Isobutyric acid

Isobutyric acid, also known as 2-methylpropanoic acid or isobutanoic acid, is a carboxylic acid with structural formula (CH3)2CHCOOH. It is an isomer of n-butyric acid. Deprotonation or esterification gives derivatives called isobutyrates.

Isobutyric acid[1][2]
Skeletal formula of isobutyric acid
Ball-and-stick model of the isobutyric acid molecule
Preferred IUPAC name
2-Methylpropanoic acid[3]
Other names
Isobutyric acid
2-Methylpropionic acid
Isobutanoic acid
3D model (JSmol)
ECHA InfoCard 100.001.087
EC Number
  • 201-195-7
RTECS number
  • NQ4375000
UN number 2529
Molar mass 88.11 g/mol
Density 0.9697 g/cm3 (0 °C)
Melting point −47 °C (−53 °F; 226 K)
Boiling point 155 °C (311 °F; 428 K)
Acidity (pKa) 4.86[4]
-56.06x10−6 cm3/mol
GHS pictograms GHS02: FlammableGHS05: CorrosiveGHS06: ToxicGHS07: Harmful
GHS Signal word Danger
H226, H301, H311, H314, H318, H335, H402, H412
P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P273, P280, P301+310, P301+330+331, P302+352, P303+361+353, P304+340, P305+351+338, P310, P312, P321, P322, P330, P361
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
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

Isobutyric acid is a colorless liquid with a somewhat unpleasant odor. It is soluble in water and organic solvents. It is found in the free state in carobs (Ceratonia siliqua), in vanilla, and in the root of Arnica dulcis, and as an ethyl ester in croton oil.[5]


Isobutyric acid is prepared by the oxidation of isobutyraldehyde, which is a byproduct of the hydroformylation of propylene.[6]

It can also be prepared by the high pressure hydrocarboxylation (Koch reaction) from propylene:[6]

CH3CH=CH2 + CO + H2O → (CH3)2CHCO2H

Niche methodsEdit

Many routes are known including the hydrolysis of isobutyronitrile with alkalis and the oxidation of isobutanol with potassium dichromate in the presence of sulfuric acid,[7] In the presence of proton donors, the action of sodium amalgam on methacrylic acid also gives isobutyric acid.[5]

Isobutyric acid can also be manufactured commercially using engineered bacteria using a sugar feedstock.[8]


When heated with a chromic acid solution it is oxidized to acetone. Alkaline potassium permanganate oxidizes it[5] to α-hydroxyisobutyric acid, (CH3)2C(OH)-CO2H.

Isobutyric acid is a retained trivial name under the IUPAC rules.[9]


  1. ^ Merck Index, 11th Edition, 5039
  2. ^ "Archived copy". Archived from the original on 2015-02-17. Retrieved 2015-03-13.CS1 maint: archived copy as title (link)
  3. ^ "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 748. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  4. ^ Bjerrum, J.; et al. (1958). Stability Constants. London: Chemical Society.
  5. ^ a b c Chisholm, Hugh, ed. (1911). "Butyric Acid" . Encyclopædia Britannica. 4 (11th ed.). Cambridge University Press. p. 892.
  6. ^ a b Riemenschneider, Wilhelm; Bolt, Hermann (2000). Esters, Organic. Ullmann's Encyclopedia of Industrial Chemistry. p. 10. doi:10.1002/14356007.a09_565. ISBN 978-3527306732.
  7. ^ I. Pierre and E. Puchot (1873). "New Studies on Valerianic Acid and its Preparation on a Large Scale". Ann. Chim. Phys. 28: 366.
  8. ^ "Biological pathways to produce methacrylate". Archived from the original on 2012-05-02. Retrieved 2011-10-07.
  9. ^ Panico R, Powell WH, Richer JC, eds. (1993). "Recommendation R-9.1". A Guide to IUPAC Nomenclature of Organic Compounds. IUPAC/Blackwell Science. ISBN 0-632-03488-2.