Hexacyanocobaltic acid

An alternative method of preparing highly active zinc hexacyano-cobaltate catalyst involved the use of hexacyanocobaltic acid prepared by passing the potassium salt through cationic exchange resin (Rohm and Haas A-15). 

The preferred methods of preparation of catalysts based on the hexacyanocobaltate and hexacyanochromate ions were with the respective acids. However, because of the instability of the acid of the latter ion, successful use depended upon using it immediately after preparation. No satisfactory preparation of a catalyst using the hexacyanoferric acid was developed. 

Hexacyanocobaltates(III) contain the extremely stable Co(CN)3 ion. An excess of KCN added to a Co +solution gives potassium hexacyanocobal-tate(II), K4Co(CN)g, which is precipitated from aqueous solution by alcohol. When boiled with even a weak acid such as acetic, aerial oxidation to the hexacyanocobaltate(III), K3Co(CN)g, occurs ... 

Potassium hexacyanocobaltate(III) crystals have a faint yellow color and belong to the monoclinic system. Their specific gravity is 1.906. The compound is not appreciably hydrolyzed iii solution, but concentrated mineral acids decompose it. On heating to moderately high temperatures it melts, with decomposition, to an olive-green mass. The crystals are very soluble in water at room temperature, only very slightly soluble in liquid ammonia at —33°, and insoluble in alcohol. The preparation of potassium hexacyanocobaltate(III) is sometimes used in qualitative analysis in the separation of cobalt and nickel. 

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