Valente E J, Smith T N, Harris M E
Department of Chemistry, Mississippi College, Clinton, Mississippi 39058-4036, USA.
Chirality. 2001 May 15;13(5):244-50. doi: 10.1002/chir.1026.
(-)-(R)-Deoxyephedrine forms poorly discriminating diastereomeric salts with 4'-fluoromandelic acid from 95% ethanol. Both less-soluble (L) (S)-4'-fluoromandelate and more-soluble (M) (R)-4'-fluoromandelate phases are monoclinic and unsolvated. Their solubility ratio (M/L) in 95% ethanol is only 1.2, which correlates with the similarity and small differences in their respective heats of fusion and fusion temperatures. The (R)-deoxyephedrinium and the related (1R;2S)-ephedrinium 4'-fluoromandelate systems show L-salts with higher ion-pair volumes and lower densities than their M-salts. (R)-Deoxyephedrinium salts have higher volumes than the comparable (1R;2S)-ephedrinium salts even though the resolving base (R)-deoxyephedrine lacks the benzylic hydroxy. In the solids, bilayered structures segregate polar and nonpolar molecular regions. The principle interionic interactions are hydrogen bonds between protonated secondary ammonium ions and carboxylates forming infinite chains with a six-atom repeating unit H-N(+)-H...O-C(-)-O [C(2)(2)(6)]. These are buttressed by mandelate hydroxy to carboxylate hydrogen bonds. Differing interactions between phenyl and 4'-fluorophenyl rings in the nonpolar layers of the salts correlate with the density and stability inversion.
（-）-（R）-脱氧麻黄碱与4'-氟扁桃酸在95%乙醇中形成的非对映体盐的区分效果较差。较难溶解的（L）（S）-4'-氟扁桃酸盐相和较易溶解的（M）（R）-4'-氟扁桃酸盐相均为单斜晶系且无溶剂化。它们在95%乙醇中的溶解度比（M/L）仅为1.2，这与其各自熔化热和熔化温度的相似性及微小差异相关。（R）-脱氧麻黄碱盐和相关的（1R；2S）-麻黄碱4'-氟扁桃酸盐体系显示，L-盐的离子对体积比M-盐更高，密度更低。（R）-脱氧麻黄碱盐的体积比可比的（1R；2S）-麻黄碱盐更大，尽管拆分碱（R）-脱氧麻黄碱缺少苄基羟基。在固体中，双层结构将极性和非极性分子区域分隔开。主要的离子间相互作用是质子化仲铵离子与羧酸盐之间的氢键，形成具有六原子重复单元H-N(+)-H...O-C(-)-O [C(2)(2)(6)]的无限链。这些氢键由扁桃酸羟基与羧酸盐之间的氢键支撑。盐的非极性层中苯基和4'-氟苯基环之间不同的相互作用与密度和稳定性反转相关。
