Petroleum reserves are running out. This creates a need for "chemical feedstocks," source chemicals for molecular synthesis.
Ethanol may be part of the solution. Although a fundamentally inefficient process, fermentation can convert biomass to ethanol.
The problem here is how to convert ethanol into other molecules. Jinlong Gong and Buddie Mullins at the University of Texas (Austin) have addressed this problem by converting ethanol molecules to acetaldehyde molecules on gold surfaces.
The surface and the characterization method.
The surface the scientists studied is gold that is 46% covered by oxygen. Ethanol molecules were adsorbed onto the surface, with 167% coverage.
The scientists intended to study the conversion of ethanol to acetaldehyde on the gold surface. For this, they turned to temperature-programmed desorption.
At low temperatures, molecules adsorb on (bind to) surfaces. As the temperature increases, the molecules desorb (un-bind). The temperature at which this desorption occurs gives information on the binding energy of the molecules.
The scientists incorporated additional instrumentation than measures the mass of molecules adsorbed to the surface as a function of temperature. In this way, further information on the identity of the molecules is provided.
Conversion of ethanol to acetaldehyde.
Ethanol, CH3CH2OH, was clearly observed to oxidize into acetaldehyde CH3CHO and water H2O molecules as a function of temperature. The scientists checked for eleven other reasonable products, such as methane, ethyl acetate, and acetic acid, but none were observed, suggesting that the conversion to acetaldehyde was selective over other molecules.
The scientists used radioactive atoms to prove that the carbon atom attached to the oxygen atom in ethanol (the β-carbon) is the reactive species in the molecular conversion, not the next carbon atom over (the γ-carbon). This further demonstrates the selectivity of their reaction.
Importance for environmental and synthetic needs.
These scientists have presented a relatively mild and selective reaction for converting ethanol molecules to acetaldehyde molecules using a gold surface. Thus, a common molecule derived from biomass can be converted to other chemically useful molecules, providing a route to molecules needed by chemists and other scientists, bypassing the need for petroleum.
for more information:
Gong, J.; Mullins, C. B.
Selective oxidation of ethanol to acetaldehyde on gold.
J. Am. Chem. Soc. 2008, 130, 16458-16459.