The Kinetics of the Hydrogen—Fluorine Reaction. II. The Oxygen-Inhibited Reaction¹

Abstract

The kinetics of the thermal, gaseous hydrogen-fluorine reaction have been investigated by a colorimetric technique. The reaction has been found to be inhibited by oxygen and the inhibited reaction was studied mainly at 132O, but also from 122 to 162'. The experiments have been performed at a total pressure of about 645 mm., with oxygen varying from about 85 to 500 mm. Nitrogen and helium have been used to maintain the total pressure at the desired value. Hydrogen and fluorine pressures have been in the general range of -20-80 mm. It has been found that the rate decreases with added oxygen but reaches a limiting value unaffected by further oxygen addition. The limiting rate obeys the expression -d(Fz)/dt = k(F2)(H2)"' fairly well, but the curves of the integrated forms are linear only for about the first 50% of reaction, dropping off thereafter. The Arrhenius plot for the rates from 132 to 162' is linear, yielding an activation energy of 16.7 kcal./mole. The results are discussed in terms of a chain reaction involving the propagation steps, H + F2 -t H F + F; F + 0 2 + M -t FOO + M; and FOO + H2 + H F + O2 + H. Evidence is presented for an activation energy of 5-7 kcal./mole for the reaction F + Hz -+ HF + H and for a heat of formation for the BOO species of +3.5 kcal./mole.

Hydrogen atom abstraction by fluorine atoms

“…This equation predicts a straight line for a graph of (Y(CH2=CH18F))~1 vs. [HI]/ C2H2] with an intercept >1.0 and a slope reflecting the relative rates of reaction 4 vs. 2. (10) The data for a series of C2H2/HI competition experiments are given in Table I. In each case, yields were also observed for SF518F (about 1%), CH=C18F (<1%), and CHs18F (<0.2%).…”

“…The similarity of these distributions to the Maxwell-Boltzmann distribution, and of k-¡_*/k2* to fci//?2, the thermal rate constants, is discussed later.) No direct measurement of the yield of (2) is possible until a hydrogen donor, usually HI, has been added and the ratio of yields of H18F to CH2=CH18F is then given' by (9), and the ratio of total available 18F (i.e., all 18F atoms that did not, while still possessing extra kinetic energy, react to form a stable chemical bond) to the yield of CH2=CH18F is given by (10). This equation predicts a straight line for a graph of (Y(CH2=CH18F))~1 vs. [HI]/ C2H2] with an intercept >1.0 and a slope reflecting the relative rates of reaction 4 vs. 2.…”

Ionic and radical processes in the .gamma. radiolysis of tetrahalomethane-arene gaseous mixtures

“…Oxygen and other conventional radical scavengers are reported to combine very slowly with halogen atoms, 19 producing addition products which can easily lose halogen and again act as effective halogenating species. 20 This behavior accounts for the small effect of 02 and N20 on the fluorination yields (Table I), whereas its remarkable dependence on XCil4 (Figures 1 and 2) can be ascribed to the high reactivity of CH4 toward halogen atoms producing hydrogen halide and methyl radicals, efficiently scavenged by 02.…”

A Kinetic and Mechanistic Study of the Low-Temperature Fluorine-Initiated Copolymerization of Tetrafluoroethylene with Oxygen

“…Both the above effects can be explained considering that during the reaction between fluorine and the fluoroolefin, one of the primary radicals formed is a fluorine atom; this species not only can add to a molecule of C 2 F 4 , but also can reversibly react with molecular oxygen, to yield FO 2 Such a reaction is known to be fast even at the lowest temperatures, and to be an equilibrium reaction, shifted to the right by an increase of the oxygen concentration .…”