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Crystallization and resolution of cis-permethric acid (cPA) with (1R)-1-phenylethanamine (PhEA) as a resolving agent was investigated by means of gas antisolvent (GAS) and supercritical antisolvent (SAS) methods. A significant pressure effect on both the yields and diastereomeric excesses of the crystallized cPA-PhEA salts was observed in a defined pressure range. The pressure effect was found to be related to the structure and dissociation of the salts. Both methods yielded diastereomeric salts with excellent diastereoselectivity, compared to data reported in literature, and a fibrous structure of uniform fiber diameter.

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Solubility parameters are widely used in the polymer industry and are often applied in the high pressure field as well as they give the possibility of combining the effects of all operational parameters on solubility in a single term. We demonstrate a statistical methodology to apply solubility parameters in constructing a model to describe antisolvent fractionation based chiral resolution, which is a complex process including a chemical equilibrium, precipitation and extraction as well. The solubility parameter used in this article, is the Hansen parameter. The evaluation of experimental results of resolution and crystallization of ibuprofen with (R)-phenylethylamine based on diastereomeric salt formation by gas antisolvent fractionation method was carried out. Two sets of experiments were performed, one with methanol as organic solvent in an undesigned experiment and one with ethanol in a designed experiment. The utilization of D-optimal design in order to decrease the necessary number of experiments and to overcome the problem of constrained design space was demonstrated. Linear models including dependence of pressure, temperature and the solubility parameter were appropriate to describe the selectivity of the GASF optical resolution method in both sets of experiments.

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