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Skeletal formula of tropolone
Space-filling model of tropolone
IUPAC name
Other names
2-Hydroxytropone; Purpurocatechol
3D model (JSmol)
ECHA InfoCard 100.007.799
EC Number 208-577-2
MeSH D014334
Molar mass 122.12 g/mol
Melting point 50 to 52 °C (122 to 126 °F; 323 to 325 K)
Boiling point 80 to 84 °C (176 to 183 °F; 353 to 357 K) (0.1 mmHg)
Acidity (pKa) 6.89 (and -0.5 for conjugate acid)
-61·10−6 cm3/mol
S-phrases (outdated) S22 S24/25
Flash point 112 °C (234 °F; 385 K)
Related compounds
Related compounds
Hinokitiol (4-isopropyl-tropolone)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tropolone is an organic compound with the formula C7H5(OH)O. It is a pale yellow solid that is soluble in organic solvents. The compound has been of interest to research chemists because of its unusual electronic structure and its role as a ligand precursor. Although not usually prepared from tropone, it can be viewed as its derivative with a hydroxyl group in the 2-position.

Synthesis and reactions[edit]

Many methods have been described for the synthesis of tropolone.[2] One involves bromination of 1,2-cycloheptanedione with N-bromosuccinimide followed by dehydrohalogenation at elevated temperatures and by acyloin condensation of the ethyl ester of pimelic acid the acyloin again followed by oxidation by bromine.

The compound readily undergoes O-alkylation to give cycloheptatrienyl derivatives, which in turn are versatile synthetic intermediates.[3] With metal cations, it undergoes deprotonation to give chelate complexes, e.g., Cu(O2C7H5)2.

Natural occurrence[edit]

Many natural products contain the tropolone skeleton. Among the simplest, and the first to be made synthetically, were α-, β- and γ-thujaplicins, by Ralph Raphael and colleagues.[4] Others include puberulic acid, stipitatonic acid, stipitatic acid, puberulonic acid, sepedonin, and theaflavins of black tea. It arises via a polyketide pathway, which affords a phenolic intermediate that undergoes ring expansion.[3]

Biological effects[edit]

It is an inhibitor of grape polyphenol oxidase[5][6] and mushroom tyrosinase.[7]


  1. ^ Tropolone at Sigma-Aldrich
  2. ^ Richard A. Minns "Tropolone" Org. Synth. 1977, volume 57, 117.doi:10.15227/orgsyn.057.0117
  3. ^ a b Pietra, F. (1973). "Seven-membered conjugated carbo- and heterocyclic compounds and their homoconjugated analogs and metal complexes. Synthesis, biosynthesis, structure, and reactivity". Chemical Reviews. 73: 293–364. doi:10.1021/cr60284a002.
  4. ^ Cook, J.W.; Scott, A.I.; Raphael, R.A. (1951). "Tropolones. Part II. The synthesis of α-, β-, and γ-thujaplicins". J. Chem. Soc.: 695–698. doi:10.1039/JR9510000695.
  5. ^ Time-dependent inhibition of grape polyphenol oxidase by tropolone. Edelmira Valero, Manuela Garcia-Moreno, Ramon Varon and Francisco Garcia-Carmona, J. Agric. Food Chem., 1991, volume 39, pp. 1043–1046, doi:10.1021/jf00006a007
  6. ^ Chedgy, Russell. Secondary metabolites of Western red cedar (Thuja plicata): their biotechnological applications and role in conferring natural durability. LAP Lambert Academic Publishing, 2010, ISBN 3-8383-4661-0, ISBN 978-3-8383-4661-8
  7. ^ Inhibition of mushroom tyrosinase by tropolone. Varda Kahn and Andrawis Andrawis, Phytochemistry, Volume 24, Issue 5, 1985, Pages 905-908, doi:10.1016/S0031-9422(00)83150-7