Pressured Microwave-assisted Hydrolysis of Crude Glycyrrhizic Acid for Preparation of Glycyrrhetinic Acid

A pressured microwave-assisted hydrolysis (PMAH) technique has been developed for hydrolyzing the crude glycyrrhizic acid (GA) extracted from licorice root to prepare glycyrrhetinic acid (GRA). In order to optimize the efficiency of PMAH, several experimental parameters were investigated, including liquid-solid ratio, hydrolysis time, sulfuric acid concentration and hydrolysis temperature. The optimized hydrolysis conditions were as follows: pressured microwave-assisted hydrolysis of crude GA for 21 min (taking 15 min to reach 150 °C, and holding it for 6 min) at 150 °C (at a radiation power of 450 W) in 3%–5% sulfuric acid solution with the liquid-solid (ml·g−1 crude GA) ratio of 25 : U1. As a result of the considerable saving in time and higher product yields (up to 90%), PMAH was proved more effective than conventional methods.