Description
4-Hydroxybenzoic acid, also known as p-hydroxybenzoic acid or 99-96-7, 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 alcohol and acetone. It is isomeric with salicylic acid (2-hydroxybenzoic acid), a forerunner to aspirin, and 3-hydroxybenzoic acid. The esters of 4-hydroxybenzoic acid, also called parabens, are widely used as preservatives in cosmetics and some ophthalmic solutions.
Chemical Properties
4-Hydroxybenzoic acid is an odorless white crystalline astringent powder. In pure form, it imparts a sweetish taste at
first, which quickly becomes acrid and disagreeable
Chemical Properties
WHITE TO BEIGE CRYSTALLINE POWDER
Occurrence
Reportedly present in apple juice, black currant, cheese, beer, grape brandy, rum, sherry, wines, cocoa, peanut,
soybean and wort.
Uses
In organic. syntheses; intermediate for dyes, fungicides.
Uses
p-Hydroxybenzoic acid is of significant commercial importance. The most familiar application is the use of several of its esters as preservatives, known as parabens. Also of interest is the use in liquid crystal polymer applications.
Application
4-Hydroxybenzoic acid can be used as a starting material to synthesize organic intermediates such as 4-acetoxybenzoic acid and 4-hydroxy-3,5-diiodobenzoic acid.
4-Hydroxybenzoic acid is used as an intermediate for dyes, antiseptics and active pharmaceutical ingredients. It is also used as a food preservative, corrosion inhibitor, anti-oxidant and an emulsifier. It reacts with 6-hydroxynaphthalene-2-carboxylic acid to prepare aromatic polyester called Vectran fiber. It acts as a precursor to prepare p-hydroxyphenylbenzoate, p-acetoxybenzoyl chloride and 4,4′-dihydroxybenzophenone. Further, it is used in paint additives, coating additives, processing aids, electrical and electronic products. In addition to this, it acts as a preservative in cosmetics and some ophthalmic solutions.
Definition
ChEBI: A monohydroxybenzoic acid that is benzoic acid carrying a hydroxy substituent at C-4 of the benzene ring.
Preparation
Prepared from p-bromophenol or p-hydroxybenzaldehyde, or from saponification of methyl salicylate, a major component
of oil of wintergreen.
Aroma threshold values
Detection at 5 ppm (water)
General Description
Pharmaceutical secondary standards for application in quality control provide pharma laboratories and manufacturers with a convenient and cost-effective alternative to the preparation of in-house working standards. 4-Hydroxybenzoic acid belongs to the class of aromatic acids, which may be used as a preservative in cosmetics, pharmaceuticals and as a synthetic flavoring agent in food products.
Flammability and Explosibility
Nonflammable
Purification Methods
Crystallise the hydroxyacid from water. [Beilstein 10 IV 345.]
