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|verifiedrevid = 443022610 |
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|Name=Pyrylium |
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|Name=Pyrylium |
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|ImageFileL1=Pyrylium.svg |
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|ImageFileL1 = Pyrylium.svg |
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|ImageFileR1 = Pyrylium-3D-balls.png |
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|PIN = Pyrylium<ref>{{cite book |author=International Union of Pure and Applied Chemistry |author-link=International Union of Pure and Applied Chemistry |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=] |page=1097 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}</ref> |
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|ImageFileR1= Pyrylium-3D-balls.png |
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|OtherNames = Pyranium |
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|ImageSizeR1=100px |
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|IUPACName= Pyrylium |
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|OtherNames= |
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|Section1={{Chembox Identifiers |
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|Section1={{Chembox Identifiers |
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|CASNo_Ref = {{cascite|correct|??}} |
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| CASNo= |
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| index1_label=salt |
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| PubChem=9548819 |
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| index2_label=family |
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| SMILES=C1=CC=C=C1 |
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|CASNo = 289-67-8 |
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}} |
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| Beilstein = 1421881 |
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|PubChem = 9548819 |
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|ChEBI_Ref = {{ebicite|correct|EBI}} |
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|ChEBI = 36120 |
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|ChEBI1 = 59658 |
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|ChEBI2 = 59657 |
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|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |
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|ChemSpiderID = 7827742 |
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| Gmelin = 558560 |
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|SMILES = 1ccccc1 |
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|InChI = 1/C5H5O/c1-2-4-6-5-3-1/h1-5H/q+1 |
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|InChIKey = WVIICGIFSIBFOG-UHFFFAOYAF |
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|StdInChI_Ref = {{stdinchicite|changed|chemspider}} |
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|StdInChI = 1S/C5H5O/c1-2-4-6-5-3-1/h1-5H/q+1 |
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|StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} |
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|StdInChIKey = WVIICGIFSIBFOG-UHFFFAOYSA-N |
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|Section2={{Chembox Properties |
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|Section2={{Chembox Properties |
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|C = 5 | H = 5 | O = 1 | Formula_Charge = + |
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| Formula=C<sub>5</sub>H<sub>5</sub>O<sup>+</sup> |
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}} |
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| MolarMass=81.09 g/mol |
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| OtherCompounds = ], ], ] |
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'''Pyrylium''' is a ] (positive ]) with formula {{chem2|C5H5O+}}, consisting of a six-membered ring of five ] atoms, each with one ] atom, and one positively charged ] atom. The bonds in the ring are ] as in ], giving it an ] character. In particular, because of the positive charge, the oxygen atom is ]. Pyrilium is a mono-] and ] compound, one of the ]s. |
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A '''pyrylium salt''' is a ] containing a pyrylium cation or a ] of it.<ref>''Heterocyclic Chemistry'', T. L. Gilchrist, ISBN 0-582-27843-0</ref> <ref>A.T. Balaban, W. Schroth and G. Fischer, “Pyrylium Salts. I. Synthesis”, in Advances in Heterocyclic Chemistry, (eds. A. R. Katritzky and A. J. Boulton), Academic Press, New York, 1969, vol. 10, pp. 241–326.</ref> <ref>A.T. Balaban, A. Dinculescu, G.N. Dorofeenko, G.W. Fischer, A.V. Koblik, V.V. Mezheritskii and W. Schroth, “Pyrylium Salts. Syntheses, Reactions and Physical Properties”, Advances in Heterocyclic Chemistry, Suppl. Vol. 2 (A. R. Katritzky, Ed.), Academic Press, New York, 1982.</ref> |
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<ref>A.T. Balaban, “The pyrylium cation as a synthon in organic chemistry”, in “New Trends in Heterocyclic Chemistry”, (eds. R.B. Mitra, N.R. Ayyangar, V.N Gogte, R.M. Acheson and N. Cromwell), Elsevier, Amsterdam, 1979, pp. 79–111.</ref> <ref>A.T. Balaban, “Pyrylium salts as useful synthons”, in “Organic Synthesis : Modern Trends” (Proc. 6th IUPAC Internat. Symp. on Organic Synthesis, Moscow), (ed. O. Chizov), Blackwell, Oxford, 1987, pp. 263–274.</ref> <ref>T.S. Balaban and A.T. Balaban, “Pyrylium Salts”. In “Science of Synthesis; Houben-Weyl Methods of Molecular Transformations”, Georg Thieme Verlag, Stuttgart, 2003, Vol 14, pp. 11–200.</ref> |
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==Synthesis== |
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The pyrylium cation is a ] 6-membered ] ring system with one carbon atom replaced by a positively charged ] atom. It is, like ], an ] compound.<br /> A '''pyrylium''' may be any derivative of the pyrylium cation. |
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Pyrylium salts are easily produced from simple starting materials through a ].<ref name="bala1977">{{cite journal |last1=Balaban |first1=A. T. |last2=Wray |first2=V. |date=1977 |title=<sup>13</sup>C n.m.r. spectra of some pyrylium salts and related compounds |journal=Organic Magnetic Resonance |volume=9 |issue=1 |pages=16–22 |doi=10.1002/mrc.1270090105}}</ref> |
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Pyrylium salts with aromatic substituents, such 2,4,6-triphenylpyrylium tetrafluoroborate, can be obtained from two moles of ], one mole of ], and excess ].<ref>{{OrgSynth|year=1969|volume=49|p=121|first1=Karl|last1=Dimroth|first2=C.|last2=Reichardt|first3=K.|last3=Vogel|title=2,4,6-Triphenylpyrylium tetrafluoroborate|collvol=5|collvolpage=1128|prep=CV5P1135}}</ref> For pyrylium salts with alkyl substituents, such as 2,4,6-trimethylpyrylium salts, the best method uses the ]-]-Praill synthesis from ] and ] in the presence of tetrafluoroboric,<ref>{{OrgSynth|year=1969|volume=49|p=121|first1=A. T.|last1=Balatan|first2=A. J.|last2=Boulton|title=2,4,6-Trimethylpyrylium tetrafluoroborate|collvol=5|collvolpages=1112–1113|prep=CV5P1112}}</ref> perchloric,<ref>{{OrgSynth|year=1968|volume=44|p=98|title=2,4,6-Trimethylpyrylium perchlorate|first1=Alexandru T.|last1=Balaban|author-link1=Alexandru Balaban|first2=Costin D.|last2=Nenitzescu|author-link2=Costin Nenitescu|collvol=5|collvolpages=1088,1106,1114,1135|prep=CV5P1106}}</ref> or trifluoromethanesulfonic acids.<ref>{{OrgSynth|first1=Alexandru T.|last1=Balaban|author-link1=Alexandru Balaban|last2=Boulton|first2=A. J.|collvol=5|collvolpages=1112,1114–1116|year=1973|title=2,4,6-Trimethylpyrylium trifluoromethanesulfonate|prep=CV5P1114}}</ref> |
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Hydroxide bases open and hydrolyze ] to an enedione base that cyclizes in very strong acids to a pyrylium cation.<ref>{{OrgSynth|last1=Gómez-Palomino|first1=Alejandro|last2=Ghiazza|first2=Clément|last3=Busch|first3=Julia|last4=Wagner|first4=Lucas|last5=Cornella|first5=Josep|year=2023|title=Preparation of Pyrylium tetrafluoroborate (Pyry-BF<sub>4</sub>)|volume=100|pages=361-381|prep=v100p0361}}</ref> |
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Enolizing conditions (strong acid) force pyrones to their pyrylium tautomer.<ref>{{OrgSynth|first1=Nana B.|last2=Murelli|last1=Agyemang|first2=Ryan P.|year=2019|title=Synthesis of 5-hydroxy-4-methoxy-2-methylpyrylium trifluoromethanesulfonate from Kojic acid|volume=96|pages=494-510|prep=v96p0494}}</ref> |
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==Chemical properties== |
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==Chemical properties== |
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Pyrylium and its derivatives form stable ]s with a variety of anions.<ref>{{cite book |author=Gilchrist, T. L. |title=Heterocyclic Chemistry |year=1997 |publisher=Longman |isbn=0-582-27843-0}}</ref><ref>{{cite book |author1=Balaban, A. T. |title=Advances in Heterocyclic Chemistry Volume 10 |author2=Schroth, W. |author3=Fischer, G. |chapter=Pyrylium Salts Part I. Syntheses |publisher=Academic Press |year=1969 |editor1=Katritzky, A. R. |volume=10 |location=New York |pages=241–326 |doi=10.1016/S0065-2725(08)60499-7 |isbn=978-0-12-020610-0 |editor2=Boulton, A. J.}}</ref><ref>{{cite book |author1=Balaban, A. T. |title=Pyrylium Salts. Syntheses, Reactions and Physical Properties |author2=Dinculescu, A. |author3=Dorofeenko, G. N. |author4=Fischer, G. W. |author5=Koblik, A. V. |author6=Mezheritskii, V. V. |author7=Schroth, W. |publisher=Academic Press |year=1982 |isbn=978-0-12-020652-0 |editor=Katritzky, A. R. |series=Advances in Heterocyclic Chemistry: Supplement |volume=2 |location=New York}}</ref><ref>{{cite book |author=Balaban, A. T. |title=New Trends in Heterocyclic Chemistry |publisher=Elsevier |year=1979 |isbn=978-0-444-41737-4 |editor1=Mitra, R. B. |series=Studies in Organic Chemistry |volume=3 |location=Amsterdam |pages= |chapter=The Pyrylium Cation as a Synthon in Organic Chemistry |editor2=Ayyangar, N. R. |editor3=Gogte, V. N. |editor4=Acheson, R. M. |editor5=Cromwell, N. |chapter-url=https://archive.org/details/comprehensivecar0000unse/page/79}}</ref><ref>{{cite book |author=Balaban, A. T. |title=Organic Synthesis: Modern Trends |publisher=Blackwell |year=1987 |isbn=0-632-02014-8 |editor=Chizov, O. |location=Oxford |pages=263–274 |chapter=Pyrylium Salts as Useful Synthons}}</ref><ref>{{cite book |author1=Balaban, T. S. |title=Hetarenes and Related Ring Systems, Six-membered Hetarenes with one Chalcogen |author2=Balaban, A. T. |publisher=Georg Thieme Verlag |year=2003 |isbn=978-3-13-118641-6 |series=Science of Synthesis; Houben-Weyl Methods of Molecular Transformations |volume=14 |location=Stuttgart |pages=11–200 |chapter=Pyrylium Salts}}</ref><!---Pyrylium ] is soluble in ]. |
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The carbon to oxygen ] is also an ], which due to aromatic stabilization is much less reactive than ordinary oxonium ions. However, the parent compound pyrylium is unstable in neutral water like oxonium salts. Pyrylium cations react with ]s in the 2,4 and 6 positions and may result in ring-opening reactions. The high electronegativity of the oxygen results in the strongest single perturbation of one heteroatom in a six-membered ring. |
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Trimethylpyrylium perchlorate has a melting point of 246–247 °C. |
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Being aromatic, pyrylium salts are easily formed from simple starting materials, and their reactivity toward nucleophiles makes them useful materials for obtaining other compounds with stronger aromatic character. Thus, pyrylium salts afford pyridines with ammonia <ref>''2,6-Di-tert-butyl-4-methylpyridine'' ], Coll. Vol. 7, p.144 (1990); Vol. 60, p.34 (1981). </ref>, pyridinium salts with primary amines, pyridine-N-oxides with hydroxylamine, phosphabenzenes with phosphine derivatives, ] salts with hydrogen sulfide, and benzene derivatives with ] or ]. |
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2,4,6-Triphenylpyrylium tetrafluoroborate, yellow needles, mp 214-215° |
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==Synthesis== |
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Pyrylium salts with aromatic substituents such 2,4,6-triphenylpyrylium tetrafluoroborate can be obtained from two moles of ] and one mole of ] in the presence of ] and an oxidizing agent ('''Dilthey synthesis'''). For pyrylium salts with alkyl substituents such as 2,4,6-trimethylpyrylium salts, the best method uses the ''']-]-Praill synthesis''' from tertiary butanol and ] in the presence of tetrafluoroboric, perchloric, or trifluoromethanesulfonic acids. <ref>A.T. Balaban and A.J. Boulton, Org. Synth., Coll. Vol.5, 1112-1113 (1973): 2,4,6-Trimethyl-pyrylium tetrafluoroborate.</ref> <ref>] and A.J. Boulton, Org. Synth., Coll. Vol.5, 1114-1116 (1973): 2,4,6-Trimethyl-pyrylium trifluoromethanesulfonate. </ref> 2,4,6-Triphenylpyrylium salts are converted by bases into stable a 1,5-enedione (pseudobase) but 2,4,6-trimethylpyrylium salts on treatment with hot alkali hydroxides afford an unstable pseudobase that undergoes an intramolecular condensation yielding 3,5-dimethylphenol. In warm deuterium oxide, 2,4,6-trimethylpyrylium salts undergo isotopic exchange of 4-methyl hydrogens faster than for the 2- and 6-methyl groups, allowing the synthesis of regioselectively deuterated compounds. |
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2-Methyl-4,6-diphenyl pyrylium chloride: light yellow, mp 125–126.--> |
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==Pyrones== |
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] |
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A pyrylium cation with a ] anion ] in the 2-position is not the ]ic aromatic compound ('''1''') but a neutral ] ] or an ] or pyran-2-one ('''2'''). Important representatives of this class are the ]s. Likewise a 4-hydroxyl pyrylium compound is a φ-pyrone or pyran-4-one ('''4''') to which group belongs a compound such like ]. |
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Like other ]s, pyrylium is unstable in neutral water. However, pyrylium is much less reactive than ordinary oxonium ions because of aromatic stabilization. The highly electronegative oxygen strongly perturbs the orbitals in the aromatic ring, and pyrylium derivatives are extremely resistant to ]. Pyrylium cations react with ]s at the ], typically through ].<ref name=":0">{{Cite journal |last1=Pang |first1=Yue |last2=Moser |first2=Daniel |last3=Cornella |first3=Josep |date=2020 |title=Pyrylium Salts: Selective Reagents for the Activation of Primary Amino Groups in Organic Synthesis |url=https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0039-1690703 |journal=Synthesis |volume=52 |issue=4 |pages=489–503 |doi=10.1055/s-0039-1690703 |s2cid=208705148}}</ref> |
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===Chemical properties=== |
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2-Pyrones are known to react with ]s in a ] to form ]s with expulsion of ], for example:<ref>''An alkynylboronic ester cycloaddition route to functionalised aromatic boronic esters'' Patrick M. Delaney, Jane E. Moore and Joseph P. A. Harrity ], '''2006''', 3323 - 3325, {{DOI|10.1039/b607322k}}</ref> |
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2,4,6-Triphenylpyrylium salts are converted by hydroxide bases into a stable 1,5-enedione (pseudobase), but 2,4,6-trimethylpyrylium salts on treatment with hot alkali hydroxides afford an unstable pseudobase that undergoes an intramolecular condensation yielding 3,5-]. In warm deuterium oxide, 2,4,6-trimethylpyrylium salts undergo isotopic exchange of 4-methyl hydrogens faster than for the 2- and 6-methyl groups, allowing the synthesis of regioselectively deuterated compounds.{{Cn|date=August 2024}} |
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==Derivatives== |
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==Chromenylium ion== |
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Pyrylium's electrophilicity makes them useful materials for producing other compounds with stronger aromatic character. Pyrylium salts afford ]s with ],<ref>{{OrgSynth |author= Anderson, A. G. |author2= Stang, P. J. |title= 2,6-Di-''tert''-Butyl-4-Methylpyridine |collvol= 7 |collvolpages= 144 |year= 1981 |volume= 60 |pages= 34 |prep= cv7p0144 |url= http://www.orgsyn.org/orgsyn/pdfs/CV7P0144.pdf}}</ref> ] salts with primary amines, ] with ], ]s with ] derivatives, ] salts with ], and benzene derivatives with ] or ]. |
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The benzo-fused pyrylium ion is also called benzopyrilium or according to ] chromenylium ion (Formula: C<sub>9</sub>H<sub>7</sub>O, molar mass: 131.15 g/mol, exact mass: 131.04968983). This is the charged version of ] or ] (IUPAC). |
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{{clear}} |
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==Flavylium ion== |
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Many important cations are formally derived from pyrylium by substitution of various ]s for some or all the hydrogens in the ring. ] reacts with ] to give ] derivatives called "] salts"; they are commonly used in metal-catalyzed ] of the amine.<ref name=":0" /> |
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In biology, the ion 2-phenylchromenylium is referred to as flavylium. A class of flavylium derived compounds are ]s and ], i.e., pigments that are responsible for the colors of many flowers.] |
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=== Pyrones === |
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{{clear}} |
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A pyrylium cation with a ] anion ] in the 2-position is not the ]ic aromatic compound ('''1'''), but the neutral ] ] ] or pyran-2-one ('''2'''). Important representatives of this class are the ]s. Likewise a 4-hydroxyl pyrylium compound is a ] or pyran-4-one ('''4'''), to which group belong compounds such as ].] |
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== See also == |
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2-Pyrones are known to react with ]s in a ] to form ] compounds with expulsion of ], for example:<ref>{{cite journal |author1=Delaney, P. M. |author2=Moore, J. E. |author3=Harrity, J. P. A. |title= An Alkynylboronic Ester Cycloaddition Route to Functionalised Aromatic Boronic Esters |journal= ] |year= 2006 |volume= 2006 |issue= 31 |pages= 3323–3325 |doi= 10.1039/b607322k|pmid=16883424 }}</ref>] |
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* 6-Membered aromatic rings with one carbon replaced by another group: ], ], ], ], ], ], ] |
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* ]s are pyrones lacking the ketone group. |
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=== Polycyclic oxonium arenes === |
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{{wiktionary|pyrylium}} |
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== References == |
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==== Chromenylium ion ==== |
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] as the ]]] |
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{{reflist|2}} |
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One ] pyrylium ion is called benzopyrylium ion (]: chromenylium ion) (formula: {{Chem2|C9H7O+}}, molar mass: 131.15 g/mol, exact mass: 131.04968983). It can be seen as a charged derivative of 2''H''-1-] (IUPAC: 2''H''-chromene, {{Chem2|C9H8O}}), or a (charged) substituted heterocyclic derivative of ] ({{Chem2|C10H8}}). |
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In biology, the 2-phenylbenzopyrylium (2-phenylchromenylium) ion is referred to as ]. A class of flavylium-derived compounds are ]s and ]s, pigments that are responsible for the colors of many flowers.{{Citation needed|date=July 2022}} |
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==== Naphthoxanthenium cation ==== |
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] |
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Higher ] derivatives of pyrylium also exist. One good example is ]. This dye is highly stable, aromatic, and planar. It absorbs in the UV and blue region and presents exceptional photophysical properties. It can be synthesized by chemical or photochemical reactions.<ref>{{cite journal |author1=Bucher, G. |author2=Bresolí-Obach, R. |author3=Brosa, C. |author4=Flors, C. |author5=Luis, J. L. |author6=Grillo, T. A. |author7=Nonell, S. |title= β-Phenyl quenching of 9-phenylphenalenones: a novel photocyclisation reaction with biological implications |journal= ] |year= 2014 |volume= 16 |issue=35 |pages= 18813–18820 |doi= 10.1039/C4CP02783C|pmid=25079707 |bibcode=2014PCCP...1618813B }}</ref> |
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==See also== |
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{{Wiktionary|pyrylium}} |
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* 6-membered aromatic rings with one carbon replaced by another group: ], ], ], ], ], ], ], ], ], ], ], ] |
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*], {{Chem2|C5H6O}} (pyrones lacking the ketone group) |
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==References== |
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{{DEFAULTSORT:Pyrylium Salt}} |
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{{Reflist}} |
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{{DEFAULTSORT:Pyrylium salt}} |
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