Routes to Alkanediazonium Ions

Another important diazotization method is the use of glacial acid for the nitrosation of alkylamines, because of the formation of an ion pair 7.12 between the acetate ion and the diazonium ion. In water the influence of acetate ion is small. 

Maltz et al. (1971) introduced disodium pentacyano(nitrosyl)ferrate (sodium nitro-prusside, 7.7) as nitrosating reagent. This compound has the advantage that it is effective for nitrosations and diazotizations at pH 9-11. This allows the synthesis of alkyldiazenolates (7.9) without deamination by-products, as well as dediazoniations in neutral or weakly alkaline solutions. 

Nitrosation in aprotic solvents is possible, either with an alkyl nitrite in the presence of an equivalent of acid, or with nitrosyl chloride (Bakke, 1967), or with dinitrogen tetroxide (Wudl and Lee, 1971 Barton and Narang, 1977). Doyle et al. (1978) generated nitrosyl chloride in situ by the reaction of titanium tetrachloride 

In all these cases, the system is not completely free of water, because in all reactions generating diazonium ions from amines and any nitrosating reagent, one equivalent of water is produced. 

This problem is not encountered in the thermal rearrangement of N-nitroso amides (7.10, R = alkyl). Aliphatic N-nitroso amides were first studied by von Pechmann (1898 a). The rearrangement was originally investigated and elucidated for aromatic A-nitroso amides by Huisgen and others (see summary by Zollinger, 1994, Sect. 6.7.5). 

---

The most important routes to alkanediazonium ions are shown in Scheme 7-3, which is an extended version of a scheme published by Kirmse (1976, 1979). 

Before we discuss those mechanisms in detail (Sects. 7.3-7.6), we will review in the following section the various methods developed for the formation of alkanediazo-nium ions, because most of these routes contributed substantially to our understanding of the reaction steps following formation of the alkanediazonium ion. 

---