Rearrangements involving diazonium salts

This and related syntheses involving diazonium salts were reviewed by Biffin et al. (1971, p. 148). The hypothesis that the triazene occurs as intermediate in Scheme 6-14 has been corroborated by the experiments of Clusius and Hiirzeler (1954) using benzenediazonium salts labeled with 15N at the a- or Impositions. Ammonia adds exclusively at the p-nitrogen no rearrangements were observed. 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

An old reaction patented by Lange [19] involves the coupling of naphthyl-diazonium salts with sodium sulfite to yield azonaphthalene. A more recent study of this reaction indicates that the first step of the reaction is the formation of an aryl-iyn-diazosulfonate which couples with another molecule of a diazonium salt and by a multicentered rearrangement ultimately affords an azo compound [20, 21]. The reaction is represented in Eq. (7). The validity of... 

The coupling of the betaines (352) with diazonium salts, however, may take an unusual course in that arylation results. The reaction may be rationalized by the formation of a covalent intermediate (353) which subsequently suffers a pericyclic rearrangement involving expulsion of nitrogen (81H(15)1349). 

Another type of pyridazine synthesis from pyrones involves coupling of the latter with diazonium salts and rearrangement of the intermediate hydrazones with either aqueous base or acid to pyrid-azinones. Thus, 4-hydroxy 6-methyl-2-pyrone (triacetic lactone) (44)... 

A simpler and more certain route to aryl azides is treatment of a diazonium salt with hydrazoic acid. This was long supposed to be an 5 1 process but tracer studies have revealed a much more complicated sequence of reactions involving rearrangements If the nitro-... 

If formed, the triazene can often be converted into the amino azo compound by even gentle warming with dilute acid this conversion is smoother if the triazene is warmed with the amine used for coupling and a small amount of its hydrochloride.368 The acid-catalysed rearrangement of triazenes involves intermediate reformation of the diazonium salt and the amine.369,370 So, if rearrangement of a triazene is carried out in the presence of a different, more readily coupling amine, the diazonium component reacts preferentially with the latter e.g., A,ALdimethyl-/ -(phenylazo)aniline is obtained from diazoaminobenzene and N,N-di-methylaniline.368... 

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