Bamberger rearrangement

The Bamberger rearrangement is the chemical reaction of N-phenylhydroxylamines with strong aqueous acid, which will rearrange to give 4-aminophenols.^[1][2] It is named for the German chemist Eugen Bamberger (1857–1932).

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N-Phenylhydroxylamines are typically synthesized from nitrobenzenes by reduction using rhodium^[3] or zinc^[4].

Reaction mechanism

The mechanism of the Bamberger rearrangement proceeds from the monoprotonation of N-phenylhydroxylamine 1. N-protonation 2 is favored, but unproductive. O-protonation 3 can form the nitrenium ion 4, which can react with nucleophiles (H₂O) to form the desired 4-aminophenol 5.^[5][6]

References

1. ^ Bamberger, E. (1894). "Uber das Phenylhydroxylamin" (Abstract). Chem. Ber. 27: 1347 & 1548–1557. doi:10.1002/cber.18940270276.
2. ^ Harman, R. E. (1955). "Chloro-p-benzoquinone". Organic Syntheses 35: 22. (also in the Collective Volume (1963) 4:148 (PDF)).
3. ^ Oxley, P. W.; Adger, B. M.; Sasse, M. J.; Forth, M. A. (1989). "N-Acetyl-N-phenylhydroxylamine via Catalytic Transfer Hydrogenation of Nitrobenzene using Hydrazine and Rhodium on Carbon". Organic Syntheses 67: 187. (also in the Collective Volume (1993) 8:16 (PDF)).
4. ^ Kamm, O. (1925). "β-Phenylhydroxylamine". Organic Syntheses 4: 57. (also in the Collective Volume (1941) 1:445 (PDF)).
5. ^ Sone, Takaaki; Hamamoto, Kazuhiro; Seiji, Yoshiyuki; Shinkai, Seiji; Manabe, Osamu (1981). "Kinetics and mechanisms of the Bamberger rearrangement. Part 4. Rearrangement of sterically hindered phenylhydroxylamines to 4-aminophenols in aqueous sulphuric acid solution". J. Chem. Soc. Perkin Trans. II: 1596–1598. doi:10.1039/P29810000298.
6. ^ George Kohnstam, W. Andrew Petch and D. Lyn H. Williams (1984). "Kinetic substituent and isotope effects in the acid-catalysed rearrangement of N-phenylhydroxylamines. Are nitrenium lons involved?". J. Chem. Soc. Perkin Trans. II: 423–427. doi:10.1039/P29840000423.

See also

• Hofmann-Martius rearrangement