STRUCTURE-REACTIVITY RELATIONSHIPS IN THE AMINOLYSIS OF O-ETHYL S-ARYL DITHIOCARBONATES IN AQUEOUS-SOLUTION

The reactions of O-ethyl S-(X-phenyl) dithiocarbonates (X = p-Cl, p-Me, and p-MeO) with a series of secondary alicyclic amines and those of the same substrates and analogous derivatives (X = H, p-NO2, and 2,4-(NO2)2) with pyrrolidine are subjected to a kinetic study in water, 25.0-degrees-C, ionic strength 0.2 M (KCl). The reactions of piperidine and pyrrolidine show second-order kinetics (first order in amine) with the formation of a zwitterionic tetrahedral intermediate (T+/-) as the rate-determining step, The reactions of the other amines exhibit orders in amine different from one, compatible with the presence of an anionic intermediate (T-), resulting from a kinetically important proton transfer from T+/- to the amine. The rate of this proton transfer is faster than that of expulsion of arylthiolate from T+/- (k2) as evidenced by the estimation of these rate coefficients. The rate constants for formation of T+/- (k1) are obtained experimentally, and those for amine expulsion from T+/- (k-1) are estimated. Equations for k1 and k-1 are derived as functions of the basicity of the amine and leaving (aryl thiolate) groups. Comparison of the k-1 and k2 values found in the present reactions with those obtained in the aminolysis of aryl dithioacetates shows that substitution of Me by EtO as the ''acyl'' group of the zwitterionic tetrahedral intermediate destabilizes this species.