Co-crystals and co-crystal hydrates of vanillic acid

Abstract

A series of co-crystals of vanillic acid (VA) with caffeine (CAF), theophylline (THP), theobromine (THB), nicotinamide (NAM), isonicotinamide (INM), acridine (ACR) and urea (U) have successfully been prepared. The co-crystals involving the methylated xanthines indicate different host: guest ratios with co-crystals VA·2CAF, 2VA·THP and the co-crystal hydrate VA·THB·2H₂O. The nicotinamide and acridine co-crystals (VA·NAM and VA·ACR) displayed 1 : 1 molar ratios in contrast to the isonicotinamide co-crystal hydrate 2VA·2INM·2H₂O. Co-crystallisation of vanillic acid with urea gave 2VA·2U. The co-crystals and co-crystal hydrates were characterised by single crystal X-ray diffraction and thermal analysis. Grinding and slurry experiments were also performed.