Cinnamic acid

Cinnamic acid is an organic compound with the formula C₆H₅-CH=CH-COOH. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents.^[4] 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.^[5]

Cinnamic acid

Skeletal formula of trans-cinnamic acid
Ball-and-stick model of the trans-cinnamic acid molecule
Sample of the compound cinnamic acid in powder form
Names
Preferred IUPAC name (2E)-3-Phenylprop-2-enoic acid
Systematic IUPAC name Cinnamic acid
Other names trans-Cinnamic acid Phenylacrylic acid[1] Cinnamylic acid 3-Phenylacrylic acid (E)-Cinnamic acid Benzenepropenoic acid Isocinnamic acid
Identifiers
CAS Number	140-10-3 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1905952
ChEBI	CHEBI:35697 Y
ChEMBL	ChEMBL27246 Y
ChemSpider	392447 Y
ECHA InfoCard	100.004.908
EC Number	205-398-1
Gmelin Reference	3731
IUPHAR/BPS	3203
KEGG	C00423 Y
PubChem CID	444539
UNII	U14A832J8D N
CompTox Dashboard (EPA)	DTXSID5022489
InChI InChI=1S/C9H8O2/c10-9(11)7-6-8-4-2-1-3-5-8/h1-7H,(H,10,11)/b7-6+ Y Key: WBYWAXJHAXSJNI-VOTSOKGWSA-N Y InChI=1/C9H8O2/c10-9(11)7-6-8-4-2-1-3-5-8/h1-7H,(H,10,11)/b7-6+ Key: WBYWAXJHAXSJNI-VOTSOKGWBT
SMILES O=C(O)\C=C\c1ccccc1
Properties
Chemical formula	C9H8O2
Molar mass	148.161 g·mol−1
Appearance	White monoclinic crystals
Odor	Honey-like[2]
Density	1.2475 g/cm3[3]
Melting point	133 °C (271 °F; 406 K)[3]
Boiling point	300 °C (572 °F; 573 K)[3]
Solubility in water	500 mg/L[3]
Acidity (pKa)	4.44
Magnetic susceptibility (χ)	−7.836×10−5 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)	1 1 0
Flash point	> 100 °C (212 °F; 373 K)[3]
Related compounds
Related compounds	Benzoic acid, Phenylacetic acid, Phenylpropanoic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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.^[6]

Natural occurrence

It is obtained from oil of cinnamon, or from balsams such as storax.^[4] It is also found in shea butter.^{[citation needed]} Cinnamic acid has a honey-like odor;^[2] 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.^[7]

Synthesis

Cinnamic acid was first synthesized by the base-catalysed condensation of acetyl chloride and benzaldehyde, followed by hydrolysis of the acid chloride product.^[5] 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.^[8] Another way of preparing cinnamic acid is by the Knoevenagel condensation reaction.^[9] 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^[5]

Synthesis of cinnamic acid via the Perkin reaction.^[10]

Metabolism

Cinnamic acid, obtained from autoxidation of cinnamaldehyde, is metabolized into sodium benzoate in the liver.^[11]

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.^[4] Cinnamic acid is a precursor to the sweetener aspartame via enzyme-catalysed amination with phenylalanine.^[5] Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.^[12]