Large-scale preparative liquid chromatography

J. L. Sandlin and Y. Ito, Large-scale preparative countercurrent chromatography with a coil planet centrifuge,/. Liquid Chromatogr. 5(12) 2153-2171 (1985). Y. Ito and R. Bhatnagar, Improved scheme for preparative CCC with a rotating coil assembly, /. Chromatogr. 207 171-180 (1981). 

Colin, H., Large-scale high-performance preparative liquid chromatography, in Preparative and Production Scale Chromatography, Ganetsos, G. and Barker, P. E. Eds., Marcel Dekker, New York, 1988, 11. 

Concerning the synthetic applications, it is clear that these reactions have allowed the obtaining of new structures and are useful for the synthesis of many polyfunctional molecules not easily obtainable by more classical ways. Moreover, starting materials are nearly always very simple and often commercially available. One limitation should be perhaps in some cases — the separation of formed products. However now, low- and high-pressure preparative liquid chromatographies become more and more usual in laboratories. Those techniques allow work on a large scale and are no more difficult to handle than other usual methods. Thus these techniques improve the interest of our reactions which lead to elaborate structures from trivial starting molecules. 

Partition or liquid-liquid chromatography is similar to solvent extraction. In fact, solvent-extraction data can be used to predict partition coefficients for LLC. The resolving power and speed of LLC are considerably greater than that of solvent extraction, however, since the equivalent of several thousand partitions takes place as the sample components move down a column. LLC is generally better suited to analytically separating complex mixtures, whereas extraction is used more for large-scale preparative separations or for separating relatively simple mixtures. 

Although overcrowded afkenes are attractive due to the efficient switching of LC handedness, the delicate synthesis of overcrowded alkenes remains a limitation for their practical applications. Normally the separation of two enantiomers of crude racemic product to obtain optically pure isomer has to rely on the preparative high performance liquid chromatography (HPLC), which is not suitable for a large-scale preparation. Consequently, researchers are seeking for other types of photoresponsive molecules for the switching of helix handedness. 

HPLC separations are one of the most important fields in the preparative resolution of enantiomers. The instrumentation improvements and the increasing choice of commercially available chiral stationary phases (CSPs) are some of the main reasons for the present significance of chromatographic resolutions at large-scale by HPLC. Proof of this interest can be seen in several reviews, and many chapters have in the past few years dealt with preparative applications of HPLC in the resolution of chiral compounds [19-23]. However, liquid chromatography has the attribute of being a batch technique and therefore is not totally convenient for production-scale, where continuous techniques are preferred by far. 

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