Potassium Z-Trioxalatocobaltate III 3-Hydrate

One gram (0.0012 mol) of Z-tris(l,10-phenanthroline)-nickel(II) perchlorate 3-hydrate (synthesis 59) is dissolved in 18 ml. of a freshly prepared 1 1 by volume acetone-water mixture. The pink solution is cooled in an ice bath to 10° not below) and added to an ice-cold solution of 1.10 g. (0.0023 mol) of potassium di-trioxalatocobaltate(III) 3-hydrate and 1 g. of potassium acetate in 20 ml. of water. The mixture is allowed to stand in an ice bath for 6 minutes with occasional stirring. Scratching the walls of the beaker may facilitate precipitation. The green diastereoisomer which precipitates is collected on a 5-cm. 

Biichner funnel and treated as described in Part B. The i-antipode is immediately precipitated from the filtrate by slow addition, with stirring, of 100 ml. of ice-cold ethanol. The green precipitate is collected on a 5-cm. Buchner funnel, washed with three 10-ml. portions of ice-cold ethanol or methanol, and air-dried. The yield is approximately 0.50 g. (91%). For a 0.032% aqueous solution in a 1-dm. tube, = —0.62°, and [a] —1940°. The high optical density of even. so dilute a solution makes observation of the field difficult. With the Rudolph high-precision polarime-ter, the half-shade angle control should be used at its maximum opening. 

The green diastereoisomer from Part A is washed with 20 ml. of ice-cold ethanol, air-dried, and suspended in 20 ml. of ice water. Two milliliters (0.0018 mol) of 3% hydrogen peroxide, two drops (approximately 0.0018 mol) of glacial acetic acid, and 1 g. (0.006 mol) of potassium iodide are added. The olive-colored mixture is stirred in an ice bath for 4 minutes and is then filtered through a 5-cm. Btichner funnel. If the oxidation continues to occur in the filtrate, it may be necessary to refilter the filtrate once.f The d-antipode is precipitated by the addition, with stirring, of 100 ml. of ice-cold ethanol to the filtrate. The product is collected, washed, and dried in the same manner as the 2-antipode. The yield is approximately 0.27 g. (49%). 

The optical antipodes of potassium tiio.xalatocobaltate-(III) are dark green salts which dissolve readily in water to give deep green solutions. Both are decomposed by light and heat  

The d-antipode is isomorphous with the corresponding rhodium(III) and iridium(III) salts. 

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