Crotonic acid
- (E )-2- butenoic acid
- (E)- β -methyl acrylic acid
- Trans - crotonic
White to yellowish crystalline needles with sharp odor
Fixed
1.02 g · cm -3
71.6 ° C
185 ° C
4.69
6.2 g · l-1 in water (20 ° C)
1.4249 (77 ° C)
Risk
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Crotonic acid, also known as trans-2- butenoic acid, a short chain unsaturated carboxylic acid. The crotonic acid owes its name to the croton oil, it was wrongly assumed that crotonic acid produced by hydrolysis of croton oil. Crotonic forms needle-like crystals. The cis isomer of crotonic acid isocrotonic acid is mentioned. The salts of crotonic acid are called crotonates.
Production and representation
Crotonic acid may be obtained by oxidation of crotonaldehyde.
By Knoevenagel condensation with malonic acid in pyridine solution of acetaldehyde produced crotonic acid.
In the alkaline hydrolysis of allyl cyanide formed by intramolecular rearrangement of the double bond also crotonic acid.
Crotonic acid is also produced from the distillation of 3- hydroxybutanoic acid.
Properties
Crotonic acid crystallizes in long needles or as large panels in the monoclinic crystal system, space group P21 / a with lattice parameters a = 971 pm, b = 690 pm, c = 775 pm, and β = 104.0 °. In the unit cell contains four formula units. The compound is soluble in water and many organic solvents such as ethanol, acetone or toluene. She has a comparable butyric odor and irritates the eyes, skin and respiratory system.
Reactions
Crotonic acid may be converted into butyric acid by hydrogenation with zinc and sulfuric acid.
With elemental chlorine or bromine to form the corresponding 2,3 - Dihalogenbutansäuren.
In the electrophilic addition of hydrogen bromide to 3- bromobutyric acid forms. Substitution results from the direction of the electron- withdrawing effect of the carboxyl group, which has the result that the more stable carbonium ion is formed at the position 3, which attaches to the bromine.
The reaction of crotonic acid with alkaline potassium permanganate solution gives 2,3- dihydroxybutanoic.
By boiling with acetic anhydride crotonic whose boiling point is at 248 ° C is produced.
The esterification of crotonic acid with methanol or ethanol with sulfuric acid as catalyst affords the corresponding esters, their boiling points at 118-120 ° C ( methyl crotonate ) or 142-143 ° C ( ethyl crotonate ) lie.
Crotonic acid reacts with hypochlorous acid to form 2- chloro-3- hydroxybutyric acid, which is reduced with sodium amalgam to butyric acid, together with sulfuric acid 2- Chlorcrotonsäure, combines with hydrogen chloride to 2,3- Dichlorbuttersäure, as well as with potassium ethoxide for 3- methyl oxirane -2- carboxylic acid is reacted.
Use
Crotonic acid used for the preparation of retinol and DL- threonine. For the production of plastics can be copolymerized with vinyl acetate.
Crotonic react with N-ethyl- 2-methylaniline ( N-ethyl -o-toluidine ), the N -ethyl -o- crotonotoluidin (INN: crotamiton ), which is used as a means for scabies mite ( scabies ).