Microwave assisted synthesis of caffeine/maleic acid co-crystals: the role of the dielectric and physicochemical properties of the solvent

In the present work microwave radiation has been used to prepare the 1 : 1 and 2 : 1 co-crystals of caffeine and maleic acid. We obtained 1 : 1 co-crystals in the presence of water and methanol and we also see Form II of the 1 : 1 co-crystal in methanol. Co-crystallisation under microwave irradiation is shown to be controlled by the saturation of solvent at the reacting interface between the co-crystal components as well as the solvent dielectric properties.