Ethylene selective formation

The effect of the catalyst-steroid ratio has been studied for the p-toluene-sulphonic acid-catalyzed ketalization of androst-4-ene-3,17-dione. Selective formation of the 3-monoketal is observed with the use of an equimolar amount of ethylene glycol and a low ratio of catalyst to steroid. ... 

The saturated 3-ketone can also be protected as the ethylene ketal, which is prepared directly by reaction with ethylene glycol or by exchange dioxo-lanation. Selective formation of 3-ethylenedioxy compounds is also possible, but the former method is not particularly effective in the presence of 6-, 17- or 20-ketones. However, the exchange dioxolanation technique is more sensitive to steric effects and good selectivity at C-3 can be achieved in the presence of a 17-ketone, provided the reagent does not contain glycol. ... 

At lower temperatures (260°C) higher operating pressures (5 bar) and high C2H4 to 02 ratios (Fig. 8.42) ethylene oxide formation and C02 formation both exhibit electrophobic behaviour over the entire Uwr range 47 Both rates vary by a factor of 200 as UWr is varied by 0.6 V (p varies between 3 and 0.015). The selectivity to ethylene oxide exhibits two local maxima 47 More interestingly, acetaldehyde appears as a new product47... 

Scheme 4. Possible scheme for selective formation of ethylene.

The feasibility of acid-catalyzed direct hydroamination has been demonstrated. Acidic zeolites afford, at low conversions, highly selective formation of ethyla-mine,297,298 isopropylamine,298 and ferf-butylamine,298-301 in the reaction of ammonia with ethylene, propylene, and isobutylene, respectively. Amine formation is explained as a reaction of surface carbocation intermediates with adsorbed or... 

The simplest possible alkene oligomerization reaction, the dimerization of ethylene to butenes, is a well-studied reaction, and an industrial process was also developed for the selective formation of 1-butene42 (IFP Alphabutol process). 

Practical Applications. IFP s Alphabutol process is used to dimerize ethylene selectively to 1-butene.43,85 The significance of this technology is the use of 1-butene as a comonomer in the polymerization of ethylene to produce linear low-density polyethylene (see Section 13.2.6). Under the reaction conditions applied in industry (50-60°C, 22-27 atm), the selectivity of 1-butene formation is higher than 90% at the conversion of 80-85%. Since no metal hydride is involved in this system, isomerization does not take place and only a small amount of higher-molecular-weight terminal alkenes is formed. 

The different degrees of water inhibition on the ether and olefin formation from ethanol on alumina, and the agreement of ether/ethylene selectivity ratios found experimentally with those calculated by the Monte Carlo simulation of the hydrated surface of alumina [144],... 

Institute for Industrial Research of Oslo, Norway. A unique metallo-organic catalyst system has been discovered which enables the selective trimerization of ethylene to 3-methyl-2-pentene. High temperature de-methanation of this compound results in the formation of isoprene in good yields. Similarly, since 1-butene and 2-butene are dimers of ethylene, they react with ethylene selectively in the liquid phase to produce 3-methyl-2-pentene. 

Ziegler discovered the selective formation of l-butene from ethylene promoted by AIR3 without undergoing the oligomerization of ethylene in the presence of a small amount of an Ni salt. This was called the Ni effect [3] which lead to the great discovery of the Ziegler catalyst, prepared by the combination of TiCU and EtjAl. 

When an oxidative coupling or addition takes place in the presence of carbon monoxide, CO insertion occurs leading to ketones. The Ru3(CO)12-catalyzed reaction of alkenylpyridyl or Af-(2-pyridyl)enamines and ethene performed under an atmosphere of carbon monoxide leads to the selective formation of a,/3-unsaturated ketones [16] (Eq. 11). After activation of the vinyl C-H bond, insertion of both carbon monoxide and ethylene takes place to give 25. 

The method in Figure 17 often gives a product which contains traces of the corresponding (E,E)-diene. This isomer can be selectively removed from the (E., Z)-isomer, as described above, by formation of its Diels-Alder adduct with excess tetracyano-ethylene in tetrahydrofuran followed by chromatography on silica gel (cf. 17,18). Alternatively, the (E.,E)-isomer can be removed in many cases by the selective formation of its crystalline urea inclusion complex in methanol (cf. 13). 

Heat catalyzes free radical formation in cellulose. Aldehydes form from C2 and C3 hydroxyls. Aldehydes oxidize to carboxyls, and with dehydration, carbon monoxide (CO) and carbon dioxide (C02) form as well as conjugated carbonyl-ethylenic chromophoric groups that selectively absorb blue light and impart yellowness (35). During the induction stage of cellulose oxidation, yellowness may increase steadily with selective carbonyl and ethylene group formation. By artificially aging... 

In view of these results, it is surprising that no rearrangement occurs during the aluminium chloride-catalyzed reaction of terf-butyl chloride with ethylene [97]. The intermediacy of a primary carbocation can, therefore, be ruled out and the selective formation of 18 may be rationalized by assuming the intermediacy of a bridged cation (tert-butyl-bridged ethylene). Alternatively, the attack of the /er/-butyl cation at ethylene may be nucleophilically assisted by the AIC14 ion because of the low stability of the 3,3-dimethyl-l-butyl cation (Scheme 22) [98],... 

Shima, T. and Hou, Z.M. (2006) Hydrogenation of carbon monoxide by tetranuclear rare earth metal poly-hydrido complexes. Selective formation of ethylene and isolation of well-defined polyoxo rare earth metal clusters. Journal of the American Chemical Society, 128, 8124. 

Although hydrogen is believed to suppress the formation of carbon deposits, coking may still occur in hydrogenation reactions as well. During ethylene hydrogenation, extensive coke deposits are noticed on the feed side of Pd-Y membranes and are believed to eventually lead to the embrittlement and rupture of the dense membranes due to carbon diffusion inside the membrane [Al-Shammary et al., 1991]. A modest deposit of carbon could actually increase the selective formation of ethane which may be indicative of some reaction taking place on the carbon deposit. 

Pettit et al. (J06) earlier proposed this propagation mechanism to explain the selective formation of propene in the reaction between ethylene and /i-methylene diiron carbonyl complexes, as shown in the following scheme ... 

In order to assess whether a catalyst optimized for epoxybutene formation was active and selective for ethylene oxide formation as well as whether a state of the art ethylene oxide catalyst (11) was active and selective for epoxybutene production, the two different catalysts were evaluated and the data summarized in Table 3. The ethylene oxide catalyst showed excellent performance (even at one atmosphere pressure) for the formation of ethylene oxide, yet was virtually inactive... 

A complete analysis of the products reported in Fig. 1 requires some more comments on cyclopentadiene and benzene. Both are typical secondary products, and are mainly the result of successive addition and condensation reactions of alkenes and unsaturated radicals. Once a significant amount of ethylene and propylene is formed, vinyl and allyl radicals are present in the reacting system and form butadiene, via butenyl radicals. Successive addition reactions of vinyl and allyl-like radicals on alkenes and dialkenes sequentially explain the formation of cyclopentadiene and benzene. These reactions are discussed in-depth in the literature and will be also analysed in the coming paragraphs (Dente et al., 1979). It seems worthwhile mentioning that these successive reactions and interactions of small unsaturated radicals and species constitute the critical sub-mechanism for the correct evaluation of ethylene selectivity. In fact, once the primary decomposition of the hydrocarbon feed has largely completed, the primary products and mainly small alkenes can be... 

This reaction is observed as a side reaction of hydroformylation. With ethylene the formation of diethyl ketone can be optimized to give high product selectivities, however, with higher, especially unsymmetrically substituted alkenes, only low ketone product selectivities and re-gioselectivities are observed. Thus, the reaction is only rarely applied to open chain ketone synthesis and little information is available about the stereochemistry of this reaction type1 -3. 

Lai j SrxFe03-y (0oxidative dehydrogenation of ethane and isobutene. Yi et al. (1996) studied the former reaction and further investigated the phase diagram to verify a phase separation between La-rich and Sr-rich perovskites. They explored the 573-1073 K temperature region and reported that the maximum ethylene selectivity occurred at 923 K. At lower temperatures, CO2 predominates and at higher temperatures, cracking and synthesis gas formation occur. DTA and XRD indicate that a phase separation occurs between La-rich and Sr-rich perovskites. This separation was reflected in both the conductivity and catalytic activity. 

Reaction of aryl halides with boronic acids catalyzed by palladium compounds (Suzuki reaction) is one of the most versatile reactions for selective formation of carbon-carbon bonds. One of the first reports of the application of microwaves to this type of reaction was published by Larhed et al. in 1996 [115]. Subsequently, Varma et al. described the Suzuld-type coupling of boronic acids and aryl halides (Eq. 80) in the presence of palladium chloride and poly(ethylene glycol) (PEG-400) under the action of MW irradiation [116]. The reactions were performed at 100 °C to give the desired coupling products in 50 to 90% yield within 50 s. The coupling reaction can be also conducted under conventional conditions (oil bath, 100 °C), but to achieve similar yields a longer reaction time was needed (15 min). It was found that addition of KE affords better yields. 

In an analogous way, HFA undergoes cycloaddition with halogenated ethylenes CF2=CFX (X = Cl, Br, H) in the presence of ACF catalyst to afford the corresponding oxetanes. The selective formation of only one regioisomer 5 (along with acyclic alcohols as minor by-products) in the reaction of CH2=CF2 is consistent with electrophilic mechanism of the process, presented by Scheme 2.8. ... 

Poisoning can affect the selectivity as well as the rate of conversion, and mild poisoning may be beneficial. The oxidation of ethylene is carried out using silver catalysts that are deliberately poisoned with chlorine compounds, and the selectivity is improved, because the total oxidation reaction is suppressed more than the rate of ethylene oxide formation [14]. The presence of sulfur compounds changes the selectivity for competitive hydrogenation, such as the hydrogenation of acetylenes or diolefins in the olefins [15]. 

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