ENNANTIOSELECTIVE REACTIONS ON A AU/PD(111) SURFACE ALLOY WITH COADSORBED CHIRAL 2-BUTANOL AND PROPYLENE OXIDE

FENG GAO; YILIN WANG; ZHENJUN LI; OCTAVIO JAVIER FURLONG; WILFRED T. TYSOE

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Año: 2008 vol. 112 p. 3362 - 3372

1932-7447

The coadsorption of R- and S-propylene oxide with R-2-butanol was studied on a dilute Au/Pd(111) alloy containing ~8% gold using temperature-programmed desorption and reflection absorption infrared spectroscopy. Alloy formation strongly affects the surface chemistry of these molecules as compared to clean Pd(111). A portion of the propylene oxide decomposes to form CO and ethylidyne species on the alloy, while on clean Pd(111), it adsorbs reversibly. 2-Butanol reacts to form a 2-butoxide species on the alloy that either rehydrogenates to form 2-butanol or undergoes a b-hydride elimination reaction to yield 2-butanone. Coadsorption of R-2-butanol with either R- or S-propylene oxide led to a larger 2-butanone yield in the presence of S propylene oxide with an enantiomeric excess (ee) of ~14%. This led to an enantioselective depletion of the 2-butoxide species such that the subsequent 2-butanol formation is highly enantioselective, with 100% ee.