Synthesis of ethylphenols and xanthenes via reaction of calcium carbide and phenol: experimental and theoretical studies

Abstract

Calcium carbide (CaC₂) is a platform chemical for various organic synthesis, and monomeric phenol (PhOH) is expected to be produced via biomass conversion in the near future. This work explores their downstream product during reaction at 300–400 °C without additional solvent and catalyst. The reaction matrix was investigated by density functional theory (DFT) calculation and characterization of the solid product. Results indicate that in addition to ethylphenols, xanthenes are unexpectedly formed with a yield of 26.0% at 350 °C. DFT calculation indicates that PhOH is firstly alkylated by CaC₂ to form vinylphenol or dehydrated intermolecularly to form diphenyl ether. Xanthenes are then formed through two pathways: dehydration of vinylphenol with PhOH and then cyclization; alkylation and cyclization of diphenyl ether with CaC₂-derived acetylene. Ethylphenols are formed through hydrogenation of vinylphenol where PhOH provides hydrogen. Vinylphenol hydrogenation for ethylphenols exhibits a competitive advantage over vinylphenol dehydration for xanthenes. X-ray diffraction (XRD) of the solid product indicates that CaC₂ is converted to calcium phenoxide. Isomolecular electrostatic potential maps suggest that calcium phenoxide exerts a catalytic effect on the alkylation and dehydration reactions. This work provides a novel protocol for xanthene synthesis and an in situ efficient utilization method of the acetenyl group.