Dialkyl polysulfide

The higher dialkyl polysulfides, such TNPS, find use as extreme-pressure lube additives, especially for cutting oils the lower dialkyl polysulfides, such as (CH3)2S as sulfur-donor agents, for example, to convert phosphites to thiophosphates ... 

Cheese flavor. C. f. is formed from milk fat, milk protein, lactose during the maturation of cheese mainly through enzymatic and microbial processes. Quantitative and, sometimes, qualitative differences are responsible for the diversity of cheese flavors. Typical aroma substances are the free C4-C,2 fatty acids, C7, C and C, 2-alkanones (also in Roquefort cheese), the butter aroma substances acetoin, 2,3-butanedione, and 5- alkanolides, (-)-(R)-l-octen-3-ol (fungus note in Camembert), 4-alkanolides and alkylpyrazines with nut-like nuances, indole, skatole, and phenols with stable-like odors, as well as numerous sulfur compounds such as methional, methyl mercaptan (moldy, coal-like), dimethyl sulfide and dialkyl polysulfides with, in part, onion- and garlic-like nuances. Furaneol" and homofuraneol (see hydroxyfura-nones) are responsible for the sweetish odor of Em-mental cheese. 

The radical will initiate another homopol5mier chain by reaction with more monomer. Finally disproportionation occurs and the sulfur rank is reduced to 3-6 sulfur atoms per block unit. The average number of sulfiir atoms between polychloroprene chains or sulfur rank has been explored by NMR. The chemical shift of the methylene hydrogen atoms adjacent to the polythionyl linkages vary from 3.45 to 3.9 ppm (27). It is believed that the sulfur rank for a typical chloroprene-sulfur copoljmier contains a predominance of S3 to Se imits. The assignment is consistent with ease of reaction of dialkyl polysulfides (Sj >2) with the chemicals normally used in the peptization reactions that follow. 

Symmetrical disulfides (73) may be prepared by reaction of alkyl halides with disodium disulfide (Scheme 43). The product is contaminated with triand polysulfides owing to the presence of impurities in the disodium disulfide however, lower members of the series of dialkyl disulfides may be purified by fractional distillation. Disulfides can also be obtained from thiols by mild oxidation, e.g. by treatment with iodine or dimethyl sulfoxide (DMSO) (Scheme 44). In the reaction with iodine, the hydriodic acid formed must be removed, otherwise the disulfide is largely reduced back to the thiol by hydriodic acid which is a powerful reducing agent. Pure unsymmetrical disulfides are more difficult to prepare owing to their tendency to undergo disproportionation they can, however, be synthesised from thiols by treatment with imides (see p. 59) or sulfenyl halides (51) (Scheme 45). 

In dialkyl di- and polysulfides, sulfur is the negative end of the dipole. The moment of a di-n-alkyl disulfide is approximately 2.00 D and of a trisulfide approximately 1.65 D, irrespective of the length of the carbon chain. In a tetrasulfide the moment is again higher thus, the alternating values 1.47, 2.00, 1.63, and 2.16 D, respectively, were obtained by Wood-row et al. (230) for the di-n-hexadecyl mono- through tetrasulfide series. 

The ultraviolet spectra of polysulfides are difficult to interpret in terms of structure. However, as first pointed out by Koch (152), the fact that the various polysulfides all display characteristic absorption of the same spectral type, resembling the dialkyl disulfide spectrum displaced towards greater wave lengths and intensities, provides (in view of the known structure of disulfides) strong evidence in favor of unbranched structures also in polysulfidcs. 

Structure determinations by X-ray and electron diffraction methods have demonstrated the presence of unbranched chains of up to six divalent sulfur atoms in inorganic polysulfides, four divalent ones in salts of polythionic acids, and three in disulfonyl, dialkyl, and cyanogen derivatives. The synthetic and Raman-spectroscopic work of Feh6r has established the presence of unbranched structures with up to five sulfur atoms in organic polysulfides, and eight in the cyanogen polysulfide, polysulfur dichloride, and hydrogen polysulfide series. The results are supported by extensive physicochemical evidence of less conclusive nature. 

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