Ionizing properties of complexes with strong symmetrical hydrogen bonds in acid solutions in aprotic solvents

The acidity functions H0 of solutions of trifluoroacetic acid (TFA) in DMF and methanesulfonic acid (MSA) in 2-pyrrolidone over an acid (HA) concentration range of 0–100% and of H2SO4 solutions in 2-pyrrolidone (66.7–100 mol % HA) at 25°C were determined using the indicator method. Data were obtained on the relative ionizing powers of the quasi-ion pairs S· · · H· · ·A (S is a solvent molecule) formed by DMF with acids (HCl, MSA, and TFA) and by MSA with DMF and 2-pyrrolidone. The effects of the acid anion (with MSA and H2SO4 solutions in 2-pyrrolidone acting as examples) and the counterion SH+ (with MSA solutions in DMF and 2-pyrrolidone acting as examples) on the ionizing power of (Ä · · ·H· · ·A)− ions with strong symmetrical H-bonds were studied. It was found that, under comparable conditions, the replacement of a 2-pyrrolidone molecule by a DMF molecule in the SH+ cation insignificantly decreased the acidity of solution, whereas the (Ä· · ·H· · ·A)− ions in H2SO4 solutions exhibited a much higher ionizing power than that of structurally similar anions in MSA solutions.