Crotonic 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 beta-Methylacrylic acid 3-Methylacrylic acid
Identifiers
CAS Number	107-93-7^N
3D model (Jmol)	Interactive image Interactive image
ChEBI	CHEBI:41131^Y
ChEMBL	ChEMBL1213528^Y
ChemSpider	552744^Y
DrugBank	DB02074^Y
ECHA InfoCard	100.003.213
PubChem	637090
UNII	YW5WZZ4O5Q^N
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	86.09 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 (pK_a)	4.69
Hazards
Safety data sheet	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
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 (what is ^YN ?)
Infobox references

Crotonic acid ((E)-2-butenoic 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. It crystallizes as needles from hot water. The cis-isomer of crotonic acid is called isocrotonic acid.

Crotonic acid acid may be obtained by several methods:

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. 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.

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

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

The electrophilic addition of hydrogen bromide forms 3-bromobutanoic acid. 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.

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

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

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

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