Insights into the Reaction Mechanism of the Tetrahydrobenzo[b]pyran by means of Kinetic Studies in the Presence of Fructose as a Green Catalyst

Extensive kinetic studies were performed to investigate the mechanism of the reaction between 4-methoxybenzaldehyde 1, malononitrile 2, and dimedone 3 in the presence of fructose as a catalyst in a mixture of water and ethanol. The synthesis reaction of tetrahydrobenzo[b]pyran followed second-order kinetics. The partial orders with respect to 1, 2 were one and one, respectively. Temperature effect has been investigated on the reaction rate, and relevant parameters have been determined with two linearized forms of Eyring equation. The proposed mechanism theoretical rate law were compatible with the experimental data. From the temperature, concentration and solvent studies, the activation energy (Ea = 70.05 ± 1.39 kJmol -1) and the related activation parameters (DG‡ = 57.35 ± 2.76 kJmol-1, DS‡ = 35.58 ± 4.42 Jmol-1 and DH‡ = 68.32 ± 1.40 kJ mol-1) were calculated.