Shell Internationale Research Maatschappij, B.v.

Wilhelmus N Ruyters

Johannes Van Berkel

A process for preparing a compound according to formula I containing substantially equimolar amounts of the 1R cis S- and the 1S cis R-isomers (the cis-2 enantiomer pair) and substantially free of the 1R cis R- and the 1S cis S-isomers (the cis-1 enantiomer pair), ##STR1## wherein R.sup.1 and R.sup.2 are each independently selected from chlorine, bromine and methyl, which process comprises contacting the cis-1 enantiomer pair, alone or in the presence of the cis-2 enantiomer pair, with an organic amine base containing from 5 to 7 carbon atoms and being a secondary amine containing two branched alkyl groups or being a tertiary amine, and then separating off a solid compound containing the cis-2 enantiomer pair and substantially free of the cis-1 enantiomer pair, characterized in that the reaction mixture is in the form a solid-liquid slurry.

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Amsterdam, Netherlands

Wilhelmus N Ruyters