Aliphatic diazonium salts rearrangement

No matter how produced, RNj are usually too unstable to be isolable, reacting presumably by the S l or 8 2 mechanism. Actually, the exact mechanisms are in doubt because the rate laws, stereochemistry, and products have proved difficult to interpret. If there are free carbocations they should give the same ratio of substimtion to ehmination to rearrangements, and so on, as carbocations generated in other 8 1 reactions, but they often do not. Hot carbocations (unsolvated and/or chemically activated) that can hold their configuration have been postulated, as have ion pairs, in which OH (or OAc, and so on, depending on how the diazonium ion is generated) is the counterion.One class of aliphatic diazonium salts of which several... 

Amino alcohols rearrange in the presence of nitrous acid to give ketones. The intermediate is an aliphatic diazonium salt, and the reactions are concerted and stereo-electronically controlled, with the migration of the group trans-anti to the departing nitrogen. 

When the electron-deficient atom is the nitrogen atom of nitrous acid or nitrosyl chloride, the products will depend on whether the amine is a primary or secondary amine. Primary aliphatic amines give rise to dia-zonium salts (RNj X) which readily decompose, sometimes with rearrangement. Aromatic diazonium salts (ArNj X ) are very important in aromatic transformations, and are discussed later. Secondary amines, on the other hand, give rise to nitrosamines... 

Primary aromatic amines (e.g., aniline) and secondary aliphatic-aromatic amines (e. g., 7V-methylaniline) usually form triazenes in coupling reactions with benzenedi-azonium salts. If the nucleophilicity of the aryl residue is increased by addition of substituents or fused rings, as in 3-methylaniline and 1- and 2-naphthylamine, aminoazo formation takes place (C-coupling). However, the possibility has also been noted that in aminoazo formation the initial attack of the diazonium ion may still be at the amine N-atom, but the aN-complex might rearrange too rapidly to allow its identification (Beranek and Vecera, 1970). 

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