The structure of 3-oxy-5-phenyl-1H-1,2,3-triazole-4-carboxylic acid was determined both experimentally (by the X-ray diffraction method) and by quantum-chemical calculations. Alkylation of 3-oxy-5-phenyl-1H-1,2,3-triazole-4-carboxylic acid (as crystal hydrate) with methyl iodide, depending on the reactant ratio, gives 1-methoxy-4-phenyl-1H-1,2,3-triazole-5-carboxylic acid and methyl 1-methoxy-4-phenyl-1H-1,2,3-triazole-5-carboxylate. Nitration of the title compound under mild conditions occurs at the 5-phenyl group with formation of meta-nitro derivative, while under more severe conditions 3,5-dinitrobenzoic acid is obtained. 3-Oxy-5-phenyl-1H-1,2,3-triazole-4-carboxylic acid was also converted into the corresponding acid chloride and substituted amide. 1,2,3-Triazole N-oxide derivatives attract interest from the viewpoint of synthetic organic chemistry due to diversity of their reactions. 1H-1,2,3-Triazole 3-oxides, which were formerly assigned the structure of N-hydroxy-1,2,3-triazoles, were synthesized as early as 1902 by treatment of diazo ketones with hydroxylamine in aqueous alcohol [1]. The first and the only review on the synthesis and reactivity of 1H-1,2,3-triazole 3-oxides was published in 1989 [2], and it stimulated further research in this field. As a result, methods for the preparation of substituted 4-amino-5-nitro-1,2,3-triazole 1-oxides via recyclization of 3,4-dinitro-and 4-alkylamino-3-nitrofuroxans [3, 4], as well as of 2-aryl-4,5-dinitro-[5] and mononitro-1,2,3-triazole 1-oxides [6] were developed. A number of 2-methyl-4(5)-nitro-5(4)-R-1,2,3-triazole 1-oxides were synthesized by nucleophilic substitution of the nitro group in 2-methyl-4,5-dinitro-1,2,3-triazole 1-oxide [7,8].We previously showed that heating of 4,5-bis-(hydroxyimino)-3-phenyl-4,5-dihydroisoxazole (I) in boiling 20% aqueous sodium hydroxide, followed by treatment with hydrochloric acid, gives 3-oxy-5-phenyl-1H-1,2,3-triazole-4-carboxylic acid (II) (Scheme 1); the product was isolated from the reaction mixture as crystal hydrate containing one water molecule [9]. The IR spectrum of N-oxide II contained absorption bands at 3490, 3371, and 3071 cm -1 , typical of NH and OH groups, carbonyl absorption band at 1747 cm -1 , and bands at 1696, 1616, 1164, 1090, and 798 cm -1 , which are typical of 1,2,3-triazoles and their N-oxides [2]. The UV spectrum of a solution of II in water displayed two maxima at λ 221 and 256 nm. According to the data of differential thermal analysis, compound II decomposes in 3 steps two of which are endothermic, and the third is exothermic. The first endothermic step starts at 90°C; it corresponds to slow elimination of water molecule and is complete at 180°C. Next follows melting (which is accompanied by decarboxylation) and fast exothermic decomposition.
