Cyclization of substituted 3,4-diaminopyridines into 1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxide derivatives during the nitration process

Abstract

The nitration of pyridine-3,4-diamine, its N,N′-diacetyl derivative, and N 4 -alkylpyridine-3,4-diamines with excess nitric acid in concentrated sulfuric acid at 60°C was accompanied by cyclization with formation of the corresponding 1-substituted 4-nitro-1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxides. 4-Chloro-1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxide derivatives were obtained under analogous conditions from 2-chloropyridine-3,4-diamine, its N,N′-diacetyl derivative, and 2-chloro-N 4 -methylpyridine-3,4-diamine. The nitration of these compounds at 80-90°C gave 4-chloro-7-nitro-1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxides. III, R = MeCO; IV. R = H.We showed previously that nitration of 3,4-bis-(formylamino)pyridine (I) with a mixture of nitric and sulfuric acids leads to the formation of 4-nitro-1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxide (II) [1]. In the present work we performed a more detailed study on this reaction, using various substituted 3,4-diaminopyridine derivatives as substrates. We found that the reactions of 3,4-bis(acetylamino)pyridine (III) and 3,4-diaminopyridine (IV) with excess nitric acid (d = 1.5 g/cm 3 ) in concentrated sulfuric acid at 60°C [1] afforded the same product which decomposed with explosion on heating above 225°C. The presence of strong absorption bands at 1310, 1365, and 1540 cm -1 in the IR spectrum of this compound indicated that its molecule contains a nitro group and an N-oxide moiety. In the 1 H NMR spectrum of the product we observed signals in the aromatic region from two vicinal protons in the pyridine fragment as two doublets at δ 7.72 and 8.04 ppm ( 3 J = 6.0 Hz). The molecular weight of the product was M 181, according to the mass spectral data. Its elemental composition was C 5 H 3 N 5 O 3 . The above findings led us to assign the structure of 4-nitro-1H-[1,2,3]triazolo[4,5-c]pyridine 2-oxide (II) to the obtained compound. Tautomeric N-hydroxy structure IIa is also possible (Scheme 1). Analysis of the mass spectrum of compound II showed that its fragmentation under electron impact involved successive elimination of the nitro and hydroxy groups (Scheme 2), in keeping with the data of [2].The reduction of nitro compound II with iron in acetic acid under the conditions described in [3] gave 1H-[1,2,3]triazolo[4,5-c]pyridin-4-amine (V) whose IR and 1 H NMR spectra were identical to those of an authentic sample of V prepared from 4-chloro-1H-[1,2,3]triazolo[4,5-c]pyridine [4].The nitration of 3-amino-4-(methylamino)pyridine (VIa) and 3-amino-4-(cyclohexylamino)pyridine (VIb) followed the same pattern as in the nitration of

4H-[1,2,3]Triazolo[4,5-c][1,2,5]oxadiazole 5-oxide and Its Salts: Promising Multipurpose Energetic Materials

“…The assembly of the 1,2,3-triazole 2-oxide framework is usually achieved by cyclization of suitable nitramines. The pyrazine- , and pyridine-annulated 1,2,3-triazole 2-oxides were obtained by nitration of the corresponding ortho-diamines (Scheme ). The cyclization mechanism was not discussed in those studies.…”