Disulphides, Diselenides, and Ditellurides

Preparation.—Many examples of the incidental formation of disulphides have been discussed in preceding sections, but few of these have undergone development as potential preparative methods, since there is no shortage of routes to these compounds. However, routes to unsymmetrical disulphides in particular, and from a wider range of starting materials, continue to be developed. Recent papers are collected at the end of this section, with brief details of their contents, where continuing development of known methods is concerned. 

Aralkyl trimethylsilyl sulphides RSSiMej give disulphides with sulphenyl chlorides, and symmetrical diselenides are formed from the selenium analogues with Ij (PhSeSiMcj - PhSeSePh + MejSil). The formation of unsymmetrical disulphides from steroidal A -diene-S-thiones and 2-nitrobenzenesulphenyl chloride is in accordance with the concept of hard and soft acids and bases, the soft thione nucleophile reacting with the soft sulphenyl halide, but not with the hard sulphonyl chloride. The resulting A -trienyl 2-nitrophenyl disulphides participate in thiol-disulphide exchange (see next section). 

An interesting observation, that (Bu 4N)2[Fe4S4(SR)4] catalyses the oxidation of thiols to disulphides, emerges from a study of this cluster as an analogue of the active site of non-haem iron—sulphur proteins. The adduct formed between thioacetamide and /)-benzoquinone is capable of non-oxidative formation of disulphides from thiols this is a curious reaction, possibly with some relevance to processes in vivo that involve flavins, but further work is required to determine the correct structure of the effective oxidant. Another unusual conversion of a thiol into the corresponding disulphide involves an arenesulphonyl chloride as reagent, with a three fold excess of a thiol, in EtOH. Benzenesulphinate anions are converted into disulphides with Et0P(0)H2.  

Full details of the preparation of symmetrical diselenides from aldehydes, with NaBH4 and HjSe in the presence of an amine (see Vol. 5, p. 65), have now been published. Symmetrical o-aminophenyl ditellurides are formed from ortho-mercuriated azobenzenes with tellurium-(ii) or -(iv) salts.  

Additional Bibiiography G. A. Olah, M. Arvanaghi, and Y. D. Vankar, Synthesis, 1979, 721 [thiols + 

---

The important chalcogenides are the disulphide, diselenide and ditelluride, and their use in lubrication is described later. Other selenides and tellurides have also been identified and studied to a limited extent, but as a class these materials tend not to be stoichiometric. One group of relatively simple compounds is that of the molybdates. These are salts of ammonia or metals with molybdic acid H2M0O4. 

Fluorine is the most electronegative of all the elements, so that the bonds it forms with most other elements have considerable ionic character. With the exception of the alkali halides most crystalline fluorides have structures different from those of the other halides of the same metal. A number of difluorides and dioxides have the same crystal structure, whereas the corresponding dichlorides, dibromides, and diiodides have in many cases structures similar to those of disulphides, diselenides, and ditellurides. The extreme electronegativity of fluorine enables it to form much stronger hydrogen bonds than any other element, resulting in the abnormal properties of HF as compared with the other acids HX, the much... 

Preparation from Disulphides, Diselenides, and Ditellurides.—The use of disulphides as sulphenylating agents towards alkenes and carbanions continue to offer a distinctive alternative to the use of sulphenyl halides for the same purpose. Although reaction conditions are more severe, cleaner results are usually obtained. The special case of the conversion of disulphides into corresponding sulphides is covered in the later section on Reactions of Disulphides. 

Aliphatic Organosulphur Compounds and their Se and Te Analogues 17 Disulphides, Diselenides, and Ditellurides... 

Kirner reported the successful use of plasma spraying for niobium diselenide, niobium ditelluride, and a mixture of tungsten disulphide and silver, but the performances in high vacuum and high temperature were inferior to those obtained with molybdenum disulphide. There has been a great deal of Russian work on the... 

Insertion reactions are particularly unprofitable for disulphides and diazomethane, though under irradiation moderate yields may be obtained (RSSR + CH2N2 RSCHjSR 4- N2). Diselenides give quantitative yields under these conditions, and ditellurides are easily inserted, in a dark... 

Diaryl ditellurides, like diaryl disulphides and diselenides, undergo disproportionation into arene tellurolates and tellurinates by alkaline treatment. 

Aromatic disulphides and diselenides adopt a conformation in which the torsion angle between the C—S—S— and —S—S—C— planes lies between 70 and 90°. Related studies of aliphatic disulphides have also been undertaken. Comparisons of S, Se, and O analogues represented by ArXMe, (At = Ph or mem-substituted phenyl) and aryl diarylmethyl sulphides have been made, in terms of their conformational behaviour. Studies of diaryl ditellurides ArTeTeAr and phenyl tellurobenzoates PhCOTeR provide dipole-moment data consistent with a non-planar C conformation and planar Z conformation,... 

---