Monatshefte f€ ur Chemie 134, 501–508 (2003) DOI 10.1007/s00706-002-0570-z Nitroxide Radicals of some N-Phenyl Substituted 1,4- and 1,2-Phenylenediamines Marek Burian 1 , Ladislav Omelka 1; , Silvie Ondra ´s ˇova ´ 1 , and Vlasta Brezova ´ 2 1 Faculty of Chemistry, Technical University of Brno, CZ-612 00 Brno, Czech Republic 2 Faculty of Chemistry, Slovak Technical University, SK-81237 Bratislava, Slovak Republic Received September 30, 2002; accepted October 4, 2002 Published online March 13, 2003 # Springer-Verlag 2003 Summary. Several N-phenyl substituted 1,4- and 1,2-phenylenediamines were oxidized using RO 2 radicals and 3-chloroperbenzoic acid. EPR spectroscopy confirmed the generation of nitroxide radicals originating from the oxidation of the bridging -NH-group. No radical products suggesting the simul- taneous reaction with the NH 2 -group were observed. Only in the case of 1,4-phenylenediamine, a low concentration of nitroxide radical H–NO –C 6 H 4 –NH 2 was obtained. In o-aminodiphenylnitroxide the steric effect of the NH 2 -group causes a partially asymmetrical spin density distribution in both phenyl rings. Keywords. 1,4-Phenylenediamine; 1,2-Phenylenediamine; Nitroxide radicals; EPR. Introduction One electron chemical or electrochemical oxidation of 1,4-phenylenediamine and its N-phenyl derivative leading to the formation of the corresponding primary cation radicals has been frequently reported in the last decades [1–4]. The analo- gous oxidation of 1,2-phenylenediamine and its N-phenyl derivative affords only the secondary radical products, which have been attributed to the dihydrophenazi- nium cation radicals [4]. On the other side, the tendency towards the formation of nitroxide radicals by oxidation with RO 2 radicals and peroxy acids is a char- acteristic feature of many primary and secondary amines. The stable nitroxide radicals R 1 –NO–R 2 are formed from secondary amines R 1 –NH–R 2 , when the -NH- bridge is situated between two aromatic substituents. Especially, the substi- tuted diphenylnitroxides (R 1 ¼ R 2 ¼ substituted phenyl) have been studied inten- sively since the early sixties, as evidenced by the numerous EPR data in catalogues [5].      Corresponding author. E-mail: omelka@fch.vutbr.cz