Kinetic studies of the pyridinolysis $(XC_5H_4N)$ of aryl dithiomethylacetates $(CH_3CH_2C(=S)SC_6H_4Z,;1)$ are carried out in acetonitrile at $60.0^{circ}C$. A biphasic Bronsted plot is obtained with a change in slope from a large $({eta}X;{cong};0.8)$ to a small $({eta}X;{cong};0.2)$ value at $pK_a^{circ}$ = 5.2, which is attributed to a change in the rate limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, $T^{pm}$, in reaction path as the basicity of the pyridine nucleophile increases. This mechanism is supported by the change of the cross-interaction constant ${ ho}xz$ from a large positive ( ${ ho}xz$ = +1.36) for the weakly basic pyridines to a small negative ( ${ ho}_xz$ = -0.22) value for the strongly basic pyridines. The magnitudes of ${ ho}z$ and activation parameters are also consistent with the proposed mechanism.