Diazotization amino-azoles

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. 

Side-chain bromination occurred when 5,6-dimethyl-2,l,3-benzothiadi-azole was treated with NBS (87CB1593). Both the 4- and the 4,7-dihaloge-nated compounds are readily made from the diazotized amino precursors (63JGU1714). 

If an aromatic o-diamine such as 1,2-diaminobenzene (2.24) is diazotized in dilute aqueous acid, the 2-aminobenzene-l-diazonium ion formed first (2.25) undergoes a rapid intramolecular N-azo coupling reaction to give 1,2,3-benzotri-azole (2.26). Both amino groups of 2.24 can, however, be diazotized in concentrated acid (Scheme 2-18), forming the bis-diazonium ion 2.27. 1,3- and 1,4-diamines must also be bisdiazotized in concentrated acids in order to avoid inter-molecular N- or C-coupling. 

Beil (Ref 1) this compd was not prepd in the free state but its prepn by Rathsburg (Ref 4) by oxidg amino tetr azole in ale sol ns with permanganate or persulfates is described in CA 17, 1147(1923). A diazotetrazole was prepd by diazotizing aminotetrazole The British abstract of the patent of Rathsburg (Ref 4) shows an azotetrazole with the structure ... 

Aminopyridines , aminopyridine-l-oxides, 3-aminoquinoline and 2-aminothi-azole are obviously diazotized by analogous processes. For 4-aminopyridine, 3-amino-quinoline and 2-aminothiazole it was shown that the monocation, protonated at the heterocyclic nitrogen, is nitrosated preferentially. 

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