Changes in Composition of Birch Outer Bark Extractives After Recrystallization with C2-C5 Alkanols

Abstract

The effects on birch outer bark (BOB) ethanolic extractives’ chemical composition after recrystallization with C2–C5 alkanols were studied in this paper. Ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol were used as solvents. The solubility of BOB extractives at the solvents boiling point was determined empirically. It was found that, with an increase of the boiling point of the solvents, the solubility of the extractives increased, reaching up to 486 g/L in 1pentanol at 142.2 °C. Recrystallization yields reached up to 67 wt% using 2-butanol and the purity of betulin up to 96 wt% using 2‐propanol as a solvent. Considering the yield of recrystallization, betulin content, boiling point of the solvent, solvent loss, toxicity and eco-friendliness of the solvent, ethanol was chosen to be the most suitable solvent for industrial scale purification of betulin in the BOB extractives. Using only one recrystallization step the content of betulin was increased by 20% — from 75 to 95 wt% and the yield of recrystallization was 32.1 g per liter of solvent.