Radikalreaktionen an N‐Heterocyclen. IV. EPR‐Untersuchung des H‐Transfers zwischen aminischen Antioxidantien und Peroxy‐Radikalen

Abstract

Radical Reactions of N‐Heterocyclic Compounds. IV. ESR Investigation of H‐Transfer between Aminic Antioxydants and Peroxy Radicals The N‐radicals of pyrazole‐, imidazole‐ and indole‐derivatives were prepared in comparatively high concentrations at room temperature in benzene or toluene and their e.s.r. signals were interpreted. In H‐abstraction by free or to Co(III)‐coordinated tert.‐butylperoxy radicals from bifunctional heterocyclic substituted amines 2–9, 11 the following efficiency was ascertained: unhindered OH > aniline‐NH > heterocyclic‐NH, hindered OH‐groups. No radical attack on the exocyclic NH 2 ‐group took place. The splitting constant concerning the heterocyclic nitrogen of nitroxyl radicals 5a, 10a was in the range a N endo = 0.7 to 0.85 mT in contrast to exocyclic nitroxyls 6a, 8a, 9a, 11a possessing a N exo = 1.0 to 1.1 mT. The interruption of the π‐conjugation between the heterocyclic and the aniline groups by insertion of a CH 2 ‐group led to the decrease of the stability of the generated N‐radicals. In the case of anilinebenzimidazole 9 the Co(III)‐complexed endocyclic aminyl radical 9b was observed simultaneously with the exocyclic nitroxyl radical 9a .