Eco-friendly synthesis of maleate ester: A comparison between solid acid and enzyme-catalyzed esterification

Abstract

In this study, two different eco-friendly methods were investigated for the synthesis of a dicarboxylic acid ester, dimethyl maleate (DMM). One method involves application of molybdate sulfuric acid (MSA) as a solid acid catalyst in the esterification of maleic acid with methanol. The effects of three parameters namely, temperature, time, and catalyst amount on the product synthesis were determined. By using response surface methodology (RSM) based on central composite rotatable design (CCRD), maximum conversion of the maleic acid (87.6%) was obtained at reaction conditions of 120 °C, 0.27 g MSA, and 103 min. In the other method, DMM was synthesized by enzymatic esterification using immobilized Candida antarctica lipase B as the catalyst. Maximum conversion was 72.3%, at the optimal conditions of 62.5 °C, 0.27 g enzyme, and 249 min. The reusability study showed that MSA lost its catalytic activity after five cycles. However, the immobilized enzyme maintained its activity and stability. The results indicated that both employed methods were efficient for the synthesis of DMM. A higher conversion could be obtained using MSA as the catalyst, which could be compensated by better reusability of the enzyme. The enzyme-catalyzed reaction was more energy efficient but it took a longer time to obtain maximum reaction yield.