Cinnamic acid is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
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, 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 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 biofuels. It is composed of two kinds of carbohydrate polymers, cellulose a ...
), 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 a lactone-like chain , forming a second six-membered h ...
s, 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, 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 phenylpropanoids. Its biosynthesis involves the action of the enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
phenylalanine ammonia-lyase
The enzyme phenylalanine ammonia lyase (EC 4.3.1.24) catalyzes the conversion of L-phenylalanine to ammonia and ''trans''-cinnamic acid.:
:L-phenylalanine = ''trans''-cinnamate + NH3
Phenylalanine ammonia lyase (PAL) is the first and committed ...
(PAL) on phenylalanine.
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 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 Semitic, Aramaic ''busma'', Arabic ''balsam'' and Hebrew ''basam'', "spice", "perfume ...
s such as storax
Storax ( la, storax; el, στύραξ, ''stúrax''), often commercially sold as styrax, is a natural resin isolated from the wounded bark of ''Liquidambar orientalis'' Mill. (Asia Minor) and '' Liquidambar styraciflua'' L. (Central America) (Ha ...
. It is also found in shea butter. 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
Ethyl cinnamate is the ester of cinnamic acid and ethanol. It is present in the essential oil of cinnamon. Pure ethyl cinnamate has a "fruity and balsamic odor, reminiscent of cinnamon with an amber note".
The ''p''-methoxy derivative is report ...
) are flavor components in the essential 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 ...
, 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 sh ...
is the major constituent.
Synthesis
Cinnamic acid was first synthesized by the base-catalysed condensation of acetyl chloride
Acetyl chloride (CH3COCl) 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 a ...
and benzaldehyde, 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, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolys ...
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
Rainer Ludwig Claisen (; 14 January 1851 – 5 January 1930) was a German chemist best known for his work with condensations of carbonyls and sigmatropic rearrangements. He was born in Cologne as the son of a jurist and studied chemistry at the u ...
described the synthesis of ethyl cinnamate
Ethyl cinnamate is the ester of cinnamic acid and ethanol. It is present in the essential oil of cinnamon. Pure ethyl cinnamate has a "fruity and balsamic odor, reminiscent of cinnamon with an amber note".
The ''p''-methoxy derivative is report ...
via the reaction of ethyl acetate
Ethyl acetate ( systematically ethyl ethanoate, commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues ...
with benzaldehyde in the presence of sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
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
Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid' ...
in the presence of a weak base, followed by acid-catalyzed decarboxylation. It can also be prepared by oxidation of 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 sh ...
, 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 o ...
and sodium acetate (followed by acid hydrolysis), and the Perkin reaction
The Perkin reaction is an organic reaction developed by English chemist William Henry Perkin that is used to make cinnamic acids. It gives an α,β-unsaturated aromatic acid or α-substituted β-aryl acrylic acid by the aldol condensation of a ...
. The oldest commercially used route to cinnamic acid involves the Perkin reaction
The Perkin reaction is an organic reaction developed by English chemist William Henry Perkin that is used to make cinnamic acids. It gives an α,β-unsaturated aromatic acid or α-substituted β-aryl acrylic acid by the aldol condensation of a ...
, which is given in the following scheme[
:]
Metabolism
Cinnamic acid, obtained from autoxidation of 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 sh ...
, is metabolized into sodium benzoate
Sodium benzoate 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.
Production
Sodium benzoate is commo ...
in the liver.
Uses
Cinnamic acid is used in flavorings, synthetic indigo, and certain pharmaceutical
A medication (also called medicament, medicine, pharmaceutical drug, 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 medical field and re ...
s. 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 ...
, ethyl cinnamate
Ethyl cinnamate is the ester of cinnamic acid and ethanol. It is present in the essential oil of cinnamon. Pure ethyl cinnamate has a "fruity and balsamic odor, reminiscent of cinnamon with an amber note".
The ''p''-methoxy derivative is report ...
, and benzyl cinnamate for the perfume industry.[ Cinnamic acid is a precursor to the sweetener aspartame via enzyme-catalysed amination to give phenylalanine.][ Cinnamic acid can ]dimerize
A dimer () ('' di-'', "two" + ''-mer'', "parts") is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular. Dimers also have significant implications in polymer chemistry, inorganic ch ...
in non-polar solvents resulting in different linear free energy relationships.
References
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Flavors
Enoic acids