Amines aromatic, diazotizations, nitrosylsulfuric acid

The diazotization of heteroaromatic amines is basically analogous to that of aromatic amines. Among the five-membered systems the amino-azoles (pyrroles, diazoles, triazoles, tetrazoles, oxazoles, isooxazoles, thia-, selena-, and dithiazoles) have all been diazotized. In general, diazotization in dilute mineral acid is possible, but diazotization in concentrated sulfuric acid (nitrosylsulfuric acid, see Sec. 2.2) or in organic solvents using an ester of nitrous acid (ethyl or isopentyl nitrite) is often preferable. Amino derivatives of aromatic heterocycles without ring nitrogen (furan and thiophene) can also be diazotized. 

Diazotization is the reaction of a primary aromatic amine with a nitrosating agent, such as sodium nitrite or, to a lesser extent, with nitrosylsulfuric acid N0S04H, nitrous gases, or organic nitrites in an aqueous acidic solution at a temperature between 0 and 5°C, converting the amine to its diazonium salt ... 

The practical applicability and accuracy of the PSC method can be demonstrated by the examples of the thermal decomposition of aromatic diazonium salts in sulfuric acid, (important intermediates for the production of dyestuffs). The diazotation of both the amines was carried out by nitrosylsulfuric acid. 

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