Efficient alcoholysis of total saponins in D. zingiberensis to diosgenin using ionic liquid-grafted MOF superacids

Diosgenin is an indispensable intermediate in the production of various steroid drugs. Conventional hydrolysis of sulfuric acid produces large amounts of acidic wastewater and has always faced stringent restrictions from environmental requirements. Here, UiO-66-NH 2 and its derivative of UiO-66-NH 2 -AT (AT = 3-amino-1,2,4-triazole) were synthesized, and these two compounds were further grafted with high-concentration CF 3 SO 3 H molecules to obtain the MOF-based solid superacids, namely UiO-66-NH 2 -[SO 3 CF 3 ] and UiO-66-NH 2 -AT-[SO 3 CF 3 ], respectively. They have been applied to the alcoholysis of total saponins to extract diosgenin, and the alcoholysis conditions, including the solid acid dosage, extraction temperature and extraction time, have been optimized by single-factor experiments. Subsequently, the alcoholysis conditions of UiO-66-NH 2 -AT-[SO 3 CF 3 ] with more prominent catalytic performance and cycle stability were further optimized by the response surface method, and under the optimum conditions, the diosgenin yield reached 20.8 %, which was close to the predicted value of 21.3 % and was superior to the conventional hydrolysis of sulfuric acid and our previously reported solid acids. Additionally, the alcoholysis pathways and alcoholysis mechanism of the total saponins catalyzed by UiO-66-NH 2 -AT-[SO 3 CF 3 ] have been proposed by the analysis of high-resolution electrospray mass spectrometry.