Effect of crystallization conditions on modafinil substance polymorphism

Abstract

The effect of the crystallization conditions of modafinil from its methanol solutions on the polymorphic state of the resulting substance was studied using the X-ray powder diffraction method. It is shown that changes in the cooling rate and the concentration of saturated solutions have an effect on obtaining samples of the modafinil substance with differences in diffractometric characteristics. Moreover, the cooling rate practically does not affect the yield of the crystalline product, which depends on the degree of saturation of crystallization solutions. It was found that the I polymorphic form of modafinil can be obtained from modafinil solutions with a concentration in the range of 0.34–0.44 M with slow cooling of solutions, mainly with a temperature gradient of 5–10 °C/hour to a temperature of 5 ± 2 °C. An increase in the cooling rate of saturated solutions and their concentration >0.44 M leads to the production of mixed polymorphic forms of modafinil crystals.