Oxidizing agent

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The international pictogram for oxidising chemicals.
Dangerous goods label for oxidising agents

In chemistry, oxidizing agent has two meanings. In one sense, an oxidizing agent is a chemical species that removes an electron from another species. It is one component in an oxidation-reduction (redox) reaction. In the second sense, an oxidizing agent or an oxidizer is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion, many explosives, and organic redox reactions involve atom-transfer reactions.

Electron acceptors[edit]

Electron acceptors participate in electron-transfer reactions. In this context, the oxidizing agent is called an electron acceptor and the reducing agent is called an electron donor. A classic oxidising agent is the ferrocenium ion [Fe(C5H5)2]+, which accepts an electron to form Fe(C5H5)2.[1]

Tetracyanoquinodimethane is an organic electron-acceptor.

Extensive tabulations of ranking the electron accepting properties of various reagents (redox potentials) are available, see Standard electrode potential (data page).

Mechanism[edit]

Of great interest to chemists are the details of the electron transfer event, which can be described as inner sphere or outer sphere.

Atom-transfer reagents[edit]

In more common usage, an oxidising agent transfers oxygen atoms to a substrate. In this context, the oxidising agent can be called an oxygenation reagent or oxygen-atom transfer (OAT) agent.[2] Examples include [MnO4] (permanganate), [CrO4]2− (chromate), OsO4 (osmium tetroxide), and especially [ClO4] (perchlorate). Notice that these species are all oxides.

In some cases, these oxides can also serve as electron acceptors, as illustrated by the conversion of [MnO4] to [MnO4]2−, manganate.

Common oxidizing agents (O-atom transfer agents)[edit]

Dangerous materials definition[edit]

The dangerous materials definition of an oxidizing agent is a substance that can cause or contribute to the combustion of other material.[3] By this definition some materials that are classified as oxidising agents by analytical chemists are not classified as oxidising agents in a dangerous materials sense. An example is potassium dichromate, which does not pass the dangerous goods test of an oxidising agent.

The U.S. Department of Transportation defines Oxidizing agent specifically. There are two definitions for oxidizing agents governed under DOT regulations. These two are Class 5; Division 5.1 and Class 5; Division 5.2. Division 5.1 "means a material that may, generally by yielding oxygen, cause or enhance the combustion of other materials." Division 5.1 of the DOT code applies to solid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria (IBR, see § 171.7 of this subchapter), its mean burning time is less than or equal to the burning time of a 3:7 potassium bromate/cellulose mixture." 5.1 of the DOT code applies to liquid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria, it spontaneously ignites or its mean time for a pressure rise from 690 kPa to 2070 kPa gauge is less than the time of a 1:1 nitric acid (65 percent)/cellulose mixture."[4]

Common oxidizing agents and their products[edit]

Agent Product(s)
O2 oxygen Various, including the oxides H2O and CO2
O3 ozone Various, including ketones, aldehydes, and H2O; see ozonolysis
F2 fluorine F
Cl2 chlorine Cl
Br2 bromine Br
I2 iodine I, I3
ClO hypochlorite Cl, H2O
ClO3 chlorate Cl, H2O
HNO3 nitric acid NO nitric oxide
NO2 nitrogen dioxide
Hexavalent chromium
CrO3 chromium trioxide
CrO42− chromate
Cr2O72− dichromate
Cr3+, H2O
MnO4 permanganate
MnO42− manganate
Mn2+ (acidic) or MnO2 (basic)
H2O2, other peroxides Various, including oxides and H2O

See also[edit]

References[edit]

  1. ^ N. G. Connelly, W. E. Geiger (1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774. 
  2. ^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7 
  3. ^ Australian Dangerous Goods Code, 6th Edition
  4. ^ 49 CFR 172.127 General Requirements for Shipments and Packagings; Subpart D