Reaction of thermally generated hydrogen atoms with propylene films at 77°K

Abstract

The reaction of C3H6 f i l m s with thermally generated H atoms at 77°K has been studied by measurement of HZ uptake rates and analysis of the hydrocarbon products. Propane and the three hexanes are the sole products, the ratio C ~H S / Z ' C ~H ~~ being about 11 and 2,3-dimethyl butane predominating in the c 6 fraction. It is shown that hydrogen uptake rates are unreliable as a measure of reaction rate. The reaction is mainly a surface process and the predicted rates of reaction, on the assumption that diffusion of olefin into the surface is the rate-determining step, are compared with experimental data. It is shown that this view is only partially correct and that limited penetration of the film by H atoms occurs. The simple reaction mechanism previously proposed is questionable and reactions of radicals with H and with olefin are important.

Study on the Tunneling Reaction of H Atoms with a Solid Thin Film of C3H6 at 10 K

“…This conclusion was derived from the fact that the ion with m/z 39 which is one of the major fragment ions for 2,3-dimethylbutane was totally absent in the mass spectrum for the product appearing at ∼150 K in Figure 2. 2-Methylpentane was found to be the second most abundant saturated C6 hydrocarbon product from the reactions of H atoms with solid C 3 H 6 at 77 K. 8,9 The absence of 2,3-dimethylbutane in this experiment indicates that reaction 3 is negligible under the present experimental conditions. 2-Methylpentane is likely to be formed by the addition reaction of an s-propyl radical to the terminal carbon of the double bond of C 3 H 6 to form the 2-methylpentyl radical followed by the recombination reaction with an H atom.…”

“…8 Hughes and Purnell studied the reaction of C 3 H 6 films with thermally generated H atoms at 77 K by measurement of H 2 uptake rates and analysis of the hydrocarbon products. 9 Propane and three hexanes (2,3-dimethylbutane, 2-methylpentane, and n-hexane) were the sole products, the ratio C 3 H 8 /ΣC 6 H 14 being about 11 and 2,3-dimethylbutane predominating in the C 6 fraction. Hill et al 10 studied the reaction of H atoms with propene at 77 K by electron spin resonance (ESR).…”

“…4,6,7,9 In this study, the reaction of H with a C 3 H 6 film at 10 K was performed where the diffusion of the molecules in the films is least likely. It was found that only 2-methylpentane was formed as the C6 product and no trace amount of 2,3-dimethylbutane was detected.…”

“…Yun and Moser investigated the reaction of thermally generated H atoms with solid films of propene at 77 K. They found that the free radicals migrated very fast on the surface of the frozen films because radical−radical reactions competed well with hydrogen atom addition to the radicals even though free hydrogen atoms were present . Hughes and Purnell studied the reaction of C 3 H 6 films with thermally generated H atoms at 77 K by measurement of H 2 uptake rates and analysis of the hydrocarbon products . Propane and three hexanes (2,3-dimethylbutane, 2-methylpentane, and n -hexane) were the sole products, the ratio C 3 H 8 /ΣC 6 H 14 being about 11 and 2,3-dimethylbutane predominating in the C 6 fraction.…”

Hydrogen atom addition to solid isobutylene at 77.deg.K

“…H = H¡¡, all t x -L, bH/bx = 0, all t The solution is H/Ho = [(cosh a)x* -tanh a(sinh a)x*] (17) where MoL2 x* = x/LThe initial rate may then be obtained by integrating over the solid volume (wT) = -Che,HdV = -A VkALHdx* \ di / init JO JO(18) …”