August 15, 2011
Here’s an unusual “green” method for producing acetone. Converting ethanol (EtOH) to acetone (Me2CO) is an unusual reaction, but it might be of commercial interest, especially as part of a “green” route to propylene and its derivatives. T. Masuda and colleagues disclose a technique for converting EtOH to Me2CO in high yield.
The method is based on passing aqueous fermentation EtOH over a Zr–Fe heterogeneous catalyst at 450–550 °C. The inventors report results at various temperatures and aqueous EtOH concentrations. The Zr–Fe catalyst is an iron oxide with 7.7% wt% zirconium.
At a 50% EtOH concentration, almost no reaction occurs at 400 °C, but the Me2CO yield is ≈30% at 2% EtOH concentration. When the reaction temperature is increased to 450 °C, the Me2CO yield is 60% even at EtOH concentrations as high as 50%. At 500 °C, the Me2CO yield increases to >70%. The reaction temperature cannot exceed 550 °C because the catalyst becomes thermally unstable above that temperature.
The inventors do not speculate about the mechanism of this unusual transformation; and unfortunately they do not report the yields of byproducts. They do mention, however, that CO2 is the primary byproduct, and that there are trace amounts of acetaldehyde (MeCHO). Based on these byproducts, it is possible that the first step in this reaction is dehydrogenation of EtOH to MeCHO. The MeCHO would undergo aldol condensation to 3-hydroxybutyraldehyde, which is then dehydrogenated to the corresponding 1,3-dicarbonyl compound. The dicarbonyl would decompose to Me2CO and CO2. (Metawater [Tokyo]; National University Corporation Hokkaido University [Sapporo-shi, Japan]. US Patent 7,973,199, July 5, 2011; Jeffrey S. Plotkin)