[696-33-3]  · C6H5IO2  · Iodylbenzene  · (MW 236.01)

(ring cleavage of indole and imidazole derivatives;2 quinone formation;3 dehydrogenation of 3-keto steroids to dienones;4 other enone dehydrogenations;5 allylic oxidations;6 the Nef reaction7)

Alternate Name: iodoxybenzene.

Physical Data: mp 230 °C, explosive decomposition 250-253 °C.

Solubility: sol H2O (2.8 g L-1 at 12 °C, 12 g L-1 at 100 °C). PhIO2 is polymeric in the solid state and dissolution in solvent is due to a chemical reaction.

Analysis of Reagent Purity: by iodiometric titration.12

Preparative Methods: by disproportionation of Iodosylbenzene,8 by treatment of Phenyliodine(III) Dichloride with Sodium Hypochlorite,9 by Peracetic Acid (40%) oxidation of iodobenzene,10 or oxidation with Potassium Bromate in Sulfuric Acid11 (which is the best method).

Purification: by crystallization from hot water8 or by washing with chloroform followed by drying.9,10

Handling, Storage, and Precautions: should be freshly prepared and should not be heated in the absence of solvent because of the danger of explosion. This reagent should be handled in a fume hood.

Iodylbenzene is a weaker oxidant compared with iodosylbenzene. The systems PhIO2/(PhSeO)2O and PhIO2/(PhSe)2 are synthetically useful and the oxidative capabilities of PhIO2 are improved by Lewis acids or p-Toluenesulfonic Acid.

Ring cleavage of amino acids using p-t-BuC6H4IO2 in chlorobenzene is a useful reaction. For example, tryptophan N-benzoyl methyl ester gives the kynurenine derivative (eq 1),2 and histidine-N-Cbz-methyl ester undergoes a similar process (eq 2).2

PhIO2 itself or m-iodylbenzoic acid as the N,N,N,N-tetramethyl-N-t-butylguanidinium salts in CH2Cl2 are useful reagents for the oxidation of phenols to benzoquinones. b-Naphthol is oxidized to 1,2-naphthoquinone in 65% yield.3 Use of m-iodylbenzoic acid has the advantage that it is recoverable as its reduction product, m-iodobenzoic acid. m-Iodylbenzoic acid is made by commercial hypochlorite solution oxidation of m-iodobenzoic acid.4

The dehydrogenation of steroidal 3-ketones either to the enone or dienone is an important process. The catalytic system of PhIO2 and Diphenyl Diselenide offers an excellent method for this transformation (eq 3).4

PhIO2/(PhSeO)2O was singularly useful in the synthesis of a 4a-methyl-4aH-fluorenone (eq 4).5

A valuable application of the PhIO2/2,2-Dipyridyl Diselenide system is illustrated in the allylic oxidation of alkenes such as (1S)-(-)b-pinene to pinocarvone (eq 5),6 cholesteryl benzoate to 4-ketocholesteryl benzoate (eq 6),6 and a-terpineol to 6-keto-a-terpineol (eq 7).6

m-Iodylbenzoic acid in the presence of excess N,N,N,,N-tetramethyl-N-t-butylguanidine is a mild and efficient reagent for the Nef reaction for conversion of secondary nitro compounds to ketones, even in the presence of other oxidizable groups (eq 8).7

1. Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine; VCH: New York, 1992; p 385.
2. Ranganathan, S.; Ranganathan, D.; Singh, S.; Battacharyya, D. CC 1987, 1887.
3. Barton, D. H. R.; Godfrey, C. R. A.; Morzycki, J. W.; Motherwell, W. B.; Stobie, A. TL 1982, 23, 957.
4. Barton, D. H. R.; Godfrey, C. R. A.; Morzycki, J. W.; Motherwell, W. B.; Ley, S. V. JCS(P1) 1982, 1947.
5. Neuhaus, D.; Rees, C. W. CC 1983, 318.
6. Barton, D. H. R.; Crich, D. T 1985, 41, 4359.
7. Barton, D. H. R.; Motherwell, W. B.; Zard, S. Z. TL 1983, 24, 5227.
8. Lucas, H. J.; Kennedy, E. R. OSC 1955, 3, 485.
9. Formo, M. W.; Johnson, J. R. OS 1955, 3, 486.
10. Sharefkin, J. G.; Saltzman, H. OSC 1973, 5, 665.
11. Banerjee, A.; Banerjee, G. C.; Bhattacharyya, S.; Banerjee, S.; Samadar, H. JIC 1981, 58, 605.
12. Lucas, H. J.; Kennedy, E. R.; Formo, M. W. OSC 1955, 3, 483.

Robert M. Moriarty & Jerome W. Kosmeder II

University of Illinois at Chicago, IL, USA

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