Crotonic acid

Production

Crotonic acid produced industrially by oxidation of crotonaldehyde: :

A number of other methods exist, including the Knoevenagel condensation of acetaldehyde with malonic acid in pyridine:

:[[File:Synthesis Crotonic acid A.svg|upright=2.5|Synthesis of crotonic acid by the Knoevenagel condensation of acetaldehyde and malonic acid]]

The alkaline hydrolysis of allyl cyanide followed by the intramolecular rearrangement of the double bond:

:[[File:Hydrolysis Allyl cyanide.svg|upright=1.5|Alkaline hydrolysis of allyl cyanide]]

Furthermore, it is formed during the distillation of 3-hydroxybutyric acid:

:[[File:Synthesis Crotonic acid D.svg|upright=1.5|Synthesis of crotonic acid from 3-hydroxybutyric acid]]

Properties

Crotonic acid crystallizes in the monoclinic crystal system in the space group P21/a (space group 14, position 3) with the lattice parameters , , and . The unit cell contains four formula units.

Reactions

Crotonic acid converts into butyric acid by hydrogenation or by reduction with zinc and sulfuric acid. :[[File:Hydration Crotonic acid.svg|upright=1.5|Hydrogenation of crotonic acid]]

Upon treatment with chlorine or bromine, crotonic acid converts to 2,3-dihalobutyric acids: :[[File:Chlorination Crotonic acid.svg|upright=1.5|Chlorination of butenoic acid]]

Crotonic acid adds hydrogen bromide to form 3-bromobutyric acid.

:[[File:Hydrobromination Crotonic acid.svg|upright=1.5|Reaction of crotonic acid with hydrogen bromide.]]

The reaction with alkaline potassium permanganate solution affords 2,3-dihydroxybutyric acid. :[[File:Oxidation Crotonic acid.svg|upright=1.5|Reaction of crotonic acid with alkaline potassium permanganate solution.]]

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

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

:[[File:Synthesis Ethyl crotonate.svg|upright=1.5|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.

:[[File:Crotonic acid Reaction B.svg|upright=1.5|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 -threonine.

Use

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

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

:[[File:Crotamiton synthesis V.svg|none|550px|Crotamiton synthesis]]

Safety

Its is 1 g/kg (oral, rats). It irritates eyes, skin, and respiratory system.

References

References

1. Dawson, R. M. C.. (1959). "Data for Biochemical Research". Clarendon Press.
2. {{Cite EB1911
3. (1984). "Organische Chemie". S. Hirzel Verlag.
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6. (1893). "Handbuch der organischen Chemie". Verlag Leopold Voss.
7. (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.
8. (1953). "Crotonic acid". Dictionary of Organic Compounds.
9. (1915). "Einige schwefelhaltige β-Substitutionsderivate der Buttersäure". [[Berichte der deutschen chemischen Gesellschaft]].
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11. (1893). "Handbuch der organischen Chemie". Verlag Leopold Voss.
12. (1955). "''dl''-Threonine".
13. "Pharmazeutische Wirkstoffe: Synthesen, Patente, Anwendungen". Georg Thieme Verlag.
14. (2005). "Crotonaldehyde and Crotonic Acid".
15. {{RömppOnline