Probing elementary steps under reaction conditions using infrared spectroscopy

STACCHIOLA, DARIO J.; CALAZA, FLORENCIA C.; BURKHOLDER, LUKE; SCHWABACHER, ALAN W.; NEUROCK, MATTHEW; TYSOE, WILFRED T.

CIENCIAS (MARACAIBO)

Oficina Editorial de CIENCIA, Facultad Experimental de Ciencias, Universidad del Zulia, Maracaibo 4001, Venezuela

Año: 2006 vol. 14 p. 189 - 195

1315-2076

The reaction pathway for the palladium-catalyzed synthesis of vinyl acetate from acetic acid, ethylene and oxygen is investigated using reflection-absorption infrared spectroscopy by monitoring the rate of acetate titration by gas-phase ethylene. This reveals that acetate species are removed by reaction with gas-phase ethylene resulting in vinyl acetate formation. Reaction with C2D4 reveals a large (~6) isotope effect indicating that hydrogen is involved in the rate-limiting step. This also results in the appearance of an infrared feature that is assigned to an acetoxyethyl- palladium intermediate. Acetate reaction rates are different for the isotopomers, CH2CD2 and CHDCHD. These observations are consistent with a reaction pathway first proposed by Samanos in which ethylene reacts with an acetate species to form an acetoxyethyl-palladium intermediate, which then reacts to form vinyl acetate by a beta-hydride elimination reaction.