Characterization of Solvates Formed by Sodium Naproxen and an Homologous Series of Alcohols

Crystal solvates of sodium naproxen with ethanol, 1-propanol, 2-propanol, 1-butanol, and isobutanol were identified and characterized. They were formed by slowly reducing the temperature of saturated solutions in the pure alcohol and allowing the resulting crystal-solution mixture to achieve equilibrium at 10 °C. Results show the crystals were not merely crystals of sodium naproxen with an inclusion of solvent. They also demonstrate that as the molecular size of the alcohol increases, the solvent-to-sodium naproxen ratio decreases, but the desolvation energy per mole of alcohol increases. The decrease in solvent-to-sodium naproxen ratio is thought to be due to instability in the crystal structure created by bulkier solvents, but the larger desolvation energy is indicative of stronger hydrogen bonding and Na−O coordination with the bulkier solvents.