3-Amino -1,2,4-triazine 2- oxides, halogenation

The presence of an TV-oxide group activates the 1,2,4-triazine ring toward electrophilic attack, for instance, in halogenation reactions. Thus, 3-methoxy- and 3-amino(alkylamino)-1,2,4-triazine 1-oxides 16 react easily with chlorine or bromine to form the corresponding 6-halo-1,2,4-triazine 1-oxides 17 (77JOC3498, 78JOC2514). 

The halogenation of 3-methoxy- or 3-methyl(dimethyl)amino-1,2,4-triazine 2-oxides 18 was found to proceed in a similar manner, resulting in 6-halo-1,2,4-triazine 2-oxides 19 (77JOC3498, 78JOC2514). 

The treatment of 3-amino-1,2,4-triazine 2-oxides 1 or 3-amino-1,2,4-benzotri-azine 1-oxides 29 with nitrous acid proceeds as a diazotization reaction, but the diazo compounds have never been isolated owing to the easy displacement of the di-azo group with nucleophiles. Thus the reaction of 3-amino-1,2,4-triazine 2-oxides 1 with sodium nitrite in hydrochloric or hydrobromic acids leads to the corresponding 3-halogen-1,2,4-tiiazine 2-oxides 119 or 3-bromo-l,2,4-benzotriazine 1-oxides 120 (77JOC546, 82JOC3886). 

When 1-aminopyrazoles were subjected to halogenation, preferential oxidation of the amino group led to 5-halogeno-l, 2,3-triazines (88CPB3838) (see also Part 1, Section B,l,a). 

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