Solubility in Different Solvents, Crystal Polymorph and Morphology, and Optimization of Crystallization Process of AIBN

The solubility of 2,2′-azobisisobutyronitrile (AIBN) in pure methanol, ethanol, acetone, benzene, ethyl acetate, and a mixture of methanol and water was measured in the temperature range from 268.15 to 325.15 K at atmospheric pressure. The AIBN solubility was sensitive to the temperature in all pure solvents. The solubility in the binary mixture of methanol and water increased as the methanol fraction and temperature increased. The data were correlated with the modified Apelblat, Van't Hoff, and Buchowski–Ksiazczak λh equations. Other results showed that two AIBN polymorphs formed after the crystallization: form I, in a monoclinic cell, and form II, in a triclinic cell, which confirmed the two AIBN crystal structures reported in the literature. Additionally, the initial concentration and cooling rate of the AIBN crystallization had dominant roles in affecting the polymorphic forms of the AIBN crystals. The crystallization conditions were optimized in a 2 L crystallizer to yield crystals with the desired morphology and polymorphs, which resolved the caking issue experienced in the industrial production of AIBN. The optimized conditions were tested in a 20 L crystallizer.