- Effect of ketene additive and Si/Al ratio on the reaction of methanol over HZSM-5 catalysts
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The influence of ketene as possible intermediate for the reaction of methanol to aromatics was investigated over HZSM-5 catalysts (Si/Al ratio of 15 and 9) using diketene-acetone (2,2,6-trimethyl-4H-1,3-dioxin-4-one) as ketene precursor under atmospheric
- Hassanpour, Javad,Zamani, Mehdi,Dabbagh, Hossein A.
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- Kinetics and regioselectivity of ring opening of 1-bicyclo[3.1.0] hexanylmethyl radical
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(Chemical Equation Presented) Rate constants for the rearrangement of 1-bicyclo[3.1.0]-hexanylmethyl radical (2) to 3-methylenecyclohexenyl radical (3) and 2-methylenecyclopentyl-1-methyl radical (1) were measured using the PTOC-thiol competition method. The ring-expansion pathway is described by the rate equation, log(k/s-1) = (12.5 ± 0.1) - (4.9 ± 0.1)/θ; the non-expansion pathway is described by log(k/s-1) = (11.9 ± 0.6) - (6.9 ± 0.8)/θ. Employing the slower trapping agent, tri-n-butylstannane, favors methylenecyclohexane over 2-methyl-methylenecyclopentane by more than 120:1 at ambient or lower temperatures.
- Kantorowski, Eric J.,Le, Daniel D.,Hunt, Caleb J.,Barry-Holson, Keegan Q.,Lee, Jessica P.,Ross, Lauren N.
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p. 1593 - 1596
(2008/09/17)
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- Deoxygenative coupling of ketones and alkenes by tungsten(II) compounds
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Tungsten(II) compounds such as WCl2(PMePh2)4 (1) react with acetone and ethylene to give a good yield of the tungsten(IV)-oxo complexes W(O)(CH2=CH2)Cl2(PMePh2)2 (4) and a moderate amount of 3-methyl-1-butene. Cyclopentanone and ethylene plus 1 yield 4 and vinylcyclopentane; methyl vinyl ketone and ethylene give 4 and 3-methyl-1,4-pentadiene. The reaction of cyclopentanone and propylene with 1 yields a small amount of 2-cyclopentylpropene. Intramolecular deoxygenative coupling occurs with 6- and 7-en-2-ones to form 1-methyl-2-methylene-substituted cyclopentyl and cyclohexyl ring systems, respectively. The net result of these reactions is transfer of the ketone oxygen atom to tungsten, accompanied with its replacement by a hydrogen and a vinyl group. The suggested mechanism for this deoxygenative coupling (Scheme I) is coordination of both the ketone and ethylene to tungsten, coupling to form a 2-oxametallacyclopentane, β-hydrogen elimination to an allyloxy hydride species, C-O bond cleavage to an oxo allyl hydride complex, and reductive elimination of alkene. Consistent with the suggestion of an oxametallacycle, hydrolysis of the reaction mixture of 1 and 6-hepten-2-one provides stereospecifically trans-1,2-dimethylcyclopentanol. The enones methyl vinyl ketone and 5-hexen-2-one react with 1 to form stable complexes in which the enone is bound in an η4 fashion, similar to the proposed mixed alkene ketone intermediates in the coupling reactions. A related tungsten(II) butadiene complex, WCl2(CH2= CHCH=CH2) (PMePh2)2, has also been isolated.
- Bryan, Jeffrey C.,Arterburn, Jeffrey B.,Cook, Gerald K.,Mayer, James M.
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p. 3965 - 3970
(2008/10/08)
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- KINETICS AND MECHANISM OF SOME VINYL RADICAL CYCLISATIONS
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The vinyl radicals 2a, 2b, and 11 each undergo fast exo ring closure to give 5a, 5b, and 12, the first two of which readily rearrange to ring-expanded radicals.
- Beckwith, Athelstan L.J.,O'Shea, Dennis M.
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p. 4525 - 4528
(2007/10/02)
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