Crotonic acid

Crotonic acid ((2E)-but-2-enoic acid) is a short-chain unsaturated carboxylic acid described by the formula CH₃CH=CHCO₂H. The name crotonic acid was given because it was erroneously thought to be a saponification product of croton oil.^[2] It crystallizes as colorless needles from hot water. With a cis-alkene, Isocrotonic acid is an isomer of crotonic acid. Crotonic acid is soluble in water and many organic solvents. Its odor is similar to that of butyric acid.

Crotonic acid

Names
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
Identifiers
CAS Number	107-93-7 N
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:41131 Y
ChEMBL	ChEMBL1213528 Y
ChemSpider	552744 Y
DrugBank	DB02074 Y
ECHA InfoCard	100.003.213
PubChem CID	637090
UNII	YW5WZZ4O5Q N
CompTox Dashboard (EPA)	DTXSID30880973
InChI InChI=1S/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+ Y Key: LDHQCZJRKDOVOX-NSCUHMNNSA-N Y InChI=1/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+ Key: LDHQCZJRKDOVOX-NSCUHMNNBH
SMILES C/C=C/C(O)=O O=C(O)/C=C/C
Properties
Chemical formula	C4H6O2
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]
Hazards
Safety data sheet (SDS)	SIRI.org
Related compounds
Other anions	crotonate
Related carboxylic acids	propionic acid acrylic acid butyric acid succinic acid malic acid tartaric acid fumaric acid pentanoic acid tetrolic acid
Related compounds	butanol butyraldehyde crotonaldehyde 2-butanone
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Production

Crotonic acid produced industrially by oxidation of crotonaldehyde:^{[3][4]: 230}

CH₃CH=CHCHO + 1/₂ O₂ → CH₃CH=CHCO₂H

A number of other methods exist, including the Knoevenagel condensation of acetaldehyde with malonic acid in pyridine:^[3]: 229

The alkaline hydrolysis of allyl cyanide followed by the intramolecular rearrangement of the double bond:^[5][6]

Furthermore, it is formed during the distillation of 3-hydroxybutyric acid:^[7]

Properties

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.^[8]

Reactions

Crotonic acid converts into butyric acid by hydrogenation or by reduction with zinc and sulfuric acid.^[9]

Upon treatment with chlorine or bromine, crotonic acid converts to 2,3-dihalobutyric acids:^[9]

Crotonic acid adds hydrogen bromide to form 3-bromobutyric acid.^[9][10]

The reaction with alkaline potassium permanganate solution affords 2,3-dihydroxybutyric acid.^[9]

Upon heating with acetic anhydride, crotonic acid converts to the acid anhydride:^[11]

Esterification of crotonic acid using sulfuric acid as a catalyst provides the corresponding 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.^[12]

Crotonic acid reacts with ammonia at the alpha position in the presence of mercury(II) acetate. This reaction provides DL-threonine.^[13]

Use

Crotonic acid is mainly used as a comonomer with vinyl acetate.^[14] The resulting copolymers are used in paints and adhesives.^[4]

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

Safety

Its LD₅₀ is 1 g/kg (oral, rats).^[4] It irritates eyes, skin, and respiratory system.^[14]

See also

• Crotyl
• Crotyl alcohol
• Isocrotonic acid
• Methacrylic acid