Article: Ethylene glycol

Properties

General
Name	Ethane-1,2-diol
Chemical formula	HOCH2CH2OH
Formula weight	62.07 u
Synonyms	Ethylene glycol Mono ethylene glycol, MEG
SMILES	OCCO
CAS number	107-21-1
Phase behavior
Melting point	260.2 K (−12.9 °C)
Boiling point	470.4 K (197.3 °C)
Thermal decomposition	? K (? °C)
Triple point	256 K (-17 °C) ? kPa
Critical point	720 K (447°C) 8.2 MPa
ΔfusH	9.9 kJ/mol
ΔfusS	38.2 J/(mol·K)
ΔvapH	65.6 kJ/mol
Solubility	Miscible with water
Liquid properties
ΔfH0liquid	-460 kJ/mol
S0liquid	166.9 J/(mol·K)
Cp	149.5 J/(mol·K)
Density	1.1132 g/cm3
Gas properties
ΔfH0gas	-394.4 kJ/mol
S0gas	311.8 J/(mol·K)
Cp	78 J/(mol·K)
Safety
Acute effects	Nausea, vomiting. CNS paralysis. Kidney damage.
Chronic effects	Kidney damage
Flash point	111 °C
Autoignition temperature	410 °C
Explosive limits	1.8–12.8%
More info
Properties	NIST WebBook
MSDS	Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

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 its precursor ethylene oxide became cheaply available.

When first introduced it created a minor revolution in aircraft design because when used in place of water as a radiator coolant, its higher boiling point allowed for smaller radiators operating at higher temperatures. Prior to the widespead 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 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

C₂H₄O + H₂O → HOCH₂CH₂OH

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 some of a large excess of water present. 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 the space by Hollis et al. (The AstroPhysical Journal, 571:L59-L62, 2002 May 20).

Uses

The major use of ethylene glycol is as an engine coolant and antifreeze. Due to its low freezing point, it has also been used as a deicing fluid for windshields and jet engines. 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 and as a chemical intermediate in the manufacture of 1,4-dioxane.

Ethylene glycol's high boiling point and affinity for water makes it an ideal dehydrator 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 also used in liquid cooling systems in some personal computers.

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.

Safety

The major danger from ethylene glycol is from its ingestion. Due to its sweet taste, children and animals will sometimes consume large quantities of it if given access to antifreeze. Symptoms of ethylene glycol poisoning follow a three-step progression. Initially, victims may appear to be intoxicated, exhibiting symptoms such as dizziness, slurred speech, and confusion. Over time, the body metabolizes ethylene glycol into another toxin, oxalic acid. Buildup of this substance results in irregularities in the victim's heartbeat and breathing. In the final stage, the victim suffers kidney failure.^[1] In developed countries, denatonium is generally added to ethylene glycol preparations in order to offset the sweet taste.

Victims of ethylene glycol poisoning who are still conscious may be given milk or water to drink to delay the effects of the poison. In any case, medical attention should be sought immediately. Ethylene glycol doses as small as 30 milliliters (2 tablespoons) can be lethal to adults. However, the most effective treatment after recent ingestion is either ethanol or fomepizole. Ethanol (usually dosed 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 limiting the formation of the toxic metabolites.

Due to its toxicity, the substance has been in the news at least at one time:

• In 1996 85 children died on Haïti through glycerine poisoned with diethylene glycol in a paracetamol syrup, supplied by a Dutch company, Vos, from a manufacturer in China.^[2]

• In 1985 diethylene glycol appeared to be added to Austrian white wine, in order to upgrade it to table wine. The amount added was not high enough to be immediately toxic (one would have to ingest 28 bottles per day for two weeks), however the adverse worldwide publicity caused very high export losses and led to severe wine laws in Austria.

Ethylene glycol may be found as a contaminant in unlawfully distilled whiskey (moonshine) made in a still constructed using an improperly washed car radiator.

The electrolysis of ethylene glycol solutions with the anode made of silver 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.

See also

• Propylene glycol