The Synthesis of Thiobenzoic Acid by Methanolysis of Benzoyl Chloride-N, N-Dimethylthioformamide Adduct

Abstract

Benzoyl chloride (BzCl) reacted easily with N, N-dimethylthioformamide (DMTF) to form an adduct, N, N-dimethyl(benzoylthio)methaneiminium chloride, which was smoothly decomposed with several neucleophiles to afford thiobenzoic acid (BzSH) together with other products.
When the above reaction was carried out in methanol, both the adduct formation and its decomposition proceeded to produce BzSH, benzoic acid (BzOH), and methyl benzoate (BzOMe). The yield of BzSH increased with increasing amount of methanol. Bz SH was obtained in 75% yield by the use of a large excess of methanol (20 molar equiv. to BzCl)at 0°C for 1 h.
In this reac tion, it is considered that the adduct formation was reversible but a polar solvent such as methanol deviated the equilibrium to the adduct side.
Similarly the reactions of p-substituted benzoyl chlorides with DMTF yielded the corresponding p-substituted thiobenzoic acids in high yields in the case of the electron-donating substituents, whereas electron-withdrawing groups increased the yields of methyl benzoate derivatives and decreased the yields of thiobenzoic acid derivatives.