Benzyl alcohol oxidation on Pd(111): aromatic binding effects on alcohol reactivity
Rhea M Williams1, J Will Medlin
1Department of Chemical and Biological Engineering, UCB 596, University of Colorado Boulder , Boulder, Colorado 80309, United States.
Abstract:
To investigate how surface oxygen participates in the reaction of important aromatic oxygenates, the surface chemistry of benzyl alcohol (PhCH2OH) and benzaldehyde (PhCHO) has been studied on oxygen-precovered Pd(111) (O/Pd(111)) using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). On both Pd(111) and O/Pd(111), TPD using isotopically labeled benzyl alcohol and low-temperature HREEL spectra show that the oxidation of benzyl alcohol proceeds through a benzyl alkoxide (PhCH2O-) intermediate to adsorbed benzaldehyde so that the sequence of bond scission is O-H followed by C(α)-H. In the presence of surface O, some benzaldehyde desorbs from the surface below 300 K, consistent with the presence of a weakly adsorbed η(1) aldehyde state that is bound to the surface through its oxygen lone pair. Benzaldehyde also reacts with surface oxygen to produce benzoate (PhCOO-). Shifts in the OCO stretching frequency suggest that the benzoate orientation changes as the surface becomes less crowded, consistent with a strong interaction between the phenyl group and the surface. Adsorbed benzaldehyde and benzoate undergo decomposition to CO and CO2, respectively, as well as benzene. Deoxygenation of benzyl alcohol to toluene occurs at high coverages of benzyl alcohol when the relative surface O coverage is low. Experiments conducted on (18)O/Pd(111) reveal exchange occurring between surface O and the benzaldehyde and benzoate intermediates. This exchange has not been reported for other alcohols, suggesting that aromatic binding effects strongly influence alcohol oxidation on Pd.
More Related Videos
05:34Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of α,β-Unsaturated Compounds and Alkynes
Published on: December 16, 2019
07:06Continuous Flow Chemistry: Reaction of Diphenyldiazomethane with p-Nitrobenzoic Acid
Published on: November 15, 2017
Related Concept Videos
Reactions at the Benzylic Position: Oxidation and Reduction
Radical Oxidation of Allylic and Benzylic Alcohols
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Oxidation of Alcohols
The process of oxidation in a chemical reaction is observed in any of the three forms:
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
