Abstract: A method of optical enantiomer resolution by preferential crystallization involves entering, each time crystallization starts, the two-phase domain containing excess enantiomer and the saturated solution, and cooling according to a well-defined kinetic schedule. A racemic mixture of fine particle size is added to the mother liquors obtained after harvesting the crystals, the mother liquors then being heated to a temperature lower than that of homogenization of the solution so that excess enantiomer is present only in a solid state in equilibrium with the solution. Further cooling produces the other enantiomer and completes the cycle of operations which may then be carried out repetitively.

Abstract: Method of resolution of chiral hydantoins of the general formula I ##STR1## in which: R.sub.1 designates a lower alkyl radical comprising 1 to 5 carbon atoms in linear or branched chain,R.sub.2 designates a phenyl radical, possibly mono-, di-, or tri-substituted by lower alkyl or alkoxy radicals or halogen atoms, whether identical of different, or a heteroaryl radical containing a ring of 5 to 7 members in which the sole hetero atom is nitrogen, oxygen or sulfur, or else an aralkyl radical the alkyl part of which comprises one or two carbon atoms and the aryl ring is a phenyl group possibly mono-, di- or tri-substituted by radicals which are lower alkyl or alkoxy radicals or halogen atoms, whether identical or different. The hydantoin (I) to be resolved is dissolved in an alcohol or an alkaline solution, and an enantiomer of .alpha.