Quaternary system of terephthalic acid +4-carboxybenzaldehyde + p-toluic acid + N-methylpyrrolidone: Mutual solubility determination and correlation together with quantum chemistry research

At 298.15 Kelvin, the method of isothermal dissolution was utilized in this current work at 101.0 kPa to obtain the experimental solubility data for the quaternary terephthalic acid (TA), p -toluic acid ( p -TLA) + 4-carboxybenzaldehyde (4-CBA) +  N -methylpyrrolidone (NMP) system. Generation of the quaternary phase diagram was made through the Jãneck approach, which was based on the mutual solubility that was determined. Three zones of neat solid crystallization, one invariant point, along with three co-saturated curves, were included in the quaternary phase diagram. The three solids that were validated by Schreinemaker approach of wet residue were pure p -TLA, pure 4-CBA, and pure TAˑ2NMP, an adduct of TA with NMP with a mole ratio of 1:2. The area where TAˑ2NMP crystallizes is larger compared to that for p -TLA and 4-CBA. In addition, the model of NRTL was used to mathematically correlate and calculate the quaternary solid-liquid phase diagram. The experimental quaternary phase diagram was found to be in good agreement with the computed one obtained from the NRTL model as evidenced by a root-mean-square deviation of 0.14632 and a relative average deviation of 5.01 %. Separating TA from its mixtures by solvent adduct crystallization might be fundamentally supported by the quaternary phase diagram and thermodynamic models. Considering the investigation on the independent gradient model based on Hirshfeld partitions, as well as the 2D fingerprint plot and difference map of electron density, density difference and difference map of ELF analysis, the van der Waals forces are viewed as favorable weak interactions during the process of forming the adduct of TAˑ2NMP.