Resolution of the Tris ethylenediamine cobalt III Ion

Submitted by J. A. Broomhead, F. P. Dwyer, and J. W. Hogarth Checked by Robert E. Sievers  

Tris (ethylenediamine) cobalt (III) chloride was first prepared by Werner.1 Resolution was effected through the chloride d-tartrate which was obtained by allowing the chloride (1 mol) to react with silver d-tartrate (1 mol). The correct ratio of chloride ion to tartrate ion is important and this has meant that it was necessary to isolate the pure solid chloride, the synthesis of which has been described by Work.2 In the present method the less soluble diastereo-isomer is isolated directly and the expensive and unstable silver d-tartrate is replaced by barium d-tartrate. The addition of activated carbon ensures rapid oxidation of the initial cobalt (II) complex and eliminates small amounts of by-products of the reaction. 

A 500-ml. filter flask is fitted with a rubber stopper carrying an open glass tube extending to the bottom of the flask, and 20.4 ml. of 88.6% w/v ethylenediamine (0.3 mol) is 

X Prepared by mixing solutions of barium chloride 2-hydrate (24.4 g. 0.1 mol) and sodium potassium tartrate 4-hydrate (28.2 g. 0.1 mol) at 90°, cooling, filtering, and washing with warm water. The precipitate and filter paper are added. 

If The solution may be cooled in ice, whereupon very small crystals result. 

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