HO₂ ELIMINATION FROM α‐HYDROXYALKYLPEROXYL RADICALS IN AQUEOUS SOLUTION

Abstract

Abstract— In aqueous solutions α‐hydroxyalkylperoxyl radicals undergo a spontaneous and a base catalysed HO 2 elimination. From kinetic deuterium isotope effects, temperature dependence, and the influence of solvent polarity it was concluded that the spontaneous reaction occurs via an HO 2 elimination followed by the dissociation of the latter into H + and O 2 ‐ . The rate constant of the spontaneous HO 2 elimination increases with increasing methyl substitution in α‐position ( k (CH 2 (OH)O 2 ) < 10s ‐1 k (CH 3 CH(OH)O 2 ) = 52s ‐1 k ((CH 3 ) 2 C(OH)O 2 ) = 665 s ‐1 ). The OH ‐ catalysed reaction is somewhat below diffusion controlled. The mixture of peroxyl radicals derived from polyhydric alcohols eliminate HO 2 at two different rates. Possible reasons for this behaviour are discussed. The mixture of the six peroxyl radicals derived from d ‐glucose are observed to eliminate HO 2 with at least three different rates. The fastest rate is attributed to the HO 2 elimination from the peroxyl radical at C‐l ( k > 7000s ‐1 ). Because of the HO 2 eliminations the peroxyl radicals derived from d ‐glucose do not undergo a chain reaction in contrast to peroxyl radicals not containing an α‐OH group. In competition with the first order elimination reactions the α‐hydroxylalkylperoxyl radicals undergo a bimolecular decay. These reactions are briefly discussed.