Resolution of Tris ethylenediamine chromium III Chloride

The tris(ethylenediamine) chromium (III) ion was first resolved by Werner6 by means of sodium 3-nitro-(+)-camphor. What has been said concerning the resolution of the corresponding rhodium compound holds true of the chromium compound, except that for the chromium compound the solubility difference of the diastereoisomeric chloride (+)-tartrates is so small that a resolution via these diastereoisomers has not been achieved.5,6 The method reported here is essentially the same as the one described for the rhodium complex but with minor alterations 

Tris(ethylenediamine)chromium(III) chloride trihydrate (39.3 g., 0.10 mole) and 22.5 g. (0.15 mole) of (+)-tartaric acid, and a magnetic stirring bar, are placed in a 400-ml. beaker. A 100-ml. volume of water is added, and the mixture is dissolved with stirring. Immediately after the dissolution, 12.6 g. (0.30 mole) of IiOH-H20 is added with continued stirring. The hydroxide dissolves, and shortly after a yellow crystalline precipitate is formed. About 5 minutes after the addition of the hydroxide, 100 ml. of ethanol is added dropwise with continued stirring during a 15-minute period. The precipitate is filtered, and the filtrate is run directly into a mixture of 15 ml. (0.18 mole) of 12 M HC1 and 600 ml. of absolute ethanol. From this system a finely crystalline precipitate of impure (—)D-chloride separates out. The filter flask is replaced, and the crystals are washed with three 50-ml. portions of a 1 1 mixture of ethanol and water and dried in air. (Yield is 27-28 g.) The precipitate of (—)D-chloride from the filtrate is filtered, washed with three 50-ml. portions of ethanol, and dried in air. (Yield is 13-14 g.) 

The crude tartrate double salt is dissolved in 500 ml. of water, and the solution is filtered. A filtered solution of 21.2 g. (0.50 mole) of LiCl in 500 ml. of ethanol is added dropwise to the stirred filtrate during a period of approximately an hour, and the stirring is continued for 15 minutes. The precipitate is filtered, washed with three 30-ml. portions of a 1 1 mixture of ethanol and water, and dried in air.f The yield is 23-24 g. 

To the recrystallized double salt (approximately 23 g. or approximately 0.04 mole) is added 30 ml. (0.36 mole) of 12 M HC1. A 300-ml. quantity of methanol is added dropwise with stirring during a period of approximately 30 minutes, and the stirring is continued for 5 minutes. The precipitate is filtered, washed with three 25-ml. portions of methanol, and dried in air. Yield is approximately 13 g. of (+)D-chloride. 

In [Co(en)3]Cl3-3H20 and 2(+)D-[Co(en)3]Cl3-NaCl-6H 0 the water molecules are enclosed in hollow channels in the structure. On the basis of the structural similarities,10 it is probably 

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Methods for the preparation of tris(ethylenediamine)rhodium-(III) chloride hydrate and for its resolution by means of the diastereoisomer Ii (—)D-lRh(en)s] (- -)-tart 2 3H20 are presented. The resolution of tris(ethylenediamine)chromium(III) chloride by means of an analogous diastereoisomeric compound is also described. 

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