The E1cB mechanism for thiocarbamate ester hydrolysis: Equilibrium and kinetic studies

The alkaline hydrolyses of a series of S-aryl thiocarbamate esters have been measured and the mechanism confirmed to be dissociative. Equilibrium constants for the synthesis of thipcarbamates from thiol and isocyanic acid have been obtained for aqueous media using both kinetic and analytical techniques. Hammett and Brønsted parameters for the equilibrium reaction indicate that there is less positive effective charge on the sulphur in the thiocarbamate compared with that on the oxygen in the oxygen analogue. Theoretical arguments are advanced to show that the dissociative reactions of simple carbamate anions involve a planar geometry of the participating atoms.