The Guerbet Reaction Network – a Ball‐in‐a‐Maze‐Game or: Why Ru‐MACHO‐BH is Poor in Coupling two Ethanol to n‐Butanol

Abstract

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.

Control in Advanced Biofuels Synthesis via Alcohol Upgrading: Catalyst Selectivity to n‐Butanol, sec‐Butanol or Isobutanol

“…For example, Beller and co‐workers have previously reported that 13 readily converts ethanol to ethyl acetate by acceptorless dehydrogenative coupling under mild reaction conditions [23a–b] . The conditions for such reactions are in open vessels to vent the hydrogen produced, i. e. analogous to Table 2, runs 13 and 15); under normal Guerbet conditions such catalysts are poor for ethanol‐ethanol homocoupling [23e] . We were intrigued as to whether these catalysts in the closed conditions for which we observe sec ‐butanol with tetradentate species would also produce this alcohol isomer.…”

Microwave-assisted pincer-ruthenium catalyzed Guerbet reaction for the upgradation of bio-ethanol to bio-butanol

“…16 From a mechanistic viewpoint, Liauw explained why Ru-MACHO-BH performance is poor in stitching two ethanols to n-butanol. 17 For Ru-based catalysts, although Mazzoni reported the highest ethanol conversion, 16b the highest turnovers and TOF was demonstrated by Szymczak. 16c Guerbet reaction with 3dmetals is reported only with aromatic alcohols.…”

H2 Pressure Dependence in the Homogeneously Catalyzed Guerbet Reaction of Ethanol to Butanol using Mn(I) and Ru(II)

“…[1][2][3] The reaction involves sequential two-fold dehydrogenation, aldol-condensation, and double hydrogenation. [1,2,[13][14][15][16][17] The primary product is 1-butanol, alongside hexanol, 2-ethylbutanol, octanol, 2-ethylhexanol, 3-ethoxybutanol, and traces of C 8 + aromatics. [1,2,16] Besides the use as solvent or building block for plasticizers, [18,19] also an application of the obtained mixture of C 4 + alcohols as a direct source for bio-based fuels with high octane numbers that can for example directly be used in diesel engines is discussed.…”