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. Classified as an unsaturated

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

, it occurs naturally in a number of plants. It exists as both a ''cis'' and a ''trans'' isomer, although the latter is more common.

Occurrence and production

Biosynthesis

Cinnamic acid is a central intermediate in the biosynthesis of a myriad of natural products including lignols (precursors to

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

and lignocellulose), flavonoids,

isoflavonoids Isoflavonoids are a class of flavonoid phenolic compounds, many of which are biologically active. Isoflavonoids and their derivatives are sometimes referred to as phytoestrogens, as many isoflavonoid compounds have biological effects via the estro ...

, coumarins,

aurones An aurone is a heterocyclic chemical compound which is a type of flavonoid. There are two isomers of the molecule, with (''E'')- and (''Z'')-configurations. The molecule contains a benzofuran element associated with a benzylidene linked in posi ...

stilbenes Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are pro ...

, catechin, and

phenylpropanoid The phenylpropanoids are a diverse family of organic compounds that are synthesized by plants from the amino acids phenylalanine and tyrosine. Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of ...

s. Its

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

involves the action of the enzyme phenylalanine ammonia-lyase (PAL) on

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...

Natural occurrence

It is obtained from oil of

cinnamon Cinnamon is a spice obtained from the inner bark of several tree species from the genus ''Cinnamomum''. Cinnamon is used mainly as an aromatic condiment and flavouring additive in a wide variety of cuisines, sweet and savoury dishes, breakfa ...

, or from balsams such as storax. It is also found in

shea butter Shea butter (, , or ; ) is a fat extracted from yellow the nut of the African shea tree (''Vitellaria paradoxa''). It is ivory in color when raw and commonly dyed yellow with borututu root or palm oil. It is widely used in cosmetics as a moi ...

. Cinnamic acid has a

honey Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...

-like odor; it and its more volatile ethyl ester ( ethyl cinnamate) are flavor components in the essential oil of

, in which related

cinnamaldehyde Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the shik ...

is the major constituent.

Synthesis

Cinnamic acid was first synthesized by the base-catalysed condensation of acetyl chloride and

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...

, followed by hydrolysis of the acid chloride product. 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. Another way of preparing cinnamic acid is by the

Knoevenagel condensation In organic chemistry, the Knoevenagel condensation () reaction is a type of chemical reaction named after German chemist Emil Knoevenagel. It is a modification of the aldol condensation. A Knoevenagel condensation is a nucleophilic addition of ...

reaction. The reactants for this are benzaldehyde and malonic acid in the presence of a weak base, followed by acid-catalyzed

decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...

. It can also be prepared by oxidation of

, 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 : Zimtsäure nach Perkin

Metabolism

Cinnamic acid, obtained from autoxidation of

, is metabolized into sodium benzoate in the liver.

Uses

Cinnamic acid is used in flavorings, synthetic indigo, and certain pharmaceuticals. A major use is as a precursor to produce

methyl cinnamate Methyl cinnamate is the methyl ester of cinnamic acid and is a white or transparent solid with a strong, aromatic odor. It is found naturally in a variety of plants, including in fruits, like strawberry, and some culinary spices, such as Sichuan p ...

, ethyl cinnamate, and

benzyl cinnamate Benzyl cinnamate is the chemical compound which is the ester derived from cinnamic acid and benzyl alcohol. Natural occurrence Benzyl cinnamate occurs in Balsam of Peru and Tolu balsam, in Sumatra and Penang benzoin, and as the main constituen ...

for the perfume industry. Cinnamic acid is a precursor to the sweetener

aspartame Aspartame is an artificial non-saccharide sweetener 200 times sweeter than sucrose and is commonly used as a sugar substitute in foods and beverages. It is a methyl ester of the aspartic acid/phenylalanine dipeptide with the trade names ...

via enzyme-catalysed amination to give

. Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.

References

{{Authority control Flavors Enoic acids