Oxidizing agent

In chemistry, an oxidising agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxide and the halogens.

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

In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In the second sense, an oxidizing agent 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
Tetracyanoquinodimethane is an organic electron-acceptor.

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 oxidizing agent is the ferrocenium ion Fe(C
5H
5)+
2, which accepts an electron to form Fe(C5H5)2. One of the strongest acceptors commercially available is "Magic blue", the radical cation derived from N(C6H4-4-Br)3.[1]

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

Atom-transfer reagents

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 MnO−
4 (permanganate), CrO2−
4 (chromate), OsO4 (osmium tetroxide), and especially ClO−
4 (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 MnO−
4 to MnO2−
4, manganate.

Common oxidizing agents

Dangerous materials definition

The dangerous goods 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 oxidizing agents by analytical chemists are not classified as oxidizing agents in a dangerous materials sense. An example is potassium dichromate, which does not pass the dangerous goods test of an oxidizing agent.

The U.S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations. These two are Class 5; Division 5.1(a)1 and Class 5; Division 5.1(a)2. Division 5.1 "means a material that may, generally by yielding oxygen, cause or enhance the combustion of other materials." Division 5.(a)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(a)2 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
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−, I−
3
ClO− hypochlorite Cl−, H2O
ClO−
3 chlorate		 Cl−, H2O
HNO3 nitric acid NO nitric oxide
NO2 nitrogen dioxide
SO2 sulfur dioxide S sulfur
(Claus process, ultramarine production, more commonly reducing agent)
Hexavalent chromium
CrO3 chromium trioxide
CrO2−
4 chromate
Cr
2O2−
7 dichromate		 Cr3+, H2O
MnO−
4 permanganate
MnO2−
4 manganate		 Mn2+ (acidic) or
MnO2 (basic)
RuO
4 ruthenium tetroxide
OsO
4 osmium tetroxide		 in organic lab scale synthesis
H2O2, other peroxides Various, including oxides and H2O
Tl(III) thallic compounds Tl(I) thallous compounds, in organic lab scale synthesis
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See also

References
  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 978-0-471-72091-1
  3. Australian Dangerous Goods Code, 6th Edition
  4. 49 CFR 172.127 General Requirements for Shipments and Packagings; Subpart D
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