Pressure Effect on d,l-Mandelic Acid Racemate Crystallization

• Published in: Journal of physical chemistry. C 2013-04, Vol.117 (14), p.7279-7285
• Main Authors: Cai, Weizhao, Marciniak, Jędrzej, Andrzejewski, Michał, Katrusiak, Andrzej
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from solutions; Materials science; Methods of crystal growth; physics of crystal growth; Physics
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp401626a

Mandelic acid, C6H5CHOHCOOH, (MA) is one of frequent exempts from the Wallach’s rule, as its racemate DL-MA is less dense than the enantiomers. This relation appears to be unfavorable for the racemate stability at high pressure; however, the racemate remains more stable than the conglomerate of enantiomers up to 1.36 GPa at least. The isochoric crystallization of DL-MA yields its orthorhombic form I, space group Pbca, and above 0.65 GPa, another centrosymmetric polymorph of monoclinic DL-MA form II, space group P21/c, becomes stable. Their structures have been determined by X-ray diffraction of the single crystals in situ grown in a diamond-anvil cell up to 1.36 GPa. Lattice-energy calculations by the semiempirical PIXEL method demonstrate that DL-MA form II is more stable than DL-MA form I, and both of these racemates are more stable than their enantiomer counterpart L-MA.