Styrene Production from Benzene and Ethylene Catalyzed by Palladium(II): Enhancement of Selectivity toward Styrene via Temperature-dependent Vinyl Ester Consumption

Oxidative ethylene hydrophenylation catalyzed by palladium(II) acetate with Cu(II) oxidants to produce styrene generally suffers from low selectivity and/or low yield. Commonly observed side products include vinyl carboxylates and stilbene. In this Article, the selectivity for styrene formation by Pd(OAc)(2) is studied as a function of reaction temperature, ethylene pressure, Bronsted acid additive, Cu(II) oxidant amount, and oxygen pressure. Under optimized conditions, at high temperatures (180 degrees C) and low olefin pressure (20 psig), nearly quantitative yield (>95%) of styrene is produced based on the limiting reagent copper(II) pivalate. We propose the selectivity for styrene versus vinyl pivalate at 180 degrees C is due to a palladium-catalyzed conversion of benzene and in situ formed vinyl pivalate to styrene.