Cobalt(III) Acetate1

Co(OAc)3

[917-69-1]  · C6H9CoO6  · Cobalt(III) Acetate  · (MW 236.07)

(one-electron oxidizing agent for aromatic4 and aliphatic hydrocarbons,10 for oxidative halogenation,15 oxidation of alcohols23 and acids26)

Physical Data: dec 100 °C.

Solubility: hydrolyzed in water; sol acetic acid, ethanol, DMSO, DMF, and MeCN; slightly sol THF, diethyl ether, CHCl3, and acetone.

Form Supplied in: dark green solid, widely available.

Analysis of Reagent Purity: cobalt(III) can be determined by treating it with excess iron(II) ammonium sulfate and titration with cerium(IV) sulfate or dichromate.2

Preparative Methods: involves oxidation of Cobalt(II) Acetate in acetic acid solution. The various oxidants used for this purpose are ozone,2 peracid,3a peroxide,3b and oxygen.4 An electrochemical procedure for the generation of Co(OAc)3 in solution is also available.3c

Handling, Storage, and Precautions: the dark green solid or solution in acetic acid is reputed to be stable at rt for three months.

Introduction.

Cobalt triacetate is a powerful one-electron oxidant in acidic media. This reagent has been successfully used in the oxidation of a variety of organic substrates.

Oxidation of Hydrocarbons.

The cobalt(III) acetate oxidation of 2-methylnaphthalene at 70 °C in acetic acid gives mainly 2-acetoxynaphthalene (eq 1).4

The reaction of toluene,4 2-methylindan,6 isodurene,7 hemimellitene,8 p-cymene,9 heptane,10 adamantane,11 and cyclohexane12 proceeds analogously under a N2 atmosphere to give the corresponding acetates as the main products; in the presence of Oxygen, oxidation furnishes aldehydes,5 ketones,10 and acids.5,12 The rate of oxidation of alkylarenes5 and alkanes10 is enhanced in the presence of strong acids.

Halogenation.

Treatment of representative substrates of alkylbenzene with Co(OAc)3 in the presence of Hydrogen Fluoride,13 Lithium Chloride,4 Sodium Bromide,15 or Potassium Iodide14 results in corresponding halogenated derivatives.

Oxidation of Alkenes and Dienes.

Treatment of styrene,16 1-phenylbutadiene,17 phenylcyclohexene,18 a-methylstyrene,19 or b-methylstyrene substituted with an electron donating group20 with Co(OAc)3 gives the corresponding 1,2-diol monoacetates as major products. However, oxidation of cis- and trans-b-methylstyrene at higher temperature affords the corresponding allylic acetate.19 Reaction of 1,5-hexadienes with Co(OAc)3 in the presence of 3-oxobutanoate under reflux conditions gives bis(dihydrofuran) and mono(dihydrofuran) (eq 2).21

Oxidation of Functionalized Substrates.

The o-, m-, and p-substituted benzyl alcohols22 and aromatic secondary alcohols23,24 are readily oxidized by Co(OAc)3/Br- to aldehydes and ketones, respectively. The reaction of 2,6-dimethylphenol with Co(OAc)3 results in the formation of 3,3,5,5-tetramethyl-4,4-diphenoquinone.25

In the presence of Co(OAc)3 along with Copper(II) Acetate, phenylacetic acids are decarboxylated to benzyl acetates.26 Aryl substituted aliphatic acids are oxidized by Co(OAc)3 to g-phenylbutyrolactone (eq 3).26,27

Co(OAc)3 can be used in an interesting dealkylation of arylalkylamines in a mixture of chloroform and acetic anhydride.28 Dihydroanisoin (DHA) and 1,2-bis(4-methoxyphenyl)propane-1,3-diol can be cleaved cleanly to p-anisaldehyde by Co(OAc)3.29


1. (a) Beletskaya, I. P.; Makhonkov, D. I. RCR 1981, 50, 534. (b) Yoshio, K. Sekiyu Gakkai Shi, 1976, 19, 723 (CA 1978, 88, 63 829).
2. Lande, S. S.; Falk, C. D.; Kochi, J. K. J. Inorg. Nucl. Chem. 1971, 33, 4101.
3. (a) Koubek, E.; Edwards, J. O. J. Inorg. Nucl. Chem. 1963, 25, 1401. (b) Onopchenko, A.; Schulz, J. G. D. JOC 1975, 40, 3338. (c) Bewick, A.; Coe, D.; Mellor, J. M.; Pekel, A. T. SC 1981, 11, 133.
4. Heiba, E. I.; Dessau, R. M.; Koehl, Jr., W. J. JACS 1969, 91, 6830.
5. Hanotier, J.; Hanotier-Bridoux, M.; de Radzitzky, P. JCS(P2) 1973, 381.
6. Sternerup, H. ACS 1974, B28, 969.
7. Baciocchi, E.; Mandolini, L.; Rol, C. JOC 1980, 45, 3906.
8. Baciocchi, E.; Eberson, L.; Rol, C. JOC 1982, 47, 5106.
9. Onopchenko, A.; Schulz, J. G. D. JOC 1972, 37, 2564.
10. Hanotier, J.; Camerman, Ph.; Hanotier-Bridoux, M.; de Radzitzky, P. JCS(P2) 1972, 2247.
11. Verstraelen, L.; Lalmand, M.; Hubert, A. J.; Teyssie, P. JCS(P2) 1976, 1285.
12. Onopchenko, A.; Schulz, J. G. D. JOC 1973, 38, 3729.
13. Feiring, A. E. JOC 1979, 44, 1252.
14. Makhon'kov, D. I.; Cheprakov, A. V.; Rodkin, M. A.; Beletskaya, I. P. ZOR 1986, 22, 1117 (CA 1988, 108, 5616p).
15. Baciocchi, E.; Crescenzi, M. T 1988, 44, 6525.
16. Hirano, M.; Morimoto, T. JCS(P2), 1984, 1033.
17. Morimoto, T.; Hirano, M.; Enokida, T.; Isomoto, A.; Hamaguchi, T. Zhung, X. JCS(P2) 1988, 1531.
18. Morimoto, T.; Hirano, M.; Koyama, T. JCS(P2) 1985, 1109.
19. Hirano, M.; Morimoto, T. JCR(S) 1979, 104.
20. Hirano, M.; Hamaguchi, T.; Zhang, X.; Morimoto, T. JCS(P2) 1989, 2141.
21. Nishino, H.; Yoshida, T.; Kurosawa, K. BCJ 1991, 64, 1097.
22. Hirano, M.; Morimoto, T.; Itoh, K. BCJ 1988, 61, 3749.
23. Hirano, M.; Morimoto, T. BCJ 1989, 62, 4069.
24. Morimoto, T.; Hirano, M.; Wachi, M.; Murakami, T. JCS(P2) 1984, 1949.
25. Hirano, M.; Ishi, T.; Morimoto, T. BCJ 1991, 64, 1434.
26. Dessau, R. M.; Heiba, E. I. JOC 1975, 40, 3647.
27. Giordano, C.; Belli, A.; Citterio, A. JOC 1980, 45, 345.
28. Rindone, B.; Scolastico, C. TL 1974, 3379.
29. DiCosimo, R.; Szabo, H.-C. JOC 1988, 53, 1673.

Mariappan Periasamy & Ukkiramapandian Radhakrishnan

University of Hyderabad, India.



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