Alkali-metal fluorides supported on γ-alumina. Surface reactions involving 18F- and 35S-labelled sulphur tetrafluoride and thionyl fluoride, 35S-labelled sulphur dioxide, 18F- and 14C-labelled carbonyl fluoride and 14C-labelled carbon dioxide

Abstract

Reactions between the Lewis acids, SF₄, F₂SO, F₂CO and CO₂, radiolabelled with ¹⁴C, ¹⁸F and ³⁵S as appropriate, and CsF or KF supported on γ-alumina have been studied under heterogeneous conditions at room temperature. Fluorine-containing Lewis acids react in two ways, with surface F^– anions to form Lewis acid–base complexes and to fluorinate surface hydroxyl groups. Maximum surface F^– anion activity occurs at a metal fluoride loading of 5.5 mmol g^–1. The reaction between CsF or KF and γ-alumina to give hexafluoroaluminate salts, which occurs during the impregnation process, becomes more important as the metal fluoride loading increases over the range 0.6–20.0 mmol g^–1. This reaction is accompanied by dehydroxylation of the surface of the support, but there is no evidence for the presence of free hydroxide anions.