Index — volume 2

Abstract

Equilibrium quotients (K') for the protonation of diethanolamine (DEA), 2-(2-aminoethoxy) ethanol or diglycolamine (DGA), and N-methyldiethanolamine (MDEA) were determined potentiometrically over the ionic strength range 0.004–4.0 at 298.2 K. Corresponding ΔH values were determined by a flow calorimetric procedure at six temperatures from 299.9 to 422.1 K. At 299.9 K the protonation reactions become less exothermic, i.e. -ΔH decreases, in the order DGA (primary amine), DEA (secondary amine), MDEA (tertiary amine). From 299.9 to 422.1 K this order remains unchanged but the differences among the ΔH values decrease. The ΔH results are used, together with the 298.2 K lg K values (valid at ionic strength, μ = 0), to calculate the dissociation constants of the corresponding protonated alkanolamines from 298.2 to 423.2 K. The effect of μ on the lg K value (valid at μ = 0) for proton ionization from protonated alkanolamines is large. The change of lg K' with μ is nearly insensitive to substitution of functional groups on the nitrogen atom. The isocoulombic reaction principle was used to extrapolate K and ΔH to 423.2 K. Equations are given describing lg K, ΔH, ΔS and ΔCp at μ = 0 from 298.2 to 423.2 K.