Tin oxide surfaces. Part 21.—Infrared study of the chemisorption of 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoropropan-2-ol, 1,1,1-trifluoropropan-2-one, 1,1,1,3,3,3-hexafluoropropan-2-one and trifluoroacetic acid on tin(IV) oxide gel

Abstract

The adsorption of trifluoroacetic acid, 1,1,1,3,3,3-hexafluoropropan-2-one, 1,1,1-trifluoropropan-2-one, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol on tin(IV) oxide gel has been studied by infrared spectroscopy. trifluoroacetic acid is adsorbed as both hydrogen-bonded molecular trifluoroacetic acid and surface trifluoroacetate, the former being totally converted into the latter by 533 K. The surface trifluoroacetate decarboxylates by 673 K to give surface trifluoromethoxide. Both of the ketones 1,1,1,3,3,3-hexafluoropropan-2-one and 1,1,1-trifluoropropan-2-one are chemisorbed as surface hemiacetal species by interaction with a surface hydroxyl group. These undergo subsequent thermal decomposition to give, respectively, surface trifluoroacetate and a mixture of surface trifluoroacetate and surface acetate. The two alcohols 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol are chemisorbed as surface alkoxy species which thermally decompose to surface formate and surface trifluoromethoxide in the case of the former and additionally in the case of the latter, surface trifluoroacetate. The thermal stability of the surface carboxylates is in the order: surface acetate > surface trifluoroacetate > surface formate.