Valente E J, Zubkowski J, Eggleston D S
Department of Chemistry, Mississippi College, Clinton 39058.
Chirality. 1992;4(8):494-504. doi: 10.1002/chir.530040807.
Resolution of mandelic acid with (-)-(1R,2S)-ephedrine in water and ethanol produces intermediate diastereomeric salts with greatly disparate solubilities and melting points. Single crystal X-ray analysis of the less (L) and more (M) soluble (-)-ephedrinium mandelates (I, II) shows crystal structures which are isosteric, each crystallizing in the monoclinic system, space group C2. Protonated ephedrines occupy the same relative positions in the L- and M-salts, and mandelates are in the same general locations. Hydrogen bonds link alternating protonated ephedrine nitrogens and mandelate carboxylate oxygens in each salt forming columns of ions. The helical H-bonded chain winds down the crystallographic 2-fold screw axis. Additional H-bonds form between 2-fold related mandelates in the L-salt. Mixed crystals, containing both mandelate isomers, (2R)- and (2S)-mandelates, are obtained from the resolving system partly depleted of the L-salt. A specimen with nearly equal amounts of the mandelates (III) is also isosteric with the commensurate structures. I (294K), L-salt: a = 18.160(7), b = 6.538(2), c = 13.898(4) A, beta = 92.02(3) degrees, V = 1649.1(9) A3; IIa (294K), M-salt: a = 17.978(11), b = 7.164(4), c = 13.574(6)A, beta = 96.41(4) degrees, V = 1737.3(16) A3; IIb (223K), M-salt: a = 17.805(8), b = 7.115(2), c = 13.50(5) A, beta = 96.89(3) degrees, V = 1697.9(15) A3; III (294K), mixed-salt: a = 18.184(22), b = 6.792(7), c = 13.808(19) A, beta = 93.74(10) degrees, V = 1701.7(35) A3.
扁桃酸与（-）-（1R，2S）-麻黄碱在水和乙醇中拆分得到溶解度和熔点差异极大的中间非对映体盐。较难溶解（L）和较易溶解（M）的（-）-麻黄碱扁桃酸盐（I、II）的单晶X射线分析表明，其晶体结构为等排体，均在单斜晶系中结晶，空间群为C2。质子化麻黄碱在L-盐和M-盐中占据相同的相对位置，扁桃酸盐也处于相同的大致位置。氢键将每种盐中交替的质子化麻黄碱氮原子和扁桃酸盐羧酸根氧原子相连，形成离子柱。螺旋形氢键链沿晶体学2次螺旋轴向下缠绕。在L-盐中，2次相关的扁桃酸盐之间形成额外的氢键。从部分耗尽L-盐的拆分体系中获得了含有两种扁桃酸异构体（2R）-和（2S）-扁桃酸盐的混合晶体。一种含有近乎等量扁桃酸盐的样品（III）也与相应结构等排。I（294K），L-盐：a = 18.160(7)，b = 6.538(2)，c = 13.898(4) Å，β = 92.02(3)°，V = 1649.1(9) ų；IIa（294K），M-盐：a = 17.978(11)，b = 7.164(4)，c = 13.574(6)Å，β = 96.41(4)°，V = 1737.3(16) ų；IIb（223K），M-盐：a = 17.805(8)，b = 7.115(2)，c = 13.50(5) Å，β = 96.89(3)°，V = 1697.9(15) ų；III（294K），混合盐：a = 18.184(22)，b = 6.792(7)，c = 13.808(19) Å，β = 93.74(10)°，V = 1701.7(35) ų。
