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Hydrogenolysis chemical bond

Hydrogenolysis is analogous to hydrolysis and ammonolysis, which involve the cleavage of a bond induced by the action of water and ammonia, respectively. Chemical bonds that are broken by hydrogenolysis reactions include carbon—carbon, carbon—oxygen, carbon—sulfur, and carbon—nitrogen bonds. An example of hydrogenolysis is the hydrodealkylation of toluene to form benzene and methane ... [Pg.206]

Previously, Ermakov et al. —2— studied Pt-Mo/SiOj catalysts and found that the presence of Mo in Pt-Mo/Si02 catalysts increased the rate of hydrogenolysis by k orders of magnitude compared to Pt/SiOj catalysts and decreased the electron density of Pt as observed from x-ray electron spectroscopy. They interpreted these data in terms of chemical bonding between Pt and Mo and suggested a Pt°-Mo + complex on silica which has catalytic activity and selectivity similar to Rh or Ir rather than to Pt. [Pg.160]

The discovery that kink sites in steps are effective in breaking C C bonds in addition to C-H and H H bonds, thereby initiating hydrogenolysis reactions, may also explain the effect of trace impurities or second component metals that introduce selectivity. Since these kink sites have fewer nearest neighbors than step or terrace sites, they are likely to bind impurities or other metal atoms with stronger chemical bonds. Thus, these sites are readily blocked by impurities. As a result selective poisoning of hydrogenolysis may be obtained by minute concentrations o veil-chosen impurities or another metal component. [Pg.60]

Electrophilic catalysis may play an important role in the case of the similar benzylic carbon, too. For an O-benzyl system, it was found in a 1997 experiment that palladium oxide is a much more effective catalyst than palladium metal when the catalyst has been prereduced with chemical reducing agents. This finding shows very clearly that the electrophilic character of the unreduced metal ions plays an important role in the hydrogenolysis of the benzyl C—O bonds. Additional support for this mechanism is the fact that a small amount of butylamine can inhibit the hydrogenolysis of the benzyl C—O bond. [Pg.122]

The alkaloid chaenorhine (C31H40O5N4 mp 263-268° dec. [a]D + 46.7°) proved to be maerocyclic containing a spermine moiety. The entire gamut of spectral studies was involved to determine its structure (60). Of special interest is the observation that the hydrogenolysis of the alkaloid with sodium in liquid ammonia occurred at the ether linkage and generated 61 with concomitant reduction of the cyclic double bond. Hydrolysis, some chemical degradation, and further spectral studies served to elucidate the entire structure (31). [Pg.273]

There are many structurally and chemically interesting hydrido derivatives of the Cp and Cp lanthanide compounds. In many of these there are double hydrido bridges (19-1), but a number of more complex structures (e.g., 19-11) are also known. The hydrido compounds are generally quite reactive and often show activity as hydrogenation catalysts. They are most commonly obtained by hydrogenolysis of Cp2LnR compounds. Ln—R bonds undergo many other reactions, of which those... [Pg.1120]

These reactions are discussed in treatises on organic chemistry. Hydrogenolysis of metal- or nonmetal-carbon bonds are used for small-scale specialty chemical syntheses ... [Pg.235]

In contrast to these cases, for the Rhir heterometallic cluster catalysts inside NaY zeolite the dramatic suppression of hydrogenolysis by increasing the Ir contents is interpreted in terms not of a simple ensemble size effect but of an electronic state associated with the electron deficiency, namely, d-hole orbital of the clusters, as discussed for the Xe NMR chemical shifts on the series Rhe- tlr /NaY (245). The remarkable difference in hydrogenolysis activity between Rh and Ir crystallites inside NaY arises from their electron-deficient sites, which favor C—C bond scission via the alkane carbonium intermediate (177). The C2/C3 selectivity is defined as the ratio of the rates of butane conversion to ethane (k ) to the rates of butane conversion to methane plus propane (k,) ... [Pg.386]

From an applied perspective, metals are probably the most important surfaces in SOMC. Whereas in SOMC on oxides we introduce the active site, in SOMC on metals the metals themselves are the active catalysts. Organometallic chemistry provides the means to modify the often unselective metal surface by introduction of organometallic complexes (most often chemically inert) to the surface and eventually by transforming the initially obtained species by thermal or chemical means. For example, the hydrogenolysis of cyclic hydrocarbons, in particular cyclohexane, on the surface of unmodified Ir particles supported on a silica carrier has been studied and clearly indicated to bimetallic mechanism of C-C bond cleavage (Scheme 4) [24, 25]. [Pg.672]

Another successful promotion is in catalytic reforming, where addition of rhenium to platinum leads to vastly improved performance, due to decreased hydrogenolysis of the hydrocarbons. " The rhenium functions perhaps as an electronic promoter, but its exact role is still being debated. Chemically, the rhenium prercremially bonds with low coordination sites on crystal plane corners, edges and steps. Since these atoms appear to be involved with the hydrogenolysis, coke-forming reactions are suppressed. ... [Pg.37]

Selective catalytic hydrogenation of aromatic nitro compounds finds many applications in fine and specialty chemical industries (1). This class of hydrogenation reactions has been studied extensively using various solvents, catalysts and under various reaction conditions (1). The hydrogenation reaction has been found to follow mainly a mechanism that was delineated by Haber in 1898 from his study of electrochemical reduction of nitrobenzene (2). The mechanism, consisting of two types of reaction pathways, is schematically described in Fig. 1. The first pathway is a monomeric one that proceeds in three consecutive steps (a) hydrogenolysis of one of the N-O bonds in the nitro group to produce the nitroso intermediate ... [Pg.247]

Surface zirconium hydrides 1 result from hydrogenolysis of the Zr-C bonds of A at 150°C. A monohydride zirconium supported complex is the major species formed, but some zirconium dihydrides are present along with surface silanes, [Sijj-H, the product of reduction of siloxane bridges by the very reducing zirconium hydrides [6]. These latter are catalytically inert. The surface zirconium hydrides are stable up to 200°C under vacuum or hydrogen. Complexes 1 were fiilly characterized by physical techniques (in situ IR, EXAFS) and their chemical reactivity determined (towards O2, H2O, R-X, ROH, olefins) [6]. [Pg.354]


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See also in sourсe #XX -- [ Pg.182 , Pg.183 ]




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