Potassium Ferrate VI

Submitted by J. M. Schre yer, G. W. Thompson, and L. T. Ockerman Checked by Bodie E. Douglas,f Milton K. Snyder, and Therald MoellerJ 

Potassium ferrate (VI) has been prepared in an impure state and in low yields by the action of chlorine or bromine on hydrous iron(III) oxide suspended in potassium hydroxide solutions. The procedure described here is a modification of the chlorine oxidation method1 which facilitates the prediction of 5- to 10-g. samples of potassium ferrate (VI) in a fair state of purity and in good yield. 

The alkaline hypochlorite solution is maintained at 25 to 30° while 25 g. of pulverized iron(III) nitrate 9-hydrate (0.06 mol) is added in small portions over a period of 45 minutes to 1 hour. Sodium hydroxide is added to the solution until saturation is reached during this operation the temperature is maintained at 30°. The mixture is then fil- University of Kentucky, Lexington, Ky. f Pennsylvania State College, State College, Pa. t University of Illinois, Urbana, 111. 

The filtrate containing the sodium ferrate is transferred to a 250-ml. beaker, which is put in a water bath at 20°, and 100 ml. of saturated potassium hydroxide solution is added with stirring. Stirring is continued for 5 minutes, after which the suspension is filtered through a fritted-glass filter of medium porosity and large surface area (centrifugation may be substituted for filtration here).f The filtrate is discarded. 

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Ferrate(VI) has powerful oxidising properties, for example ammonia is oxidised to nitrogen. Potassium ferrate(VI) is isomorphous with potassium chromatefVI), and both anions are tetrahedral. 

Decomposition of potassium ferrate(VI) at 1000 K gives a fer-rate(V), K3Fe04, and several types of ferrateflV), for example FeO, Fe04 are known these ferrates(IV) have no solution chemistry and are probably best regarded as mixed oxides, since the Fe04 ion has no identifiable structure. 

Potassium (ethylenediaminetetra-acetato)cobaltate(III), 5 186 dextro- and levo-, 6 193, 194 Potassium ferrate(VI), 4 164... 

By this procedure, samples ranging in purity from 90 to 97% potassium ferrate (VI) are obtained in yields as high as 50%. If centrifugation is used instead of filtration, yields up to 75% can be obtained. ... 

If it is desirable to obtain a sample of greater purity than those prepared by the recommended procedure, the sample may be subjected to an additional reprecipitation from 6 M potassium hydroxide solution, using the same procedure as described above. Such additional purifications of samples give products ranging in purity from 98.5 to 99% potassium ferrate (VI) however, a large amount of the potassium ferrate (VI) is lost in the process. 

Saturated sodium hydroxide, reducing-agent-free 0.05 g. of potassium ferrate(VI) is added to 500 ml. of cooled, saturated sodium hydroxide solution, and the solution is decolorized by boiling. 

Potassium ferrate(VI), K2Fe04. Mol. wt. 198.05, purple crystals. The. salt should be protected from moisture. 

Oxidation. Potassium ferrate (VI) is a reagent for selective oxidation of primary alcohols and amines to aldehydes and of secondary alcohols to ketones. Double bonds, aldehyde functions, tertiary hydroxyl groups, and tertiary amino groups are resistant to oxidation. The reaction is carried out at room temperature either in water or in aqueous solvents. In fact water is essential for oxidation. The reaction is carried out at an initial pH of 11.5 the final pH is 13.5. In a typical procedure K.2pe04 (0.(X)2 mole)... 

Oxidations. Potassium ferrate(VI) supported on clay has been used in the oxidation of alcohols to carbonyl compounds, of thiols to disulfides, and of organonitrogen compounds. Another method for oxidizing alcohols involves acyl nitrates absorbed in days. ... 

Potassium ferrate(VI) added to benzylamine in water, and shaken 1 min. until the purple color of the ferrate(VI) has disappeared benzaldehyde. Y 70%. -Similarly during 7 min. Cinnamyl alcohol cinnamaldehyde. Y 75%. - Unsaturation in the molecule as well as aldehyde, tert. alcohol, and tert. amine... 

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