New orthorhombic form of 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid (diclofenac acid).

acid, is a non-steroidal anti-flammatory drug. The structures of two monoclinic forms of diclofenac acid with space groups of P21/c (HD1) and C2/c (HD2) were reported by Castellari and Ottani.1 In this paper, we report on a new orthorhombic form of diclofenac acid (HD3) with the space group Pcan. Diclofenac sodium, a sodium salt of 2-[(2,6dichlorophenyl)amino]benzeneacetic acid (2 g) was dissolved in water. The solution was acidified with 1 M HCl until a white precipitate of diclofenac acid was observed. The precipitate was filtered, washed with distilled water and dried in vacuo. The precipitate (HD3) was recrystallized from hot methanol by slow evaporation. X-ray diffraction data were collected at room temperature using a Bruker SMART CCD area detector. The collected data were reduced using SAINT,2 and an empirical absorption correction was performed using SADABS.3 A total of 19487 reflections were measured, of which 4267 reflections (R(int) = 0.1079) were unique. The structure was solved by direct methods and refined with anisotropic displacement parameters for all non-hydrogen atoms by full-matrix least-squares using the SHELX-97 package for PC.4 The coordinates of the hydrogen atoms were calculated from the riding model, except 1465 ANALYTICAL SCIENCES DECEMBER 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry