Enthalpies of interaction of nitrogen base solutes with organic solvents

Abstract

Heats of solution of triethylamine, aniline, pyridine, and model compounds (3-ethylpentane, benzene) in 17 organic solvents (n-heptane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane, α,α,α-trifluorotoluene, triethylamine, butyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, benzene, toluene, mesitylene, t-butyl alcohol, 1-octanol, methanol, 2,2,2-trifluoroethanol) have been combined with solute heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → s)). Differences between solute and model values (ΔΔH(v → s) = ΔH(v → s) (solute) – ΔH(v → s) (model)) were used to evaluate nitrogen base solute–solvent polar interactions. Correlations of ΔΔH(v → s) with Taft–Kamlet solvatochromic parameters (π*, α, β) have been determined.Aniline was found to be a better hydrogen bond donor acid than hydrogen bond acceptor base. Nevertheless, alcohols donate H-bonds to aniline. Triethylamine and pyridine are stronger HBA bases than aniline. The π* (dipolarity–polarizability) parameter of aniline (as a solute) is calculated to be 1.10.