Aroxylation in aromatic systems

Abstract

The thermal decomposition of benzoyl peroxide in anisole at 80° gave 10.8 mol% methoxyphenyl benzoate, with an ortho:para ratio of 3:2. The inclusion of copper(II) benzoate in acetonitrile increased the yield to about 20 mol%. The yield and isomer distribution of methoxy-phenyl benzoate varied significantly with the temperature, and depended also upon the anisole:benzoyl peroxide:copper(II)benzoate ratio, and were influenced by deuterium at the ortho-or para- position.Kinetic analysis, using galvinoxyl, showed that copper(II) benzoate slightly increased the rate of the primary homolysis of benzoyl peroxide at 60-75°, but the rate was slower than in the uncatalysed decomposition at 80-82°.Visible spectroscopic analysis showed that benzoylperoxide reacted with copper(II) benzoate in acetonitrileto form a new species with a maximum absorption at 388 nm(E max ~ 256 000 M -1cm -1). The rate of its formation wasproportional to the concentration of benzoyl peroxide, and increased with temperature. The preformed species could not oxygenate anisole effectively.The investigation was extended to halogenated anisoles, which gave high yields of methoxyphenyl benzoate, and to the polynuclear systems, naphthalene and methylnaphthalenes.The thermal decomposition of benzoyl peroxide in anisole was investigated in the presence of other additives, such as copper(II) chloride, copper(II) bromide, iodine, N-bromosuccinimide, bromine, and tin(IV) chloride, in acetonitrile .As another method of oxygenation, the benzoyl peroxide initiated reaction of halogenated aromatic compounds with acetate ions gave results which agreed with previous literature reports. This reaction could not be extended to anisole and highly fluorinated aromatic compounds.Perbenzoic acid was found to be an ineffective reagent for oxygenation of aromatic compounds, even in the presence of additives .