Green Chem., 2014, 16,3358-3363
DOI: 10.1039/C4GC00191E, Paper
DOI: 10.1039/C4GC00191E, Paper
Open Access
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Enrique V. Ramos-Fernandez, Norbert J. Geels, N. Raveendran Shiju, Gadi Rothenberg
Set them free? Combining a solid catalyst and a solid free-radical scavenger, gives a free-radical oxidation that gives high selectivity even at high concentrations.
We research here the catalytic oxidative dehydrogenation of ethyl lactate, as an alternative route to ethyl pyruvate. Testing various solid catalysts (Fe2O3, TiO2, V2O5/MgO–Al2O3, ZrO2, CeO2 and ZnO), we find that simple and inexpensive TiO2 efficiently catalyses this reaction under mild conditions. Furthermore, molecular oxygen was used as the terminal oxidant. Importantly, this reaction runs well also using inexpensive commercial solvent mixtures. Both the desired reaction and the by-products formation follow a free-radical mechanism. Remarkably, adding activated carbon, a solid radical scavenger, hardly affects the catalytic activity, but enhances the product selectivity. This is because this solid radical scavenger hampers the formation of undesired products in solution, without suppressing the oxidation at the catalyst surface.
Set them free? Combining a solid catalyst and a solid free-radical scavenger, gives a free-radical oxidation that gives high selectivity even at high concentrations.
We research here the catalytic oxidative dehydrogenation of ethyl lactate, as an alternative route to ethyl pyruvate. Testing various solid catalysts (Fe2O3, TiO2, V2O5/MgO–Al2O3, ZrO2, CeO2 and ZnO), we find that simple and inexpensive TiO2 efficiently catalyses this reaction under mild conditions. Furthermore, molecular oxygen was used as the terminal oxidant. Importantly, this reaction runs well also using inexpensive commercial solvent mixtures. Both the desired reaction and the by-products formation follow a free-radical mechanism. Remarkably, adding activated carbon, a solid radical scavenger, hardly affects the catalytic activity, but enhances the product selectivity. This is because this solid radical scavenger hampers the formation of undesired products in solution, without suppressing the oxidation at the catalyst surface.
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