Pholcodine monohydrate: Crystal structure and polymorphism

• Polymorph screening of pholcodine monohydrate has been carried out.
• Crystallization from different solvents afforded single crystalline modification, identical to the commercial form of pholcodine monohydrate.
• For the first time crystal and molecular structure of pholcodine monohydrate was authenticated by means of single crystal X-ray diffraction.

The first crystal structure elucidation of pholcodine monohydrate, an important antitussive active pharmaceutical ingredient is reported herein. The studied compound crystallizes in the orthorhombic system in the space group P212121. Each H2O molecule is shared by two pholcodine molecules via three strong hydrogen bonds. The detailed crystallization screening from several different organic solvents afforded single crystals with various quality, all exhibiting prism-to-needlelike micro morphology. The investigation of the obtained single crystals by means of several physico-chemical, solid-state instrumental techniques (FT-IR, DSC, TG/DTG and XRPD) proved that pholcodine monohydrate exists in a single crystalline modification, identical to the commercial form of the compound.