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A Toolkit to Enable Hydrocarbon Conversion in Aqueous Environments
Published on: October 2, 2012
Achieving optimum selectivity in oxygen assisted alcohol cross-coupling on gold
Bingjun Xu1, Robert J Madix, Cynthia M Friend
1Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States.
Journal of the American Chemical Society
|October 28, 2010
Summary
This study reveals how gold surfaces control ester production selectivity in alcohol cross-coupling. Key factors include alkoxy surface concentration and beta-H elimination ease, guiding efficient synthetic routes.
Area of Science:
- Surface Science
- Catalysis
- Organic Chemistry
Background:
- Oxidative coupling of alcohols is crucial for synthesizing esters, widely used in various applications.
- Achieving high selectivity in cross-coupling reactions remains a significant challenge in developing efficient synthetic pathways.
Purpose of the Study:
- To quantitatively investigate the factors governing esterification selectivity in the oxidative cross-coupling of alcohols.
- To elucidate the role of oxygen-covered Au(111) in mediating this reaction and controlling product distribution.
Main Methods:
- Utilized a quantitative study on oxygen-covered Au(111) single crystals.
- Employed vibrational spectroscopy to analyze surface-bound alkoxy species and their stabilities.
- Investigated the activation energies for beta-H cleavage of different alkoxy species.
Main Results:
- Gold's high reactivity stems from atomic oxygen forming surface-bound alkoxy species.
- Product distribution is dictated by relative alkoxy surface concentrations and ease of beta-H elimination.
- Alkoxy stabilities correlate with alcohol gas-phase acidities; beta-H cleavage activation energies follow a specific order (methoxy > ethoxy > butoxy).
Conclusions:
- Mechanistic insights from fundamental surface science studies can guide the control of selectivity in real-world catalytic conditions.
- Optimized cross-coupling is achieved by controlling reactant composition, favoring excess lower molecular weight alcohols.
- The findings provide a basis for designing more efficient ester synthesis routes using gold catalysts.
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