FOURIER-TRANSFORM INFRARED STUDY OF THE GAS-PHASE THERMOLYSIS OF TRIFLUOROACETIC-ACID

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 greater-than-or-equal-to ca. 85% of reaction with rate constants varying from 3.42 x 10(-3) s-1 at 573 K to 5.74 x 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.