SYNTHESIS OF BETULIN DIFORMATE AND ALLOBETULIN FORMATE DIRECTLY FROM OUTER BIRCH BARK

Abstract

One of the promising directions of birch bark utilization is its extractive treatment with obtaining a number of valuable chemical components among which the most relevant is betulin. As a rule, the methods of betulin esters are multistage and based on classical reactions of betulin acylation; betulin should be preliminarily extracted from birch bark. The purpose of the present research was synthesis of the betulin diformate and allobetulin formate directly from the birch bark without a separate stage of the betulin preparation. The external layer of the bark of birch, Betula pendula Roth was ground to particle size of 10–20 mm and used as the raw material. The method is based on combined extraction of betulin from outer birch bark and its formylation with formic acid at reflux for 16 hours. During the treatment of birch bark with formic acid, along with betulin extraction into solution, its formylation into betulin diformate and allobetulin formate occurs. The yield of the formation of betulin diformate and allobetulin formate of the mass of acylated upper bark (a.u.b.) was 40 and 10%, respectively. The first fraction of betulin diformate was obtained from the resulted solution by evaporating 3/4 of the solution and poured it in water to form beige precipitate, whereas the second fraction was extracted by treating the resulted birch bark by acetone followed by evaporation. However, the allobetulin formate was formed from the second treatment of resulted birch bark by chloroforrm followed by evaporation. Betulin diformate was found to be the main component of this extraction, and it was recrystallized from ethyl alcohol to afford beige powder, and its melting point is 165 °C. The structures of betulin diformate and allobetulin formate are confirmed by 1H NMR, 13C NMR, and FTIR spectroscopy.