Thiobenzoic acid

Thiobenzoic acid is an organosulfur compound with molecular formula C₆H₅COSH. 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 CCSH group is planar with syn geometry. The C=O and C-S lengths are respectively 120 and 177 pm.

Synthesis and reactions

Thiobenzoic acid is prepared by treatment of benzoyl chloride with potassium hydrosulfide:
With a pK_a near 2.5, this acid is almost 100x more acidic than benzoic acid. The conjugate base is thiobenzoate, C₆H₅COS⁻.
Oxidation of thiobenzoic acid gives the disulfide.