Formula C4H6O2 Boiling point 184.7 °C | Molar mass 86.09 g/mol Density 1.02 g/cm³ | |
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Crotonic acid meaning
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.
Contents
What does crotonic acid mean
Production
Crotonic acid acid may be obtained by several methods:
Properties
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.
Reactions
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:
Butenoic reacts with hypochlorous acid to 2-chloro-3-hydroxybutanoic acid. This can either be reduced with sodium amalgam to butanoic 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.
Use
Crotonic acid is used for the preparation of (racemic) DL-threonine by alpha-functionalization using mercury(II) acetate. For the production of plastics, it may be copolymerized with vinyl acetate.
Crotonyl chloride reacts with N-ethyl-2-methylaniline (N-ethyl-o-toluidine) to provide crotamiton, which is used as an agent against scabies.