Solubility of 5-nitroisophthalic acid in pseudo-binary mixtures containing water and betaine-based deep eutectic solvents: effect of benzene ring substituents in the benzene carboxylic acid-based compounds on their solubility values.

This work aimed to report the equilibrium solubility of 5-nitroisophthalic acid (5-NIPA) in solvent mixtures of betaine/propylene glycol (Bet/PG) deep eutectic solvent (DES) (1:5 molar ratio) + water, betaine/ethylene glycol (Bet/EG) DES (1:3 molar ratio) + water, betaine/glycerol (Bet/Gly) DES (1:3 molar ratio) at 293.15 K to 313.15 K. At the same temperature and mass fraction of DESs, the mole fraction solubility of 5-NIPA was greater in Bet/PG DES + water than the other systems which explained in terms of solute-solvent interactions by comparing Hansen solubility parameters of 5-NIPA and DESs or water. The effect of benzene ring substituents in the benzene carboxylic acid-based compounds including salicylic acid, 5-aminosalyciclic acid, isophthalic acid and 5-NIPA were examined by comparing each solubility data in the same Bet-based DESs + water mixtures. The outcomes revealed that salicylic acid with one hydroxyl functional group placed in the meta position relative to the carboxylic acid functional group on the benzene ring had the highest solubility in compared with the other compounds. In addition, the solubility of 5-NIPA was mathematically modelled by commonly used cosolvency models achieving average relative deviations lower than 25.7%. Finally, an endothermic process with an enthalpy as a main contributor of the Gibbs energy in the mixtures was determined via thermodynamic analysis of 5-NIPA dissolution process according to the modified van't Hoff equation.