Solns. for recovery of enantiomers by fractional crystallisation - contain organic solvents and 0-15 wt. per-cent water and one of the enantiomers in excess and when seeded with racemate, crystallise out racemate

摘要

Solns. contg. organic solvent(s) and 0-15 wt.% water and one of the two enantiomers of formula (I) in excess and from which pref. the racemate crystallises out, enriching the amt. of the enantiomer originally in excess, are new. (where R1 = H, F, Cl, Br or Me; R2 = H or Me). USE/ADVANTAGE - The solns. can be used in the sepn. of enantiomers of chiral organic cpds. by fractional distn. without the need to convert (I) into diastereomeric salts e.g. hydrogen tartrate and then liberate (I) repeatedly. One conversion into the hydrogen tartrate using the cheaper (2R,3R)-(+)-tartaric acid suffices and one crystallisation step gives solns. of (I) with excess of an enantiomer used to crystallise out the racemate, further enriching the enantiomer in excess. This saves time and materials. The sepn. of racemates of (I) is achieved with high yields. The enantiomer is enriched in the soln. to an amt. of up to 97% of the specific optical rotation.