Semidine rearrangement

ZININ Benzidine (semidine) Rearrangement Acid catatyzed rearrangement of hydrazobenzenes to benzidines and sermdines... 

The next benzidine-type rearrangement studied by Shine and coworkers was the p-semidine rearrangement of 4-methoxyhydrazobenzene26. In this reaction, 4-methoxy hydrazobenzene rearranges in acidic medium to form p-semidine (4) and an o-semidine (5) see equation 12. 

Further complications of the reduction of aromatic nitro compounds are the possibility of complete reduction to aromatic amines (which may condense with nitroso compounds to give the desired azo compounds), reduction of azo compounds to the corresponding hydrazo compounds, followed by a benzidine (or semidine) rearrangement. It is clear, therefore, that the level of reducing agent used and other reaction conditions are quite critical. 

As shown by the above equation, the rearrangement involves rupture of the N-N bond and rotation of the radicals. Another method of stating the rearrangement (which makes no assumption as to the mechanism) is that it involves a migration of the amino to the para positions. When these positions are occupied by another group an incomplete arrangement, called semidine rearrangement, takes place. 

However, the benzidine and semidine rearrangements may occur in acid solution if the hydrazo stage is not further reduced sufficiently fast, and in such cases it is preferable to carry out the reduction in an alkaline medium. 

Other references related to the benzidine rearrangement and semidine rearrangement are cited in the literature. ... 

Also known as benzidine rearrangement or semidine rearrangement. Acid-promoted rearrangement of hydrazobenzene to 4,4-diaminobiphenyl (benzidine) and 2,4-diaminobiphenyl. 

Acid-catalyzed rearrangement of hydrazobenzenes to 4,4 -diaminobiphenyls. If the hydrazobenzene contains a para substituent, then the favored product is p-aminodiphenylamine (Semidine rearrangement) ... 

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