Cinnamic acid is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

with the formula C₆H₅-CH=CH- COOH. It is a white crystalline compound that is slightly

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

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 Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

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

and

lignocellulose Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of Biofuel, biofuels. It is composed of two kinds of carbohydrate polymers, c ...

flavonoids Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

, isoflavonoids,

coumarin Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by an unsaturated lactone ring , forming a second six-me ...

s, aurones, stilbenes,

catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...

, and

phenylpropanoid The phenylpropanoids are a diverse family of organic compounds that are biosynthesized by plants from the amino acids phenylalanine and tyrosine in the shikimic acid pathway. Their name is derived from the six-carbon, aromatic phenyl group and ...

s. Its

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

involves the action of the

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

phenylalanine ammonia-lyase The enzyme phenylalanine ammonia lyase (EC 4.3.1.24) catalysis, catalyzes the conversion of L-phenylalanine to ammonia and cinnamic acid, ''trans''-cinnamic acid.: :L-phenylalanine = ''trans''-cinnamate + NH3 Phenylalanine ammonia lyase (PAL) i ...

(PAL) on

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

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, biscuits, b ...

, or from

balsam Balsam is the resinous exudate (or sap) which forms on certain kinds of trees and shrubs. Balsam (from Latin ''balsamum'' "gum of the balsam tree," ultimately from a Semitic source such as ) owes its name to the biblical Balm of Gilead. Ch ...

s such as

storax Storax (; , ''stúrax''), often commercially sold as styrax, is a natural fragrant resin isolated from the wounded bark of ''Liquidambar orientalis'' Mill. (Asia Minor) and ''Liquidambar styraciflua'' L. (Eastern US, Mexico, Central America) (A ...

. It is also found in

shea butter Shea butter ( , , or ; ) is a fat (triglyceride; mainly oleic acid and stearic acid) extracted from the nut of the African shea tree ('' Vitellaria paradoxa''). It is ivory in color when raw and commonly dyed yellow with borututu root or ...

. Cinnamic acid has a

honey Honey is a sweet and viscous substance made by several species of 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 pl ...

-like odor; and its more volatile ethyl ester, ethyl cinnamate, is a flavor component in the essential oil of

, in which related

cinnamaldehyde Cinnamaldehyde is an organic compound with the formula or . 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 shikimate pathway ...

is the major constituent. It is also found in wood from many diverse tree species.

Synthesis

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

acetyl chloride Acetyl chloride () is an acyl chloride derived from acetic acid (). It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl. Synthesis On an ...

and

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

, followed by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of the

acid chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

product. In 1890, Rainer Ludwig Claisen described the synthesis of ethyl cinnamate via the reaction of

ethyl acetate Ethyl acetate commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This flammable, colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues, nail polish removers, ...

with benzaldehyde in the presence of

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

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 o ...

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 ...

. It can also be prepared by oxidation of

, condensation of

benzal chloride Benzal chloride is an organic compound with the formula C6H5CHCl2. This colourless liquid is a lachrymator and is used as a building block in organic synthesis. Preparation and usage Benzal chloride is produced by the free radical chlorination ...

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 :

Metabolism

Cinnamic acid, obtained from autoxidation of

, is metabolized into

sodium benzoate Sodium benzoate also known as benzoate of soda is the sodium salt of benzoic acid, widely used as a food preservative (with an E number of E211) and a pickling agent. It appears as a white crystalline chemical with the formula C6H5COONa. Pro ...

in the liver.

Uses

Cinnamic acid is used in flavorings, synthetic indigo, and certain

pharmaceutical Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the ...

s. A major use is as a precursor to produce methyl cinnamate, ethyl cinnamate, and benzyl cinnamate for the perfume industry. Cinnamic acid is a precursor to the sweetener

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

via enzyme-catalysed amination with

. Cinnamic acid can

dimerize In chemistry, dimerization is the process of joining two identical or similar Molecular entity, molecular entities by Chemical bond, bonds. The resulting bonds can be either strong or weak. Many symmetrical chemical species are described as dim ...

in non-polar solvents resulting in different linear free energy relationships.

References

{{Authority control Flavors Enoic acids Phenylpropanoids