Thioacetic acid
Thioacetic acid is an organosulfur compound with the molecular formula . It is a thioic acid: the sulfur analogue of acetic acid (), as implied by the thio- prefix. It is a yellow liquid with a strong thiol-like odor. It is used in organic synthesis for the introduction of thiol groups () in molecules. Synthesis and properties Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide: (CH3C(O))2O + H2S -> CH3C(O)SH + CH3C(O)OH It has also been produced by the action of phosphorus pentasulfide on glacial acetic acid, followed by distillation. CH3C(O)OH + P2S5 -> CH3C(O)SH + P2OS4 Thioacetic acid is typically contaminated by acetic acid. The compound exists exclusively as the thiol tautomer, consistent with the strength of the double bond. Reflecting the influence of hydrogen-bonding, the boiling point (93 °C) and melting points are 20 and 75 K lower than those for acetic acid. Reactivity Acidity With a pKa near 3.4, thioacetic acid is about 15 times more acidic than acetic acid. The conjugate base is thioacetate: CH3C(O)SH -> CH3C(O)S- + H+ In neutral water, thioacetic acid is fully ionized. Reactivity of thioacetate Most of the reactivity of thioacetic acid arises from the conjugate