BAMBERGER Phenylhydroxylamine

BAMBERGER Phenylhydroxylamine Rearrangement Rearrangement of N-arylhydroxylamine to aminoptienol. 

The single-step -duoroaruline [31-40-4] process based on duorodeoxygenation of nitrobenzene (via in situ generation of /V-phenylhydroxyl amine) in anhydrous hydrogen duoride (94—96) has not been commercialized primarily due to concurrent formation of aniline, as well as limited catalyst life. The potential attractiveness of this approach is evidenced by numerous patents (97—101). Concurrent interest has been shown in the two-step process based on /V-phenylhydroxylamine (HF-Bamberger reaction) (102—104). 

The reactions of arenediazonium ions with 7V-alkyl- or 7V-arylhydroxylamines were investigated by Bamberger (1920b, and earlier papers). Mitsuhashi et al. (1965) showed that the l,3-diaryl-3-hydroxytriazenes are tautomeric with 1,3-diaryltriazene-3-oxides (Scheme 6-16). Oxidation of 1,3-diaryltriazenes with peroxybenzoic acid in ether yields the same product as that from diazonium salts and TV-arylhydroxyl-amine. The infrared spectrum of the product obtained by coupling diazotized relabeled aniline with A/-phenylhydroxylamine indicates that the diaryltriazene-oxide is the preponderant tautomer. 

TV-Ethyl substitution had very little effect on the measured rate constant, whereas a 4-methyl substituent increased the rate constant by a factor of ca 100. In this case the initial product (identified by Bamberger) is the iminocyclohexadienol 39, which slowly hydrolyses to the quinone 40. These substituent effects suggest that in the transition state the developing positive change is located mostly at the 4-position (stabilized by the 4-Me substituent) and very little on the nitrogen atom (no stabilization by a TV-Et substituent), so that the intermediate is more properly described by the iminium ion. This is supported by an earlier observation46 that whilst full incorporation of 180 from the solvent H2180 occurs in the product, there is no detectable 180 incorporation into the reactant phenylhydroxylamine. 

Montmorillonite KIO clay and its various cation-exchanged forms have been found to promote the formation of an unexpected product, p-nitrosodiphenylamine, from iV-phenylhydroxylamine, rather than the typical Bamberger products. A Bamberger rearrangement has been shown to occur during the metabolism of 2,4,6-trinitrotoluene... 

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 ... 

Although phenylhydroxylamine may be prepared by catalytic reduction,1 by the oxidation of aniline,2 and by electrolytic reduction of nitrobenzene,3 the most feasible method is still based upon the original zinc reduction method of Bamberger 4 and of Wohl.5 Various solvents and catalysts have been used in this reduction, and copper-coated and amalgamated zinc, as well as aluminium amalgam,6 have been substituted for zinc dust. The method herein recommended is essentially one previously described 7 but it has been found 8 that cooling is not an essential, as claimed in the patents. The preparation of the oxalate is also a more recent contribution.9... 

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). 

N,a-DiphenyInitrone was first obtained by Bamberger from N-phenylhydroxylamine and benzaldehyde. The procedure described above is analogous to that of Wheeler and Gore. ... 

Zinc and Weak Alkali The mechanism of reduction with zinc and strongly alkaline solutions leads to the formation of azoxybenzene as the first stable product in the reduction of nitrobenzene. Bamberger has shown that, when faintly alkaline systems are employed, the principal initial stable product of reduction is N-phenylhydroxylamine. The systems —zinc + calcium chloride and zinc + ammonium chloride—are not neutral but quite alkaline to phenolphthalein. In the preparation of N-phenylhy-droxylamine from nitrobenzene by means of zinc dust and aqueous calcium chloride, the reduction liquid has a pH Between 10.5 and 11.7, which corresponds to the alkalinity of 0.01 N alkali. When NH4CI is substituted for CaCb in the reducing system, the pH is between 8 and 9. 

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. 

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. 

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