Shin‐ichi Hirashima, A. Itoh
Oct 10, 2006
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Abstract
Oxidation, especially introduction of oxygen-containing functional groups to hydrocarbon, is a fundamental and most important reaction in the synthesis of a large number of chemicals from fossil fuel. However, most of them involve the use of large quantities of heavy metals which results in the discharge of considerable amounts of contaminants, and are not at all environmentally benign.1 With this background in mind, we discovered in the course of our study of photooxidation that 4-tert-butyltoluene (1) is oxidized directly to 4-tert-butyl benzoic acid (2) in ethyl acetate in an oxygen atmosphere in the presence of LiBr.2 The mechanism of this reaction has not yet been determined; however, we believe that HBr is formed in situ from a bromo radical, which is formed under irradiation from LiBr, and a hydrogen radical, which is abstracted from the benzylic position. If addition of hydrobromic acid, which is an inexpensive and easily handled reagent as an aqueous solution of HBr, is enough to effect the oxidation, this reaction is expected to be a useful and convenient oxidation method in view of the use of molecular oxygen as the terminal oxidant and the nonrequirement of environmentally detrimental heavy metals and halogenated solvents.3 In this letter we report in detail our investigation of the generality of this aerobic photooxidation of a methyl group at the aromatic nucleus with hydrobromic acid.