Glycol, any of a class of organic compounds belonging to the alcohol family; in the molecule of a glycol, two hydroxyl (−OH) groups are attached to different carbon atoms. The term is often applied to the simplest member of the class, ethylene glycol
In the 1993 ranking of chemicals according to the quantity produced in the United States, ethylene glycol ranked 30th, with 5.23 billion lb (2.37 × 109 kg). Much of this ethylene glycol is used as antifreeze in automobile radiators. The addition of ethylene glycol to water causes the freezing point of the latter to decrease, thus the damage that would be caused by the water freezing in a radiator can be avoided by using a mixture of water and ethylene glycol as the coolant. An added advantage of using such a mixture is that its boiling point is higher than that of water, which reduces the possibility of boil-over during summer driving. In addition to ethylene glycol, commercial antifreeze contains several additives, including a dye to reduce the likelihood of the highly toxic ethylene glycol being accidentally ingested. Concern over the toxicity of ethylene glyco-the lethal dose of ethylene glycol for humans is 1.4 ml/kg-resulted in the introduction, in 1993, of antifreeze based on non-toxic propylene glycol.
The second major use of ethylene glycol is in the production of poly(ethylene terephthalate), or PET. This polymer, a polyester, is obtained by reacting ethylene glycol with terephthalic acid (IUPAC name: 1,4-benzenedicarboxylic acid) or its dimethyl ester (Figure 4).
Poly(ethylene terephthalate) is used to produce textiles, large soft-drink containers, photographic film, and overhead transparencies. It is marketed under various trademarks including DACRON®, Terylene®, Fortrel®, and Mylar®. Textiles containing this polyester are resistant to wrinkling, and can withstand frequent laundering. Poly(ethylene terephthalate) has been utilized in the manufacture of clothing, bed linen, carpeting, and drapes.
Other glycols are also used in polymer production; for example, tetramethylene glycol is used to produce polyesters, and diethylene glycol is used in the manufacture of polyurethane and unsaturated polyester resins. Propylene glycol is used in the manufacture of the polyurethane foam used in car seats and furniture. It is also one of the raw materials required to produce the unsaturated polyester resins used to make car bodies and playground equipment.