Selecting ethanol as a model organic solvent in radiation chemistry--3. Radiolysis of glycyrrhetinic acid (GL)-ethanol system and structure modification of GL by γ radiation method

CH3CHOH, H·, esolv- are the main active radicals in the ethanol system irradiated by γ-ray without the presence of oxygen. In this study, GL ethanolic solution saturated with nitrogen was γ-irradiated, the radiolytic products were isolated by HPLC and the molecular structure was determined with UV, IR, MS spectra and elementary analysis methods. In this system GL reacts with H· and CH3CHOH radicals. CH3CHOH adds to the C-C double bond of GL, then the formed radicals disproportionate to the final products RP1 (olean 29-oic acid,3-hydroxy-11-oxo-12-ethoxyl-13-hydro-,(3β, 20β)-) and RP3. H· reacts with GL in the similar way. The rate constant of H· reacting with GL was obtained as kGL+H·=2.0x1010 dm3 mol-1 s-1. The rate constant of CH3CHOH reacting with GL was calculated as result of (1.2±0.1)x104 dm3 mol-1 s-1 by using steady state method and by using the numerical quadrature method with computer. G(-GL), G(H2 ), G(2,3-butanediol), G(CH3CHO) and G values of the radiolytic products of ethanolic solution with different GL concentration were measured. A material balance was obtained. Results show that the active site of a GL molecule is the C-C double bond. The radiation chemistry technique can be used to modify the structure of glycyrrhetinic acid