Butene reactions, normal

Butenes or butylenes are hydrocarbon alkenes that exist as four different isomers. Each isomer is a flammable gas at normal room temperature and one atmosphere pressure, but their boiling points indicate that butenes can be condensed at low ambient temperatures and/or increase pressure similar to propane and butane. The 2 designation in the names indicates the position of the double bond. The cis and trans labels indicate geometric isomerism. Geometric isomers are molecules that have similar atoms and bonds but different spatial arrangement of atoms. The structures indicate that three of the butenes are normal butenes, n-butenes, but that methylpropene is branched. Methylpropene is also called isobutene or isobutylene. Isobutenes are more reactive than n-butenes, and reaction mechanisms involving isobutenes differ from those of normal butenes. 

Normal Butene Reactions. Under alkylation conditions, all four butene isomers are believed to undergo isomerization, dimerization, and co-dimerization when first coming in contact with HF catalyst, i.e., immediately following protonation. These are very rapid, Ionic reactions and take place competitively along with isobutane alkylation. Alkylate compositions from the four butenes are basically similar (see Table VII). However, l-butene produces a C3 fraction containing nearly two times... 

Results from this laboratory for steam pyrolysis of isobutene were reported earlier (I), and this chapter describes the pyrolysis of the three normal butene isomers 1-butene, m-2-butene, and trans-2-butene. Reaction schemes are derived from the product distributions, and kinetic parameters are established. 

Oxydehydrogenation of /i-Butenes. Normal butenes can be oxidatively dehydrogenated to butadiene in the presence of high concentration of steam with fairly high selectivity (234). The conversion is no longer limited by thermodynamics because of the oxidation of hydrogen to water. Reaction temperature is below about 600°C to minimise over oxidation. Pressure is about 34—103 kPa (5—15 psi). 

Normal butenes and isobutylene are separated by a selective reaction-extraction... 

Of greater importance is the reaction of unsaturated compounds with sulfur at 200-250°C, which normally leads to l,2-dithiole-3-thiones (trithiones) but especially with 2-aryIsubstituted 2-butenes and 1- aryl- or 2-aryl-1-butenes, thiophenes are obtained in 15-60% Thus p-methoxy-a-ethylstilbene (50) gives 2-phenyl-3-... 

A solution of 61 parts 4-chloro-l,l-di-(4-fluorophenyl)-l-butene in 400 parts 2-propanol is hydrogenated at normal pressure and at room temperature in the presence of 5.5 parts palladium-on-charcoal catalyst 10% (exothermic reaction, temperature rises to about 30°C). After the calculated amount of hydrogen is taken up, hydrogenation is stopped. The catalyst is filered off and the filtrate is evaporated. The oily residue is distilled in vacuo, yielding l-chloro-4,4-di-(4-fluorophenyl)-butane, boiling point 166° to 168°C at 6 mm pressure ... 

The addition of one olefin molecule to a second and to a third, etc. to form a dimer, a trimer, etc. is termed oligomerization. The reaction is normally acid-catalyzed. When propene or butenes are used, the formed... 

The initial screening of the resin catalysts was done in a batch reactor at supercritical for butene-1 conditions of temperature 155 °C, pressure of 1000 psig and at molar ratio of 1-butene water of 5.5. The reaction was stopped after predetermined period of time and the products analyzed. It was found that under the standard reaction conditions, for all of the catalysts studied, a constant concentration in the sec-butanol concentration was achieved within a 1-2 hour reaction time. Using only the linear section of the concentration-time plot, the one hour result was used to evaluate the catalyst activity, which was normalized as mmol of SBA/ per proton/ per hour (a), as mmol of product/ per gram of dry catalyst/ per hour (b) and mmol of product/ per ml of wet catalyst/ per hour (c). 

An important feature of biphasic hydroformylation is the separability due to density differences. Because of the differences in density of the polar compound water (1.0 gem"1) and the hydrophobic oxo products (average 0.8), no problems occur. Additionally, the hydroformylation products are not sensitive to water. Another important question is to what extent water and the reactants are mixed. Therefore, the reactor in Figure 5.3 b), a continuously stirred tank reactor (CSTR) [22], normally contains usual installations to guarantee excellent mixing. For the lower alkenes with their significant water solubility (propene, butene) this is no problem. In these cases, the hydroformylation reaction takes place at the interfacial region [23]. 

Small amounts of hydrocarbons added to the normal tetrahydrofuran or diglyme solvent system result in improved WGSR activity, but larger quantities inhibit the reaction (Table II). When 1-butene or 1-hexene is used, hydroformylation competes with the WGSR (4 ), but the rate of this process is small compared with the rate of H2 production. With pentane, no olefin or aldehyde products could be detected. Calderazzo (29) has reported that Ru(C0) is the principal product when the acetylacetonate of ruthenium is treated with synthesis gas in heptane,... 

Isobutylene is the most chemically reactive of the butylene isopiers. If the objective is just to get the isobutylene out of the C4 stream, it can be removed by reaction with methanol (CH3OH) to make MTBE (methyl tertiary butyl ether), by reaction with water to make TBA (tertiary butyl alcohol), by polymerization, or by solvent extraction. After that, butene-1 can be removed by selective adsorption or by distillation. That leaves the butene-2 components, together with iso- and normal butane, which are generally used as feed to an alkylation plant. 

The a-hydrogen abstraction leads to an a ketoperoxide, which has been tentatively identified by Pitts in the case of cM-2-butene. Further reactions of the ketoperoxide include the formation of the normal products, i.e., the carbonyl products that can also be explained by the Criegee mechanism. The /3-hydrogen abstraction accounts for the ob-... 

Water has also been shown to be essential for the liquid phase polymerization of isobutylene with stannic chloride as catalyst (Norrish and Russell, 87). The rates of reaction were measured by a dilatometric method using ethyl chloride as common solvent at —78.5°. With a mixture consisting of 1.15% stannic chloride, 20 % isobutylene, and 78.8% ethyl chloride, the rate of polymerization was directly proportional to the amount of added water (up to 0.43% of which was added). A rapid increase in the rate of polymerization occurred as the stannic chloride concentration was increased from 0.1 to 1.25% with higher concentrations the rate increased only gradually. It was concluded that a soluble hydrate is formed and functions as the active catalyst. The minimum concentration of stannic chloride below which no polymerization occurred was somewhat less than half the percentage of added water. When the concentration of the metal chloride was less than about one-fifth that of the added water, a light solid precipitated formation of this insoluble hydrate which had no catalytic activity probably explains the minimum catalyst concentration. The addition of 0.3% each of ethyl alcohol, butyl alcohol, diethyl ether, or acetone in the presence of 0.18% water reduced the rate to less than one-fifth of its normal value. On the other hand, no polymerization occurred on the addition of 0.3 % of these substances in the absence of added water. The water-promoted reaction was halved when 1- and 2-butene were present in concentrations of 2 and 6%, respectively. 

Schuster and coworkers also demonstrated that trans olefins show distinctly lower normalized (negative) entropies of activation AS for the ene reaction than cis, and suggested that a reversible exciplex can be formed, followed by an allylic hydrogen-oxygen interaction in the rate-determining step. In the reaction of c -2-butene, the activation entropy AS is less negative by 10 e.u. than that of the trawi-2-butene, while the activation enthalpies are very similar. The considerable difference in the activation entropies was attributed to the fact that transition states in the case of cis olefins require more... 

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... 

Another large use of normal butenes in the petrochemical industry is in the production of 1,3-butadiene (CH2 = CH = CH = CH2). In the process, a mixture of n-butenes, air, and steam is passed over a catalyst at a temperature of 500°C to 600°C. Butadiene is used extensively to produce synthetic rubbers (see Isoprene) in polymerization reactions. The greatest use of butadiene is for styrene-butadiene rubber, which contains about a 3 1 ratio of butadiene to styrene. Butadiene is also used as a chemical intermediate to produce other synthetic organics such as chloroprene, for adhesives, resins, and a variety of polymers. 

In practice, short-chain alkanes and alkenes are normally used as feedstock for shape-selective catalytic formation of isooctanes at relatively low temperatures. Until the 1980s, lead alkyls (Section 18.1) were added to most automotive fuels to help suppress engine knock, but they have been phased out in North America because of the chronic toxicity of lead and lead compounds. The most commonly used nonlead antiknock additive is now methyl tert-butyl ether [MTBE CH30C(CH3)3], which is made by the reaction of methanol with 2-methylpropene, (CHs C—CH2 (see Section 7.4). The latter is obtained by catalytic cracking of petroleum fractions to give 1-butene, which is then shape-selectively isomerized on zeolitic catalysts. 

More information is available about orientation, when a second alkyl group is introduced into the aromatic ring, and about relative rates. As might be expected, propene reacts more easily than ethylene [342,346] and isobutene more easily than propene [342]. Normal butenes are sometimes isomerised in the process practically the same product composition, consisting mainly of 2,2,4-trimethylpentane, is obtained in the alkylation of isobutane whether the olefin component is isobutene or 2-butene [339]. In the alkylation of aromatic hydrocarbons, this side reaction is negligible. 

The molecular mechanism of the selective oxidation pathway is believed to be the one shown in Scheme 2 (Section I). Adsorbed butene forms adsorbed 7r-allyl by H abstraction in much the same way as xc-allyl is formed from propene in propene oxidation (28-31). A second H abstraction results in adsorbed butadiene. Indeed, IR spectroscopy has identified adsorbed 71-complexes of butene and 7t-allyl on MgFe204 (32,33). On heating, the 7r-complex band at 1505 cm 1 disappears between 100-200°C, and the 7t-allyl band at 1480 cm-1 disappears between 200-300°C. The formation of butadiene shows a deuterium isotope effect. The ratio of the rate constants for normal and deuterated butenes, kH/kD, is 3.9 at 300°C and 2.6 at 400°C for MgFe204 (75), 2.4 at 435°C for CoFe204, and 1.8 at 435°C for CuFe204 (25). The large isotope effects indicate that the breaking of C—H (C—D) bonds is involved in the slow reaction step. 

A very useful three-carbon olefin is acrolein dimethyl acetal (5). Acrolein itself cannot be used because it polymerizes and/or reacts with amines under the normal reaction conditions. With piperidine or morpholine as the base, acrolein acetals react in good yield with a wide variety of vinylic bromides to give dienal acetals and/or ami-noenal acetals. These product mixtures, after being treated with excess aqueous oxalic acid and being steam distilled, yield E,E-conjugated dienals, usually in good yields. Methacrolein acetals and 3-buten-2-one ethylene ketal also react well, but the crotonaldehyde acetals do not. 

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