Phenylpropanoic acid or hydrocinnamic acid is a

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 ...

with the formula C₉H₁₀O₂ belonging to the class of

phenylpropanoids 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 ...

. It is a white, crystalline solid with a sweet, floral scent at room temperature. Phenylpropanoic acid has a wide variety of uses including cosmetics,

food additives Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives have been used for centuries as part of an effort to preserve food, for example vinegar (pickling), salt (salt ...

, and pharmaceuticals.

Preparation and reactions

Phenylpropanoic acid can be prepared from

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. Classified as an unsaturated carboxylic acid, it occurs n ...

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

. Originally it was prepared by reduction with

sodium amalgam Sodium amalgam, commonly denoted Na(Hg), is an alloy of mercury and sodium. The term amalgam is used for alloys, intermetallic compounds, and solutions (both solid solutions and liquid solutions) involving mercury as a major component. Sodium am ...

in water and by

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

. A characteristic reaction of phenylpropanoic acid is its cyclization to 1-indanone. When the side chain is homologated by the

Arndt–Eistert reaction In organic chemistry, the Arndt–Eistert reaction is the conversion of a carboxylic acid to its homologue. Named for the German chemists Fritz Arndt (1885–1969) and Bernd Eistert (1902–1978), the method entails treating an acid ...

, subsequent cyclization affords

2-tetralone 2-Tetralone is an organic chemical compound with the molecular formula C10H10O. This colourless oil is an intermediate in organic synthesis. It is a ketone derivative of tetralin, a hydrogenated derivative of naphthalene. A related compound ...

, derivatives.

Uses

Phenylpropanoic acid is widely used for flavoring, food additives, spices, fragrance, and medicines as it acts as a fixative agent, or a

preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...

Food industry

Phenylpropanoic acid is used in the food industry to preserve and maintain the original aroma quality of frozen foods. It can also be used to add or restore original color to food. Shelved foods are protected from

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

by adding phenylpropanoic acid to prevent deterioration to the food by microorganisms as well as acting as an

antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

to prolong shelf life foods. This compound is used as a sweetener as well to sweeten food and can be found in table top sweeteners. It can also act as an

emulsifier An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...

, to keep oil and water mixtures from separating. Phenylpropanoic acid is also added to food for technological purposes in a wide variety including manufacturing, processing, preparation, treatment, packaging, transportation or storage, and food additives. It also provides flavorings for ice cream, bakery, and

confectionery Confectionery is the art of making confections, which are food items that are rich in sugar and carbohydrates. Exact definitions are difficult. In general, however, confectionery is divided into two broad and somewhat overlapping categories ...

Cosmetics

This compound is used frequently in cosmetic products such as perfumes, bath gels, detergent powders, liquid detergents, fabric softeners, and soaps as it gives off a floral scent. The acid is commonly used as flavoring for toothpastes and mouthwashes in addition to providing floral scents and possible fruity, minty, spearmint, strawberry,

lychee Lychee (US: ; UK: ; ''Litchi chinensis''; ) is a Monotypic taxon, monotypic taxon and the sole member in the genus ''Litchi'' in the Sapindus, soapberry family, ''Sapindaceae''. It is a tropical tree native to Southeast and Southwest China (t ...

, and herbal flavorings.

References

{{reflist Phenyl alkanoic acids Phenylpropanoids Sweet-smelling chemicals