H-1- and C-13-NMR investigations on sigma-adduct formation of 1,2,4-triazine 4-oxides and 3-chloro-6-phenyl-1,2,4-triazine with liquid ammonia and alkylamines

H-1- and C-13-NMR spectra of the sigma -adducts formed between 6-phenyl-1,2 ,4-triazine 4-oxide (la), 3-ethyl-6-phenyl-1,2,4-triazine 4-oxide (Ib) and liquid ammonia, methylamine or dimethylamine are described, together with H -1 NMR spectra of 3-chloro-6-phenyl-1,2,4-triazine (7) in liquid ammonia. T he results of the NMR study have shown that the carbon C-5 in 1a-b and 7 is the preferred site for nucleophilic attack by liquid ammonia and alkylamin es at low temperatures (from -75 degrees to -20 degreesC). The sigma -adduc t (5e) formed between la and dimethylamine at -75 degreesC on heating to -2 0 degreesC irreversibly converts to open-chain product (3a), via intermedia ry C-3 sigma -adduct (6). The amination of 7 into 3-amino-6-phenyl-1,2,4-tr iazine (10) occurs via S-N(AE) mechanism involving the isomerisation of the C-5 sigma -adduct (8) into the C-3 sigma -adduct (9) as confirmed by a N-1 5 study with labeled liquid ammonia.