Cerium(IV) Ammonium Sulfate1


[7637-03-8]  · CeH16N4O16S4  · Cerium(IV) Ammonium Sulfate  · (MW 596.52) (.2H2O)

[10378-47-9]  · H20CeN4O18S4  · Cerium(IV) Ammonium Sulfate  · (MW 632.55)

(convenient reagent for oxidation of aromatic rings,2 and halophenols to quinones,6 for regioselective Baeyer-Villiger oxidation,11 and oxidative aromatization12)

Alternate Name: ceric ammonium sulfate; CAS.

Physical Data: mp 140 °C (dec).

Solubility: sol water, dil. H2SO4, dil. H2SO4-MeCN.

Form Supplied in: orange solid, widely available.

Handling, Storage, and Precautions: cerium(IV) ammonium sulfate is a stable reagent and precautions required for handling strong oxidizing agents such as Potassium Permanganate will be sufficient. Cerium is reputed to be of low toxicity.

Cerium(IV) ion is a potent one-electron oxidant.1 Cerium(IV) Ammonium Nitrate (CAN), is the most widely utilized cerium(IV) oxidizing agent, but cerium(IV) ammonium sulfate (CAS) is a good substitute when complications due to the involvement of nitrate ligands occur, resulting in side products such as nitrate esters.1

Synthesis of Quinones by Oxidation of Aromatic Rings.

The most important application of CAS is in the oxidation of aromatic rings. CAN oxidizes polycyclic aromatic hydrocarbons only in moderate yields (20-60%),1 and these reactions are often complicated by the formation of nitrate esters.2 In contrast, CAS generally oxidizes aromatic hydrocarbons to quinones in good yields. For example, naphthalene is oxidized to 1,4-naphthoquinone in excellent yield by CAS in a dilute mixture of H2SO4 and MeCN (eq 1).3

Other polycyclic aromatic hydrocarbons such as phenanthrene, anthracene, and fluoranthene are converted to the corresponding quinones on oxidation with CAS. Whereas 1-methylnaphthalene gives 1-naphthaldehyde under the conditions,3 1-phenyl- and 1-bromonaphthalene react to form some 2-substituted naphthoquinones through an interesting rearrangement (eq 2).4

Oxidation of 1,4-diphenylnaphthalene gives 2,3-diphenyl-1,4-naphthoquinone or 4-hydroxy-2,4-diphenyl-1(4H)-naphthalenone, depending upon the reaction conditions (eq 3).5

A process utilizing catalytic amounts of CeIV and AgII has also been reported (eq 4).6

Unfortunately, this reagent system is not suitable for the oxidation of substrates of higher ionization potential nor for oxygen-substituted compounds.

The major product isolated from the reaction of CAS with benzo[b]fluoranthene is a lactone (eq 5).7

Oxidation of Phenols to Quinones.

Halophenols are conveniently oxidized by CAS to haloquinones in good yields (eq 6).8 On oxidation with CAS, halonaphthols furnish 1,2-diones as minor products in addition to 1,4-quinones.

A direct and convenient route for the conversion of gentisic acid to the corresponding quinone has been developed through the use of CAS in CHCl3 (10% within 15 min) (eq 7).9

Baeyer-Villiger Oxidation.

Oxidation of 1,3-bishomocubanone with a slurry of CAS gives rise to the corresponding lactone (eq 8),10 which is obtained only as a minor product in the peroxy acid Baeyer-Villiger oxidation conditions.

Oxidative Halogenation.

The reaction of RPh (R = H, Cl, Br, I, Me) with Potassium Iodide in CF3CO2H containing CAS gives a mixture of 2- and 4-RC6H4I. Oxidation of methyl 4-methylbenzoate with CAS under the reaction conditions gives exclusively methyl 3-iodo-4-methylbenzoate.11

Oxidative Aromatization.

A new type of oxidative aromatization of cyclohexenone with the CAS-Iodine system has been developed (eq 9).12

1. (a) Ho, T. L. S 1973, 347. (b) Beletskaya, I. P.; Makhankov, D. I. RCR 1981, 50, 534.
2. Rindone, B.; Scolastico, C. JCS(B) 1971, 2238.
3. Periasamy, M.; Bhatt, M. V. S 1977, 330.
4. Periasamy, M.; Bhatt, M. V. TL 1977, 2357.
5. Bhatt, M. V.; Periasamy, M. T 1994, 50, 3575.
6. Sharzewski, J. T 1984, 40, 4997.
7. Balanikas, G.; Hussain, N.; Amin, S.; Hecht, S. S. JOC 1988, 53, 1007.
8. Gopinathan, M. B.; Bhatt, M. V. IJC(B) 1981, 20B, 71.
9. Holmes, Jr., J. T.; Vennerstorm, J. J.; Choi, K. E. JOC 1984, 49, 4736.
10. Mehta, G.; Pandey, P. N.; Ho, T. L. JOC 1976, 41, 953.
11. Makhonkov, D. I.; Cheprakov, A. V.; Rodkin, M. A.; Beletskaya, I. P.; ZOR 1986, 22, 1117 (CA 1988, 108, 5616p).
12. Horiuchi, C. A.; Fukunishi, H; Kajita, M; Yamaguchi, A; Kiyomiya, H; Kiji, S. CL 1991, 1921.

Mariappan Periasamy & Ukkiramapandian Radhakrishnan

University of Hyderabad, India

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