Ethylene glycol
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| Missing image Ethylene_glycol_chemical_structure.png Chemical structure of ethylene glycol |
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General |
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| Name | Ethane-1,2-diol |
| Chemical formula | HOCH2CH2OH |
| Formula weight | 62.07 amu |
| Synonyms | Ethylene Glycol |
| CAS number | 107-21-1 |
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Phase behavior |
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| 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)
? bar |
| Critical point | 720 K (447°C)
82 bar |
| ΔfusH | 9.9 kJ/mol |
| ΔfusS | 38.2 J/mol·K |
| ΔvapH | 65.6 kJ/mol |
| Solubility | Miscible with water. |
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Liquid properties |
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| ΔfH0liquid | -460 kJ/mol |
| S0liquid | 166.9 J/mol·K |
| Cp | 149.5 J/mol·K |
| Density | 1.1132 ×103 kg/m3 |
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Gas properties |
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| ΔfH0gas | -394.4 kJ/mol |
| S0gas | 311.8 J/mol·K |
| Cp | 78 J/mol·K |
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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% |
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More info | |
| Properties | NIST WebBook (http://webbook.nist.gov/cgi/cbook.cgi?ID=&Units=SI) |
| MSDS | Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals1/8/7680.html) |
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SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references </font> | |
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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 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
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 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.
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.
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.
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 consumption of ethanol - usually in the form of a strong spirit such as whisky, vodka or gin. Ethanol acts by competing with ethylene glycol for the enzyme alcohol dehydrogenase thus limiting the formation of toxic metabolites, whilst the ethylene glycol is flushed from the system.
Due to its toxicity, the substance has been in the news at least at one time:
- In 1996 60 children died on Haïti through glycerine poisoned with ethylene glycol in a cough syrup, supplied by a Dutch company, Vos, from a manufacturer in China.
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
- NASA Apollo 1 catastrophe (http://www.hq.nasa.gov/office/pao/History/SP-4009/v4p2b.htm)de:Glykol