Acids ortho-mercaptobenzoic

Mercaptobenzoic acids (ortho, meta and para isomers) were prepared in fair to good yields from the reaction of the chlorobenzoic acids with elemental sulfur and molten NaOH-KOH (1 1 molar ratio) at 270 "C for 3 min. Both 2- and 4-chloropyridine gave the mercaptopyridines by an analogous procedure.198 Use of selenium instead of sulfur gave poor yields and mixtures of isomeric products. 

Thimerosal (Merthiolate) has been used as a topical antiseptic for many years. Its antimicrobial effect is mostly due to the toxicity of the mercury atom that is bound and stabilized by the thiol group of ortho-mercaptobenzoic acid. The carboxylate salt of the acid is used to enhance solubility of this organomercurial compound. 

More recently. Miller and coworkers reported that ortho-mercaptobenzoic acid and ortho-mercaptophenols 159 could be used as efficient thiol catalysts in both the intramolecular MBH and Rauhut-Currier reaction and they also demonstrated that chiral mercaptophenol afforded the reaction with low to moderate enantiose-lectivities (Scheme 31.53) [64]. Under estabhshed conditions, chiral catalysts (S)-and (R)-160 afforded high yields and moderate asymmetric inductions in the MBH reactions. The obtained enantioselectivities remained largely unaffected by the amount of water and base added, catalyst loading, and substrate concentration but were markedly influenced by the reaction temperature. Interestingly, both increasing and decreasing the temperature from the established value of 70 °C resulted in lower ee values. The complete absence of catalytic activity of (R)-161 further emphasizes the crucial importance of a protic substituent at the ortho-position to the nucleophilic thiol. 

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