Rate of olefins

The complete reduction of coal proceeds from aromatic rings through rings containing olefinic double bonds to saturated compounds. While reduction of the benzene ring takes place at a current efficiency of about 80% (8), current efficiency for reducing an olefin (1-decene) is only 27% as shown in this paper. The slow step in the coal reduction may very well be reduction of olefinic double bonds. An increase in the rate of olefinic double bond reduction may therefore lead to a considerable increase in current efficiency. 

An added complication in the interpretation of long-wavelength ketene photolysis is demonstrated by Cundall s discovery of ketene sensitized cis-trans isomerization of the 2-butenes.33 As the pressure of olefin increases, the rate of ketene decomposition decreases and the rate of olefin isomerization increases. At high olefin concentrations part of the apparent nonstereospecificity of cyclopropane formation can thus result from stereospecific singlet addition to already isomerized olefin. 

The comparison of the reaction rates of 03, H02, and CH302 with olefin, paraffin, and NO reveals that the predominant reactions of these reactive species are the oxidations of NO [(V1II-18), (VI11-21 a), and (VI11-24)]. The major destruction processes of olefin are the reactions with 03 and with OH. (The rate of olefin destruction is proportional to the rate constant times the concentration of the active species.) The destruction process of olefins by H02 is less important and those by O atoms and CH302 radicals are also minor. 

Previous work has shown that the electronic characteristics of the benzene substituent in triarylphosphine chlororhodium complexes have a marked influence on the rate of olefin hydrogenation catalyzed by these compounds. Thus, in the hydrogenation of cyclohexene using L3RhCl the rate decreased as L = tri-p-methoxyphenylphosphine > triphenylphosphine > tri-p-fluorophenylphosphine (14). In the hydrogenation of 1-hexene with catalysts prepared by treating dicyclooctene rhodium chloride with 2.2-2.5 equivalents of substituted triarylphosphines, the substituent effect on the rate was p-methoxy > p-methyl >> p-chloro (15). No mention could be found of any product stereochemistry studies using this type of catalyst. 

Correlation of rates of olefin reactions of the type shown in Figure 8 was first pointed out by Skell and Garner for the reactions with peracetic... 

The effects of added triphenylphosphine and changing temperature on ligand dissociation and equilibria were studied also. The above dimer was an active hydrogenation catalyst. The equilibrium concentration of the dimer and the rate of olefin hydrogenation catalysis by the system depend inversely on the concentration of excess phosphine ligand. 

It was shown that the rate of olefin production was dependent on the size of the metal cation (Li+, Na+, K+, Rb+, and Cs+) of the base. The increase in olefin production with an increase in cation size was explained as an increase in cation solvation by solvent with the larger cations, making t-butoxide a stronger base and thus increasing the rate of proton abstraction. Possibly these differences in cation solvation influence the reactivity of the carbanion intermediate for the conversion of benzothiophene and account for increased reactivity with the larger cation, potassium. 

Figure 3.13 Variation in the rate of olefin polymerisation in the presence of the MgCl2/TiCl4—A1( -Bu)3 catalyst with time A, ethylene B, propylene. Reproduced by permission of John Wiley Sons, Inc. from Ref. 241. Copyright 1989 Wiley New York...

FIG. 7. Rate of olefin formation from isobutanol at 220°C on 6-AI2O3 [expressed as olefin pressure (mm Hg) formed at constant contact time] versus integrated band area (arbitrary units) of band at 2870 cm-1. [Reproduced with permission from Knozinger and Stolz (47).]... 

Rates of Olefin Hydrogenation by Various Titanium Metallocenes ... 

Non-ideal conditions occur, for example, when the rate of (de)hydrogenation is less than that of cracking, so that the rate of olefin desorption will be low relative to (3-scission, leading to multiple cracking events, and lighter products. In this case a higher iso/normal ratio will be observed in the products than in the ideal case, since secondary isomerisation (i.e. of primary cracked products) is now possible. The results of a classical study of ideal vs. non-ideal HC are shown in Fig. 6.3 (cf. also ref. 27). 

A cis addition mechanism is generally accepted for the reaction, because cis addition to an olefinic bond generally occurs with predominant attack at trans bonds, and the Simmons-Smith reagent attacks preferentially one of the trans olefinic bonds of trans,trans,cis-1,5,9-cyclodode-catriene and then the cis double bond of the monoadduct (378). The close correspondence in relative rates of olefins for the cyclopropane formation by the Simmons-Smith reaction with those for diimide reduction and peroxide epoxidation supports the concept 409). The latter two reactions are generally considered to proceed via cis addition. 

Grubbs Phosphine exchange reaction kinetics on (3 a) and (4 a) The ratio of rates of olefin coordination to phosphine reassociation dictate rate of reaction, and permit the slower to initiate heteroleptic (3a) and (4a) to be more active catalysts. 

Propylene conversion over three SAPO molecular sieves (SAPO-5, SAPO-11, and SAPO-34) was conducted at a variety of operating conditions. Catalyst behavior was correlated with the physical and chemical properties of the SAPO molecular sieves. The objective of this work was to determine the relative importance of kinetic and thermodynamic factors on the conversion of propylene and the distribution of products. The rate of olefin cracldng compared to the rate of olefin polymerization will be addressed to account for the observed trends in the product yields. The processes responsible for deactivation will also be addressed. 

In addition to the rates of olefin reactions, mass transfer also plays an important role in determining the extent of propylene conversion and the product distribution from SAPO molecular sieves. Restrictions on molecular movement may be severe in the SAPO catalysts, due to pore diameters (4.3 A for SAPO-34) and structure (one-dimensional pores in SAPO-5 and SAPO-11). The deactivation of SAPO-5 and SAPO-11 catalysts may be more directly related to mass transfer than the coking of SAPO-34. Synthesis of large or highly-branched products, having low diffusivities, inside the pores of SAPO-5 or SAPO-11 essentially block internal acid... 

Mode/ equations. The mathematical model requires eight concentration-independent coefficients a to fcf, k, and k2l. From these it calculates the five A coefficients with eqns 11.8 to 11.12 from these, the rates of aldehyde and alcohol with eqns 11.6 and 11.7 and finally the rates of olefin, paraffin, H2, and CO with eqns 11.2, 11.5, 11.10, 11.11, 11.3, and 11.4, respectively. Alternatively, eqns 11.8 to 11.12 can be used to replace the A coefficients in eqns 11.6 and 11.7 in order to obtain explicit rate equations for aldehyde and alcohol in terms of the phenomenological coefficients. However, the resulting rate equations are more cumbersome. 

Example 12.2. Potential mass transfer-induced instability in olefin hydroformylation [14]. The rate of olefin hydroformylation with cobalt hydrocarbonyl catalysts in a liquid phase obeys in good approximation the Martin equation... 

Our cofeed studies were carried out at typical FT synthesis conditions and often in the added presence of water, an indigenous product of the FT reaction that also inhibits the rate of olefin hydrogenation and of other secondary reactions (4,30). In our studies, the addition of a-olefins to the H2/CO feed did not affect the rate of CO conversion also, at low concentrations (<5 mol%), added a-olefins did not affect the value of the chain growth probability. Thus, a-olefins act predominantly as chain initiators in our studies of FT synthesis on Co and Ru catalysts. 

Ethylene Cofeed Studies Effect of Water and of Reactor Inlet Bypass on Relative Rates of Olefin Hydrogenation and Chain Initiation... 

The rate of olefin hydrogenation reactions, however, increases markedly as CO disappears from the effluent stream (Fig. 12b). For example, propy-... 

Chain Oxidation of Propylene by OH Radicals. The potential role of OH radicals in explaining the excess rate of olefin consumption was discussed by Leighton in his monograph in 1961 (25), but no definite assessment of the importance was possible at that time. A quantitative analysis of the crucial role of an OH chain in explaining the excess rate during the NO-NO2 conversion was made by the authors in 1969 (11). This was an early report of our analysis of the data discussed here. Heicklen presented an independent discussion of this question (6). 

Ulman, M., Grubbs, R. H. Relative Reaction Rates of Olefin Substrates with Ruthenium(ll) Carbene Metathesis Initiators. Organometallics 1998, 17, 2484-2489. 

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