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The international pictogram for oxidizing chemicals.

An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent (called the reductant, reducer, or electron donor). In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

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

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.^[2]

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 oxidizing agent transfers oxygen atoms to a substrate. In this context, the oxidizing agent can be called an oxygenation reagent or oxygen-atom transfer (OAT) agent.^[3] 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,ie permanganate to manganate.

Common oxidizing agents

Oxygen (O₂)
Ozone (O₃)
Hydrogen peroxide (H₂O₂) and other inorganic peroxides, Fenton's reagent
Fluorine (F₂), chlorine (Cl₂), and other halogens
Nitric acid (HNO₃) and nitrate compounds such as potassium nitrate (KNO₃), the oxidizer in black powder
Potassium chlorate (KClO₃)
Peroxydisulfuric acid (H₂S₂O₈)
Peroxymonosulfuric acid (H₂SO₅)
Hypochlorite, chlorite, chlorate, perchlorate, and other analogous halogen oxyanions
Fluorides of chlorine, bromine, and iodine
Hexavalent chromium compounds such as chromic and dichromic acids and chromium trioxide, pyridinium chlorochromate (PCC), and chromate/dichromate compounds such as Sodium dichromate (Na₂Cr₂O₇)
Permanganate compounds such as potassium permanganate (KMnO₄)
Sodium perborate ([Na⁺
]
₂·[B
₂O
₄(OH)
₄]²⁻
)
Nitrous oxide (N₂O), Nitrogen dioxide/Dinitrogen tetroxide (NO₂ / N₂O₄)
Sodium bismuthate (NaBiO₃)
Cerium (IV) compounds such as ceric ammonium nitrate and ceric sulfate
Lead dioxide (PbO₂)

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.^[4] 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."^[5]

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)
SbF₅ antimony pentafluoride	SbF₆^- hexafluoroantimonate or SbF₃ antimony trifluoride
PtF₆ platinum hexafluoride	PtF₆^- hexafluoroplatinate
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

References

^ "Metals". Bitesize. BBC. Archived from the original on November 3, 2022.
^ 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.
^ 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
^ Australian Dangerous Goods Code, 6th Edition
^ 49 CFR 172.127 General Requirements for Shipments and Packagings; Subpart D