Mercapto group, replacement with hydrogen

The action of aniline on 3-phenyl-5-mercapto-l,2,4-thiadiazole under restrained conditions is reported to remove the mercapto group as hydrogen sulfide, with formation of the corresponding 5-anilino compound.75,200 This replacement, normally difficult in aromatic systems, may be due to the unusual reactivity of the thiol grouping in this particular structural environment. 

In 2-mercaptobenzothiazole, energetic oxidation with hydrogen peroxide leads to the replacement of the mercapto group by hydrogen, probably via oxidation to sulfinic acid (equation 550) [1197]. 

If the hydroxy group of a 2-amino alcohol is replaced by a mercapto group (XCIX) the reaction with carbon disulfide yields thiazolidine-2-thiones (C) with liberation of hydrogen sulfide. This method though is practically never used since thiazolidine-2-thiones are more simply obtained from 2-halo amines (see further under Section IV.l) which are themselves starting materials for the 2-amine thiols. 

Thiamine anhydride (77) is a useful source of sulphur analogues of thiamine. Thus, it reacts with thioacetic acid to give the thiazolinethione (78), which on successive desulphurization by the action of hydrogen peroxide and treatment with barium chloride affords acetylthioethylthiamine (79) hydrolysis finally produces mercaptoethylthiamine (80), the sulphur analogue of thiamine. This is convertible into further derivatives, particularly by replacement of the mercapto-group of the 5-side-chain by amino-, sul-phenyl-, sulphinyl-, and sulphonyl-residues [e.g. (81), (82)]. ... 

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