A novel approach for distillation of paeonol and simultaneous extraction of paeoniflorin by microwave irradiation using an ionic liquid solution as the reaction medium

In the present work, a simple and efficient method for steam distillation of paeonol and simultaneous extraction of paeoniflorin from the root bark of Paeonia suffruticosa Andr. (Cortex Moutan) was developed using an ionic liquid as the reaction medium and microwave irradiation. A series of 1-alkyl-3-methylimidazolium ionic liquids with different anions and alkyl chain lengths were evaluated for this method. The optimum conditions were 1.25 M 1-butyl-3-methylimidazolium bromine as the extraction solvent, 20 mL/g liquid-solid ratio, 25 min microwave irradiation time, 700 W microwave irradiation power, and 60-80 mesh particle size. Under these conditions, satisfactory yields of paeoniflorin (80.49 ± 2.58 mg/g) and paeonol (10.52 ± 0.36 mg/g) were obtained. The initial purity of paeonol was 84.95%, and this increased to >99% with simple recrystallization. The ionic liquid extraction solution, either with or without trace paeonol, was passed through HPD100B macroporous resin for enrichment and separation of paeoniflorin and recycling of the ionic liquid used. Recycling and reuse of the ionic liquid were achieved successfully, which could reduce ionic liquid requirements and the process cost. The method was validated using stability, recovery, and repeatability experiments. The proposed method is very promising for separation of natural compounds, especially for small molecules that can be isolated by steam distillation.