Thermodynamics of ionization of aqueous alkanolamines

Abstract

We have made electrochemical measurements with a glass electrode that have yielded pK values at T = 298.15 K for monothanolamine (MEA), triethanolamine (TEA), diisopropanolamine (DIPA), and methyldiethanolamine (MDEA) relative to the already well-known pK for diethanolamine (DEA), with all pK values referring to equilibria of the type AmH+(aq) = Am(aq) + H+(aq) in which Am(aq) represents an alkanolamine in aqueous solution and AmH+(aq) represents the corresponding protonated alkanolamine. We have also made calorimetric measurements leading to ΔH0 values for dissociation of the protonated species of all five of these alkanolamines in aqueous solution at T = 298.15 K. These pK and ΔH0 values have led to ΔG0 and ΔS0 values for the corresponding dissociation reactions of all five AmH+(aq) species.