Sulphides synthesis from halides

Preparation.—In addition to a number of reactions of thiols, discussed in the preceding section, a variety of other routes have been explored for the preparation of sulphides. U.v. irradiation of thiolesters gives mixtures (CHa CO SPh gives PhSH, PhSMe, o- and p-AcPhSH, and disulphides as major products), while addition of an alkyl halide to a thiolester in the presence of strong base (LiH, PhgCLi, etc.) provides a one-step route. A novel /3-keto-sulphide synthesis from a 1,2-diketone is illustrated by the conversion of (29) into (30). ° Alternative routes to jS-keto-sulphides often... 

On the other hand, much stronger evidence is available in favour of the earlier formula,4 which accords well with the relationship between the acid and the polythionic acids.5 The formation of sodium thiosulphate by Spring s synthesis from sodium sulphide and sodium sulphite (p. 194) is definitely favourable to this constitution, as also especially is the fact that an alkali thiosulphate will react with only an equimoleeular proportion of an organic (alkyl) halide,6 the product... 

A superior and relatively versatile procedure for the synthesis of unsymmetrical dialkyl thioethers, which avoids the unattractive direct use of thiols, utilizes the stable l-alkylthioethaniminium halides, which are readily obtained from thioacet-amidc [32] (Scheme 4.4). The reaction has also been used for the synthesis of alkyl aryl thioethers from activated aryl halides [33], but it cannot be used for the synthesis of cyclic thioethers, as polymeric sulphides are formed from a,co-dihaloalkanes. A similar sequence to that which leads to the thioethers has been used for the synthesis of S-alkyl thioesters [34] (see 4.1.26). 

Formation of a symmetrical sulphide (a) (e.g. dipropyl sulphide, Expt 5.204), is conveniently effected by boiling an alkyl halide (the source of carbocations) with sodium sulphide in ethanolic solution. Mixed sulphides (b) are prepared by alkylation of a thiolate salt (a mercaptide) with an alkyl halide (cf. Williamson s ether synthesis, Section 5.6.2, p. 583). In the case of an alkyl aryl sulphide (R-S Ar) where the aromatic ring contains activating nitro groups (see Section 6.5.3, p. 900), the aryl halide is used with the alkyl thiolate salt. The alternative alkylation of a substituted thiophenol is described in Section 8.3.4, p. 1160. The former procedure is illustrated by the preparation of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) from l-chloro-2,4-dinitrobenzene and 2-methylpropane-1-thiol. 

Conditions have been worked out for the synthesis of methyl polyfluoroalkyl sulphides and 2-bromo-l,l-difluoroethyI phenyl sulphide by halogen-substitution reactions involving sodium thiolates. / -Nitrothiophenol reacts with 1,2-dichlorohexafluorocyclopentene to give the l,2-bis(p-nitrophenylthio)-analogue. Aryl alkyl tellurides PhTeR and bis(phenyltelluro)methane PhTeCHgTePh can be obtained from PhTeLi and an alkyl halide, or di-iodomethane, respectively. 

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