Hindered amine mechanisms. III: Investigations using isotopic labelling

The literature "peroxide" mechanism and a proposed mechanism for the regeneration of hindered amine nitroxyls have been tested with isotopically labelled reactants. Both mechanisms deal with the reaction of alkylperoxy radicals with N-alkyloxy hindered amines, which are products of the reaction of nitroxyl radicals with alkyl radicals. The "peroxide" mechanism predicts the regeneration of nitroxyl and formation of dialkyl peroxide. The proposed mechanism predicts the regeneration of nitroxyl and formation of ketones, alcohols and carboxylic acids, depending on the oxidizing substrate. The results confirm the new proposed regeneration mechanism, but not the previous "peroxide" mechanism. The features of the confirmed mechanism are NOR + R'OO - > NO + R = O + R'OH. This basic mechanism is also proposed for acylperoxy radicals NOR + R'C(O)OO - > NO + R = O + R'COOH. 8 ref.--AA