Phenylhydroxylamine Explained

Phenylhydroxylamine is the organic compound with the formula C₆H₅NHOH. It is an intermediate in the redox-related pair C₆H₅NH₂ and C₆H₅NO. Phenylhydroxylamine should not be confused with its isomer α-phenylhydroxylamine or O-phenylhydroxylamine.

Preparation

This compound can be prepared by the reduction of nitrobenzene with zinc in the presence of NH₄Cl.^{[1] [2]}

Alternatively, it can be prepared by transfer hydrogenation of nitrobenzene using hydrazine as an H₂ source over a rhodium catalyst.^[3]

Reactions

Phenylhydroxylamine is unstable to heating, and in the presence of strong acids easily rearranges to 4-aminophenol via the Bamberger rearrangement. Oxidation of phenylhydroxylamine with dichromate gives nitrosobenzene.

Like other hydroxylamines it will react with aldehydes to form nitrones, illustrative is the condensation with benzaldehyde to form diphenylnitrone, a well-known 1,3-dipolar compound:^[4]

C₆H₅NHOH + C₆H₅CHO → C₆H₅N(O)=CHC₆H₅ + H₂O

Phenylhydroxylamine is attacked by NO⁺ sources to give cupferron:^[5]

C₆H₅NHOH + C₄H₉ONO + NH₃ → NH₄[C₆H₅N(O)NO] + C₄H₉OH

Notes and References

1. E. Bamberger “Ueber das Phenylhydroxylamin” Chemische Berichte, volume 27 1548-1557 (1894). E. Bamberger, "Ueber die Reduction der Nitroverbindungen" Chemische Berichte, volume 27 1347-1350 (1894) (first report)
2. Organic Syntheses. O. Kamm . Phenylhydroxylamine . 4 . 57. 1941 . 10.15227/orgsyn.004.0057.
3. Organic Syntheses. P. W. Oxley, B. M. Adger, M. J. Sasse, M. A. Forth . N-Acetyl-N-Phenylhydroxylamine via Catalytic Transfer Hydrogenation of Nitrobenzene using Hydrazine and Rhodium on Carbon . 67. 187. 1989. 10.15227/orgsyn.067.0187.
4. I. Brüning, R. Grashey, H. Hauck, R. Huisgen, H. Seidl . 2,3,5-Triphenylisoxazolidine . Organic Syntheses . 46 . 127. 1966 . 10.15227/orgsyn.046.0127.
5. 10.15227/orgsyn.004.0019. Cupferron. Organic Syntheses. 1925. 4. 19. C. S. Marvel.