Kinetics of the thermal decomposition of bis(trifluoromethyl) peroxide

Abstract

The pyrolysis of CF3OOCF3 (BTMP) was studied in the gas phase from 1 to 200 Torr pressure and between 236 and 272 °C in a nickel reactor by the static method. Decomposition was limited to 5% to avoid complications. The reaction proceeds according to the overall stoichiometry BTMP CF3OF + COF2, as determined by analysis of the products. The reaction is self-inhibited by COF2 and accelerated by the addition of inert gases N2, CO2, and C2F6. Addition of 1-400 Torr of C2F6 was studied at 232 and 260 °C. A mechanism is proposed that accounts for the initial rate. Its main features are: (1) steady-state concentration of CF3O radicals maintained by the equilibrium BTMP 2CF3O;(2) the rate-determining step is the unimolecular decomposition of the CF3O radical which is pressure dependent and reversible: CF3O (+M) 4n COF2 + F (+M); this also accounts for the inhibition by COF2. The expression for initial rate is = 2! (A 1 /A 5) [BTMP])1/2, with ko pressure dependent. The observed experimental activation energy of 49.7 kcal/mol therefore corresponds to E2 + %(Ei -E5).

A reexamination of the pyrolysis of bis trifluoromethyl peroxide

“…The pyrolysis of the peroxide has been studied using monel [$I, aluminum [9,10], magnesium [lo], or nickel [11,12] reaction vessels. Kennedy and Levy [9] studied the kinetics of both the forward and the reverse steps of reaction (9).…”

“…The main difference between the two peroxides is the slowness of step (20) [9,12]: (20) 2CF30 -+ CF30F + CFzO compared to the very fast step (21) [23]:…”

“…In neat peroxide, Descamps and Forst found that the order of the reaction varied between 0.89 and 1.04 over the temperature range of 236-272°C. They considered two mechanisms, one of which was identical to that of Kennedy and Levy [9] and the other involved the thermoneutral chain step in the place of reaction (13): (19) F + CF300CF3 -CF30F + CF3O followed by (12) CF3O -CFzO + F The chain step is a displacement process which therefore probably has a high activation energy. The chain length appears to be 0.5 [12], so that it is difficult to differentiate between the two mechanisms.…”

“…An extrapolation is required [12] in order to obtain 1212(m). Using the calculated value jfor k l l of 101O.lM-l-s-l and 10l6s-l for A10 (Table I) (20): (20) 2CF30 -CF20 + CF30F…”

Infrared photochemistry of bis(trifluoromethyl) peroxide

“…The thermal unimolecular decomposition of bis(trifluoromethy1) peroxide (BTMP) has been studied by Kennedy and Levy [6] and by Descamps and Forst [7,8]. The generally accepted mechanism is initial homolytic cleavage at the 0-0 bond,…”