Ethylene glycol ('''monoethylene glycol''' ('''MEG'''), 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 Wurtz . It was produced on a small scale during
World War I as a coolant and as an ingredient in
Explosive s. 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 → HOCH
2CH
2OH
This
Reaction can be
Catalyzed by either
Acid s or
Base s, 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
Oligomer s
Diethylene Glycol ,
Triethylene Glycol , and
Tetraethylene Glycol .
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
Windshield s and
Jet Engine s. Ethylene glycol has become increasingly important in the
Plastic s industry for the manufacture of
Polyester fibers and
Resin s, including
Polyethylene Terephthalate , which is used to make plastic bottles for
Soft Drink s. 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
Capacitor s 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
Vaccine s, 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.
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
Heart beat and
Breathing . In the final stage, the victim suffers
Kidney failure. 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
1985 Diethylene Glycol appeared to be added to
Austria n 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
External links
References
- Barceloux D G, Krenzelok E P et al. American Academy of Clinical Toxicology Practise Guidelines on the Treatment of Ethylene Glycol Poisoning. Clin Toxicol 1999; 37: 537-60.
