Oxide Supported Organic Layer Catalysts

[摘要] A study has been made of the production of oxide supported organic layer catalysts at room temperature. The preparation involves the fluorination of the oxide surface with SF4, which enhances the Lewis acidity of the surface. This is followed by conditioning with CH3CCl3, a reaction in which CH3CCl3 is dehydrochlorinated to CH2=CCl2 and HCl. The dehydrochlorination product, CH2=CCl2 undergoes further dehydrochlorination resulting in the laydown of an oligomeric organic layer on the surface. This organic layer is active, at room temperature, as a catalyst for fluorination of CH3CCl3 with HF. Comparisons have been made among ?-alumina, chromia prepared by hydrolysis of chromium nitrate and "volcano chromia" prepared by pyrolysis of ammonium dichromate. The catalytic properties of chromia-based materials have been demonstrated in, for example the reaction between HF and CH3CCl3 at temperatures >600K. [18F]-Fluorine radiotracer studies have been used to examine the behaviour of fluorine species on these materials. This aspect of the work indicates that gamma-alumina, chromia and "volcano chromia" behave similarly. A "pool" of labile fluorine exists on these materials. The large values determined for fluorine exchange indicate that not only surface fluorine, but also bulk fluorine species are involved in the exchange process. Examination of the conditioning process by G.C. and in situ I.R. analysis of the volatile products indicates that SF4 fluorination of gamma-alumina, chromia and volcano chromia creates Lewis acid sites capable of dehydrochlorinating CH3CCl3. Hydrofluorination reactions are also observed, producing CH3CCl2F, CH3CClF2 and CH3CF3, with the product distribution dependent on the support material. [36Cl]-Chlorine radiotracer studies were used to examine the conditioning process. It is demonstrated that H36Cl is adsorbed on fluorinated materials and that the conditioning process has little effect on H36Cl adsorption. Studies of the reactions of [36Cl]-CH3CCl3 indicate that chlorine containing organic material is laid down on SF4 fluorinated gamma-alumina, chromia and volcano chromia. Treatment of fluorinated materials that had been pretreated with CH3CCl3 with [36Cl]-CH3CCl3 also results in incorporation of [36Cl]-chlorine containing material on the surfaces: it is suggested that this material is adsorbed on the surface and also incorporated into the organic layer material. Introduction of HCl to [36Cl]-CH3CCl3 treated materials indicates that a portion of the [36Cl]-chlorine containing material can be displaced. In situ I.R. analysis of the reaction of HCl with conditioned materials indicates that hydrochlorinated and hydrofluorinated materials can be displaced from the oligomeric organic layer. Determination of the activity at room temperature of the oxide supported organic layers as catalysts in the reaction of CH3CCl3 with HF indicate that both gamma-alumina and "volcano chromia" are effective supports for these catalysts. Reactions on both surfaces result in hydrofluorination reactions, producing CH3CCl2F and also other fluorinated products. From the results obtained, it appears that "volcano chromia" is more active initially, but ?-alumina is able to sustain the reaction over a longer time. The organic material has been removed from the solid supports by solvent extraction. GCMS studies indicate that this material is based on C2 units and contains fluorine and chlorine, although the chlorine is lost by hydrolysis on exposure to atmosphere.

[发布机构] University:University of Glasgow

[关键词] Organic chemistry