(E)-2-butenoic acid

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
β-Methylacrylic acid
3-Methylacrylic acid
3D model (JSmol)
ECHA InfoCard 100.003.213 Edit this at Wikidata
  • InChI=1S/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+ checkY
  • InChI=1/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+
  • C/C=C/C(O)=O
  • O=C(O)/C=C/C
Molar mass 86.090 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 SIRI.org
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) is a short-chain unsaturated carboxylic acid, described by the formula CH3CH=CHCO2H. It is called crotonic acid because it was erroneously thought to be a saponification product of croton oil.[2] It crystallizes as colorless needles from hot water. The cis-isomer of crotonic acid is called isocrotonic acid. Crotonic acid is soluble in water and many organic solvents. Its odor is similar to butyric acid.


Crotonic acid may be obtained by several methods:

Oxidation of crotonaldehyde
Synthesis of crotonic acid by the Knoevenagel condensation of acetaldehyde and malonic acid
Alkaline hydrolysis of allyl cyanide
Synthesis of crotonic acid from 3-hydroxybutyric acid


Crotonic acid crystallizes in the monoclinic crystal system in the space group P21/a (space group 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.[7]


Crotonic acid converts into butyric acid by hydrogenation or by reduction with zinc and sulfuric acid.[8]

Hydrogenation of crotonic acid

Upon treatment with chlorine or bromine, crotonic acid converts to 2,3-dihalobutyric acids:[8]

Chlorination of butenoic acid

Crotonic acid adds hydrogen bromide to form 3-bromobutyric acid.[8][9]

Reaction of crotonic acid with hydrogen bromide.

The reaction with alkaline potassium permanganate solution affords 2,3-dihydroxybutyric acid.[8]

Reaction of crotonic acid with alkaline potassium permanganate solution.

Upon heating with acetic anhydride, crotonic acid converts to the acid anhydride:[10]

Esterification of crotonic acid using sulfuric acid as a catalyst provides the corresponding crotonate esters:

Preparation of crotonate esters.

Crotonic acid reacts with hypochlorous acid to 2-chloro-3-hydroxybutyric acid. This can either be reduced with sodium amalgam to butyric 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.[11]

Reaction of crotonic acid into 2-chloro-3-hydroxybutanoic acid and subsequent reactions

Crotonic acid reacts with ammonia at the alpha position in the presence of mercury(II) acetate. This reaction provides DL-threonine.[12]


Crotonic acid is mainly used as a comonomer with vinyl acetate.[13] The resulting copolymers are used in paints and adhesives.[14]

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


Its LD50 is 1 g/kg (oral, rats).[14] It irritates eyes, skin, and respiratory system.[13]

See also[]


  1. ^ Dawson, R. M. C.; et al. (1959). Data for Biochemical Research. Oxford: Clarendon Press.
  2. ^ Chisholm, Hugh, ed. (1911). "Crotonic Acid" . Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 511.
  3. ^ a b Beyer, Hans; Walter, Wolfgang (1984). Organische Chemie (in German). Stuttgart: S. Hirzel Verlag. ISBN 3-7776-0406-2.
  4. ^ Rinne, A.; Tollens, B. (1871). "Ueber das Allylcyanür oder Crotonitril" [On allyl cyanide or crotononitrile]. Justus Liebigs Annalen der Chemie. 159 (1): 105–109. doi:10.1002/jlac.18711590110.
  5. ^ Pomeranz, C. (1906). "Ueber Allylcyanid und Allylsenföl" [On allyl cyanide and allylic mustard oil]. Justus Liebigs Annalen der Chemie. 351 (1–3): 354–362. doi:10.1002/jlac.19073510127.
  6. ^ Beilstein, F. (1893). Handbuch der organischen Chemie (in German). 1 (3rd ed.). Verlag Leopold Voss. p. 506.
  7. ^ Shimizu, S.; Kekka, S.; Kashino, S.; Haisa, M. (1974). "Topochemical Studies. III. The Crystal and Molecular Structures of Crotonic Acid, CH3CH=CHCO2H, and Crotonamide, CH3CH=CHCONH2". Bulletin of the Chemical Society of Japan. 47 (7): 1627–1631. doi:10.1246/bcsj.47.1627.
  8. ^ a b c d Heilbron (1953). "Crotonic acid". Dictionary of Organic Compounds. 1: 615.
  9. ^ Lovén, J. M.; Johansson, H. (1915). "Einige schwefelhaltige β-Substitutionsderivate der Buttersäure" [Some sulfur-containing β-substitution derivatives of butyric acid]. Berichte der deutschen chemischen Gesellschaft. 48 (2): 1254–1262. doi:10.1002/cber.19150480205.
  10. ^ Clover, A. M.; Richmond, G. F. (1903). "The Hydrolysis of Organic Peroxides and Peracids". American Chemical Journal. 29 (3): 179–203.
  11. ^ Beilstein, F. (1893). Handbuch der organischen Chemie (in German). 1 (3rd ed.). Verlag Leopold Voss. p. 562.
  12. ^ Carter, H. E.; West, H. D. (1955). "dl-Threonine". Organic Syntheses.; Collective Volume, 3, p. 813
  13. ^ a b Entry on Butensäuren. at: Römpp Online. Georg Thieme Verlag, retrieved January 7, 2020.
  14. ^ a b Schulz, R. P.; Blumenstein, J.; Kohlpaintner, C. (2005). "Crotonaldehyde and Crotonic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_083.
  15. ^ Kleemann, A.; Engel, J. Pharmazeutische Wirkstoffe: Synthesen, Patente, Anwendungen. 5 (2nd rev. and updated ed.). Stuttgart & New York: Georg Thieme Verlag. p. 251. ISBN 3-13-558402-X.