ONE-ELECTRON OXIDATION OF ALKYLBENZENES IN ACETONITRILE BY PHOTOCHEMICALLY PRODUCED NO3. - EVIDENCE FOR AN INNER-SPHERE MECHANISM

The reaction between NO3. and polyalkylbenzenes was studied using 308-nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the alkylbenzenes in acetonitrile solution. For all benzenes, with the exception of monoalkylbenzenes and o- and m-xylene, the reaction with NO3. was found to yield the corresponding radical cations and to proceed in an apparently straightforward bimolecular manner. For monoalkylbenzenes and o- and m-xylene, radicals were seen which are derived from the parents by formal loss of H. from the side chain of the aromatic. This reaction proceeds via a complex between the aromatic and NO3. with the decomposition of the complex being rate determining at higher concentrations of aromatic (rate constants for decomposition between 6 x 10(5) and 4 x 10(7) s-1). In the complex, electron transfer from the aromatic to NO3. is suggested to be concerted with deprotonation of the incipient radical cation. Formation of a complex between NO3. and aromatic is likely even in those cases where radical cations are observed, with the assumption that in these cases the complex decomposition rate is greater-than-or-equal-to 6 x 10(7) s-1.