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Alkynes

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Bogdan Z. Dlugogorski – 1st expert on this subject based on the ideXlab platform

  • Inhibition and Promotion of Pyrolysis by Hydrogen Sulfide (H2S) and Sulfanyl Radical (SH).
    Journal of Physical Chemistry A, 2016
    Co-Authors: Zhe Zeng, Mohammednoor Altarawneh, Ibukun Oluwoye, Peter Glarborg, Bogdan Z. Dlugogorski

    Abstract:

    This study resolves the interaction of sulfanyl radical (SH) with aliphatic (C1–C4) hydrocarbons, using CBS-QB3 based calculations. We obtained the C–H dissociation enthalpies and located the weakest link in each hydrocarbon. Subsequent computations revealed that, H abstraction by SH from the weakest C–H sites in alkenes and Alkynes, except for ethylene, appears noticeably exothermic. Furthermore, abstraction of H from propene, 1-butene, and iso-butene displays pronounced spontaneity (i.e., ΔrG° < −20 kJ mol–1 between 300–1200 K) due to the relatively weak allylic hydrogen bond. However, an alkyl radical readily abstracts H atom from H2S, with H2S acting as a potent scavenger for alkyl radicals in combustion processes. That is, these reactions proceed in the opposite direction than those involving SH and alkene or alkyne species, exhibiting shallow barriers and strong spontaneity. Our findings demonstrate that the documented inhibition effect of hydrogen sulfide (H2S) on pyrolysis of alkanes does not appl...

  • Inhibition and promotion of pyrolysis by hydrogen sulfide (H2S) and sulfanyl radical (SH)
    Journal of Physical Chemistry A, 2016
    Co-Authors: Zhe Zeng, Mohammednoor Altarawneh, Ibukun Oluwoye, Peter Glarborg, Bogdan Z. Dlugogorski

    Abstract:

    © 2016 American Chemical Society. This study resolves the interaction of sulfanyl radical (SH) with aliphatic (C 1 -C 4 ) hydrocarbons, using CBS-QB3 based calculations. We obtained the C-H dissociation enthalpies and located the weakest link in each hydrocarbon. Subsequent computations revealed that, H abstraction by SH from the weakest C-H sites in alkenes and Alkynes, except for ethylene, appears noticeably exothermic. Furthermore, abstraction of H from propene, 1-butene, and iso-butene displays pronounced spontaneity (i.e., Δ r G° < -20 kJ mol -1 between 300-1200 K) due to the relatively weak allylic hydrogen bond. However, an alkyl radical readily abstracts H atom from H 2 S, with H 2 S acting as a potent scavenger for alkyl radicals in combustion processes. That is, these reactions proceed in the opposite direction than those involving SH and alkene or alkyne species, exhibiting shallow barriers and strong spontaneity. Our findings demonstrate that the documented inhibition effect of hydrogen sulfide (H 2 S) on pyrolysis of alkanes does not apply to alkenes and Alkynes. During interaction with hydrocarbons, the inhibitive effect of H 2 S and promoting interaction of SH radical depend on the reversibility of the H abstraction processes. For the three groups of hydrocarbon, Evans-Polanyi plots display linear correlations between the bond dissociation enthalpies of the abstracted hydrogens and the relevant activation energies. In the case of methane, we demonstrated that the reactivity of SH radicals toward abstracting H atoms exceeds that of HO 2 but falls below those of OH and NH 2 radicals. (Figure Presented).

Midori Goto – 2nd expert on this subject based on the ideXlab platform

  • facile regio and stereoselective hydrometalation of Alkynes with a combination of carboxylic acids and group 10 transition metal complexes selective hydrogenation of Alkynes with formic acid
    ChemInform, 2012
    Co-Authors: Ruwei Shen, Tieqiao Chen, Yalei Zhao, Yongbo Zhou, Xiangbo Wang, Midori Goto

    Abstract:

    The catalytic hydrogenation of Alkynes such as (I) with formic acid can be controlled by changing the conditions to selectively produce (Z)-alkenes such as (II), (E)-alkenes such as (III), or alkanes such as (IV).

  • facile regio and stereoselective hydrometalation of Alkynes with a combination of carboxylic acids and group 10 transition metal complexes selective hydrogenation of Alkynes with formic acid
    Journal of the American Chemical Society, 2011
    Co-Authors: Ruwei Shen, Tieqiao Chen, Yalei Zhao, Yongbo Zhou, Xiangbo Wang, Midori Goto

    Abstract:

    A facile, highly stereo- and regioselective hydrometalation of Alkynes generating alkenylmetal complex is disclosed for the first time from a reaction of alkyne, carboxylic acid, and a zerovalent group 10 transition metal complex M(PEt3)4 (M = Ni, Pd, Pt). A mechanistic study showed that the hydrometalation does not proceed via the reaction of alkyne with a hydridometal generated by the protonation of a carboxylic acid with Pt(PEt3)4, but proceeds via a reaction of an alkyne coordinate metal complex with the acid. This finding clarifies the long proposed reaction mechanism that operates via the generation of an alkenylpalladium intermediate and subsequent transformation of this complex in a variety of reactions catalyzed by a combination of Brϕnsted acid and Pd(0) complex. This finding also leads to the disclosure of an unprecedented reduction of Alkynes with formic acid that can selectively produce cis-, trans-alkenes and alkanes by slightly tuning the conditions.

Akiya Ogawa – 3rd expert on this subject based on the ideXlab platform

  • Selective Thiolative Lactonization of Internal Alkynes Bearing a Hydroxyl Group with Carbon Monoxide and Organic Disulfides Catalyzed by Transition-Metal Complexes
    Journal of Organic Chemistry, 2015
    Co-Authors: Shinya Higashimae, Taichi Tamai, Akihiro Nomoto, Akiya Ogawa

    Abstract:

    Although many transition-metal catalysts are ineffective for the addition and carbonylative addition of organic disulfides to internal Alkynes, dicobalt octacarbonyl and palladium complexes such as Pd(PPh3)4 and Pd(OAc)2 were found to exhibit excellent catalytic activity for the thiolative lactonization of internal Alkynes bearing a hydroxyl group. In the presence of the cobalt or palladium catalyst, internal Alkynes bearing a hydroxy group, such as homopropargyl alcohol derivatives, successfully undergo thiolative carbonylation with carbon monoxide and an organic disulfide regio- and stereoselectively to afford the corresponding thio group bearing-lactones in good yields. In the Co-catalyzed reaction, the cobalt–alkyne complex from dicobalt octacarbonyl and internal alkyne acts as a key species, making it possible to attain thiolative lactonization of internal Alkynes with a hydroxyl group. In the Pd-catalyzed reaction, the coordination of the hydroxy group to the palladium catalyst plays an important ro…

  • synthesis of selenium compounds by free radical addition based on visible light activated se se bond cleavage
    Mini-reviews in Medicinal Chemistry, 2013
    Co-Authors: Akihiro Nomoto, Yoshihiro Higuchi, Yohsuke Kobiki, Akiya Ogawa

    Abstract:

    Upon irradiation with near-UV or visible light, organic diselenides undergo homolytic cleavage of their
    selenium-selenium linkage to generate the corresponding seleno radicals, which can add to Alkynes, allenes, and related
    unsaturated compounds. In the case of Alkynes, vicinally diselenated alkenes are synthesized successfully. Photoinduced
    bisselenation of allenes takes place selectively at the terminal double bond of allenes. In sharp contrast, photoinduced
    addition of organic diselenides to alkenes is an inefficient process. However, combination of diselenides and disulfides
    under photoirradiation conditions results in highly regioselective thioselenation of alkenes based on the higher reactivity
    of thio radicals toward alkenes and the higher carbon radical capturing ability of diselenides. Similar conditions can be
    employed with a variety of unsaturated compounds such as Alkynes, allenes, conjugated dienes, vinylcyclopropanes, and
    isocyanides. This protocol can also be applied to selenotelluration, selenophosphination, and perfluoroalkylselenation of
    unsaturated compounds. The excellent carbon radical capturing ability of diselenides makes it possible to attain sequential
    addition of diselenides to several unsaturated compounds by suppression of polymerization of unsaturated compounds.
    When the sequential addition takes place intramolecularly under photoirradiation conditions, cyclic products are obtained
    successfully via a radical cyclization process. In addition, novel photoinduced electrocyclic reaction of o-alkynylaryl
    isocyanides with diselenides efficiently affords diselenated quinoline derivatives.