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Concept
Phloroglucinol
Summary
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.
In 1855, phloroglucinol was first prepared from phloretin by the Austrian chemist Heinrich Hlasiwetz (1825–1875).
A modern synthesis of phloroglucinol involves hydrolysis of benzene-1,3,5-triamine and its derivatives. Representative is the following route from trinitrobenzene.
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.
Phloroglucinol is a weak triprotic acid. The first two pKa's are 8.5 and 8.9.
As an enol, phloroglucinol in principle exists in equilibrium with keto tautomers. Evidence for this equilibrium is provided by the formation of the oxime:
C6H3(OH)3 + 3 NH2OH → (CH2)3(C=NOH)3 + 3 H2O
But it behaves also like a benzenetriol as the three hydroxyl groups can be methylated to give 1,3,5-trimethoxybenzene.
For the neutral compound, the keto tautomers are undetectable spectroscopically. Upon deprotonation, the keto tautomer predominates.
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.
Pentacarbon dioxide, described in 1988 by Günter Maier and others, can be obtained by pyrolysis of 1,3,5-cyclohexanetrione (phloroglucin).
Official source
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