Crotonic acid
Chemical compound
From Wikipedia, the free encyclopedia
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.
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| Names | |
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| 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 | |
3D model (JSmol) |
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.003.213 |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| 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 3-Butenoic acid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Production
Crotonic acid produced industrially by oxidation of crotonaldehyde:[3][4]: 230
- CH3CH=CHCHO +1⁄2O2 → 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]
