The aminolysis of S-aryl O-ethyl dithiocarbonates with benzylamines are studied in acetonitrile at -25.0 °C. The βX (βnuc) values are in the range 0.67-0.77 with a negative cross-interaction constant, ρXZ = -0.24, which are interpreted to indicate a concerted mechanism. The kinetic isotope effects involving deuterated benzylamine nucleophiles (XC6H4CH2ND2) are large, kH/kD = 1.41-1.97, suggesting that the N-H(D) bond is partially broken in the transition state by forming a hydrogen-bonded four-center cyclic structure. The concerted mechanism is enforced by the strong push provided by the EtO group which enhances the nucleofugalities of both benzylamine and arenethiolate from the putative zwitterionic tetrahedral intermediate.
在乙腈中以-25.0°C条件下研究了苯基乙基二硫代碳酸酯与苄胺的氨解反应。βX(βnuc)值在0.67-0.77范围内,具有负的交叉作用常数ρXZ = -0.24,这被解释为指示了一个协同机制。涉及氘代苄胺亲核试剂(XC6H4CH2ND2)的动力学同位素效应很大,kH/kD = 1.41-1.97,表明在过渡态中N-H(D)键部分断裂,形成一个氢键四中心环结构。协同机制由EtO基团提供的强推动力加强了苄胺和芳硫醇从假定的带电离子四面体中间体的亲核性。