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1,4-Dioxane

physical science Maturity 11-13 Next article →

1,4-Dioxane is a colorless, heterocyclic organic compound. In chemistry, a heterocyclic compound is a ring-shaped molecule that contains atoms other than carbon. This specific substance belongs to a group of chemicals called ethers. It has a faint, sweet odor that is similar to diethyl ether. Most people simply call it dioxane. This is because other versions, known as isomers, are rarely seen in practice.

Dioxane isomers named
Dioxane isomers named

The molecule is quite flexible in its shape. It can move between two different forms called the chair conformation and the boat conformation. Because these shapes change easily, the substance is often used as an internal standard in nuclear magnetic resonance spectroscopy. This is a scientific method used to study the structure of molecules. Dioxane is also considered one of the smallest crown ethers. A crown ether is a type of molecule that can trap certain metal ions.

Industrially, dioxane is produced through a specific chemical process. Since the 1920s, factories have used the acid-catalyzed dehydration of diethylene glycol to make it. Diethylene glycol is itself obtained through the hydrolysis of ethylene oxide. This method was developed in 1906 by Alexey Favorsky. He was also the scientist who determined the exact structure of the dioxane molecule. During the 1980s, global production capacity reached between 11,000 and 14,000 tons. In 1990, the United States alone produced between 5,250 and 9,150 tons.

One major use for dioxane is as a stabilizer. In the 1980s, most production was used to stabilize 1,1,1-trichloroethane. This chemical is often transported in aluminum containers. Normally, aluminum is protected by a thin layer called a passivating oxide layer. If this layer is disturbed, the metal reacts with trichloroethane. This reaction creates aluminum trichloride, which causes the remaining chemical to break down. Dioxane prevents this by forming an adduct with the aluminum trichloride. An adduct is a product formed by the combination of two substances.

Dioxane is also a versatile aprotic solvent. This means it is a liquid that can dissolve many substances without donating protons. It is used in the manufacturing of inks, adhesives, and cellulose esters. Some industries use it instead of tetrahydrofuran, also known as THF. Dioxane is preferred in some cases because it has a higher boiling point. Its boiling point is 101 °C, while THF boils at only 66 °C.

Binary phase diagram dioxane-water
Binary phase diagram dioxane-water

While some ethers do not mix well with water, dioxane is miscible. This means it can dissolve in water in any proportion. It is also hygroscopic, which means it can absorb moisture from the air. When mixed with water in a specific mass ratio of 17.9 to 82.1, it forms a positive azeotrope. This is a mixture that boils at a constant temperature of 87.6 °C. The oxygen atoms in the molecule are weakly Lewis-basic. This allows it to form adducts with various Lewis acids.

Despite its uses, dioxane is a hazardous contaminant. It is highly flammable and can produce toxic vapors when heated. These vapors can irritate the eyes and the respiratory tract. High levels of exposure in the air can injure the nasal cavity, liver, or kidneys. There is also an explosion hazard. If dioxane is exposed to air for a long time, it can form explosive peroxides. This makes the process of distillation very dangerous if not handled correctly.

Traces of dioxane are often found in consumer products like shampoos, perfumes, and toothpastes. This happens because of a process called ethoxylation. This process is used to make cleansing agents, like sodium laureth sulfate, less abrasive and better at foaming. However, dioxane can appear as a byproduct of this reaction. In the past, levels in cosmetic products reached as high as 279 ppm. Because of health concerns, many manufacturers now use vacuum or steam stripping to remove it.

Dioxane isomers named
Dioxane isomers named

Environmental safety is a major concern for many governments. Dioxane is considered a potential carcinogen, which is a substance that may cause cancer. The IARC classifies it as a Group 2B carcinogen. In 2024, the U.S. Environmental Protection Agency labeled it a probable human carcinogen. It can contaminate groundwater through manufacturing runoff or waste disposal. In 2010, dioxane was found at 67 different sites in New Hampshire. Some sites showed concentrations as high as 11,000 ppb. To protect people, the State of New York set a strict drinking water limit of 1 part per billion.

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File:Binary phase diagram dioxane-water.svg
Binary phase diagram dioxane-water.svg
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