Effect of the Consolute Point of Isobutyric Acid+Water on the Rate of an SN1 Hydrolysis Reaction

The rate constant for the SN1 hydrolysis of 2-chloro-2-methylbutane was measured near the consolute point of the liquid mixture isobutyric acid+water. At temperatures far from the upper critical solution temperature, Tc , of this mixture, the rate constant obeyed the Arrhenius equation.In the one-phase region just above Tc , however, the rate constant decreased below the Arrhenius background, while in the two-phase region below Tc , it increased.This combination of slowing-down with speeding-up appears to be beyond the scope of explanation of the current theories of dynamic critical slowing-down.