Abstract
The solubility of pharmacologically active poorly water-soluble compound isatin in nine different green solvents [water, ethanol, butanol-2, Transcutol [2-(2-ethoxyethoxy)ethanol], ethylene glycol (EG), ethyl acetate (EA), isopropyl alcohol (IPA), propylene glycol (PG), and polyethylene glycol-400 (PEG-400)] was measured from (298.15 to 338.15) K at atmospheric pressure. The measured solubilities of isatin were correlated with the Apelblat and ideal equations. For the Apelblat equation, the root-mean-square deviations (RMSD) and correlation coefficients (R2) (n = 5) were found to be (0.20 to 1.45) % and 0.9964 to 0.9999, respectively. However, for an ideal equation, the RMSD and R2 (n = 5) were obtained as (0.19 to 3.00) % and 0.9940 to 0.9990, respectively. The mole fraction solubility of isatin was observed highest in Transcutol (5.23.101 at 298.15 K) followed by PEG-400 (9.85.102 at 298.15 K), EG (7.54.103 at 298.15 K), PG (6.73.103 at 298.15 K), EA (5.68.103 at 298.15 K), butanol-2 (5.16.103 at 298.15 K), IPA (4.19.103 at 298.15 K), ethanol (4.09.103 at 298.15 K), and water (5.14.105 at 298.15 K) from (298.15 to 338.15) K. The mass fraction solubility of isatin was also observed highest in Transcutol (1.20 kg.kg(-1) at 298.15 K) followed by PEG-400 (4.02.102 kg.kg(-1) at 298.15 K), EG (1.80.102 kg.kg(-1) at 298.15 K), PG (1.32.102 kg.kg(-1) at 298.15 K), ethanol (1.31.102 kg.kg(-1) at 298.15 K), IPA (1.04.102 kg.kg(-1) at 298.15 K), butanol-2 (1.03.102 kg.kg(-1) at 298.15 K), EA (9.54.103 kg.kg(-1) at 298.15 K), and water (4.20.104 at 298.15 K) from (298.15 to 338.15) K. The data of dissolution enthalpy, Gibbs energy, and dissolution entropy indicated endothermic, spontaneous, and entropy-driven dissolution of isatin in most of the green solvents investigated.