Butene isomerization constants

Table IV. Surface basicity (0g), posTtional (kj 2) and geometric (kc t)isomerization constant of 1- and 2-Butene at 297 K and energy of activation for diffusion of 1-Butene adsorbed on SnSbO catalysts.

We shall demonstrate the use of these equations by calculating the effect of a 20% decrease in the rate constants and k of the butene isomerization system discussed in Section II,B. The rate constants for this system are [Eq. (129)]... 

Fig. 31. The effect of a 20% decrease in the value of the rate constants fea and kjs for the butene isomerization system.

Figure 17 (a) Dependence of catalytic activities of aluminophosphate catalysts on the P/Al ratio (I) reaction rate constant for isobutanol dehydration, (II) reaction rate for I-butene isomerization, (b) H MAS-NMR spectra of aluminophosphate catalysts with different P/Al ratios A 1.6 B 1.4 C 1.0 D 0.5 E model compound AI(H2P04)2. Spinning sidebands are indicated by asterisks. Centerband chemical shifts are indicated in the plot. (From Ref. 14.)... 

Worked Example 4.15 The isomerization of 1-butene (X) to form frans-2-butene (XI). The equilibrium constants of reaction are given below. Determine the enthalpy of reaction AH using a suitable graphical method. 

Figure 4.8 The equilibrium constant K for the isomerization of 1-butene depends on the temperature van t Hoff isochore plot of In K (as y) against 1 7 (as x) from which a value of A//°...

However, (TMS)3Si radicals are found to add to a variety of double bonds reversibly and therefore to isomerize alkenes [19]. An example is shown for the interconversion of ( )- to (Z)-3-hexen-l-ol and vice versa by (TMS)3Si radicals (Reaction 5.1). Figure 5.1 shows the time profile of this reaction under standard experimental conditions (AIBN, 80 °C). The equilibration of the two geometrical isomers is reached in ca 10 h, and the percentage of Z/E = 18/82 after completion corresponds to an equilibrium constant of = 4.5. The difference in the stability of the two isomers in 2-butenes, i.e., AG°( -isomer) - AG° (Z-isomer) = — 3.1kJ/mol, corresponds to K = 3.5, since... 

A reaction of particular relevance with respect to applied catalysis is the oxidative dehydrogenation (ODH) of hydrocarbon by VmOn ions according to reaction 2, which involves a two-electron reduction of the cluster. By means of a systematic study of the reactions of various YmOn ions as well as the related oxo-vanadium hydroxides VmO H+ ions with a set of C4-hydrocarbons, it was demonstrated recently that the ODH activity of the cluster ions shows a clear correlation with the formal valence of vanadium in the cluster ions with a maximum reactivity for formal vanadium (V) (Fig. 3) [84]. In such a kind of reactivity screening, it is essential to include more than a single reagent as a probe for the reactivity of the different ions in order to reduce interferences by kinetic barriers of one particular combination of neutral and ionic reactants [85]. Accordingly, the sums of the relative rate constants for the ODH reactions of the four different butenes are considered and normalized to the most reactive ion studied, which turns out to be the formally pure vanadium (V) compoimd In addition to isomeric... 

The isomerization in hexane was allowed to proceed at room temperature until the ratio of the area of l-butene-3-hydroperoxide (13.5 minutes) to the new peak (at 25.5 minutes) became constant in 14 days. The combined peak areas for a constant sample size (30 //liters) showed little decrease on longer standing. The isomerized mixture (0.7 ml.) was stirred with 0.3 ml. of 1.0M sodium sulfite for 16 hours. The hexane layer was separated, and the aqueous layer was saturated with sodium sulfate and extracted twice with 0.5-ml. portions of hexane. The combined extracts were found to contain 81% 3-butene-2-ol and 19% crotyl alcohol. 

Different but still comparatively easy to understand is the reaction over the Sn/Sb catalyst. If it is in excess, the conversion of butene—90% to butadiene—is constant and independent of the composition indicating that reduction is fast and limited by the amount of oxygen available on the surface. Isomerization is absent, further proof of the speed of the reduction. At lower hydrocarbon pressures the rate is proportional to butene pressure. Consumption of. is never complete, showing that the reoxidation is slow, and it is only when 02 is in excess that oxygen consumption manages to keep pace with reduction. Here we encounter a situation where the surface reduction is fast, as it should be according to... 

Table 6 shows the composition of polymers prepared at different temperatures using aluminum chloride coinitiator. These data are compared with those for poly(3-methyl-l-butene) (4) in Fig. 21 where the logarithm of 1 is plotted versus the reciprocal absolute temperature. Since / is the ratio of the rate constants of isomerization and propagation of the initially formed secondary ion, the slope... 

Kinetics. Two series of experiments were performed, isomerizing about 55 cc (STP) of n-butenes or n-pentenes over 76 mg (dry basis) of catalyst I using 2 H20/cage as co-catalyst. The rate constant ratios were determined by either the extended Wei and Prater method (3) or the zero intercepts of the extrapolated product ratios obtained starting with different isomers. These ratios determined at different temperatures were plotted in Figure 1. The rate constant are defined as ... 

The isomerizations of n-butenes and n-pentenes over a purified Na-Y-zeolite are first-order reactions in conversion as well as time. Arrhenius plots for the absolute values of the rate constants are linear (Figure 2). Similar plots for the ratio of rate constants (Figure 1), however, are linear at low temperatures but in all cases except one became curved at higher temperatures. This problem has been investigated before (4), and it was concluded that there were no diffusion limitations involved. The curvature could be the result of redistribution of the Ca2+ ions between the Si and Sn positions, or it could be caused by an increase in the number of de-cationated sites by hydrolysis (6). In any case the process appears to be reversible, and it is affected by the nature of the olefin involved. In view of this, the following discussion concerning the mechanism is limited to the low temperature region where the behavior is completely consistent with the Arrhenius law. 

The isomerization of butene-1 has been reported in the presence of a mixture of AlEtg and NiCl2py2 (79), and Cramer has found that a very rapid isomerization of this olefin occurs in acidic solutions of Ni[P(OEt)3]4 (122). The initially formed butene-2 has a cis-to-trans ratio of 2.5 1, although as time progresses the ratio changes to 1 3 in favor of the trans isomer. The relative rate constants for the isomerization of linear butenes with Ni[P(OEt)g]4 and H2SO4 at 25° have been given as shown in Fig. 9 (122). 

Fig. 9. Relative rate constants for the isomerization of linear butenes with Ni-[P(OEt)3]4.

This isomerization with Ni[P(OEt)a]4 in acid solution has been studied in some detail by Tolman (282). No evidence for the isomerization of butene-1 could be found in the absence of added acid, but, in the presence of acids, both butene-2 and a little butane were formed. The reaction was first order in NiH[P(OEt)3]4 and butene-1, and a rate order was found which was inversely proportional to the concentration of the phosphite. The rate expression is given by (L = P(OEt)3 and is a composite rate constant)... 

The isomerization of n-butene (shown for -butene) involves three isomers related by six rate constants. The overall rate of DBI is k, + kj. The initial (kinetic) cis/trans mole ratio (C/T) is k,/kj and measures the stereoselectivity of DBI. 

Hence, for the isomerization of butenes over pure alumina catalyst at 230° in an all glass flow reactor, the relative rate constants are... 

Considerable data are available for triplet yields of benzene in dilute solutions of different solvents (see Table 13). In the main, two techniques have been used sensitized phosphorescence of biacetyl, sensitized cis-trans isomerization of butene-2, octene-2, and stllbene. All yield comparable results. In saturated hydrocarbon solvents at room temperature, the triplet yield for CgHg is found to be about 0.24 0.01. There is a solvent dependence of this quantity, the yield dropping to 0.15 in ethanol, 0.13 in methanol, and 0.09 in acetonitrile (91). In determining the effect of environment on the rate constant controlling intersystem crossing, values for emission lifetimes in the various systems are needed. These are, as mentioned previously, often unreliable. Cundall and Pereira (91) have reported... 

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