N-Unsubstituted 1,2,4-Triazole-3-carbaldehydes

Abstract

A series of N-unsubstituted 1,2,4-triazole-3-carbaldehydes has been prepared by acid hydrolysis of their methyl or ethyl acetals. Those with 5-aryl substituents have been shown to dimerize in the solid state to carbonyl-free hemiaminals. P.m.r. and infrared spectra indicate that monomeric 1,2,4-triazole-3-carbaldehydes are present in solution, the dimers being reformed on removal of the solvents. Parallels are drawn with benzimidazole-2-carbaldehyde, to which a similar structure has been assigned. With non-aromatic 5-substituents the hemiaminal becomes less stable, and 1,2,4-triazole-3-carbaldehyde, itself, exists predominantly in the carbonyl form. Mass spectra were consistent with essentially normal aldehyde structures.