Kinetics and mechanism of Pechmann condensation reaction over sulphated zirconia-supported zinc oxide

Abstract

An investigation of the kinetics of the Pechmann condensation reaction over ZnO supported on sulphated zirconia (ZnO/SZ) catalyst has been performed. The ZnO/SZ catalyst contains both Lewis (L) and Brønsted (B) acid sites. The maximum B/L ratio was obtained with a ZnO content of 6%. The reaction is first-order half in both acetoacetate and resorcinol, which supports the proposed reaction mechanism. The reaction temperature was found to have a great effect on the kinetics of coumarin synthesis, and the activation energy was determined to be 42.29 kJ mol−1. The experimental activation parameters for the reaction were calculated to be ΔH≠ = 39.20 kJ mol−1, ΔS≠ = −152.62 J mol−1 K−1 and ΔG≠ = 99.18 kJ mol−1 at 393 K. The negative value of the activation entropy (ΔS≠) indicates that the entropy decreases upon forming the transition state, which proves that the transition state is more highly ordered than the reactants. Keywords: Zinc oxide/sulphated zirconia, Ethyl acetoacetate, Resorcinol, Brønsted acid sites, Pechmann reaction, Kinetics and activation parameters