Thiols coupling with peroxides

Hydrogen peroxide used over a wide pH range has been employed to oxidize sulfur compounds. The scope of the oxidation using hydrogen peroxide includes coupling of thiols to disulfides355 and thiols coupled with amines,356 which are used to produce industrially important compounds. For example, sulfenamides are accelerators for rubber vulcanization (Figure 3.91).357... 

The efficient reductions observed for various organic halides when treated with Et3SiHin two-fold excess in the presence of catalytic amounts of a thiol and di-tert-butyl hyponitrite as initiator confirmed the validity of this approach. Silane-thiol couples were also used, in boiling octane with di-terf-butyl peroxide as initiator, for the reduction of the methylxanthate of 1,2 5,6-di- O -isopropylidene-a-D-glucofuranose, to yield the corresponding deoxy sugar in 60%173 and 70%174... 

The chemiluminescence-redox detector (CRD) is based on specific redox reactions coupled with chemiluminescence measurement. An attractive feature of this detector is that it responds to compounds such as ammonia, hydrogen sulfide, carbon disulfide, and sulfur dioxide. Hydrogen peroxide, hydrogen, carbon monoxide, sulfides, and thiols that are not sensitively detected by flame ionization detection can be detected with the CRD detector. Compounds that typically constitute a large portion of the matrix of many industrial samples are not detected, thus simplifying matrix effects and sample cleanup procedures for some applications. 

Early examples of such branched polysulphides, e.g. Thiokol FA, are believed to possess hydroxyl end groups and are coupled by means of zinc compounds such as the oxide, hydroxide, borate and stearate by a mechanism which is not understood. Later elastomers, e.g. Thiokol ST, have been modified by a restricted reductive cleavage (see below) and this generates thiol (mercaptan) end groups. These may be vulcanised by oxidative coupling as illustrated below with lead peroxide ... 

Gilbert and coworkers18 were able to detect ESR spectra of sulfinyl radicals together with other sulfur-centered radicals during the oxidation of disulfides and thiols with a titanium(III)-peroxide couple reaction mechanisms involving sulfenic acids as intermediates have been discussed. 

In a further exanple. Smith and Wan exploited the nucleophilic capability of l-phenyl-2-tetrazoline-5-thione in the Mitsunobu reaction, followed by oxidation to the sulfone with hydrogen peroxide and ammonium heptamolybdate tetrahydrate as a key step in a synthesis of the ansamycin antiobiotic, (+ )-thiazinotrienomycin-E (eq 8). Importantly, use of the phenyltetrazolylthione-derived sulfone gave an 13Z ratio of 10 1 in this coupling whereas the more conventional benzthiazole-2-thiol-derived system resulted in a selectivity of only 1.5 1 in favor of the -isomer. 

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