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Ethylene glycol

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Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound primarily used as a raw material in the manufacture of polyester fibers and fabric industry, and polyethylene terephthalate resins (PET) used in bottling. A small percent is also used in industrial applications like antifreeze formulations and other industrial products. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid. Ethylene glycol is toxic, and ingestion can result in death.

Production Edit

Historical aspects and natural occurrenceEdit

Although almost all sources state that French chemist Charles-Adolphe Wurtz (1817-1884) first prepared ethylene glycol in 1859, he actually first prepared it in 1856.[1] He first treated "ethylene iodide" (C2H4I2) with silver acetate and then hydrolyzed the resultant "ethylene diacetate" with potassium hydroxide. Wurtz named his new compound "glycol" because it was intermediate to ethyl alcohol (with one hydroxyl group) and glycerin (with three hydroxyl groups).[2] In 1860, Wurtz prepared ethylene glycol from the hydration of ethylene oxide. There appears to have been no commercial manufacture or application of ethylene glycol prior to World War I, when it was synthesized from ethylene dichloride in Germany and used as a substitute for glycerol in the explosives industry.

In the United States, semicommercial production of ethylene glycol via ethylene chlorohydrin started in 1917. The first large-scale commercial glycol plant was erected in 1925 at South Charleston, West Virginia, by Carbide and Carbon Chemicals Co. (now Union Carbide Corp.). By 1929, ethylene glycol was being used by almost all dynamite manufacturers.

In 1937, Carbide started up the first plant based on Lefort's process for vapor-phase oxidation of ethylene to ethylene oxide. Carbide maintained a monopoly on the direct oxidation process until 1953, when the Scientific Design process was commercialized and offered for licenses.

This molecule has been observed in outer space.[3]

Uses Edit

EG is primarily used as a raw material in the manufacture of polyester fibers and fabric industry, and polyethylene terephthalate resins (PET) used in bottling. A small percent is also used in industrial applications like antifreeze formulations and other industrial products.

Precursor to polymersEdit

In the plastics industry, ethylene glycol is important precursor to polyester fibers and resins. Polyethylene terephthalate, used to make plastic bottles for soft drinks, is prepared from ethylene glycol.

Hydrate inhibitionEdit

Because of its high boiling point and affinity for water, ethylene glycol is a useful desiccant. Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to an onshore processing facility. Ethylene glycol can be recovered from the natural gas and reused as an inhibitor after purification treatment that removes water and inorganic salts.

Natural gas is dehydrated by ethylene glycol. In this application, ethylene glycol flows down from the top of a tower and meets a rising mixture of water vapor and hydrocarbon gases. Dry gas exits from the top of the tower. The glycol and water are separated, and the glycol recycled. Instead of removing water, ethylene glycol can also be used to depress the temperature at which hydrates are formed. The purity of glycol used for hydrate suppression (monoethylene glycol) is typically around 80%, whereas the purity of glycol used for dehydration (triethylene glycol) is typically 95 to more than 99%. Moreover, the injection rate for hydrate suppression is much lower than the circulation rate in a glycol dehydration tower.

Chemical reactionsEdit

Ethylene glycol is used as a protecting group for carbonyl groups in organic synthesis. Treating a ketone or aldehyde with ethylene glycol in the presence of an acid catalyst (e.g., p-toluenesulfonic acid; BF3•Et2O) gives the corresponding a 1,3-dioxolane, which is resistant to bases and other nucleophiles. The 1,3-dioxolane protecting group can thereafter be removed by further acid hydrolysis.[4] In this example, isophorone was protected using ethylene glycol with p-toluenesulfonic acid in moderate yield. Water was removed by azeotropic distillation to shift the equilibrium to the right.[5]

Toxicity Edit

Main article: ethylene glycol poisoning

Ethylene glycol is moderately toxic with an oral LDLO = 786 mg/kg for humans.[6] The major danger is due to its sweet taste. Because of that, children and animals are more inclined to consume large quantities of it than of other poisons. Upon ingestion, ethylene glycol is oxidized to glycolic acid which is, in turn, oxidized to oxalic acid, which is toxic. It and its toxic byproducts first affect the central nervous system, then the heart, and finally the kidneys. Ingestion of sufficient amounts can be fatal if untreated.[7]

According to the annual report of the American Association of Poison Control Centers' National Poison Data System in 2007, there were about 1000 total cases resulting in 16 deaths. The 2008 American Association of Poison Control Centers' National Poison Data System annual report lists 7 deaths.(Toxicity, Ethylene Glycol)

Antifreeze products for automotive use containing propylene glycol in place of ethylene glycol are available, and are generally considered safer to use, as it possesses an unpleasant taste in contrast to the perceived "sweet" taste of toxic ethylene glycol-based coolants, and only produces lactic acid in an animal's body, as their muscles do when exercised.[8]

Australia, the U.K., and seventeen U.S. states (as of 2012) require the addition of a bitter flavoring (denatonium benzoate) to antifreeze; in 2012, U.S. antifreeze manufacturers agreed voluntarily to add a bitter flavoring to all antifreeze that is sold in the consumer market of the U.S.[9]

In the environmentEdit

Ethylene glycol breaks down in air in about ten days, and in water or soil in a few weeks. It enters the environment through the disposal of ethylene glycol-containing products, especially at airports where it is used in deicing agents for runways and airplanes.[10] It has been linked as a teratogen in certain species of birds.

References Edit

  1. Adolphe Wurtz (1856) "Sur le glycol ou alcool diatomique" (On glycol or diatomic alcohol), Comptes rendus, 43 : 199-204.
  2. Wurtz (1856), page 200: "… je propose de le nommer glycol, parce qu'il se rapproche à la fois, par ses propriétés, de l'alcool proprement dit et de la glycérin, entre lesquels il se trouve placé." (… I propose to call it glycol because, by its properties, it is simultaneously close to [ethyl] alcohol properly called and glycerin, between which it is placed.)
  3. J. M. Hollis, F. J. Lovas, P. R. Jewell, L. H. Coudert (2002-05-20). Interstellar Antifreeze: Ethylene Glycol. The Astrophysical Journal 571 (1): L59–L62.
  4. Theodora W. Greene, Peter G. M. Wuts (1999). Protective Groups in Organic Synthesis, Third, 312–322, John Wiley & Sons.
  5. J. H. Babler, N. C. Malek and M. J. Coghlan (1978). Selective hydrolysis of α,β- and β,γ-unsaturated ketals: method for deconjugation of β,β-disubstituted α,β-unsaturated ketones. J. Org. Chem. 43 (9): 1821–1823.
  6. Safety Officer in Physical Chemistry. Safety (MSDS) data for ethylene glycol. Oxford University. URL accessed on December 30, 2009.
  7. Ethylene glycol. National Institute for Occupational Safety and Health. Emergency Response Database. August 22, 2008. Retrieved December 31, 2008.
  8. Pieter Klapwijk. Ethylene Glycol Poisoning. The Rested Dog Inn. URL accessed on October 11, 2012.
  9. Consumer Specialty Products Association: Antifreeze and engine coolant being bittered nationwide
  10. (CDC ToxFAQs)

External links Edit

Template:Sugar alcohols

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