Mixing thermodynamic properties of ester-containing solutions: A study on the ternary (methyl alkanoate (pentanoate and methanoate) + methanol) and the corresponding binaries. New contributions to the (ester + ester) interactions

• Excess properties were measured for two methyl esters and methanol.
• Mixing behavior for (ester + ester) and (ester + methanol) were analysed by 1H-NMR.
• Correlations with a polynomial model reproduce well the mixing properties.
• UNIFAC predictions for hE were not acceptable for the systems studied.

This work studies the volumetric (VmE) and energetic (HmE) properties resulting from the mixing processes of binary systems and the corresponding ternary of two methyl esters (methanoate and pentanoate) with methanol. The three binaries produce net endothermic mixing effects, with important energetic interactions, with maximum values of HmE ≅≅ 400 J ⋅ mol−1, for the (ester + ester) system. This produces expansive effects VmE > 0, but the binaries of the (methyl esters + methanol) give rise to contractions VmE < 0, due to the formation of molecular aggregates. The endothermicity in the mixing processes is a net effect which is justified by interactions of different nature, especially dipolar interactions and hydrogen bonds of the substances involved. The overall results in the ternary respond to the individual contributions of the binaries and the increment due to the simultaneous presence of the three compounds in the solution. The experimental results are correlated with our own model that gives a good representation of the properties of the solutions studied. The analysis of the behavior of the solutions is reinforced by spectral data obtained by 1H NMR, supporting the structural model established. The application of UNIFAC to estimate the HmE in the ternary improves when one takes into account the individual contributions of the (ester + ester) interactions whose parameter are predetermined.