4- Aminophenol, Bamberger rearrangement

Aryl hydroxylamines treated with acids rearrange to aminophenols. Although this reaction (known as the Bamberger rearrangement) is similar in appearance to... 

Recently, a Bamberger rearrangement in gas phase was reported. The rearrangement of A-phenylhydroxylamine (210, R, R, R = H) into 4-aminophenol (214, R , R, R = H) occurred on the acid sites of H-ZSM-5 zeolite. However, A-phenylhydroxylamine with K-10 montmoriUonite clay and its various cation-exchanged forms failed to rearrange into aminophenols ... 

It is now apparent that nitrenium ions occur in a variety of contexts including the so-called Bamberger rearrangement (i.e., acid-catalyzed isomerization of N-hydroxyaniline 14 to 4-aminophenol 15, Fig. 13.9), and the aforementioned catabolism of arylamines. The earlier workers, however, for the most part did not explicitly consider the possibility of such a species. Heller et al. were the first to present kinetic evidence for such an intermediate. Interestingly, they chose to represent it as the iminocyclohexadienyl cation (16), With the customary ellipsis of allowing a single valency structure to represent mesomeric systems. ... 

Aryl hydroxylamines treated with acids rearrange to aminophenols.255 Although this reaction (known as the Bamberger rearrangement) is similar in appearance to 1-32 to 1-36, the attack on the ring is not electrophilic but nucleophilic. The rearrangement is intermolecular, with the following mechanism ... 

There are a number of less frequently used methods for the preparation of phenols that are worthy of mention. The rearrangement of 2-hydroxy-benzaldehydes brought about by reaction with alkaline hydrogen peroxide and leading to dihydroxybenzenes (the Dakin reaction ) is discussed in Section 4.8. The acid-catalysed rearrangement of phenylhydroxy-lamines, known as the Bamberger rearrangement, is useful for the synthesis of 4-aminophenols (Scheme 4.3). 

Nitrobenzenes also undergo the Bamberger rearrangement, being the most convenient and economical method for the synthesis of p-aminophenols, particularly on an industrial scale . The process is normally carried out by catalytic hydrogenation under highly acidic conditions, where Af-phenylhydroxylamine has been shown to be the intermediate (equation 65). 

The Bamberger Rearrangement, 116 (R=OH, R =H)- p-Aminophenol The Bamberger rearrangement is summarized by the transformation of A(-phenylhydroxylamine (118) to /)-aminophenol (122), and its para-selective mechanism is shown in Scheme 18.19. 

Nishino and Spain (41) isolated a Pseudomonas pseudoalcaligenes that reduced nitrobenzene to hydroxylaminobenzene. Hydroxylaminobenzene was further converted to 2-aminophenol (Fig. 4B) and not to catechol and ammonium, as depicted in Figure 4A. This enzyme-mediated reaction parallels the chemical Bamberger rearrangement (55). 

Sone, T., Y. Tokuda, T. Sakai, S. ShinkaiandO.Manabe. 1981. Kinetics and mechanisms of the Bamberger rearrangement. Part 3. Rearrangement of phenylhydroxylamines top-aminophenols in aqueous sulphuric acid solution. J. Chem. Soc. Perkin. Trans. II 1981 298-302. 

BAMBERGER Phenylhydroxylamlne Rearrangement Rearrangement ot N-arylhydroxylamme to aminophenol... 

The decomposition of aryl azides in aqueous acid was known to produce para-aminophenols even before Bamberger began his work on the rearrangement of N-arylhydroxylamines. Bamberger recognized that N-arylhydroxyl-amines and aryl azides produced identical product mixtures when decomposed under the same conditions in aqueous acid, and he proposed a... 

The enzyme-mediated transformation of a hydroxylamino arene into an ortho-2Vcm-nophenol corresponds to a chemical rearrangement known as the Bamberger reaction (25), which generates the 4-aminophenol from hydroxylaminobenzene under acidic conditions. It is likely that this intermolecular rearrangement proceeds via an arylnitrene, which by the additional function of a hydroxylamino lyase can generate protocatechuate plus ammonia rather than 4-amino-3-hydroxybenzoate from 4-hydroxylaminobenzoate. 

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