A study of the oxidation of ethers with the enzyme laccase under mediation by two N-OH-type compounds

The oxidation of ethers of various structure by molecular oxygen with two laccase/mediator systems (i.e., HBT, 1-hydroxybenzotriazole, and HPI, N-hydroxyphthalimide) is described. The process affords carbonylic products in reasonable-to-good yields. The oxidation is carried out by the intermediate aminoxyl radical of the two mediators, through a radical H-atom abstraction (HAT) route that represents an elaboration of the HAT route followed with benzyl alcohols. Alternative mechanisms have been considered and dismissed. A comparison with a similar oxidation of ethers by the laccase/TEMPO system, reported previously, is made. A clear-cut specialisation of the mediator vs. the substrate emerges, i.e. the laccase/HBT system results more competent for the oxidation of ethers, whereas the laccase/TEMPO system resulted most proficient in the oxidation of benzyl alcohols.