Determination by pulse radiolysis of the distribution of solubilizates between micellar and nonmicellar phases. Naphthalene and its reduced free radical in aqueous sodium dodecyl sulphate solutions

Abstract

Hydrated electrons, hydrogen atoms and hydroxyl radicals react with naphthalene with rate constants of (5.0 ± 0.46), (3.4 ± 0.6) and (5 ± 2)× 10⁹ mol^–1 dm³ s^–1, respectively. Hydrated electrons do not react with naphthalene when it is solubilized in SDS micelles. From the rate of disappearance of hydrated electrons in solutions containing various concentrations of naphthalene and SDS, the partition coefficient K, defined as the ratio of the concentration of naphthalene in the micelles to that in the aqueous phase, is 550 at 20°C. The naphthalene electron adduct protonates by reaction with water with a rate constant of 1.8 × 10⁵ s^–1. The radicals so-produced disappear in mutual reactions (alcohol radicals present) with a rate constant of (3.59 ± 0.13)× 10⁹ mol^–1 dm³ s^–1 independent of ionic strength. The radicals disappear more slowly in the presence of micelles. If it is assumed that this is because of rapid equilibration of the radicals between aqueous and micellar phases, with reaction occurring only in the aqueous phase, the partition coefficient for the naphthalene radicals can be calculated to be 25–30.