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Orientation in the Addition of HD Molecules to Buta-1,3-diene over ZnO Catalyst. A Method of Judging Heterolytic and Homolytic Dissociation of Hydrogen in Catalysis

DOI: 10.1039/f19817701697

Source and publish data:

Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 1697 - 1706 (1981)

Update date:2022-08-02

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Authors:

Tanaka, Ken-ichiTanaka, Ken-ichi

Aomura, KazuoAomura, Kazuo

Okuhara, ToshioOkuhara, Toshio

Miyahara, KoshiroMiyahara, Koshiro

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Article abstract of DOI:10.1039/f19817701697

Selective 1,2-addition of HD molecules to butadiene on ZnO catalyst yielded 75percent of <3-(2)H1>but-1-ene and 25percent of <4-(2)H1>but-1-ene.Although the adsorption of HD on ZnO prefers <*> conformation at room temperature and the reverse conformation <*> at -40 deg C, reaction of HD at these two temperatures gave an identical ratio of <3-(2)H1>/<4-(2)H1> = 3.The dissociation of HD is in general expressed by <*> In the case of homolytic dissociation H(I) and H(II) or D(I) and D(II) should be identical, i.e. β = 1, but in heterolytic dissociation it may not be unity.Provided that the hydrogen molecular identity is maintained in the hydrogenated products, the following equations were derived for n- and sec-butenyl intermediates: <3-(2)H1>/<4-(2)H1> = <(2)H0>(1+ΑΒ)/<(2)H2>(Α+Β) for sec-butenyl and <3-(2)H1>/<4-(2)H1> = <(2)H2>(Α+Β)/<(2)H0>(1+ΑΒ) for n-butenyl, where Α is a relative rate constant of the reaction of H(I) and H(II) or D(I) and D(II) with butadiene.Accordingly, in homolytic dissociation the simple relations <3-(2)H1>/<4-(2)H1> = <(2)H0>/<(2)H2> or <(2)H2>/<(2)H0> should be established for homolytic dissociation, because α = 1 and Β = 1, whereas <3-(2)H1>/<4-(2)H1> will be equal to neither <(1)H0>/<(2)H2> nor <(2)H2>/<(2)H0> in heterolytic dissociation.It was confirmed that the hydrogenation on MoS2 is brought about by homolytic dissociation but that on ZnO it is caused by heterolytic dissociation.A plausible mechanism assuming ?-allyl anionic intermediates. <*> was proposed and it is explainable in terms of first-order kinetics in hydrogen pressure and the temperature-independent orientation in the 1,2-addition of HD.

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Product name:<3-(2)H>but-1-ene

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