PNNL

Abstract

Metallic Pd surfaces are selective toward the non-hydrogenolytic cleavage of the strong aromatic C–O bond for a series of diaryl and aryl alkyl ethers in aqueous phase at relatively mild temperatures and pressures of H2. At quantitative conversions of some aryl ether models (e.g., diphenyl ether and cyclohexyl phenyl ether), reductive hydrolysis can account for up to 90% selectivity. The novel pathway for Pd-catalyzed hydrolysis of aryl ethers involves partial hydrogenation on the metal, water addition to double bonds, and phenol/alkanol elimination. The formation of the highly reactive vinyl ether-type intermediates, which instantaneously hydrolyzes even in the absence of H2 and catalyst, is concluded to be key to both ring hydrogenation and hydrolysis. This new pathway has also been identified to determine the initial selectivities for other aryl ethers.