Butanol (also calledbutyl alcohol) is a four-carbonalcohol with aformula ofC4H9OH, which occurs in fiveisomeric structures (four structural isomers), from a straight-chainprimary alcohol to a branched-chain tertiary alcohol;[1] all are abutyl orisobutyl group linked to ahydroxyl group (sometimesrepresented asBuOH,sec-BuOH,i-BuOH, andt-BuOH). These are1-butanol, twostereoisomers ofsec-butyl alcohol,isobutanol andtert-butyl alcohol. Butanol is primarily used as asolvent and as an intermediate inchemical synthesis, and may be used as afuel. Biologically produced butanol is calledbiobutanol, which may ben-butanol or isobutanol.
The unmodified termbutanol usually refers to thestraight chain isomer with the alcoholfunctional group at the terminal carbon, which is also known as1-butanol. The straight chain isomer with the alcohol at an internal carbon issec-butyl alcohol or2-butanol. The branched isomer with the alcohol at a terminal carbon isisobutanol or 2-methyl-1-propanol, and the branched isomer with the alcohol at the internal carbon istert-butyl alcohol or 2-methyl-2-propanol.
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| 1-Butanol (n-butanol) | 2-Butanol (sec-butyl alcohol) | Isobutanol (2-methylpropan-1-ol) | tert-butyl alcohol (2,2-methylethanol) |
The butanol isomers have different melting and boiling points. 1-Butanol and isobutanol have limited solubility,sec-butyl alcohol has substantially greater solubility, whereastert-butyl alcohol ismiscible with water. The hydroxyl group makes the molecule polar, promoting solubility in water, while the longer hydrocarbon chain mitigates the polarity and reduces solubility.
Butanol exhibits a low order of toxicity in single dose experiments with laboratory animals[2][3] and is considered safe enough for use in cosmetics. Brief, repeated overexposure with the skin can result indepression of the central nervous system, as with othershort-chain alcohols. Exposure may also cause severe eye irritation and moderate skin irritation. The main dangers are from prolonged exposure to the alcohol's vapors. In extreme cases this includes suppression of thecentral nervous system and even death. Under most circumstances, butanol is quickly metabolized tocarbon dioxide. It has not been shown todamage DNA or causecancer.
Butanol is used as asolvent for a wide variety of chemical and textile processes, in organic synthesis, and as a chemical intermediate. It is also used as apaint thinner and a solvent in other coating applications where a relatively slow evaporating latent solvent is preferable, as with lacquers and ambient-cured enamels. It is also used as a component ofhydraulic andbrake fluids.[4]
A 50% solution of butanol in water has been used since the 20th century to retard the drying of fresh plaster infresco painting. The solution is usually sprayed on the wet plaster after the plaster has been trowelled smooth and extends the working period during which frescos can be painted up to 18 hours.[5]
Butanol is used in the synthesis of2-butoxyethanol. A major application for butanol is as a reactant withacrylic acid to producebutyl acrylate, a primary ingredient of water based acrylic paint.[6]
It is also used as a base forperfumes, but on its own has a highly alcoholic aroma.
Salts of butanol are chemical intermediates; for example,alkali metal salts oftert-butanol aretert-butoxides.
2-Methyl-2-butanol is a central nervous systemdepressant with a similar effect upon ingestion to ethanol. Case reports have been documented demonstrating its potential for abuse.[7]
Butanol (n-butanol or isobutanol) is a potentialbiofuel (butanol fuel).[8] Butanol at 85 percent concentration can be used in cars designed for gasoline (petrol) without any change to the engine (unlike 85% ethanol), and it contains more energy for a given volume than ethanol and almost as much as gasoline, and a vehicle using butanol would return fuel consumption more comparable to gasoline than ethanol. Butanol can also be added to diesel fuel to reduce soot emissions.[9] Photoautotrophic microorganisms, like cyanobacteria, can be engineered to produce 1-butanol indirectly from CO2 and water.[10]
Butanols are normally present infusel alcohol.
Since the 1950s, most butanol in theUnited States is produced commercially fromfossil fuels. The most common process starts withpropene (propylene), which is put through ahydroformylation reaction to formbutanal, which is then reduced withhydrogen to 1-butanol and/or 2-butanol.tert-butanol is derived fromisobutane as a co-product ofpropylene oxide production.
Butanol can also be produced byfermentation ofbiomass by bacteria. Prior to the 1950s,Clostridium acetobutylicum was used inindustrial fermentation to producen-butanol.
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