Investigations of reactions of selected azaarenes with radicals in water. 2. Chlorine and bromine radicals

The halogen radicals that react with azaarenes are produced by the photooxidation of halogenide anions with hydroxyl and sulfate radicals and exist as complexes of the radical and the respective halogenide anion in the aqueous phase. The main reaction products of the reactions are identified, and in the case of the bromine radicals, the second order rate constants are determined. Oxidation takes place according to the different redox potentials of the two reactants and is especially observed for chlorine radicals. A typical product spectrum comparable with that in reactions with hydroxyl and sulfate radicals has been found. The formation of some oxidation products in reactions of bromine radicals is in contradistinction to the oxidation potentials of the azaarenes and can be understood only by the reaction of their excited states. The halogenation is the main reaction of the azaarenes. Halogenation products of both, the benzene and the pyridine/diazine rings, have been found. The halogenation of the pyridine/diazine ring again requires the reaction of excited states. The majority of derivatives is halogenated in substitution reactions, but in the reaction of benzo[h]quinoline, addition is also observed. The resonance energy per electron is responsible for the change in the halogenation mechanism from substitution to addition.