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Oxidation of Alcohols02:37

Oxidation of Alcohols

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In this lesson, the oxidation of alcohols is discussed in depth. The various reagents used for oxidation of primary and secondary alcohols are detailed, and their mechanism of action is provided.
The process of oxidation in a chemical reaction is observed in any of the three forms:
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Redox Titration: Other Oxidizing and Reducing Agents01:26

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Besides iodine, other oxidizing or reducing agents can serve as titrants in redox titrations. Common oxidizing titrants include KMnO4, cerium(IV), and K2Cr2O7. The choice of oxidizing titrants depends on factors like stability, cost, analyte strength, and reaction rate between the analyte and titrant. KMnO4 is a strong oxidizing titrant that reduces from Mn(VII) to Mn(II) in a highly acidic solution, simultaneously oxidizing the analyte to a higher oxidation state. In this case, KMnO4 acts as a...
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In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
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Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3–12 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d orbital is partially occupied before the f orbitals.
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Oxidation-reduction or redox reactions involve the transfer of electrons from one molecule or atom to another. When an atom gains an electron, another atom must lose an electron, meaning oxidation and reduction must occur together. Since the redox occurs in pairs, the atom that gets oxidized is also called the reducing agent or reductant, and the atom that is reduced is also called the oxidizing agent or oxidant. A straightforward way to remember the definitions of oxidation and reduction is...
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Redox reactions are vital biochemical processes that underpin energy metabolism in cells. These reactions involve the transfer of electrons between molecules, occurring in tandem as oxidation and reduction. Oxidation refers to the loss of electrons, while reduction denotes their gain. This coupling ensures the seamless flow of electrons through metabolic pathways. For example, in bacterial metabolism, glucose undergoes oxidation to carbon dioxide, while oxygen is simultaneously reduced to...
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Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems
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Different Pathways for Cr(III) Oxidation: Implications for Cr(VI) Reoccurrence in Reduced Chromite Ore Processing

Weizhen Liu1,2, Jing Li1,2, Jiayi Zheng1,2

  • 1School of Environment and Energy, Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling, South China University of Technology, Guangzhou, Guangdong 510006, P. R. China.

Environmental Science & Technology
|September 9, 2020
PubMed
Summary

Hexavalent chromium (Cr(VI)) contamination often recurs in alkaline environments. This study reveals Cr(III) solids oxidize via oxygen, manganese dioxide, and catalytic Mn(II) pathways, with the latter dominating long-term Cr(VI) formation.

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Area of Science:

  • Environmental Chemistry
  • Geochemistry
  • Inorganic Chemistry

Background:

  • Hexavalent chromium (Cr(VI)) contamination is a persistent global environmental challenge, frequently observed in alkaline reduced chromite ore processing residues (rCOPR).
  • The oxidation of Cr(III) solids within rCOPR is a suspected but understudied cause of Cr(VI) reoccurrence.
  • Understanding Cr(III) oxidation mechanisms in alkaline environments is crucial for mitigating Cr(VI) pollution.

Purpose of the Study:

  • To investigate the oxidation pathways of chromium(III) hydroxide (Cr(OH)3), a representative Cr(III) species in rCOPR.
  • To elucidate the role of oxygen and manganese oxides (δ-MnO2) in Cr(III) oxidation under alkaline conditions (pH 9-11).
  • To develop a kinetic model for quantifying the contributions of different oxidation pathways over time.

Main Methods:

  • Experimental investigation of Cr(OH)3 oxidation by δ-MnO2 under varying pH and oxic/anoxic conditions.
  • X-ray Absorption Near Edge Structure (XANES) spectroscopy to identify manganese reduction products and catalytic species.
  • Development and application of a kinetic model to simulate and quantify oxidation pathway contributions.

Main Results:

  • Three Cr(III) oxidation pathways were identified under oxic conditions: direct oxidation by O2, oxidation by δ-MnO2, and catalytic oxidation by Mn(II).
  • Oxidation by δ-MnO2 and catalytic oxidation by Mn(II) were found to be efficient, with the latter increasing significantly with pH.
  • Kinetic modeling indicated that δ-MnO2 (Pathway 2) was the primary source of Cr(VI) in the short term (<10 days), while catalytic Mn(II) oxidation (Pathway 3) dominated in the long term (>365 days).

Conclusions:

  • Cr(III) solids can be effectively oxidized to Cr(VI) in alkaline, oxic environments, even with minimal manganese oxide presence.
  • The catalytic oxidation by Mn(II) becomes increasingly significant over time and with rising pH, highlighting long-term environmental risks.
  • These findings offer new insights into Cr(VI) reoccurrence mechanisms in rCOPR and underscore the environmental hazards of Cr(III) solids in alkaline settings.