关键词: 熊果酸, 溶解度, 介稳区, 乙醇-水, 反应结晶

Abstract: The solubility of ursolic acid in ethanol-water system was measured in the pH value range of 7~10 and ethanol concentration range of 60%~90%(w) under room temperatures (20 and 30℃) using a dynamic method. It was found that increasing pH value and ethanol concentration resulted in the enhancement of solubility. The ursolic acid solubility increased sharply with pH value only at higher pH range (9~10), and just in this pH range, the increase of ethanol concentration could significantly raise the solubility. Ursolic acid solubility was more sensitive to pH value than ethanol concentration at room temperatures and hence reaction crystallization by adding acid was suitable to ursolic acid recovery. Based on the variation trend of solubility with pH value and ethanol concentration, empirical equations were used to correlate the relationship between solubility and pH and ethanol concentration with a high relative coefficient of 0.998. In addition, the reaction crystallization metastable zones of ursolic acid in ethanol-water system were determined using laser monitoring technique. The metastable zone width (DpH) decreased, then increased with increasing saturation concentration of ursolic acid and seemed to increase with the increase of temperature. When 80% ursolic acid from loquat leaves was dissolved in 90%(w) ethanol-water at pH 10, a bench-scale reaction crystallization process was carried out at appropriate acid concentration and acid-adding rate, and 98% ursolic acid was obtained with a overall yield of 78%. The ursolic acid crystals were rod-like and white glossy particles.

Key words: ursolic acid, solubility, metastable zone, ethanol-water, reaction crystallization