Synthesis of isobutyl cinnamate based on DESs catalyst: Optimization and kinetics

In this work, the optimum process conditions and kinetics of the green synthesis of isobutyl cinnamate using deep eutectic solvents (DESs) as catalysts were investigated. Isobutyl cinnamate is a spice with low toxicity and is widely used in the food industry. However, there is a lack of reports on its green synthesis. Three DESs were prepared by adjusting the mixing ratio of choline chloride (ChCl) and p-toluenesulfonic acid (PTSA). Response surface methodology with Box-Behnken design (RSM-BBD) was used to optimize the process parameters of the esterification of cinnamic acid with isobutanol. The effects of catalyst loading, stirring speed, cinnamic acid/isobutanol molar ratio, and temperature on the conversion of cinnamic acid over time were evaluated. Using ChCl-PTSA as a catalyst, the kinetics data and chemical equilibrium constants of the esterification were determined at a temperature range of 353.15–383.15 K. The pseudo-homogeneous (PH) model based on activity was then adopted to describe the kinetics of the reaction, and the relative deviations between the experimental values and the calculated ones by PH model are less than 5.5%. Thermodynamic data (Δ_rH⁰, Δ_rS⁰, Δ_rG⁰) for the esterification reaction was calculated as well. In addition, the results of six consecutive cycles of the catalyst showed that ChCl-PTSA has good stability and recyclability.