Pyrazoles. XII. Preparation of 3(5)-nitropyrazoles by thermal rearrangement of N-nitropyrazoles

Abstract

3(5)-Nitropyrazoles, such as 3,5-dmitropyrazole (2f), can be readily synthesized by thermal rearrangement of A-nitropyrazoles. In turn, 3 (5 ),4-dinitropyrazoles are obtained by further nitration of some 3(5)-nitropyrazoles.The direct nitration of pyrazole, using nitric acid or mixtures of nitric acid and sulfuric acid,4,5 leads to substitution in the 4 position, in line with the behavior of other electrophilic reagents. Moreover, no further nitration of 4-nitropyrazoles has been reported in the literature. Reports on formation of 3-nitropyrazoIes either concern compounds synthesized by other methods such as ring closure reactions4,6 or by nitration of 1,4disubstituted pyrazo!es,7,8a,b neither of which appear to be general methods for the synthesis of 3-nitropyrazoles. It is worth notice that in the latter case further nitration to 3,5-dinitropyrazoles can occur.7 Recently three different groups of workers independently reported on the synthesis of the unsubstituted 3(5)-nitropyrazole (2a). Bagal, et al.,e obtained 2a via diazotation of 3(5)-aminopyrazole, and Birkofer10 substituted the trimethylsilyl group in 3(5)-trimethylsilylpyrazole by a nitroso group, which

Direct nitration of five membered heterocycles

“…Pyrazoles Acetyl nitrate has been employed to nitrate pyrazoles at one of the nitrogen atoms and subsequent rearrangement at 140 ºC has been observed to give 3-or 5-nitropyrazoles, sometimes as a mixture. 40 Pyrazole (12) on treatment with our nitrating system following method B gave a 41% yield of the 3,4-dinitrated derivative (13) while N-methylpyrazole under the same reaction condition gave a 65% yield of the 3-nitro product (13). This orientation was confirmed by nOe experiments (Scheme 5) ( Table 3).…”

Energetic Nitrate, Perchlorate, Azide and Azolate Salts of Hexamethylenetetramine

“…3,5-Dinitropyrazole, [42] 4,5-dinitroimidazole, [43] 3,5-dinitro-1,2,4-triazolate [25] 5-nitrotetrazole [44] and silver 3,5-dinitro-1,2,4-triazolate [26] were synthesized according to literature procedures.…”

Theoretical studies on the structure and detonation properties of amino-, methyl-, and nitro-substituted 3,4,5-trinitro-1H-pyrazoles

“…Hüttel and Büchele [6] have synthesized N-nitropyrazole and its substituted derivatives. Polynitropyrazoles in which NO 2 groups attached to ring carbon atoms are known and the majority of them are synthesized by the thermal rearrangement of N-nitropyrazole derivatives [7][8][9][10][11][12][13][14][15]. The hydrogen atom on the 1-position is known to be highly labile or acidic in nature.…”