A high-pressure polymorph of chlorpropamide formed on hydrostatic compression of the α-form in saturated ethanol solution.

The crystal structure of the high-pressure polymorph (α') of an antidiabetic drug, chlorpropamide [4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C(10)H(13)ClN(2)O(3)S], which is formed at ~2.8 GPa from the α-polymorph (P2(1)2(1)2(1)) on hydrostatic compression in saturated ethanol solution, has been determined. As a result of the phase transition, the a, c and α parameters change jumpwise, whereas the changes in b parameter are continuous through the phase transition point. The high-pressure form is monoclinic (P2(1)11) and has Z' equal to 2, the two independent molecules differing in their conformations. The hydrogen bonds expand slightly in the high-pressure polymorph after the transition, and this expansion is interrelated with the changes in molecular conformations enabling a denser packing. The transition is reversible, but the crystal quality deteriorates as a result of multiple compression-decompression cycles, and a pseudomerohedral twinning accompanies the transformation.