Unexpected effects of catalytic amounts of additives on crystallization from the gas phase: Depression of the sublimation temperature and polymorph control

Sublimation of carbamazepine, piracetam, diflunisal, and p-aminobenzoic acid is enhanced by the presence of additives. Temperature reductions and polymorph control have been observed. Sublimation of carbamazepine containing less than 5% by weight of acetamide reduces the sublimation temperature by 20 °C and yields pure form I. In the absence of acetamide, carbamazepine sublimation yields forms I and III. The enhancement mechanism appears to involve more volatile adduct formation. Sublimation of carbamazepine onto polycrystalline powder templates of carbamazepine forms I, II, and III yields pure samples of these forms. Valeric acid is an effective additive in sublimations of diflunisal, piracetam, and p-aminobenzoic acid.