Background: Tetrazoles are imperative nitrogen rich heterocyclic compounds with a wide range of
applications in the field of organic synthesis, coordination chemistry, material sciences, and medicinal
chemistry. A most common approach for the synthesis of 5-substituted-1H-tetrazoles is achieved by
[3+2] cycloaddition reaction of azides to nitriles. In this paper a new acidic ionic liquid is introduced
as a catalyst to promote the mentioned reaction.
Methods: Piperazinium dihydrogen sulfate:as a new acidic ionic compound was obtained by treatment of piperazine with
sulfuric acid, which is further was applied as a catalyst for the [3+2] cycloaddition reaction of azides to organic nitriles.
Results: The [3+2] cycloaddition reaction of sodium azide with structurally different organic nitriles using only 1.5 mol%
of the piperazinium dihydrogen sulfate proceeded well at 100°C and 5-substituted-1H-tetrazoles were prepared in good to
excellent yields. Herein, piperazinium dihydrogen sulfate has a dual role of catalyst and reaction medium, which circumvents
the use of any organic solvent. The catalyst is also recyclable. This method is particularly suitable for benzonitriles
carrying deactivating groups which furnished the corresponding products in excellent yields. By this method, mono [3+2]
cycloaddition product of dicyanides was obtained.
Conclusion: In conclusion, piperazinium dihydrogen sulfate as a new acidic ionic compound was applied to promote synthesis
of 5-substituted-1H-tetrazoles through [3+2] cycloaddition reaction of organic nitriles with sodium azide. This new
ionic compound can be easily separated from the reaction mixture which resulted to a simple work-up of the products.