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Related Concept Videos

Reduction of Alkenes: Catalytic Hydrogenation02:13

Reduction of Alkenes: Catalytic Hydrogenation

Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the surface of...
Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation01:28

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
Oxidation of Alkenes: Syn Dihydroxylation with Potassium Permanganate02:21

Oxidation of Alkenes: Syn Dihydroxylation with Potassium Permanganate

Alkenes can be dihydroxylated using potassium permanganate. The method encompasses the reaction of an alkene with a cold, dilute solution of potassium permanganate under basic conditions to form a cis-diol along with a brown precipitate of manganese dioxide.
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide02:44

Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide

Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
Catalysis02:50

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
Catalysis01:27

Catalysis

Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...

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Related Experiment Video

Updated: May 20, 2026

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
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Published on: October 5, 2019

Catalytic hydrogen evolution from a covalently linked dicobaloxime.

Carolyn N Valdez1, Jillian L Dempsey, Bruce S Brunschwig

  • 1Beckman Institute, California Institute of Technology, Pasadena, CA 91125.

Proceedings of the National Academy of Sciences of the United States of America
|July 13, 2012
PubMed
Summary

A novel dicobaloxime catalyst facilitates proton reduction for hydrogen evolution, with rates comparable to monomeric analogues. The study suggests a mechanism involving protonation of a cobalt hydride intermediate.

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A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions
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A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions
06:32

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

Published on: August 17, 2016

Area of Science:

  • Inorganic Chemistry
  • Electrochemistry
  • Catalysis

Background:

  • Dicobaloxime complexes are investigated for catalytic applications.
  • Proton reduction is a key step in hydrogen evolution reactions.

Purpose of the Study:

  • To synthesize and characterize a dicobaloxime catalyst linked by octamethylene bis(glyoxime).
  • To evaluate the electrocatalytic activity of the dicobaloxime for proton reduction.
  • To elucidate the mechanism of hydrogen evolution.

Main Methods:

  • Electrochemical synthesis and characterization of the dicobaloxime complex.
  • Cyclic voltammetry to determine electrocatalytic activity.
  • Kinetic analysis to determine the rate law and rate constants.

Main Results:

  • The dicobaloxime catalyzed proton reduction from p-toluenesulfonic acid at -0.4 V vs. SCE.
  • Observed rate constant for hydrogen evolution was k(app) = 1100 ± 70 M(-1) s(-1).
  • No significant rate enhancement was observed compared to a monomeric analogue.

Conclusions:

  • The catalytic activity is first order in both catalyst and acid concentration.
  • Hydrogen evolution likely proceeds via protonation of a reductively generated cobalt hydride species (Co(II)H).
  • The dimeric structure does not offer a kinetic advantage over monomeric cobaloximes for this reaction.