Formation of Nitroso Oxides in the Photolysis of Aromatic Azides: Analysis of Products; Reaction Kinetics and Mechanism

The formation of nitroso oxides (ArNOO) IIa–IIc and IIf was observed in the flash photolysis of solutions of phenylazide (Ia), 4-methylphenylazide (Ib), 4-nitrophenylazide (Ic), and 4-bromophenylazide (If) in acetonitrile in the presence of oxygen, and the optical spectra of these nitroso oxides were obtained. The kinetics of generation (using IIa and IIc as examples) and decay of nitroso oxides IIa–IIc and IIf were studied. The activation parameters of the formation of IIa by the reaction of triplet phenylnitrene with molecular oxygen ( $$\log k_{O_2}$$ = (9.6±0.4)-(18±2)/2.303RT ( $$k_{O_2}$$ , 1 mol-1s-1;E a,kJ/mol)) and the unimolecular isomerization of IIa into dioxaziridine ( $$\log k_{iso}$$ = (9.0±0.8)-(56±)/2.303RT( $$k_{iso}$$ ,1 mol-1s-1;E a,kJ/mol)) were determined. The kinetics of formation of the molecular products of Ia photooxidation were studied using high-performance liquid chromatography. Nitrobenzene was the only stable reaction product (except for tars). A reaction scheme which is consistent with the experimental results was proposed for the photooxidation of Ia.