Publisher Summary This chapter focuses on the chemistry of monocyclic1,2,3-triazoles as much of the chemistry of benzotriazoles and other fused systems has little in common with monocyclic triazole chemistry and provides a broad survey of methods of synthesis and reactions of triazoles. There has been considerable interest in 1,2,3-triazoles as light stabilizers and as optical brightening agents. They are also used as precursors for azapurines and similar heterocyclic systems that are potential carcinostatic agents. Three recognized classes of 1,2,3-triazoles are 1 H -, 2 H -, and 4 H -1,2,3-triazoles. Triazoles unsubstituted on nitrogen can be regarded either as 1 H - or as 2 H -derivatives, depending upon what tautomer is preferred. The first two classes can be regarded as aromatic systems whereas the third, the 4 H -system, cannot. This is reflected in the abundance of examples of 1 H - and 2 H -triazoles and the rarity of 4 H -triazoles. The thermal cycloaddition of azides to acetylenes is the most versatile route to 1 H -1,2,3-triazoles because of the wide range of substituents that can be incorporated into the acetylene and azide components. The base-catalyzed condensation of azides with activated methylene compounds is a well-established route to 1 H -triazoles and is the best route to triazoles bearing a 5-amino or hydroxy substituent and an aryl or carbonyl-containing function in the 4-position. The structure and spectroscopic and physical properties of triazole are discussed in the chapter.

1,2,3-Triazoles

4.11 – 1,2,3-Triazoles and their Benzo Derivatives

Nitrogen-14 nuclear magnetic resonance of azoles and their benzo-derivatives

4.13 – Tetrazoles

The thermal decomposition of 5-aminotetrazole was studied theoretically using the G3 multilevel procedure and DFT B3LYP technique. The unimolecular primary decomposition reactions of the three most stable isomers of 5-ATZ were studied in the gas phase and in the melt using a simplified model of the latter. The influence of the melt on the elementary reaction barrier was taken into account by the calculation of the solvation free energies using the PCM model. In contrast to all previous publications, we considered the bimolecular reactions of 5-ATZ and demonstrated that they are very important especially in the condensed phase. It was found that the imino form undergoes fast isomerization to the amino form in the H-bonded dimers and does not participate in the 5-ATZ thermolysis. On the contrary, amino and, probably, the 2H isomer are the main isomers of 5-ATZ in the melt and gas phase. The N2 elimination reaction was found to be the dominant unimolecular channel of the amino and 2H isomer decomposition in both the gas phase and melt. The significant lowering of the activation barriers of decomposition reactions in H-bonded dimers was found. In agreement with the existing experimental data, HN3 elimination dominates for some of the considered complexes. It was concluded that the initial stages of thermolysis of 5-ATZ cannot be satisfactory described by the simple unimolecular reactions proposed in the literature.

P. Viallefont

Papers

Recherches dans la serie des azoles.