Description
Gallic acid is a trihydroxybenzoic acid, a type of phenolic acid, a type of organic acid, also known as 3,4,5- trihydroxy benzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C
6H
2(OH)
3COOH. Gallic acid is found both free and as part of hydrolyzable tannins.
Salts and esters of gallic acid are termed 'gallates'. Despite its name, it does not contain gallium.
Gallic acid is commonly used in the pharmaceutical industry. It is used as a standard for determining the phenol content of various analytes by the Folin - Ciocalteau assay; results are reported in gallic acid equivalents. Gallic acid can also be used as a starting material in the synthesis of the psychedelic alkaloid mescaline.
Gallic acid seems to have anti-fungal and antiviral properties. Gallic acid acts as an antioxidant and helps to protect human cells against oxidative damage. Gallic acid was found to show cytotoxicity against cancer cells, without harming healthy cells. Gallic acid is used as a remote astringent in cases of internal haemorrhage. Gallic acid is also used to treat albuminuria and diabetes. Some ointments to treat psoriasis and external haemorrhoids contain gallic acid.
Chemical Properties
Gallic acid, also known as trihydroxybenzoic acid, is a colorless crystalline needles or prisms that is obtained from nutgall tannins. It is soluble in hot water, ether, ethanol, acetone and glycerin, insoluble in cold water, insoluble in benzene and chloroform and has a melting point of 235 to 240 °C (decomposition). When heated to 100-120°C, crystal water will be lost, and when heated above 200°C, carbon dioxide will be lost to generate pyrogallic acid (ie, pyrogallol). It is used in photography, tanning, ink manufacture and pharmaceuticals.
Occurrence
Gallic acid is found in a number of land plants. It is also found in the aquatic plant Myriophyllum spicatum and shows an allelopathic effect on the growth of the blue-green alga Microcystis aeruginosa.
In food Areca nut
Bearberry (Arctostaphylos sp)
Bergenia sp
Blackberry
Hot chocolate
Juglans regia (Common walnut)
Mango in peels and leaves
Phyllanthus emblica (Indian gooseberry) in fruits
Raspberry
Syzygium aromaticum (clove)
Vinegar
wine
Witch hazel (Hamamelis virginiana)
White tea.
History
Gallic acid is an important component of iron gall ink, the standard European writing and drawing ink from the 12 th to 19th century with a history extending to the Roman empire and the Dead Sea Scrolls. Pliny the Elder (23-79 AD) describes his experiments with it and writes that it was used to produce dyes. Galls (also known as oak apples) from oak trees were crushed and mixed with water, producing tannic acid (a macromolecular complex containing gallic acid). It could then be mixed with green vitriol (ferrous sulfate) — obtained by allowing sulfate - saturated water from a spring or mine drainage to evaporate — and gum arabic from acacia trees; this combination of ingredients produced the ink.
Gallic acid was one of the substances used by Angelo Mai (1782–1854), among other early investigators of palimpsests, to clear the top layer of text off and reveal hidden manuscripts underneath. Mai was the first to employ it, but did so "with a heavy hand", often rendering manuscripts too damaged for subsequent study by other researchers.
Early photographers, including Joseph Bancroft Reade (1801– 1870) and William Fox Talbot (1800 – 1877), used gallic acid for developing latent images in calotypes. It has also been used as a coating agent in zincography.
Uses
gallic acid is a potential bleaching agent and anti-oxidant, it is also astringent and potentially anti-microbial and anti-fungal. Scientists are finding that gallic acid may serve as a skin-lightening agent by inhibiting the action of the tyrosinase and peroxidase enzymes. Some studies indicate that it is more effective than hydroquinone when combined with the proper ingredients. It is also incorporated into anti-aging formulations for its ability to prevent mucopolysaccaride deterioration. It is a constituent of witch hazel and oak bark, among many other plants; however, it is generally obtained from nutgalls for commercial purposes.
Uses
Gallic acid is a cyclooxygease inhibitor substance found in plants. It has antioxidant, anti-inflammatory, and antineoplastic properties. It can be used to produce polyesters based on phloretic acid and gallic acid.
Definition
ChEBI: Gallic acid is a trihydroxybenzoic acid in which the hydroxy groups are at positions 3, 4, and 5. It has a role as an astringent, a cyclooxygenase 2 inhibitor, a plant metabolite, an antioxidant, an antineoplastic agent, a human xenobiotic metabolite, an EC 1.13.11.33 (arachidonate 15-lipoxygenase) inhibitor, an apoptosis inducer and a geroprotector. It is a conjugate acid of a gallate.
Production Methods
Gallic acid, a component of many tanning agents is an endogenous product in plants. The acid occurs free or bound to tannin [1401-55-4] (e.g., in divi-divi, oak bark, gallnuts, pomegranate roots, sumac, and tea). The acid is produced from tannin-rich aqueous gallnut extracts by acidic or alkaline hydrolysis. It is also obtained by using the enzyme tannase [9025-71- 2] or molds (Penicillium glaucum, Aspergillus niger) to cleave tannin by fermentation. Both the metabolism of gallic acid and its impact on plant growth enzymes have been studied.
Biotechnological Production
The production of gallic acid is challenging. Conventionally, it has been produced
by acid hydrolysis of tannic acid. However, this process is expensive due to low
yields and high impurities. To overcome this problem, microbial production
of gallic acid has been suggested. For example, in a solid-state fermentation
of Teri pod cover powder containing tannin using Rhizopus oryzae, a yield
of 90.9 % based on the tannin content of 58 % of the substrate was observed.
In a submerged culture of Aspergillus aceleatus DBF9 growing on a medium with
3 % tannin, a maximal product concentration of 6.8 g.L-1 was reported.
With tannic acid, even higher product concentrations of up to 25 g.L-1, a yield of
0.83 g of gallic acid per gram of tannic acid, and a productivity of 0,56 g.L-1.h-1
were shown using Apergillus fischeri MTCC 150 in submerged cultivation.
An alternative is the enzymatic hydrolysis of tannic acids using tannase produced
by microorganisms (e.g. Aspergillus fischeri or R. oryzae). For example,
propyl gallate could be produced using a tannase from Emericela nidulans
immobilized on ionic and covalent supports.
General Description
Gallic acid is a phenol that has been found in C. sinensis and has diverse biological activities. It scavenges DPPH and hydroxyl radicals in cell-free assays (IC50s = 9.4 and 191 μM, respectively). Gallic acid (1-100 μM) reverses abscisic acid-induced inhibition of hypocotyl growth in A. caudatus seedlings. In vivo, gallic acid (21.8 g/kg) inhibits morpholine- and sodium nitrite-induced adenocarcinoma formation in mice. It also inhibits passive cutaneous anaphylaxis in mice when administered at a dose of 50 mg/kg.
Air & Water Reactions
Sparingly water soluble
Reactivity Profile
Phenols, such as Gallic acid, do not behave as organic alcohols, as one might guess from the presence of a hydroxyl (-OH) group in their structure. Instead, they react as weak organic acids. Phenols and cresols are much weaker as acids than common carboxylic acids (phenol has Ka = 1.3 x 10^[-10]). These materials are incompatible with strong reducing substances such as hydrides, nitrides, alkali metals, and sulfides. Flammable gas (H2) is often generated, and the heat of the reaction may ignite the gas. Heat is also generated by the acid-base reaction between phenols and bases. Such heating may initiate polymerization of the organic compound. Phenols are sulfonated very readily (for example, by concentrated sulfuric acid at room temperature). The reactions generate heat. Phenols are also nitrated very rapidly, even by dilute nitric acid.
Health Hazard
Inhalation of dust may irritate nose and throat. Contact with eyes or skin causes irritation.
Fire Hazard
Flash point data for Gallic acid are not available. Gallic acid is probably combustible.
Flammability and Explosibility
Not classified
Biochem/physiol Actions
Gallic acid is a water soluble phenolic acid present in grapes and in the leaves of many plants. Gallic acid esters, such as tannins, catechin gallates and aliphatic gallates are potent antioxidants in vitro. However, gallic acid itself also appears to have antioxidant, anticarcinogenic and antiangiogenic activity in vitro.
Side effects
It is a weak carbonic anhydrase inhibitor.
Metabolism
Biosynthesis Chemical structure of 3,5- didehydro shikimate Gallic acid is formed from 3-dehydro shikimate by the action of the enzyme shikimate dehydro genase to produce 3,5-didehydro shikimate. This latter compound tautomerizes to form the redox equivalent gallic acid, where the equilibrium lies essentially entirely toward gallic acid because of the coincidently occurring aromatization.
Degradation Gallate dioxygenase is an enzyme found in Pseudomonas putida that catalyzes the reaction :
gallate + O
2 → (1E)-4-oxobut-1-ene-1,2,4-tri carboxylate.
Gallate decarboxylase is another enzyme in the degradation of gallic acid.
Conjugation Gallate 1-beta-glucosyltransferase is an enzyme that uses UDPglucose and gallate, whereas its two products are UDP and 1-galloylbeta- D-glucose.
Purification Methods
Crystallise gallic from water. The tri-O-acetyl derivative has m 172o (from MeOH), and the anilide has m 207o(from EtOH). [Beilstein 10 H 470, 10 IV 1993.]
