Purification methods described for the mixed isomers are applicable here. The individual isomers can be separated by very efficient fractional distillation, followed by fractional crystallisation by partial freezing. The cis-isomer reacts preferentially with AlCl3 and can be removed from the trans-isomer by stirring the mixture with a limited amount of AlCl3 for 48hours at room temperature, filtering and distilling. [Seyer & Walker J Am Chem Soc 60 2125 1938, Baker & Schuetz J Am Chem Soc 69 1250 1949.] A very pure authentic sample is best obtained by synthesis from cis-1,2-bis-chloroethylcyclohexane [Whitesides & Gutowski J Org Chem 41 2882 1976, Beilstein 5 IV 310.]
