Selective oxidation of 2,3,6-trimethylphenol into 2,3,5-trimethyl-1,4-benzoquinone with dioxygen over heterogeneous Co catalysts

Abstract

The selective oxidation of 2,3,6-trimethylphenol is an important approach to prepare 2,3,5-trimethyl-1,4-benzoquinone, which is a key intermediate for the synthesis of vitamin E. Previous studies have shown that Co–N–C materials prepared through a pyrolysis process at temperatures between 250 and 400 °C exhibit high catalytic activity for the oxidation of 2,3,6-trimethylphenol, rather than the typical range of 600 to 1000 °C. In addition to these unusual findings, activated carbon-supported Co(Phen)₂ after pyrolysis showed significantly lower catalytic activity compared to its unsupported counterpart, and the pyrolyzed Co(Salen)₂ complex did not display the same high catalytic activity as the homogeneous counterpart. The presence of pyridinic nitrogen (N) on the surface, rather than pyrrolic N, is closely associated with the efficient formation of 2,3,5-trimethyl-1,4-benzoquinone. Active catalytic sites with highly disordered structures are formed alongside the first apparent weight loss during pyrolysis. These results provide important insights into the oxidation of phenolic compounds and catalyst design.