Reaction Kinetics and Critical Phenomena: Saponification of Ethyl Acetate at the Consolute Point of 2-Butoxyethanol + Water

Abstract

The rate of sponification of ethyl acetate by sodium hydroxide was measured near the consolute point of the liquid mixture, 2-butoxyethanol + water. At temperatures far below the lower critical solution temperature, Tc, the apparent rate constant obeyed the Arrhenius equation. In the one-phase region just beneath Tc, the rate constant decreased below the Arrhenius background, indicating critical slowing down. Because the kinetics of this reaction are second order, the net reaction rate depends upon both (∂ΔG/∂ξ)e and (∂ΔG/∂ξ)e, where Δ G is the Gibbs free energy difference between products and reactants, ξ is the extent of reaction, and subscript “e” refers to chemical equilibrium. On the basis of the Principle of Universality, it is argued that as the temperature approaches Tc, both of these thermodynamic derivatives should go to zero, and the net reaction rate should slow down as is actually observed.