Quaternary and its sub-ternary systems of 4-formylbenzoic acid + p-toluic acid + p-phthalic acid + N,N-dimethylformamide: Phase diagrams and DFT studies on adduct of p-phthalic acid with N,N-dimethylformamide

Abstract

The equilibrated solubility of the three systems p-phthalic acid (PTA) + p-toluic acid (p-TLA) + N,N-dimethylformamide (DMF), PTA + 4-formylbenzoic acid (4-FBA) + DMF, and p-TLA + 4-FBA + DMF at 298.15 K, 323.15 K and 353.15 K, as well as the quaternary system PTA + p-TLA + 4-FBA + DMF at 298.15 K, was ascertained through experimentation by a Schreinemakers' wet residue method under p = 101.0 kPa. One quaternary isothermal phase diagram and nine ternary isothermal phase diagrams were developed based on the solubility obtained herein. Two distinct neat compounds were produced in ternary systems, comprising the PTA·2DMF adduct (mole ratio of PTA to DMF, 1:2) at 323.15 K and 298.15 K, or PTA at a temperature of 353.15 K, along with p-TLA in the PTA + p-TLA + DMF system; 4-FBA and p-TLA in the 4-FBA + p-TLA + DMF system; and the PTA·2DMF adduct at 298.15 K and 323.15 K, or PTA at 353.15 K, combined with 4-FBA in the PTA + 4-FBA + DMF system. The adduct PTA·2DMF was observed at temperatures below 323.15 K for PTA in DMF. Each diagram for ternary systems comprised two cosaturated point curves, one cosaturated point, and three crystalline regions. The ternary and quaternary phase diagrams presented in this study may serve as a foundation for the separation of PTA from p-TLA, 4-FBA, and PTA mixtures. The formation of the PTAˑ2DMF adduct involves favorable weak interactions, specifically hydrogen bonds and van der Waals forces, as analyzed through the Hirshfeld partitions-based independent gradient model, electron density difference maps, density differences, ELF difference maps, and 2D fingerprint plot analysis.