Cyclohexane oxidation continues to be a challenge

Many efforts have been made to develop new catalysts to oxidize cyclohexane under mild conditions. Herein, we review the most interesting systems for this process with different oxidants such as hydrogen peroxide, tert-butyl hydroperoxide and molecular oxygen. Using H2O2, Na-GeX has been shown to be a most stable and active catalyst. Mesoporous TS-I and Ti-MCM-41 are also stable, but the use of other metals such as Cr, V, Fe and Mo leads to leach ing of the metal. Homogeneous systems based on binuclear manganese(IV) comp lexes have also been shown to be interesting. When t-BuOOH is used, the act ive systems are those phthalocyanines based on Ru, Co and Cu and polyoxomet alates of dinuclear ruthenium and palladium. Microporous metallosilicates c ontaining different transition metals showed leaching of the metal during t he reactions. Molecular oxygen can be used directly as an oxidant and decre ases the leaching of active species in comparison to hydrogen peroxide and tert-butyl hydroperoxide. Metal aluminophosphates (metal: Mn, Fe, Co, Cu, C r V) are active and relatively stable under such conditions. Mn-AlPO-36 yie lds directly adipic acid, but large amounts of carboxylic acids should be a voided, as they cause metal leaching from the catalysts. Rare earth exchang ed zeolite Y also shows good selectivity and activity. In the last part of the review, novel alternative strategies for the production of cyclohexanol and cyclohexanone and the direct synthesis of adipic acid are discussed. ( C) 2001 Elsevier Science B.V. All rights reserved.