| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4996031 | Thermochimica Acta | 2017 | 9 Pages |
•Pure components in the given resolution system are sought and studied.•Detailed analytical (XRD, FTIR, and DSC) features of all pure substances are compared.•Single crystal X-ray structure of two compounds of this system has been determined.•Structural implications are drawn for salts without known structures based on analytical features.•Binary and ternary eutectic phase diagrams in the resolution system are constructed.
The system of intermolecular interactions is very similar in the solid state of the chiral and racemic α-methoxyphenylacetic acids (α-MPAA) indicated by both Differential Scanning Calorimetry (DSC) and FTIR-spectroscopy, and even proved by single crystal structure determination. It makes the resolution of such a racemate compound challenging even by supercritical fluid extraction. The chiral (S)-α-methoxyphenylacetic acid (1) crystallizes in orthorhombic crystal system (space group P212121, a = 6.8795(3) Å, b = 7.0124(3) Å, c = 17.4578(8) Å, Z = 4, R = 0.0373), while its 1:1 salt formed with (S)-1-cyclohexylethyl amine (3) is found to be monoclinic (s.g. P21, a = 9.5290(12) Å, b = 6.5909(10) Å, c = 13.869(2) Å, β = 103.13(3)°, Z = 2, R = 0.0477). The packing arrangement in the (S)-(S) ammonium carboxylate type salt is columnar. The columns are hydrophylic inward and hydrophobic outward, that results in fibrous growth of the salt crystals melting at 163 °C. The crystal habit of the higher melting diastereomeric (S)-(R) salt (mp. 187 °C) is also fibrous, its structure is closely related to the (S)-(S)-salt by the similarities observed in their IR spectra. The DSC and powder XRD studies on the chiral and racemic acids, and on the pair of diastereomeric salts helped us to construct and calculate the binary and ternary phase diagrams of the system components, including their eutectic temperatures and compositions, as well.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (214 K)Download as PowerPoint slide
