Potassium Ferrate

K2FeO4

[13718-66-6]  · FeK2O4  · Potassium Ferrate  · (MW 198.05)

(selective oxidant for alcohols and amines1)

Solubility: sol water; insol typical organic solvents.

Form Supplied in: violet solid; typical impurities present include potassium chloride and iron(III) oxide.

Analysis of Reagent Purity: analysis of K2FeO4 by chromite ion has been reported.2 The ferrate concentration may be determined by measurement of the absorption band at 510 nm.3

Preparative Methods: NaOCl (20 g) is added to a solution of NaOH (30 g in 75 mL H2O) while keeping the solution temperature under 20 °C. Solid NaOH (70 g) is added with stirring, while maintaining the solution temperature at 25-30 °C, the solution cooled to 20 °C and filtered. Fe(NO3)3.9H2O (25 g) is added slowly, and the solution saturated with NaOH while being kept at 30 °C. After filtration, the filtrate of sodium ferrate is placed in a 20 °C bath and treated with saturated aqueous KOH (100 mL), stirred for 5 min, and filtered. The precipitate is washed several times with 10 mL portions of 3 M KOH into 50 mL of chilled saturated KOH solution, and a further 50 mL of chilled saturated KOH solution added to the washings. After stirring for 5 min, the solution is filtered, and the precipitate washed with benzene (10 mL) and several times with ethanol (20 mL). The precipitate is stirred with ethanol (1 L) for 20 min and the ethanol removed by filtration; this process is repeated three times. The precipitate is finally washed with Et2O under a drying tube, and drying continued in a vacuum desiccator.4

Handling, Storage, and Precautions: dry K2FeO4 is stable and should be stored in a desiccator. K2FeO4 is very unstable in acidic solutions, but decomposes only slowly in basic solutions.

Oxidations.

Potassium ferrate has been reported to be a mild reagent for the oxidation of primary and secondary alcohols to aldehydes and ketones, respectively (eq 1).1,5,6 In addition, primary and secondary amines are also oxidized to aldehydes and ketones (eq 2). Allylic and benzylic alcohols react much more readily than saturated ones, and primary alcohols react more readily than secondary ones. Reactions are normally carried out in basic aqueous (or water/t-butanol) solution. Yields are normally high with allylic and benzylic alcohols and amines, but much more variable for saturated alcohols. Several functional groups are stable to this reagent, including carbon-carbon double bonds, nitro groups, tertiary alcohols and amines, aldehydes, and ketones. Sulfur compounds (sulfides, sulfoxides) do not tolerate this reagent.

A modification employing a two-phase system (benzene/10% aqueous NaOH) and Benzyltriethylammonium Chloride as a phase-transfer catalyst has been reported to be highly successful for allylic and benzylic substrates (eq 3).7 A second modification using a mixture of K2FeO4 (8 mmol), aluminum oxide (0.8 g), and CuSO4.5H2O (0.8 g) for 2 mmol of substrate affords a simple workup and highly selective oxidations (eq 4).6


1. (a) Audette, R. J.; Quail, J. W.; Smith, P. J. TL 1971, 279. (b) BeMiller, J. N.; Kumari, V. G.; Darling, S. D. TL 1972, 4143. (c) Tsuda, Y.; Nakajima, S. CL 1978, 1397.
2. Schreyer, J. M.; Thompson, G. W.; Ockerman, L. T. Anal. Chem. 1950, 22, 1426.
3. Sharma, V. K.; Bielski, B. H. J. IC 1991, 30, 4306.
4. Thompson, G. W.; Ockerman, L. T.; Schreyer, J. M. JACS 1951, 73, 1379.
5. BeMiller, J. N.; Kumari, V. G.; Darling, S. D. TL 1972, 4143.
6. Kim, K. S.; Chang, Y. K.; Bae, S. K.; Hahn, C. S. S 1984, 866.
7. Kim, K. S.; Chang, Y. K.; Bae, S. K.; Hahn, C. S. TL 1986, 27, 2875.

James R. Green

University of Windsor, Ontario, Canada



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