John M. Winfield

Halogen-promoted γ-alumina. I, The interactions of 36Cl- and 14C-labelled carbon tetrachloride and of 36Cl- and 2H-labelled hydrogen chloride with γ-alumina

Abstract The behaviour of [ 36 Cl]-chlorine and [ 14 C]-carbon labelled carbon tetrachloride at 500 K and of [ 36 Cl]-chlorine and [ 2 H]-hydrogen labelled anhydrous hydrogen chloride at 293 K towards calcined γ-alumina has been investigated under static conditions. Two types of surface chlorine species are formed using CCl 4 ; one type is inert with respect to [ 36 Cl]-chlorine exchange with anhydrous HCl at 293 K, the other is labile and behaves identically to the surface species resulting from treatment with HCl. Radiotracer and neutron activation analyses indicate that more chlorine is retained by samples treated with CCl 4 under the conditions used. The results of isotopic exchange reactions together with an examination of the CCl 4 reaction using IR spectroscopy and 27 Al MAS NMR spectra of chlorinated γ-alumina are used to make proposals about the nature of the acidic sites formed.

Radiotracers in fluorine chemistry: Part XVHalogen exchange and isomerization reactions involving chlorofluoroethanes on fluorinated chromia surfaces labelled with anhydrous hydrogen [18F]-fluoride, hydrogen [36Cl]-chloride or 1,1-di[36Cl]chlorotetrafluoroethane

Abstract Series of fluorination and chlorination reactions are observed when CCl2FCClF2 or C2Cl2F4 isomers are flowed at ca. 700 K over fluorinated chromia catalysts that have been labelled by prior treatment with H18F or H36Cl. These reactions result in the incorporation of the radiolabel in each component of the mixtures of C2Cl6-nFn that are formed. The probability of a radiolabel, [18F] or [36Cl], in a given component correlates directly with the degree to which that component has been fluorinated or chlorinated on the surface. The isomerization of CCl2FCClF2 to CCl3CF3 is an important reaction on fluorinated chromia at 700 K; [36Cl] tracer experiments indicate that the process is intramolecular. Isomerization of CClF2CClF2 probably occurs also but is less dominant in the overall behaviour observed.

Acetonitrile, a convenient solvent for inorganic fluorides

Abstract A procedure is described for the purification of acetonitrile to a level suitable for synthetic, spectroscopic, and electrochemical work involving high oxidation state fluorides. Lewis acid-base and redox reactions in this solvent are discussed.

Halogen-promoted γ-alumina Part II. The catalytic dehydrochlorination of 1,1,1-trichloroethane at room temperature on chlorinated γ-alumina

Abstract The dehydrochlorination of 1,1,1-trichloroethane vapour to give 1,1-dichloroethene and hydrogen chloride is catalysed by γ-alumina which has been chlorinated with carbon tetrachloride or carbonyl chloride at 500 K. Chlorination of γ-alumina with hydrogen chloride does not result in a catalyst for this reaction. 1,1-Dichloroethene reacts further to produce a purple, oligomeric material on the surface of chlorinated γ-alumina. The overall reaction of CH 3 CCl 3 has been followed using IR spectroscopy and [ 36 Cl]-chlorine as a radiotracer. The results obtained are consistent with dehydrochlorination occurring at strong Lewis acid surface sites, although the chlorine associated with these sites is not involved directly in the reaction.

Redox reactions involving molybdenum, tungsten and uranium hexafluorides in acetonitrile

Abstract The redox properties of molybdenum, tungsten and uranium hexafluorides in acetonitrile at 298 K have been compared with other redox couples using cyclic voltammetry, and by carrying out appropriate redox reactions under carefully controlled conditions. The order of oxidizing ability established is UF 6 > MoF 6 > NO +1 > solvated Cu 2+ ⩾ WF 6 . The position of the solvated Tl 3+ cation probably lies between MoF 6 and Cu 2+ Reactions which occur in the Cu metal/solvated Cu n+ (n = 1 or 2)/WF 6 system are accounted for by redox and fluoride-ion-transfer equilibria.

Radiotracers in fluorine chemistry.: Part X, catalysis by fluorinated surfaces. The interaction of hydrogen fluoride or hydrogen [18F]-fluoride with chromia catalysts

Abstract The behaviour of fluorinated, [ 18 F]-fluorine, chromia catalysts, labelled by treatment with hydrogen [ 18 F]-fluoride at 623 K, towards hydrogen fluoride at 623 K has been examined at various stages of the catalysts life. The results, together with temperature programmed reduction and exchangeable hydrogen studies, are interpreted on the basis of the slow, progressive replacement of Cr III O by Cr III F bonds and the existence of three types of fluorine-containing species. Only one of the latter is catalytically active.

Ambient temperature catalytic fluorination of C1 to C3 chlorohydrocarbons and related compounds using oxide-supported organic layer catalysts

Abstract 1,1,1-Trichloroethane is fluorinated by HF at ambient temperature and pressure in the presence of organic layer catalysts, derived from CH 3 CCl 3 , C 3 Cl 4 or CH 3 CCl 2 CH 3 and supported on SF 4 -fluorinated γ-alumina or CCl 4 -chlorinated γ-alumina, to give CH 3 CCl 3− n F n . Related behaviour is observed when CH 3 CCl 2 CH 3 , CH 2 ClCCl 3 , CHCl 2 CHCl 2 and CHClCCl 2 are fluorinated using the supported organic layer catalyst derived from CH 3 CCl 3 . The product distributions observed suggest that the reactivity of the substrates can be correlated with their ability to undergo dehydrochlorination. The behaviour of CHCl 3 , CCl 4 , CCl 2 FCClF 2 and CCl 3 CF 3 under similar conditions is also reported.

Fluorination of polycrystalline diamond films and powders. An investigation using FTIR spectroscopy, SEM, energy-filtered TEM, XPS and fluorine-18 radiotracer methods

Polycrystalline diamond films and diamond powders, treated with elementary fluorine, chlorine trifluoride or anhydrous hydrogen fluoride under various conditions, have been examined using spectroscopic and microscopy techniques. Formation of C–F bonds occurs when F2 or ClF3 are used, the surface groups present being tentatively identified from XPS and FTIR measurements. Surprisingly, the interaction between HF and diamond is substantial and its extent has been quantified using fluorine-18 labelling. Hydrogen fluoride deposited on diamond is labile with respect to exchange with H18F and undergoes slow hydrolysis on exposure to moist air. This treatment, therefore, results in an unusual hydrophilic surface. In contrast, there is no observable [18F] exchange between F-terminated diamond and HF.

Radiotracers in fluorine chemistry : XIII. Catalysis by Fluorinated Surfaces: The Interaction of [36Cl]-Chlorine Labelled Hydrogen Chloride and 1,1-Dichlorotetrafluoroethane with Fluorinated Chromia Catalysts

Abstract The behaviour of the [ 36 Cl]-chlorine labelled compounds, anhydrous hydrogen chloride and 1,1-dichlorotetrafluoroethane, towards fluorinated chromia catalysts has been investigated under flow conditions at 623 and 688 K respectively. In each case [ 36 Cl]-chlorine activity was deposited on the catalyst. Uptakes of chlorine, determined from radiochemical measurements and from neutron activation analyses, were comparable for a given catalyst irrespective of the reagent used. Flow of anhydrous hydrogen fluoride at 623 K or reactions of dichlorotetrafluoroethane isomers and 1,1,2-trichlorotrifluoroethane over [ 36 Cl]-chlorine labelled fluorinated chromia, led to the removal of 75–85% of the radioactivity. The remainder was retained even on basic hydrolysis of the catalyst. The results are discussed in terms of a halogen exchange model for the behaviour of chlorofluoroethanes and suggestions are made regarding the nature of the catalytically active halogenating species.

Coupling sol-gel synthesis and microwave-assisted techniques: a new route from amorphous to crystalline high-surface-area aluminium fluoride.

A non-aqueous sol-gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 degrees C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 degrees C) the metastable form beta-AlF3 was obtained with a very large surface area of 125 m2 g(-1). The mechanism of the amorphous=crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 degrees C) a multi-component material mixture exhibiting a huge surface area of 525 m2 g(-1) has been obtained and further investigated after mild post-treatment fluorination using F2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m2 g(-1). HRTEM revealed that the solid is built from large particles (50 nm) identified as alpha-AlF3, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.