Fourier-transform infrared study of the gas-phase thermolysis of trifluoroacetic acid

Abstract

The decomposition of trifluoroacetic acid in the gas phase has been studied in the temperature range 573–643 K using Fourier-transform infrared spectroscopy. Major products are carbon dioxide and trifluoromethane together with smaller quantities of silicon tetrafluoride, carbon monoxide and hydrogen fluoride. The loss of trifluoroacetic acid follows first-order kinetics over ca. 85% of reaction with rate constants varying from 3.42 × 10^–3 s^–1 at 573 K to 5.74 × 10^–2 s^–1 at 643 K. The activation energy determined from least-squares analysis of the resulting Arrhenius plot is evaluated to be 114 ± 7 kJ mol^–1. Production of carbon dioxide continues after all the TFA has disappeared from the gas phase and the amount of CO₂ produced is related to the amount of TFA decomposed by the relationship [CO₂]=(97 ± 11 – 9.2 ± 1.1[TFA]^1/2). A mechanism involving the formation and subsequent decomposition of adsorbate species on the internal walls of the infrared cell rather than a homogeneous gas-phase reaction is proposed.