Thiobenzoic acid
# Thiobenzoic acid

Thiobenzoic acid is an organosulfur compound with molecular formula $C_6H_5COSH.$ 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:

    $C_6H_5C(O)Cl$ + KSH → $C_6H_5C(O)SH$ + KCl

## Acidity

With a $pK_a$ near 2.5, this acid is almost 100x more acidic than benzoic acid. The conjugate base is thiobenzoate, $C_6H_5COS^−.$

