Hydrazo benzene Rearrangement

Exercise 23-36 Treatment of a mixture of 2,2 dimethylhydrazobenzene and hydrazo-benzene with acid gives only 4,4 -diaminobiphenyl and 4,4 -diamino-2,2 -dimethyl-biphenyl. What does this tell you about the mechanism of this type of rearrangement Write a mechanism for the rearrangement of hydrazobenzene that is in accord with the acid catalysis (the rate depends on the square of the H concentration) and the lack of mixing of groups as described above. 

This 4- 4-di-amino di-phenyl is benzidine which yields a very important group of dyes and which is formed by a molecular rearrangement from hydrazo benzene (p. 578). ... 

Triphenylamine is a strong base in liquid hydrogen chloride s, 44 hydrazo-benzene is protonated with subsequent rearrangement to give benzidine Tri-phenylphosphine is protonated in all three liquid hydrogen halides42,43 and can be reacted with boron halides... 

The similarity of the rearrangement of aromatic hydrazo-compounds to the exchange reactions with which they were compared above becomes more marked in those cases where the -positions of the two benzene nuclei are occupied. Then, as a rule, a diphenyl base is not produced, but the radicle which separates moves so that its nitrogen atom takes up the o-position with respect to the other nitrogen atom derivatives of o-aminodiphenylamine are thus produced, e.g. 

The ferrocene nucleus proved to be absolutely unable to undergo the rearrangements characteristic of the benzene ring, so the Claisen rearrangement of allyl ferrocenyl ether 291), the benzidine rearrangement of hydrazo-ferrocene 294-296), and the Sommelet rearrangement in the ferrocene series were all unsuccessful. 

Schmidt reaction (see review ). This reaction provides a method for the conversion of a carboxylic acid into an amine in one step. On reaction with hydrazoic acid in benzene in the presence of sulfuric acid, an acid is converted beyond the stage of the acyl azide (a) into the conjugate acid (b), which loses nitrogen more easily than the azide itself, with rearrangement to the isocyanate (d). The one-step... 

For the identification of simple aromatic hydrazo compounds paper chromatography can be used successfully on papers impregnated with dimethylformamide (cyclohexane as the mobile phase) or formamide (cyclohexane or benzene as the mobile phase). Hydrazo compounds can be spotted on the paper in the form of an alcoholic or ethereal solution in concentrations from 0.5 to 200 pg. Detection is carried out by spraying with p-dimethylaminobenzaldehyde (p. 349). Under the influence of the hydrochloric acid present in the reagent, a rearrangement to benzidines or semidines takes place, and they then react with the reagent, with the formation of orange spots (53). 

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