Abstract
The polymorphic transition of anhydrous caffeine was investigated by differential scanning calorimetry (DSC) and X-ray powder diffractometry. The water content of caffeine hydrate was determined by means of thermogravimetry, a phase diagram of the water-caffeine system, and a water vapor sorption experiment. All the results indicated that caffeine hydrate does not exist as a monohydrate, but contains 0.8 mol of water per mol of caffeine. Some thermodynamic parameters including the enthalpies of transition, fusion, and dehydration were determined by DSC of two anhydrous polymorphs and the hydrated form. The effect of dehydration on the micromeritic properties of caffeine was studied by electron microscopy and BET gas adsorption analysis.
