Gentisic acid

Gentisic acid is a dihydroxybenzoic acid. It is a derivative of benzoic acid and a minor (1%) product of the metabolic break down of aspirin, excreted by the kidneys.^[4]

Gentisic acid^[1]

Names
Preferred IUPAC name 2,5-Dihydroxybenzoic acid
Other names DHB 5-Hydroxysalicylic acid Gentianic acid Carboxyhydroquinone 2,5-Dioxybenzoic Acid Hydroquinonecarboxylic acid
Identifiers
CAS Number	490-79-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:17189 Y
ChEMBL	ChEMBL1461 Y
ChemSpider	3350 Y
ECHA InfoCard	100.007.017
KEGG	C00628 Y
PubChem CID	3469
UNII	VP36V95O3T Y
CompTox Dashboard (EPA)	DTXSID4060078
InChI InChI=1S/C7H6O4/c8-4-1-2-6(9)5(3-4)7(10)11/h1-3,8-9H,(H,10,11) Y Key: WXTMDXOMEHJXQO-UHFFFAOYSA-N Y InChI=1/C7H6O4/c8-4-1-2-6(9)5(3-4)7(10)11/h1-3,8-9H,(H,10,11) Key: WXTMDXOMEHJXQO-UHFFFAOYAO
SMILES O=C(O)c1cc(O)ccc1O
Properties[2]
Chemical formula	C7H6O4
Molar mass	154.121 g·mol−1
Appearance	white to yellow powder
Melting point	204 °C (399 °F; 477 K)
Solubility in water	very soluble
Solubility in ethanol	very soluble
Solubility in diethyl ether	very soluble
Solubility in acetone	soluble
Acidity (pKa)	2.97[3]
Related compounds
Related compounds	2,3-Dihydroxybenzoic acid 2,4-Dihydroxybenzoic acid 2,6-Dihydroxybenzoic acid 3,4-Dihydroxybenzoic acid 3,5-Dihydroxybenzoic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

It is also found in the African tree Alchornea cordifolia and in wine.^[5]

Production

Gentisic acid is produced by carboxylation of hydroquinone.^[6]

C₆H₄(OH)₂ + CO₂ → C₆H₃(CO₂H)(OH)₂

This conversion is an example of a Kolbe–Schmitt reaction.

Alternatively the compound can be synthesized from salicylic acid via Elbs persulfate oxidation.^[7][8]

Reactions

In the presence of the enzyme gentisate 1,2-dioxygenase and oxygen, gentisic acid undergoes a ring-opening reaction to give maleylpyruvate:^{[citation needed]}

C₇H₆O₄ + O₂ ⇌ C₇H₆O₆

Applications

As a hydroquinone, gentisic acid is readily oxidised and is used as an antioxidant excipient in some pharmaceutical preparations.^{[citation needed]}

In the laboratory, it is used as a sample matrix in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, and has been shown to conveniently detect peptides incorporating the boronic acid moiety by MALDI.^[9][10]