Phloroglucinol is an organic compound with the formula C6H3(OH)3. It is a colorless solid. It is used in the synthesis of pharmaceuticals and explosives. Phloroglucinol is one of three isomeric benzenetriols. The other two isomers are hydroxyquinol (1,2,4-benzenetriol) and pyrogallol (1,2,3-benzenetriol). Phloroglucinol, and its benzenetriol isomers, are still defined as "phenols" according to the IUPAC official nomenclature rules of chemical compounds. Many such monophenolics are often termed "polyphenols" by the cosmetic and parapharmaceutical industries, but they cannot be by any scientifically-accepted definition.
phloroglucine, 1,3,5-trihydroxybenzene, 1,3,5-benzenetriol, or cyclohexane-1,3,5-trione
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||126.11 g/mol|
|Appearance||colorless to beige solid|
|Melting point||219 °C (426 °F; 492 K)|
|1 g/100 mL|
|Solubility||soluble in diethyl ether, ethanol, pyridine|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|5 g/kg (rat, oral)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Synthesis and occurrence
A modern synthesis of involves hydrolysis of 1,3,5-triaminobenzene and its derivatives. Representative is the following route from trinitrobenzene.
Tautomerism and acid-base behavior
Phloroglucinol is a weak triprotic acid. The first two pKa's are 8.5 and 8.9.
- C6H3(OH)3 + 3 NH2OH → (CH2)3(C=NOH)3 + 3 H2O
From water, phloroglucinol crystallizes as the dihydrate, which has a melting point of 116–117 °C, but the anhydrous form melts at a much higher temperature, at 218–220 °C. It does not boil intact, but it does sublime.
The Hoesch reaction allows the synthesis of 1-(2,4,6-Trihydroxyphenyl)ethanone from phloroglucinol.
Leptospermone can be synthesized from phloroglucinol by a reaction with isovaleroylnitrile in the presence of a zinc chloride catalyst.
Phloroglucinol is also generally found in the flavonoid ring A substitution pattern. Indeed, it was originally prepared from phloretin, a compound isolated from fruit trees, using potassium hydroxide. Additionally, the compound can be similarly prepared from glucosides, plant extracts and resins such as quercetin, catechin and phlobaphenes.
Phloroglucinols are secondary metabolites that occur naturally in certain plant species. It is also produced by brown algae and bacteria.
Acyl dervatives are present in the fronds of the coastal woodfern, Dryopteris arguta or in Dryopteris crassirhizoma. The anthelmintic activity of the root of Dryopteris filix-mas has been claimed to be due to flavaspidic acid, a phloroglucinol derivative.
Formylated phloroglucinol compounds (euglobals, macrocarpals and sideroxylonals) can be found in Eucalyptus species. Hyperforin and adhyperforin are two phloroglucinols found in St John's wort. Humulone is a phloroglucinol derivative with three isoprenoid side-chains. Two side-chains are prenyl groups and one is an isovaleryl group. Humulone is a bitter-tasting chemical compound found in the resin of mature hops (Humulus lupulus).
Brown algae, such as Ecklonia stolonifera, Eisenia bicyclis or species in the genus Zonaria, produce phloroglucinol and phloroglucinol derivatives. Brown algae also produce a type of tannins known as phlorotannins.
In Pseudomonas fluorescens, biosynthesis of phloroglucinol is performed with a type III polyketide synthase. The synthesis begins with the condensation of three malonyl-CoAs. Then decarboxylation followed by the cyclization of the activated 3,5-diketoheptanedioate product leads to the formation of phloroglucinol.
The enzyme pyrogallol hydroxytransferase uses 1,2,3,5-tetrahydroxybenzene and 1,2,3-trihydroxybenzene (pyrogallol) to produce 1,3,5-trihydroxybenzene (phloroglucinol) and 1,2,3,5-tetrahydroxybenzene. It is found in the bacterium species Pelobacter acidigallici.
The legume-root nodulating, microsymbiotic nitrogen-fixing bacterium species Bradyrhizobium japonicum is able to degrade catechin with formation of phloroglucinol carboxylic acid, further decarboxylated to phloroglucinol, which is dehydroxylated to resorcinol and hydroxyquinol.
It has antispasmodic properties.
It is also used as a treatment for gallstones, spasmodic pain and other related gastrointestinal disorders. It has a non-specific spasmolytic action on the vessels, bronchi, intestine, ureters and gall bladder, and is used for treating disorders of these organs. It is the main ingredient of the drug Spasfon, commercialized in France, where it is one of the most sold drugs.
Phloroglucinols acylated derivatives have a fatty acid synthase inhibitory activity.
It has the A03AX12 code in the A03AX Other drugs for functional bowel disorders section of the ATC code A03 Drugs for functional gastrointestinal disorders subgroup of the Anatomical Therapeutic Chemical Classification System. It also has the D02.755.684 code in the D02 Organic chemicals section of the Medical Subject Headings (MeSH) codes by the United States National Library of Medicine.
Phloroglucinol is mainly used as a coupling agent in printing. It links diazo dyes to give a fast black.
Phloroglucinolysis is an analytical technique to study condensed tannins by means of depolymerisation. The reaction makes use of phloroglucinol as nucleophile. Phlobaphenes formation (tannins condensation and precipitation) can be minimized in using strong nucleophiles, such as phloroglucinol, during pine tannins extraction.
Phloroglucinol is used in plant culture media. It demonstrates both cytokinin-like and auxin-like activity. Phloroglucinol increases shoot formation and somatic embryogenesis in several horticultural and grain crops. When added to rooting media together with auxin, phloroglucinol further stimulates rooting.
Use in tests
A solution of hydrochloric acid and phloroglucinol is also used for the detection of lignin (Wiesner test). A brilliant red color develops, owing to the presence of coniferaldehyde groups in the lignin. A similar test can be performed with tolonium chloride.
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