Efficient Catechol Production from 2-Acetylfuran in Subcritical Water with ZnCl2 as a Lewis-Acid Catalyst

Abstract Catechol (1,2-benzenediol) is a critical platform chemical with a growing global market, currently produced primarily through the fossil-based Hock process to produce phenol from benzene, followed by its hydroxylation to catechol. As the transition toward a bio-based economy intensifies, identifying sustainable production routes from renewable resources like lignocellulosic biomass is essential. To that end, different biomass-to-catechol strategies have been developed, such as (i) lignin depolymerization, followed by catalytic conversion of their alkylated/methoxylated phenol monomers, or (ii) glucose fermentation to catechol. Yet both approaches face specific challenges that hamper strong market integration. As an alternative, this present study reports an interesting, yet long-neglected alternative, catechol synthesis in subcritical water from 2-acetylfuran, a biomass-derived furan obtained from, e.g., sorbitol dehydration or acylation of furan. Since the subcritical reaction of 2-acetylfuran to catechol essentially entails a rearrangement, a higher atom economy can be persued, compared to lignin and fermentation-based routes. After initial exploration, a systematic optimization of the reaction temperature, time, and Lewis catalyst concentration (ZnCl2) through response surface modeling, a catechol yield of 52% was achieved (i.e., a 10-fold increase over what was previously achieved) at a conversion of 82% and a selectivity of 61% (applying catalyst concentration of 2.4 mol % ZnCl2, 310 °C reaction temperature and 366 min reaction time). Mass balance closures reached 92–93%, identifying acetic acid as the primary side product formed through competing α-dicarbonyl cleavage, with virtually no catechol degradation under these reaction conditions. These findings establish 2-acetylfuran as a high-potential feedstock for sustainable aromatic production, offering a robust pathway for integrating green catechol into industrial biorefinery schemes.