The reactions of trifluoromethyl radicals with hydrogen isotopes

Abstract

The photolytic decomposition of hexafiuoroacetone has been used to produce trifluoromethyl radicals for a study of their reactions with hydrogen isotopes. Activation energies for the four reactions : CF3 + HZ + CF3H, CF3 + HD + CF3H, CF3 + HD 3 CF3D and CF3 + D2 3 CF3D were found to be, respectively, 9-5 f 0.7, 10.5 f 15, 102 f 1.5 and 10-2 4 0.7 kcal mole-1. The results are discussed in detail in terms of the collision theory and the absolute theory of reaction rates. Evidence is adduced for a progressive decline in pre-exponential factor down the series of reactions: H + H2, CH3 + H2, CF3 + H 2 .

The mercury (63P1) photosensitized hydrogenation of ethylene. Kinetics of the reaction C2H5 + H2 = C2H6 + H

“…The important influence of hydrogen pressure and ethylene pressure at 320 "C is shown in Fig. 4 As would be expected, small amounts of n-hexane were found under conditions favoring reaction [7 ] ; butene-1 was also found under similar conditions but in considerably smaller quantities. Reaction [lo] is a negligible source of ethane even at high ethylene pressures, but the rate of formation of butene-1 correlates nicely with the ethylene pressure, as shown in Fig.…”

“…This will be favored at high concentrations of hydrogen and at the high concentrations of ethylene required for the formation of butyl radicals by [7]. Since its kinetic parameters will be similar to those of reaction [5] it will be considerably more important at high temperatures than at low temperatures.…”

“…Since the basic mechanism predicts that the rate of ethane formation is inde~endent of ethvlene concentration, it will not be valid if the ethylene concentration is too low. Some years ago, Pinder and Le Roy (20) made a detailed study of reaction [7] using a system similar to the present one, but at temperatures (< 123 "C) a t which reaction [5] was of no importance and with ethylene pressures (20-50 Torr) considerably higher than those used in the present work. Since [7] is a chain-stopping step it would deplete the ethyl radical concentration and lead to low values of (C2H6).…”

“…Some years ago, Pinder and Le Roy (20) made a detailed study of reaction [7] using a system similar to the present one, but at temperatures (< 123 "C) a t which reaction [5] was of no importance and with ethylene pressures (20-50 Torr) considerably higher than those used in the present work. Since [7] is a chain-stopping step it would deplete the ethyl radical concentration and lead to low values of (C2H6). It was therefore important to ascertain the upper limits for the ethylene concentrations that would minimize the importance of [7] as well as the reactions which would follow from it.…”

“…Since [7] is a chain-stopping step it would deplete the ethyl radical concentration and lead to low values of (C2H6). It was therefore important to ascertain the upper limits for the ethylene concentrations that would minimize the importance of [7] as well as the reactions which would follow from it. That such upper limits exist is illustrated by the decrease in the rate of ethane production at high ethylene pressures shown i n Fig.…”