ChemInform Abstract: Enantiomer‐Differentiation Induced by an Enantiomeric Excess During Chromatography with Achiral Phases

Tsai, Wen‐Liang; Hermann, Kurt; Hug, E.; Rohde, Bernhard; Dreiding, Aǹdré S.

doi:10.1002/chin.198611076

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“…This is responsible for other remarkable phenomena, such as nonlinear behavior of optical rotation 1,2 and UV absorbance, 3 nonlinear effects in asymmetric catalysis, [4][5][6][7] as well as enantiomeric enrichment through chromatography on achiral stationary phases. [8][9][10][11][12][13][14][15][16] Among other examples, the enantiomeric purity of nonracemic mixtures of the enantiomers of the chiral 2,2′-dihydroxy-1,1′-binaphthyl (binaphthol in the following) in different solvents has been increased through chromatography on different silica gel based achiral columns. 12,15 As shown in Figure 1, in the case of the enantiomers of bi-naphthol in chloroform using an achiral Licrosphere 100 NH 2 column, we have recently been able to collect two fractions constituted of the pure enantiomer present in excess (reaching 100% e.e.)…”

Section: Introductionmentioning

confidence: 99%

Measurement of the Dimerization Equilibrium Constants of Enantiomers

et al. 2002

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The formation of homochiral and heterochiral dimers in solutions of enantiomers causes a number of remarkable phenomena, such as the enantiomeric enrichment of nonracemic mixtures on achiral chromatographic columns when chiral monomers and dimers exhibit different retention behavior. In this work, such effects on optical rotation and UV absorbance are analyzed theoretically and experimentally. In particular, it is demonstrated how optical rotation measurements can be used to estimate the dimerization equilibrium constants. It is shown how significant this is for polarimeter calibration, as well as for the determination of enantiomer concentrations in process streams, when optical rotation and UV absorbance measurements are combined. All experimental measurements refer to the enantiomers of the chiral 2,2′-dihydroxy-1,1′-binaphthyl in chloroform, at a temperature of 23 °C. The measured values of its dimerization equilibrium constants are 1.3 ( 0.5 and 3.1 ( 1.0 L/mol for the formation of homochiral and of heterochiral dimers, respectively.

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