Isotope effects in the oxidative functionalization of methane in the presence of rhodium-containing homogeneous catalytic systems

The combined oxidation of carbon monoxide, CH 4 , and CD 4 by molecular oxygen ( 16 O 2 and 18 O 2 ) in aqueous solutions of trifluoroacetic acid labeled with 18 O in the presence of rhodium and copper compounds and potassium iodide has been studied. The distribution of 18 O in isotopically substituted products suggests that oxygen entered into the methane molecule from an active oxidizing agent. This oxidizing agent was produced from molecular oxygen under the action of reagents and catalytic system components. The kinetic isotope effect observed for methane ( k H / k D =3.9−4.3) suggests a nonradical character of the step at which the oxygen atom passes from an active oxidizing agent to the methane molecule or its fragments—transition-state components of the corresponding step.