Silica-Supported Cu2O Nanoparticles in Advancement of Ullmann Reaction

Abstract

Ullman condensation or Ullman C-O arylation is a reaction that uses Cu metal and thermal conditions to convert aryl halide and phenolic compounds to aryl ethers. The catalytic performance of silica-based nanoparticles of Cu2O (Cu2O-NP) on Ullmann C-O arylation was studied by varying the amount and the ratio of Cu2O-NP: silica combination while keeping the amount of reactants and all other conditions constant. Iodobenzene and phenol were used as C-O arylation precursors in the presence of Cu2ONP on silica in DMSO and K2CO3 at the reflux condition. In parallel, we performed the same reaction under conventional conditions in that the Cu2O-bulk material was used as the monitoring system. The product formation of the reaction was monitored by using TLC and gas chromatography methods. Cu2O-NP and supported silica demonstrated significant catalytic activity in the Ullmann C-O arylation. Among the various ratios of Cu2O-NP and silica catalysts, maximum yield (52%) of diphenyl ether was obtained for the catalyst mixture of Cu2O-NP: silica (2:1 W/W) and the Cu2O-NP: iodobenzene (1:20 mole ratio) while 63% yield of diphenyl ether was obtained in the conventional method where Cu2O bulk: iodobenzene (1:1 mole) ratio was used. Moreover, with silicabased Cu2O-NP as the catalyst, the reaction temperature was successfully reduced from 180◦C (conventional method) to 160◦C (with Cu2O-NP and silica). Accordingly, the Ullman C-O arylation was enhanced economically and environmentally benign manner with the support of Cu2O-NP and silica.