Methyl tert-butyl ether

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Methyl tert-butyl ether
Skeletal formula of MTBE
Ball-and-stick model of the MTBE molecule
Names
IUPAC name
2-Methoxy-2-methylpropane
Other names
Methyl tertiary-butyl ether; Methyl tert-butyl ether; Methyl t-butyl ether; MTBE; tert-Butyl methyl ether; tBME; tert-BuOMe
Identifiers
1634-04-4 YesY
ChEBI CHEBI:27642 YesY
ChemSpider 14672 YesY
Jmol 3D model Interactive image
KEGG C11344 YesY
PubChem 15413
  • InChI=1S/C5H12O/c1-5(2,3)6-4/h1-4H3 YesY
    Key: BZLVMXJERCGZMT-UHFFFAOYSA-N YesY
  • InChI=1/C5H12O/c1-5(2,3)6-4/h1-4H3
    Key: BZLVMXJERCGZMT-UHFFFAOYAA
  • O(C(C)(C)C)C
Properties
C5H12O
Molar mass 88.15 g·mol−1
Density 0.7404 g/cm³
Melting point −109 °C (−164 °F; 164 K)
Boiling point 55.2 °C (131.4 °F; 328.3 K)
26 g/L (20 °C)[1]
Vapor pressure {{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Methyl tert-butyl ether (also known as MTBE, tert-butyl methyl ether, tertiary butyl methyl ether and tBME) is an organic compound with molecular formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble[1] in water. It has a minty odor vaguely reminiscent of diethyl ether, leading to unpleasant taste and odor in water. MTBE is a gasoline additive, used as an oxygenate to raise the octane number. Its use is controversial in the US and declining in use in part because of its occurrence in groundwater and legislation favoring ethanol. However, worldwide production of MTBE has been constant at about 18 million tons/y (2005) owing to growth in Asian markets.[2]

Production and properties

MTBE is manufactured via the chemical reaction of methanol and isobutylene. Methanol is derived from natural gas, and isobutylene is derived from butane obtained from crude oil or natural gas, thus MTBE is derived from fossil fuels. In the United States, it was produced in very large quantities (more than 200,000 barrels (32,000 m3) per day in 1999) during its use as a fuel additive.

Uses

MTBE is almost exclusively used as a fuel component in fuel for gasoline engines. It is one of a group of chemicals commonly known as oxygenates 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 tetraethyl lead and to increase its octane rating helping prevent engine knocking. Oxygenates help gasoline burn more completely, reducing tailpipe emissions from pre-1984 motor vehicles; dilutes or displaces gasoline components such as aromatics (e.g., benzene) and sulfur; and optimizes the oxidation during combustion. Most refiners chose MTBE over other oxygenates primarily for its blending characteristics and low cost.

Alternatives to MTBE as an anti-knock agent

Other compounds are available as additives for gasoline including ethanol and some ethers such as tert-amyl methyl ether (TAME).

Ethanol has been advertised as a safe alternative by the agricultural and other interest groups in the US and Europe. In 2003, California was the first US state to start replacing MTBE with ethanol. Several other states started switching soon thereafter.

Advocates of both sides of the debate in the US sometimes claim that gasoline manufacturers have been forced to add ethanol 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.

An alternative to straight ethanol is the related ether ETBE, which is manufactured from ethanol and isobutene. Its performance as an additive is similar to MTBE, but due to the higher price of ethanol compared to methanol, it is more expensive.

Higher quality gasoline is also an alternative, so that additives such as MTBE are unnecessary. Iso-octane itself is used. MTBE plants can be retrofitted to produce iso-octane from isobutylene.[3][4]

As a solvent

TBME is extensively used in industry as a safer alternative to diethyl ether (which is commonly used in academic research) as the tert-butyl group prevents TBME from forming potentially explosive peroxides. It is also used as a solvent in academic research,[5][6][7] although it is less commonly used than diethyl ether. Although an ether, MTBE is a poor Lewis base and does not support formation of Grignard reagents. It is also unstable toward strong acids. It reacts dangerously with bromine.[8]

MTBE forms azeotropes with water (52.6 °C; 96.5% MTBE)[9] and methanol (51.3 °C; 68.6% MTBE).[10]

A solvent for gallstones

In a procedure called contact dissolution therapy, MTBE is injected directly into the gallbladder to dissolve gallstones.[11][12]

Persistence and pervasiveness in the environment

MTBE gives water an unpleasant taste at very low concentrations, and thus can render large quantities of groundwater undrinkable. MTBE is often introduced into water-supply aquifers by leaking underground storage tanks (USTs) at gasoline stations or by gasoline containing MTBE spilled onto the ground. The higher water solubility and persistence of MTBE cause it to travel faster and farther than many other components of gasoline when released into an aquifer.[13][14]

MTBE is biodegraded by the action of bacteria. In the proper type of bioreactor, such as a fluidized bed bioreactor, MTBE can be rapidly and economically removed from water to undetectable levels. Activated carbon produced from coconut shells and optimized for MTBE adsorption may reduce MTBE to undetectable levels,[15] although this level of reduction is likely only in the most ideal circumstances. There are currently no known published cases of any in-situ treatment method which has been capable of reducing contaminant concentrations to baseline (pre-development) conditions within the aquifer soil matrix itself.

According to the IARC, a cancer research agency of the World Health Organization, MTBE is not classified as a human carcinogen. MTBE can be tasted in water at concentrations of 5 – 15 µg/l.[16]

As of 2007, researchers have limited data about the health effects of ingestion of MTBE. The United States Environmental Protection Agency (EPA) has concluded that available data are inadequate to quantify health risks of MTBE at low exposure levels in drinking water, but the data support the conclusion that MTBE is a potential human carcinogen at high doses.[17]

Legislation and litigation in the U.S.

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Main article: MTBE controversy

MTBE removal from groundwater and soil contamination in the U.S. is estimated to cost from $1 billion[18] to $30 billion,[19] including removing the compound from aquifers and municipal water supplies and replacing leaky underground oil tanks. 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.[20] In another case, the City of New York estimated a $250 million cost for cleanup of a single wellfield in Queens, NY.[21] More recently, a jury awarded the State of New Hampshire $236 million in damages[22] in order to treat groundwater contaminated by MTBE.

MTBE is banned in the US states of California and New York, starting January 1, 2004. As of September 2005, twenty-five states had signed legislation banning MTBE. (A table of state by state information, as of 2007, is available at the United States Department of Energy website.[23])

In 2000, the U.S. 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 U.S. House of Representatives, 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, then chairman of the Energy and Commerce Committee.[24] This bill did include a provision that gives MTBE makers, including some major oil companies, $2 billion in transition assistance while MTBE was phased out over the next nine years.[25] Due to opposition in the Senate,[26] the conference report dropped all MTBE provisions. The final bill was passed by both houses and signed into law by President Bush.[27] The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive.

The U.S. EPA currently lists MTBE as a candidate for a maximum contaminant level (MCL) in drinking water.[28] MCLs are determined by the EPA using toxicity data.

See also

References

  1. ↑ 1.0 1.1 Record in the GESTIS Substance Database of the IFA
  2. ↑ M. Winterberg, E. Schulte-Korne, U. Peters, F. Nierlich "Methyl Tert-Butyl Ether" in Ullmann's Encyclopedia of Industrial Chemistry, 2010, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_543.pub2
  3. ↑ http://www.nesteengineering.com/default.asp?path=111,360,362,477 Archived January 6, 2006 at the Wayback Machine
  4. ↑ http://www.halliburton.com/kbr/hydroChem/petroChem/nexoctane.jsp[dead link]
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Zeon Corporation
  10. ↑ CRC Handbook of Chemistry and Physics, 90th edition
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ http://www.handpmg.com/lustline31-mtbe-or-benzene.htm
  14. ↑ San Francisco Bay Area Regional Water Quality Control Board Integrated Basin Management Plan (2004)
  15. ↑ link text
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ http://www.epa.gov/mtbe/faq.htm#concerns
  18. ↑ SIGMA - Weekly Report
  19. ↑ Long Island Utility Fighting to Defeat MTBE Safe Harbor - Napoli Bern - Attorneys
  20. ↑ AmeriScan: February 17, 2005
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Website U.S. Department of Energy
  24. ↑ http://www.cnn.com/2005/POLITICS/04/21/energy.bill.mtbe.ap/
  25. ↑ http://www.msnbc.msn.com/id/7574562/+MTBE&hl=en
  26. ↑ 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).
  27. ↑ http://thomas.loc.gov/cgi-bin/bdquery/z?d109:h.r.00006:
  28. ↑ CCL 2 List

External links

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