COMPETITIVE REACTIONS OF ATOMIC OXYGEN WITH ACETONE ON AG(110) - NUCLEOPHILICITY VERSUS BASICITY

Acetone (2-propanone, (CH3)(2)CO) exposed to oxygen-activated Ag(110) at 110 K reacts via both nucleophilic attack of oxygen at the electron-deficient carbonyl carbon and C-H bond activation. The former process results in the reversible formation of the metallacycle (CH3)(2)COO(a), an outcome indicated by the incorporation of O-18((a)) into all products evolving at greater than or equal to 215 K during temperature-programmed reaction spectroscopy experiments in which O-18 atoms an preadsorbed. This facile exchange of surface oxygen atoms with (CH3)(2)COO(a) indicates that this reversible transfer is a general type of reaction on Ag(110). Cleavage of a C-O bond in (CH3)(2)COO(a) occurs at 215 and 330 K to liberate acetone from the surface. C-H bond activation by O-(a) yields acetone enolate (CH2 double bond C .(CH3)O-(a)) and results in both the evolution of H2O(g) at 220 K and the disproportionation of hydroxyl groups (OH(a)) to yield additional H2O(g) at 300-330 K. The activation of the C-H bond is predicted from the gas-phase acidity of acetone. Acetone is re-formed by enolate disproportionation at 445 K, but no acetone enol is detected in the gas phase. Partial oxidation of adsorbed species yields CO2((g)) at 405 and 475 K, H2O(g) at 450 K, and residual adsorbed hydrocarbon fragments.