Efficient alcoholysis of saponins to diosgenin catalyzed by sulfonated biochar from Dioscorea zingiberensis residue

Diosgenin represents a key precursor in the synthesis of steroidal pharmaceuticals, yet its conventional production relies on strong acid hydrolysis, which generates substantial acidic wastewater and poses serious environmental concerns. To circumvent these issues, a sustainable strategy for precise engineering of acid site in biochar catalysts derived from Dioscorea zingiberensis residues is presented. The carbon supports were prepared by direct calcination of the biomass residues across a controlled temperature range without exogenous additives, allowing tailored specific surface parameters. Subsequent sulfonation introduced sulfonic acid groups as the primary active sites, along with carboxylic acid groups and other weak acid species. A linear correlation was identified between the specific surface area and total acid site density, enabling rational regulation of acidic properties. Alcoholysis of saponins catalyzed by C-800-SO 3 H (derived from calcination at 800 °C with subsequent sulfonation) enabled a diosgenin yield of 23.26% based on crude saponins, equivalent to 4.39% relative to the raw rhizome mass. Catalytic performance correlated strongly with sulfonic acid density, indicating that sulfonic acid groups dominate the catalytic conversion. The catalyst also retained considerable activity over five reuse cycles. This work establishes a rational and eco-compatible route for designing high-performance solid acid catalysts from biomass waste, demonstrating promising potential for green production of pharmaceutical intermediates.