The Guerbet reaction from two alcohols to a long-chain alcohol and water requires a redox catalyst and a strong base in homogeneous liquid systems. Especially, the reaction from ethanol to n-butanol is a challenging example of the reaction that suffers from low yields and selectivities in comparison with reactions of higher alcohols. The most important side reactions are the polymerization of acetaldehyde to C 6 + -components and the saponification of ethyl acetate under consumption of the base. This work pursues the systematic kinetic investigation of the Guerbet reaction network by experiments with isolated subsystems of the network. In-situ-infrared spectroscopy is applied to determine time-resolved concentration profiles. Adapted kinetic models of the single steps are integrated into a microkinetic model of the whole network. The simulation of the reaction network reveals dependencies between temperature, hydrogen pressure, initial concentrations and the yield and selectivity of n-butanol. Finally, it is shown that Ru-MACHO does not lead to high yields in the reaction, because the dehydrogenation to ethyl acetate exhibits a too low activation barrier.
Invited for this month's cover is the group of Marcel A. Liauw at the RWTH Aachen University (Germany). The cover picture shows a playable version of the homogeneously catalyzed Guerbet‐coupling from ethanol to n‐butanol. The 2D ball‐in‐a‐maze‐game is shown here because the reaction steps are either performed in presence of a redox catalyst (top‐down) or in presence of a base (left‐right). Both axes can be moved independently from each other and substances are connected with humps in the height of the activation barrier. Playing the game repeatedly for a defined time and writing down the outcomes (see blackboard) yields the composition of the reaction mixture at a given time. Alas, the highly active redox catalyst Ru‐MACHO shows unsatisfying yields and selectivities of n‐butanol. But why? Read the full text of their Full Paper at 10.1002/cmtd.202000056.
The Front Cover shows a playable version of the homogeneously catalyzed Guerbet‐coupling from ethanol to n‐butanol. The 2D ball‐in‐a‐maze‐game is shown here because the reaction steps are either performed in presence of a redox catalyst (top‐down) or in presence of a base (left‐right). Both axes can be moved independently from each other and substances are connected with humps in the height of the activation barrier. Playing the game repeatedly for a defined time and writing down the outcomes (see blackboard) yields the composition of the reaction mixture at a given time. Alas, the highly active redox catalyst Ru‐MACHO shows unsatisfying yields and selectivities of n‐butanol. But why? More information can be found in the Full Paper by Andreas Ohligschläger et al.
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