Kinetic studies on the pyridinolysis of aryl dithiocyclopentanecarboxyaltes 2 were carried out at $60.0^{circ}C$ in acetonitrile. In the aminolysis of 2, the $eta_X$ values were 0.5 - 0.8 with anilines, and there was no breakpoint. However, in the pyridinolysis of 2, biphasic Bronsted plots were obtained, with a change in slope from a large value ($eta_X{cong}0.7$) to a small value ($eta_X{cong}0.4$) at $pK_{a}^0$ = 5.2. This was attributed to a change in the rate-limiting step from breakdown to the formation of a zwitterionic tetrahedral intermediate, $T^{pm}$, in the reaction path, with an increase in the basicity of the pyridine nucleophile. An obvious change in the cross-interaction constant ${ ho}_{XZ}$ from a large positive ($ ho_{XZ}$ = +1.02) value to a small negative value (${ ho}_{XZ}$ = -0.17) supports the proposed mechanistic change.