Diffusion 1-butene

OH radicals react very fast (almost in a diffusion-controlled rate) with simple alkenes (k = 7.0 x 109 for 1-butene or cyclopentene and 8.8 x 109 M 1 s 1 for cyclohexene) and there is almost no change for 1,3- or 1,4-cyclohexadiene. Cycloheptatriene reacts very fast with all the three radicals formed in the radiolysis of water k = 6 x 109 with eaq, 8 x 109 with H atoms and 1 x 101CI M 1 s 1 with hydroxyl radicals13. 

The most notable feature of these intrazeolite photooxygenations (Fig. 30) is that the oxygen CT band experiences a dramatic bathochromic shift in comparison to solution. This was detected initially by recording the product growth as a function of irradiation wavelength (laser reaction excitation spectrum)98,110 and was later verified by direct observation using diffuse reflectance UV-Vis spectroscopy.111 For example, 2,3-dimethyl-2-butene CT-absorbance is shifted to lower energy by more than 300 nm... 

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.

Sampling in inverse coannular diffusion flames [62] in which propene was the fuel has shown the presence of large quantities of allene. Schalla et al. [57] also have shown that propene is second to butene as the most prolific sooter of the n-olefins. Indeed, this result is consistent with the data for propene and allene in Ref. 72. Allene and its isomer methylacetylene exhibit what at first glance appears to be an unusually high tendency to soot. However, Wu and Kem [111] have shown that both pyrolyze relatively rapidly to form benzene. This pyrolysis step is represented as alternate route C in Fig. 8.23. 

DAF-1, butene diffusion in, 42 36 Dangling bonds, 34 138 Data analysis, in extended X-ray absorption fine structure studies, 35 31-33 Dawson structure... 

Volume changes due to diffusion of butene from, and air into, a 5 mm thick foam sheet of density 28 kg m, with... 

When generated in zeolites, alkene or arene radical cations react with the parent molecules to form ti-dimer radical cations. For example, 2,3-dimethyl-l-butene and benzene formed 91 + and 92 +, respectively. The confinement and limited diffusion of the radical cation in the zeolite favor an interaction between a radical cation and a neutral parent in the same channel. 

C12H18O, Mr 178.28, does not occur in nature. It is a colorless liquid, >/ o.oi3kPa 86-91 °C, 20 0.960-0.964, Up 1.511-1.514, with a long lasting diffusive, fresh, floral, rose odor. The alcohol is prepared by hydrogenation of tetrahydro-4-methylene-5-phenylpyran which is obtained by cyclocondensation of benzaldehyde with 3-methyl-3-buten-l-ol in the presence of -toluenesulfonic acid [144]. 

Bell et al. (81) presented forced diffusion calculations of butene isomers in the zeolite DAF-1. DAF-1 (82) is a MeALPO comprising two different channel systems, both bounded by 12-rings. The first of these is unidimensional with periodic supercages, while the other is three-dimensional and linked by double 10-rings. The two channel systems are linked together by small 8-ring pores. It is a particularly useful catalyst for the isomerization of but-l-ene to isobutylene (S3) its activity and selectivity are greater than those of ferrierite, theta-1, or ZSM-5. 

Favorable sorption sites for the butene isomers were found to be the double 10-rings of the three-dimensional channel system. Thus, diffusion was investigated between adjacent 10-rings. Results showed that the diffusion was an activated process the lowest barrier was 17.5 kJ/mol (but-l-ene) and the largest 22.5 kJ/mol (m-but-2-enc). The authors concluded that all of the three-dimensional channel system is accessible by the four butene isomers, since the diffusion barriers are small enough to be overcome at ambient temperatures. 

It is well known that the butene oxidation rate is practically the same in the presence as (initially) in the absence of oxygen, which confirms the validity of a redox model. In contrast to the propene oxidation, the activity does not seem to decline very rapidly with increasing reduction as demonstrated, for instance, by Batist et al. [43]. This is evidence that much more than one surface layer of oxygen can be consumed and, moreover, implies that diffusion of oxygen through the lattice is a fast process. The latter is also confirmed, for instance, by the reduction—oxidation experiments of Beres et al. [47]. 

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. 

It is reasonable to consider that in titanium silicate-catalyzed reactions the oxidizing species also acts as an electrophile. The different order of reactivity of the C4 olefins in the presence of titanium silicates relative to that observed with soluble catalysts must therefore arise from the fact that alkyl substitution at the double bond is responsible not only for inductive effects, but also for increases in the size and the steric requirements of the molecules. Since the rates of diffusion of the different butenes cannot be the cause of the different reaction rates, a restricted transition-state selectivity must be operating. 

The reasons for these effects are simple. First, during their diffusion from the inside to outside of the zeolite crystallites, butene molecules inevitably must... 

Mechanistic investigations by Chapman and co-workers (99) indicated that these reactions occurred via a nonfluorescent singlet exciplex intermediate. While the rate constant for quenching of - -t5 by 2,3-dimethy 1-2-butene is slower than the rate of diffusion (Table 8), the limiting quantum yield for cycloaddition is 1.0. Thus, highly efficient exciplex cycloaddition may account for the absence of exciplex fluorescence, as in the case of t-1 photodimerization. Photochemical [2+2] cycloaddition reactions have also been observed to occur upon irradiation of the cyclic c-1 analogues diphenylcyclobutane (7) and diphenyl-vinylene carbonate (10) with 2,3-dimethyl-2-butene (96) however, the mechanistic aspects of these reactions have not been investigated. 

The enhanced diffusivity of polynuclear compounds in sc C02 has been utilized to enhance catalyst lifetimes in both 1-butene/isoparaffin alkylations (Clark and Subramaniam, 1998 Gao et al., 1996). The former may be catalyzed using a number of solid acid catalysts (zeolites, sulfated zeolites, etc.), and the use of sc C02 as a solvent/diluent permits the alkylations to be carried out at relatively mild temperatures, leading to the increased production of valuable trimethylpentanes (which are used as high-octane gasoline blending components). The enhancement of product selectivity in the latter process is believed to result from rapid diffusion of ethylbenzene product away from the Y-type zeolite catalysts, thus preventing product isomerization to xylenes. 

Addition of Blowing Agents to Styrene Solutions of Polystyrene. If the pentane is added to a suspension polymerization of styrene after the bead identity point has been reached, the formation of blisters is avoided and the diffusion of pentane into the bead is rapid. Thus, the two objections to the pentane-in-monomer process and the post-polymerization impregnation processes are avoided (31, 119). The same system has also been used to introduce normally gaseous blowing agents, such as butane, propane, st/m-dichlorotetrafluoroethane, propylene, butene, and butadiene (51, 91,115). 

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