Crystallisation of organic salts by sublimation: salt formation from the gas phase

Abstract

Crystals of organic salts can be grown by sublimation in two systems: succinic acid with hexamethylenetetramine, and oxalic acid with 4,4′-bipyridine. Both systems also form co-crystals by sublimation. Additionally, salts and co-crystals are able to re-sublime once formed, allowing the separation of different multicomponent crystal forms using sublimation. Preliminary experiments indicate that ion pairs may be present in the gas phase during the sublimation of salts. Crystallisation by sublimation is compared to solution crystallisation and mechanochemical methods.