The mechanism of olefin disproportionation

Crain, D. L.

doi:10.1016/0021-9517(69)90380-7

Cited by 25 publications

(3 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The above equilibrium constants when corrected by a factor of two for the reduced activity of water in the mixed solvent fall within a range characteristic of secondary cyclic amines (76-1600 M~l) and are to be compared to values of 2-40 M-1 for formaldehyde affinity of acyclic secondary amines. 4 The large differences in Ki between various amine types (primary, secondary, cyclic, etc.) has been attributed to steric effects on carbinolamine stability since Ki is nearly insensitive to amine pKaA The above values, however, probably also include binding of formaldehyde at the kinetically unproductive N-4 of the model substrates but not to any measurable extent at the exocyclic amino group owing to an absence of inhibition in kobsd at high formaldehyde concentrations.…”

Section: Resultsmentioning

confidence: 99%

Studies on models for tetrahydrofolic acid. II. Additional observations on the mechanism for condensation of formaldehyde with tetrahydroquinoxaline analogs

Benkovic

Chrzanowski

1970

J. Am. Chem. Soc.

View full text Add to dashboard Cite

The condensation of formaldehyde with additional tetrahydroquinoxaline model systems in which the basicity of the exocyclic amino group has been varied through alterations in para substitution has been studied. Supporting evidence for a mechanism involving general base catalysis of attack by the exocyclic amino group on the iminium cation to yield the imidazolidine adduct is derived from these investigations. Experiments with a similar tetrahydroquinoline model indicate the importance of the nitrogen-8 of the tetrahydropyrazine ring on the rate of acid-catalyzed dehydration of the intermediate carbinolamine. The implication of these results as to the mechanism of action of the natural cofactor is discussed.

show abstract

Section: Resultsmentioning

confidence: 99%

Studies on models for tetrahydrofolic acid. II. Additional observations on the mechanism for condensation of formaldehyde with tetrahydroquinoxaline analogs

Benkovic

Chrzanowski

1970

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…A heterogeneous catalyst for the reaction was discovered over 30 years later by Banks and Bailey, who found that alumina-supported molybdena catalyzed the metathesis of propylene to ethylene and butene with rather high selectivity below ∼650 K with an activation energy of ∼6 kcal/mol, , substantially lower than the value in the absence of a catalyst. Early theories for the effectiveness of the metathesis catalyst were framed in terms of lowering the activation barrier of a surface C 4 intermediate transition state − by having the substrate orbital participate in bonding with the reaction transition state and act as an electron sink to lower the transition state energy. This situation has been discussed in detail in a classical paper by Schachtschneider …”

Section: Introductionmentioning

confidence: 99%

Surface and Catalytic Chemistry of Small Hydrocarbons on Oxidized Molybdenum

Bartlett

1998

Langmuir

View full text Add to dashboard Cite

It is shown that model oxides grown on metallic substrates catalyze propylene metathesis to form ethylene and butene with an activity that mimics that of supported catalysts for reaction below ∼650 K. Another reaction regime is found for olefin metathesis above ∼650 K, where the reaction proceeds with a much higher activation energy of ∼60 kcal/mol. Unfortunately, alkenes do not react to any detecable extent on the model oxide surfaces in ultrahigh vacuum. However, the high-temperature (>650 K) metathesis rate is found to be affected by the presence of oxygen overlayers, which also modify the chemistry of alkenes on Mo(100) in ultrahigh vacuum. It is found that methane is formed by reaction of alkenes on O/Mo(100). The only other products detected are ascribed to either hydrogenation or total thermal decomposition into carbon and hydrogen. It is shown, using iodine-containing molecules to graft hydrocarbon fragments onto the surface, that alkenes can dissociate, forming carbenes which react to yield methane. This chemistry is in accord with that found catalytically at high temperatures, where the product distribution from the reaction of ethylene is well described by a Schulz-Florey distribution and the product distribution from propylene is well described by copolymerization of carbenes and methyl carbenes.

show abstract

“…deron et Zuech, 1968), that are active for disproportionating olefins have been disclosed. The abundance of data, including results of mechanistic studies (Bradshaw et al, 1967;Clark, 1968;Crain, 1969;Mol et al, 1968), indicates that the reaction proceeds by two unsaturated pairs of carbon atoms combining in a four-center transition state which dissociates by breaking either set of opposite bonds.…”

mentioning

confidence: 99%

Synthesis of Isoamylene via Olefin Disproportionation

Banks¹,

Regier²

1971

Product R&D

View full text Add to dashboard Cite

rates of all the isomerization reactions; the cis-and transisomers are simply indicated as lumped in Equation 4. The important result here is that the secondary isomerization step (Equation 4) is not immeasurably fast compared with the primary dealkylation step (Equation 3), but rather the rates are commensurable under the conditions of ester dealkylation over an acidic catalyst. The rate constants measured by the slopes of the lines in Figure 3 pertain to ky in Reaction 3, since all the butenes are lumped in the computation of conversion.If the simplified schematic indicated by Equations 3 and 4 is correct, we may expect in general that different activation energies would characterize the two reactionsfor example, Hightower et al. (1967) on the isomerization kinetics of 1-butene over fluorided alumina. If this occurs, the extent of secondary isomerization would be different at the two temperatures, for a given conversion. Our data bear out this expectation, although the effect is not great. At a conversion of about SOU, for example, the butenes produced at 178.5°C contained about 26' --butene; for the same conversion at 189°C they contained about 33'7 1-butene. A similar, small difference was

show abstract

The mechanism of olefin disproportionation

Cited by 25 publications

References 3 publications

Studies on models for tetrahydrofolic acid. II. Additional observations on the mechanism for condensation of formaldehyde with tetrahydroquinoxaline analogs

Studies on models for tetrahydrofolic acid. II. Additional observations on the mechanism for condensation of formaldehyde with tetrahydroquinoxaline analogs

Surface and Catalytic Chemistry of Small Hydrocarbons on Oxidized Molybdenum

Synthesis of Isoamylene via Olefin Disproportionation

Contact Info

Product

Resources

About