(544u) MoO3-Catalyzed Conversion of Guaiacol into Alkyphenols in Supercritical Ethanol

With the depletion of fossil fuel and the increasing concern of environment, the utilization of lignin, one of the three main components of biomass, has drawn great attention for the production of aromatic compounds. Guaiacol, containing both hydroxyl and methoxyl groups, is recognized as a lignin model compound because the guaiacyl unit is a primary structure in lignin. In this work, selective conversion of guaiacol into diverse alkylphenols including ethylphenols, iso-propylphenols, butylphenols and tert-amylphenol is achieved over bulk MoO₃ at 280 ^oC in supercritical ethanol without the addition of external H₂ (Figure 1). The supercritical ethanol here serves as the solvent as well as hydrogen-donor. The overall selectivity to alkylphenols reaches 86% at a conversion of >99%. It has been demonstrated that the higher alkyphenols are formed through deoxygenation followed by consecutive α-alkylation with methyl and ethyl groups (Figure 2). Control experiments with other reactants show that catechol and ethylphenols are the intermediate products rather than phenol. The XRD and XPS characterizations of spent catalysts indicate that the peculiar MoO_xC_yH_zphase containing Mo⁵⁺ species formed by partial carbonization of MoO₃ play a crucial role in the reaction. The catalyst undergo deactivation due to the reduction of Mo⁵⁺ and carbon deposition but can be easily regenerated with a simple calcination. Our study has great significance to the utilization of lignin.