- Gas-Phase Synthesis of Triphenylene (C18H12)
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For the last decades, the hydrogen-abstraction?acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C14H9].) with vinylacetylene (C4H4), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH – triphenylene (C18H12) – via an unconventional hydrogen abstraction–vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level.
- Zhao, Long,Xu, Bo,Ablikim, Utuq,Lu, Wenchao,Ahmed, Musahid,Evseev, Mikhail M.,Bashkirov, Eugene K.,Azyazov, Valeriy N.,Howlader, A. Hasan,Wnuk, Stanislaw F.,Mebel, Alexander M.,Kaiser, Ralf I.
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- Migration of redundant ethynyl substituents along polycyclic aromatic hydrocarbon peripheries. Consequences for polycyclic aromatic hydrocarbon build up
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The formation of cyclopenta[cd]pyrene (5) and benzo[ghi]fluoranthene (6) upon FVT of 3,9-bisethynylphenanthrene (1) and 8-ethynylfluoranthene (2), respectively, suggests that redundant ethynyl substituents, which cannot give five- and/or six-membered ring formation via ethynyl ethylidene carbene equilibration followed by carbene C-H insertion, can migrate along the PAH periphery at high temperatures.
- Sarobe, Martin,Jenneskens, Leonardus W.,Kleij, Arjan,Petroutsa, Maria
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- The ethyne-ethylidene rearrangement: Formation of indeno[2,1-α]indene and fluoranthene on flash vacuum pyrolysis of 1,4-diphenylbutadiyne
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Diphenylbutadiyne on flash vacuum pyrolysis at 1120√0.03 Torr gave a pyrolysate (22% mass recovery) consisting of the diyne (7%), indeno[2,1-a]indene (19%), fluoranthene (59%), acephenanthrylene (13%) and aceanthrylene (2%). It is proposed that indeno[1,2-a]indene is formed via 3-phenyl-1,2-didehydronaphthalene and fluoranthene via 1-phenyl-2,3-didehydronaphthalene.
- Brown,Eastwood,Wong
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- Benzene Ring Contractions at High Temperatures. Evidence from the Thermal Interconversions of Aceanthrylene, Acephenanthrylene, and Fluoranthene
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The predicted interconversions of the title compounds (11, 13, and 15) at high temperatures have been verified (Table I) and represent the first examples of thermal rearrangements of aromatic hydrocarbons in which one benzenoid skeleton is transformed into another benzenoid skeleton.Equilibrium concentrations of 11:13:15 were found to be 17:9:74 at 1100 deg C.Acephenanthrylene (13) is the primary product of thermal rearrangement when starting from either aceanthrylene (11) or fluoranthene (15).It is also shown that acephenanthrylene rearranges more rapidly to fluoranthene than to aceanthrylene.These data are summarized in the qualitative energy profile in Figure 1.The mechanism by which these rearrangements occur appears to involve a carbon 1,2-shift (benzene ring contraction) and a hydrogen 1,2-shift, both across the same carbon-carbon bond but in opposite directions.The precise timing of these two shifts relative to each other remains uncertain.The range of possibilities is conveniently illustrated in the More O'Ferrall-Jencks diagram in Figure 2.The demonstration that aceanthrylene, acephenanthrylene, and fluoranthene can be interconverted thermally constitutes the first solid evidence for benzene ring contractions at high temperatures.
- Scott, Lawrence T.,Roelofs, Nicolas H.
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- Aryl-aryl bond formation by flash vacuum pyrolysis of benzannulated thiopyrans
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(Chemical Equation Presented) In contrast to fully unsaturated 7-membered ring sulfur heterocycles (thiepines), some of which extrude sulfur and give the ring-contracted hydrocarbon even at room temperature in solution, benzannulated thiopyrans (6-membere
- Amick, Aaron W.,Wakamiya, Atsushi,Scott, Lawrence T.
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p. 5119 - 5122
(2008/12/20)
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- Characterization of the combustion products of polyethylene
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Polyethylene (PE) was burned in a tube-type furnace with an air flow at a temperature of 600~900°C. Combustion products were collected with glass wool, glass fiber filter, and XAD-2 adsorbent. The analysis of the products was performed with GC-FID and GC-MSD. At low temperature, hydrocarbons were the major components, while at higher temperature the products were composed of polycyclic aromatic hydrocarbons. With the high performance of the Hewlett-Packard 6890GC-5973MSD, more compounds were identified in comparison with previous studies.
- Piao, Mingjun,Chu, Shaogang,Zheng, Minghui,Xu, Xiaobai
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p. 1497 - 1512
(2007/10/03)
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- Origin of Pyrene under High Temperature Conditions in the Gas Phase. The Pivotal Role of Phenanthrene
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4-Ethynylphenanthrene (15), and the latent precursors for 2-ethynyl- (18) and 3-ethynylphenanthrene (19), viz., 2-(1-chloroethenyl)- (16) and 3-(1-chloroethenyl)phenanthrene (17), respectively, have been subjected to flash vacuum thermolysis (FVT). Whereas at 800°C 15 is quantitatively converted into pyrene (1), 16 and 17 only give 18 and 19, respectively. Both 18 and 19 contain redundant ethynyl substituents, i.e., after ethynyl-ethylidene carbene equilibration neither five-nor six-membered ring formation can occur by carbene C-H insertion. At T ≥ 1000°C 16 and 17 gave pyrolysates containing the same set of 11 (non)-alternant polycyclic aromatic hydrocarbons (PAH), albeit in a different ratio. The different product ratio suggests that redundant ethynyl substituents migrate along the phenanthrene periphery presumably via transient cyclobuta-PAH intermediates toward positions suitable for either five- or six-membered ring formation by carbene C-H insertion. The results provide an explanation for the ubiquitous formation of pyrene (1), acephenanthrylene (9), and fluoranthene (3) during (incomplete) combustion. Phenanthrene (2) appears to be a point of divergence in PAH growth by C2 addition.
- Sarobe, Martin,Jenneskens, Leonardus W.,Steggink, Ralph G. B.,Visser, Tom
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p. 3861 - 3866
(2007/10/03)
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- Unexpected high temperature behaviour of 2,2′-diethynylbiphenyl in the gas phase - A precursor for acephenanthrylene instead of pyrene
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Flash Vacuum Thermolysis (FVT) of 2,2′-diethynylbiphenyl (6) gave, instead of pyrene (5), acephenanthrylene (10) and fluoranthene (11) as major products. The unequivocal identification of 9-ethynylphenanthrene (12) at T ≤ 800°C suggests that 12 is the initial stable product derived from 6. It is documented that under high-temperature conditions in the gas phase compound 12 is efficiently converted into 10, which subsequently rearranges to 11. The formation of 12 from 6 is rationalized by invoking the transient formation of cyclobuta[l]phenanthrene (13) by intramolecular cyclization of the ethynyl moieties of 6 followed by a reiro-carbene C-H insertion and a 1,2-H shift. This interpretation is supported by the results of independent FVT of 2,2′-bis(1-chloroethenyl)biphenyl (15). Wiley-VCH Verlag GmbH, 1997.
- Sarobe, Martin,Van Heerbeek, Rieko,Jenneskens, Leonardus W.,Zwikker, Jan W.
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p. 2499 - 2503
(2007/10/03)
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- Cyclopentindene (Benzopentalene) and Pentalene: Pyrolytic Formation from 3-Phenyl- and 3-Vinyl-phthalic Anhydrides
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Pyrolysis of 3-phenylphthalic anhydride at 900 deg/0.02 mm gives cyclopentindene, characterized by 1H n.m.r. at -70 deg and by formation of a cyclopentadiene adduct and of a dimer at room temperature.Pyrolysis of 3,4-, 3,5- and 3,6-diphenylphthalic anhydrides also gives much cyclopentindene by loss of the additional phenyl group. 3,4-diphenylphthalic anhydride forms triphenylene as the major product.The pyrolysate from 3-vinylphthalic anhydride contains the known dimer of pentalene, and phenylacetylene.Pyrolyses of 3-(1-naphthyl)phthalic anhydride and of 4-phenylphenanthrene-2,3-dicarboxylic anhydride are described.
- Brown, Roger F. C.,Choi, Neil,Eastwood, Frank W.
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p. 185 - 198
(2007/10/02)
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- Proposed Fullerene Precursor Corannulene Identified in Flames Both in the Presence and Absence of Fullerene Production
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Corannulene, C20H10, a bowl-shaped polycyclic aromatic hydrocarbon whose curvature and carbon framework are similar to those of fullerenes, has been widely hypothesized to be a fullerene precursor but has never been identified in flames, either in the presence or absence of fullerene production.In research on the mechanism and prevalence of fullerene formation in flames, we have identified corannulene in fullerene-producing flames and also in conventional flames that do not produce fullerenes.The identification was achieved using a combination of analytical methods including high performance liquid chromatography with UV-vis spectrometric detection, and gas chromatography coupled with infrared and mass spectrometric detection.The presence of corannulene in fullerene-forming flames is consistent with the hypothesis that corannulene is a fullerene precursor.The presence of corannulene in fullerene-deficient flames does not necessarily contradict this hypothesis and instead may suggest that at least some stages of fullerene formation chemistry are more generally operative in flames than had previously been known.
- Lafleur, Arthur L.,Howard, Jack B.,Marr, Joseph A.,Yadav, Tapesh
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p. 13539 - 13543
(2007/10/02)
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- The Pyrolysis of Phenylnaphthalene-dicarboxylic Anhydrides: Products of Ring Contraction and of Radical Cyclization
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Naphthalene-1,2-dicarboxylic anhydrides with neighbouring phenyl substituents give on flash vacuum pyrolysis (850-900 deg C/ 0.02-0.04 mm) ring-contracted carbenes which insert into the phenyl groups.The 8-phenyl anhydride (7) gives acephenanthrylene (10) as the major product, and the 3-phenyl anhydride (15) gives 1,2:4,5-dibenzopentalene (indenoindene) (18).The anhydides (7) and (15) were synthesized by pyrolisis of the corresponding 1-naphthylmethyl propynoates (2) and (13) through a new one-step process of intramolecular Diels-Alder addition/retro-Diels-Alder elimination of acetylene. 1-Phenylnaphthalene-2,3-dicarboxylic anhydride (19) on pyrolysis at 960 deg C/0.02 mm gives fluoranthene (11) as the major product.The behaviour of the 1-C6D5 compound (24) suggests involvement of radical cyclization process.
- Anderson, Mark R.,Brown, Roger F. C.,Coulston, Karen J.,Eastwood, Frank W.,Ward, Annemarie
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p. 1137 - 1150
(2007/10/02)
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