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Related Concept Videos

Heterogeneous Catalysis01:22

Heterogeneous Catalysis

78
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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Catalysis02:50

Catalysis

32.0K
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.
32.0K
Halogenation of Alkenes02:46

Halogenation of Alkenes

21.0K
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
21.0K
Base-Promoted α-Halogenation of Aldehydes and Ketones00:51

Base-Promoted α-Halogenation of Aldehydes and Ketones

4.3K
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base.  The reaction begins with the abstraction of  α hydrogen by the base to produce a nucleophilic enolate ion. This intermediate undergoes a subsequent nucleophilic substitution with the halogen to produce a monohalogenated carbonyl compound. If the starting substrate has more than one α hydrogen, it is difficult to stop the reaction...
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Acid-Catalyzed α-Halogenation of Aldehydes and Ketones01:21

Acid-Catalyzed α-Halogenation of Aldehydes and Ketones

5.1K
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
5.1K
Reactions at the Benzylic Position: Halogenation01:11

Reactions at the Benzylic Position: Halogenation

3.9K
Benzylic halogenation takes place under conditions that favor radical reactions such as heat, light, or a free radical initiator like peroxide.
3.9K

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Related Experiment Video

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Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes
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Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

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Halogen Chemistry on Catalytic Surfaces.

Maximilian Moser1, Javier Pérez-Ramírez2

  • 1Institute for Chemical and Bioengineering, Department of Chemical and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1 CH-8093 Zurich, Switzerland.

Chimia
|May 1, 2016
PubMed
Summary

Catalytic oxidation of hydrogen chloride (HCl) and hydrogen bromide (HBr) is crucial for sustainable chemical production. TiO2 excels at HBr oxidation, unlike in HCl oxidation, revealing reaction complexities.

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Area of Science:

  • Catalysis
  • Materials Science
  • Chemical Engineering

Background:

  • Halogens are vital for manufacturing chemicals, plastics, and pharmaceuticals.
  • Catalytic oxidation of HCl and HBr offers a sustainable route for halogen recovery.
  • Existing catalysts like RuO2 and CeO2 are effective for HCl oxidation, but HBr oxidation requires further investigation.

Purpose of the Study:

  • To compare the catalytic oxidation of HCl and HBr.
  • To understand the molecular-level mechanisms of these reactions on different catalysts.
  • To identify next-generation catalysts for efficient halogen recycling.

Main Methods:

  • Comparative experimental studies of HCl and HBr oxidation.
  • Utilizing rutile-type catalysts (RuO2, IrO2, TiO2) and ceria-based catalysts.
  • Employing advanced experimental and theoretical methods for mechanistic insights.

Main Results:

  • Ruthenium dioxide (RuO2) and ceria-based catalysts show efficacy in HCl oxidation.
  • Titanium dioxide (TiO2) demonstrates outstanding performance in HBr oxidation, despite inactivity in HCl oxidation.
  • The study reveals significant differences in reaction mechanisms between HCl and HBr oxidation.

Conclusions:

  • HBr oxidation is more complex than initially assumed, requiring tailored catalytic approaches.
  • Understanding the distinct catalytic behaviors of TiO2, RuO2, IrO2, and ceria is key for catalyst design.
  • This research provides fundamental knowledge for developing advanced catalysts for halogen recovery and sustainable chemical manufacturing.