doiSerbia

A study of esterification of caffeic acid with methanol using p-toluenesulfonic acid as a catalyst

Wang Jun (School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, P.R. China)
Gu Shuangshuang (School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, P.R. China)
Pang Na (School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, P.R. China)
Wang Fangqin (School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, P.R. China)
Wu Fuan (School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, P.R. China + Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, P.R. China)

Caffeic acid (CA) can be considered as an important natural antioxidant. However, the low solubility and stability of CA in various solvent systems is a major limiting factor governing the overall application in the lipid industry, so the synthesis of methyl caffeate (MC)using CA and methanol is a feasible way to improve its lipophilicity. Here, the reaction conditions and kinetic parameters for the synthesis of MC using p-toluenesulfonic acid (PTSA) as a catalyst were firstly investigated, and the product was confirmed byliquid chromatography-mass spectrometry (LC-MS),Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and melting point analysis. The highest yield of MC catalyzed by PTSA reached 84.0% under the optimum conditions as follows: molar ratio of methanol to CA of 20:1, reaction temperature of 65°C, mass ratio of catalyst to substrate of 8 %, and reaction time of 4 h. The esterification kinetics of CA and methanol is described by the pseudo-homogeneous second order reversible model, the relationship between temperature and the forward rate constant is k1 = exp (358.7 - 2111/T), and the activation energy is 17.5 kJ mol-1. These results indicated that the PTSA possesses high catalytic activity in the synthesis of MC, which is an efficient catalyst suitable for MC production in the chemical industry.

Keywords: caffeic acid, catalysis, esterification, kinetics, methyl caffeate, p-toluenesulfonic acid(PTSA)