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Phloroglucinol structure.png
IUPAC name
Other names phloroglucine, 1,3,5-trihydroxybenzene, 1,3,5-benzenetriol, or cyclohexane-1,3,5-trione
CAS number 108-73-6 Yes check.svgY
RTECS number UX1050000
Molecular formula C6H6O3
Molar mass 126.11 g/mol
Appearance white solid
Melting point

218-220 °C, 271 K, -146 °F

Solubility in water 1 g/100 mL
EU classification Harmful (Xn)
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phloroglucinol is an organic compound that is used in the synthesis of pharmaceuticals and explosives. This molecule exists in two forms, or tautomers, 1,3,5-trihydroxybenzene, which has phenol-like, and 1,3,5-cyclohexanetrione (phloroglucin), which has ketone-like character. These two tautomers are in equilibrium. Phloroglucinol is a useful intermediate because it is polyfunctional.

Tautomeric equilibrium

From water, phloroglucinol crystallizes as the dihydrate, which has a melting point of 116-117 °C, but the anhydrous form melts much higher, at 218-220 °C. It does not boil intact, but it does sublime.


Isolation, synthesis, and reactions

Phloroglucinol was originally isolated from bark of fruit trees. It is synthesized via a number of processes, but representative is the following route from trinitrobenzene:[1]


The synthesis is noteworthy because ordinary aniline derivatives are unreactive toward hydroxide. Because the triaminobenzene also exists as its imine tautomer, it is susceptible to hydrolysis.

The compound behaves like a ketone in its reaction with hydroxylamine, forming the tris(oxime). But it behaves also like a triphenol (Ka1 = 3.56 × 10–9, Ka2 1.32×10–9), as the three hydroxyl groups can be methylated to give 1,3,5-trimethoxybenzene.[1]

Natural occurrence

Phloroglucinols occur naturally in certain plant species. For example, they (and sometimes their acyl dervatives) are present in the fronds of the Coastal woodfern, Dryopteris arguta.[2]


Phloretin hydrolase uses phloretin and H2O to produce phloretate and phloroglucinol.


Phloroglucinol is mainly used as a coupling agent in printing. It links diazo dyes to give a fast black.

It is useful for the industrial synthesis of pharmaceuticals[3] and explosives.[4] It is also used as a treatment for gastrointestinal disorders.[5] [6] [7]

See also


  1. ^ a b Helmut Fiege, Heinz-Werner Voges, Toshikazu Hamamoto, Sumio Umemura, Tadao Iwata, Hisaya Miki, Yasuhiro Fujita, Hans-Josef Buysch, Dorothea Garbe, Wilfried Paulus "Phenol Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Wienheim, 2005. DOI: 10.1002/14356007.a19_313. Published online: 15 June, 2002.
  2. ^ C. Michael Hogan. 2008. Coastal Woodfern (Dryopteris arguta}, GlobalTwitcher, ed. N. Stromberg
  3. ^ "Intermediate Pharmaceutical Ingredients - Flopropione". Univar Canada. Retrieved 24 April 2009.  
  4. ^ "Synthesis of trinitrophloroglucinol". The United States Patent and Trademark Office. 1984. Retrieved 24 April 2009.  
  5. ^ "PHLOROGLUCINOL". Biam. 1999. Retrieved 24 April 2009.   (in French)
  6. ^ "Phloroglucinol Summary Report". EMEA. Retrieved 24 April 2009.  
  7. ^ Chassany O et al. (2007). "Acute exacerbation of pain in irritable bowel syndrome: efficacy of phloroglucinol/trimethylphloroglucinol. A randomized, double-blind, placebo-controlled study.". Alimentary pharmacology & therapeutics 1 (25): 1115–23.   PubMed

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