Studies on mesoionic compounds. Part 4. Protonation equilibria of 2,3-diaryl-2H-tetrazolium-5-thiolates and 1,3,4-thiadiazolium-2-thiolates in aqueous perchloric acid solutions

Abstract

The pK_BH⁺ values of five 2,3-diaryl-2H-tetrazolium-5-thiolate and six 1,3,4-thiadiazolium-2-thiolate mesoionic compounds were determined spectrophotometrically in aqueous perchloric acid solutions at 15, 25, 35, and 45 °C. Our results have shown that both types of mesoionic compounds behave as Hammett bases and that protonation was suggested to occur at the exocyclic sulphur atom. The thermodynamic functions (ΔG°, ΔH°, and ΔS°) of ionization have been determined and are discussed.