Glycerol (ˈglɪsərɒl), also called glycerine or glycerin, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known as glycerides. Because it has antimicrobial and antiviral properties, it is widely used in wound and burn treatments approved by the U.S. Food and Drug Administration. Conversely, it is also used as a bacterial culture medium. Its presence in blood can be used as an effective marker to measure liver disease. It is also widely used as a sweetener in the food industry and as a humectant in pharmaceutical formulations. Because of its three hydroxyl groups, glycerol is miscible with water and is hygroscopic in nature.
Although achiral, glycerol is prochiral with respect to reactions of one of the two primary alcohols. Thus, in substituted derivatives, the stereospecific numbering labels the molecule with a sn- prefix before the stem name of the molecule.
Glycerol is generally obtained from plant and animal sources where it occurs in triglycerides, esters of glycerol with long-chain carboxylic acids. The hydrolysis, saponification, or transesterification of these triglycerides produces glycerol as well as the fatty acid derivative:
Triglycerides can be saponified with sodium hydroxide to give glycerol and fatty sodium salt or soap.
Typical plant sources include soybeans or palm. Animal-derived tallow is another source. Approximately 950,000 tons per year are produced in the United States and Europe; 350,000 tons of glycerol were produced per year in the U.S. alone from 2000 to 2004. The EU directive 2003/30/EC set a requirement that 5.75% of petroleum fuels were to be replaced with biofuel sources across all member states by 2010. It was projected in 2006 that by 2020, production would be six times more than demand, creating an excess of glycerol as a byproduct of biofuel production.
Glycerol from triglycerides is produced on a large scale, but the crude product is of variable quality, with a low selling price of as low as US$0.
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