Purification Methods
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.]