On the basis of crystal engineering, two similar esters of phenyl pyridine-2-carboxylate (I) and phenyl pyrazine-2-carboxylate (II) were designed and synthesized. The compounds were characterized using FT-IR, mass spectrometry, CHN-elemental analyses, NMR and PXRD. For each compound, two polymorphs were obtained (Ia, Ib and IIa, IIb) and identified by TGA, DSC and SCXRD. A comparison of the crystal structures of the polymorphs revealed that the different torsion angles of the pyrazine (τ1) and phenyl (τ2) rings to the ester backbone resulted in the conformers I and II, respectively. Theoretical criteria (max(Δθ), rmsd[r]-crystal, energy profile) confirmed that the structural differences in the conformers are in the range of acceptable values for the detection of conformational changes. The phase stability of the polymorphs was investigated by slurry and grinding methods as well as by the HSM technique. Since the orientations of pyrazine and phenyl moieties were altered in the polymorphs, the hydrogen bond donor and acceptors exhibited meaningful supramolecular architectures in the crystal packing as well as C–H⋯N, C–H⋯O and C–H⋯π interactions. The energetic study of the noncovalent interactions in the molecular pairs (dimers) of the polymorph crystal structures was performed by DFT-D calculations.

Orientation-dependent conformational polymorphs in two similar pyridine/pyrazine phenolic esters

2-((2,6-Dichlorophenyl)amino)benzoic acid (2-DCABA), a potential non-steroidal anti-inflammatory drug and an analog of 2-((2,6-dimethylphenyl)amino)benzoic acid (HDMPA) was synthesized and its polymorphism was studied to investigate the effect of double Cl-CH3 exchange....

Polymorphism and cocrystal salt formation of 2-((2,6-dichlorophenyl)amino)benzoic acid, harvest of a second form of 2-((2,6-dimethylphenyl)amino)benzoic acid, and isomorphism between the two systems

Substitution on both aromatic rings of fenamic acid led to a highly polymorphic system in 5-methyl-2- m -tolylamino-benzoic acid, in contrast to the two mono-substituted analogs, which had only one or two forms obtained. 

Double substitution leads to a highly polymorphic system in 5-methyl-2-m-tolylamino-benzoic acid

Addition of methyl group(s) to either or both aromatic rings of fenamic acid (FA) afforded three FA derivatives (1–3), designed to investigate the effect on the polymorphic behavior of these compounds exerted by substitution. A relatively comprehensive polymorph screen led to the discovery of four polymorphs for compound 3, for which substitution took place on both aromatic rings, in contrast to the production of either two or one form(s) for compounds 1 and 2, both of which are mono-substituted. The observation indicated that both substitution position and pattern are important in the polymorphism of these compounds. The thermal properties of each system were investigated by differential scanning calorimetry (DSC). Conformational scans and Hirshfeld surface analyses were performed to study the mechanism of polymorphism and the intermolecular interactions contributing to the stability of each crystal form.

Double substitution leads to a highly polymorphic system in 5-methyl-2-m-tolylamino-benzoic acid

To probe the effect of substitution on the benzoic acid ring on the polymorphism of phenylaminobenzoic acids, five 3-methyl-2-(phenylamino)benzoic acids (MPABAs) were synthesized. A preliminary polymorph screen led to one...

Conformational Flexibility and Substitution Pattern Lead to Polymorphism of 3-Methyl-2-(phenylamino)benzoic acid

We report the discovery of two new forms (II and III) of a potential non-steroidal anti-inflammatory and thyroid drug, 2-((2,6-dimethylphenyl)amino)benzoic acid (HDMPA) through solution growth and thermal treatment of crystals. Form II has been discovered through crystal growth in a variety of solvents, and characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), FT-IR, and Raman spectroscopy. Form II converts into form III upon thermal treatment, as indicated by the phase behavior study of form II with differential scanning calorimetry (DSC). Form III has been characterized by IR, Raman and PXRD. Conformational flexibility of the molecule seems to lead to the polymorphism of the system. A conformational scan shows the conformational minima correspond to the conformers in the polymorphs. Lattice energy calculations show energies of −48.14 and −50.31 kcal mol−1 for forms I and II, providing information on the relative stability for each form. Hirshfeld analysis revealed that intermolecular interactions such as C⋯C, H⋯H, C⋯H, and H⋯O contribute to the stability of the crystal forms.

/pdf/solution-growth-and-thermal-treatment-of-crystals-lead-to-29p7nk4ag1.pdf

Solution growth and thermal treatment of crystals lead to two new forms of 2-((2,6-dimethylphenyl)amino)benzoic acid

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Solution growth and thermal treatment of crystals lead to two new forms of 2-((2,6-dimethylphenyl)amino)benzoic acid