Asymmetric Hydrogenation
Asymmetric Hydrogenation - Related Videos
02:17
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
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2023
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry. The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
08:19
Asymmetric Walkway: A Novel Behavioral Assay for Studying Asymmetric Locomotion
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Cited by 4 •
2016
Here, we present a protocol to quantify precise stepping in rodents. Cortical and the spinal central pattern generator signals are required for precise foot-placement during obstructed locomotion. We report here the novel constrained walking task that directly examines precise stepping behavior.
06:06
Hydrogenation
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2023
Source: Vy M. Dong and Zhiwei Chen, Department of Chemistry, University of California, Irvine, CA This experiment will demonstrate the hydrogenation of chalcone as an example of an alkene hydrogenation reaction (Figure 1). In this experiment, palladium on carbon (Pd/C) will be used as a heterogeneous catalyst for the process. A balloon will be used to supply the hydrogen atmosphere. Figure 1: Diagram showing the hydrogenation of chalcone to 3-phenylpropiophenone.
01:11
Rotation of Asymmetric Top
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2023
By definition, a spherically symmetric body has the same moment of inertia about any axis passing through its center of mass. This situation changes if there is no spherical symmetry. Since most rigid bodies are not spherically symmetric, these require special treatment. The relationship between the angular momentum of any rigid body and its angular velocity, both of which are vectors, involves the moment of inertia. The moment of inertia is a scalar quantity only for spherically symmetric...
08:56
Catalytic Reactor: Hydrogenation of Ethylene
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2023
Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA The hydrogenation of ethylene (C2H4) to ethane (C2H6) has often been studied as a model reduction reaction in characterizing new metal catalysts.1-2 While supported nickel is not the most active metal catalyst for this reaction, it is active enough that reaction can take place at < 200°C. The reaction typically involves adsorbed, dissociated hydrogen (H2) reacting...
FAQs
The chiral ligand creates an uneven catalytic environment around the metal center, making one pathway for hydrogen delivery more favorable than its mirror-image alternative. This preference determines which enantiomer forms predominantly. Ligand-controlled selectivity is therefore central to obtaining products with high enantiomeric purity rather than an approximately equal mixture of enantiomers.
The metal catalyst coordinates with both molecular hydrogen and the prochiral unsaturated substrate. Within the chiral catalytic environment, the substrate is oriented so that hydrogen delivery to one face of its carbon–carbon or carbon–heteroatom double bond is favored. That facial preference establishes the product’s dominant stereochemical outcome.
Controlled reaction conditions help preserve the balance between catalytic efficiency and stereoselectivity. If the process does not maintain conditions that support the desired catalytic pathway, formation of the preferred enantiomer may become less effective. Careful control is consequently important when the target is both efficient conversion and high enantiomeric purity.
The method applies to prochiral unsaturated compounds containing carbon–carbon or carbon–heteroatom double bonds. Because these substrates present two possible faces for hydrogen addition, a chiral catalyst can favor one stereochemical pathway. This broad substrate scope connects the reaction to the preparation of diverse chiral molecules in synthetic chemistry.
A prochiral unsaturated compound is combined with a metal catalyst coordinated to a chiral ligand, and molecular hydrogen is supplied under controlled reaction conditions. The catalyst activates hydrogen and the substrate, then promotes selective delivery across the unsaturated bond. The resulting product is enriched in one enantiomer.
Pharmaceuticals and agrochemicals often require chiral molecules with a defined three-dimensional arrangement. This reaction provides a route to favor one enantiomer while constructing the molecular framework, which can simplify access to biologically active compounds. Its use also extends to fine chemicals, where stereochemical control is an important synthetic objective.
Asymmetric hydrogenation can support more sustainable routes by combining catalytic reactivity with direct use of molecular hydrogen and selective formation of a desired enantiomer. High stereoselectivity may reduce the need to manage unwanted stereochemical products. These features make the process relevant to developing efficient routes for biologically active and other fine chemicals.