Pyrolysis of Ethyl Iodide by the Toluene-Carrier Flow Technique

The pyrolysis of tagged ethyl iodide has been studied in the presence of the radical scavenger toluene in a flow system. The rate constants for the formation of C2H4(kD), C2H6(kS), and bibenzyl have been determined as a function of the contact time, toluene pressure (2–18 mm Hg), and C2H5I pressure PE(0.6–40×10−3 mm Hg) at 774°K. It is concluded that kD≈k1 and kS≈k2 at low kiPE, where C2H5I→ lim k1C2H4+HI,C2H5I→ lim k2C2H5+I.The first reaction appears to be first order at 14 mm Hg of toluene pressure with a high-pressure Arrhenius rate constant k1∞ of 1.27×1014 exp (−52.8×103/RT) sec−1. The second reaction is not first order at any pressure, but by extrapolation k2∞ was estimated to be 4.5×1013 exp (−50×103/RT) sec−1. The RRKM theory was used to fit the pressure dependence of k1 and k2 in the approximation that the same degrees of freedom are active in the energized molecule A* for both reactions. The disagreement between theory and experiment could be the result of fewer of the rotational degrees of freedom of A* being active in the second reaction than in the first.