IUPAC name
Other names
Isobutyl alcohol, IBA, 2-methyl-1-propanol, 2-methylpropyl alcohol, Isopropylcarbinol
78-83-1 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:46645 YesY
ChEMBL ChEMBL269630 YesY
ChemSpider 6312 YesY
ECHA InfoCard 100.001.044
EC Number 201-148-0
KEGG C14710 YesY
PubChem 6560
RTECS number NP9625000
Molar mass 74.122 g/mol
Appearance Colorless liquid
Odor sweet, musty[2]
Density 0.802 g/cm3, liquid
Melting point −108 °C (−162 °F; 165 K)
Boiling point 107.89 °C (226.20 °F; 381.04 K)
8.7 mL/100 mL[3]
log P 0.8
Vapor pressure 9 mmHg (20°C)[2]
Viscosity 3.95 cP at 20 °C
Safety data sheet ICSC 0113
Irritant (Xi)
R-phrases R10 R37/38 R41, R67
S-phrases (S2) S7/9 S13 S26 S37/39 S46
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 28 °C (82 °F; 301 K)
415 °C (779 °F; 688 K)
Explosive limits 1.7–10.9%
Lethal dose or concentration (LD, LC):
3750 mg/kg (rabbit, oral)
2460 mg/kg (rat, oral)[4]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 100 ppm (300 mg/m3)[2]
REL (Recommended)
TWA 50 ppm (150 mg/m3)[2]
IDLH (Immediate danger)
1600 ppm[2]
Related compounds
Related butanols
Related compounds
Isobutyric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Isobutanol (IUPAC nomenclature: 2-methylpropan-1-ol) is an organic compound with the formula (CH3)2CHCH2OH (sometimes represented as i-BuOH). This colorless, flammable liquid with a characteristic smell is mainly used as a solvent. Its isomers, the other butanols, include n-butanol, 2-butanol, and tert-butanol, all of which are important industrially.


Isobutanol is produced by the carbonylation of propylene. Two methods are practiced industrially, hydroformylation is more common and generates a mixture of isobutyraldehydes, which are hydrogenated to the alcohols and then separated. Reppe carbonylation is also practiced.[5]

Biosynthesis of Isobutanol

Higher-chain alcohols have energy densities close to gasoline, are not as volatile or corrosive as ethanol, and do not readily absorb water. Furthermore, branched-chain alcohols, such as isobutanol, have higher-octane numbers, resulting in less knocking in engines. Although produced naturally during the fermentation of saccharides and may also be a byproduct of the decay process of organic matter, Isobutanol or C5 alcohols have never been produced from a renewable source with yields high enough to make them viable as a gasoline substitute before the 2008 Nature article that produced over 20g/L isobutanol from glucose in E.coli.[6]

To modify an organism to produce these compounds usually results in toxicity in the cell. This difficulty was bypassed by leveraging the native metabolic networks in E. coli but altered its intracellular chemistry using genetic engineering to produce these alcohols. Key pathways in E. coli were modified to produce several higher-chain alcohols from glucose, including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethanol. This strategy exploits the E. coli host's highly active amino acid biosynthetic pathway by shifting part of it to alcohol production. It is proposed that these unusual alcohols can be produced as efficiently as the biosynthesis of ethanol.[6]

Escherichia coli

Escherichia coli, or E. coli, is a Gram-negative, rod-shaped bacteria. E. coli is the microorganism most likely to move on to commercial production of isobutanol.[6][7] In its engineered form E. coli produces the highest yields of isobutanol of any microorganism.[6] Methods such as elementary mode analysis have been used to improve the metabolic efficiency of E. coli so that larger quantities of isobutanol may be produced.[8] E. coli is an ideal isobutanol bio-synthesizer for several reasons:

The primary drawback of E. coli is that it is susceptible to bacteriophages when being grown. This susceptibility could potentially shut down entire bioreactors.[7]


While cellulosic biomass like corn stover and switchgrass is abundant and cheap, it is much more difficult to utilize than corn and sugar cane. This is due in large part because of recalcitrance, or a plant's natural defenses to being chemically dismantled. Adding to the complexity is the fact biofuel production that involves several steps—pretreatment, enzyme treatment and fermentation—is more costly than a method that combines biomass utilization and the fermentation of sugars to biofuel into a single process.

To make the conversion possible, researchers had to develop a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, that could synthesize isobutanol directly from cellulose. This proof of concept research sets the stage for studies that will likely involve genetic manipulation of other consolidated bioprocessing microorganisms.[10]


Cyanobacteria, are a phylum of photosynthetic bacteria.[11] Cyanobacteria are suited for isobutanol biosynthesis when genetically engineered to produce isobutanol and its corresponding aldehydes.[12] Isobutanol producing species of cyanobacteria offer several advantages as biofuel synthesizers:

The primary drawbacks of Cyanobacteria are:

Bacillus subtilis

Bacillus subtilis is a gram-positive rod-shaped bacteria. Bacillus subtilis offers many of the same advantages and disadvantages of E. coli, but it is less prominently used and does not produce isobutanol in quantities as large as E. coli.[7] Similar to E. coli, Bacillus subtilis is capable of producing isobutanol from lignocellulose, and is easily manipulated by common genetic techniques.[7] Elementary mode analysis has also been used to improve the isobutanol-synthesis metabolic pathway used by Bacillus subtilis, leading to higher yields of isobutanol being produced.[16]

Saccharomyces cerevisiae

Saccharomyces cerevisiae, or S. cerevisiae is a species of yeast. S. cerevisiae naturally produces isobutanol in small quantities via its valine biosynthetic pathway.[17] S. cerevisiae is an ideal candidate for isobutanol biofuel production for several reasons:

Overexpression of the enzymes in the valine biosynthetic pathway of S. cerevisiae has been used to improve isobutanol yields.[17][18][19] S. cerevisiae, however, has proved difficult to work with because of its inherent biology:

Ralstonia eutropha

Ralstonia eutropha is a gram-negative soil bacterium of the betaproteobacteria class. Ralstonia eutropha is capable of converting electrical energy into isobutanol. This conversion is completed in several steps:

This method of isobutanol production offers a way to chemically store energy produced from sustainable sources.[20]


Isobutanol has a variety of technical and industrial applications:

Second-generation biofuel

Isobutanol can be used as a biofuel substitute for gasoline in the current petroleum infrastructure. Isobutanol has not yet been put into mainstream use as a biofuel and would serve as a replacement for ethanol. Ethanol is a first-generation biofuel, and is used primarily as a gasoline additive in the petroleum infrastructure. Isobutanol is a second-generation biofuel with several qualities that resolve issues presented by ethanol.[7]

Isobutanol's properties make it an attractive biofuel:[7]

Safety and regulation

Isobutanol is one of the least toxic of the butanols with an LD50 of 2460 mg/kg (rat, oral).

In March 2009, the Canadian government announced a ban on isobutanol use in cosmetics.[23]

See also


  1. 1 2 Isobutanol, International Chemical Safety Card 0113, Geneva: International Programme on Chemical Safety, April 2005.
  2. 1 2 3 4 5 "NIOSH Pocket Guide to Chemical Hazards #0352". National Institute for Occupational Safety and Health (NIOSH).
  3. "Iso-butanol". ChemicalLand21.
  4. "Isobutyl alcohol". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
  5. Hahn, Heinz-Dieter; Dämbkes, Georg; Rupprich, Norbert (2005), "Butanols", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a04_463.
  6. 1 2 3 4 Atsumi, Shota; Hanai, Taizo; Liao, James C. "Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels". Nature. 451 (7174): 86–89. doi:10.1038/nature06450.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Peralta-Yahya, Pamela P.; Zhang, Fuzhong; del Cardayre, Stephen B.; Keasling, Jay D.; Del Cardayre, Stephen B.; Keasling, Jay D. (15 August 2012). "Microbial engineering for the production of advanced biofuels". Nature. 488 (7411): 320–328. Bibcode:2012Natur.488..320P. doi:10.1038/nature11478. PMID 22895337.
  8. 1 2 Trinh, Cong T. (9 June 2012). "Elucidating and reprogramming Escherichia coli metabolisms for obligate anaerobic n-butanol and isobutanol production". Applied Microbiology and Biotechnology. 95 (4): 1083–1094. doi:10.1007/s00253-012-4197-7. PMID 22678028.
  9. 1 2 Nakashima, Nobutaka; Tamura, Tomohiro (1 July 2012). "A new carbon catabolite repression mutation of Escherichia coli, mlc∗, and its use for producing isobutanol". Journal of Bioscience and Bioengineering. 114 (1): 38–44. doi:10.1016/j.jbiosc.2012.02.029. PMID 22561880.
  10. Higashide, Wendy; Li, Yongchao; Yang, Yunfeng; Liao, James C. (2011-04-15). "Metabolic Engineering of Clostridium cellulolyticum for Production of Isobutanol from Cellulose". Applied and Environmental Microbiology. 77 (8): 2727–2733. doi:10.1128/AEM.02454-10. ISSN 0099-2240. PMC 3126361Freely accessible. PMID 21378054.
  11. Cyanobacteria
  12. Atsumi, Shota; Higashide, Wendy; Liao, James C. "Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde". Nature Biotechnology. 27 (12): 1177–1180. doi:10.1038/nbt.1586.
  13. 1 2 3 4 Machado, Iara M.P.; Atsumi, Shota (1 November 2012). "Cyanobacterial biofuel production". Journal of Biotechnology. 162 (1): 50–56. doi:10.1016/j.jbiotec.2012.03.005. PMID 22446641.
  14. 1 2 3 4 Varman, A. M.; Xiao, Y.; Pakrasi, H. B.; Tang, Y. J. (26 November 2012). "Metabolic Engineering of Synechocystis sp. Strain PCC 6803 for Isobutanol Production". Applied and Environmental Microbiology. 79 (3): 908–914. doi:10.1128/AEM.02827-12. PMID 23183979.
  15. 1 2 Singh, Nirbhay Kumar; Dhar, Dolly Wattal (11 March 2011). "Microalgae as second generation biofuel. A review". Agronomy for Sustainable Development. 31 (4): 605–629. doi:10.1007/s13593-011-0018-0.
  16. 1 2 Li, Shanshan; Huang, Di; Li, Yong; Wen, Jianping; Jia, Xiaoqiang (1 January 2012). "Rational improvement of the engineered isobutanol-producing Bacillus subtilis by elementary mode analysis". Microbial Cell Factories. 11 (1): 101. doi:10.1186/1475-2859-11-101.
  17. 1 2 Kondo, Takashi; Tezuka, Hironori; Ishii, Jun; Matsuda, Fumio; Ogino, Chiaki; Kondo, Akihiko (1 May 2012). "Genetic engineering to enhance the Ehrlich pathway and alter carbon flux for increased isobutanol production from glucose by Saccharomyces cerevisiae". Journal of Biotechnology. 159 (1–2): 32–37. doi:10.1016/j.jbiotec.2012.01.022. PMID 22342368.
  18. MATSUDA, Fumio; KONDO, Takashi; IDA, Kengo; TEZUKA, Hironori; ISHII, Jun; KONDO, Akihiko (1 January 2012). "Construction of an Artificial Pathway for Isobutanol Biosynthesis in the Cytosol of Saccharomyces cerevisiae". Bioscience, Biotechnology, and Biochemistry. 76 (11): 2139–2141. doi:10.1271/bbb.120420.
  19. Lee, Won-Heong; Seo, Seung-Oh; Bae, Yi-Hyun; Nan, Hong; Jin, Yong-Su; Seo, Jin-Ho (28 April 2012). "Isobutanol production in engineered Saccharomyces cerevisiae by overexpression of 2-ketoisovalerate decarboxylase and valine biosynthetic enzymes". Bioprocess and Biosystems Engineering. 35 (9): 1467–1475. doi:10.1007/s00449-012-0736-y. PMID 22543927.
  20. Li, H.; Opgenorth, P. H.; Wernick, D. G.; Rogers, S.; Wu, T.-Y.; Higashide, W.; Malati, P.; Huo, Y.-X.; Cho, K. M.; Liao, J. C. (29 March 2012). "Integrated Electromicrobial Conversion of CO2 to Higher Alcohols". Science. 335 (6076): 1596–1596. Bibcode:2012Sci...335.1596L. doi:10.1126/science.1217643.
  21. Lu, Jingnan; Brigham, Christopher J.; Gai, Claudia S.; Sinskey, Anthony J. (4 August 2012). "Studies on the production of branched-chain alcohols in engineered Ralstonia eutropha". Applied Microbiology and Biotechnology. 96 (1): 283–297. doi:10.1007/s00253-012-4320-9. PMID 22864971.
  22. Ting, Cindy Ng Wei; Wu, Jinchuan; Takahashi, Katsuyuki; Endo, Ayako; Zhao, Hua (8 September 2012). "Screened Butanol-Tolerant Enterococcus faecium Capable of Butanol Production". Applied Biochemistry and Biotechnology. 168 (6): 1672–1680. doi:10.1007/s12010-012-9888-0. PMID 22961352.
  23. "Cosmetic Chemicals Banned in Canada", Chem. Eng. News, 87 (11): 38, 2009-03-16.
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