Oxidizing agent
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.
Contents
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 oxidising agent is the ferrocenium ion [Fe(C5H5)2]+, which accepts an electron to form Fe(C5H5)2.[1]
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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
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
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)
- Oxygen (O2)
- Ozone (O3)
- Hydrogen peroxide (H2O2) and other inorganic peroxides
- Fluorine (F2), chlorine (Cl2), and other halogens
- Nitric acid (HNO3) and nitrate compounds
- Sulfuric acid (H2SO4)
- Peroxydisulfuric acid (H2S2O8)
- Peroxymonosulfuric acid (H2SO5)
- Chlorite, chlorate, perchlorate, and other analogous halogen compounds
- Hypochlorite and other hypohalite compounds, including household bleach (NaClO)
- Hexavalent chromium compounds such as chromic and dichromic acids and chromium trioxide, pyridinium chlorochromate (PCC), and chromate/dichromate compounds
- Permanganate compounds such as potassium permanganate
- Sodium perborate
- Nitrous oxide (N2O)
- Potassium nitrate (KNO3), the oxidizer in black powder
Dangerous materials definition
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
| 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 |
