RESOLUTION OF A RACEMATE

Reaction of the racemic mixture with a single enantiomer of a reactant yields a mixture of two diastereomeric products. These may then be physically separated by exploiting their different physical properties (solubilities, chromatography, etc.). The individual enantiomers may then be released from the separated diastereomers.

The accompanying frames show the molecules involved in a hypothetical resolution of 2-methyl butanoic acid by esterification with a single enantiomer of a substituted butan-2-ol.

Frames 1 and 2 show the (R)- and (S)- enantiomers of the racemic acid. Frame 3 shows the (S)-alcohol.

Reaction of the racemic acid with the single enantiomer of the alcohol gives a mixture of two physically different diastereomeric esters, shown in the lower row. These may be separated and hydrolysed to release the required separated (R)- and (S)-2-methylbutanoic acids.