Resolution of DL-Valine by Countercurrent Solvent Extraction with Continuous Sample Feeding

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Abstract
DL-Valine was resolved completely by a solvent extraction system with a continuous sample feeding process called continuous countercurrent fractional extraction (CFE). The two-phase system contained n-butanol and water with a copper(II) complex of N-n-dodecyl-L-hydroxproline as a resolving reagent. The upper (alcohol-rich) phase and the lower (water-rich) phase proceeded in the segmented extraction columns countercurrently; the D-isomer was recovered in the upper phase, while the L-isomer was recovered in the lower phase. The optical purity of the enantiomers obtained was consistently 99.5% or higher. The D-isomer extracted in the upper phase was recovered completely by using a backextraction column in series after the extraction column, allowing the upper phase to be used repeatedly for the resolution. The efficiency of the CFE system was estimated at more than 24 theoretical stages.

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