Mass Spectrometry Study of the Reaction of Fluorine Atoms with Benzene
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ICAL KINETICS AND CATALYSIS
Mass Spectrometry Study of the Reaction of Fluorine Atoms with Benzene E. S. Vasilieva,*, N. D. Volkova, G. V. Karpova, S. V. Savilovb, I. I. Morozova, and V. V. Luninb a
Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, 117977 Russia b Department of Chemistry, Moscow State University, Moscow, 119991 Russia *е-mail: [email protected] Received March 20, 2020; revised March 20, 2020; accepted April 14, 2020
Abstract—The kinetics of the reaction between fluorine and benzene is studied experimentally at T = 293 K. Competitive reactions are used to find a reaction rate constant. The interaction is studied in a low-pressure flow reactor, and mass spectrometry is used to control the concentration of reagents and products. The reaction between fluorine atoms and methane is used as a competitive one. The ratio of rate constants of the studied reaction (k1) and a competitive one (k2) is found for the first time: k1/k2 = 4.4 ± 0.3. A rate constant is calculated for the reaction of fluorine atoms with benzene using literature data: k1 (293 K) = (2.7 ± 0.5) × 10‒10 cm3 molecule−1 s−1. Keywords: benzene, fluorine, reaction rate constant, mass spectrometry DOI: 10.1134/S0036024420100295
INTRODUCTION Benzene is one of the most common chemicals used in industry. It has a negative impact on the environment [1, 2], so its reactions with the main agents of atmospheric oxidation (hydroxyl radicals and chlorine atoms) are of considerable interest:
reaction with the detachment of a hydrogen atom (k1a) to that of the reaction between fluorine atom and methane (k2) was determined at room temperature, k1a/k2 = 0.97
F • + C6H6 → Products, F • + C6H6 → HF + • C6H5,
С6Н6 + R • → С6Н5• + НR. The resulting phenyl radical then reacts with molecular oxygen in the atmosphere. The reactions between hydrocarbons and fluorine are a convenient source of radicals that form in the atmosphere during laboratory studies of atmospheric chemistry. Precise kinetic parameters of the reaction between fluorine and benzene allow modeling of an experiment to determine the rate constant for the reaction between molecular oxygen and phenyl radicals. There is a relatively small number of works that describe the kinetic parameters for reactions between benzene molecules and fluorine atoms [3–5]. Unfortunately, they partially contradict one another. It is therefore of interest to supplement the data available to the scientific community. The interaction between fluorine and other organic compounds (CH4, C2H6, (CH3)2O, CH3CHO, and C6H6) was studied via luminescence and competitive reactions [3]. The ratio of the rate constant for the
ΔH R0 (Iа) = −108.4 kJ/mol [6], F •+ C6H6 → H •+ C6H5F, ΔH R0 (Ib) = −53.2 kJ/mol [6], F • + CH4 → Products.
(I) (Ia)
(Ib) (II)
IR spectroscopy showed that two channels are possible for the reaction between fluorine atoms and benzene: the detachment of a hydrogen atom from a molecule (Ia) and the substitution of a hydrogen atom with a fluorine one (Ib) [4]. Anal
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