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Ethylene Glycol

Science EncyclopediaScience & Philosophy: Ephemeris to Evolution - Historical Background

Ethylene glycol is an organic (carbon based) molecule most widely used as antifreeze in automobile engines and as an industrial solvent, a chemical in which other substances are dissolved. The addition of ethylene glycol to water raises the boiling point of the engine coolant and reduces the chances of a car's radiator "boiling over." The name ethylene glycol communicates much information about the chemical's structure. The "ethylene" portion of the name indicates that the molecules of ethylene glycol have two carbon atoms in them, and the "glycol" part of the name indicates that there are two hydroxy groups (OH units) attached on carbon atoms. Ethylene glycol has a freezing point of 8.6°F (-13°C) and a boiling point of 388°F (198°C), and is completely miscible with water.

Ethylene glycol is sweet tasting but highly toxic. It must therefore be kept away from children and pets. As little as 2 oz (56.7 g) can cause death in an adult, and much smaller doses can kill a child or a small animal. Ethylene glycol itself is metabolized by enzymes in the liver and becomes highly poisonous oxalic acid. Enzymes are protein catalysts, molecules that speed up the rates of chemical reactions. Pure ethylene glycol is colorless, syrupy liquid. The color of commercial antifreeze (usually green) is due to a dye that is added to help identify the source of a leak from a car.

Pure water has a boiling point of 212°F (100°C) at sea level. A special pressure cap is used on car radiators to make the boiling point higher, but even so, most cars would "boil over" were it not for the addition of other chemicals that raise the boiling point. Many chemicals can be used to raise the boiling point of water (including salt and sugar), but ethylene glycol is used because it does not damage parts of the car and is inexpensive and long-lasting. It also lowers the freezing point, thus requiring a lower temperature for the water to freeze. Ethylene glycol could just as well be called "anti-boil." In industries, ethylene glycol is used as a solvent (a substance that dissolves other chemicals) and as starting material for the production of Dacron and some types of polyurethane foam.

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