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
3D model (Jmol)
ECHA InfoCard 100.001.825
EC Number 202-007-6
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
B05CA06 (WHO) J01XX06 (WHO)
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. The molecule is chiral. The racemic mixture is known as paramandelic acid.

Isolation, synthesis, occurrence[edit]

Mandelic acid was discovered in 1831 by the German pharmacist Ferdinand Ludwig Winckler (1801–1868) while heating amygdalin, an extract of bitter almonds, with diluted hydrochloric acid.[3] 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,[4] 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:[5]

Preparation of mandelic acid.png

Alternatively, it can be prepared by base hydrolysis of phenylchloroacetic acid and dibromacetophenone.[6] It also arises by heating phenylglyoxal with alkalis.[7][8]

It arises from the biodegradation of styrene, as detected in urine.[9]


Mandelic acid has a long history of use in the medical community as an antibacterial, particularly in the treatment of urinary tract infections.[10] It has also been used as an oral antibiotic, and as a component of "chemical face peels", along with other alpha-hydroxy acids (AHAs).

  1. The drugs cyclandelate and homatropine are esters of mandelic acid.
  2. Pemoline is synthesized by the condensation of the ethyl ester of mandelic acid with guanidine.
  3. Amolanone


  1. ^ Merck Index, 11th Edition, 5599.
  2. ^ Bjerrum, J., et al. Stability Constants, Chemical Society, London, 1958.
  3. ^ See:
  4. ^ 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
  5. ^ Corson, B. B.; Dodge, R. A.; Harris, S. A.; Yeaw, J. S. (1941). "Mandelic Acid". Org. Synth.  ; Coll. Vol., 1, p. 336 
  6. ^ J. G. Aston, J. D. Newkirk, D. M. Jenkins, and Julian Dorsky (1952). "Mandelic Acid". Org. Synth.  ; Coll. Vol., 3, p. 538 
  7. ^ Pechmann, H. von (1887). "Zur Spaltung der Isonitrosoverbindungen". Berichte der deutschen chemischen Gesellschaft. 20 (2): 2904–2906. doi:10.1002/cber.188702002156. 
  8. ^ Pechmann, H. von; Muller, Hermann (1889). "Ueber α-Ketoaldehyde". Berichte der deutschen chemischen Gesellschaft. 22 (2): 2556–2561. doi:10.1002/cber.188902202145. 
  9. ^ 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.
  10. ^ Putten, P. L. (1979). "Mandelic acid and urinary tract infections". Antonie van Leeuwenhoek. 45 (4): 622. doi:10.1007/BF00403669.