Insight into the Co(II)/NaOH and Cu(II)/NaOH catalytic oxidation of 4-methyl guaiacol: Structures of catalysts and reaction pathways

In excess alkali, 4-methylguaiacol was successfully oxidized to vanillin by Co-salt/NaOH catalytic system with conversion of 100% and selectivity of 90%; however, with conversion of 87% and selectivity of 9% when the catalytic system was replaced by Cu-salt/NaOH. To explore the different catalytic effects, the detailed structural characterizations of the catalysts were carried out by EPR, DLS, and UV–vis technologies. The results suggest that both Co(II)/NaOH and Cu(II)/NaOH systems are heterogeneous and the Co(IV) = O might be an essential factor for the high selectivity in Co(II)-catalysis.