γ-radiolysis of N2O-saturated aqueous glycerol solutions: product yields and free radical mechanism

The yields of products, glyceraldehyde (I), dihydroxyacetone (II), 3-hydroxypropanal (III), hydroxyacetone (IV), 2,3-bis(hydroxymethyl)-1,4-butandial (V), 1,2-bis(glycolyl)ethane (VI), 3-(glycolyl)-2-(hydroxymethyl)-propanal (VII), 2-(hydroxymethyl)-3,4,5-trihydroxy pentanal (VIII), 3-deoxyhexulose (IX), hexitol (X), 2-(hydroxymethyl)-pentitol (XI) and trimer (XII) formed during the γ-radiolysis of N2O-saturated aqueous solutions containing glycerol have been quantitatively determined by gas liquid chromatography. It is evident that four radicals generated from the initial substrate participate in disproportionation, dimerisation and hydrogen abstraction reactions leading to these products. These radicals comprise two hydroxyalkyl radicals and their corresponding carbonyl-conjugated product radicals formed after water elimination. The initial radicals lead directly to products I, II, X and XI and the water-eliminated radicals to products III, IV, VI and VII. Products VIII and IX result from combination of the hydroxy-alkyl and carbonyl-conjugated radicals. Dimerisation and disproportionation of the hydroxy-alkyl radicals are favoured at higher dose rates while there is a reduction in water elimination and the products resulting. Hydrogen abstraction from glycerol by carbonyl-conjugated radicals in a chain mechanism is responsible for the large increase in yields of products III and IV when the initial substrate concentration is increased. (author)