Methyl tert-butyl ether 391568 224595674 2008-07-09T16:05:00Z Vuo 143648 /* Alternatives */ {{Chembox new | Name = '''Methyl tert-butyl ether''' | ImageFile = MTBE-2D-skeletal.png | ImageSize = 150px | ImageName = MTBE | ImageFile1 = MTBE-3D-sticks.png | ImageSize1 = 150px | ImageName1 = MTBE | IUPACName = 2-Methoxy-2-methylpropane | OtherNames = Methyl ''tertiary''-butyl ether<br />Methyl ''tert''-butyl ether<br />Methyl ''t''-butyl ether<br />MTBE<br />''tert''-Butyl methyl ether<br />tBME | Section1 = {{Chembox Identifiers | CASNo = 1634-04-4 | SMILES = CC(C)(C)OC }} | Section2 = {{Chembox Properties | Formula = C<sub>5</sub>H<sub>12</sub>O | MolarMass = 88.15 g/mol | Density = 0.7404 g/cm³ | MeltingPt = -109 °C | BoilingPt = 55.2 °C }} | Section7 = {{Chembox Hazards | FlashPt = -10 °C | NFPA-H = 1 | NFPA-F = 3 | NFPA-R = }} }} '''Methyl ''tert''-butyl ether''', also known as '''methyl tertiary butyl ether''' and '''MTBE''', is a [[chemical]] compound with molecular formula C<sub>5</sub>H<sub>12</sub>O. MTBE is a volatile, flammable and colorless liquid that is [[immiscible]], yet reasonably soluble in water. MTBE has a minty odour vaguely reminiscent of [[diethyl ether]], leading to unpleasant taste and odour in water. MTBE is a [[gasoline]] additive, used as an [[oxygenate]] and to raise the [[octane number]], although its use has declined in the United States in response to environmental and health concerns. It has been found to easily [[pollute]] large quantities of [[groundwater]] when gasoline with MTBE is spilled or leaked at gas stations. MTBE is also used in [[organic chemistry]] as a relatively inexpensive [[solvent]] with properties comparable to diethyl ether but with a higher [[boiling point]] and lower [[solubility]] in [[water (molecule)|water]]. It is also used medically to dissolve [[gallstones]]. ==Production== MTBE is manufactured via the [[chemical reaction]] of [[methanol]] and [[isobutylene]]. Methanol is derived from natural gas, and isobutylene is made from [[crude oil]] or [[natural gas]], thus MTBE, as used in motor gasoline, is a fossil fuel. In the United States, it was produced in very large quantities (more than 200,000 [[barrel (unit)|barrel]]s per day in the [[United States]] in [[1999]]) during its use as a fuel additive. Due to widespread releases of MTBE-containing gasoline from [[Underground Storage Tank]]s all over the US, various jurisdictions banned the use of MTBE and production was reduced. MTBE contamination in drinking water [[aquifers]] is a serious concern in many states (the most famous cases are [[Lake Tahoe]] and Santa Monica). By late 2006, most American gasoline retailers had ceased using MTBE as an oxygenate, and accordingly, US production had declined. Similarly, lack of growth or even decline of MTBE production has been seen in Western Europe. This is not due to environmental concerns; on the contrary, it is because the alternative ethanol-derived ether [[ETBE]] has been given more favorable tax treatment. Nevertheless, in other parts of the world, which account for about a half of 2004 production, the use of MTBE will continue and even grow.<ref>Michael Malveda, Hossein Janshekar, Masahiro Yoneyama. Gasoline Octane Improvers/Oxygenates. SRI Consulting. http://www.sriconsulting.com/CEH/Public/Reports/543.7500/</ref> ==Physical properties== MTBE forms [[azeotrope]]s with water (52.6 °C) and methanol (51.3 °C). ==Uses== MTBE is almost exclusively used as a fuel component in motor [[petrol|gasoline]]. It is one of a group of chemicals commonly known as [[oxygenate]]s because they raise the [[oxygen]] content of gasoline. ===As anti-knocking agent=== In the US it has been used in gasoline at low levels since 1979 to replace [[tetra-ethyl lead]] to increase its [[octane]] rating and help prevent [[engine knocking]]. Oxygen helps gasoline burn more completely, [[Automobile emissions control|reducing tailpipe emissions]] from pre-1984 motor vehicles. In more modern vehicles, the emissions reduction is negligible. In one respect, the oxygen dilutes or displaces gasoline components such as aromatics (e.g., [[benzene]]) and sulfur. In another, oxygen optimizes the oxidation during combustion. Most refiners have chosen to use MTBE over other oxygenates primarily for its blending characteristics and for economic reasons. It is produced from natural gas, which is less expensive than oil. Since [[1992]], MTBE has been used at higher concentrations in some gasoline to fulfill the oxygenate requirements set by the [[United States Congress]] in [[Clean Air Act]] amendments; however, since 1999, in California and other locations MTBE has begun to be phased out because of groundwater contamination (California Air Resources Board, 2004). Due to its higher solubility in water MTBE moves more quickly than other fuel components (California Air Resources Board, 2004). The Energy Policy Act of 2005 reduces the federal requirement for oxygen content in reformulated gasoline<ref name="http://www.epa.gov/otaq/rfg_regs.htm#usage">[http://www.epa.gov/otaq/rfg_regs.htm#usage http://www.epa.gov/otaq/rfg regs.htm#usage]</ref>. In 1995 high levels of MTBE were unexpectedly discovered in the [[water well]]s of [[Santa Monica, California]], and the [[U.S. Geological Survey]] reported detections.<ref name="http://pubs.er.usgs.gov/pubs/fs/fs11495">[http://pubs.er.usgs.gov/pubs/fs/fs11495 U.S. Geological Survay detections]</ref> Subsequent U.S. findings indicate tens of thousands of contaminated sites in water wells distributed across the country. As per toxicity alone, MTBE is not classified as a hazard for the environment. The [[maximum contaminant level of MTBE]] in drinking water has not yet been established by the EPA. The leakage problem is partially attributed to the lack of effective regulations for underground storage tanks, but spillage from overfilling remains an important upset scenario. As an ingredient in unleaded gasoline, MTBE is the most soluble part. When dissolved in groundwater, MTBE will lead the contaminant plume with the remaining components such as [[benzene]], [[toluene]], etc. to follow. Thus the discovery of MTBE in public groundwater wells indicates that the contaminant source was a gasoline release. Its criticism and subsequent decreased usage, some claim, is more a product of its easy detectability (taste) in extremely low concentrations (ppb) than its toxicity, as benzene is much more toxic but remains a fuel additive. The MTBE concentrations used in the EU (usually 1.0–1.6%) and allowed (maximum 5%) in Europe are lower than in California.<ref name="European Commission">[[European Commission]]. MTBE and the Requirements for Underground Storage Tank Construction and Operation in Member States.</ref> ====Alternatives==== Other compounds are available as oxygenate additives for gasoline, for example [[alcohol fuel|ethanol]] and related ethers, e.g. [[tert-amyl methyl ether]] (TAME). Reasons for using MTBE include economic considerations, as some of the production is obtained by adding [[methanol]] to [[isobutylene]] produced as a by-product of other processes. However, most MTBE facilities have to manufacture the methanol and isobutylene required to produce MTBE. Ethanol has been advertised as a safe alternative by the agricultural interest groups in the USA and Europe. Its lack of toxicity is not different from MTBE, but as a polar solvent, it drives off nonpolar hydrocarbons from the gasoline, a problem that MTBE does not cause. Volatile hydrocarbons in gasoline vapors are known carcinogens and produce [[photochemical smog]]. Advocates of both sides of the debate in the United States sometimes claim that gasoline manufacturers have been forced to add MTBE to gasoline by law. It might be more correct to say they have been induced to do so, although any [[oxygenate]] would fulfill the law. In 2003, California was the first state to start replacing the MTBE with ethanol. Several other states started switching soon afterward. Higher quality gasoline is also an alternative, i.e. so that additives such as MTBE are unnecessary. [[Iso-octane]] itself is used. MTBE plants can be retrofitted to produce iso-octane from isobutylene.<ref name="http://www.nesteengineering.com/default.asp?path=111,360,362,477">[http://www.nesteengineering.com/default.asp?path=111,360,362,477 http://www.nesteengineering.com/default.asp?path=111,360,362,477]</ref><sup>,</sup><ref name="http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp">[http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp]</ref> Iso-octane is the ideal gasoline, being the standard reference for the [[octane rating]]. In the long run, [[diesel]] fuel is also an alternative, although it requires a major switchover to diesel-run cars. There are several varieties of [[biodiesel]]; both oxygen-containing esters and oxygen-free alkyl biodiesels are available. ===As a solvent=== As a solvent, MTBE possesses one distinct advantage over most ethers- it has a much lower tendency to form explosive [[organic peroxide]]s. Opened bottles of [[diethyl ether]] or [[tetrahydrofuran|THF]] can build up dangerous levels of these peroxides in months, whereas samples of MTBE are usually safe for years (but they should still be tested periodically). For this reason (as well as its higher boiling point), it is used as a solvent extensively in industry, where safety concerns and regulations make working with diethyl ether, THF, or other ethers much more difficult and expensive. However, despite the popularity of MTBE in industrial settings, it is rarely used as a solvent in academia. Research volumes are much smaller, leading to lower risks from other ethers, and in addition the use of MTBE as a solvent is very rare in literature synthetic procedures. ===As a chemical reagent=== Being an ether, MTBE is a [[Lewis base]]. However, unlike other ethers such as [[diethyl ether]] or [[THF]], it does not coordinate well enough with magnesium to be used for making [[Grignard reagent]]s. The ''tert''-[[butyl]] group is easily cleaved off under strongly acidic conditions (forming a moderately stable [[carbocation]]), particularly if heated ([[isobutylene]] is lost), something which can limit the use of MTBE as a solvent. ==Persistence and pervasiveness in the environment== The main environmental risk of MTBE is that it gives water an unpleasant taste at even very low concentrations, and thus can easily render large quantities of groundwater non-potable. MTBE is often introduced into water-supply aquifers by leaking [[underground storage tank]]s (USTs) at gasoline stations. Although USTs are much better constructed now than in the 1980s, accidental releases still take place because of the very large number of USTs. The high solubility and persistence of MTBE cause it to travel faster and farther than many other components of gasoline when released into an aquifer. It is also released when gasoline containing MTBE is spilled onto the ground. Because it is water soluble, it easily moves through soil, polluting both surface and groundwater.<ref>[http://www.sierraclub.org/policy/conservation/mtbe.asp Sierra Club on Gasoline Additive: MTBE]</ref> MTBE has widespread occurrences in the [[aquifer]]s of [[North America]], where the majority of groundwater chemistry data has been acquired. As one regional example, the [[San Francisco Bay Area]] Regional Water Quality Control Board has indicated MTBE is one of the groundwater pollutants of most widespread concern in this metropolitan region.<ref>[http://www.swrcb.ca.gov/rwqcb2/download/WMI%202004%20Executive%20Summary.pdf San Francisco Bay Area Regional Water Quality Control Board Integrated Basin Management Plan (2004)]</ref> MTBE is biodegradable to CO<sub>2</sub> and water under aerobic conditions with the correct bacteria. However, the natural occurrence of these bacteria with the ability to break ether bonds is not high, and it appears that most strains of MTBE-oxidizing bacteria are slow-growing bacteria with low biomass production per unit MTBE oxidized. In the proper type of [[bioreactor]], such as a [[fluidized bed]] bioreactor, MTBE can be rapidly and economically removed from water to undetectable levels. ==Health risks== The [[IARC]], a cancer research agency of the [[World Health Organization]], maintains MTBE is not classifiable as a human [[carcinogen]]. MTBE can be tasted in water at concentrations of 5 – 15 µg/l<ref>{{cite journal | journal = Environ Sci Pollut Res Int | year = 2005 | volume = 12 | issue = 6 | pages = 381–6. | title = Biotic and abiotic transformations of methyl tertiary butyl ether (MTBE) | author = Fischer A, Oehm C, Selle M, Werner P. | pmid = 16305145 | doi = 10.1065/espr2005.08.277}}</ref>. MTBE is not classified as a human [[carcinogen]] at low exposure levels by the International Agency for Research on Cancer (IARC).<ref name="http://monographs.iarc.fr/ENG/Monographs/vol73/volume73.pdf">[http://monographs.iarc.fr/ENG/Monographs/vol73/volume73.pdf http://monographs.iarc.fr/ENG/Monographs/vol73/volume73.pdf]</ref> However, exposure to large doses of MTBE carries significant non-cancer-related health risks. The effects of the prolonged presence of this alcohol derivative are not fully understood. As of 2007, researchers have limited data about the health effects of ingestion of MTBE. The [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA) has concluded that available data are not adequate to quantify health risks of MTBE at low exposure levels in drinking water, but that the data support the conclusion that MTBE is a potential human [[carcinogen]] at high doses.<ref name="http://www.epa.gov/mtbe/faq.htm#concerns">[http://www.epa.gov/mtbe/faq.htm#concerns http://www.epa.gov/mtbe/faq.htm#concerns]</ref> ==Legislation and litigation== ===United States=== MTBE is difficult to clean up due to its high solubility in water. Estimates of the cost of removing MTBE from groundwater and [[soil contamination]] range from $1<ref>[http://www.sigma.org/wr/reports/05/050523.html SIGMA - Weekly Report<!-- Bot generated title -->]</ref> to $30<ref>[http://www.mtbe-eresource.com/liu.cfm Long Island Utility Fighting to Defeat MTBE Safe Harbor - Napoli Bern - Attorneys<!-- Bot generated title -->]</ref>[[1000000000 (number)|billion]], including removing the compound from aquifers and municipal water supplies and replacing leaky underground oil tanks. There is some controversy centered around the question of who will pay the costs of this [[remediation]]. In one case, the cost to oil companies to clean up the MTBE in wells belonging to Santa Monica is estimated to exceed $200 million.<ref>[http://www.ens-newswire.com/ens/feb2005/2005-02-17-09.asp#anchor2 AmeriScan: February 17, 2005<!-- Bot generated title -->]</ref> However, if one used the presently available [[fluidized bed]] bioreactor technology to remove the MTBE in this Santa Monica case, the cost would be a small fraction of the suggested $200 million. It would be hard to justify the litigation cost, in this case, if it cost only a few million to clean it up. Recent state laws have been passed to ban MTBE in certain areas. [[California]] and [[New York]], which together accounted for 40% of U.S. MTBE consumption, banned the chemical starting [[January 1]], [[2004]], and as of September 2005, twenty-five states had signed legislation banning MTBE. (A table of state by state information, as of 2002, is available at the [[United States Department of Energy]] website.<ref>[http://www.eia.doe.gov/oiaf/servicerpt/mtbeban/table1.html Website U.S. Department of Energy]</ref> In 2000, the U.S. [[United States Environmental Protection Agency|EPA]] drafted plans to phase out the use of MTBE nationwide over four years. As of fall 2006, hundreds of lawsuits are still pending regarding MTBE contamination of public and private drinking water supplies. The [[Energy Policy Act of 2005]], passed in the House on April 21, 2005, did not include a provision for shielding MTBE manufacturers from [[water contamination]] lawsuits. This provision was first proposed in 2003 and had been thought by some to be a priority of [[Tom DeLay]] and Rep. [[Joe Barton]], chairman of the Energy and Commerce Committee.<ref>[http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/ http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/]</ref> This bill did include a provision that gives MTBE makers, including some major [[oil industry|oil companies]], $2 billion in transition assistance as MTBE is phased out over the next nine years.<ref>[http://www.msnbc.msn.com/id/7574562/+MTBE&hl=en http://www.msnbc.msn.com/id/7574562/+MTBE&hl=en]</ref> Due to opposition in the Senate,<ref>Charles Babington, House Again Passes GOP Energy Measures, Washington Post, June 16, 2004, at A4 (House passes Energy Bill, but Senate opponents of MTBE provision in House Bill have the votes to prevent its enactment).</ref> the conference report dropped all MTBE provisions. The final bill was passed by both houses and signed into law by President Bush.<ref>[http://thomas.loc.gov/cgi-bin/bdquery/z?d109:h.r.00006: http://thomas.loc.gov/cgi-bin/bdquery/z?d109:h.r.00006:]</ref> The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive, which is in limited supply as of April 2006. Some traders and consumer advocates are blaming this for an increase in gasoline prices.<ref>[http://money.cnn.com/2006/04/18/news/economy/gas prices ethanol/index.htm?cnn=yes http://money.cnn.com/2006/04/18/news/economy/gas prices ethanol/index.htm?cnn=yes]</ref> Certain patents important in the manufacture of MTBE are not held by American companies; for example, United States patent 5536886, ''Process for preparing alkyl ethers'',<ref>[http://www.freepatentsonline.com/5536886.html http://www.freepatentsonline.com/5536886.html]</ref> is owned by the Finnish company [[Neste]]. The same corporation also went on to patent the replacement of the MTBE process, an octane production process trademarked NExOCTANE. The United States Environmental Protection Agency ([[EPA]]) currently lists methyl tertiary butyl ether ([[MTBE]]) as a candidate for a maximum contaminant level ([[Maximum Contaminant Level|MCL]]) in drinking water<ref name="epa">[http://www.epa.gov/safewater/ccl/ccl2.html#chemical CCL 2 List]</ref>. MCLs are determined by the EPA using [[toxicity]] data. ==References== {{refimprove|date=February 2008}} <references/> ==See also== *[[ETBE]] ==External links== * [http://www.mtbe.us * [http://www.efoa.org EFOA] * [http://www.iarc.fr/ Agency on Cancer Research, ([[IACR]]) a division of the [[World Health Organization]]] * [http://www.epa.gov/mtbe/ MTBE webpage from the EPA] * [http://www.inchem.org/documents/iarc/vol73/73-13.html Summary of health effects data] from [[IACR]] * [http://firstgovsearch.gov/search?v%3aproject=firstgov&v%3afile=viv_606%4018%3a2jU0T7&v%3astate=root%7croot&opener=full-window&url=http%3a%2f%2fwww.eia.doe.gov%2fpub%2foil_gas%2fpetroleum%2ffeature_articles%2f2006%2fmtbe2006%2fmtbe2006.pdf&rid=Ndoc1&v%3aframe=redirect&rsource=firstgov-msn&v%3astate=%28root%29%7croot&rrank=1& Eliminating MTBE in Gasoline in 2006 (pdf)] * [http://www.mtbelitigationinfo.com/ An online resource about MTBE litigation and the surrounding issues] * [http://www.ewg.org/reports/withknowledge/ MTBE: What The Oil Companies Knew And When They Knew It (from the Environmental Working Group)] [[Category:Hazardous air pollutants]] [[Category:Ethers]] [[Category:Ether solvents]] [[Category:Pollutants]] [[Category:Petroleum]] [[Category:Soil contamination]] [[Category:Water pollution]] [[Category:Oxygenates]] [[af:Metiel-tersiêre-butieleter]] [[da:MTBE]] [[de:Methyl-tert-butylether]] [[es:MTBE]] [[it:Metil-t-butil etere]] [[nl:Methyl-tert-butylether]] [[ja:メチルターシャリーブチルエーテル]] [[no:MTBE]] [[pl:Eter metylo-tert-butylowy]] [[ru:Метил-трет-бутиловый эфир]] [[fi:Metyylitertiääributyylieetteri]] [[sv:MTBE]] [[zh:甲基叔丁基醚]]