Gallic acid
[3,4,5-trihydroxybenzoic acid, C6H2(OH)3COOH]
is obtained from nutgalls and other plants or by the hydrolysis of tannic acid with
sulfuric acid. Gallic acid has two functional
groups in the same molecule, hydroxyl groups and a carboxylic acid group. They
can yield numerous esters and salts including digallic acid
which is formed by the reaction of two moles of gallic
acid with one another. If
gallic acid lose carbon dioxide,
pyrogallol
is formed. Gallic acid and its derivatives are used in making dyes
and inks, photographic developers and has been used as astringents in medically. Some
gallates are used as antioxidants in foods. Tannins (tannic acid or gallotannic
acid) are esters of digallic acid. They are widely used in tanning leather,
dyeing fabrics, manufacturing inks, and in various medical applications (as
astringents and to treat some skin diseases). Benzoic acid
derivatives substituted by hydroxyl group or ether containing oxygen atom have
bacteriostatic and fragrant properties. They are typically used in
pharmaceutical and perfumery industry. The destructive metabolic property of
oxygen containing benzoic acid derivatives such as protocatechuic acid
(3,4-dihydroxybenzoic acid) and veratric acid (3,4-dimethoxybenzoic acid) is
used in the application for pharmaceuticals. Protocatechuic acid is a catabolite
of epinephrine. Prazosin, a peripheral vasodilator and
antihypertensive, is also an example of the application of veratric
acid. Hydroxy and ether substituted benzoic acids feature
analogue metabolite of aspirin (acetylsalicylic Acid). They are
used as intermediates for
pharmaceuticals (especially for antipyetic anlgesic,
antirheumatism) and other organic synthesis. They are used as matrix for
ionization of peptides, proteins and carbohydrates.