Potassium tetraoxalatouranate 6-hydrate

Potassium tetraoxalatouranate(IV) 5-hydrate has been prepared by the reaction of a potassium oxalate solution with an excess of uranium(IV) oxalate 6-hydrate.This excess prevents contamination of the product by potassium oxalate, since both potassium tetraoxalatouranate(IV) and potassium oxalate are precipitated from aqueous solution by absolute alcohol. 

A solution of 5 g. (0.027 mol) of potassium oxalate 1-hydrate in 20 ml. of water is added to a slurry of 6 g. (0.014 mol) of uranium(IV) oxalate 6-hydrate in 50 ml. of water. The reaction is complete after the mixture has been heated on a steam bath for 1 hour. The dark green filtrate is treated with 200 ml. of absolute alcohol, which is added drop by drop from a separatory funnel while the mixture is stirred. J Small light green crystals are obtained, which are quickly dried by washing them several times with absolute alcohol and finally with ether. To avoid oxidation, potassium tetraoxalatouranate(IV) is stored in a desiccator over phosphorus (V) oxide. 

The compound is only slightly soluble in water and dilute acids but is soluble in warm concentrated hydrochloric acid to form a dark green solution. It can be reprecipitated by cooling or by diluting such a solution. Concentrated nitric acid effects oxidation to the uranyl salt. With solutions of the alkali carbonates or hydrogen carbonates, uranium(IV) hydroxide is formed. With an excess of a solution of potassium carbonate and by atmospheric oxidation, potassium uranyl carbonate results. Uranium(IV) oxalate 6-hydrate is also soluble in solutions of alkali and ammonium oxalates to form the tetraoxalatouranate(IV)... 

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