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31 P NMR enantiomeric purity determination of free 1‐aminoalkylphosphonic acids via their diastereoisomeric Pd(II) complexes
Author(s) -
Głowacki Zdzisław,
Topolski Marek,
MatczakJon Ewa,
Hoffmann Maria
Publication year - 1989
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260271004
Subject(s) - chemistry , enantiomer , enantiomeric excess , chelation , proton nmr , diastereomer , nmr spectra database , carbon 13 nmr , stereochemistry , analytical chemistry (journal) , organic chemistry , spectral line , enantioselective synthesis , catalysis , physics , astronomy
A convenient 31 P NMR method for determining the enantiomeric excess of free 1‐aminoalkylphosphonic acids is presented. It was found by NMR that the interaction of Pd II ions with 1‐aminophosphonate ligands (L) yields, in a non‐diastereoselective manner, diastereoisomeric chelate pairs (PdL 2 ) observable in alkaline D 2 O solutions. The chelate complexes give two peaks in the 31 P NMR spectra; one corresponds to the chiral species e (both ligands are R or S enantiomers) and the second to the meso forms ( R and S ligands). The shapes of these peaks and the differences in the chemical shifts for the species (Δδ) depend on the temperature and the resonance frequency, typical for a dynamic process. Under the experimental conditions used (273–293 K and 40.48 or 121.5 MHz) Δδ values in the range 0.03–0.18 ppm were obseved. The separation of the 31 P NMR signals of eight of the ten investigated racemic acids allowed the determination of the enantiomeric purity. The measured enantiomeric excess of an enantiomerically enriched sample of 1‐aminobenzylphosphonic acid (prepared by weighing) was in excellent agreement with the expected value.