Captan (N-(trichloromethylthio)-4-cyclohexene-1,2-dicarboximide) undergoes hydrolysis readily in water with a maximum half-life of 710 min. Over the pH range 2-6, the reaction is pH independent and the pseudo-first-order rate constant is (1.8 + or - 0.1) x 10 to the -5th power/s. Above pH 7 the reaction is pH dependent and the second-order rate constant for alkaline hydrolysis is (5.7 + or - 0.4) x 10 to the 2nd power/MS. The products are 4-cyclohexene-1,2-dicarboximide, carbon dioxide, hydrochloric acid, and sulfur. Folpet (N-(trichloromethylthio)phthalimide) and captafol (N-(1,1,2,2-tetrachloroethylthio)-4-cyclohexene-1,2-dicarboxide) hydrolyze at pH 7 with rates similar to that of captan. It is very likely that hydrolysis will be an important degradative pathway for these fungicides in the aquatic environment. Copyright (c) 1976 by the American Chemical Socity.