A Quantum Mechanical Study of the Decomposition of CF₃OCF₃ and CF₃CF₂OCF₂CF₃ in\nthe Presence of AlF₃

Abstract

The effect of AlF₃ on the decomposition of CF₃OCF₃ and CF₃CF₂OCF₂CF₃ is investigated using ab initio\ntheory. Previous work by Pancansky et al. [Pacansky, J.; Waltman, R. J. <i>J Fluorine Chem.</i> <b>1997</b>, <i>83</i>, 41]\nshowed that AlF₃ significantly reduces the activation energy of the decomposition of CF₃OCF₃ due to the\nstrong electrostatic interaction between the aluminum trifluoride and the reactant. In this work, a new transition-state structure and reaction mechanism have been identified for the decomposition of CF₃OCF₃ in the presence\nof AlF₃. This new mechanism shows that AlF₃ functions by accepting a fluorine atom from one carbon and\nsimultaneously donating a fluorine atom to the other carbon. We show that the same pathway is obtained\nindependently of the level of theory. The reaction rate, generated via statistical mechanics and transition-state theory, is 2−3 orders of magnitude higher for the new transition state when compared to that of the old\none. The study was also performed for CF₃CF₂OCF₂CF₃ in order to ascertain the effect of chain length on the\nreaction mechanism and rate. We find that an analogous transition state, with lower activation energy, provides\nthe lowest-energy path for decomposition of the longer chain.