Soluble in alcohols, ethyl acetate, THF, and dioxane. Miscible with DCM and slightly miscible with diethyl ether. Not miscible with toluene or hexanes.
Ethylene glycol (IUPAC name: ethane-1,2-diol) is anorganic compound (avicinal diol[7]) with the formula(CH2OH)2. It is mainly used for two purposes: as a raw material in the manufacture of polyester fibers and forantifreeze formulations. It is an odorless, colorless, flammable, viscous liquid. It has a sweet taste but istoxic in high concentrations. This molecule has been observed in outer space.[8]
Ethylene glycol is produced fromethylene (ethene), via the intermediateethylene oxide. Ethylene oxide reacts withwater to produce ethylene glycol according to thechemical equation
C2H4O + H2O → HO−CH2CH2−OH
Thisreaction can becatalyzed by eitheracids orbases or can occur at neutralpH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH with a large excess of water. Under these conditions, ethylene glycol yields of 90% can be achieved. The major byproducts are the oligomersdiethylene glycol,triethylene glycol, andtetraethylene glycol. The separation of these oligomers and water is energy-intensive. World production of ethylene glycol was ~20 Mt in 2010.[9]
A higher selectivity is achieved by the use ofShell'sOMEGA process. In the OMEGA process, the ethylene oxide is first converted withcarbon dioxide (CO2) toethylene carbonate. This ring is then hydrolyzed with a base catalyst in a second step to produce mono-ethylene glycol in 98% selectivity.[10] The carbon dioxide is released in this step again and can be fed back into the process circuit. The carbon dioxide comes in part from ethylene oxide production, where a part of the ethylene is completelyoxidized.
Ethylene glycol is produced fromcarbon monoxide in countries with large coal reserves and less stringent environmental regulations. The oxidative carbonylation of methanol todimethyl oxalate provides a promising approach to the production ofC 1-based ethylene glycol.[11] Dimethyl oxalate can be converted into ethylene glycol in high yields (94.7%)[12] byhydrogenation with a copper catalyst:[13]
Because the methanol is recycled, only carbon monoxide, hydrogen, and oxygen are consumed. One plant with a production capacity of200000 tons of ethylene glycol per year is inInner Mongolia, and a second plant in the Chinese province ofHenan with a capacity of250000 tons per year was scheduled for 2012.[14] As of 2015[update], four plants in China with a capacity of200000 t/a each were operating, with at least 17 more to follow.[15]
According to most sources, French chemistCharles-Adolphe Wurtz (1817–1884) first prepared ethylene glycol in 1856.[17] He first treated "ethylene iodide" (1,2-Diiodoethane) with silver acetate and then hydrolyzed the resultant "ethylene diacetate" withpotassium hydroxide. Wurtz named his new compound "glycol" because it shared qualities with bothethyl alcohol (with one hydroxyl group) andglycerin (with three hydroxyl groups).[18] In 1859, Wurtz prepared ethylene glycol via thehydration ofethylene oxide.[19] There appears to have been no commercial manufacture or application of ethylene glycol beforeWorld War I when it was synthesized fromethylene dichloride in Germany and used as a substitute forglycerol in theexplosives industry.
In the United States, semicommercial production of ethylene glycol viaethylene chlorohydrin started in 1917. The first large-scale commercial glycol plant was erected in 1925 atSouth Charleston, West Virginia, by Carbide and Carbon Chemicals Co. (nowUnion Carbide Corp.). By 1929, ethylene glycol was being used by almost alldynamite 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 licensing.
A major use of ethylene glycol is as an antifreeze agent incoolants. This can be useful for automobiles andair-conditioning systems that either have externalchillers orair handlers or must cool below the freezing temperature of water. Ingeothermal heating/cooling systems, ethylene glycol is thefluid that transports heat through the use of ageothermal heat pump. The ethylene glycol either gains energy from the source (lake, ocean,water well) or dissipates heat to the sink, depending on whether the system is being used for heating or cooling.
Pure ethylene glycol has aspecific heat capacity about one-half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 1:1 mix by mass has a specific heat capacity of about 3140 J/(kg·°C) (0.75 BTU/(lb·°F)), three-quarters that of pure water, thus requiring increased flow rates in same-system comparisons with water.
The mixture of ethylene glycol with water provides additional benefits to coolant and antifreeze solutions, such as preventing corrosion and acid degradation, as well as inhibiting the growth of most microbes and fungi.[20] Mixtures of ethylene glycol and water are sometimes informally referred to in the industry as glycol concentrates, compounds, mixtures, or solutions.
Table of thermal and physical properties of saturated liquid ethylene glycol:[21][22]
Pure ethylene glycol freezes at about −12 °C (10.4 °F) but, when mixed with water, the mixture freezes at a lower temperature. For example, a mixture of 60% ethylene glycol and 40% water freezes at −45 °C (−49 °F).[23]Diethylene glycol behaves similarly. The freezing point depression of some mixtures can be explained as acolligative property of solutions but, in highly concentrated mixtures such as the example, deviations from ideal solution behavior are expected due to the influence ofintermolecular forces. It's important to note that though pure and distilled water will have a greater specific heat capacity than any mixture of antifreeze and water, commercial antifreeze also typically contain an anti-corrosive additive to prevent pure water from corroding coolant passages in the engine block, cylinder head(s), water pump and radiator.
There is a difference in the mixing ratio, depending on whether it is ethylene glycol or propylene glycol. For ethylene glycol, the mixing ratios are typically 30/70 and 35/65, whereas the propylene glycol mixing ratios are typically 35/65 and 40/60. The mixture must be frost-proof at the lowest operating temperature.[24]
Because of the depressed freezing temperatures, ethylene glycol is used as ade-icing fluid forwindshields and aircraft,[25] as anantifreeze in automobile engines, and as a component ofvitrification (anticrystallization) mixtures for low-temperature preservation of biological tissues and organs.
The use of ethylene glycol not only depresses the freezing point of aqueous mixtures but also elevates their boiling point. This results in the operating temperature range for heat-transfer fluids being broadened on both ends of the temperature scale. The increase in boiling temperature is due to pure ethylene glycol having a much higher boiling point and lowervapor pressure than pure water.
Ethylene glycol is used in the natural gas industry to remove water vapor from natural gas before further processing, in much the same manner astriethylene glycol (TEG).
Because of its high boiling point and affinity for water, ethylene glycol is a usefuldesiccant. Ethylene glycol is widely used to inhibit the formation ofnatural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to a gas processing facility. Ethylene glycol can be recovered from 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 andhydrocarbon gases. Dry gas exits from the top of the tower. The glycol and water are separated, and the glycol is recycled. Instead of removing water, ethylene glycol can also be used to depress the temperature at whichhydrates 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 aglycol dehydration tower.
Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of1,4-dioxane, as an additive to preventcorrosion in liquid cooling systems forpersonal computers, and inside the lens devices of cathode-ray tube type of rear projection televisions. Ethylene glycol is also used in the manufacture of somevaccines, but it is not present in these injections. It is used as a minor (1–2%) ingredient inshoe polish and also in some inks and dyes. Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after damage. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats and is relatively cheap. Ethylene glycol may also be one of the minor ingredients in screen cleaning solutions, along with the main ingredientisopropyl alcohol. Ethylene glycol is commonly used as apreservative for biological specimens, especially in secondary schools duringdissection as a safer alternative toformaldehyde. It is also used as part of the water-based hydraulic fluid used to control subsea oil and gas production equipment.
Although dwarfed by its use as a precursor topolyesters, ethylene glycol is useful in more specialized areas of organic chemistry.
It serves as aprotecting group inorganic synthesis for the manipulation ofketones and aldehydes.[26][27] By reacting with the carbonyl to form an acetal product, it reduces the likelihood of nucleophilic attack at that carbonyl carbon. After the desired reaction is completed, the carbonyl can be regenerated using acid-catalyzed hydrolysis. In one example,isophorone was protected using ethylene glycol:[28]
Ethylene glycol has relatively high mammalian toxicity when ingested, roughly on par withmethanol, with an oralLDLo = 786 mg/kg for humans.[31] The major danger is due to its sweettaste, which can attract children and animals. Upon ingestion, ethylene glycol is oxidized toglycolic acid, which is, in turn, oxidized tooxalic acid, which istoxic. It and its toxic byproducts first affect thecentral nervous system, then the heart, and finally the kidneys. Ingestion of sufficient amounts is fatal if untreated.[32] Several deaths are recorded annually in the U.S. alone.[33]
Antifreeze products for automotive use containingpropylene glycol in place of ethylene glycol are available. They are generally considered safer to use, as propylene glycol is not as palatable[note 1] and is converted in the body tolactic acid, a normal product of metabolism and exercise.[36]
Australia, the UK, and seventeen US states (as of 2012) require the addition of a bitter flavoring (denatonium benzoate) to antifreeze. In December 2012, US antifreeze manufacturers agreed voluntarily to add a bitter flavoring to all antifreeze that is sold in the consumer market of the US.[37]
Ethylene glycol is ahigh-production-volume chemical. It breaks down in air in about 10 days and in water or soil in a few weeks. It enters the environment through the dispersal of ethylene glycol-containing products, especially at airports, where it is used inde-icing agents for runways and airplanes. Ethylene glycol is apollutant that impactswater quality, by exerting high levels ofbiochemical oxygen demand during degradation in water bodies. The pollution can harm fish, insects and other aquatic life by consuming oxygen needed by these organisms.[40]: 2–23 [41]
While prolonged low doses of ethylene glycol show no toxicity, at near-lethal doses (≥ 1000 mg/kg per day) ethylene glycol acts as ateratogen. "Based on a rather extensive database, it induces skeletal variations and malformations in rats and mice by all routes of exposure."[42]
^Pure propylene glycol does not taste bitter, and pure propylene glycol is often used as a food additive, for instance in cake icing and shelf-stable whipped cream. Industrial-grade propylene glycol usually has a slightly bitter or acrid taste due to impurities. See the article onpropylene glycol for more information. The relative sweetness of ethylene glycol[34] and propylene glycol[35] is discussed in the Merck Index, and neither compound is described as bitter.
^Scott D. Barnicki, "Synthetic Organic Chemicals", inHandbook of Industrial Chemistry and Biotechnology edited by James A. Kent, New York: Springer, 2012. 12th ed.ISBN978-1-4614-4259-2.
^983 EP 046 983, S. Tahara et al., "Process for continuously preparing ethylene glycol", assigned to Ube Industries and H. T. Teunissen and C. J. Elsevier,Ruthenium catalyzed hydrogenation of dimethyl oxalate to ethylene glycol, J. Chem. Soc., Chem. Commun., 1997, 667–668),doi:10.1039/A700862G.
^S. Zhang et al.,Highly-Dispersed Copper-Based Catalysts from Cu–Zn–Al Layered Double Hydroxide Precursor for Gas-Phase Hydrogenation of Dimethyl Oxalate to Ethylene Glycol, Catalysis Letters, Sept. 2012,142 (9), 1121–1127,doi:10.1007/s10562-012-0871-8.
^Wurtz (1856), page 200:"… je propose de le nommerglycol, 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 itglycol because, by its properties, it is simultaneously close to [ethyl] alcohol properly called and glycerin, between which it is placed.)
^Holman, Jack P. (2002).Heat Transfer (9th ed.). New York, NY: McGraw-Hill Companies, Inc. pp. 600–606.ISBN9780072406559.
^Frank P. Incropera, David P. Dewitt, heodore L. Bergman, Adrienne S. Lavigne (2007).Fundamentals of Heat and Mass Transfer (6th ed.). Hoboken, NJ: John Wiley and Sons, Inc. pp. 941–950.ISBN9780471457282.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Theodora W. Greene; Peter G. M. Wuts (1999).Protective Groups in Organic Synthesis (Third ed.). John Wiley & Sons. pp. 312–322.ISBN978-0-471-16019-9.
^J. H. Babler; N. C. Malek; 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.doi:10.1021/jo00403a047.
^Panten, Johannes; Surburg, Horst (2016). "Flavors and Fragrances, 3. Aromatic and Heterocyclic Compounds".Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–45.doi:10.1002/14356007.t11_t02.ISBN978-3-527-30673-2.
