Pressure Effect on D,L-Mandelic Acid Racemate Crystallization
Pressure Effect on D,L-Mandelic Acid Racemate Crystallization
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DOI：
10.1021/jp401626a
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发表时间：
2013-04-11
影响因子：
3.7
通讯作者：
Katrusiak, Andrzej
中科院分区：
文献类型：
--
作者：
Cai, Weizhao;Marciniak, Jedrzej;Katrusiak, Andrzej
扁桃酸，C6 H5 CHOHCOOH，（MA）是Wallach规则的常见豁免之一，因为其外消旋体DL-MA的密度低于对映体。这种关系似乎是不利的外消旋体在高压下的稳定性，然而，外消旋体保持更稳定的对映异构体的聚集体高达至少1.36 GPa。DL-MA的等容结晶产生其正交晶型I，空间群Pbca，并且在0.65 GPa以上，单斜晶型DL-MA II的另一中心对称多晶型，空间群P2（1）/c变得稳定。它们的结构已被确定的X射线衍射的单晶体原位生长在金刚石压砧室高达1.36 GPa。晶格能计算的半经验PIXEL方法表明，DL-MA形式II比DL-MA形式I更稳定，这两种外消旋体都比它们的对映体对应物L-MA更稳定。
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 P2(1)/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.