The elimination of HF from vibrationally excited fluoroethanes. The decomposition of 1,1,1‐trifluoroethane‐d₀ and d₃

Abstract

The vibrationally excited molecules CF,CH,* and CF,CD,* have been synthesized by radical combination (produced by ketone photolysis), and HF and DF elimination from them studied as a function of temperature and pressure. Using RRK theory many calculations have recently been made of critical energies for the decomposition of "hot" fluoroethane molecules. Taking CF,CH,* as an example, it is concluded that the empiricism involved in such calculations renders results of doubtful significance. The non-equilibrium kinetic isotope effect is k,/k, = 3.1 at 470°K. Arrhenius parameters are also presented for radical abstraction reactions from the ketone source molecules.

Rate constants for radical recombination. III. The trifluoromethyl radical

“…(9) is presumably MeI, 2 While single values as high as 2.9 have been obtained for the high pressure limit of this cross-combination ratio, [ 1 11 multiple measurements show considerable scatter [9,10,11] for which a safe average appears to be 2.5 [9,10,11] in the temperature range of this work. 3 The most likely alternative, Having no instantaneous rate data, kll/kFli2 was calculated by two approximate methods: (1) RatecFJH and Ratec,F6 were taken arbitrarily as the fraction of total radicals found as that substance timesthe rate of radical production at P = P0/2.…”

“…products, other than MeI, are small (Table 11). The total of CF3 groups in identified products is, however, significantly less than CF31 loss and presumably is indicative of the process (9) CF3. + X H + CF3H + X .…”

Reactions of hydrogen atoms with hexafluoroacetone

“…In the system on \vhich we carried out product analysis, this process is ruled out since no %-hydrogens are present and the secondary allcoxy radical can only give 0-scission to give an aldehyde or ketone, abstract an H from hydrogen to h r m an alcohol; or recombine to give a peroxide. It seeins unlikely that the assumptions involved in the derivatio~i of [23] could introduce so large an error except that \\hich requires [9] as written to regresent the sole interaction betiveen H and HFA. Indeed.…”

“…the rather large nurnbcr of heavier products detected in (ic) suggests that a substantial portion of the H -k HFA interactions proceed to other products. In that event, the rate of H disappearance by reaction with HFA should not be equated to the rate of CF, formation in that interaction as was done in the derivation of [23], but rather only some as yet unknown fraction of that rate should be used. It is evident that much inore work will be required before a quantitative descriptioil of these systems can bc given.…”

The Competitive dehydrohalogenation of 1,1,1‐trifluoro‐2‐chloroethane in reflected shock waves

“…Critical energies were evaluated using classical RRK theory, and values of 53 and 64 kcal/mole were found for the elimination of DF and HF, respectively. However, these values are in considerable error as was subsequently pointed out by Pritchard and Perona [9]. Most recently, it has been shown [lo] on the basis of R R K M theory calculations that EOQ.Q is only about 2 kcal/mole higher than EoQ,B.…”