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

Abstract

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

Ultrasound irradiation accelerates the lipase-catalyzed synthesis of methyl caffeate in an ionic liquid

“…For example, Shin et al described the esterification of CA and methanol in the presence of sulfuric acid in 10 h with an MC yield of 71.0% [6]. Then, Wang et al described a similar process catalyzed by p-toluenesulfonic acid (PTSA) for the preparation of MC in 4 h, achieving a relatively higher MC yield of 84.0% [7]. However, acidic catalysts are hazardous, requiring special energy-inefficient processes to dispose of the waste acid.…”

Enzymatic Synthesis and Antioxidant Activity of 1‐Caffeoylglycerol Prepared from Alkyl Caffeates and Glycerol

“…Alkyl caffeates, serving as substrates for lipase‐catalyzed transesterification, were synthesized following the procedure previously reported with slight modifications (Wang, Gu, Pang, Wang, & Wu, ). CA (9 g) was refluxed with 40 mL of alcohol, serving as acyl acceptor, with 2.7 g of p ‐toluenesulfonic acid catalyst.…”

Research into esterification of mixture of lower dicarboxylic acids by 2-ethylhexan-1-ol in the presence of p-toluensulfonic acid

“…In the presence of catalytic amount of 0.5 mol % of pTSA, both aromatic and aliphatic alcohols efficiently react with carbonic acids with moderate and high yields of esters (from 55 to 92 %). Maximal yield of esters is observed for alcohols containing electron donor groups [12].…”