Solid-to-solid kinetic resolution: Determination of the enantiomeric ratio

Enzymatic kinetic resolution can be carried out with a suspension of incompletely dissolved solid substrate. In favorable cases, the slowly converted enantiomer may remain as an incompletely dissolved solid and can be easily recovered. Then, such a 'solid-to-solid' resolution process will also show a significantly improved yield and productivity when compared to the reaction with completely dissolved substrate. The determination of the enantiomeric ratio (E) for reactions with suspended racemates requires equations that are different than for reactions with completely dissolved substrate. This determination becomes very complex in case of mass transfer limitation and is greatly facilitated when mass transfer limitations are absent. If the latter condition has been checked, E can be obtained from measurement of the extent of conversion and the enantiomeric excess, either of the product or of the remaining solid substrate, but not of the remaining dissolved substrate.