Cinnamic acid

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Cinnamic acid
Skeletal formula of cinnamic acid
Ball-and-stick model of the cinnamic acid molecule
Sample of compound
Preferred IUPAC name
(2E)-3-Phenylprop-2-enoic acid
Other names
Cinnamic acid
trans-Cinnamic acid
Phenylacrylic acid[1]
Cinnamylic acid
3-Phenylacrylic acid
(E)-Cinnamic acid
Benzenepropenoic acid
Isocinnamic acid
3D model (JSmol)
ECHA InfoCard 100.004.908
Molar mass 148.16 g·mol−1
Appearance White monoclinic crystals
Density 1.2475 g/cm3[2]
Melting point 133 °C (271 °F; 406 K)[2]
Boiling point 300 °C (572 °F; 573 K)[2]
500 mg/L[2]
Acidity (pKa) 4.44
-78.36·10−6 cm3/mol
Irritant (Xi)
R-phrases (outdated) R36
S-phrases (outdated) S25
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point > 100 °C (212 °F; 373 K)[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cinnamic acid is an organic compound with the formula C6H5CHCHCO2H. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents.[3] 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.[4]

Occurrence and production[edit]

Natural occurrence[edit]

It is obtained from oil of cinnamon, or from balsams such as storax.[5] It is also found in shea butter. Cinnamic acid has a honey-like odor;[6] it and its more volatile ethyl ester (ethyl cinnamate) are flavor components in the essential oil of cinnamon, in which related cinnamaldehyde is the major constituent. Cinnamic acid is also part of the biosynthetic shikimate and phenylpropanoid pathways. Its biosynthesis is performed by action of the enzyme phenylalanine ammonia-lyase (PAL) on phenylalanine.


The original synthesis of cinnamic acid involves the Perkin reaction, which entails the base-catalysed condensation of acetic anhydride and benzaldehyde. Rainer Ludwig Claisen (1851–1930) described the synthesis of cinnamate esters by the reaction of benzaldehyde and esters.[7] The reaction is known as the Aldol condensation (with accompanying hydrolysis of the anhydride).

Synthesis of cinnamic acid via Perkin reaction

It can also be prepared from cinnamaldehyde and benzal chloride.[4]

Another way of preparing Cinnamic acid is by the Knövenaegel–Hans condensation reaction.[8] The reactants for this are the corresponding benzaldehyde and malonic acid in the presence of a weak base, followed by acid hydrolysis.


Cinnamic acid is used in flavors, synthetic indigo, and certain pharmaceuticals. A major use is in the manufacturing of the methyl, ethyl, and benzyl esters for the perfume industry.[5] Cinnamic acid is a precursor to the sweetener aspartame via enzyme-catalysed amination to phenylalanine.[4] Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.[9]


  1. ^ Wikisource-logo.svg "Cinnamic Acid". Encyclopædia Britannica. 6 (11th ed.). 1911. p. 376. 
  2. ^ a b c d e Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ^ "Open Notebook Science Challenge: Solubilities of Organic Compounds in Organic Solvents". Nature Precedings. 2010. doi:10.1038/npre.2010.4243.3. 
  4. ^ a b c Dorothea Garbe "Cinnamic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, 2000, Wiley-VCH, Weinheim. doi:10.1002/14356007.a07_099
  5. ^ a b Budavari, Susan, ed. (1996), The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (12th ed.), Merck, ISBN 0911910123 
  6. ^ Cinnamic acid,
  7. ^ Claisen, L. (1890) "Zur Darstellung der Zimmtsäure und ihrer Homologen" (On the preparation of cinnamic acid and its homologues), Berichte der deutschen chemischen Gesellschaft, 23 : 976–978.
  8. ^ L. Tieze, Reactions and Synthesis in the Organic Chemistry Laboratory, Mill Vall, California, 1988, p. 1988.
  9. ^ J-C Bradley et al., “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”, Chemistry Central Journal 9:11 (2015)