THE FUNCTIONALIZATION OF SATURATED-HYDROCARBONS .21. THE FE(III)-CATALYZED AND THE CU(II)-CATALYZED OXIDATION OF SATURATED-HYDROCARBONS BY HYDROGEN-PEROXIDE - A COMPARATIVE-STUDY

The selective functionalisation of saturated hydrocarbons catalyzed by copper or iron salts are compared. In addition to further studies on the homogeneous oxidation by Cu(II)-H2O2 in pyridine-acetic acid (GoChAgg system), we introduce a heterogeneous Gif(III)-analog based on Cu0 and dioxygen in pyridine-acetic acid. Both Cu-based systems display Gif-type reactivity. The intermediacy of alkyl hydroperoxides in the Cu(II)-catalyzed reaction has been proven spectroscopically (following the reaction on [1-C-13]-cyclohexane by C-13-N.M.R. spectroscopy) and chemically (quenching the reaction with triphenylphosphine to reduce the hydroperoxide to alcohol). The same holds for the Cu0/O2 system, as shown by the effect of triphenylphosphine added to the reaction mixture. Thus, both reactions follow the pathway alkane --> alkyl hydroperoxide --> alcohol or ketone. Experiments running the GoChAgg reaction (H2O2-based) under an O-18(2)-atmosphere showed the incorporation of O-18(2) into the hydroperoxide and the alcohol (which derives itself from the alkyl hydroperoxide). The relative reactivity of this Cu(II) system was studied for a series of cycloalkanes. The participation of another reaction intermediate (A) has also been demonstrated. However, some important differences are presented, that show that the chemical properties of the Cu-A and the Fe-A intermediates are different. Thus, Gif-type reactivity is metal-dependent and involves two chemically different non-radical species.