Iron(III) and copper(II) catalysed cyclohexane oxidation by molecular oxygen in the presence of tert-butyl hydroperoxide

Abstract

In the presence of cyclohexane soluble iron and copper catalysts, tert-butyl hydroperoxide selectively oxidises cyclohexane to cyclohexanol and cyclohexanone (with cyclohexene for the copper catalysts). Under reflux for 24 h, the conversions are 4 to 5% (turnover numbers of 70 to 90) and the selectivities above 90%. Under 25 bar of oxygen at 70°C for 24 h, conversions with the iron catalysts are 9% (turnover numbers of up to 166) but the selectivities are below 80%, as large amounts of adipic acid are also formed. The copper catalysts are more selective under these conditions. Using Cu(tma) 2 the conversion is 11% (turnover number of 192) and the selectivity is 91%. Reactions in the presence of cyclohexanone show that the iron catalysts deactivate by complexation with the adipic acid formed by its over-oxidation. The copper catalysts rapidly produce cyclohexene at the beginning of the reactions; this is further oxidised to cyclohexen-3-one and cyclohexen-3-ol, thus reducing the catalyst activity for cyclohexane oxidation.