JOHN M WINFIELD

Email johnwin@chem.gla.ac.uk

Halogens are important since these elements form compounds with the vast majority of other elements in the periodic table. Our aim is to make and study interesting compounds which are also useful; this can involve reactions in non-aqueous solvents or at surfaces. An unusual feature of our work is the extensive use that is made of radioactive isotopes, long-lived isotopes such as [³⁶Cl] and short-lived like [¹⁸F]. Much of the work is collaborative, with other chemists in Glasgow or in Industry or with other disciplines. It helps to be a good communicator.

Fluorination or chlorination of high surface area oxides such as gamma-alumina or chromia is an excellent way of enhancing the catalytic properties of these oxides by the formation of new strong Brønsted or Lewis acidic surface sites. With this fundamental work as a background we have developed new heterogeneous catalysts, oxide-supported organic layers, which are active for the room temperature synthesis of hydrochloro-fluorocarbons HCFCs, compounds that are CFC alternatives. A good example is the reaction

CH₃CCl₃ + HF --> CH₃CCl₂F + HCl

This class of catalyst is also likely to be important in Friedel Crafts chemistry. We are also studying the `thermodynamically difficult' halogen exchange reaction,

CF₃CH₂Cl + HF --> CF₃CH₂F + HCl

important because it is a large-scale production route to a CFC-alternative refrigerant. Very active and selective catalysts recently developed, are required and [¹⁸F] and [³⁶Cl] radiotracer studies enable active sites to be described and mechanistic information to be obtained. Catalytic work is carried out in collaboration with Professor Webb.

Halogen-containing compounds such as Br₂, HOCl and HF are important reagents for the chemomechanical polishing of optical electronic and optoelectronic materials. This is the process whereby through the combination of selective chemical reactions and the mechanical action of a polishing pad, a plane specular surface is produced on SiO₂, Si, GaAs or LiNbO₃ wafers. We have developed a general model to describe the action of reagents such as H₂O₂, [OCl]^- and Br₂ in aqueous or CH₃OH solution by the identification of key reaction intermediates using tracer techniques, SEM, FTIR, Raman and MAS NMR. A good example is provided by silica which can be polished by CeO₂ with or without the intervention of the [HF₂]^- anion.

The behaviour of a reagent can be modified drastically by the intervention of a macrocycle ligand that either delivers the reagent to the wafer surface or removes a product from the polishing reaction. This gives is the opportunity to study coordinative chemistry at a solution-solid interface (work in collaboration with Dr Peacock).