Bamberger rearrangement

The Bamberger rearrangement is the chemical reaction of phenylhydroxylamines with strong aqueous acid, which will rearrange to give 4-aminophenols.[1] It is named for the German chemist Eugen Bamberger (1857–1932).[2][3]

The starting phenylhydroxylamines are typically synthesized by the transfer hydrogenation of nitrobenzenes using rhodium[4] or zinc[5] catalysts.

One application is in the synthesis of fenhexamid.

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.[6][7]

See also

References
  1. Harman, R. E. (1955). "Chloro-p-benzoquinone" (PDF). Organic Syntheses. 35: 22; Collected Volumes, vol. 4, p. 148.
  2. Bamberger, E. (1894). "Ueber die Reduction der Nitroverbindungen". Chemische Berichte. 27 (2): 1347–1350. doi:10.1002/cber.18940270229.
  3. Bamberger, E. (1894). "Ueber das Phenylhydroxylamin". Chemische Berichte. 27 (2): 1548–1557. doi:10.1002/cber.18940270276.
  4. Oxley, P. W.; Adger, B. M.; Sasse, M. J.; Forth1, M. A. (1989). "N-Acetyl-N-Phenylhydroxylamine Via Catalytic Transfer Hydrogenation of Nitrobenzene Using Hydrazine and Rhodium on Carbon". Organic Syntheses. 67: 187. doi:10.15227/orgsyn.067.0187.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  5. Kamm, O. (1925). "β-Phenylhydroxylamine". Organic Syntheses. 4: 57; Collected Volumes, vol. 1, p. 445. (download PDF)
  6. Sone, T.; Hamamoto, K.; Seiji, Y.; Shinkai, S.; Manabe, O. (1981). "Kinetics and Mechanisms of the Bamberger Rearrangement. Part 4. Rearrangement of Sterically Hindered Phenylhydroxylamines to 4-Aminophenols in Aqueous Sulphuric Acid Solution". Journal of the Chemical Society, Perkin Transactions 2. 1981 (2): 1596–1598. doi:10.1039/P29810000298.
  7. Kohnstam, G.; Petch, W. A.; Williams, D. L. H. (1984). "Kinetic Substituent and Isotope Effects in the Acid-Catalysed Rearrangement of N-Phenylhydroxylamines. Are Nitrenium Ions Involved?". Journal of the Chemical Society, Perkin Transactions 2. 1984 (3): 423–427. doi:10.1039/P29840000423.
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