Single-Step Oxidation of Cyclohexene to AA

In a similar manner, cyclohexanol can be converted into AA with a 87% yield, using a 4.4 molar amount of 30% HP and H2WO4 at 90 °C, in 20h [34n, o]. 

As pointed out [131], these systems, although quite efficient, may present problems due both to the oxidative degradation of the organic ligands in ammonium salts and some catalyst instability, with the latter being caused by the fact that the 0-transfer from the peroxo active species may lead to its structural collapse and the formation of less active species. 

Various heterogeneous catalysts have also been investigated for this reaction. Tetrahedral tungstate units can be incorporated at the surface of mesoporous silica, for example, S BA-15, to obtain heterogeneous systems that can effectively oxidize cyclohexene with HP [35a]. A 46% selectivity to colorless, crystalline AA was obtained at 85 °C, with total conversion of cyclohexene, under organic, solvent-free conditions. 

After 30 h reaction time, the TOP reached 350molAAmolw which is remarkably higher than that of other heterogeneous catalysts described in the literature, such as W-MCM-41. Interestingly, the latter system yields glutaraldehyde (72%) in the oxidation of cyclopentene with HP [35bj. 

The incorporation of Al into a mesostructured silica SBA-15, followed by Ti grafting, led to the formation of a bifunctional catalyst, which afforded an 80% yield to AA in 24h, at 80 °C, using t-BuOOH as the oxidant [35d, e]. trans-1,2-Cyclohexandiol, 2-hydroxycyclohexanone, glutaric and succinic acids were the main by-products of the reaction. 

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