Ortho-bifunctional thiol-carboxylic acid exhibiting strong metal-chelating (Hg²⁺, Ag⁺, Fe³⁺), antioxidant and mild antibacterial activity. It is a key intermediate for synthesising thio-indigo dyes, the antimicrobial preservative thimerosal, optical brighteners and benzothiazole UV-absorbers. In analytical chemistry it serves as a spectrophotometric reagent for iron determination and as a derivatising agent for LC-MS quantitation of ethyl-mercury compounds. Recent research utilises its thiol group for preparing farnesyl-thiosalicylate conjugates that inhibit Ras-driven tumour growth and for constructing redox-sensitive drug-delivery nanoparticles. Industrial manufacture involves copper-catalysed reaction of o-chlorobenzoic acid with alkali hydrogen sulfide or hydrolysis of methyl thiosalicylate; continuous-flow protocols achieve >98 % yield with 90 % waste-water reduction. Store sealed, dry and under nitrogen; avoid contact with oxidants to prevent disulfide formation
