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
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	138.12 g/mol
Density	1.46 g/cm³
Melting point	214-217 °C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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. 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^[1]. It is one of the main catechins metabolites found in humans after consumption of green tea infusions.^[2]

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).^[3]

Chemical production

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

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.^[5]

Chemical reactions

It is about 10x less acidic than benzoic acid, K_a = 3.3 x 10⁻⁵ M at 19 °C:

HOC₆H₄CO₂H $\overrightarrow{\leftarrow}$ 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. ^ Pacheco-Palencia LA, Mertens-Talcott S, Talcott ST (Jun 2008). "Chemical composition, antioxidant properties, and thermal stability of a phytochemical enriched oil from Acai (Euterpe oleracea Mart.)". J Agric Food Chem 25 (56): 4631–6. doi:10.1021/jf800161u. PMID 18522407. 
4. ^ 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
5. ^ C. A. Buehler and W. E. Cate (1943), "p-Hydroxybenzoic acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0341 ; Coll. Vol. 2: 341