3- Bromo-1,2,4-triazine 2-oxide, reaction with

Chloro(bromo)-3-amino-l,2,4-tiiazines 76 were obtained by the reaction of the 3-amino-1,2,4-triazine 2-oxides 42 with HCl or HBr (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). 

A number of 1,2,4-triazines such as the parent compound, the 3-methylthio, 3-methoxy and 3-amino-6-bromo derivatives add ammonia in liquid ammonia at -44 °C to the N(4) —C(5) bond to give adducts of type (lOl), as was shown by XH and 13CNMR spectroscopy. No reaction was observed with 3-methoxy-l,2,4-triazine 1-oxide (71), other 3-amino-l,2,4-triazines, or compounds with a substituent in the 5-position. As was shown using lsN-enriched ammonia, an equilibrium between the covalent addition products (101) and the open-chain isomers (102) does not occur (78RTC273). 

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