Volume changes in the proton ionization of amines in water. 2. Amino alcohols, amino ethers, and diamines

Abstract

From density measurements (25 °C) of aqueous solutions at various concentrations of solute, apparent molar\nvolumes of some open-chain bifunctional amines, with the amine group being primary, secondary, and tertiary,\nhave been determined. The compounds studied were 2-aminoethanol, 3-amino-1-propanol, 2-methoxyethylamine,\n3-methoxy-l-propylaminee,t hylenediamine, 1,3-diaminopropane,2 -(methylamino)ethanol, 2-(ethylamino)ethanol,\n2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, and their mono- and dihydrochlorides. The volume changes\nfor the first and second steps of proton ionization have been calculated from the limiting partial molar volumes.\nThe volume change values of the above bifunctional amines are compared with the corresponding values for monofunctional\namines. The difference in the volume changes caused by the introduction of the second hydrophilic center is discussed. The\nvolumes and entropies of ionization of the amines and carboxylic acids are compared and the deviations of\nthese functions from predictions based on simple electrostatic theories are considered.