Highly Efficient Synthesis of Hydrophilic Phytosterol Derivatives Catalyzed by Ionic Liquid

Phytosterols and their derivatives have been attracting much attention because of their potential beneficial effects on human health. However, the free phytosterols are insoluble in water and poorly soluble in oil and fat, thus limiting their application. So far, many studies have been done to improve the oil solubility of phytosterols, but little research has been reported to improve their water solubility. In this study, hydrophilic phytosterol derivatives (phytosteryl polyethylene glycol succinate, PPGS) was efficiently synthesized, through an intermediate phytosteryl hemisuccinate (PSHS), which was first chemically prepared and subsequently coupled with polyethylene glycol (PEG) using acidic ionic liquids (IL) as catalyst via 2-batch or 1-pot stepwise esterification routes. The chemical structure of the products was characterized by thin layer chromatography, Fourier transform infrared spectroscopy, and mass spectroscopy, suggesting that hydrophilic phytosterol derivatives were successfully synthesized. As for 2-batch esterification route, the mass and molar conversion of PSHS to PPGS could reach above 97 and 88% under the optimum conditions: [BSO(3)HMim][HSO4] as the catalyst, IL load of 6%, molar ratio of PEG 2000 to PSHS at 1:1.25, 110 degrees C, and 1 hour. Using the 1-pot stepwise route, the conversion of phytosterols to PSHS could achieve above 92% for 2 hours, and the mass and molar conversion of PSHS to PPGS could achieve above 97 and 90% for 12 extra hours. Both 2-batch and 1-pot stepwise routes using the same IL displayed high conversion, suggesting that IL [BSO(3)HMim][HSO4] could be used as the potential catalyst and 2 routes could be used as highly efficient route for PPGS synthesis.