On novel sol-gel catalytic materials for selective alcohol oxidation

There is high need of efficient heterogeneous catalysts for liquid-phase alcohol oxidations ('philosophers stones'). Sol-gel technology and stable nitroxyl radicals to the family of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) may ineed offer the long awaited breakthrough in catalytic oxidations and the technology has been patented. Organic nitroxyl radicals are highly efficient molecular catalysts for selective, liquid-phase homogeneous oxidations of primary and secondary alcohols in the presence of a primary oxidant (including air) due to mildness and reactivity of the active species, the cyclic nitrosonium ion (TEMPO+). Sol-gel is by far the best technique to entrap organic molecules in inorganic porous solids whose physical and chemical properties can be aptly tailored by varying reaction conditions of the polymerization process ('sol-gel science'). Sol-gel microporous glasses doped with TEMPO have been prepared which do not lead to leaching of the radicals in solution and catalyse the selective oxidation of D-methylglucose and cinnamyl alcohol either in H2O or in organic solvent. Reaction rate have to be enhanced and work is in progress toward the preparation of sol-gel mesoporous membranes to be used in continuous oxidative processes.