The kinetics and mechanism of the silver ion-promoted hydrolysis of thiolurethanes in aqueous solution

Abstract

The hydrolysis of thiolurethanes p-RC₆H₄NHCOSEt (1, R = Cl, H, OMe) in dilute aqueous acid is promoted by silver ions. The promoted hydrolysis involves the slow decomposition of low concentrations of complexes of 2 Ag⁺:1-thiolurethane stoichiometry, which are formed from relatively stable 1:1-complexes. The (positively charged) 1:1-complex (2) undergoes N-H dissociation to give a formally neutral 1:1-complex, 3. The 2:1-complexes are formed from both 2 and 3. The formation constants, K₁, and the acid dissociation constants, K_a, of (2, R = Cl, H, MeO) have been obtained from a kinetic analysis using a range of silver and hydrogen ion concentrations, and different temperatures. The results suggest that the 2:1-complexes undergo nucleophilic attack by water in an overall A2-like process. Thiolurethanes 1 are ca. 10⁵-fold more reactive in Ag⁺ ion-promoted hydrolysis than are the corresponding ethyl thiolbenzoates.