Kinetics and Mechanism of Hydrogenolyses. The Addition of Hydrogen Atoms to Propylene, Toluene, and Xylene

Previously measured rates of hydrogenolysis of propylene, toluene, and xylene fit −d[RCH3]/dt=10(11.5±1)−(55±3)/θ[RCH3][H2]1/2 mole liter−1·sec−1 (where θ is 2.3RT kcal mole−1) over an unusually wide range of conditions. In the case of toluene, for example, the range is 107 in rate, 105 in hydrogen pressure, and 500°C in temperature. We propose the mechanism H2⇄2H,H+RCH3⇄RH+CH3,CH3+H2⇄CH4+H,giving −d[RCH3]/dt=K11/2k2[RCH3][H2]1/2. Substitution of values for K1 and k2 gives rate constants and Arrhenius parameters in excellent agreement with all reliable data.