Catalytic alcoholysis of saponins in D. zingiberensis C. H. Wright (Curcuma longa L) with magnetic solid acid to prepare diosgenin by response surface methodology

[Display omitted] •A magnetic solid acid was prepared and can be recycled.•A alcoholysis method was used to extract diosgenin from saponins.•The parameters for the alcoholysis were optimized by Response Surface Methodology.•The yield of diosgenin obtained in this work is higher than traditional method. Diosgenin is an important intermediate of steroid hormone drugs, green production of diosgenin with high yield is a key research issue. In this study, a convenient, efficient, and eco-friendly approach was developed to produce diosgenin from saponins in D. zingiberensis C. H. Wright (Curcuma longa L) using a magnetic solid acid. Fe3O4@SiO2-Pr-S-SO3H is a heterogeneous catalyst and was obtained by loading 3-(mercaptopropyl) trimethoxysilane on the surface of Fe3O4@SiO2, followed by sulfonation with chlorosulfonic acid. The magnetic solid acid catalyst was fully characterized by Fourier Transform-Infrared (FT-IR) spectra, thermo gravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS), scanning electron microscope(SEM), transmission electron microscope (TEM), NH3-TPD, elemental mapping analysis. The effects of single factors, such as the solid acid mass, alcoholysis temperature, extraction time, and solvent volume on the diosgenin yield were analyzed. The extraction parameters for diosgenin were optimized by response surface methodology (RSM). The optimized values for the solid acid mass, solvent volume, extraction time, and temperature were 0.22 g, 7.8 mL, 7.4 h, and 100 °C, respectively. Under the optimized conditions, the maximum yield of diosgenin was 19.15 %. The solid acid reported in this work exhibited higher catalytic activity at a smaller dosage than traditional sulfuric acid and other solid acids. The alcoholysis products were identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS). Alcoholysis catalysed by an as-prepared magnetic solid acid is clearly superior in terms of catalytic activity, dosage, and reusability. It is a promising strategy for the green production of diosgenin.