Dioxin

Dioxin is commonly used to refer to :

In chemistry, a dioxin is a heterocyclic 6-membered ring, where two carbon atoms have been replaced by oxygen atoms:

See also

1,4-Dioxin

1,4-Dioxin (also referred as dioxin or p-dioxin) is a heterocyclic, organic, non-aromaticcompound with the chemical formula C₄H₄O₂. There is an isomeric form of 1,4-dioxin, 1,2-dioxin (or o-dioxin). 1,2-Dioxin is very unstable due to its peroxide-like characteristics.

The term “dioxin” is most commonly used for a family of derivatives of dioxin, known as polychlorinated dibenzodioxins (PCDDs).

Preparation

1,4-Dioxin can be prepared by cycloaddition, namely by the Diels–Alder reaction of furan and maleic anhydride. The adduct formed has a carbon-carbon double bond, which is converted to an epoxide. The epoxide then undergoes a retro-Diels–Alder reaction, forming 1,4-dioxin and regenerating maleic anhydride.

Derivatives

The word “dioxin” can refer in a general way to compounds which 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.

1,2-Dioxin

1,2-Dioxin is a heterocyclic, organic, antiaromatic compound with the chemical formula C₄H₄O₂. It is an isomeric form of 1,4-dioxin (or p-dioxin).

Due to its peroxide-like characteristics, 1,2-dioxin is very unstable and has not been isolated. Even substituted derivatives are very labile, e.g. 1,4-diphenyl-2,3-benzodioxin. Indeed, in 1990, 3,6-bis(p-tolyl)-1,2-dioxin was wrongly accounted as the first stable derivative. It was subsequently shown that the initial compound was not a derivative of 1,2-dioxin, but a thermodynamically more stable dione.

The isomers 1,2-dioxin (left) and 1,4-dioxin (right)

The isomers 1,2-dioxin (left) and 1,4-dioxin (right)

Structure of the transient 1,4-diphenyl- 2,3-benzodioxin

Structure of the transient 1,4-diphenyl- 2,3-benzodioxin

Dioxin (1) and dione form (2)

Dioxin (1) and dione form (2)

References