Solvent effect on the solution, ionization, and structure of aminosulfonic acids

Abstract

We have determined thermodynamic parameters for the solution and ionization in dimethylsulfoxide and water of four aminosulfonic acids: NH 2 (CH 2 ) n SO 3 H with n = 0,1, and 2, and NH 2 C 6 H 4 SO 3 H. Potentiometric and calorimetric methods were used. The solubilities of the four acids in Me 2 SO are either nearly equal to or lower than in water, but the enthalpies of solution are 15–40 kJ mol −1 more exothermic in Me 2 SO. The three aliphatic acids are much weaker (2.1 ≤ ΔpK a ≤ 5.5) in Me 2 SO than in water and their heats of ionization are some 30 kJ mol −1 more endothermic in Me 2 SO. The discussion of our results is based on comparisons with corresponding data for related substituted amines and ammonium ions, and sulfonic acids and sulfonate ions. We conclude that the four aminosulfonic acids are mostly present as zwitterions in Me 2 SO just as in water.