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4-Hydroxybenzoic acid

Names
IUPAC name 4-Hydroxybenzoic acid
Other names p-Hydroxybenzoic acid para-Hydroxybenzoic acid
Identifiers
CAS Number	99-96-7
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30763
ChEMBL	ChEMBL441343
ChemSpider	132
DrugBank	DB04242
ECHA InfoCard	100.002.550
KEGG	C00156
PubChem CID	135
CompTox Dashboard (EPA)	DTXSID3026647
InChI InChI=1S/C7H6O3/c8-6-3-1-5(2-4-6)7(9)10/h1-4,8H,(H,9,10)Key: FJKROLUGYXJWQN-UHFFFAOYSA-N InChI=1/C7H6O3/c8-6-3-1-5(2-4-6)7(9)10/h1-4,8H,(H,9,10)Key: FJKROLUGYXJWQN-UHFFFAOYAQ
SMILES O=C(O)c1ccc(O)cc1 c1cc(ccc1C(=O)O)O
Properties
Chemical formula	C7H6O3
Molar mass	138.12 g/mol
Density	1.46 g/cm³
Melting point	214–217 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) 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 occurrence

4-Hydroxybenzoic acid can be found naturally in Cocos nucifera. It is one of the main catechins metabolites found in humans after consumption of green tea infusions.

Açaí oil, obtained from the fruit of the açaí Palm (Euterpe oleracea), is rich in p-hydroxybenzoic acid (892 ± 52 mg/kg), protocatechuic acid (630 ± 36 mg/kg) and ferulic acid (101 ± 5.9 mg/kg).

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

Chemical production

4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction.

4-Hydroxybenzoic acid can also be produced in the laboratory by heating potassium salicylate with potassium carbonate to 240 °C, followed by treating with acid.

Chemical reactions

It is about 10x less acidic than benzoic acid, K_a = 3.3 x 10 M at 19 °C:

HOC₆H₄CO₂H ${\displaystyle {\overrightarrow {\leftarrow }}}$ HOC₆H₄CO₂ + H

Safety

4-Hydroxybenzoic acid is popular antioxidant in part because of its low toxicity. The LD₅₀ is 2200 mg/kg in mice (oral).

References

1. Profiling C6–C3 and C6–C1 phenolic metabolites in Cocos nucifera. Gargi Dey, Moumita Chakraborty and Adinpunya Mitra, Journal of Plant Physiology, Volume 162, Issue 4, 22 April 2005, Pages 375-381 doi:10.1016/j.jplph.2004.08.006
2. Catechin metabolites after intake of green tea infusions. P. G. Pietta, P. Simonetti, C. Gardana, A. Brusamolino, P. Morazzoni and E. Bombardelli, BioFactors, 1998, Volume 8, Issue 1-2, pp. 111–118, doi:10.1002/biof.5520080119
3. "Chemical composition, antioxidant properties, and thermal stability of a phytochemical enriched oil from Acai (Euterpe oleracea Mart.)". J Agric Food Chem. 56 (12): 4631–6. 2008. doi:10.1021/jf800161u. PMID 18522407. {{cite journal}}: Unknown parameter |authors= ignored (help); Unknown parameter |month= ignored (help)
4. Cryptanaerobacter phenolicus gen. nov., sp. nov., an anaerobe that transforms phenol into benzoate via 4-hydroxybenzoate. Pierre Juteau, Valérie Côté, Marie-France Duckett, Réjean Beaudet, François Lépine, Richard Villemur and Jean-Guy Bisaillon, IJSEM, January 2005, vol. 55, no. 1, pages 245-250, doi:10.1099/ijs.0.02914-0
5. 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
6. C. A. Buehler and W. E. Cate (1943). "p-Hydroxybenzoic acid". Organic Syntheses; Collected Volumes, vol. 2, p. 341.

• Monomers
• Monohydroxybenzoic acids