# 1,4-Dioxane

1,4-Dioxane (/daɪˈɒkseɪn/) is a heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers (1,2- and 1,3-) are rarely encountered.
1,4-Dioxane is miscible in water, essentially nonvolatile when dissolved in water, not well adsorbed by activated carbon, not readily oxidized by common oxidants.
Dioxane is used as a solvent for a variety of practical applications as well as in the laboratory, and also as a stabilizer for the transport of chlorinated hydrocarbons in aluminium containers.

## History and synthesis

The compound was discovered by Portuguese professor Agostinho Vicente Lourenço in 1860 by a reaction of diethylene glycol with 1,2-dibromoethane. He initially designated it ether of glycol and correctly identified its empirical formula, but measured its boiling point at about 95°C. Three year later C. A. Wurtz obtained it by another method, called it dioxyethylene and studied some of its chemical properties.
Dioxane is industrially produced since the 1920s by the acid-catalysed dehydration of diethylene glycol, which in turn is obtained from the hydrolysis of ethylene oxide. This method was developed by Alexey Favorsky in 1906, who also determined the structure of the compound.
In 1985, the global production capacity for dioxane was between 11,000 and 14,000 tons. In 1990, the total U.S. production volume of dioxane was between 5,250 and 9,150 tons.

## Structure

Three isomers of dioxane exist, but only the 1,3- and 1,4- isomers are significant. The 1,4-dioxane molecule is conformationally flexible: the centrosymmetric chair and the boat conformations easily interconvert such that the H NMR spectrum shows only one signal. For this reason, it is sometimes used as an internal standard for nuclear magnetic resonance spectroscopy in deuterium oxide. With only two ethyleneoxyl units, dioxane is one of the smallest crown ethers.

## Uses
### Trichloroethane transport

In the 1980s, most of the dioxane produced was used as a stabilizer for 1,1,1-trichloroethane for storage and transport in aluminium containers. Normally aluminium is protected by a passivating oxide layer, but when these layers are disturbed, the metallic aluminium reacts with trichloroethane to give aluminium trichloride, which in turn catalyses the dehydrohalogenation of the remaining trichloroethane to vinylidene chloride and hydrogen chloride. Dioxane "poisons" this catalysis reaction by forming an adduct with aluminium trichloride.

### As a solvent

Dioxane is used in a variety of applications as a versatile aprotic solvent (usually considered non-polar, although some sources state otherwise), e.g. for inks, adhesives, and cellulose esters. It is substituted for tetrahydrofuran (THF) in some processes, because of its lower toxicity and higher boiling point (101 °C, versus 66 °C for THF).
While diethyl ether is rather insoluble in water, dioxane is miscible and in fact is hygroscopic. At standard pressure, the mixture of water and dioxane in the ratio 17.9:82.1 by mass is a positive azeotrope that boils at 87.6 °C.
The oxygen atoms are weakly Lewis-basic. It forms adducts with a variety of Lewis acids. It is classified as a hard base and its base parameters in the ECW model are E$_B$ = 1.86 and C$_B$ = 1.29.
Dioxane produces insoluble coordination polymers by linking metal centers. In this way, it is used to drive the Schlenk equilibrium, allowing the synthesis of dialkyl magnesium compounds. Dimethylmagnesium is prepared in this manner:
    2 CH$_3$MgBr + (C$_2$H$_4$O)$_2$ → MgBr$_2$(C$_2$H$_4$O)$_2$ + (CH$_3$)$_2$Mg

## Toxicology
### Safety

Dioxane has an LD$_{50}$ of 5170 mg/kg in rats. It is irritating to the eyes and respiratory tract. Exposure may cause damage to the central nervous system, liver and kidneys. In a 1978 mortality study conducted on workers exposed to 1,4-dioxane, the observed number of deaths from cancer was not significantly different from the expected number. Dioxane is classified by the National Toxicology Program as "reasonably anticipated to be a human carcinogen". It is also classified by the IARC as a Group 2B carcinogen: possibly carcinogenic to humans because it is a known carcinogen in other animals. The United States Environmental Protection Agency classifies dioxane as a probable human carcinogen (having observed an increased incidence of cancer in controlled animal studies, but not in epidemiological studies of workers using the compound), and a known irritant (with a no-observed-adverse-effects level of 400 milligrams per cubic meter) at concentrations significantly higher than those found in commercial products. Studies with rats suggest that the greatest health risk may be associated with inhalation. The State of New York has adopted a first-in-the-nation drinking water standard for 1,4-Dioxane and set the maximum contaminant level of 1 part per billion.

### Explosion hazard

Like some other ethers, dioxane combines with atmospheric oxygen upon prolonged exposure to air to form potentially explosive peroxides. Distillation of these mixtures is dangerous. Storage over metallic sodium could limit the risk of peroxide accumulation.

### Environment

It biodegrades through a number of pathways.
Dioxane has affected groundwater supplies in several areas. Dioxane at the level of 1 μg/L (~1 ppb) has been detected in many locations in the US. In the U.S. state of New Hampshire, it had been found at 67 sites in 2010, ranging in concentration from 2 ppb to over 11,000 ppb. Thirty of these sites are solid waste landfills, most of which have been closed for years. In 2019, the Southern Environmental Law Center successfully sued Greensboro, North Carolina's Wastewater treatment after 1,4-Dioxane was found at 20 times above EPA safe levels in the Haw River.

### Cosmetics

As a byproduct of the ethoxylation process, a route to some ingredients found in cleansing and moisturizing products, traces of dioxane can be found in cosmetics and personal care products such as deodorants, perfumes, shampoos, toothpastes,, and mouthwashes. The ethoxylation process makes the cleansing agents, such as sodium laureth sulfate and ammonium laureth sulfate, less abrasive and offers enhanced foaming characteristics. 1,4-Dioxane is found in small amounts in some cosmetics, a yet unregulated substance used in cosmetics in both China and the U.S. Research has found the chemical in ethoxylated raw ingredients and in off-the-shelf cosmetic products. The Environmental Working Group (EWG) found that 97% of hair relaxers, 57% of baby soaps and 22 percent of all products in Skin Deep, their database for cosmetic products, are contaminated with 1,4-dioxane.
Since 1979 the U.S. Food and Drug Administration (FDA) have conducted tests on cosmetic raw materials and finished products for the levels of 1,4-dioxane. 1,4-Dioxane was present in ethoxylated raw ingredients at levels up to 1410 ppm (~0.14%wt), and at levels up to 279 ppm (~0.03%wt) in off the shelf cosmetic products. Levels of 1,4-dioxane exceeding 85 ppm (~0.01%wt) in children's shampoos indicate that close monitoring of raw materials and finished products is warranted. While the FDA encourages manufacturers to remove 1,4-dioxane, it is not required by federal law.
On 9 December 2019, New York passed a bill to ban the sale of cosmetics with more than 10 ppm of 1,4-dioxane as of the end of 2022. The law will also prevent the sale of household cleaning and personal care products containing more than 2 ppm of 1,4-dioxane at the end of 2022.