CLAY COLUMN CHROMATOGRAPHY FOR OPTICAL RESOLUTION: FIRST CLUES, DEVELOPMENT AND FUTURE

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The attempt of optical resolution by use of smectite clays is reviewed. The first clue was given by the discovery that the pure enantiomer of [Ru(1,10-phenanthroline)₃]²⁺ was adsorbed by sodium montmorillonite within the CEC of a clay, while the racemic mixture was adsorbed to two times excess of CEC. It was proposed that a vacant space capable of chiral discrimination was generated when a clay surface was modified with the enantiomeric chelates. This model lead to the method of optical resolution using an ion-exchange adduct of a smectite clay and chiral chelates as an adsorbent. A clay column prepared for high performance liquid chromatography is now commercially available and has been applied for separating a wide range of chiral organic and inorganic compounds. Further improvement is now under progress.