Kinetics and Mechanism of the Aminolysis of Aryl Dithiocyclopentanecarboxylates in Acetonitrile

The two common mechanisms for the aminolysis of carbonyl, I, and thiocarbonyl, II, esters and carbonates are (i) concerted through a tetrahedral transition state (TS) and (ii) stepwise through a tetrahedral intermediate.1 The latter reaction pathway can be described by eq. (1), where R and L are nonleaving and leaving groups, and N represents an amine and Y is either O (I) or S (II). A nonlinear Brönsted plot results from a change in the rate-determining step, from that of kb at low amine basicity (with βnuc ≥ 0.8) to that of ka at high amine basicity (with βnuc ≤ 0.3). Applying the steady-state condition to T ± in eq. (1), the equation kN = ka kb /(k-a + kb) ≅ (ka/k-a) × kb = K·kb is obtained, and this accounts for the change in the rate-determining step at pKao where k−a = kb applies. The aminolysis mechanisms naturally depend on Y, R, L, N in eq. (1) and solvent. Fixing L ( = SC6H4Z