{{Chembox |Verifiedfields = changed |Watchedfields = changed |verifiedrevid = 476994181 |Name = Cinnamic acid |ImageFile = Zimtsäure - Cinnamic acid.svg |ImageName = Skeletal formula of trans-cinnamic acid |ImageClass = skin-invert |ImageFile1 = Cinnamic acid 3D ball.png |ImageName1 = Ball-and-stick model of the trans-cinnamic acid molecule |ImageClass1 = bg-transparent |ImageFile2 = Cinnamic acid.jpg |ImageName2 = Sample of the compound cinnamic acid in powder form |PIN = (2''E'')-3-Phenylprop-2-enoic acid |SystematicName = Cinnamic acid |OtherNames = ''trans''-Cinnamic acid<br>Phenylacrylic acid<ref>{{cite EB1911|wstitle=Cinnamic Acid|volume=6|page=376|short=1}}</ref><br>Cinnamylic acid<br>3-Phenylacrylic acid<br />(''E'')-Cinnamic acid<br>Benzenepropenoic acid<br>Isocinnamic acid |Section1={{Chembox Identifiers |IUPHAR_ligand = 3203 |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |ChemSpiderID = 392447 |ChEMBL_Ref = {{ebicite|correct|EBI}} |ChEMBL = 27246 |InChI = 1/C9H8O2/c10-9(11)7-6-8-4-2-1-3-5-8/h1-7H,(H,10,11)/b7-6+ |ChEBI_Ref = {{ebicite|correct|EBI}} |ChEBI = 35697 |SMILES = O=C(O)\C=C\c1ccccc1 |InChIKey = WBYWAXJHAXSJNI-VOTSOKGWBT |StdInChI_Ref = {{stdinchicite|correct|chemspider}} |StdInChI = 1S/C9H8O2/c10-9(11)7-6-8-4-2-1-3-5-8/h1-7H,(H,10,11)/b7-6+ |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |StdInChIKey = WBYWAXJHAXSJNI-VOTSOKGWSA-N |CASNo_Ref = {{cascite|correct|CAS}} |CASNo = 140-10-3 |UNII_Ref = {{fdacite|changed|FDA}} |UNII = U14A832J8D |PubChem = 444539 |KEGG_Ref = {{keggcite|correct|kegg}} |KEGG = C00423 |Gmelin = 3731 |Beilstein = 1905952 |EINECS = 205-398-1 |3DMet = B00108 }} |Section2={{Chembox Properties |C=9 | H=8 | O=2 |Appearance = White monoclinic crystals |Odor = Honey-like<ref name="flavornet.org">{{cite web|url=http://www.flavornet.org/info/140-10-3.html|title=Cinnamic acid|website=flavornet.org}}</ref> |Solubility = 500 mg/L<ref name="GESTIS-IOSH">{{GESTIS|ZVG=25910}}</ref> |Density = 1.2475 g/cm<sup>3</sup><ref name="GESTIS-IOSH"/> |MeltingPtC = 133 |MeltingPt_ref = <ref name="GESTIS-IOSH"/> |BoilingPtC = 300 |BoilingPt_ref = <ref name="GESTIS-IOSH"/> |pKa = 4.44 |MagSus = {{val|-7.836e-5|u=cm<sup>3</sup>/mol}} }} |Section3={{Chembox Hazards |NFPA-H = 1 |NFPA-F = 1 |NFPA-R = 0 |GHSPictograms = {{GHS07}} |GHSSignalWord = Warning |HPhrases = {{H-phrases|315|319|335}} |PPhrases = {{P-phrases|261|264|271|280|302+352|304+340|305+351+338|312|321|332+313|337+313|362|403+233|405|501}} |FlashPt = > |FlashPtC = 100 |FlashPt_ref = <ref name="GESTIS-IOSH"/> }} |Section4={{Chembox Related |OtherCompounds = Benzoic acid, Phenylacetic acid, Phenylpropanoic acid }} }}
'''Cinnamic acid''' is an organic compound with the formula C<sub>6</sub>H<sub>5</sub>−CH=CH−COOH. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents.<ref name="Merck-1996"/> Classified as an unsaturated carboxylic acid, it occurs naturally in a number of plants. It exists as both a ''cis'' and a ''trans'' isomer, although the latter is more common.<ref name="Garbe-2012"/> The ''cis''-isomer is called allocinnamic acid.
==Occurrence and production== ===Biosynthesis=== Cinnamic acid is a central intermediate in the biosynthesis of a myriad of natural products including lignols (precursors to lignin and lignocellulose), flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. Its biosynthesis involves the action of the enzyme phenylalanine ammonia-lyase (PAL) on phenylalanine.<ref>{{cite journal|journal=Molecular Plant|year=2010|volume=3|issue=1|pages=2–20|doi=10.1093/mp/ssp106|title=Phenylpropanoid Biosynthesis|last=Vogt|first=T.|pmid=20035037|doi-access=free}}</ref>
===Natural occurrence=== It is obtained from oil of cinnamon, or from balsams such as storax.<ref name="Merck-1996">{{Merck12th}}</ref> It is also found in shea butter.{{cn|date=June 2023}} Cinnamic acid has a honey-like odor;<ref name="flavornet.org">{{cite web|url=http://www.flavornet.org/info/140-10-3.html|title=Cinnamic acid|website=flavornet.org}}</ref> and its more volatile ethyl ester, ethyl cinnamate, is a flavor component in the essential oil of cinnamon, in which related cinnamaldehyde is the major constituent. It is also found in wood from many diverse tree species.<ref>{{cite web |last1=Oldach |first1=Laurel |title=Forensic researchers use mass spectrometry to identify smuggled wood |url=https://cen.acs.org/analytical-chemistry/mass-spectrometry/Forensic-researchers-use-mass-spectrometry-to-identify-smuggled-wood/101/i7 |website=Chemical and Engineering News |publisher=American Chemical Society |date=February 22, 2023}}</ref>
===Synthesis=== Cinnamic acid was first synthesized by the base-catalysed condensation of acetyl chloride and benzaldehyde, followed by hydrolysis of the acid chloride product.<ref name="Garbe-2012">{{Ullmann|first=Dorothea|last=Garbe|title=Cinnamic Acid|doi=10.1002/14356007.a07_099|year=2012}}</ref> In 1890, Rainer Ludwig Claisen described the synthesis of ethyl cinnamate via the reaction of ethyl acetate with benzaldehyde in the presence of sodium as base.<ref>{{cite journal|last=Claisen|first=L.|date=1890|url=https://babel.hathitrust.org/cgi/pt?id=uc1.b3481786;view=1up;seq=992|title=Zur Darstellung der Zimmtsäure und ihrer Homologen|trans-title=On the preparation of cinnamic acid and its homologues|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=23|pages=976–978|doi=10.1002/cber.189002301156}}</ref> Another way of preparing cinnamic acid is by the Knoevenagel condensation reaction.<ref>{{cite book|first=L.|last=Tieze|title=Reactions and Synthesis in the Organic Chemistry Laboratory|location=Mill Vall, CA|date=1988|page=1988}}</ref> The reactants for this are benzaldehyde and malonic acid in the presence of a weak base, followed by acid-catalyzed decarboxylation. It can also be prepared by oxidation of cinnamaldehyde, condensation of benzal chloride and sodium acetate (followed by acid hydrolysis), and the Perkin reaction. The oldest commercially used route to cinnamic acid involves the Perkin reaction, which is given in the following scheme<ref name="Garbe-2012"/> :[[File:Zimtsäure nach Perkin.svg|450px|center|thumb|Synthesis of cinnamic acid via the Perkin reaction.<ref>{{cite journal |doi=10.15227/orgsyn.005.0083|author=F. K. Thayer|title=''m''-Nitrocinnamic Acid|journal=Organic Syntheses|year=1925|volume=5|page=83}}</ref>]]
==Metabolism== Cinnamic acid, obtained from autoxidation of cinnamaldehyde, is metabolized into sodium benzoate in the liver.<ref name="Jana-2013">{{cite journal | vauthors = Jana A, Modi KK, Roy A, Anderson JA, van Breemen RB, Pahan K | title = Up-regulation of neurotrophic factors by cinnamon and its metabolite sodium benzoate: therapeutic implications for neurodegenerative disorders | journal = Journal of Neuroimmune Pharmacology | volume = 8 | issue = 3 | pages = 739–755 | date = June 2013 | pmid = 23475543 | pmc = 3663914 | doi = 10.1007/s11481-013-9447-7 | url = | issn = }}</ref>
==Uses== Cinnamic acid is used in flavorings, synthetic indigo, and certain pharmaceuticals. A major use is as a precursor to produce methyl cinnamate, ethyl cinnamate, and benzyl cinnamate for the perfume industry.<ref name="Merck-1996"/> Cinnamic acid is a precursor to the sweetener aspartame via enzyme-catalysed amination with phenylalanine.<ref name="Garbe-2012"/> Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.<ref>{{cite journal | doi = 10.1186/s13065-015-0080-9 | pmid = 25798191 | pmc = 4369286 | title = Determination of Abraham model solute descriptors for the monomeric and dimeric forms of ''trans''-cinnamic acid using measured solubilities from the Open Notebook Science Challenge | journal = Chemistry Central Journal | volume = 9 | article-number = 11 | year = 2015 | last1 = Bradley | first1 = J.-C. | last2 = Abraham | first2 = M. H. | last3 = Acree | first3 = W. E. | last4 = Lang | first4 = A. | last5 = Beck | first5 = S. N. | last6 = Bulger | first6 = D. A. | last7 = Clark | first7 = E. A. | last8 = Condron | first8 = L. N. | last9 = Costa | first9 = S. T. | last10 = Curtin | first10 = E. M. | last11 = Kurtu | first11 = S. B. | last12 = Mangir | first12 = M. I. | last13 = McBride | first13 = M. J. | doi-access = free }}</ref>
Cinnamic acid can be modified by substituting one or more fluorine atoms for hydrogen in the phenyl ring to form fluorocinnamic acid. Fluorocinnamic acid may be used in medicinal chemistry and functional materials. It can serve as an intermediate in the synthesis of pharmaceuticals and agrochemicals.<ref>{{cite web |title=3-Fluorocinnamic acid |url=https://www.chemimpex.com/products/45436 |publisher=Chem-Impex International |access-date=23 February 2026}}</ref>
==References== {{Reflist|30em}}
{{Hydroxycinnamic acid}}
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Category:Flavors Category:Enoic acids Category:Phenylpropanoids