Reactions of Nitrosoarenes with Nitrogen Monoxide (Nitric Oxide) and Nitrogen Dioxide: Formation of Diarylnitroxides.

Nitrosoarenes react with nitrogen monoxide (nitric oxide) at room temperature and in aprotic media to afford the corresponding diarylnitroxides by the intermediate formation of N-nitrosoarylnitroxides. However, these latter spin adducts, in contrast with literature reports, have never been detected by us. N-nitrosophenylnitroxide is obtained only in the oxidation of the ammonium salt of N-nitrosophenylhydroxylamine (cupferron) with trace amounts of lead tetraacetate. However, it evolves with time to diphenylnitroxide, as demonstrated by following the reaction course in the ESR cavity, On a macroscale level, the reaction between nitrosobenzene and nitric oxide leads to the formation of N-nitrosodiphenylamine, 4-nitro-N-nitrosodiphenylamine, 4-nitrodiphenylamine and 4,4'-dinitrodiphenylamine, in addition to diphenylnitroxide. Diarylnitroxides are also obtained when nitrosoarenes react with small amounts of nitrogen dioxide; the mechanism of this reaction is proposed and discussed. The structure of 4-nitro-N-nitrosodiphenylamine was determined by X-ray analysis.