Preparation of the trams-Form

4 m7is-[Co(en)2Cl2]Cl-HCl + 2H2O ra s-[Co(en)2Cl2]ClHCl frans-[Co(en)2Cl2]Cl + HCl 

Conversion to the cis form is brought about by evaporating a neutral solution of the tram form to dryness on the steam bath. The unchanged tram form may be washed 

Forty grams of the finely powdered racemic cis form is dissolved as quickly as possible in 1120 ml. of water, previously cooled to 15 to 17°. The solution is quickly filtered, and 88 g. of solid ammonium d-a-bromocamphor-7r-sulfonate is added. The mixture is stirred for 30 minutes, while the temperature is maintained at 15 to 17°. The t-m-dichloro-bis (ethylenediamiiie) cobalt (III) d-a-bromocamphor-r-sul-fonate is filtered and washed with alcohol and then with ether. Yield 20 to 25 g. 

This salt is ground, in an ice-cold mortar, with an ice-cold mixture of concentrated hydrochloric acid, alcohol, and ether (1 1 1) 75 ml. of the mixture is used for each 10 g. of salt. After several minutes, the l-cis-[Co(en)2Cl2]Cl is filtered and washed with alcohol and then with ether. The yield is 5 g.—nearly the theoretical value. The specific rotation (Naa) of a 0.4 per cent solution is —200° and of a 0.1 per cent solution is -1-215.° 

The other optical isomer of the complex salt cannot be precipitated from the solution, and evaporation causes decomposition. It is therefore lost. 

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