Diazonium salts coupling with aliphatic compounds

Since A,A -disubstituted hydrazines are readily available from a variety of sources (see Volume I, Chapter 14), their dehydrogenation constitutes a widely applicable route to both aliphatic and aromatic azo compounds. Such oxidative procedures are of particular value in the aliphatic series because so many of the procedures applicable to aromatic compounds, such as the coupling with diazonium salts, have no counterpart. The oxidation reactions permit the formation not only of azoalkanes, but also of a host of azo compounds containing other functional groups, e.g., a-carbonyl azo compounds [83], a-nitrile azo compounds [84], azo derivatives of phosphoric acid [85], phenyl-phosphoric acid derivatives [86],... 

Amino-3-pyrazolin-5-ones (4-imino-3-pyrazolidinones) react with nitrous acid as do ordinary aromatic amines to form diazonium salts.426,984,1353 These then couple readily with aromatic amines,1017,1018,1060 phenols992,1323 and aliphatic compounds having active hydrogen atoms,428,1017 such as acetoacetic esters. The products are 4-azo-3-pyrazolin-5-ones (eq. 200). The diazonium salts also couple... 

When the ester (4) is coupled with diazonium salts from p-nitroaniline, 3,4,5-triiodoaniline, or 3,5-diiodo-p-anisidine (NH2 = 1), the unstable azo compounds (5) can be isolated as crystalline intermediates, which, however, pass into the hydrazones if warmed or treated with dilute alkali.333 334 In recent years,335 however, the isolation of various, relatively stable aliphatic arylazo compounds has been reported. 

In individual cases, also, aliphatic hydrocarbons can couple with diazonium salts e.g.9 Meyer338 obtained crystalline azo compounds from butadiene and its homologs. 

Primary aliphatic nitro compounds can be coupled with diazonium salts, for example, with diazotized metanilic acid, with the formation of an orange to red color. Secondary aliphatic nitro compounds do not react (4, 5). 

Primary aromatic amines (e.g. aniline) and secondary aliphatic-aromatic amines (e.g. N-methylaniline) usually form diazoamino compounds in coupling reactions with ben nediazonium salts. If the nucleophilic reactivity of the aryl residue is raised by sutetituents or fused rinp, as in m-toluidine and I - and 2-naphthylamine, aminoazo formation takes place (C-coupling). Hov ver, the possibility has also been noted that in aminoazo formation, initial attack of the diazonium ion may still be at the amine N-atom, but the a -complex might rearrange too rapidly to allow its identification... 

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