, Volume 25, Issue 4, pp 1025-1036

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, T c, the apparent rate constant obeyed the Arrhenius equation. In the one-phase region just beneath T c, 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 T c, both of these thermodynamic derivatives should go to zero, and the net reaction rate should slow down as is actually observed.