Dry Mechanochemical Synthesis of Caffeine/Oxalic Acid Cocrystals and Their Evaluation by Powder X-Ray Diffraction and Chemometrics

We report the effects of dry mechanochemical synthesis conditions on the crystallization of caffeine (CA) and oxalic acid (OX) 2:1 cocrystal. CA anhydrate and OX dihydrate were grinded at various temperatures, rotation speeds, and grinding time. The cocrystal was also synthesized by an organic solvent evaporation method, as a reference. The produced samples were measured by a powder X-ray diffraction (PXRD) analysis. The PXRD spectra suggest that the grinded cocrystal has a lower crystallinity than the evaporated one. The diffractograms for the cocrystals synthesized by 2 kinds of methods were further evaluated by multivariate curve resolution-alternating least squares method. Sources of the mathematical models constructed were assigned to the cocrystal and unreacted mixture of CA and OX dihydrate. The present approach is concluded to be useful for the improvement of pharmaceutical property because cocrystallization is closely relating to the solubility characteristics, bioavailability, stability, and so on of drugs.