Tropolone

Tropolone[1]
Skeletal formula of tropolone	Space-filling model of tropolone
Names
	IUPAC name 2-Hydroxy-2,4,6-cycloheptatrien-1-one
	Other names 2-Hydroxytropone; Purpurocatechol
Identifiers
CAS Number	533-75-5 ;
3D model (JSmol)	Interactive image;
ChEMBL	ChEMBL121188 ;
ChemSpider	10333 ;
ECHA InfoCard	100.007.799
EC Number	208-577-2;
KEGG	C15474 ;
MeSH	D014334
PubChem CID	10789;
UNII	7L6DL16P1T ;
CompTox Dashboard (EPA)	DTXSID8049416 ;
	InChI InChI=1S/C7H6O2/c8-6-4-2-1-3-5-7(6)9/h1-5H,(H,8,9) Key: MDYOLVRUBBJPFM-UHFFFAOYSA-N ; InChI=1/C7H6O2/c8-6-4-2-1-3-5-7(6)9/h1-5H,(H,8,9) Key: MDYOLVRUBBJPFM-UHFFFAOYAW;
	SMILES C1=CC=C(C(=O)C=C1)O;
Properties
Chemical formula	C7H6O2
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)
Magnetic susceptibility (χ)	-61·10−6 cm3/mol
Hazards
S-phrases (outdated)	S22 S24/25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).
	verify (what is ?)
	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

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, while another uses acyloin condensation of the ethyl ester of pimelic acid the acyloin again followed by oxidation by bromine.[3]

The compound readily undergoes O-alkylation to give cycloheptatrienyl derivatives, which in turn are versatile synthetic intermediates.[4] With metal cations, it undergoes deprotonation to give chelate complexes, e.g., Cu(O₂C₇H₅)₂.[3]

Natural occurrence

Hinokitiol (β-thujaplicin) is a naturally-occurring tropolone.[5]

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.[6] 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.[4]

Biological effects

It is an inhibitor of grape polyphenol oxidase[7][8] and mushroom tyrosinase.[9]

References

Tropolone at Sigma-Aldrich
Minns, Richard A. (1977). "Tropolone". Org. Synth. 57: 117. doi:10.15227/orgsyn.057.0117.
Pauson, Peter L. (1955). "Tropones and Tropolones". Chem. Rev. 55 (1): 9–136. doi:10.1021/cr50001a002.
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.
Chedgy, Russell J.; Lim, Young Woon; Breuil, Colette (2009). "Effects of leaching on fungal growth and decay of western redcedar". Canadian Journal of Microbiology. 55 (5): 578–86. doi:10.1139/W08-161. PMID 19483786.
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.
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
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
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

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[1] Tropolone at Sigma-Aldrich

[2] Minns, Richard A. (1977). "Tropolone". Org. Synth. 57: 117. doi:10.15227/orgsyn.057.0117.

[Paulson1955-3] Pauson, Peter L. (1955). "Tropones and Tropolones". Chem. Rev. 55 (1): 9–136. doi:10.1021/cr50001a002.

[CR-4] 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.

[5] Chedgy, Russell J.; Lim, Young Woon; Breuil, Colette (2009). "Effects of leaching on fungal growth and decay of western redcedar". Canadian Journal of Microbiology. 55 (5): 578–86. doi:10.1139/W08-161. PMID 19483786.

[6] 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.

[7] 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

[8] 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

[9] 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