Hexenes metathesis

A series of zeolite-Y hosts containing different proton concentrations has been used for MTO encapsulation [80], and the resulting materials were studied for 1-hexene metathesis. The MTO molecule was activated by intra-zeolite protons, and simultaneously blocks their isomerisation activity. The ability to tune intra-zeolite acidity and the doping levels of the intact MTO precatalyst permits control over selectivity in the metathesis reaction. 

In this process, which has been jointly developed by Institute Francais du Petrole and Chinese Petroleum Corp., the C4 feed is mainly composed of 2-butene (1-butene does not favor this reaction but reacts differently with olefins, producing metathetic by-products). The reaction between 1-butene and 2-butene, for example, produces 2-pentene and propylene. The amount of 2-pentene depends on the ratio of 1-butene in the feedstock. 3-Hexene is also a by-product from the reaction of two butene molecules (ethylene is also formed during this reaction). The properties of the feed to metathesis are shown in Table 9-1. Table 9-2 illustrates the results from the metatheses reaction at two different conversions. The main by-product was 2-pentene. Olefins in the range of Ce-Cg and higher were present, but to a much lower extent than C5. 

The most thoroughly studied reactions are the metathesis of propene to ethene and 2-butene, and the metathesis of 2-pentene to 2-butene and 3-hexene. Generally, the thermodynamic equilibrium ratio of the trans and cis components of the products is obtained. The reacting alkene molecules need not be identical, two different alkenes react with each other in the same way. 

It also explains the /Z selectivity of products at low conversions (kinetic ratio. Scheme 19). In the case of propene, a terminal olefin, E 2-butene is usually favoured (E/Z - 2.5 Scheme 19), while Z 3-heptene is transformed into 3-hexene and 4-octene with EjZ ratios of 0.75 and 0.6, respectively, which shows that in this case Z-olefins are favoured (Scheme 20). At full conversion, the thermodynamic equilibriums are reached to give the -olefins as the major isomers in both cases. For terminal olefins, the E olefin is the kinetic product because the favoured pathway involved intermediates in which the [ 1,2]-interactions are minimized, that is when both substituents (methyls) are least interacting. In the metathesis of Z-olefins, the metallacyclobutanes are trisubstituted, and Z-olefins are the kinetic products because they invoke reaction intermediates in which [1,2] and especially [1,3] interactions are minimized. 

Cross Metathesis of Nitrile Rubber with 1-Hexene... 

Soluble metathesis catalysts yield trans products in reactions with // / v-2-pentene, but generally are not very stereospecific with c/.v-2-pen-tene. In the latter case, the initially formed butenes and hexenes are typically about 60 and 50% cis, respectively. Basset noted (19) that widely diverse catalyst systems behaved similarily, and so it was suggested that the ligand composition about the transition metal was not a significant factor in the steric course of these reactions. Subsequently, various schemes to portray the stereochemistry have been proposed which deal only with interactions involving alkyl substituents on the reacting olefin or on the presumed metallocyclobutane intermediate. 

With these guidelines, the results from the metathesis of 4-methyl-2-pentene now appear to be reasonably accountable for. Most importantly, the lack of formation of c7s-2,5-dimethyl-3-hexene indicates that cis- 1,2-diisopropyl-substitution on the ring is highly unfavored, and trans-1,2-substitution leading to adjacent equatorial substituents is acceptable ... 

Cross-metathesis of methyl oleate with 3-hexene under similar conditions led, in addition to the above products [Eq. (54)], to 3-dodecene and the methyl ester of 9-dodecenoic acid. 

The reaction is called metathesis of olefins.557 In the example shown above, 2-pentene (either cis, trans, or a cis-trans mixture) is converted to a mixture of about 50% 2-pentene, 25% 2-butene, and 25% 3-hexene. The reaction is an equilibrium and the same mixture can be obtained by starting with equimolar quantities of 2-butene and 3-hexene.558 In general, the... 

In die last 10 years or so an exciting new strategy has emerged for the formation of carbon-carbon double bonds, namely olefin metathesis. This work grew out of the development of Ziegler-Natta catalysts for die polymerizarion of cyclic olefins. It was found that when 2-pentene was treated with a catalyst prepared from tungsten hexachloride and ethylaluminum dichloride, a mixture of 2-pentene, 2-butene, and 3-hexene was produced in minutes at room temperature (rt) ... 

In 1967, Calderon, Chen, and Scott4) reported a homogeneous catalyst system comprised of tungsten hexachloride, ethanol, and ethylaluminum dichloride would disproportionate internal olefins. These authors used the term olefin metathesis to describe the reaction. At room temperature 2-pentene was transformed in one to three minutes into a mixture containing, at equilibrium, 25, 50, and 25 mole per cent of 2-butene, 2-pentene, and 3-hexene, respectively. Double-bond isomerization was not detected and a quantitative reaction selectivity was obtained. Additional reports by Calderon and cowor-... 

The olefin metathesis of biodiesel (mixture of fatty acid methyl esters) in the presence of 1 -hexene was used by Meier et al. as a way to improve the distillation... 

Olefin metathesis can be very useful in the CM mode, as shown in the synthesis of insect phere-mones.46 In the first example for the synthesis of the peach twig borer pheromone 23, an excess of 1-hexene was used to increase the yield of the desired product. However, both of the other products could be recycled (Scheme 28.17). In the second example, CM was used to change the ester groups of meadowfoam oil (24) through cleavage of the alkenes rather than ester bonds. The sequence resulted in the synthesis of the mosquito pheromone (25) (Scheme 28.18). 

Davidson et al.m have also found that mixtures of [WBr2(CO)2(T/4-diene)] (diene = nbd, cod, cot)/AlCl2Et initiate the metathesis of cis-2-pentene to yield 2-butene and 3-hexene. For the norbornadiene complex, the reactions have been found to be catalytic. 

Analyses of the products obtained from the metathesis of 2-butene and 2-butene-dg (2, 5) and also from the metathesis of 3-hexene and 2-butene-d8 (5), proved that the interchange process in Reaction 1 definitely does not proceed via a simple transalkylation process—i.e.y a cleavage and reformation of the carbon-to-carbon single bond situated a to the double bond. The data are, however, consistent with a trans-alkylidenation process—i.e., a scheme which contemplates an interchange... 

Description Ethylene feedstream (plus recycle ethylene) and butenes feedstream (plus recycle butenes) are introduced into the fixed-bed, metathesis reactor. The catalyst promotes reaction of ethylene and 2-butene to form propylene and simultaneously isomerizes 1-butene to 2-butene. Effluent from the metathesis reactor is fractionated to yield high-purity, polymerization-grade propylene, as well as ethylene and butenes for recycle and small byproduct streams. Due to the unique nature of the catalyst system, the mixed C4 feed stream can contain a significant amount of isobutylene without impacting performance of the OCT process. A variation of OCT—Automet Technology—can be used to generate ethylene, propylene and the comonomer—hexene-1—by metathesis of n-butenes. 

WC16 Na[Re04] [C4C im][BF4] [C4C1im]Cl-AlCl3 Cross-metathesis of linear olefins, e.g. conversion of 1-hexene to 4-octene and 5-decene rather low conversions (<15-30%) addition of 10-30% SnBu4 significantly increases the yield and the selectivity for 4-octene (> 95%). [25]... 

Simple olefins undergo cycloaddition, one way or another, in the metathesis process with remarkable ease e.g., with a tungsten halide catalyst at room temperature, 2-pentene is converted to an equilibrium mixture of 2-butene, 2-pentene and 3-hexene in a few seconds >. One should reasonably expect a similar transformation of simple acetylenes, e.g., 26 - -27. The transformation 26 27 might appear, at first inspection, to be symmetry-allowed. 

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