New Crystalline Forms of Mebendazole with n‐Alkyl Carboxylic Acids: Neutral and Ionic Status

Structural information on the crystalline forms of mebendazole, an anti‐parasitic drug, is limited, although three polymorphic forms of this drug have been reported. The present work investigates the structures and properties of different crystalline forms of mebendazole with a series of n‐alkyl carboxylic acids, including trifluroacetic acid (1), formic acid (2), acetic acid (3), propanoic acid (4), butanoic acid (5), valeric acid (6) and hexanoic acid (7). These compounds were characterized by thermogravimetric analysis, IR spectra, as well as powder and single‐crystal X‐ray diffraction analysis. The R22(8) structural motif was detected in all the seven products, which was formed by a pair of NH···O/OH···N hydrogen bonds between mebendazole and carboxylic acid. Forms 3–7 were found to be neutral solvate, while in forms 1 and 2, proton transfer was observed from carboxylic acid to mebendazole.