The solid−liquid equilibrium of benzoic acid has been determined in six monosolventstributyl phosphate, diacetone alcohol, methyl-npropyl ketone, methyl acetate, amyl acetate, and isooctaneat temperatures from 283.15 to 328.15 K and five binary systemsethanol + hexane (288.15− 328.15 K), isopropyl alcohol + hexane and chloroform + hexane (288.15− 323.15 K), acetone + hexane (288.15−318.15 K), and acetone + water (288.15−318.15 K)at atmospheric pressure with varying mole fraction of the binary mixture. The solubility was estimated by three different methods titrimetry, gravimetry, and high-pressure liquid chromatography methods. The solubility of benzoic acid was found to increase with an increase in temperature and mole fraction. Experimental solubility data was correlated with various thermodynamic models such as the Buchowski equation, the NRTL model, and the modified Apelblat−Jouyban−Acree model. The mathematical models demonstrated that the calculated and experimental solubilities of benzoic acid in the solvents were in good agreement.

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The solid−liquid phase equilibrium of para-tertbutylbenzoic acid in methanol, ethanol acetic acid, propan-2-ol, hexane, toluene, 1-octanol, para-tert-butyltoluene, methyl 4-tert-butylbenzoate, and binary (methanol + methyl 4-tertbutylbenzoate) mixed solvent have been determined experimentally within the temperature range of 293.15−333.15 K at atmospheric pressure using a static equilibrium method. The solubility of para-tert-butylbenzoic acid increased with the increase in temperature for the pure solvents, while in the case of methanol + methyl 4-tert-butylbenzoate a maximum solubility effect is achieved at 0.6115 solute-free mole fraction of methanol. The experimental solubility data in pure and binary solvent system were correlated by the modified Apelbat equation, the λh (Buchowski) equation, and the NRTL model, among which the modified Apelbat equation provided better agreement than those with the other models. Furthermore, to understand the nature of interactions involved in a solute−solvent system, the dissolution thermodynamic properties, including enthalpy, entropy, and Gibbs free energy, were determined. This experimental data will be an aid for the design and optimization of the separation and purification processes involving para-tert-butylbenzoic acid.

The saturated vapor pressure of methyl 4-tertbutylbenzoate was measured from (1.21 to 34.66) kPa in the temperature range from (398.3 to 492.4) K using a Swietoslawski-type ebulliometer. The experimental data were fitted with the Antoine and Clarke−Glew equations, which yielded Antoine parameters (A = 18.031, B = 7261.445, C = 8.857 K) and standard vaporization enthalpy (Δ l g H m θ (298.15 K) = 57.49 kJ mol −1 ), respectively. The critical properties were estimated on the basis of group contribution method. The acentric factor was calculated using these critical parameters and the saturated vapor pressures with the Antione equation. Furthermore, density, refractive indices, and viscosity of methyl 4tert-butylbenzoate were also measured in the temperature range of 293.15 to 353.15 K. Temperature-dependence correlation equations for the density (second-order polynomial equation) and viscosity (Vogel−Tamman−Fulcher) were proposed. Modified Rackett equation was used with group contribution methods to predict the density of methyl 4-tert-butylbenzoate. Group contributions and group interactions method of Nannoolal et al. were used to predict the viscosity in the temperature range of 293.15 to 353.15 K.