Thiols desulphurization

Desulphurization of thiols has been accomplished in high yield under phase-transfer conditions using tri-iron dodecacarbonyl (or dicobalt octacarbonyl). The mechanism proposed for the formation of the alkanes and the dialkyl sulphide byproducts involves a one electron transfer to the thiol from the initially formed quaternary ammonium hydridoiron polycarbonyl ion pair [14], Similar one electron transfers have been postulated for the key step in the cobalt carbonyl promoted reactions, which tend to give slightly higher yields of the alkanes (Table 11.18). 

Roberts had reported that the low reactivity of alkyl and/or phenyl substituted organosilanes in the reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols (vide supra)49. The general reaction mechanism (Scheme 11) shows that alkyl radicals abstract hydrogen atom from thiols and the resulting thiyl radicals abstract hydrogen from the silane. This procedure has been applied in dehalogenation, deoxygenation and desulphurization reactions. This approach has also been extended by the same... 

Initial rates and product distributions in thiophen hds and in reaction of possible intermediates over sulphided M0/AI2O3 and C0-M0/AI2O3 catalysts (521 K, < 1 atm) were also consistent with reaction via tetrahydro-thiophen according to Scheme 4 butane-1-thiol was not an intermediate. Relative initial rates were (i), 1 (ii), 5-10 (v), to butenes 20, and then to butane 0.1. Co promoted the desulphurization rate and, to a lesser extent, the olefin hydrogenation rate. Desulphurization [C-S scission, step (zY)] occurred on a site involving Co and Mo and hydrogenation on a Mo site. 

Decomposition of organic matter results in sulphide (and some thiol) generation through the action of desulphydrases. This process of desulphuration is analogous to ammonification in the N cycle. In the marine environment a major product is dimethylsul-... 

A convenient synthesis of sulphenyl chlorides has been developed in which a thiol is reacted with chlorocarbonylsulphenyl chloride and the resulting adduct desulphurized by triphenylphosphine. Further examples - have been enumerated in which olefins are stereospecifically synthesized by a two-fold extrusion process, one of which is the removal of sulphur by a phosphine, e.g. in the synthesis of bicyclobutylidene (25). 

Thiols and thioethers are the most commonly encountered sulphur derivatives which can be directly reduced to alkanes. For this purpose, Raney Ni has been traditionally used. An example of its use is the synthesis of let- and 7j5-eremophilanes from a tricyclic thiophene precursor (equation 29) However, more recently nickel complex reducing agents ( NiCRA ) have been profitably and effectively used for this purpose, as indicated by the reduction of dodecanethiol to dodecane (equation 30)". Similarly, nickelocene in the presence of LAH has been used to effect desulphurization of thiols . A combination of NaEtaBH and FeCl2 also achieves the thiol-to-alkane transformation quite satisfactorily The increasing utility of nickel boride has also been exploited for the transformation of sulphides to alkanes as indicated in equation 31. ... 

Desulphuration (desulphydration) of cysteine may play a role in thiol catabolism, but there is considerable confusion concerning the existence of a distinct cysteine desulphydrase. 

A particular example of overoxidation is the oxidative desulphurization of heteroaromatic thiols by hydrogen peroxide which may lead to the... 

Dehydrogenation and desulphurization of thiols, and related processes, are involved in reactions of simple alkanethiols with H and O atoms, and in... 

Alper and his co-workers have reported two new methods for the desulphurization of aliphatic, aromatic, and benzylic thiols. In one method thiols are treated with hexacarbonylmolybdenum, either in acetic acid or following pre-adsorption on silica/ An alternative and milder procedure uses anhydrous ferrous chloride and sodium triethylhydroborate in THF at -78 The 2-benzothiazolylthio-group, useful for stabilizing carbanions, is conveniently removed by electroreduction at a carbon electrode in a cathode cell (e.g. Scheme 4). ... 

The reactions of phosphines with disulphides have been studied extensively due to the importance of these reactions in organic syntheses. Under appropriate conditions tertiary phosphines can act as desulphurizing agents (producing R P=S and the thioether) or reduce disulphides to thiols. Hie reaction of disulphides with phosphines has also been used as the dehydration step in the syntheses of peptides and nucleotides. The subject has been reviewed by Mukaiyama and Takei. ... 

Oxidation and Reduction.— The electrochemical oxidation of benzothiazole-2-thiol to its disulphide has been further studied. This conversion may be accomplished with ozone in the presence of potassium iodide to prevent ozoniza-tion. > Desulphurization of benzothiazoles as a preparative procedure does not appear to have been exploited to the extent that it has in the field of thiophen chemistry. Noteworthy, however, is the desulphurization of sugars (17 e.g., n = 3, R = H) to l-deoxy-l-(iV-methylanilino)-alditals. ... 

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