Mandelic acid is an

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

alpha hydroxy acid Alpha hydroxy carboxylic acids, or α-hydroxy carboxylic acids (AHAs), are a group of carboxylic acids featuring a hydroxy group located ''one'' carbon atom away from the acid group. This structural aspect distinguishes them from beta hydroxy aci ...

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

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

s. It is a useful precursor to various drugs. The molecule is

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

. The

racemic In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

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 Amygdalin (from Ancient Greek: ' 'almond') is a naturally occurring chemical compound found in many plants, most notably in the seeds (kernels, pips or stones) of apricots, bitter almonds, apples, peaches, cherries and plums, and in the roots ...

, an extract of bitter almonds, with diluted

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

. The name is derived from the

German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...

"Mandel" for "almond". Mandelic acid is usually prepared by the acid-catalysed hydrolysis of mandelonitrile, which is the

cyanohydrin In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is , where R is H, alkyl, or aryl. Cyanohyd ...

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful. It is a colorless liquid with a characteristic almond-li ...

. Mandelonitrile can also be prepared by reacting benzaldehyde with

sodium bisulfite Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite is not a real compound, but a mixture of salts that dissolve in water to give solutions compose ...

to give the corresponding adduct, forming mandelonitrile with

sodium cyanide Sodium cyanide is a compound with the formula Na C N and the structure . 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 expl ...

, which is then

hydrolyzed Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

: : Alternatively, it can be prepared by base

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of phenylchloroacetic acid as well as dibromacetophenone. It also arises by heating

phenylglyoxal Phenylglyoxal is the organic compound with the formula C6H5C(O)C(O)H. It contains both an aldehyde and a ketone functional group. It is yellow liquid when anhydrous but readily forms a colorless crystalline hydrate. It has been used as a reagen ...

with alkalis.

Biosynthesis

Mandelic acid is a substrate or product of several biochemical processes called the mandelate pathway.

Mandelate racemase Mandelate racemase () is a bacterial enzyme which catalyzes the interconversion of the enantiomers of mandelate via an enol intermediate. This enzyme catalyses the following chemical reaction : (S)-mandelate \rightleftharpoons (R)-mandelate It i ...

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 Phenylpyruvic acid is the organic compound with the formula C6H5CH2C(O)CO2H. It is a keto acid. Occurrence and properties The compound exists in equilibrium with its (''E'')- and (''Z'')-enol tautomers. It is a product from the oxidative deamin ...

is another precursor to mandelic acid. Derivatives of mandelic acid are formed as a result of metabolism of

adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

and

noradrenaline Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone, neurotransmitter and neuromodulator. The name "noradrenaline" (from ...

monoamine oxidase Monoamine oxidases (MAO) () are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group. They are found bound to the outer membrane of mitochondria in most cell types of the body. The fi ...

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 struc ...

. The

biotechnological Biotechnology is a multidisciplinary field that involves the integration of natural sciences and engineering sciences in order to achieve the application of organisms and parts thereof for products and services. Specialists in the field are kn ...

production of 4-hydroxy-mandelic acid and mandelic acid on the basis of

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

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 fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'', in which the hydroxymandelate synthase naturally occurring in the bacterium ''

Amycolatopsis ''Amycolatopsis'' is a genus of high GC-content bacteria within the family Pseudonocardiaceae. The genus is known for producing many types of antibiotics, including *Epoxyquinomicin, related to ''Amycolatopsis sulphurea'', are a class of weak ant ...

'' 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 Styrene is an organic compound with the chemical formula C6H5CH=CH2. Its structure consists of a vinyl group as substituent on benzene. Styrene is a colorless, oily liquid, although aged samples can appear yellowish. The compound evaporates easi ...

and

ethylbenzene Ethylbenzene is an organic compound with the formula . It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as a reaction intermediat ...

, 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

s. The drugs cyclandelate and

homatropine Homatropine (Equipin, Isopto Homatropine) is an anticholinergic medication that is an antagonist at muscarinic acetylcholine receptors and thus the parasympathetic nervous system. It is used in eye drops as a cycloplegic (to temporarily paral ...

are

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s of mandelic acid.

References

* {{Authority control Alpha hydroxy acids Phenylacetic acids

Isolation, synthesis, occurrence

Biosynthesis

Uses

See Also

References