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

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 Bronsted (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 Delta H-not equal = 39.20 kJ mol(-1), Delta S-not equal = -152.62 J mol(-1) K-1 and Delta G(not equal) = 99.18 kJ mol(-1) at 393 K. The negative value of the activation entropy (Delta S-not equal) indicates that the entropy decreases upon forming the transition state, which proves that the transition state is more highly ordered than the reactants. (C) 2019 Published by Elsevier B.V.