Linear Deracemization Kinetics during Viedma Ripening: Autocatalysis Overruled by Chiral Additives
摘要:
Viedma ripening proceeds through an autocatalytic feedback mechanism which exponentially deracemizes an initially racemic solid state to an enantiopure end state. Here we show that, in the presence of enantiopure additives with a concentration of as low as 2.5 × 10–2 mol %, Viedma ripening proceeds with an overall linear and faster increase in enantiomeric excess. These experimental results can be explained using a simple model which assumes a difference in growth and dissolution rates between the enantiomers. This model also accounts for the generally observed linearity during the initial stages of Viedma ripening without additives.
Enantioselective Symmetry Breaking Directed by the Order of Process Steps
作者:Wim L. Noorduin、Hugo Meekes、Willem J. P. van Enckevort、Bernard Kaptein、Richard M. Kellogg、Elias Vlieg
DOI:10.1002/anie.200907231
日期:2010.3.29
configuration of the product of grinding‐induced symmetrybreaking can be controlled simply by the order in which the different reaction‐mixture components are combined (see scheme: I) glass beads, II) racemic mixture (enantiomers differentiated by color), III) solvent, IV) racemization catalyst). The underlying mechanism is based on a subtle balance between enantioselective crystal growth and dissolution.
Complete Deracemization by Attrition-Enhanced Ostwald Ripening Elucidated
作者:Wim L. Noorduin、Hugo Meekes、Willem J. P. van Enckevort、Alessia Millemaggi、Michel Leeman、Bernard Kaptein、Richard M. Kellogg、Elias Vlieg
DOI:10.1002/anie.200801846
日期:2008.8.11
Controlling the Effect of Chiral Impurities on Viedma Ripening
作者:René R. E. Steendam、Bram Harmsen、Hugo Meekes、Willem J. P. van Enckevort、Bernard Kaptein、Richard M. Kellogg、Jan Raap、Floris P. J. T. Rutjes、Elias Vlieg
DOI:10.1021/cg400927m
日期:2013.11.6
Spontaneous symmetry breaking and chiral amplification by means of Viedma ripening by definition should result in complete deracemization of a racemic conglomerate into either one of the enantiomers with equal probability. In practice, however, chiral impurities influence Viedma ripening and one enantiomer is obtained in preference over the other. Here, we show that by increasing the attrition intensity during Viedma ripening, the effect of chiral impurities is suppressed and deracemization does yield either enantiomer with equal probability. The reason for this is that the resulting smaller crystals lead to such a low surface density of chiral impurities that they no longer inhibit the crystal growth sufficiently to determine the chiral outcome. Furthermore, we show that even for low attrition intensities, the effect of chiral impurities can be canceled by using the right amount (10 ppm) of chiral additives.
Attrition-enhanced total resolution leads to homochiral families of amino acid derivatives
作者:Michel Leeman、Jesse M. de Gooier、Karin Boer、Karen Zwaagstra、Bernard Kaptein、Richard M. Kellogg
DOI:10.1016/j.tetasy.2010.04.007
日期:2010.5
The total resolution of five structurally similar racemizable amino acid derivatives, three of which have racemic crystal structures, was performed simultaneously. By enantioselective incorporation in an amino acid derivative that forms a conglomerate the other four were deracemized on attrition-induced grinding. The outcome of the resolution was random (R) or (S), but all compounds had the same absolute configuration and high enantiomeric purities. (C) 2010 Published by Elsevier Ltd.