Production of phenols from a cyclic sugar alcohol in high-temperature water over a charcoal-supported platinum catalyst

Abstract

Biomass is a useful carbon-neutral feedstock for the production of various chemicals. The conversion of cyclic sugar alcohols to aromatic compounds can be expected to promote greater use of biomass resources. Here, we examined the conversion of myo-inositol, a cyclic sugar alcohol present in high amounts in rice bran, to aromatic compounds over supported metal catalysts in high-temperature water. We confirmed that myo-inositol could be converted into phenolic compounds such as phenol and catechol over several charcoal-supported metal catalysts in high-temperature water at 250 °C; the yield of phenolic compounds decreased in the order of Pt/C (42%) > Rh/C (24%) > Ru/C (12%) > Pd/C (0.8%) > no catalyst (0%). To understand more about the reaction pathway, the conversion was repeated using various other cyclic alcohols and phenolic compounds. The yields of phenolic compounds decreased progressively with decreasing number of hydroxy groups in the cyclic alcohols; however, phenolic compounds were also produced from cyclohexanetriol and cyclohexanediol, indicating that the formation of aromatic rings from these compounds cannot be explained only by dehydration or dehydroxylation reactions. Therefore, the aromatic ring formation potentially involves dehydrogenation of the cyclic alcohols. Recycling tests confirmed that the Pt/C catalyst retained its catalytic activity after being reused twice.