An aprotic imidazole based zwitterionic-salt, 4-(3-methylimidazolium)butane sulfonate (MBS) has been found to be an efficient organocatalyst for the synthesis of 5-substituted 1H-tetrazoles by the cycloaddition of aryl nitriles with NaN₃ under solvent-free conditions. Both the cation and the anion cooperatively affect the reaction and the C2–H of the imidazolium moiety plays a crucial role in “electrophilic activation” of the nitrile through hydrogen bond formation.