Diethylene glycol (DEG) is an organic compound with the formula (HOCH2CH2)2O. It is a colorless, practically odorless, and hygroscopic liquid with a sweetish taste. It is a four carbon dimer of ethylene glycol. It is miscible in water, alcohol, ether, acetone, and ethylene glycol. DEG is a widely used solvent. It can be a contaminant in consumer products; this has resulted in numerous epidemics of poisoning since the early 20th century.
Preparation
DEG is produced by the partial hydrolysis of ethylene oxide. Depending on the conditions, varying amounts of DEG and related glycols are produced. The resulting product is two ethylene glycol molecules joined by an ether bond.
"Diethylene glycol is derived as a co-product with ethylene glycol (MEG) and triethylene glycol. The industry generally operates to maximize MEG production. Ethylene glycol is by far the largest volume of the glycol products in a variety of applications. Availability of DEG will depend on demand for derivatives of the primary product, ethylene glycol, rather than on DEG market requirements."
Structure of DEG and related polyols
Diethylene glycol is one of several glycols derived from ethylene oxide. Glycols related to and coproduced with diethylene glycol and have the formula HOCH2CH2(OCH2CH2)nOH are: n = 0 ethylene glycol ("antifreeze"); monoethylene glycol MEG n = 1 DEG n = 2 triethylene glycol, TEG, or triglycol n = 3 tetraethylene glycol n = 4 pentaethylene glycol n > 4 polyethylene glycol These compounds are all hydrophilic, more so than most diols, by virtue of the ether functionality.
Uses
Diethylene glycol is used in the manufacture of saturated and unsaturated polyester resins, polyurethanes, and plasticizers. DEG is used as a building block in organic synthesis, e.g. of morpholine and 1,4-dioxane. It is a solvent for nitrocellulose, resins, dyes, oils, and other organic compounds. It is a humectant for tobacco, cork, printing ink, and glue. It is also a component in brake fluid, lubricants, wallpaper strippers, artificial fog and haze solutions, and heating/cooking fuel. In personal care products (e.g. skin cream and lotions, deodorants), DEG is often replaced by selected diethylene glycol ethers. A dilute solution of diethylene glycol can also be used as a cryoprotectant; however, ethylene glycol is much more commonly used. Most ethylene glycol antifreeze contains a few percent diethylene glycol, present as a byproduct of ethylene glycol production.
Toxicology
Despite the discovery of DEG's toxicity in 1937 and its involvement in mass poisonings around the world, the information available regarding human toxicity is limited. Some authors suggest the minimum toxic dose is estimated at 0.14 mg/kg of body weight and the lethal dose is between 1.0 and 1.63 g/kg of body weight, while some suggest the LD50 in adults is of ~1 mL/kg, and others suggest this is the LD30. Because of its adverse effects on humans, diethylene glycol is not allowed for use in food and drugs (in many countries). The U.S. Code of Federal Regulations allows no more than 0.2% of diethylene glycol in polyethylene glycol when the latter is used as a food additive. The Government of Australia does not allow DEG as a food additive due to its toxicity; it is only allowed at less than 0.25% w/w of DEG as an impurity of polyethylene glycol (PEG) even in toothpaste.
Diethylene glycol has "moderate to low" acute toxicity in animal experiments. The LD50 for small mammals has been tested at between 2 and 25 g/kg, less toxic than its relative ethylene glycol, but still capable of causing toxicity in humans (in high concentration only). It appears diethylene glycol may be more hazardous to humans than implied by oral toxicity data in laboratory animals.
Toxicokinetics
Although there is limited information about toxicokinetics in humans, observations in mass poisonings and experimental studies suggest the following information:
Absorption and distribution
The principal method of absorption is through oral ingestion. Dermal absorption is very low, unless it is administered on broken or damaged skin. After ingestion, DEG is absorbed through the gastrointestinal tract and distributed by the bloodstream throughout the body, reaching peak blood concentrations within 30 to 120 minutes. Once DEG reaches the liver, it is metabolized by enzymes.
