A solution of 17.2 g (0.1 mol) m-chloroperbenzoic acid in 200 mL of dichloromethane at -30℃ is added slowly to a solution of 3.1 g (0.05 mol) of ethanethiol in 10 mL of dichloromethane (also at -30℃). The reaction mixture is allowed to stand overnight at -30℃ and the precipitated m-chlorobenzoic acid is removed by filtration. The filtrate is cooled to -80℃ and refiltered to remove residual m-chlorobenzoic acid, after which the solvent is evaporated in a stream of nitrogen. Analytically pure ethanesulfinic acid is obtained in 80–85% yield.
