Rate constants for the abstraction of hydrogen from alkyl aromatics by alkoxyl radicals and excited state ketones: relevance to the photodegradation of the water-soluble fraction of crude oil

The rate constants for hydrogen atom abstraction from a series of alkyl benzenes have been measured using laser flash photolysis techniques. Cumyloxyl radicals and excited-state triplet benzophenone were employed as hydrogen abstractors following irradiation of dicumyl peroxide and benzophenone as ground state precursors. The rate constants are quite similar for the two hydrogen abstractors, and show a modest dependence on the alkyl side chain, which can be accounted for largely on statistical grounds and the stabilities of the benzyl radicals formed. Since the alkyl benzenes chosen here make up part of the water-soluble fraction of crude oil, the results of this investigation are discussed in relation to the overall mechanism for the photodegradation of oils in seawater.