Published data on methods for the synthesis of substituted 4(5)-nitro-1,2,3-triazoles and their properties are reviewed.Against the background of the extremely large amount of published information about methods for the production of vicinal triazoles and their properties the chemistry of nitro-substituted triazoles of this series is in an embryonic state. At the same time, according to existing data, vicinal nitrotriazoles may find use in the synthesis of medicines, dyes, agents for the struggle against agricultural pests, energy-rich components of propellants, special-purpose powders, and in other regions of technology. However, the practical application of these compounds has been restrained by the lack of technologically convenient methods for their production. Until now sufficiently effective preparative methods have not been developed for their synthesis. With respect to their properties it is known only that the nitro group of the triazoles is capable of being reduced catalytically to an amino group and substituted by various nucleophilic fragments, while the triazole ring is alkylated by alkyl halides and adds to an activated multiple bond. The limited information is probably explained by the poor availability of vicinal nitrotriazoles, which is most likely due to the passivity of the 1,2,3-triazole in electrophilic substitution reactions at carbon atoms and particularly in nitration processes. In this connection it seems expedient to examine methods for the synthesis of nitro-substituted 1,2,3-triazoles by direct nitration with due regard to the conditions determining the entry of the nitro group into the azole ring and also methods for the construction of nitrotriazoles by the cyclization of open-chain nitro compounds and to assess their properties.
SYNTHESIS OF NITRO-1,2,3-TRIAZOLES
Nitration of 1,2,3-TriazolesThe inertness of the carbon atoms of the triazole ring toward electrophilic reagents is due to distribution of the electron density of the ring in such a way that the carbon atoms carry a partial positive charge, preventing the addition of a nitronium cation. Therefore, the path to direct nitration of the ring of unsubstituted vicinal triazole has not so far been realized. Attempts to introduce a nitro group into the ring of the heterocycle of 1-phenyl-and 4-phenyl-1,2,3-triazoles were unsuccessful. 1-Phenyl-1,2,3-triazole (1) does not form 4(5)-nitrosubstituted triazole during nitration even under rigid conditions. Here, only the phenyl ring is nitrated-initially at the para position and then at the ortho position [1-3].
