Theoretical and Experimental Study on the 7‐Hydroxy‐4‐Methylcoumarin Synthesis with H‐Beta Zeolite

Abstract

AbstractCoumarin is an important chemical in agricultural and pharmaceutical industries. This work studied the synthesis of 7‐hydroxy‐4‐methylcoumarin via the Pechmann condensation reaction catalyzed by H‐Beta zeolite catalyst using a combination of experimental and theoretical means. Adsorptions and reactions taking place inside the 34T cluster (T=Si or Al atoms) of H‐Beta zeolite were examined by using density functional theory with the M06‐2X functional. The coumarin synthesis reaction was proposed to be a three‐step mechanism: the transesterification, the intramolecular hydroxyalkylation and the dehydration. The total activation energies for each step were calculated to be 17.8, 3.5 and 13.5 kcal⋅mol−1, respectively. The zeolite framework stabilized the adsorption complexes and decreased the activation barriers for the Pechmann condensation reaction. The synthesis of 7‐hydroxy‐4‐methylcoumarin from resorcinol and ethyl acetoacetate on H‐Beta zeolite was experimentally examined without solvent at various conditions. The adsorption of 7‐hydroxy‐4‐methylcoumarin on H‐Beta zeolite was detected by the FT‐IR spectroscopy technique. The experimental activation energy of 6.7 kcal⋅mol−1 agreed very well with the calculated apparent value of 10.6 kcal⋅mol−1. The H‐Beta zeolite can be reused at least four times with persistently high percent yield.