SCHEDULED MAINTENANCE
Efficient microwave synthesis of novel aromatic esters catalyzed by zirconia and its modified forms: a kinetic study†
Abstract
A series of solid acids such as ZrO2, 5%Mo(VI)/ZrO2, 10%Mo(VI)/ZrO2, 20%Mo(VI)/ZrO2 and SO42−/ZrO2 were prepared. These solid acids were characterized by BET, NH3-TPD/n-butylamine back titration, powder-XRD, FT-IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ICP-OES techniques. The catalytic performance of these solid acids was evaluated in the synthesis of novel aromatic esters by the assistance of microwave irradiation and the catalytic activity of these solid acids was compared with pTsOH. The results clearly indicated that the zirconia based solid acids are efficient green catalysts for esterification reactions, which gave a maximum yield of the ester in a shorter reaction time and comparable catalytic activity of the pTsOH Brönsted acid. Kinetic studies were carried out to calculate the temperature coefficients (1.66 and 1.56) and energy of activation (66.82 kJ mol−1 and 58.93 kJ mol−1) for SO42−/ZrO2 and pTsOH respectively. Pre-adsorption studies revealed that the reaction follows the Langmuir–Hinshelwood mechanism. The SO42−/ZrO2 solid acid catalyst was found to be reactivable and reusable.
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