Mechanistic study on the crystal habit of 3,3′-diaminobenzidine in the presence of solvents and additives†

Abstract

In this study, the solubility of 3,3′-diaminobenzidine in two mixed solvents (N,N-dimethylacetamide + water and dimethyl sulfoxide + water) was determined. The affecting mechanism of solvents and additives on the crystal behavior of 3,3′-diaminobenzidine was discussed. The interactions between 3,3′-diaminobenzidine and solvents or additives were analyzed from the aspects of crystal surface properties, diffusion coefficient, surface electrostatic potential distribution and radial distribution function. It was found that solvents and additives can significantly affect the crystal growth of 3,3′-diaminobenzidine in many ways. Hydrogen bonding and van der Waals forces play major roles in crystal packing. The interaction between solvent and crystal face can affect the growth of 3,3′-diaminobenzidine in different solvents by synergistic action. The presence of additives would affect the diffusion of molecules near the crystal surface and additive molecules are more easily adsorbed on (1 1 −1) and (1 0 0) faces. Meanwhile, the interaction between the (1 1 −1) face and additives is stronger and hence the area of the (1 1 −1) face is the largest in the final crystal habit. These findings could provide thermodynamic basis for the development of separation and purification technology for 3,3′-diaminobenzidine products, as well as theoretical guidance for regulating the crystal habit of 3,3′-diaminobenzidine crystals.