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

CH3(C) over dotHOH, H-., e(solv)(-) are the main active radicals in the ethanol system irradiated by gamma-ray without the presence of oxygen. In this study, GL ethanolic solution saturated with nitrogen was gamma-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 CH3(C) over dotHOH radicals. CH3(C) over dotHOH 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-,(3 beta, 20 beta)-) and RP3. H-. reacts with GL in the similar way. The rate constant of H-. reacting with GL was obtained as k(GL+H.) =2.0 x 10(10) dm(3) mol(-1) s(-1). The rate constant of CH3(C) over dotHOH reacting with GL was calculated as result of (1.2 +/- 0.1) x 10(4) dm(3) mol(-1) s(-1) by using steady state method and by using the numerical quadrature method with computer. G(-GL), G(H-2), G(2,3-butanediol), G(CH3CHD) 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. (C) 1998 Elsevier Science Ltd. All rights reserved.Chemistry, PhysicalNuclear Science & TechnologyPhysics, Atomic, Molecular & ChemicalSCI(E)EI2ARTICLE2151-1605