Solubility of solid intermediate of pharmaceutical compounds in pure organic solvents using semi-empirical models.

A new semi-theoretical equation is suggested for correlation of solid-liquid solubility data with temperature. The (solid + liquid) equilibrium for Terephthaldialdehyde, 4-Nitro-o-phennylenediamine, 2,4-dihydro- 5-methyl-2-(4-methylphenyl)-3H-pyrazol-3-one (also named 1-(p-tolyl)-3-methyl-5pyrazolone (PTMP)), 2-Amino-5-methylthiazole and 5-chloro-1-methyl-4-nitroimidazole in 18 solvents is correlated with semi-empirical models at temperatures T = 273.15-318.15 K under a pressure of 101.2 kPa. Moreover, a modified Apelblat model, λh model, Wilson model, NRTL model, new flexible equation as Akbari, Dideban and Farhang model (ADF) and for first time the modified Scatchard-Hildebrand equation were utilized to calculate the experiment values. The performance of both ADF and modified Scatchard-Hildebrand equation have been checked by calculating the solubility data with the AARD% of 1.3808% (for 775 data points) and 0.65% (for 100 data points), respectively. The Wilson model is applied to estimate the mixing Gibbs energy, mixing enthalpy, mixing entropy, activity coefficient (ln γ1∞) and reduced excess enthalpy (H1E, ∞) at infinitesimal concentration were calculated.