Ternary Phase Diagrams for Systems Formed by Terephthalic Acid, p-Toluic Acid, and 4-Carboxybenzaldehyde in N-Methyl-2-Pyrrolidone

The mutual solubility of terephthalic acid + p -toluic acid + N -methyl-2-pyrrolidone (NMP), terephthalic acid + 4-carboxybenzaldehyde + NMP and p -toluic acid + 4-carboxybenzaldehyde + NMP systems at T = 353.15, 323.15, and 298.15 K were experimentally determined by means of a static technique under local atmospheric pressure ( P = 101.2 kPa). Nine isothermal phase diagrams were constructed in terms of the solubility data determined. Two neat solids were formed in each isothermal system, which were adduct 1:2 terephthalic acid–NMP (298.15 and 323.15 K) or terephthalic acid (353.15 K) and p -toluic acid for the ternary terephthalic acid + p -toluic acid + NMP system, 4-carboxybenzaldehyde and p -toluic acid for the ternary 4-carboxybenzaldehyde + p -toluic acid + NMP system, and adduct 1:2 terephthalic acid–NMP (298.15 and 323.15 K) or terephthalic acid (353.15 K) and 4-carboxybenzaldehyde for the terephthalic acid + 4-carboxybenzaldehyde + NMP system. The adduct terephthalic acid–NMP (mole ratio, 1:2) appeared at below 323.15 K when the terephthalic acid dissolved in NMP. Each diagram consisted of two co-saturated curves, one co-saturated point, and three crystalline areas. The phase diagram determined in this contribution could provide the basis for separating the mixtures of p -toluic acid, 4-carboxybenzaldehyde, and terephthalic acid.