Catalyst-free process for oxidation of furfural to maleic acid by high frequency ultrasonic activation

Maleic acid is an important intermediate in chemical industries. The synthesis of maleic acid from renewable furfural is one of the most sought after processes for the sustainability of the human society. It is produced in multimillion tonne-scale annually. Traditional methods of oxidation of furfural to maleic acid can be improved on various parameters such as substitution of heavy metal catalysts, simplification of the process, the recyclability of catalysts and the management of toxic waste or increased concentration of committed raw materials. Herein, we demonstrate a catalyst-free process for the gram-scale synthesis of maleic acid from furfural using high frequency ultrasound irradiations. A 70% selectivity of maleic acid with 92% of furfural conversion were achieved without any catalyst under mild conditions using H2O2 as the oxidant. Our alternative approach enables the use of biomass instead of petroleum to synthesize maleic acid from furfural in an eco-friendly and energy-efficient process.