Preparation and Crystal Structure of a Trihydrate of Paracetamol

This work reports the preparation and crystal structure of a trihydrate of paracetamol. Crystals were grown by slow cooling of an aqueous solution of paracetamol to 0°C. Single-crystal X-ray diffraction shows that the trihydrate crystallizes in the orthorhombic crystal system, space group Pbca, Z=8, a=7.3324(16), b=12.590(3), c=22.636(6) Å, V=2089.7(9) Å3. The crystals of the trihydrate dehydrate rapidly at 20°C to give anhydrous paracetamol as its monoclinic form. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1308–1311, 2002