Mandelic acid

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Mandelic acid[1]
Structural formula of mandelic acid
Ball-and-stick model of the mandelic acid molecule
IUPAC name
2-Hydroxy-2-phenylacetic acid
Other names
Mandelic acid
Phenylglycolic acid
α-Hydroxyphenylacetic acid
90-64-2 YesY
611-71-2 (R) YesY
17199-29-0 (S) YesY
ChEBI CHEBI:35825 YesY
ChemSpider 1253 YesY
EC Number 202-007-6
Jmol interactive 3D Image
PubChem 1292
RTECS number OO6300000
Molar mass 152.15 g·mol−1
Appearance White crystalline powder
Density 1.30 g/cm3
Melting point 119 °C (246 °F; 392 K) optically pure: 132 to 135 °C (270 to 275 °F; 405 to 408 K)
Boiling point 321.8 °C (611.2 °F; 595.0 K)
15.87 g/100 mL
Solubility soluble in diethyl ether, ethanol, isopropanol
Acidity (pKa) 3.41[2]
0.1761 kJ/g
ATC code B05CA06
Flash point 162.6 °C (324.7 °F; 435.8 K)
Related compounds
Related compounds
mandelonitrile, phenylacetic acid, vanillylmandelic acid
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

Mandelic acid is an aromatic alpha hydroxy acid with the molecular formula C6H5CH(OH)CO2H. It is a white crystalline solid that is soluble in water and polar organic solvents. It is a useful precursor to various drugs. Since the molecule is chiral, it exists in either of two enantiomers as well as the racemic mixture, known as paramandelic acid.

Isolation, synthesis, occurrence[edit]

Mandelic acid was discovered while heating amygdalin, an extract of bitter almonds, with diluted hydrochloric acid. The name is derived from the German "Mandel" for "almond". Derivatives of mandelic acid are formed as a result of metabolism of adrenaline and noradrenaline by monoamine oxidase and catechol-O-methyl transferase.

Mandelic acid is usually prepared by the acid-catalysed hydrolysis of mandelonitrile,[3] which is the cyanohydrin of benzaldehyde. Mandelonitrile can also be prepared by reacting benzaldehyde with sodium bisulfite to give the corresponding adduct, forming mandelonitrile with sodium cyanide, which is hydrolyzed:[4]

Preparation of mandelic acid.png

Alternatively, it can be prepared by base hydrolysis of phenylchloroacetic acid and dibromacetophenone.[5] It also arises by heating phenylglyoxal with alkalis.

It arises from the biodegradation of styrene, as detected in urine.[6]


Mandelic acid has a long history of use in the medical community as an antibacterial, particularly in the treatment of urinary tract infections.[7] It has also been used as an oral antibiotic, and as a component of "chemical face peels", along with other alpha-hydroxy acids (AHAs).

The drugs cyclandelate and homatropine are esters of mandelic acid.


  1. ^ Merck Index, 11th Edition, 5599.
  2. ^ Bjerrum, J., et al. Stability Constants, Chemical Society, London, 1958.
  3. ^ Edwin Ritzer and Rudolf Sundermann "Hydroxycarboxylic Acids, Aromatic" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a13_519
  4. ^ Corson, B. B.; Dodge, R. A.; Harris, S. A.; Yeaw, J. S. (1941). "Mandelic Acid". Org. Synth. ; Coll. Vol. 1, p. 336 
  5. ^ J. G. Aston, J. D. Newkirk, D. M. Jenkins, and Julian Dorsky (1952). "Mandelic Acid". Org. Synth. ; Coll. Vol. 3, p. 538 
  6. ^ Engström K, Härkönen H, Kalliokoski P, Rantanen J. "Urinary mandelic acid concentration after occupational exposure to styrene and its use as a biological exposure test" Scand. J. Work Environ. Health. 1976, volume 2, pp. 21-6.
  7. ^ Putten, P. L. (1979). "Mandelic acid and urinary tract infections". Antonie van Leeuwenhoek 45 (4): 622. doi:10.1007/BF00403669.