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Not to be confused with dioxane or digoxin.

1,4-Dioxin
IUPAC name	1,4-dioxin
Other names	p-dioxin, dioxin
Identifiers
CAS number	[290-67-5]
Properties
Molecular formula	C4H4O2
Molar mass	84.07 g/mol
Appearance	Colorless liquid
Boiling point	75°C (348°K)
Hazards
EU classification	Toxic (T)
Main hazards	highly flammable
Related compounds
Related compounds	dibenzodioxin
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Dioxin is a heterocyclic, organic, antiaromatic compound with the chemical formula C₄H₄O₂. There are two isomers, 1,2-dioxin (or o-dioxin) and 1,4-dioxin (or p-dioxin). Their chemical structures are shown at right. The ortho isomer 1,2-dioxin is very unstable due to its peroxide-like characteristics. The known properties of 1,4-dioxin are listed in the infobox to the right.

1,4-dioxin can be prepared by cycloaddition, namely by the Diels-Alder reaction. ^[1]

Dioxin is used as a blanket term for a family of chemical compounds that are formed through combustion, chlorine bleaching and manufacturing processes.^[2] The combination of heat and chlorine creates dioxin.^[2] Since chlorine is often a part of the earth's environment, natural ecological activity such as volcanic activity and forest fires can lead to the formation of dioxin.^[2] Nevertheless, dioxin, a highly carcinogenic and toxic compound, is mostly created by human activity.^[2]

Other meanings

Skeletal formulas and substituent numbering schemes of Dioxin isomers

The skeletal formula and substituent numbering scheme of dibenzo-1,4-dioxin, the parent compound of PCDDs

The word dioxin can also in a general way refer to compounds whose molecules have a dioxin core skeletal structure with substituent molecular groups attached to it. For example, dibenzo-1,4-dioxin is a compound whose structure consists of two benzo- groups fused onto a 1,4-dioxin ring as shown below (see also Dibenzodioxin).

Because of their extreme importance as environmental pollutants, current scientific literature uses the name dioxins commonly for simplification to denote the chlorinated derivatives of dibenzo-1,4-dioxin, more precisely the polychlorinated dibenzodioxins (PCDDs), among which TCDD, a tetrachlorinated derivative, is the best known. The polychlorinated dibenzodioxins, which can also be classified in the family of halogenated organic compounds, have been shown to bioaccumulate in humans and wildlife due to their lipophilic properties, and are known teratogens, mutagens, and carcinogens. References under the main article on polychlorinated dibenzodioxins.

Additionally, sometimes with dioxins a similar, but unrelated compound type the polychlorinated dibenzofurans of like importance are also implied.

Toxicity

Some dioxin derivatives are carcinogenic, and directly correllated with an increase in the likelihood of attaining cancer (see above). Scientists are working to establish their exact toxicity. The job is made difficult because dioxins are not a single compound, but a mixture. Toxicity depends on the particular molecular arrangement of the compound. The compound of highest known toxicity is 2,3,7,8-tetrachlorodibenzo-1,4-dioxin (pictured here as well).

Polychlorinated dibenzodioxins

For more details on this topic, see polychlorinated dibenzodioxins.

The word dioxins sometimes refers to polychlorinated dibenzodioxins (PCDDs), a class of chlorinated dioxin derivatives. PCDD exposures are suspected in famous cases including Vietnam War veteran illnesses, the Seveso disaster, and the poisoning of Viktor Yushchenko.

Health and Safety

Preventing dioxin release into the environment

In January, 1997, The U.S. Environmental Protection Agency's New England office and the Maine Department of Environmental Protection announced a precedent-setting program to control levels of dioxin in waste water discharges from Lincoln Pulp & Paper Company of Lincoln Maine.^[3] Per EPA, "The dioxin limits in the Lincoln permit are the most stringent ever required of a paper mill by EPA anywhere in the country. Lincoln, an integrated bleached kraft paper mill making recycled products from waste sawdust, has agreed to the terms of federal and state waste water discharge permits that will require the company to achieve the following:

• A non-detect (10 parts per quadrillion [ppq]) dioxin limit at the bleach plant, the most stringent limit ever issued in the country. (The company's current permit has no dioxin limit or requirements.) This is the first permit ever issued that requires the elimination of detectable levels of dioxin at the bleach plant;
• A reopener provision which allows the permit to be modified to include any more stringent national technology-based dioxin controls which may become effective during the life of the permit;
• No increases in dioxin, even if the plant expands production;
• Compliance within one year (the law allows up to 3 years);
• An 80% Total Suspended (TSS) removal limit to assure efficient treatment plant removal of dioxin;
• An extensive biological monitoring program in collaboration with the US Fish and Wildlife Service;
• A reopener provision which allows for the permit to be modified if future dioxin concentrations in fish warrant further action."^[3]

Per EPA: "It sets a high standard for other mills and substantially advances our efforts to achieve Governor King's goal of lifting dioxin related fish consumption advisories and ultimately eliminating the discharge of dioxin."^[3]

References