Thioacids, oxidation

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... 

The anodic oxidation of a variety of organo-sulfur compounds containing the SH or S group, like thioacids, RCOSH [20], dithioacids, RCS2H [21], alkyl xanthates, ROCSJ [22], N, A-dialkyldithiocarbamates, R2NCSJ [23, 24], and l,l-dicyanoethylene-2,2-dithio-late, [(NC)2C = CS2] [25], has been examined using solid electrodes, and the formation of the following products with a disulfide bond was established. 

A strategy based on silver-ion mediated selective activation of a C-terminal thiolcarboxyl group initially reported by Blake [48] was modified by Aimoto et al., employing the more oxidation- and hydrolysis-resistant thioester in place of thioacid and HOBt or 3,4-dihydro-3-hydroxy-4-oxo-l,2,3-benzotriazine (HOOBt) as an additive to facilitate the formation of the activated ester (Scheme 8) [49,143]. This activated ester-based coupling requires the protection of side-chains of Lys... 

Gangwani, H., Sharma, P. K., and Banegi, K. K., Kinetics and Mechanism of the oxidation of some thioacids by hexamethytenetetramine-bromine, React Kinet CataL Lett., 69(2) 369-374 (2002). 

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. 

Sulfur exhibits a rich variety of oxoacids and thioacids. Sulfuric acid, prepared industrially on a massive scale by the contact process, is a strong dibasic acid. It is both an oxidizing and effective dehydrating agent, and forms sulfate and hydrogen sulfate salts. 

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