Cinnamic acid is an organic compound with the formula phenyl-CH=CH-Carboxylic acid. It is a white crystalline compound that is slightly soluble in water, and freely soluble in many organic solvents.
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,
,
aurones,
stilbenes,
catechin, and
. Its
biosynthesis involves the action of the
enzyme phenylalanine ammonia-lyase (PAL) on
phenylalanine.
Natural occurrence
It is obtained from oil of
cinnamon, or from
such as
storax.
It is also found in
shea butter. Cinnamic acid has a
honey-like odor;
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.
Synthesis
Cinnamic acid was first synthesized by the base-catalysed condensation of
acetyl chloride and
benzaldehyde, 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 reaction.
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
- .
Metabolism
Cinnamic acid, obtained from autoxidation of
cinnamaldehyde, is metabolized into
sodium benzoate in the liver.
Uses
Cinnamic acid is used in flavorings, synthetic indigo, and certain
. 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 via enzyme-catalysed amination with
phenylalanine.
Cinnamic acid can dimerize in non-polar solvents resulting in different linear free energy relationships.
