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40.1.1.4.1.5.4 Variation 4: Bamberger Rearrangement

DOI: 10.1055/sos-SD-040-00241

Purchase, R.; Sainsbury, M.Science of Synthesis, (200940391.

The reaction known as the Bamberger rearrangement involves the conversion of an N-phenylhydroxylamine into the corresponding 4-aminophenol through treatment with an aqueous mineral acid such as sulfuric acid.[‌145‌,‌146‌] A recent recommendation highlights phosphinic acid as a bifunctional reagent for a catalytic version of this rearrangement.[‌147‌] Prior to the commencement of the Bamberger rearrangement, N-protonation of the nitrogen atom of the hydroxylamine is favored, but as this is unproductive, less favored O-protonation is needed to facilitate a subsequent loss of water and the formation of a nitrenium ion. This last species then reacts with water to form the rearrangement product 4-aminophenol {Scheme 39; for an experimental procedure, see Science of Synthesis, Vol. 31b [AreneX (X=N, P) (Section 31.28.1.33.7)]}.[‌148‌‌150‌] Besides N-phenylhydroxylamine the rearrangement has been studied for a range of methylated derivatives as well as N-(2-chlorophenyl)hydroxylamine and, where appropriate, only the para-substituted aminophenol is detected. However, the addition of sodium halides (NaCl or NaBr) gives reduced yields and leads to the incorporation of a halogen rather than a hydroxy group. When sodium bromide is present the parent aniline may be obtained.[‌151‌] The Bamberger rearrangement of N,S-diarylsulfenamides to give 4-sulfanylanilines is discussed in Science of Synthesis, Vol. 31b [AreneX (X=N, P) (Section 31.28.1.33.131.28.1.33.1)].

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