C6H5NO was first prepared by Adolf von Baeyer by the reaction of diphenylmercury and nitrosylbromide:
[C6H5]2Hg + BrNO → C6H5NO + C6H5HgBr
The modern synthesis entails reduction of nitrobenzene to phenylhydroxylamine, C6H5NHOH, which is then oxidized by Na2Cr2O7. C6H5NO can also be prepared by oxidation of aniline using peroxymonosulfuric acid, Caro's acid. It is usually purified by steam distillation, where it comes over as a green liquid that solidifes to a colorless solid.
The monomer undergoes Diels-Alder reactions with dienes. Most characteristically nitrosobenzene condenses with "active" methylene and amine groups, e.g. of malonic esters. Condensation with anilines affords azobenzene derivatives (Mills reaction) and condensation with benzylcyanide PhCH2CN the imine PhC(CN)=NPh (The Ehrlich-Sachs Reaction).