Efficient solvent-controlled crystallization of pure polymorphs of 1-nitro-4-(4-nitrophenylmethylthio)benzene

Abstract

Four pure polymorphs (I–IV) and a monohydrate of 1-nitro-4-(4-nitrophenylmethylthio)benzene (abbreviated as NNB) were readily obtained in bulk quantities through a solvent-control strategy. A total of 15 common solvents were used to explore the crystallization behaviour of NNB. Forms II and IV and the monohydrate exhibit solvent-dependent polymorphic selectivity. Form I can be preferentially crystallized from solvents with high dielectric constants, while III is obtainable from solvents with low dielectric constants. All of the forms were characterized via single-crystal X-ray determination, and the rationalization of structural features is discussed. Phase behaviours of the polymorphs were observed through differential scanning calorimetry (DSC) and powder X-ray diffraction. This study may contribute to the strategic discovery and development of a desirable polymorph of any organic drug substance via solvent control.