Photocatalytic oxidation of alkanes with dioxygen by visible light and copper(II) and iron(III) chlorides: Preference oxidation of alkanes over alcohols and ketones

Visible light irradiation of alkanes in acetonitrile with CuCl, and FeCl3 catalysts under atmospheric dioxygen gave the corresponding alcohols and ketones effectively; in these reactions, the total selectivity of the products did not decrease so much With increase of alkane conversion. For example, cyclohexanol and cyclohexanone were formed with ca. 70% selectivity at 50% conversion, because overoxidation of the products took place more slowly than cyclohexane oxidation. The relative reactivity values of cycloalkanes increased as their ring-sizes decreased. In the oxidation of hexane. the reactivity ratio of C1-/C2-/C-3-H was found to be 1.0/1.4/1.8 With CuCl2 and 1.0/4.6/6.6 with FeCl3, respectively. Toluene and diphenylmethane were more reactive than cyclohexane with FeCl3, as expected, whereas the alkane was oxidized faster than the benzylic compounds in the separate reaction with CuCl2. Moreover, the alkane oxidation could be comparably performed by sunlight instead of an artificial lamp.