Caffeine Catalyzed Synthesis of Tetrahydrobenzo[b]pyran Derivatives: Synthesis and Insight into Kinetics and Mechanism

It was observed that the yield was a function of temperature, as the yield increased, the reaction temperature rose. At 70 ºC, the product was obtained with an excellent yield and higher temperatures did not increase the reaction yield any more. Also, 20 mol% was elected as a suitable amount of catalyst for this reaction. It is understood from the result that the rate of reaction speeds up in a solvent with a high dielectric constant (H2O/EtOH, 2:1) compared to those with a low dielectric constant (Ethanol and methanol) at all temperatures. In the studied temperature range, the second-order rate constant of the reaction was inversely proportional to the temperature, which was in agreement with the Arrhenius and Eyring equations. It was obvious that the high positive values of the activation parameters leads to a stiff reaction progress. The first step of the proposed mechanism was identified as a rate-determining step (k1) and this was confirmed based on the steady-state approximation.