Related Experiment Video
Updated: May 16, 2026
06:52
Synthesis of Esters Via a Greener Steglich Esterification in Acetonitrile
Published on: October 30, 2018
Ni-catalyzed cleavage of aryl ethers in the aqueous phase
Jiayue He1, Chen Zhao, Johannes A Lercher
1Department of Chemistry and Catalysis Research Center, Technische Universität München, 85747 Garching, Germany.
Journal of the American Chemical Society
|November 30, 2012
Summary
This study introduces a new nickel catalyst for breaking down lignin-derived aromatic ethers. The process selectively cleaves ether bonds and hydrogenates intermediates in water at 120°C.
Area of Science:
- Catalysis
- Green Chemistry
- Biomass Conversion
Background:
- Lignin valorization is crucial for sustainable chemical production.
- Selective cleavage of ether bonds in lignin derivatives is challenging.
- Aqueous-phase processing offers environmental benefits.
Purpose of the Study:
- To develop a novel Ni/SiO(2)-catalyzed method for selective ether bond cleavage in lignin-derived aromatic ethers.
- To investigate the hydrogenation of oxygen-containing intermediates.
- To understand the reaction mechanisms and kinetics.
Main Methods:
- Utilized a Ni/SiO(2) catalyst for hydrogenolysis and hydrogenation reactions.
- Conducted reactions in the aqueous phase at 120 °C and 6 bar H(2).
- Analyzed reaction pathways for α-O-4, β-O-4, and 4-O-5 linkages.
Main Results:
- Selective cleavage of α-O-4 and β-O-4 ether bonds via hydrogenolysis.
- Parallel hydrogenolysis and hydrolysis observed for the 4-O-5 linkage.
- Apparent activation energies correlate with bond dissociation energies.
- C-O bond cleavage is rate-determining for β-O-4 and 4-O-5 linkages.
- Hydrogen pressure influences reaction rates and product desorption.
Conclusions:
- The Ni/SiO(2) catalyst enables efficient and selective deconstruction of lignin-derived aromatic ethers.
- Reaction mechanisms differ based on the type of ether linkage.
- Understanding kinetics and the role of hydrogen pressure is key for process optimization.
More Related Videos
Related Concept Videos
02:18Ethers to Alkyl Halides: Acidic Cleavage
Ethers are generally unreactive and unsuitable for direct nucleophilic substitution reactions since the alkoxy groups are strong bases and, therefore, poor leaving groups. However, ethers readily undergo acidic-cleavage reactions. Ethers can be converted to alkyl halides when heated with strong acids such as HBr and HI in a sequence of two substitution reactions.
02:01Alkynes to Carboxylic Acids: Oxidative Cleavage
Alkynes undergo oxidative cleavage in the presence of oxidizing reagents like potassium permanganate and ozone. The triple bond — one σ bond and two π bonds — is completely cleaved, and the alkyne is oxidized to carboxylic acids. When warm and basic aqueous potassium permanganate is used as an oxidizing agent, alkynes are first converted to carboxylate salts via an unstable α-diketone intermediate. Further, a mild acid treatment protonates the carboxylate anions generating free carboxylic acid...
01:12Acid Halides to Esters: Alcoholysis
Alcoholysis is a nucleophilic acyl substitution reaction in which an alcohol functions as a nucleophile. Acid halides react with alcohol to produce esters. The mechanism proceeds in three steps:
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
00:57C–C Bond Cleavage: Retro-Aldol Reaction
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
02:45E2 Reaction: Kinetics and Mechanism
SN2 substitutions and E2 eliminations of alkyl halides proceed via a concerted pathway. While the nucleophile attacks the alpha carbon in SN2 reactions, it functions as a strong base and abstracts a beta hydrogen in the E2 mechanism. The rate-limiting transition state in E2 elimination reactions is characterized by partially broken carbon–hydrogen and carbon–halogen bonds and a partially formed pi bond between the alpha and beta carbons. The beta hydrogen and halide are eliminated...