[696-33-3] · C6H5IO2 · Iodylbenzene · (MW 236.01)
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).
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
Robert M. Moriarty & Jerome W. Kosmeder II
University of Illinois at Chicago, IL, USA