Benzoate derivatives, chiral recognition

Polysaccharide-based CSPs also exhibit a chiral recognition for alcohols and a large number of resolutions have been reported. Chiral alcohols can usually be directly resolved with hexane containing a small amount of an alcohol as the eluent. For aliphatic alcohols, which cannot be directly resolved, their resolution is often efficiently attained as phenylcarbamate or benzoate derivatives on OD (Figure 17).85 For example, 2-butanol and 2-pentanol are completely resolved with a very high selectivity on OD as their phenylcarbamates. The derivatization of alcohols to phenylcarbamates and benzoates can be easily achieved by the reaction with phenyl isocyanates and benzoyl chlorides, respectively. In most cases, the phenylcarbamates are better resolved than the benzoates. For chiral compounds bearing phenolic hydroxy groups, the addition of a small amount of an acid to an eluent is recommended to depress its dissociation. 

Expansion of these investigations to other types of polysaccharide derivatives led to the development of silica-coated versions of cellulose and amylose carbamates and benzoates [100-102]. These CSPs showed particularly versatile chiral recognition profiles, resolving an extremely broad assortment of chiral analytes. Several of these CSPs have been commercialized by Daicel Chemical Industries, Ltd., the most important ofwhich are depicted in Fig. 7.5. 

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