Thiobenzoic acid is an organosulfur compound with molecular formula C<sub>6</sub>H<sub>5</sub>COSH. It is the parent of aryl thiocarboxylic acids. It is a pale yellow liquid that freezes just below room temperature. The structure of thiobenzoic acid has not been examined by X-ray crystallography but the 4-methyl derivative has been reported. The CC(O)SH group is planar with syn geometry. The C=O and C-S lengths are respectively 120 and 177 pm.
Thiobenzoic acid is prepared by treatment of benzoyl chloride with potassium hydrosulfide:
With a pK<sub>a</sub> near 2.5, this acid is almost 100x more acidic than benzoic acid. The conjugate base is thiobenzoate, C<sub>6</sub>H<sub>5</sub>COS<sup>âÂÂ</sup>.
Oxidation of thiobenzoic acid gives the disulfide .