[en] Kinetic studies on the pyridinolysis of aryl dithiocyclopentanecarboxyaltes 2 were carried out at 60.0 .deg. C in acetonitrile. In the aminolysis of 2, the β_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 (β_X ≅ 0.7) to a small value (β_X ≅ 0.4) at pK_a".deg. = 5.2. This was attributed to a change in the rate-limiting step from breakdown to the formation of a zwitterionic tetrahedral intermediate, T"±, in the reaction path, with an increase in the basicity of the pyridine nucleophile. An obvious change in the cross-interaction constant ρ_X_Z from a large positive (ρ_X_Z = +1.02) value to a small negative value (ρ_X_Z = -0.17) supports the proposed mechanistic change