OXIDATION OF DIPHENYLAMINE TO DIPHENYLNITROXIDE IN FAUJASITE ZEOLITE STUDIED BY ELECTRON-PARAMAGNETIC-RESONANCE

Oxidation of diphenylamine to diphenylnitroxide in neutral, K-exchange d, X-type faujasite zeolite (K-X) has been observed. The oxidation, as assessed by the intensity of the diphenylnitroxide electron paramagne tic resonance (EPR) spectrum, is favored in K-X in comparison with dip henylamine doped into X-type faujasite zeolites exchanged with Li, Na, Rb or Cs. Similar experiments with analine gave no detectable free ra dical product. The weakly allowed Delta m(x)=+/-2 half-field peak of a triplet state EPR spectrum with root D-2+3E(2)/g(e) beta(e)=1200+/-15 0 G is observed. The triplet spectrum is attributed to molecular oxyge n probably immobilized at a cation site in the zeolite. We proposed th at O-2 also binds to Lewis acid sites in the zeolite and hydrogen bond s to diphenylamine. This diphenylamine-O-2 complex rearranges to form diphenylnitroxide and the OH. radical. The mechanism implies that the OH. is somewhat stabilized by the zeolite. The temperature dependence of the diphenylnitroxide EPR spectrum indicates a restricted degree of molecular motion in the zeolite cages.