On the mechanism of the Guerbet reaction

Veibel, Stig; Nielsen, Jakob Blæsbjerg

doi:10.1016/s0040-4020(01)82571-0

Cited by 137 publications

(67 citation statements)

References 14 publications

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“…This carbanion would act as the main intermediate for the formation of the various products that are generated during an ETB reaction: if attacked by the carbanion, a neighboring adsorbed acetaldehyde molecule would transform into crotyl alcohol (3), which would go on to be dehydrated into BD (4); if attacked by the carbanion, a neighboring adsorbed ethanol molecule would instead form 1-butanol (5), which can be dehydrated into 1-butene (6); in the absence of neighboring molecule, the remaining hydroxy group of the carbanion would dissociate, resulting in ethylene (7). The conversion of ethanol to 1-butanol-through the so-called "Guerbet reaction"-is believed to follow a similar pathway to that of the ETB mechanism indicated above [20][21][22]. C4 carbonaceous intermediates are thought to be formed by aldol condensation of acetaldehyde, like in the Kagan mechanism, with 1-butanol being formed in the absence of dehydration active sites.…”

Section: The Cavani Mechanismmentioning

confidence: 89%

“…The conversion of ethanol to 1-butanol-through the so-called "Guerbet reaction"-is believed to follow a similar pathway to that of the ETB mechanism indicated above [20][21][22]. C4 carbonaceous intermediates are thought to be formed by aldol condensation of acetaldehyde, like in the Kagan mechanism, with 1-butanol being formed in the absence of dehydration active sites.…”

Section: The Cavani Mechanismmentioning

confidence: 95%

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Recent Breakthroughs in the Conversion of Ethanol to Butadiene

et al. 2016

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1,3-Butadiene is traditionally produced as a byproduct of ethylene production from steam crackers. What is unusual is that the alternative production route for this important commodity chemical via ethanol was developed a long time ago, before World War II. Currently, there is a renewed interest in the production of butadiene from biomass due to the general trend to replace oil in the chemical industry. This review describes the recent progress in the production of butadiene from ethanol (ETB) by one or two-step process through intermediate production of acetaldehyde with an emphasis on the new catalytic systems. The different catalysts for butadiene production are compared in terms of structure-catalytic performance relationship, highlighting the key issues and requirements for future developments. The main difficulty in this process is that basic, acid and redox properties have to be combined in one single catalyst for the reactions of condensation, dehydration and hydrogenation. Magnesium and zirconium-based catalysts in the form of oxides or recently proposed silicates and zeolites promoted by metals are prevailing for butadiene synthesis with the highest selectivity of 70% at high ethanol conversion. The major challenge for further application of the process is to increase the butadiene productivity and to enhance the catalyst lifetime by suppression of coke deposition with preservation of active sites.

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Section: The Cavani Mechanismmentioning

confidence: 89%

Section: The Cavani Mechanismmentioning

confidence: 95%

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

et al. 2016

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“…(19)]. [224,225] The Guerbet reaction proceeds through a number of sequential steps including dehydrogenation of the alcohol to the corresponding carbonyl compounds; aldol condensation between the carbonyl compounds, followed by elimination of water; and hydrogenation of the unsaturated aldehydes to a saturated alcohol. [224,225] As a side reaction, two molecules of aldehyde may undergo Cannizzaro-like disproportionation into alcohol and carboxylic acid.…”

Section: Nonaqueous Sol-gel Chemistry For Metal Oxide Synthesismentioning

confidence: 99%

Organic Reaction Pathways in the Nonaqueous Synthesis of Metal Oxide Nanoparticles

Niederberger

Garnweitner

2006

Chemistry A European J

462

457

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Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods.

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“… The rate of production of the coupled product was proportional to aldehyde concentration [29,33,36].…”

Section: Reaction Pathmentioning

confidence: 99%

Carbon-Carbon Bond Forming Reactions Over Metal Oxide Catalysts

Kozlowski¹

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Alcohol coupling, also known as the Guerbet reaction, is a potentially important process to increase the value of short chain alcohols. Metal oxides, metal phosphates and supported transition metals like copper are some examples of heterogeneous catalysts for the reaction.However, the wide variety of catalyst compositions, reaction conditions, and reactor configurations used to study the reaction complicates a direct comparison of various catalysts.Herein, rates over different catalysts will be compared. One existing gap in the current literature is a thorough comparison of the surface acid and base properties of catalysts employed in the Guerbet coupling of alcohols. In this work, various bifunctional materials were synthesized, characterized, and used in Guerbet alcohol coupling and other probe reactions of acid and base catalysts.One well-studied reaction catalyzed by acids and bases is transesterification. Two series of Mg:Zr mixed oxides, prepared by either co-precipitation or sol-gel synthesis, were characterized and evaluated in the base-catalyzed transesterification of tributyrin with methanol.A co-precipitated Mg-rich mixed oxide catalyst with Mg:Zr 11:1 was approximately 300% more active than MgO on a surface area basis, whereas pure ZrO 2 was inactive for the reaction. To explore the nature of the activity enhancement, samples were characterized by X-ray diffraction, N 2 adsorption, CO 2 adsorption microcalorimetry and DRIFTS of adsorbed CO 2 and CH 3 OH.Although the sol-gel synthesis method provided better atomic-level mixing of Mg and Zr, the resulting catalysts were not as effective as mixed oxides prepared by co-precipitation. The most active mixed oxide (Mg:Zr 11:1) exhibited a high initial heat of CO 2 adsorption and modified modes of methanol adsorption compared to MgO. However, the CO 2 adsorption capacity did not correlate to catalyst activity.

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On the mechanism of the Guerbet reaction

Cited by 137 publications

References 14 publications

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

Organic Reaction Pathways in the Nonaqueous Synthesis of Metal Oxide Nanoparticles

Carbon-Carbon Bond Forming Reactions Over Metal Oxide Catalysts

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