Thermodynamic Analysis of DSC Data for Acetaminophen Polymorphs

This article provides a thermodynamic analysis of DSC data for acetaminophen polymorphic forms I and II by measurement of heat capacity. Form I is found to have lower heat capacity and free energy and hence better stability than Form II down to at least –30°C. The transition temperature below which Form II becomes more stable was determined to be less than –120°C. Form I is more stable than Form II as a consequence of its higher entropy, since its crystallographic packing arrangement is of larger energy. This revised version was published online in August 2006 with corrections to the Cover Date.