4-Hydroxybenzoic acid

4-Hydroxybenzoic acid
IUPAC name 4-Hydroxybenzoic acid
Other names p-Hydroxybenzoic acid para-Hydroxybenzoic acid
Identifiers
CAS number	99-96-7 Y
PubChem	135
ChemSpider	132 Y
EC number	202-804-9
DrugBank	DB04242
KEGG	C00156 Y
ChEBI	CHEBI:30763 Y
ChEMBL	CHEMBL441343 Y
Jmol-3D images	Image 1 Image 2
SMILES O=C(O)c1ccc(O)cc1 c1cc(ccc1C(=O)O)O
InChI InChI=1S/C7H6O3/c8-6-3-1-5(2-4-6)7(9)10/h1-4,8H,(H,9,10) Y Key: FJKROLUGYXJWQN-UHFFFAOYSA-N Y InChI=1/C7H6O3/c8-6-3-1-5(2-4-6)7(9)10/h1-4,8H,(H,9,10) Key: FJKROLUGYXJWQN-UHFFFAOYAQ
Properties
Molecular formula	C7H6O3
Molar mass	138.121 g/mol
Appearance	white crystalline
Odor	odorless
Density	1.46 g/cm³
Melting point	214.5 °C; 418.1 °F; 487.6 K
Solubility in water	0.5 g/100 mL
Solubility	soluble in alcohol, ether, acetone slightly soluble in chloroform negligible in CS2
log P	1.58
Acidity (pKa)	4.54
Hazards
MSDS	HMDB
Main hazards	Irritant
NFPA 704	0 2 0
Autoignition temperature	250 °C; 482 °F; 523 K
LD50	2200 mg/kg (oral, mouse)
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

4-Hydroxybenzoic acid is a monohydroxybenzoic acid, a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble in polar organic solvents such as alcohols and acetone. 4-Hydroxybenzoic acid is primarily known as the basis for the preparation of its esters, known as parabens, which are used as preservatives in cosmetics and some ophthalmic solutions. It is isomeric with 2-hydroxybenzoic acid, known as salicylic acid, a precursor to aspirin.

Natural occurrences

Cryptanaerobacter phenolicus is a bacterium species that produces benzoate from phenol via 4-hydroxybenzoate.^[1]

p-Hydroxybenzoic acid glucoside can be found in mycorrhizal and non-mycorrhizal roots of Norway spruces (Picea abies).^[2]

Violdelphin is ananthocyanin, a type of plant pigments, found in blue flowers and incorporating two p-hydroxy benzoic acid residues, one rutinoside and two glucosides associated with a delphinidin.

Occurrences in food

4-Hydroxybenzoic acid can be found naturally in Cocos nucifera.^[3] It is one of the main catechins metabolites found in humans after consumption of green tea infusions.^[4] It is also found in wine^[5] and in vanilla.

Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), is rich in p-hydroxybenzoic acid (892 ± 52 mg/kg).^[6]

Chemical production

4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction.^[7] It can also be produced in the laboratory by heating potassium salicylate with potassium carbonate to 240 °C, followed by treating with acid.^[8]

Chemical reactions

4-Hydroxybenzoic acid has about one tenth the acidity of benzoic acid, having an acid dissociation constant K_a = 3.3 x 10⁻⁵ M at 19 °C.^{[citation needed]} Its acid dissociation follows this equation:

HOC₆H₄CO₂H HOC₆H₄CO₂⁻ + H⁺

Safety

4-Hydroxybenzoic acid is a popular antioxidant in part because of its low toxicity. The LD₅₀ is 2200 mg/kg in mice (oral).^{[citation needed]}

References