Thioacids, oxidative acylation

Fig. 7.9 Oxidative acylation of thioacids. The second reaction step is fast, the third slow (Liu and Orgel, 1997)...

While thiocarboxylic acids themselves are not effective acylating reagents in aqueous solution, the diacyldisulfides 26, that are formed when thioacids are oxidized, are extremely effective [151]. 

The alkyl halides (halogenoalkanes), thiols and amines are at the same oxidation level as the alcohols, while acyl halides, thioacids and amides are similarly related to the carboxylic acids. Like oxygen, sulfur can be inserted into a chain to generate the equivalent of an ether such as the thioether... 

Type C Syntheses [N—C—N—C—S]. From amidino-thiono-compounds. The general synthesis of 1,2,4-thiadiazoles by the oxidative cyclization of compounds incorporating the amidino-thiono-grouping [—C(=NH)NHCS—] has been extended by the synthesis of l-acyl(and -sulphonyl)-3-thioacyl-guanidines (41) from acyl- or sulphonyl-guanidines (40) with thioacid O-esters in the presence of sodium hydride, followed by their oxidation with hydrogen peroxide in pyridine. 

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