Abstract
Polyvinylpyrrolidone (PVP) assisted aerobic oxidation of bulk iodosylbenzene or hydrolysis/oxidation of iodobenzene diacetate under mild conditions leading to the formation of nanostructured iodylbenzene is reported. AFM and FESEM-EDX analyses confirmed the formation of dendrimer iodylbenzene-polyvinylpyrrolidone nanocomposite (PhIO2-PVP) through the two top-down approaches. The formation of PhIO2 was confirmed by 1H NMR spectroscopy. Strong interactions between iodylbenzene molecules and the polymer through secondary intermolecular O---I bonds was evident from the large difference between the morphology of PVP (cubic) and PhIO2-PVP (dendrimer) nanoparticles. FESEM images showed a maximum width and length of 70 and 1000 nm for the dendrimers, respectively. The dual role played by PVP, i.e., facilitating the oxidation of I(III) to I(V) and stabilization the hypervalent I(V) compound was attributed to the formation of strong secondary hetero-intermolecular O---I bonds, between the polymer and iodine centre. The very fine aqueous and dichloromethane suspensions of PhIO2-PVP were indistinguishable to the naked eye. Efficient direct oxidation of cyclohexene and methylene blue with PhIO2-PVP at room temperature and a short reaction time provided evidence of significantly increased reactivity of PhIO2-PVP compared to that of the bulk oxidant. PhIO2-PVP was also used in the oxidation of methyl phenyl sulfide and styrene in water and dichloroethane, using water soluble and insoluble metalloporphyrins, respectively. The former led to the formation of the corresponding sulfoxide as the sole product in the two solvents. In addition to styrene oxide formed in both solvents, benzaldehyde was also formed with a selectivity of 24% in water. Almost complete oxidation of the organic substrates was observed in dichloroethane. The results of this study show that the nanostructured iodine(V) compound can be used as an efficient terminal oxidant in biomimetic oxidations.
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