Environmentally friendly liquid phase oxidation: enhanced selectivity in the aerial oxidation of alkyl aromatics, epoxidations and the Baeyer–Villiger oxidation using novel silica supported transition metal ions

✍ Scribed by Ian C Chisem; Janet Chisem; John S Rafelt; Duncan J Macquarrie; James H Clark; Katherine A Utting

• Publisher: Wiley (John Wiley & Sons)
• Year: 1999
• Tongue: English
• Weight: 127 KB
• Volume: 74
• Category: Article
• ISSN: 0268-2575
• DOI: 10.1002/(sici)1097-4660(199910)74:10<923::aid-jctb124>3.0.co;2-8

✦ Synopsis

Active transition metal species (Co, Cu, Cr, Ni or Mn) supported on a chemically modi®ed silica gel are used as heterogeneous catalysts in a range of liquid phase oxidation reactions: alkyl aromatic side chain oxidations, epoxidations of alkenes and Baeyer±Villiger oxidations of linear ketones to esters and cyclic ketones to lactones. The catalyst employs metal centres bound to the silica surface via a hydrophobic spacer chain and is thus chemically robust and has a relatively high loading for a supported reagent (c 0.4 mmol g À1 ). The Cr version of the catalyst promotes the oxidation of ethylbenzene to acetophenone in a solvent-free system at a rate of 5.5% h À1 (b370 turnover h À1 ). It is also active for the oxidation of p-chlorotoluene and p-xylene to p-chlorobenzoic acid and p-toluic acid respectively. Cyclohexene is converted to its oxide at room temperature at a rate of c 28% h À1 (c 12 turnover h À1 ) using either the Ni or Cu versions of the catalyst. The room temperature Baeyer±Villiger oxidation of cyclohexanone is achieved at a rate of 44% h À1 (49 turnover h À1 ) using the Ni-containing catalyst. The same material also promotes the Baeyer±Villiger oxidation of linear aliphatic ketones and aromatic side chains. All the above systems use either air or molecular oxygen as the oxidant rather than peroxides or peracids.