Mandelic acid is an

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

alpha hydroxy acid with the molecular formula C₆H₅CH(OH)CO₂H. It is a white crystalline solid that is soluble in water and polar organic

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

s. It is a useful precursor to various drugs. The molecule is chiral. The racemic mixture is known as ''paramandelic acid''.

Isolation, synthesis, occurrence

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 Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

. The name is derived from the German "Mandel" for "almond". Mandelic acid is usually prepared by the acid-catalysed hydrolysis of

mandelonitrile In organic chemistry, mandelonitrile is the nitrile of mandelic acid, or the cyanohydrin derivative of benzaldehyde. Small amounts of mandelonitrile occur in the pits of some fruits. Occurrence Mandelonitrile is the aglycone part of the c ...

, which is the cyanohydrin of benzaldehyde.

Mandelonitrile In organic chemistry, mandelonitrile is the nitrile of mandelic acid, or the cyanohydrin derivative of benzaldehyde. Small amounts of mandelonitrile occur in the pits of some fruits. Occurrence Mandelonitrile is the aglycone part of the c ...

can also be prepared by reacting benzaldehyde with sodium bisulfite to give the corresponding adduct, forming

with

sodium cyanide Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its h ...

, which is hydrolyzed: : Alternatively, it can be prepared by base hydrolysis of phenylchloroacetic acid as well as dibromacetophenone. It also arises by heating phenylglyoxal with alkalis.

Biosynthesis

Mandelic acid is a substrate or product of several biochemical processes called the mandelate pathway. Mandelate racemase interconverts the two enantiomers via a pathway that involves cleavage of the alpha-CH bond. Mandelate dehydrogenase is yet another enzyme on this pathway. Mandelate also arises from trans- cinnamate via phenylacetic acid, which is hydroxylated. Phenylpyruvic acid is another precursor to mandelic acid. Derivatives of mandelic acid are formed as a result of metabolism of adrenaline and noradrenaline by monoamine oxidase and

catechol-O-methyl transferase Catechol-''O''-methyltransferase (COMT; ) is one of several enzymes that degrade catecholamines (neurotransmitters such as dopamine, epinephrine, and norepinephrine), catecholestrogens, and various drugs and substances having a catechol st ...

. The biotechnological production of 4-hydroxy-mandelic acid and mandelic acid on the basis of

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...

was demonstrated with a genetically modified yeast ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...

'', in which the hydroxymandelate synthase naturally occurring in the bacterium '' Amycolatopsis'' was incorporated into a wild-type strain of yeast, partially altered by the exchange of a gene sequence and expressed.Mara Reifenrath, Eckhard Boles: ''Engineering of hydroxymandelate synthases and the aromatic amino acid pathway enables de novo biosynthesis of mandelic and 4-hydroxymandelic acid with Saccharomyces cerevisiae.'' Metabolic Engineering 45, Januar 2018; S. 246-254. . It also arises from the biodegradation of styrene and ethylbenzene, as detected in urine.

Uses

Mandelic acid has a long history of use in the medical community as an antibacterial, particularly in the treatment of urinary tract infections. It has also been used as an oral antibiotic, and as a component of chemical face peels analogous to other alpha hydroxy acids. The drugs cyclandelate and homatropine are

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

s of mandelic acid.

References

* {{Authority control Alpha hydroxy acids Benzene derivatives