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| Names | |||
|---|---|---|---|
| Preferred IUPAC name 2-Hydroxycyclohepta-2,4,6-trien-1-one | |||
| Other names 2-Hydroxytropone; Purpurocatechol | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.007.799 | ||
| EC Number |
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| KEGG |
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| MeSH | D014334 | ||
| UNII | |||
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| Properties | |||
| 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 (−0.5 for conjugate acid) | ||
| −61·10−6 cm3/mol | |||
| Hazards | |||
| GHS labelling:[2] | |||
   | |||
| Danger | |||
| H314,H317,H410 | |||
| P260,P264,P272,P273,P280,P301+P330+P331,P302+P352,P303+P361+P353,P304+P340,P305+P351+P338,P310,P333+P313,P363,P391,P405,P501 | |||
| 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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Tropolone is anorganic compound with the chemical formulaC7H5(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 fromtropone, it can be viewed as its derivative with ahydroxyl group in the 2-position.
Many methods have been described for the synthesis of tropolone.[3] One involves bromination of 1,2-cycloheptanedione withN-bromosuccinimide followed bydehydrohalogenation at elevated temperatures, while another usesacyloin condensation of the ethylester ofpimelic acid theacyloin again followed by oxidation bybromine.[4]
An alternate route is a [2+2]cycloaddition ofcyclopentadiene with aketene to give a bicyclo[3.2.0]heptyl structure, followed byhydrolysis and breakage of the fusion bond to give the single ring:[3]
Thy hydroxyl group of tropolone isacidic, having apKa of 7, which is in between that ofphenol (10) andbenzoic acid (4). The increased acidity compared to phenol is due toresonance stabilization with the carbonyl group, as avinylogous carboxylic acid.[4]
The compound readily undergoesO-alkylation to give cycloheptatrienyl derivatives, which in turn are versatile synthetic intermediates.[5] With metal cations, it undergoes deprotonation to form abidentate ligand, such as in theCu(O2C7H5)2 complex.[4]
The carbonyl group is also highly polarized, as common fortropones. There can be substantialhydrogen bonding between it and the hydroxyl group, leading to rapidtautomerization: the structure is symmetric on the NMR timescale.[6]
Around 200 naturally occurring tropolone derivatives have been isolated, mostly fromplants andfungi.[7][8][9][10] Tropolone compounds and their derivatives include dolabrins, dolabrinols,thujaplicins, thujaplicinols,stipitatic acid, stipitatonic acid, nootkatin, nootkatinol,puberulic acid, puberulonic acid, sepedonin, 4-acetyltropolone, pygmaein, isopygmaein, procein, chanootin, benzotropolones (such aspurpurogallin, crocipodin, goupiolone A and B),theaflavin and derivatives bromotropolones, tropoisoquinolines and tropoloisoquinolines (such as grandirubrine, imerubrine, isoimerubrine, pareitropone, pareirubrine A and B),colchicine, colchicone and others.[11] Tropolone arises via apolyketide pathway, which affords aphenolic intermediate that undergoes ring expansion.[5]
They are especially found in specific plant species, such asCupressaceae andLiliaceae families.[9] Tropolones are mostly abundant in the heartwood, leaves and bark of plants, thereby the essential oils are rich in various types of tropolones. The first natural tropolone derivatives were studied and purified in the mid-1930s and early-1940s.[12]Thuja plicata,Thujopsis dolabrata,Chamaecyparis obtusa,Chamaecyparis taiwanensis andJuniperus thurifera were in the list of trees from which the first tropolones were identified. The first synthetic tropolones werethujaplicins derived byRalph Raphael.[13]
| Name | Chemical structure | Natural sources |
|---|---|---|
| Tropolone |  | Pseudomonas lindbergii,Pseudomonas plantarii[14][15][16] and mushroomtyrosinase.[17] |
| Hinokitiol |  | Cupressaceae trees[18] |
| Stipitatic acid |  | Talaromyces stipitatus[19] |
| Colchicine |  | Colchicum autumnale,Gloriosa superba[20] |
| Class | Examples | Main natural sources[11][9][21][22] | Research directions[9][23][11][24][25] | Patented in products[9][26] |
|---|---|---|---|---|
| Simple tropolones | Tropolone | Pseudomonas lindbergii,Pseudomonas plantarii | Antibacterial, antifungal, insecticidal, pesticidal, plant growth inhibition, anti-inflammatory, antioxidant, neuroprotection, anti-protease, anti-browning (anti-tyrosinase and anti-polyphenol oxidase), antineoplastic, chelating | - |
| Dolabrins | β-dolabrin, α-dolabrinol | Caragana pygmaea,Cupressus goveniana,Cupressus abramsiana,Thujopsis dolabrata | Antibacterial, antifungal, insecticidal, pesticidal, plant growth inhibition, protease inhibition | Insect repellent, deodorant |
| Thujaplicins | α-thujaplicin, β-thujaplicin (hinokitiol), γ-thujaplicin, thujaplicinol | Chamaecyparis obtusa,Thuja plicata,Thujopsis dolabrata,Juniperus cedrus,Cedrus atlantica,Cupressus lusitanica,Chamaecyparis lawsoniana,Chamaecyparis taiwanensis,Chamaecyparis thyoides,Cupressus arizonica,Cupressus macnabiana,Cupressus macrocarpa,Cupressus guadalupensis,Juniperus chinensis,Juniperus communis,Juniperus californica,Juniperus occidentalis,Juniperus oxycedrus,Juniperus sabina,Calocedrus decurrens,Calocedrus formosana,Platycladus orientalis,Thuja occidentalis,Thuja standishii,Tetraclinis articulata,Cattleya forbesii,Carya glabra | Antifungal, antibacterial, anti-browning (anti-tyrosinase), chelating, insecticidal, pesticidal, antimalarial, antiviral, anti-inflammatory, plant growth inhibition, anti-protease, antidiabetic, antineoplastic, chemosensitizing, antioxidant, neuroprotection, veterinary medicine | Insect repellent, deodorant, toothpaste, oral spray, skin and hair care, wood preservative,food additive, food packaging |
| Sesquiterpene tropolones | Nootkatin, nootkatinol, nootkatol, nootkatene, valencene-13-ol, nootkastatin | Chamaecyparis nootkatensis,Grapefruit | Antifungal, anti-browning (anti-tyrosinase), insecticidal, fungicidal, antineoplastic | Insect repellents, flavor, perfumery |
| Pygmaeins | Pygmaein, Isopygmaein | Caragana pygmaea,Cupressus goveniana,Cupressus abramsiana | - | - |
| Benzotropolones | Purpurogallin, crocipodin, goupiolone A and B | Quercus species,Leccinum crocipodium,Goupia glabra | Antibacterial, plant growth inhibition, protease inhibition, antineoplastic, antimalarial, antioxidant, antiviral | Food additive |
| Theaflavins | Theaflavin, theaflavic acid, theaflavate A and B | Camellia sinensis,Quercus species | Antibacterial, anti-inflammatory, antioxidant, antiviral, antidiabetic, chemosensitizing | - |
| Tropoisoquinolines and tropoloisoquinolines | Grandirubrine, imerubrine, isoimerubrine, pareitropone, pareirubrine A and B | Cissampelos pareira,Abuta grandifolia | Antileukemic | - |
| Troponealkaloids | Colchicine,demecolcine | Colchicum autumnale,Gloriosa superba | Antimitotic, anti-inflammatory, anti-gout, plant breeding | Pharmaceutical drug |
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