Crotonic acid
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 460108491
| Name = Crotonic acid
| ImageFile = Crotonic acid.svg
| ImageSize = 160px
| ImageAlt = Skeletal formula of crotonic acid
| ImageFile1 = Crotonic acid 3D ball.png
| ImageAlt1 = Ball-and-stick model of the crotonic acid molecule
| PIN = (2E)-But-2-enoic acid
| OtherNames = (E)-But-2-enoic acid
(E)-2-Butenoic acid
Crotonic acid
trans-2-Butenoic acid
β-Methylacrylic acid
3-Methylacrylic acid
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 552744
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1213528
| PubChem = 637090
| InChI = 1/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+
| InChIKey = LDHQCZJRKDOVOX-NSCUHMNNBH
| SMILES1 = O=C(O)/C=C/C
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C4H6O2/c1-2-3-4(5)6/h2-3H,1H3,(H,5,6)/b3-2+
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = LDHQCZJRKDOVOX-NSCUHMNNSA-N
| CASNo_Ref = {{cascite|changed|??}}
| CASNo = 107-93-7
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 41131
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = YW5WZZ4O5Q
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB02074
| SMILES = C/C=C/C(O)=O
}}
|Section2={{Chembox Properties
| C=4|H=6|O=2
| Density = 1.02 g/cm3
| MeltingPtC = 70 to 73
| MeltingPt_notes =
| BoilingPtC = 185 to 189
| BoilingPt_notes =
}}
|Section3={{Chembox Hazards
| ExternalSDS = [http://siri.org/msds/mf/cards/file/0423.html SIRI.org]
}}
|Section4={{Chembox Related
| OtherAnions = crotonate
| OtherFunction_label = carboxylic acids
| OtherFunction = propionic acid
acrylic acid
butyric acid
succinic acid
malic acid
tartaric acid
fumaric acid
pentanoic acid
tetrolic acid
| OtherCompounds = butanol
butyraldehyde
crotonaldehyde
2-butanone
}}
}}
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.{{Cite EB1911|wstitle=Crotonic Acid|volume=7|page=511}} 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.
Production
Crotonic acid produced industrially by oxidation of crotonaldehyde:{{cite book|first1=Hans|last1=Beyer|first2=Wolfgang|last2=Walter|title=Organische Chemie|language=de|publisher=S. Hirzel Verlag|location=Stuttgart|date=1984|isbn=3-7776-0406-2}}{{rp|230}}
:{{chem2|CH3CH\dCHCHO + 1/2 O2 -> CH3CH\dCHCO2H}}
A number of other methods exist, including the Knoevenagel condensation of acetaldehyde with malonic acid in pyridine:{{rp|229}}
:File:Synthesis Crotonic acid A.svg
The alkaline hydrolysis of allyl cyanide followed by the intramolecular rearrangement of the double bond:{{cite journal|first1=A.|last1=Rinne|author2-link=Bernhard Tollens|first2=B.|last2=Tollens|title=Ueber das Allylcyanür oder Crotonitril|trans-title=On allyl cyanide or crotononitrile|journal=Justus Liebigs Annalen der Chemie|date=1871|volume=159|issue=1|pages=105–109|doi=10.1002/jlac.18711590110|url=https://zenodo.org/record/1427303}}{{cite journal|first1=C.|last1=Pomeranz|title=Ueber Allylcyanid und Allylsenföl|trans-title=On allyl cyanide and allylic mustard oil|journal=Justus Liebigs Annalen der Chemie|date=1906|volume=351|issue=1–3|pages=354–362|doi=10.1002/jlac.19073510127|url=https://zenodo.org/record/1427569}}
:File:Hydrolysis Allyl cyanide.svg
Furthermore, it is formed during the distillation of 3-hydroxybutyric acid:{{cite book|first1=F.|last1=Beilstein|title=Handbuch der organischen Chemie|language=de|edition=3rd|volume=1|publisher=Verlag Leopold Voss|date=1893|page=506|url=http://www26.us.archive.org/stream/handbuchderorgan00beil#page/506/mode/2up}}
Properties
Crotonic acid crystallizes in the monoclinic crystal system in the space group P21/a (space group 14, position 3) with the lattice parameters {{nowrap|a {{=}} 971 pm}}, {{nowrap|b {{=}} 690 pm}}, {{nowrap|c {{=}} 775 pm}} and {{nowrap|β {{=}} 104.0°}}. The unit cell contains four formula units.{{cite journal|first1=S.|last1=Shimizu|first2=S.|last2=Kekka|first3=S.|last3=Kashino|first4=M.|last4=Haisa|title=Topochemical Studies. III. The Crystal and Molecular Structures of Crotonic Acid, CH3CH=CHCO2H, and Crotonamide, CH3CH=CHCONH2|journal=Bulletin of the Chemical Society of Japan|date=1974|volume=47|issue=7|pages=1627–1631|doi=10.1246/bcsj.47.1627|doi-access=free}}
Reactions
Crotonic acid converts into butyric acid by hydrogenation or by reduction with zinc and sulfuric acid.{{cite journal|last1=Heilbron|journal=Dictionary of Organic Compounds|title=Crotonic acid|volume=1|date=1953|page=615|url=https://archive.org/stream/dictionaryoforga011095mbp#page/n633/mode/2up}}
:File:Hydration Crotonic acid.svg
Upon treatment with chlorine or bromine, crotonic acid converts to 2,3-dihalobutyric acids:
:File:Chlorination Crotonic acid.svg
Crotonic acid adds hydrogen bromide to form 3-bromobutyric acid.{{cite journal|first1=J. M.|last1=Lovén|first2=H.|last2=Johansson|title=Einige schwefelhaltige β-Substitutionsderivate der Buttersäure|trans-title=Some sulfur-containing β-substitution derivatives of butyric acid|journal=Berichte der deutschen chemischen Gesellschaft|date=1915|volume=48|issue=2|pages=1254–1262|doi=10.1002/cber.19150480205|url=https://zenodo.org/record/1426589}}
:File:Hydrobromination Crotonic acid.svg
The reaction with alkaline potassium permanganate solution affords 2,3-dihydroxybutyric acid.
:File:Oxidation Crotonic acid.svg
Upon heating with acetic anhydride, crotonic acid converts to the acid anhydride:{{cite journal|first1=A. M.|last1=Clover|first2=G. F.|last2=Richmond|title=The Hydrolysis of Organic Peroxides and Peracids|journal=American Chemical Journal|date=1903|volume=29|issue=3|pages=179–203|url=https://archive.org/stream/americanchemical291903balt#page/178/mode/2up}}
Esterification of crotonic acid using sulfuric acid as a catalyst provides the corresponding crotonate esters:
:File:Synthesis Ethyl crotonate.svg
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.{{cite book|first1=F.|last1=Beilstein|title=Handbuch der organischen Chemie|edition=3rd|volume=1|language=de|publisher=Verlag Leopold Voss|date=1893|page=562|url=http://www26.us.archive.org/stream/handbuchderorgan00beil#page/562/mode/2up}}
:File:Crotonic acid Reaction B.svg
Crotonic acid reacts with ammonia at the alpha position in the presence of mercury(II) acetate. This reaction provides threonine.{{OrgSynth|last1=Carter|first1=H. E.|last2=West|first2=H. D.|title=dl-Threonine|collvol=3|collvolpages=813|year=1955|prep=cv3p0813}}
Use
Crotonic acid is mainly used as a comonomer with vinyl acetate. The resulting copolymers are used in paints and adhesives.
Crotonyl chloride reacts with N-ethyl-2-methylaniline (N-ethyl-o-toluidine) to provide crotamiton, which is used as an agent against scabies.{{cite book|first1=A.|last1=Kleemann|first2=J.|last2=Engel|title=Pharmazeutische Wirkstoffe: Synthesen, Patente, Anwendungen|edition=2nd rev. and updated|volume=5|publisher=Georg Thieme Verlag|location=Stuttgart & New York|isbn=3-13-558402-X|page=251}}
Safety
Its {{LD50}} is 1 g/kg (oral, rats).{{Ullmann|first1=R. P.|last1=Schulz|first2=J.|last2=Blumenstein|first3=C.|last3=Kohlpaintner|title=Crotonaldehyde and Crotonic Acid|year=2005|doi=10.1002/14356007.a08_083}} It irritates eyes, skin, and respiratory system.{{RömppOnline|ID=RD-02-03102|Name=Butensäuren|Datum=January 7, 2020}}