Kinetics of gas-phase fluorination of halomethanes

Abstract

The rates of the hydrogen abstraction reactions of fluorine atoms with five halomethanes and two alkanes in the gas phase were studied using competitive methods. The main competitors were arranged in the following series in which adjacent pairs were fluorinated competitively: (i) CH₃Cl, CH₂Cl₂, CHClF₂, CHCl₂F, CH₃Cl (ii) CHCl₃, CH₂Cl₂, CHClF₂, CHCl₂F, CHCl₃(iii) CH₃Cl, CH₂Cl₂, CHCl₃, CHCl₂F, CH₃Cl.

The relative rates obtained were all internally consistent. The results for n-butane and neopentane agreed with reported values. Absolute Arrhenius parameters for the halomethanes were derived from reported data for n-butane and the A factors compared with theoretical values. The activation energies in the chloromethane series pass through a minimum in going from methane to chloroform similar to the minima found in the chlorination and bromination of chloro and fluoromethanes. The results are discussed in terms of changes in bond strength and in the repulsive force methanes. The results are discussed in terms of changes in bond strength and in the repulsive force between the nascent products. This force depends upon the dipole moment of the hydrogen donor.