Aliphatic diazonium salts synthesis

Until recently no satisfactory procedure for the direct conversion of a primary aliphatic amine into an alkyl halide was available. This contrasts sharply with the ready conversion of primary aromatic amines into aryl halides via the diazonium salt (Section 6.7, p.922). However a useful method has not been discovered which is not only applicable to the synthesis of simple alkyl and aralkyl chlorides, bromides, iodides and fluorides, but could clearly be of value when it is required to replace an amino group in a naturally occurring amine by a halogen.92... 

A few examples of the reduction of aliphatic diazo compounds to hydrazines exist," but this is not a generally applicable method for the synthesis of alkylhydrazines. On the other hand, arylhydrazines can be prepared by reduction of aromatic diazonium salts.The most commonly used reagents for this conversion are sulfur dioxide (or sodium sulfite) and tin(II) chloride, these being used to reduce arenediazo-nium chlorides in aqueous solution. Several other reagents, including sodium amalgam and triphenylphosphine, have been used for specific reductions of this type. Arenediazonium tetrafluoro-borates have been reduced to the correspwnding hydrazinium salts (3) by benzeneselenol in dichloro-... 

The diazo transfer method 6 is also used for aromatic diazonium salts (see Zollinger, 1994, Sect. 2.6). Diazo transfer is, however, more relevant for the synthesis of aliphatic diazo compounds. In addition to the schematic presentation in Table 2-1, the transfer of N2 from the azide to the carbanion may be combined with the dissociation of certain groups attached to the anionic carbon (see Sects. 2.6 and 2.7). 

One of the most versatile classes of intermediates for the synthesis of other aromatic compounds are the aryl diazonium ions formed by diazotization of anilines in acidic solution." Unlike aliphatic diazonium ions, which decompose very rapidly to molecular nitrogen and the aliphatic carbonium ion, aryl diazonium ions have sufficient stability to permit controlled reactions, and in some cases salts of the diazonium ions can be isolated. The usual procedure for nitrosation involves reaction with nitrous acid in aqueous solution ... 

Two common synthetic routes have been used for the synthesis of tetrazoles (Scheme 5). First, the phenyl sulfonyUiydrazones (23) react with the freshly prepared diazonium salts (24) in pyridine under cooled conditions to produce the desired tetrazole products (25) with moderate to good yields [25]. The hydrazones (23) can be synthesized easily from the aliphatic or aromatic aldehydes (21) and the diazonium salts from the corresponding amines with NaNOa under acidic conditions. The second method has been used to prepare the thiophene conjugated tetrazoles (29) which exhibit longer photoactivation wavelength [26-28]. 

Diazonium salts (Sections 20.6A, 20.6B, 20.7, and 20.8) Salts synthesized from the reaction of primary amines with nitrous acid. Diazonium salts have the structure [R-N N]+ X. Diazonium salts of primary aliphatic amines are unstable and decompose rapidly those from primary aromatic amines decompose slowly when cold, and are useful in the synthesis of substituted aromatics and azo compounds. 

---