A new perspective of enthalpies of proton transfer of aliphatic amines, hydroxyamines, and aminoalkylsulfonic acids in methanol-water mixtures by direct calorimetry

Abstract

The enthalpies of proton transfer in methanol–water mixtures (0–90 wt.% methanol) of the aliphatic amines: triethylamine (Et3N), t-butylamine, and quinuclidine (Q); the hydroxyamines:2-amino-2-methyl-1-propanol (Amp), 2-amino-2-methyl-1,3-propanediol (Bis), tris(hydroxymethyl)-aminomethane (Tris), and 2,2-bis(hydroxymethyl)-2,2′,2′′-nitrilotriethanol (Bis-Tris); and the aminoalkylsulfonic acids: 3-(N-morpholino)-propanesulfonic acid (MOPS), N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (Bes), and N-(2-hydroxyethyl)piperazine-N′-2-ethanesulfonic acid (HEPES), have been measured by direct calorimetry at 25°C. The results of the protonation reactions have been reported. All the salient features are now examined together with a view to assessing the success of interpretations using classical electrostatic formulation and three-dimensional structures in methanol–water mixtures. The objective is to find answers to the complex phenomena of solvation.