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Discrimination in resolving systems. V. Pseudoephedrine — fluoromandelic acid diastereomers
Author(s) -
Valente Edward J.,
Moore Michael C.
Publication year - 2000
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/(sici)1520-636x(2000)12:1<16::aid-chir4>3.0.co;2-4
Subject(s) - chemistry , orthorhombic crystal system , diastereomer , monoclinic crystal system , crystallography , hydrogen bond , crystal structure , stereochemistry , protonation , hydrate , crystallization , ion , molecule , organic chemistry
Resolution of the isomeric 2′‐, 3′‐, and 4′‐fluoromandelic acids with (+)‐(1S;2S)‐pseudoephedrine in 95% ethanol produces both well and poorly discriminating, hydrated and unsolvated binary salts. Seven observed diastereomeric phases are represented by five crystal structure types including three of the four types observed in the pseudoephedrine mandelates. Type a : monoclinic hemihydrate less‐soluble (L) (R)‐3′‐fluoromandelate and more‐soluble (M) (R)‐4′‐fluoromandelate (I); type b : orthorhombic unsolvated M (S)‐2′‐fluoromandelate; type c : orthorhombic unsolvated L (R)‐2′‐fluoromandelate; type d : orthorhombic dihydrate M (S)‐3′‐fluoromandelate and L (S)‐4′‐fluoromandelate; type e : monoclinic unsolvated M (R)‐4′‐fluoromandelate (II). Largest (15‐fold) discriminating solubilities in 95% ethanol are found between the diastereomers with 2′‐fluoromandelic acid, 50% more than in the corresponding ephedrine system. Principle interionic interactions are hydrogen‐bonds between protonated secondary ammonium ions and carboxylates. Infinite chains of these are found in type c , with a four‐atom repeating unit H‐N + ‐H···O(−C − −O) [C 2 1 (4)], and in types b and d , with a six‐atom repeating unit H‐N + ‐H···O‐C − −O [C 2 2 (6)]. Water of crystallization intervenes in the chains of type a but not of type d hydrated salts, according with higher average dehydration temperatures in the former. Hydrated salts in general are excessively soluble in 95% ethanol. Chirality 12:16–25, 2000. © 2000 Wiley‐Liss, Inc.