| Effect of crystallization conditions on polymorphic diversity of malic acid RS — Racemate |
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| 作者姓名： | Isakov A I Kotelnikova E N Kryuchkova L Yu Lorenz H |
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| 作者单位： | St.Petersburg State University,St.Petersburg 199034,Russia;Max Planck Institute for Dynamics of Complex Technical Systems,Magdeburg 39106,Germany |
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| 基金项目： | Supported by the Russian Fund for Basic Research （RFBR） under Grant No. 10-05-00891 and 12-05-00876. |
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| 摘 要： | Enantiomers (R(+) and S(-)),RS-racemate (double compound) and (R+S)-conglomerate (mechanical mixture of enantiomers) of malic acid C 4 H 6 O 5 have been investigated by means of X-ray diffractometry and high temperature X-ray diffraction method.The RS-racemate was found to be able to form three polymorphic modifications,which we denominated as M1 (monoclinic,space group P2 1 /c),M2 (monoclinic,space group Cc),and Tc (triclinic,space group P-1),the latter modification having been unknown before.Modification Tc was also described,and its Xray diffraction characteristics,including interplanar spacings d,hkl indices,unit cell parameters,were defined.In addition,X-ray diffraction characteristics for both reported earlier M1 and M2 monoclinic polymorphic modifications were measured with higher accuracy.The ability of RS-racemate to form one of the above three modifications (M1,M2,and Tc) or their mixtures containing various proportions and combinations of the components (M1+M2,M1+Tc,or M2 +Tc) was found to depend on the type of crystallization medium (a melt,aqueous medium,ethanol or acetone solution),crystallization rate (from 2-3 minutes to 4 months),and crystallization temperature.Heating S-enantiomer and M1 RS-racemate up to their respective melting points (100 ℃ and 124 ℃,correspondingly) only made them undergo thermal deformations,while heating (R+S)-conglomerate in the temperature range of 96-110 ℃ resulted in its homogenization to form M2 RS-racemate,which,near the melting point (118 ℃),namely,in the range of 112-116 ℃,was transformed into M1 RS-racemate.
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| 关 键 词： | polymorphism racemic chiral |
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