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More Stahl Aerobics

“Highly Practical Copper(I)/TEMPO Catalyst System for Chemoselective Aerobic Oxidation of Primary Alcohols” Hoover, J. M.,; Stahl, S. S.  J. Am. Chem. Soc. 2011. ASAP. DOI: 10.1021/ja206230h

To quickly follow up yesterday’s post on aerobic alcohol oxidation, I thought that this new paper from the Stahl lab on the same topic was worth mentioning.  While their continuous flow process for alcohol oxidation was a pretty big improvement over many existing methods, the reagents necessary were not ideal.  Toluene and pyridine are both toxic, and palladium is not extremely abundant, especially compared to 1st row transition metals.  So there was plenty of room for improvement, which is why I was really psyched to see this new catalyst system for primary alcohol oxidation that was published a few days ago. Virtually all of the reaction components have been replaced by greener reagents:  acetonitrile instead of toluene, N-methylimidazole instead of pyridine, and catalytic TEMPO/(bpy)Cu(I) instead of palladium acetate.  Unlike most aerobic alcohol oxidations, an atmosphere of pure oxygen was not necessary – the oxygen present in ambient air was enough for the reaction to run efficiently.  And the reaction is run at room temperature to boot.  It’s hard to imagine that this reaction would be more difficult to scale up using their flow reactor than the Pd-catalyzed version, although you never know I suppose.

There’s loads more in the paper on their catalyst development studies, and on the chemoselectivity of this process for primary alcohols versus secondary ones – definitely worth reading!

Oxygen, Nature’s Oxidant for Nature’s Feedstocks.

“Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen”R. Wolfel, N. Taccardi,  A. Bosmann, P. Wasserscheid, Green Chemistry, 2011, DOI: 10.1039/c1gc15434f

Graphical abstract: Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen

All of us have a very personal relationship to the oxidizing power of oxygen. We use oxygen to turn our food into energy, CO2 and water. There are a number of enzymes and pathways that aid this process, each aiding the reaction of food and oxygen toward the creation of CO2 and water.  Now the key to turning complex biomass into usable small molecules is the ability to control this reaction so that we can extract usable chemical building blocks without ending up back at CO2 and water. As you can see in this video over-oxidation can be a real concern.  This paper demonstrates the use of a polyoxometalate (POM) catalyst to promote the oxidation of biomass to formic acid.