Diethylene glycol (DEG) is an organic compound described by the structural formula HO-CH2-CH2-O-CH2-CH2-OH. It is a clear, hygroscopic, odorless liquid. It is miscible with water and polar organic solvents such as alcohols and ethers.
Diols and polyols
Diethylene glycol is one of several diols (hydrocarbon containing two alcohol groups). They are derived from ethylene oxide and are described with the formula HO-CH2-CH2(-O-CH2-CH2)n-OH:
- n = 0 ethylene glycol ("antifreeze")
- n = 1 DEG
- n = 2 triethylene glycol, TEG, or triglycol is also a colorless odourless viscous liquid. It is used as a plasticizer for vinyl. It is also used in Air-Sanitizer products, like "Oust" or "Clean and Pure." When aerosolized, it acts as a disinfectant. Glycols are also used as liquid desiccants for natural gas and in air conditioning systems. It is an additive for hydraulic fluids and brake fluids.
- n = 3 tetraethylene glycol
- n = 4 pentaethylene glycol
- Higher numbers for n describe a non-toxic polymer called polyethylene glycol.
Like ethylene glycol, a solution of diethylene glycol and water is used as a coolant. It both lowers the freezing point of the solution and elevates its boiling point making it more suitable for hot climates. DEG is also 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 can be also found in some hydraulic fluids and brake fluids.
In personal care products (e.g. skin cream and lotions, deodorants) DEG is often replaced by the much less toxic diethylene glycol ethers.
Diethylene glycol is also illegally used as counterfeit glycerin in some nations and sold internationally as a component of cough syrup and toothpaste. 
Diethylene glycol is toxic to humans and animals, and death can occur by renal failure. The LD50 for small mammals has been tested at between 2 and 25 g/kg - much less toxic than its relative ethylene glycol, but still inappropriate for even minor consumption. Several poisonings have occurred when DEG is substituted for the non-toxic naturally-occurring "triol" glycerine (HOCH2CH(OH)CH2OH, also called glycerol) in foodstuffs and pharmaceuticals. Glycerine, which is higher melting (18 vs. -10.45 °C) and more viscous than DEG, costs about three times the price of DEG.
Because of its toxicity, diethylene glycol is not allowed for food and drugs. 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.
Mass poisonings attributed to DEG
It has been responsible for a number of mass poisonings:
- In recent years, deaths from medicines adulterated with diethylene glycol have been reported from South Africa, India, Nigeria, Argentina, Haiti, and Panama. In Haiti in 1996, 85 children died due to glycerine contaminated with diethylene glycol in a paracetamol syrup produced by Pharval Laboratories, a Haitian company, which did not use standard quality assurance procedures to verify the purity of the glycerine (which was supplied by a Dutch company, Vos, from a manufacturer in China, but the point of contamination with DEG was never determined).
- In 1985 a small number of producers of Austrian wine were found to be adulterating their product with diethylene glycol in order to give the wine a sweeter and more full-bodied taste. The amount added was not high enough to be immediately toxic (one would have to ingest about 28 bottles per day for two weeks); however, exports of Austrian wine collapsed. As a result of this incident, stricter regulations were imposed on Austrian wine makers, and the industry shifted its emphasis from the production of bulk, somewhat sweet wines to lower yields of higher quality, drier wines. Thus, the 'antifreeze scandal' is regarded as having been positive for the industry in the long-term.
- In 1990, in Bangladesh, 339 children developed kidney failure, and most of them died, after being given paracetamol (acetaminophen) syrup contaminated with diethylene glycol.
- Toxic syrup: In October 2006 the CDC and the Ministry of Health of Panama detected toxic levels of diethylene glycol in a sugarless liquid expectorant during an investigation of 46 deaths from a syndrome characterized by gastrointestinal symptoms, renal failure and paralysis. Almost all the victims were hypertension and diabetes patients in their 40s to 80s. Criminal investigations are ongoing. The source of the contamination was found to be the Taixing Glycerine Factory, a Chinese company in Hengxiang, China. Taixing Glycerine sold diethylene glycol labeled as TD glycerine, which is an industrial name, through the state-owned Chinese trading company CNSC Fortune Way, based in Beijing. And a Spanish middleman ordered these TD glycerine, but when filled the custom declaration the name was changed to glycerine. A government agency in Panama purchased the falsely labeled product containing diethylene glycol and incorporated it into 260,000 bottles of cold medicine. The United States Food and Drug Administration issued an Industry Guidance Document highlighting appropriate testing procedures for use of glycerin in response to product contamination and misrepresentation.
- In May 2007, a Panamanian named Eduardo Arias discovered that toothpaste sold in his country was labeled as containing DEG, the same ingredient that had tainted cough syrup and killed 138 Panamanians in 2006. Panamanian officials discovered that the toothpaste had come from China and initiated a global response.
- Also in May 2007 the same toothpaste was found in some Costa Rican stores. Fast action by the Ministry of Health, and notification through the media, prevented poisonings due to this product. This event was linked to the death sentence of a former pharmaceuticals control officer in China, as the Costa Rican newspaper La Nación reported on its issue of May 30th. On June 4, 2007, a press release by the Chinese Foreign Ministry  cited an earlier study in China  which concluded that up to 15.6% diethylene glycol in toothpaste is safe.
- In June 2007, phony Colgate toothpaste imported from China was found to be contaminated with DEG, and several people in eastern US reported experiencing headaches and pain after using the product.. The same occurred in Spain with a false Colgate toothpaste, which contained 6% of DEG. The tainted products could be identified by the claim to be manufactured in South Africa by Colgate-Palmolive South Africa LTD; they are 5oz/100ml tubes (a size which Colgate does not sell in the United States) and their packaging contains numerous misspellings on the labels. Colgate-Palmolive claims that it does not import their products from South Africa into the United States or Canada and that DEG is never and was never used in any of its products anywhere in the world. These counterfeit products were found in smaller "mom and pop" stores, dollar stores and discount stores in at least four states. 
- In July 2007, diethylene glycol was found in counterfeit Sensodyne toothpaste, on sale at a car boot sale in Derbyshire, England 
Because of the natural sweetness of the substance, domesticated animals have been victims of DEG poisoning after consuming spilled or leaking antifreeze from vehicles.
- Merck Index, 12th Edition, 3168.