Bamberger rearrangements

m Aromatic Rearrangement Elsevier New York, 1967, pp 182-190. (Review). 

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

Hughes JB, C Wang, K Yesland, A Richardson, R Bhadra, G Bennett, F Rudolph (1998) Bamberger rearrangement during TNT metabolism by Clostridium acetobutylicum. Environ Sci Technol 32 494-500. 

Schenzle A, H Lenke, JV Spain, H-J Knackmuss (1999) 3-hydroxylaminophenol mutase from Ralstonia eutropha JMP134 catalyzes a Bamberger rearrangement. J Bacteriol 181 1444-1450. 

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... 

Chemists at the Naval Air Warfare Center (NAWC), Weapons Division, China Lake, have reported many examples of polynitroarylamine synthesis via Bamberger rearrangements of arylnitramines. " " The nitration of 4-amino-2,5-dinitrotoluene (36) with a mixture of nitric acid and acetic anhydride in glacial acetic acid at room temperature yields the nitramine (37) which on treatment with neat sulfuric acid, provides 4-amino-2,3,5-trinitrotoluene (38) as the sole product. " Nitration of 3,4-dinitroaniline (39) with a solution of nitric acid in acetic anhydride yields A,3,4-trinitroaniline (40) acid-catalyzed rearrangement of the latter in neat sulfuric acid furnishes a 74 % yield of isomeric 2,3,4- (41) and 2,4,5- (42) trinitroanilines in a 4 6 ratio.Accordingly, a mixture of products can be expected when an unsymmetrical arylnitramine has two unsubstituted ortho positions available. 

More recently, Polish chemists have reported a synthesis of both aryl and aliphatic secondary nitramines by treating amine substrates with ethyl magnesium bromide followed by reaction with n-butyl nitrate (Equation 5.8). This method, which uses nonpolar solvents like hexane or benzene, has been used to synthesize aliphatic secondary nitramines, and At-nitro-A-methylanilines which otherwise undergo facile Bamberger rearrangement in the presence of acid. The direct nitration of At-unsubstituted arylamines usually requires the presence of an electron-withdrawing group. Reactions are retarded and yields are low for sterically hindered amines. 

Ridd and Yoshida explored the At-nitration of aromatic nitroanilines with nitronium hex-afluorophosphate in nitromethane with the aim of studying the Bamberger rearrangement (Chapter 4, Section 4.5). In was found that amines of low basicity essentially undergo complete A -substitution if the amine is in excess 2,4-dinitroaniline and 2,3-dinitroaniline form A, 2,4-trinitroaniline and At,2,3-trinitroaniline, respectively, as the sole products. More basic nitroanilines give mixtures of C-substituted, At-substituted and poly-substimted materials. The use of nitronium salts for At-nitration has been extensively reviewed. ... 

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. ... 

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