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  • 1
    Electronic Resource
    Electronic Resource
    On the Thermal Cycloisomerization of Long-Chain Alkylacetylenes in the Gas Phase (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 715-719 
    Details
    ISSN: 0009-2940
    Keywords: Alkyne ; Carbene ; Cycloisomerization ; Pyrolysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Über die thermische Cycloisomerisierung langkettiger Alkylacetylene in der GasphaseDie thermische Cycloisomerisierung einiger Alkylacetylene wurde in einem Laborrohrreaktor aus Quarzglas untersucht. 1-Hexin (1) wird dabei durch 1,2-H-Verschiebung und 1,5-C,H-Insertion des intermediär gebildeten Pentylidencarbens (vgl. Schema 1) in 3-Methyl-1-cyclopenten (5) umgelagert. 5-Methyl-1-hexin (2) reagiert analog; es entsteht 3,3-Dimethyl-1-cyclopenten (6). Im Gegensatz zur Bildung von in 3-Stellung methylierten Cyclopentenen aus 1-Alkinen ensteht aus 2-Hexin (3) 1-Methyl-1-cyclopenten (7). Offenbar ist die Acetylen-Vinyliden-Umlagerung nicht auf 1,2-H-Verschiebung beschränkt. Der Mechanismus der Cycloisomerisierung von Alkylacetylenen wird durch Untersuchungen mit D-markierten Alkinen bestätigt. Die Ergebnisse lassen den Schluß zu, daß die Cycloisomerisierung ohne weiteres mit dem überwiegend nach einem Radikalketten-Mechanismus verlaufenden thermischen Zerfall konkurrieren kann.
    Notes: The thermal cycloisomerization of some alkylacetylenes was investigated in a tubular quartz reactor. At 570°C 1-hexyne (1) rearranges to 3-methyl-1-cyclopentene (5) with a selectivity of about 27 by a reaction sequence including an acetylene-vinylidene rearrangement and 1,5-C,H insertion of the intermediately formed alkylidenecarbene species. 5-methyl-1-hexyne (2) behaves analogously forming 3,3-dimethyl-1-cyclopentene (6), while 2-hexyne (3) provides 1-methyl-1-cyclopentene (7) indicating that the acetylene-vinylidene rearrangement is obviously not restricted to 1,2-H shifts. The mechanism of the cycloisomerization of alkylacetylenes is investigated by means of D-labeled parent alkynes. The results show that the unimolecular cycloisomerization via alkylidenecarbenes obviously can be an important channel despite the dominance of a radical chain course.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220419
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  • 2
    Electronic Resource
    Electronic Resource
    Zur Gasphasenpyrolyse von 2-Ethinyl-1,3-butadien und dessen thermischer Cycloisomerisierung (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1375-1380 
    Details
    ISSN: 0009-2940
    Keywords: Cross-conjugated alkynes ; Alkadienynes ; Pyrolysis, gas-phase ; Cycloisomerization ; Vinylidenecarbenes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Gas-Phase Pyrolysis of 2-Ethinyl-1.3-butadiene and Its Thermal CycloisomerizationThe gas-phase pyrolysis of 2-ethinyl-1,3-butadiene (2) has been investigated in the 500-to-700°C temperature range. Besides several fragmentation products (≤C4 hydrocarbons) benzene and fulvene (5) are the main products. Under the same conditions 2-([2-D1]ethinyl)-1,3-butadiene (2a) furnishes the monodeuteriofulvenes 5a-c. The cycloisomerization of 2/2a presumably begins with an acetylene-vinylidenecarbene rearrangement, which may be followed by a deuterium scrambling mechanism involving either benzvalene (9) or vinylcyclobutadiene (10) intermediates. When 1-ethinyl-1-cyclohexene (6) is employed as a precursor for 2, styrene is produced in significant amounts besides the products observed from 2. Pyrolysis of 1-([2-D1]ethinyl)cyclohexene (6a) provides [D1]-styrene whose isotopic label is scrambled over both the vinyl substituent and the aromatic nucleus.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230629
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  • 3
    Electronic Resource
    Electronic Resource
    Naphthalene Isotopomers from Isotope-Labelled Phenyl-Annelated 1,3-Hexadien-5-ynes Facilitate an Evaluation of Competing Radical Cycloisomerization Pathways (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2135-2142 
    Details
    ISSN: 1434-193X
    Keywords: Pyrolysis ; 1,3-Hexadien-5-ynes ; Cyclization, radical ; 13C, D labelling ; Naphthalene isotopomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal cycloisomerization of the isotope-labelled 1-phenyl-1-buten-3-ynes 1 {including the [3-13C,4-D]1-phenyl-1-buten-3-yne (6) and the [4-D]1-phenyl-1-buten-3-yne (9) formed as intermediates} has been studied. The investigations were performed in a quartz flow system at a temperature of 650 °C (1, 6) [and over the range 625-750 °C for (9)] at a reaction time of 0.3 s in the presence of different diluent gases (H2, N2, N2-toluene). Spectroscopic analyses of the naphthalene isotopomers formed allow the evaluation of competing radical reaction channels in addition to reactions occuring by electrocyclic and carbene-like ring closure.[1] A mechanistic analysis for the conversion of 1 undoubtedly suggests a predominant reaction course via phenyl-type radical intermediates (1c/6c), followed by their exocyclization to the indenylcarbenyl radicals 1f/6f and the homoallyl-like rearrangement of the latter to the 1,2-dihydronaphthyl radicals 1i/6i at 650 °C. With increasing temperature, other competing reactions (endocyclizations of vinyl- and phenyl-type radicals as well as neophyl-like rearrangements of the indenylcarbinyl radicals 1f/6f) gain in importance.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, 3Part 2: K. Guthier, P. Hebgen, K.-H. Homann, J. Hofman, G. Zimmermann, Liebigs Ann. 1955, 637-644. A mechanistic study of the thermal cycloisomerization of 1,4-diphenyl-1-buten-3-yne (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 841-848 
    Details
    ISSN: 0947-3440
    Keywords: Pyrolysis, gas-phase ; Cycloisomerization ; Vinyl radical ; Vinylidene carbene ; Rearrangement, homoallyl ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase pyrolysis of 1,4-diphenyl-1-buten-3-yne (1) was investigated in the temperature range between 600 and 800°C and in the presence of different carrier gases (N2, N2/toluene, H2). By a detailed analysis (GC, GC/MS, GC/FTIR) all volatile reaction products were identified and quantitatively determined. Besides several fragmentation products (substituted benzenes C7-C10) and some carbon-rich deposits the main products are benzene (4), naphthalene (5) as well as 1- (2) and 2-phenylnaphthalene (3). Under similar conditions 4-(4-fluorophenyl)-1-phenyl-1-buten-3-yne (1a) furnished mainly fluorobenzene (4a), naphthalene (5), 1- (2a) and 2-(4-fluorophenyl)naphthalene (3a). - If sufficient H atoms are available in the reactive gas phase the conversion of 1/1a is predominantly controlled by radical processes. The cycloisomerization of 1/1a presumably starts with previously formed vinyl radicals, which might initiate a multi-step reaction cascade involving a 1,x-H shift and homoallyl reactions. However, if the reaction system is poor in H atoms (or other chain carrier radicals), a cycloisomerization path via vinyl-idene carbene species and their subsequent stabilization by intramolecular 1,6-C,H insertion into 3/3a obviously dominates the reaction events. It is concluded that the 1,2-dihydro-2-phenyl-1-naphthyl radicals 19/19a and the 1,2-dihydro-1-phenyl-2-naphthyl radicals 21/21a are important intermediates which are not only precursors of the aromatics 2/2a and 3/3a but also thought to be key intermediates for the most important degradation products 4/4a and 5.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199505122
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  • 5
    Electronic Resource
    Electronic Resource
    Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, I. Detailed analysis of the reaction products of ethynylbenzene (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 631-636 
    Details
    ISSN: 0947-3440
    Keywords: Pyrolysis, gas phase ; Vinyl radicals ; Cycloisomerization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis of ethynylbenzene (C8H6, 1) was studied in a flow system between 700 and 1100°C (reaction time about 0.3 s) by using a mixture of 5 mol-% of 1 in nitrogen and also in hydrogen at 700°C. The products were analyzed gas chromatographically. At 700°C in nitrogen, the main products were 1- and 2-phenylnaphthalene (2, 3), 1-methylene-2-phenyl-1H-indene (4), 1-methylene-3-phenyl-1H-indene (5), and 5,10-dihydroindeno[2,1-α]indene (6). At higher temperatures, ethynylaromatics and more stable aromatics such as benzene, naphthalene, acenaphthylene, biphenyl, pyrene, fluoranthene, and six further C16H10 isomers where detected. With hydrogen as diluent, the dimer formation was reduced, mainly in favor of styrene. - The complex mixture of reaction products and the dependence of its composition on the pyrolysis temperature cannot be explained in terms of one reaction scheme only. It is suggested that H atoms act as important chain carriers. At temperatures around 700°C they mainly add to 1 yielding the phenylvinyl radicals 1a and 1b. These add to 1 forming dimers C16H12 via radicalic intermediates C16H13. With increasing temperature the 2-phenylvinyl radical 1a not only reacts back to H + 1 but also decomposes by β(C—C) cleavage into phenyl and ethyne. The latter channel is more endothermic by 33 kJ/mol. Additionally, isomeric ethynylphenyl radicals are increasingly formed by bimolecular H abstraction. Thus, with increasing temperature product formation is controlled by reactions of phenyl-type radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950488
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