Phenylacetic acid

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Phenylacetic acid
Structural formula
Ball-and-stick model
IUPAC name
Phenylacetic acid
103-82-2 YesY
ChEBI CHEBI:30745 YesY
ChemSpider 10181341 YesY
Jmol interactive 3D Image
Molar mass 136.15 g/mol
Density 1.0809 g/cm3
Melting point 76 to 77 °C (169 to 171 °F; 349 to 350 K)
Boiling point 265.5 °C (509.9 °F; 538.6 K)
15 g/L
Acidity (pKa) 4.31[1]
Safety data sheet External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phenylacetic acid (abr. PAA and synonyms are: α-toluic acid, benzeneacetic acid, alpha tolylic acid, 2-phenylacetic acid, β-phenylacetic acid) is an organic compound containing a phenyl functional group and a carboxylic acid functional group. It is a white solid with a disagreeable odor. Because it is used in the illicit production of phenylacetone (used in the manufacture of substituted amphetamines), it is subject to controls in countries including the United States and China.[2]


Phenylacetic acid has been found to be an active auxin (a type of plant hormone),[3] found predominantly in fruits. However, its effect is much weaker than the effect of the basic auxin molecule indole-3-acetic acid. In addition the molecule is naturally produced by the metapleural gland of most ant species and used as an antimicrobial. It is also the oxidation product of phenethylamine in humans following metabolism by monoamine oxidase and subsequent metabolism of the intermediate product, phenylacetaldehyde, by the aldehyde dehydrogenase enzyme; these enzymes are also found in many other organisms.


This compound may be prepared by the hydrolysis of benzyl cyanide:[4][5]

Synthesis of phenylacetic acid from benzyl cyanide.png
Phenylacetic acid


Phenylacetic acid is used in some perfumes, possessing a honey-like odor in low concentrations, and is also used in penicillin G production. It is also employed to treat type II hyperammonemia to help reduce the amounts of ammonia in a patient's bloodstream by forming phenylacetyl-CoA, which then reacts with nitrogen-rich glutamine to form phenylacetylglutamine. This compound is then secreted by the patient's body. It's also used in the illicit production of phenylacetone (used in the manufacture of meth/amphetamine)

See also[edit]


  1. ^ Dippy, J. F. J.; Hughes, S. R. C.; Rozanski, A. (1959). "The dissociation constants of some symmetrically disubstituted succinic acids". Journal of the Chemical Society 1959: 2492–2498. doi:10.1039/JR9590002492. 
  2. ^ "List of Regulated Drug Precursor Chemicals in China". Retrieved 27 April 2015. 
  3. ^ Wightman, F.; Lighty, D. L. (1982). "Identification of phenylacetic acid as a natural auxin in the shoots of higher plants". Physiologia Plantarum 55 (1): 17–24. doi:10.1111/j.1399-3054.1982.tb00278.x. 
  4. ^ Adams R.; Thal, A. F. (1922). "Phenylacetic acid". Org. Synth. 2: 59. ; Coll. Vol. 1, p. 436 
  5. ^ Wenner, W. (1952). "Phenylacetamide". Org. Synth. 32: 92. ; Coll. Vol. 4, p. 760