Ethylene glycol
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Ethylene glycol (monoethylene glycol (MEG), IUPAC name: ethane-1,2-diol) is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze. In its pure form, it is an odorless, colorless, syrupy liquid with a sweet taste. Ethylene glycol is toxic, and its accidental ingestion should be considered a medical emergency.
History
Ethylene glycol was first prepared in 1859 by the French chemist Charles-Adolphe Wurtz. It was produced on a small scale during World War I as a coolant and as an ingredient in explosives. Widespread industrial production began in 1937 when ethylene oxide, a component in its synthesis, became cheaply available.
When first introduced it created a minor revolution in aircraft design because when used in place of water as an engine coolant, its higher boiling point allowed for smaller radiators operating at higher temperatures. Prior to the widespread availability of ethylene glycol, many aircraft manufacturers tried to use evaporative cooling systems which used water at high pressure. Invariably, these proved to be rather unreliable and were easily damaged in combat because they took up large amounts of room on the plane, where they were easily hit by gunfire.
Production
Ethylene glycol is produced from ethylene, via the intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol according to the chemical equation
This reaction can be catalyzed by either acids or bases, or can occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH with a large excess of water. Under these conditions, ethylene glycol yields of 90% can be achieved. The major byproducts are the ethylene glycol oligomers diethylene glycol, triethylene glycol, and tetraethylene glycol.
This molecule has been observed in space by Hollis, et al.[1]
Uses
The major use of ethylene glycol is as a coolant or antifreeze in, for example, automobiles and personal computers. Due to its low freezing point, it is also used as a deicing fluid for windshields and aircraft. Ethylene glycol has become increasingly important in the plastics industry for the manufacture of polyester fibers and resins, including polyethylene terephthalate, which is used to make plastic bottles for soft drinks. The antifreeze capabilities of ethylene glycol have made it an important component of vitrification mixtures for low-temperature preservation of biological tissues and organs.
Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of 1,4-dioxane and as an additive to prevent the growth of algae in liquid cooling systems for personal computers.
Ethylene glycol's high boiling point and affinity for water makes it an ideal desiccant for natural gas production. In the field, excess water vapor is usually removed by glycol dehydration. Glycol flows down from the top of a tower and meets a rising mixture of water vapor and hydrocarbon gases from the bottom. The glycol chemically removes the water vapor, allowing dry gas to exit from the top of the tower. The glycol and water are separated, and the glycol cycles back through the tower.
Ethylene glycol is also used in the manufacture of some vaccines, but it is not itself present in these injections. It is used as a minor (1–2%) ingredient in shoe polish and also in some inks and dyes.
Ethylene glycol is commonly used in laboratories to precipitate out proteins in solution. This is often an intermediary step in fractionation, purification and/or crystallization. It can be used to protect functional groups from reacting during organic synthesis. To get the functional group back to its original composition, simply add water and acid.
Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after the fact. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats, and is relatively cheap.
Ethylene glycol is commonly used as a preservative for specimens in schools, frequently during dissection. It is said to be safer than formaldehyde, but the safety is questionable.
Ethylene glycol is also commonly used in chilled water Air Condtioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water.
Toxicity
The major danger from ethylene glycol is following ingestion. Due to its sweet taste, children and animals will sometimes consume large quantities of it if given access to antifreeze. Ethylene glycol may also be found as a contaminant in moonshine distilled using an improperly washed car radiator. In developed countries, a bittering agent called denatonium/denatonium benzoate, is generally added to ethylene glycol preparations as an adversant (to prevent accidental ingestion). If one has ingested ethylene glycol, give the person an alcoholic beverage while the paramedics arrive. Alcohol acts as a competitive inhibitor to the active site of the enzyme that converts ethylene glycol to its toxic form. Once alcohol binds, the ethylene glycol is harmlessly excreted out of the body.
Ethylene glycol poisoning is a medical emergency and in all cases a poison control center should be contacted or medical attention should be sought. It is highly toxic with an estimated LD100 in humans of approximately 1.4 ml/kg.[2] However, as little as 30 milliliters (2 tablespoons) can be lethal to adults.[3]
Symptoms
Symptoms of ethylene glycol poisoning usually follow a three-step progression, although poisoned individuals will not always develop each stage or follow a specific time frame.[2] Stage 1 consists of neurological symptoms including victims appearing to be intoxicated, exhibiting symptoms such as dizziness, headaches, slurred speech, and confusion. Over time, the body metabolizes ethylene glycol into other toxins, it is first metabolized to glycolaldehyde, which is then oxidized to glycolic acid, glyoxylic acid, and finally oxalic acid. Stage 2 is a result of accumulation of these metabolites and consists of tachycardia, hypertension, hyperventilation, and metabolic acidosis. Stage 3 of ethylene glycol poisoning is the result of kidney injury, leading to acute kidney failure.[4] Oxalic acid reacts with calcium and forms calcium oxalate crystals in the kidney.
Treatment
Initial treatment consists of stabilizing the patient and gastric decontamination. As ethylene glycol is rapidly absorbed, gastric decontamination needs to be performed soon after ingestion to be of benefit. Gastric lavage or nasogastric aspiration of gastric contents are the most common methods employed in ethylene glycol poisoning. Ipecac-induced vomiting or activated charcoal (charcoal does not adsorb glycols) are not recommended. [2]
The antidotes for ethylene glycol poisoning are ethanol or fomepizole; antidotal treatment forms the mainstay of management following ingestion. Ethanol (usually given IV as a 5 or 10% solution in 5% dextrose and water, but, also sometimes given in the form of a strong spirit such as whisky, vodka or gin) acts by competing with ethylene glycol for the enzyme alcohol dehydrogenase thus limiting the formation of toxic metabolites. Fomepizole acts by inhibiting alcohol dehydrogenase, thus blocking the formation of the toxic metabolites.[5]
In addition to antidotes, hemodialysis can also be used to enhance the removal of unmetabolized ethylene glycol, as well as its metabolites from the body. Hemodialysis also has the added benefit of correcting other metabolic derangements or supporting deteriorating kidney function caused by ethylene glycol ingestion. Often both antidotal treatment and hemodialysis are used together in the treatment of poisoning.
Industrial hazards
Ethylene glycol can begin to breakdown at 230° – 250°F. Note that breakdown can occur when the system bulk (average) temperature is below these limits because surface temperatures in heat exchangers and boilers can be locally well above these temperatures.
The electrolysis of ethylene glycol solutions with a silver anode results in an exothermic reaction. The Apollo 1 fire catastrophe was caused by this reaction. The ethylene glycol–water mixture was ignited and was able to burn in the atmosphere of pure low pressure oxygen.
Carbonyl chemistry
Ethylene glycol may also be used as a protecting group for carbonyls during synthesis. Acid catalysis, and a ketone or aldehyde with ethylene glycol will form a cyclic structure at the carbonyl. Other chemistry can then be done to the molecule before more acid will break open the protecting ring and restore the carbonyl.
See also
References
- ↑ J. M. Hollis, F. J. Lovas, P. R. Jewell, L. H. Coudert (2002 May 20). "Interstellar Antifreeze: Ethylene Glycol". The AstroPhysical Journal. 571: L59–L62. doi:10.1086/341148. Check date values in:
|date=(help) - ↑ 2.0 2.1 2.2 Brent J (2001). "Current management of ethylene glycol poisoning". Drugs. 61 (7): 979–88. PMID 11434452.
- ↑ Field D (1985). "Acute ethylene glycol poisoning". Crit Care Med. 13 (10): 872–3. PMID 4028762.
- ↑ Barceloux DG, Krenzelok EP, Olson K, Watson W. (1999). "American Academy of Clinical Toxicology Practice Guidelines on the Treatment of Ethylene Glycol Poisoning. Ad Hoc Committee". J Toxicol Clin Toxicol. 37 (5): 537–60. PMID 10497633.
- ↑ Brent J, McMartin K, Phillips S, Burkhart K, Donovan J, Wells M, Kulig K (1999). "Fomepizole for the treatment of ethylene glycol poisoning. Methylpyrazole for Toxic Alcohols Study Group". N Engl J Med. 340 (11): 832–8. PMID 10080845.
External links
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