather than the allylic double bond, was suggested to be the primary reaction centre. Reactivities were compared for the percentage yield of sulphoxide (A) and for the yield of hydroperoxide (B), viz. 

Condensations of amines with 1-chlorocycloheptene in the presence of the complex base , sodamide and sodium t-butoxide, gave mixtures of enamines and cyclo-hepta-1,2-diene dimer. Excess n-butyl-lithium has been used to convert vinyl and aryl bromides into organolithium compounds which undergo useful reactions with, for example, benzophenone, dimethyl disulphide, diphenyl disulphide, trimethylsilyl chloride, and methyl iodide. Hence 1-bromo-cis-cyclononene was converted into 1-methylthio-cis-cyclononene via 1-lithio-cis-cyclononene the 1-methylthio... 

Tilak and co-workers have continued their investigations on the synthesis of 2-ethoxycarbonyl-3-hydroxythiophanes, through the base-catalysed condensation of methyl vinyl ketone, chalcones, ethyl 2-benzoyl-acrylate, and Mannich bases with ethyl thioglycollate. Dehydration of the thiophanes with polyphosphoric add followed by dehydrogenation using chloranil or diphenyl disulphide affords thiophens. 

Tetramethyldiphosphine adds photochemically to vinyl and vinylidene fluoride to give the bisphosphines Me2P-CH2-CXF-PMe2 (X H or F), and tetrakis(trifluoromethyl)diphosphine similarly adds thermally (at 50 Q or photochemically to the same olefins and to tetrafluoroethylene. Free-radical additions of trifluorothioacetic acid to the olefins CHF CF2, CHarCFa, and CH2 CHF (see p. 138) have been described only one-way addition was observed. Bis(trifluoromethyl) disulphide adds to fluoro-olefins with u.v. Irradiation in Pyrex or silica apparatus in the vapour phase to yield a variety of 1 1 and telomeric adducts. The products are consistent with the following mechanism ... 

Di-2- propenyl disulphide, Di-2-propenyl trisulphide, di-2-propenyl-tetrasulfide, 2- di-propenyl thiocyanate, 3//-l,2-dithiolene, 2-vinyl-4//-l,3-dithiin, 4//-l,2,3-trithiin, 5-methyl-l,2,3,4-tetrathiane and A(Af-di-2-propenyl thiourea as major compound... 

Benati L, Montevecchi PC, Spagnolo P. Free-radical reactions of benzenethiol and diphenyl disulphide with alkynes. Chemical reactivity of intermediate 2-(phenylthio) vinyl radicals. J. Chem. Soc., Perkin Trans 11991 2103-2109. 

Aliphatic thiols have been subjected to i.r., Raman, and microwave spectroscopic studies. Methyl and ethynyl groups are gauche in ethyl vinyl sulphide, as judged from microwave data. I.r./Raman studies of aliphatic sulphides and disulphides similarly include interpretation in terms of conformation or bonding. Comparative i.r./Raman studies of dimethyl sulphide, sulphoxide, and sulphone and the corresponding diphenyl series have been described. I.r. spectra of selenuranes and sulphones and sulphimides have been inter-... 

Electron Diffraction.— Bond-length and bond-angle data have become available for trifluoromethanethiol, phenyl vinyl sulphide, dimethyl disulphide, ethyl methyl disulphide, dimethyl sulphurdi-imide, and benzenesulphonyl chloride. ... 

Barton and his group have prepared the interesting new di-t-butyl thio-ketone (7) in high yield by reaction of carbon disulphide with the lithium salt of the corresponding ketone imine. Independently, Ohno and his co-workers have published an analogous synthesis of this non-enethiolizable thioketone (7). Aliphatic thiones and, possibly, enethiols have been obtained by reaction of arylimines with benzoic anhydride and a stream of hydrogen sulphide. Treatment of a vinyl chloride with sodium monosulphide led to the isolation of thio-dimedone (8 R = H), which has an enethiol ketone structure. Basic hydrolysis... 

The disulphide (75) and the dihydrothiophen (76) were produced in small (<1%) yield upon photolysis of O-ethyl thioacetate in 1,2-dimethylenecyclo-hexane. The probable pathway to (76) involved rearrangement of the intermediate vinyl episulphide (77). The disulphide (75) could arise from (76) by... 

Syntheses of vinyl sulphides based on alkynes include disulphide bond insertion (R2S2+CH=CH->RSCH=CHSR ) or thiol addition (e.g. prop-2-ynethiol+cyanoalkyne gives CH CCH2SCR==CHCN ). 

The seven-membered-ring disulphide (77) has been isolated from a species of Hawaiian alga " and the structure confirmed by the following synthesis the reaction of 2-nonenal with vinyl-lithium followed by oxidation with DDQ gave the undeca-l,4-dien-3-one, which readily added thiolacetic acid to each double bond. The dithiol ester thus produced was hydrolysed to the dithiol with methanol-HCl. Cyclization to (77) was effected with iodine in pyridine. A dimeric fourteen-membered-ring tetrasulphide was obtained as by-product. 

Vulcanisates which withstand oils and ozone can be produced with blends of NBR with about 30 % ethylene vinyl acetate rubber (vinyl acetate content > 40 %). Compared with NBR/PVC blends such blends have the advantage of being more resistant to ageing. Thiuram disulphide or peroxide can be used for crosslinking.The physical properties are inferior to those of all-NBR vulcanisates. Small additions of NBR to EVAC compounds improve the mould release and the peelability of electric wires. 

---