Chemoenzymatic conversion of furfural to methyl-2-furotate

Furfural (FF) is an important bio-based platform compound derived from lignocellulose. It can be converted into many industrially valuable chemicals, a typical one being methyl-2-furoate (MF). At present, MF production depends largely on vigorous one-step chemical catalysis (oxidative esterification), in which expensive catalysts (precious metals) and a high temperature (60-120 degrees C) are required. To reduce the costs of this procedure, a mild, green, and cheap chemoenzymatic process is proposed where FF is initially chemically oxidized to furoic acid (FA), and then FA is enzymatically esterified to MF. Neither step requires an expensive catalyst, and both occur at low temperatures (30-50 degrees C). For the chemical oxidation process, the optimized FA yield of 83.7% was obtained at 40 degrees C with an FF/BTIC (1,3-bis(2,4,6-trimethylphenyl) imidazolium chloride) molar ratio of 0.18, 10 mL N-methyl pyrrolidone, and 0.1 MPa oxygen pressure. For the enzymatic esterification, the optimized MF yield reached 80.6% at 50 degrees C with 50 mg center dot mL(-1) enzyme loading and an alcohol/acid ratio of 7:1. Kinetic studies demonstrated the oxidation to be a sixth-order reaction, and the esterification to be an endothermic reaction. For both oxidation and esterification reactions, the relationship between the rate constant and temperature agreed well with the Arrhenius equation. For esterification, the relationship between the equilibrium constant and the temperature also agreed with the Van't Hoff equation. A 67.5% MF yield was obtained when sequential oxidation and esterification were initiated from FF. The development of chemoenzymatic processes for MF production from FF is effective and has potential value in decreasing the production cost of MF. (c) 2021 Society of Chemical Industry and John Wiley & Sons, Ltd