Ea. Castro et al., STRUCTURE-REACTIVITY RELATIONSHIPS IN THE AMINOLYSIS OF O-ETHYL S-ARYL DITHIOCARBONATES IN AQUEOUS-SOLUTION, Journal of organic chemistry, 58(20), 1993, pp. 5400-5404
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 a
nd 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 orde
rs in amine different from one, compatible with the presence of an ani
onic intermediate (T-), resulting from a kinetically important proton
transfer from T+/- to the amine. The rate of this proton transfer is f
aster than that of expulsion of arylthiolate from T+/- (k2) as evidenc
ed by the estimation of these rate coefficients. The rate constants fo
r formation of T+/- (k1) are obtained experimentally, and those for am
ine 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 (ary
l thiolate) groups. Comparison of the k-1 and k2 values found in the p
resent reactions with those obtained in the aminolysis of aryl dithioa
cetates shows that substitution of Me by EtO as the ''acyl'' group of
the zwitterionic tetrahedral intermediate destabilizes this species.