Kinetic Aspects of Tetrahydrobenzo[b]pyran Formation in the Presence of Agar as a Green Catalyst: A Mechanistic Investigation

Abstract

The kinetic and mechanism of the reaction between benzaldehyde, malononitrile and dimedone has been studied in the presence agar as a highly efficient homogenous catalyst in a mixture of (water/ethanol, 2:1). Based on the experiment data, the overall order of reaction for the formation of tetrahydrobenzo[b]pyran followed second-order kinetics and under pseudo-order conditions the partial orders with respect to 1, 2 and 3 were one, one and zero, respectively. From the temperature, concentration and solvent studies, the activation energy (Ea) and the related kinetic parameters (ΔG‡, ΔS‡ and ΔH‡) are calculated. The first step of the proposed mechanism is recognized as a rate-determining step (k1) and this is proved by the steady state approximation.