Carbonato bis ethylenediamine cobalt III Chloride and Bromide

The following procedure is based on the reaction of an aqueous solution of cobalt(II) chloride with the equivalent amount of (2-aminoethyl)carbamic acid, followed by oxidation with hydrogen peroxide and the subsequent formation of bis(ethylene-diamine)cobalt(III) ions. The bis(ethylenediamine)cobalt(lII) species are converted to the carbonato complex by reaction with lithium hydroxide and carbon dioxide. During the entire preparation a vigorous stream of carbon dioxide is bubbled through the reaction mixture. This procedure appears to be essential in order to minimize the formation of tris(ethylenediamine)cobalt(III) chloride as a by-product. However, the formation of a negligible amount of the tris salt cannot be avoided. The crude salts have a purity suitable for preparative purposes. The pure salts are obtained by recrystallization from aqueous solution. 

The optical antipodes have been obtained recently by resolution using the (+)D-(ethylenediamine)bis(oxalato)cobalt(III) anion, and have been isolated as the iodide salt.2 The exchange reaction with carbonate and the racemization reaction in aqueous solution have been investigated kinetically.3 

A stream of carbon dioxide is bubbled through a mixture of 133 ml. (1.64 moles) of ethylenediamine monohydrate and 133 ml. of water cooled in ice. The stream of carbon dioxide is maintained during the entire preparation. A solution of 195 g. (0.82 mole) of cobalt(II) chloride hexahydrate in 175 ml. of water at room temperature is added to the cold solution, which is continually stirred. The addition of the cobalt(II) salt causes a violent evolution of carbon dioxide gas, and the solution becomes red-violet. (Sometimes the mixture coagulates and becomes gel-like.) The cooling and the stirring are continued, and the mixture is oxidized by dropwise addition of 200 ml. of 30% 

The pure chloride salt is obtained by reprecipitation from water. A 5-g. quantity is dissolved in 30 ml. of water at approximately 90°C. The solution is Filtered quickly. To the hot (50-60°C.) 

The preparation of the bromide salt follows the above synthesis for the chloride salt with minor modifications. With the above quantities, a solution of 268 g. (0.82 mole) of cobalt(II) bromide hexahydrate in 300 ml. of water is substituted for the cobalt(II) chloride solution. With one exception, the above directions are followed exactly. The bromide salt is isolated by cooling in an ice bath without the addition of methanol. The precipitate is filtered, washed with 200 ml. of 50% v/v ethanol and two 200-ml. portions of 95% ethanol, and allowed to dry in air. The yield is 186 g. (71%). Anal. Calcd. for [Co(en)2 (C03)]Br Co, 18.47 N, 17.56 C, 18.82 H, 5.06 Br, 25.05. Found Co, 17.65 N, 15.27 C, 17.72 H, 5.10 Br, 26.82. 

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