Crystallization and characterization of cocrystals of piroxicam and 2,5-dihydroxybenzoic acid

Abstract

A cocrystal of piroxicam (PRX) and 2,5-dihydroxybenzoic acid (HBA), PRX–HBA, and an acetone (ACT) solvate of the cocrystal, PRX–HBA–ACT, were crystallized on a microfluidic platform via solvent evaporation. The inclusion of ACT was found serendipitously, with the ACT probably being introduced into the crystallization system as an impurity in HBA. The crystal structures of PRX–HBA and PRX–HBA–ACT obtained by X-ray diffraction both exhibit the P2₁/c space group. Bulk quantities of the cocrystals were synthesized using a slurry method and their physical properties were characterized with thermogravimetric analysis and differential scanning calorimetry. Additionally, the phase behavior of PRX–HBA–ACT during desolvation was monitored with powder X-ray diffraction. The powder diffraction of PRX–HBA–ACT after complete desolvation has the same peak positions as the PRX–HBA, suggesting that PRX–HBA–ACT re-arranges to the structure of PRX–HBA.