Methyl tert-butyl ether From Wikipedia, the free encyclopedia
Methyl tert-butyl ether
IUPAC name[hide] 2-Methoxy-2-methylpropane Other names[hide] Methyl tertiary-butyl ether; Methyl tert-butyl ether; Methyl t-butyl ether; MTBE; tert-Butyl methyl ether; tBME; tert-BuOMe Identifiers CAS number
1634-04-4
PubChem
15413
ChemSpider
14672
KEGG
C11344
ChEBI
CHEBI:27642
Jmol-3D images
Image 1 SMILES
[show]
InChI [show]
Properties Molecular formula
C5H12O
Molar mass
88.15 g mol−1
Density
0.7404 g/cm³
Melting point
-109 °C, 164 K, -164 °F
Boiling point
55.2 °C, 328 K, 131 °F
Solubility in water
26 g/L (20 °C)[1] Hazards
NFPA 704
3 1 0 −10 °C (14 °F)
Flash point
(verify) (what is: / ?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references Methyl tert-butyl ether, also known as methyl tertiary butyl ether and MTBE, is anorganic 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 agasoline 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 ingroundwater 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 which are less subject to ethanol subsidies.[2]
Contents [hide]
1 Production and properties 2 Uses o 2.1 As anti-knocking agent 2.1.1 Alternatives to MTBE as an anti-knock agent o 2.2 As a solvent 3 Persistence and pervasiveness in the environment 4 Health risks
5 Legislation and litigation in the U.S. 6 See also 7 References 8 External links
Production and properties[edit] 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 ornatural 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[edit] 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 theoxygen content of gasoline.
As anti-knocking agent[edit] In the US it has been used in gasoline at low levels since 1979 to replace tetraethyl leadand 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[edit] 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 USA and Europe. It has been proposed that as a polar solvent, ethanol may separate nonpolar hydrocarbons from the gasoline, a problem that MTBE does appear to cause. Some volatile hydrocarbons in gasoline vapors are carcinogens, and gasoline vapors produce photochemical smog. In 2003, California was the first U.S. state to start replacing MTBE with ethanol. Several other states started switching soon thereafter. 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.
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, 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.[3],[4]
As a solvent[edit] As a solvent, MTBE possesses one distinct advantage over most ethers - it has a reduced tendency to form explosive organic peroxides. Opened bottles of diethyl ether or 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), MTBE 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 with some exceptions. [5] MTBE forms azeotropes with water (52.6 °C; 96.5% MTBE).[6] and methanol (51.3 °C; 68.6% MTBE).[7] 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]
