Nitro triazoles structure

Most 3-hydroxy-l,2,4-triazoles exist in the hydroxy form 123 [76AHC(S1), pp. 377,389 84CHEC-I(5)733]. An exception is the 5-nitro derivative, which in the solid state possesses the 0x0 structure 124 (97JPC3605). 

A nitro group in the 4-position markedly increases the instability of the isoxazole ring in alkaline medium. This effect is clearly demonstrated by 3,5-dime thy 1-4-nitroisoxazole. Whereas 3,5-dimethyl-isoxazole is not affected by alkali, its 4-nitro-derivative (134) is cleaved by 2% sodium hydroxide. The structure of the product was proved by its conversion into a triazole (135) with phenyl diazonium chloride, according to the original authors. ... 

Similarly, the structure of 5-nitro-2,4-dihydro-377-l,2,4-triazol-3-one (NTO) 6 has been scrutinized using molecular orbital calculations using the 6-31+G and 6-311+G basis sets. These calculations examined the various tautomers of NTO and give an insight into the molecular mechanisms involved in its explosive decomposition <1996JA8048>. 

Analyses of the structures and properties of a large number of energetic materials reveal that a combination of amino and nitro groups in a molecule often leads to better thermal stability, lower sensitivity to shock and impact, and increased explosive performance because of an increase in crystal density. Such observations are attributed to both intermolecular and intramolecular hydrogen bonding interactions between adjacent amino and nitro groups. Some modern triazole-based explosives have been designed and synthesized with this in mind. 

Intramolecular [3+2] dipolar cycloadditions have also been employed as a post-Ugi transformation to generate heterobicyclic structures, namely fused isoxazolines [130], isoxazoles [130] and triazoles [131] (Fig. 31). Isoxazoles were obtained through intramolecular nitrile oxide cycloaddition. The precursor of the nitrile oxide (a nitro group) was introduced into the carboxylic component, while a triple bond was positioned in the starting amine. Treatment of 152 with POCl3/Et3N gave the intermediate nitrile oxide, which spontaneously cyclized to isoxazoles 153. 

PATO has also been synthesized by a Chinese team [68] by the condensation of tetryl with 3-amino-l,2,4-triazole and their data on its thermal stability is in agreement with American investigators [69]. Chinese researchers have also reported two nitro derivatives of PATO with the following structures based on IR and NMR [68]. 

Nitro-l,2,4-triazol-5-one (NTO) [Structure (2.49)] or oxynitrotriazole (ONTA)has been reported as another IHE coupled with better performance [152-157]. Almost all aspects of NTO-synthesis, structural aspects, chemical and explosive properties including thermal behavior have been investigated [158-161]. NTO exists in two polymorphic forms, that is, -form and P-form. It has been established that a-NTO is the stable and dominating form whereas P-NTO is only found in the product on recrystallization of NTO from a methanol or ethanol/methylene chloride mixture [162]. French researchers have recently reported its evaluation as an explosive for warhead filling without a binder and also as a PBX [155]. Further, synthesis of NTO is easy consisting of only two steps (Scheme 2.9) and uses inexpensive starting materials. 

The benzodiazepines are widely used sedative-hypnotics. All of the structures shown in Figure 22-2 are 1,4-benzodiazepines, and most contain a carboxamide group in the 7-membered heterocyclic ring structure. A substituent in the 7 position, such as a halogen or a nitro group, is required for sedative-hypnotic activity. The structures of triazolam and alprazolam include the addition of a triazole ring at the 1,2-position. 

Under mild conditions 2-(4-nitrophenyl)-1,2,3-triazole forms the dinitro derivative, and under harsh conditions it forms the trinitro derivative. In turn, 2-(4-nitrophenyl)-4-nitro-l,2,3-triazole, which was initially assigned the structure of 2-(2-nitrophenyl)-l,2,3-triazole [245], also forms 2-(2,4-dinitrophenyl)-4-ni-tro-1,2,3-triazole during further nitration [244, 246], At the same time... 

It is not possible to introduce a nitro group into the 1,2,4-triazole ring by the action of the sulfuric-nitric acid mixture because of the disactivation of the cycle by two pyridine nitrogen atoms furthermore, their disactivation effect is aggravated by the heterocycle protonation in the acid medium. The only exception is the nitration of l,2,4-triazolon-5 [250-264], This is probably due to the specific electronic structure of the substrate (the azolone form) (Scheme 32). 

It is interesting to note that the bond lengths C-S in two structurally related compounds l-(mesityl-2-sulfonyl)-3-nitro-l,2,4-triazole [120] and l-(mesitylsulfonyl)-4-nitroimidazole [121] are similar (1.761 and 1.758 A), while the S-N bond in imidazole analog is significantly shorter (1.736 and 1.708 A). 

The molecule of 3-nitro-3 -chloro-l//-bi-l,2,4triazole-5,l -yl has transoid conformation, where the substituents (chlorine and nitro group) are most distant from each other and the rotation angle of two triazole rings is 5°, while the nitro group is rotated by 4° with respect to the triazole cycle [156], Molecular and crystalline structures of 1-methyl-3,5-dinitro-l, , 4-triazole [153] and l-(mesityl-2-sulfonyl)-3-nitro-l,2,4-triazole were determined [119]. 

The structure of 3,5-disubstituted 1,2,4-triazole, including 5-amino-3-nitro-l,... 

Pevzner et al. widely used NMR spectroscopy in their structural investigations of diverse 1,2,4-triazole nitro derivatives [566-581], In the series of 5-substituted l-methyl-3-nitro-1,2,4-triazoles the correlation between the A-methyl group proton chemical shifts induced by 5-substituents (A8) and the substituent Hammett constants has been found to divide into two branches [577], This nonordinal event is explained by impossibility of any additional contribution to the shielding of substituents having two and more lone electron pairs [577],... 

In the reaction of 3-nitro-177-1,2,4-triazole with benzyl chloride it was possible to obtain l-benzyl-3-nitro-177-l,2,4-triazole (60%), l-benzyl-5-nitro-17/-l,2,4-triazole (10%), and 4-benzyl-3-nitro-177-l,2,4-triazole (4%), whose structures were determined by H and 13C NMR with homonuclear NOE difference spectroscopy (Table 3.21) [559], The tautomerism of C-nitro-substituted 1,2,4-triazoles was studied by NMR and IR spectroscopy [582], 31P NMR spectroscopy was employed for the identification of nitrated triazolyl-1 phosphates [583, 584],... 

In the reaction of 3-nitro-5-R-l,2,4-triazolate-anion with 3,5-dinitro-l-(2-oxo-propyl)-l,2,4-triazole both the products of nucleophilic substitution in position 5 and condensed compounds [5-methyl-5-(3-nitro-5-R-l,2,4-triazol-l-yl)-5,6-dihydroxazolo[3,2-b]-l,2,4-triazoles] are formed. Their structures were established by H NMR and IR spectroscopy [585],... 

The structural, theoretical, and NMR spectroscopic assessments of differences in the properties of and the likely origin of the differences in the impact sensitivity of isomeric 4-nitro-l-picryl- and 4-nitro-2-picryl-1,2,3-triazoles have been discussed [607] ... 

Structure and ratio of N-l- and (V-2-alkyl isomers of 4-nitro-l,2,3-triazole obtained by alkylation reaction in various solvents have been investigated by IR spectroscopy [620], The structure of 4-aryl-5-nitro-l,2,3-triazoles [1610-1615 (double bonds), 1510-1530 and 1374-1380 (N02), 990-1022 (triazole ring) cm1] [553], l-aryl(heteryl)- and 2-aryl(heteryl)-4-nitro-l,2,3-triazoles [141, 177, 602-604] have been confirmed by infrared spectra. 

The IR spectroscopy data for l-(l-adamantyl)-3-nitro-l,2,4-triazole [1072] and other substituted nitrotriazoles [574-576, 582, 583, 621-625, 1066, 1073-1077] are mainly reported to confirm the structure. 

This can be of help in structural assignments in the chemistry of heterocycles. The electron spectra of 1- and 2-alkylderivatives of 4-nitro-l,2,3-triazole, which show an identical band /w 257 nm also independent on the medium (pH 1 or 11 or ethanol), are described [634], However for l-alkyl-4-nitro-5-amino-l,2,3-triazoles the absorption maximum is shifted to the long-wave region (332-356 nm). 

The mass spectral characteristics are considered as a proof of the structure of l-aryl(heteryl)- and 2-aryl(heteryl)-4-nitro-l, 2,3-triazoles 141,177,602-604,1-org-anyl-4-nitro-l,2,3-triazoles [597], some 4-nitro-l,2,3-triazoles of potential interest as antiprotozoal agents [1328], The molecular ion peaks of the following 4-nitro-1,2,3-triazole derivatives are reported (Scheme 3.66) [1328],... 

Fig. 1.7 Molecular structures of 5-nitro-l,2,4-triazol-3-one (NTO), 1,3,3-trinitroazetidine (TNAZ), hexanitrohexaazaisowurtzitane (CL-20), octanitrocubane (ONC) and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX).

This reaction (cf. 95CHE1251), earlier described as being dependent on unusual TP structures or extreme conditions, was now found to be predominant in the series of 3-alkyl-5-methyl-6-nitro-7-oxo TPs unsubstituted in the 2-position (e.g., 136, Scheme 37) (01RCB682). The triazole ring is exclusively cleaved in the presence of strong bases or C-nucleophiles to obtain pyrimidones such as 145. Under the influence of ethanolic alkali, after short reaction times, a mixture of intermediate cyanamide 144 and product 145 was obtained. 

A three-component condensation of 3-amino-l, 2,4-triazole (or its 5-Me and 5-methylthio derivatives), 1 and DMF-dimethylacetal afforded 8,9-dihydro[l,2,4]triazolo[l,5-fl]quinazolin-6(7H)-ones (06RCB1224). Condensation of 3,4,5-triamino-l,2,4-triazole with aromatic aldehydes and dimedone afforded partially hydrogenated 9-aryl-[l,2,4]triazolo[5,l-frJquinazolin-8-ones. The structure of 2-amino-6,6-dimethyl-3-(4-nitro-benzylidene)amino-9-(4-nitrophenyl)-5,6,7,9-tetrahydro[l,2,4]triazolo[5,l-fr]-quinazolin-8-one was confirmed by X-ray analysis (05RCB2903). 

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