Control of Pharmaceutical Cocrystal Polymorphism on Various Scales by Mechanochemistry: Transfer from the Laboratory Batch- to the Large-Scale Extrusion Processing

We demonstrate a controllable mechanochemical synthesis of cocrystal polymorphs of ascorbic acid (vitamin C) and nicotinamide (vitamin B3) on different scales and without using bulk solvents. Next to the previously described polymorph of the 1:1 cocrystal, which is one of the first cocrystals approved for human consumption, we report here a new, thermodynamically more stable polymorph detected during in situ synchrotron powder X-ray diffraction monitoring of milling reactions. The new polymorph is currently available exclusively by mechanochemical synthesis, and its crystal structure was determined from powder X-ray diffraction data. Laboratory in situ monitoring by Raman spectroscopy provided direct insight into the cocrystals formation and was further used to optimize the manufacturing procedure. Sub-gram synthesis using laboratory mixer mill was transferred to the 10 g scale on a planetary ball mill and continuous manufacturing using a twin-screw extruder. Both cocrystal polymorphs perform excellently in tableting, thus alleviating the notoriously poor compactible properties of vitamin C, while the mechanochemical cocrystallization does not harm its antioxidant properties.