Crotonic acid

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Crotonic acid
Skeletal formula of crotonic acid
Ball-and-stick model of the crotonic acid molecule
Preferred IUPAC name
(2E)-But-2-enoic acid
Other names
(E)-But-2-enoic acid
(E)-2-Butenoic acid
Crotonic acid
trans-2-Butenoic acid
beta-Methylacrylic acid
3-Methylacrylic acid
3D model (JSmol)
ECHA InfoCard 100.003.213
Molar mass 86.09 g·mol−1
Density 1.02 g/cm3
Melting point 70 to 73 °C (158 to 163 °F; 343 to 346 K)
Boiling point 185 to 189 °C (365 to 372 °F; 458 to 462 K)
Acidity (pKa) 4.69 [1]
Safety data sheet
Related compounds
Other anions
propionic acid
acrylic acid
butyric acid
succinic acid
malic acid
tartaric acid
fumaric acid
pentanoic acid
tetrolic acid
Related compounds
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

Crotonic acid ((2E)-but-2-enoic acid) or is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. It is also called crotonic acid because it was erroneously thought to be a saponification product of croton oil.[2] It crystallizes as needles from hot water. The cis-isomer of crotonic acid is called isocrotonic acid.


Crotonic acid may be obtained by several methods:

Oxidation von Crotonaldehyd
Darstellung von Crotonsäure durch Knoevenagel-Kondensation von Acetaldehyd und Malonsäure
Alkalische Hydrolyse von Allylcyanid
Synthese von Crotonsäure aus 3-Hydroxybutansäure


Crotonic acid acid crystallizes in long needles or as large panels in the monoclinic crystal system in the space group P21/a (space group no. 14, position 3) with the lattice parameters a = 971 pm, b = 690 pm, c = 775 pm and β = 104.0°. The unit cell contains four formula units.[8] The compound is soluble in water and many organic solvents such as ethanol, acetone or toluene. Its odor is similar to butanoic acid and irritates eyes, skin and respiratory system.[9]


Crotonic acid can be converted into butanoic acid by hydrogenation with zinc and sulfuric acid.[10]

Hydration of butenoic acid

It forms with elemental chlorine or bromine 2,3-dihalogenbutanoic acids:[10]

Chlorination of butenoic acid

The electrophilic addition of hydrogen bromide forms 3-bromobutanoic acid.[10][11] The substitution pattern arises from the electron-withdrawing effect of the carboxyl group. The carbenium ion is more stable at position 3, this is where the bromine anion attaches.

Reaction of butenoic acid with hydrogen bromide.

The reaction with alkaline potassium permanganate solution affords 2,3-dihydroxybutanoic acid.[10]

Reaction of butenoic acid with alkaline potassium permanganate solution.

Heating with acetic anhydride leads to (E)-2-butenoic-anhydride:[12]

The esterification of crotonic acid with methanol or ethanol using sulfuric acid as a catalyst provides the corresponding esters:

Preparation of butenoic esters.

Butenoic reacts with hypochlorous acid to 2-chloro-3-hydroxybutanoic acid. This can either be reduced with sodium amalgam to butanoic acid, can form with sulfuric acid 2-chlorobutenoic acid, react with hydrogen chloride to 2,3-dichlorobutenoic acid or with potassium ethoxide to 3-methyloxirane-2- carboxylic acid.[13]

Reaction of butenoic acid to  2-chloro-3-hydroxybutanoic acid and subsequent reactions


Crotonic acid is used for the preparation of (racemic) DL-threonine by alpha-functionalization using mercury(II) acetate.[14] For the production of plastics, it may be copolymerized with vinyl acetate.[9]

Crotonyl chloride reacts with N-ethyl-2-methylaniline (N-ethyl-o-toluidine) to provide crotamiton, which is used as an agent against scabies.[15]

Crotamiton synthesis

See also[edit]


  1. ^ Dawson, R. M. C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ Wikisource Chisholm, Hugh, ed. (1911). "Crotonic Acid". Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 511. 
  3. ^ Hans Beyer und Wolfgang Walter: Organische Chemie, S. Hirzel Verlag, Stuttgart 1984, ISBN 3-7776-0406-2, S. 230.
  4. ^ Hans Beyer und Wolfgang Walter: Organische Chemie, S. Hirzel Verlag, Stuttgart 1984, ISBN 3-7776-0406-2, S. 229–230.
  5. ^ A. Rinne, B. Tollens: "Ueber das Allylcyanür oder Crotonitril", in: Justus Liebigs Annalen der Chemie, 1871, 159 (1), S. 105–109; doi:10.1002/jlac.18711590110.
  6. ^ C. Pomeranz: "Ueber Allylcyanid und Allylsenföl", in: Justus Liebigs Annalen der Chemie, 1906, 351, S. 354–362; doi:10.1002/jlac.19073510127.
  7. ^ F. Beilstein: "Handbuch der organischen Chemie", 3. Auflage, 1. Band. Verlag Leopold Voss, 1893. S. 506 (Volltext).
  8. ^ S. Shimizu, S. Kekka, S. Kashino, M. Haisa: "Topochemical Studies. III. The Crystal and Molecular Structures of Crotonic Acid, CH3CH=CHCOOH, and Crotonamide, CH3CH=CHCONH2", in: Bulletin of the Chemical Society of Japan, 1974, 47 (7), S. 1627–1631.
  9. ^ a b Eintrag zu Butensäure. In: Römpp Online. Georg Thieme Verlag, retrieved on March 10, 2014.
  10. ^ a b c d Heilbron: Dictionary of organic compounds, Volume One, 1953, S. 615 (Fulltext).
  11. ^ J. M. Lovén, H. Johansson: "Einige schwefelhaltige β-Substitutionsderivate der Buttersäure", in: Berichte der deutschen chemischen Gesellschaft, 1915, 48 (2), S. 1254–1262; doi:10.1002/cber.19150480205.
  12. ^ A. M. Clover, G. F. Richmond: "The Hydrolysis of Organic Peroxides and Peracids", in: American Chemical Journal, 1903, 29 (3); S. 179–203 (Fulltext).
  13. ^ F. Beilstein: "Handbuch der organischen Chemie", 3. Auflage, 1. Band. Verlag Leopold Voss, 1893. S. 562 (Volltext).
  14. ^ Carter, H. E.; West, H. D. (1955). "dl-Threonine". Organic Syntheses. ; Collective Volume, 3, p. 813 
  15. ^ A. Kleemann u. J. Engel: Pharmazeutische Wirkstoffe: Synthesen, Patente, Anwendungen, 2. neubearb. u. erw. Aufl., Band 5, Georg Thieme Verlag Stuttgart, New York, ISBN 3-13-558402-X, S. 251.