A molecular modeling study of the crystal morphology of adipic acid and its habit modification by homologous impurities

The crystal morphology of adipic acid (AA) and its mediation by the action of the homologous additives, caproic acid, glutaric acid, and succinic acid, has been investigated via computational molecular modeling-based simulation techniques (Clydesdale, G.; Docherty, R.; Roberts, K. J. HABIT95, Quantum Chemistry Program Exchange (QCPE), Bloomington, IN 47405, Program Number 670, 1996). With the aid of intermolecular and interatomic energetic analyses, the experimental effect of these impurities has been rationalized. The predicted morphologies are in good agreement with sublimation-grown experimental data. This is not so for solution growth data, reflecting the possible adsorption of water molecules onto exposed carboxylic acid groups via hydrogen bonding on the {100} faces, thus allowing this form to become dominant. Modeling the adsorption of the additives reveals preferential adsorption onto the {302} faces, consistent with good additive/host templating at the growth interface, as demonstrated experimentally. Intermolecular bonding interactions examined those that disappeared in the presence of the additives. It was shown that impurity incorporation disrupted the hydrogen-bonding network within the system, due to an increase in interaction distances and in atom-atom repulsions. Despite its industrial significance, this is the first detailed study of the intermolecular interactions involved in impurity incorporation within adipic acid crystallization, and so any conclusions concerning the effect of impurities within the crystallizing mixture will be most useful. © 2005 American Chemical Society.