4-Hydroxybenzoic acid

Names
IUPAC name 4-Hydroxybenzoic acid
Other names p-Hydroxybenzoic acid para-Hydroxybenzoic acid
Identifiers
CAS Number	99-96-7 Y
3D model (JSmol)	Interactive image Interactive image
ChemSpider	132 Y
ECHA InfoCard	100.002.550
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	138.12074 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 [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

4-Hydroxybenzoic acid, or p-hydroxybenzoic acid, is a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble 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.

Production

4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction.^[1]

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.^[2]

Reactions

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

HOC₆H₄CO₂H 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