Selective cleavage of C-O bond in benzyl phenyl ether over Pd/AC at room temperature

Selectively cleaving the C-O bonds in lignin to produce aromatic products are challenging problems. Currently, catalytic hydrogenolysis of C-O bonds in lignin requires harsh conditions. Herein, selectively cleaving C-O bond of benzyl phenyl ether (BPE) was studied over Pd/AC, Ru/AC and Ni/AC. Among these catalysts, Pd/AC efficiently cleaved C-O bond in BPE under super mild conditions (25 degrees C, 2 h and 0.1 MPa H-2). The products were toluene and phenol without hydrogenation of the aromatic ring. The main competitive step of hydrogenolysis and hydrogenation is sensitive to reaction temperature over Pd catalyst. A mild temperature is preferred for hydrogenolysis, since the H center dot species nearby the oxygen atom are more strongly adsorbed than nearby the benzene rings. With the different H-donor solvents, the highest conversion of BPE was obtained in isopropanol. Based on the experiments, the reactions occurred via cleavage of the C-aliphatic-O bond in BPE and the synergetic effects between the H center dot from absorbed H-2 on the surface of the Pd and the intermediates radicals of benzyl and phenoxy should be the key points to such an optimum result.