Aqueous solubility of organic salts. Investigating trends in a systematic series of 51 crystalline salt forms of methylephedrine

S. de Moraes, Lygia and Edwards, Darren and Florence, Alastair J. and Johnston, Andrea and Johnston, Blair F. and Morrison, Catriona A. and Kennedy, Alan R. (2017) Aqueous solubility of organic salts. Investigating trends in a systematic series of 51 crystalline salt forms of methylephedrine. Crystal Growth and Design, 17 (6). pp. 3277-3286. ISSN 1528-7483 (https://doi.org/10.1021/acs.cgd.7b00255)

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Abstract

A dataset consisting of structures and aqueous solubility and melting point data for 51 salt forms of the phenylethylamine base methylephedrine is presented. Analysis showed correlation between solubility and melting point and between melting point of the salt and melting point of the parent acid, but no correlation of salt solubility with solubility of the parent acid. Identification of associations was aided by examining chemically sensible subgroups of the dataset, and this approach highlighted significantly different relationships between solubility and melting point for these subgroups. Thus, for example, the expected negative correlation between solubility and melting point was found for 24 anhydrous benzoate salts, but a positive correlation observed for 8 halide salts. Hydrated forms were anomalous. Packing analysis identified groups of structures that were isostructural with respect to cation packing. Correlation between solubility and melting point was found to be greatest within these isostructural groups, implying a role for packing structure in determining solubility.

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