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.

Thiobenzoic acid is prepared by treatment of benzoyl chloride with potassium hydrosulfide:
 * C6H5C(O)Cl + KSH → C6H5C(O)SH + KCl

Acidity
With a pKa near 2.5, this acid is almost 100x more acidic than benzoic acid. The conjugate base is thiobenzoate, C6H5COS−.