Mechanisms of Catalytic Cleavage of Benzyl Phenyl Ether in Aqueous and Apolar Phases
He J, L Lu, C Zhao, D Mei, and JA Lercher. 2014. "Mechanisms of Catalytic Cleavage of Benzyl Phenyl Ether in Aqueous and Apolar Phases." Journal of Catalysis 311:41-51. doi:10.1016/j.jcat.2013.10.024
Catalytic pathways for the cleavage of the ether bonds in benzyl phenyl ether (BPE) in the condensed liquid phases using Ni and zeolite based catalysts are explored. In absence of catalysts, the C−O bond is selectively cleaved in water by hydrolysis forming phenol and benzyl alcohol as intermediates, followed by C−C bond alkylation. The hydronium ions catalyzing the reactions are provided by the dissociation of water at the high temperature (523 K). Upon addition of a solid acid (HZSM-5), rates of hydrolysis and alkylation are markedly increased in proportion to the acid concentrations. In the presence of a metal (Ni/SiO2), the selective hydrogenolysis dominates for cleaving the Caliphatic−O bond. Catalyzed by the dual-functional Ni/HZSM-5, hydrogenolysis occurs as the major route rather than hydrolysis (minor). In the apolar undecane, the non-catalytic thermal pyrolysis route dominates. Hydrogenolysis of BPE appears to be the major reaction pathway in undecane in presence of Ni/SiO2 or Ni/HZSM-5, almost suppressing the radical reactions completely. The density functional theory (DFT) calculations perfectly support the proposed C−O bond cleavage mechanisms on BPE in the aqueous and apolar phases. DFT calculations show that BPE is initially protonated and subsequently hydrolyzed in the aqueous phase. The radical reaction plays a significant role for generating primary benzyl and phenoxy radicals in undecane evidenced by DFT calculation, which leads to heavier condensation products without the aid of metals for providing dissociated hydrogen radicals. J.H., L.L., and C.Z. gratefully acknowledge support from the graduate school (Faculty Graduate Center of Chemistry) of the Technische Universität München and the Elitenetzwerk Bayern (graduate school NanoCat). D.M. and J.A.L. thank the support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) and by the National Energy Research Scientific Computing Center (NERSC). EMSL is a national scientific user facility located at Pacific Northwest National Laboratory (PNNL) and sponsored by DOE’s Office of Biological and Environmental Research.