Chemical and Phase Equilibrium of Formic Acid-Trialkylamine Complexes

In this work, we investigate the effect of the alkyl chain length of the nitrogenous cation on the ionicity of formic acid-trialkylamine mixtures at 298.15 K, and the nature of the formed bonds using a combination of Fourier transform infrared (FTIR) and ¹H NMR. FTIR revealed the formic acid-trialkylamine complexes to be a mixture of ionic and neutral species. Besides chemical equilibria, the studied systems also have a phase equilibrium. Our results reveal the phase equilibrium to be independent of alkyl chain length at a molar ratio of 1.5:1 acid to amine. Interestingly, it was observed that while the degree of proton transfer decreases as a function of alkyl chain length, the hydrogen bonding characteristic increases, resulting in a constant acid-to-amine ratio of 1.5 mol of formic acid per mole of amine.