1- butene isomerization

The industrial reactions involving cis- and trans-2-butene are the same and produce the same products. There are also addition reactions where both 1-butene and 2-butene give the same product. For this reason, it is economically feasible to isomerize 1-butene to 2-butene (cis and trans) and then separate the mixture. The isomerization reaction yields two streams, one of 2-butene and the other of isobutene, which are separated by fractional distillation, each with a purity of 80-90%. Table 2-3 shows the boiling points of the different butene isomers. 

The process includes steps for isomerizing 1-butene into 2-butene at temperatures below 0 °C over alumina treated with alkaline metal and for disproportionating the 2-butene with isobutene over rhenium heptaoxide on alkaline-... 

What causes this problem This is a formalism, so there is no problem. The assignment of oxidation numbers in organic chemistry should not be overly burdened by questions of whether the procedure really makes sense. The important feature of the butenes of Figure 17.8 lies with the fact that the C atoms in the butenes on average possess the same oxidation number. The average oxidation numbers are (-3 -2 -l -2)14 = -2 for 1-butene and (-3 -1 -1 -3)/4 = -2 for 2-butene. The isomerization 1-butene —> 2-butene leaves the average oxidation... 

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. 

In HE alkylation, the processing of 1-butene leads to a significantly lower RON. Therefore, to avoid this octane loss, HF units often employ upstream selective hydrogenation/isomerization to isomerize 1-butene to 2-butene. 

Alkali Metals Supported on Metal Oxides. Alkali metals loaded on supports by deposition of the metal vapor have been reported as highly active catalysts for the isomerization of alkenes and the related compounds (31). For example, sodium metal deposited on alumina (Na/Al203) isomerizes 1-butene and 1-pentene at room temperature (31). Sodium metal deposited on MgO (Na/MgO) showed a high-catalytic activity for the isomerization of alkenes at 293 K and gave the basic sites stronger than = 35 (32). 

Many transition metal hydrides and low-valent complexes that can generate an M—H bond by protonation catalyze hydrogen migrations in olefins. Rhodium trichloride or rhodium(I) compounds plus HCl rapidly isomerize 1-butene to an equilibrium mixture of butenes in which trans-2-butene is the largest single component. Most of the complexes that catalyze olefin dimerization also catalyze isomerization. The isomerization mechanism postulated by Cramer is similar to his dimerization mechanism except that no insertion step is involved (185). 

Since ions analysed with a quadnipole instniment have low translational kinetic energies, it is possible for them to undergo bimoleciilar reactions with species inside an RF-only quadnipole. These bimoleciilar reactions are often iisefiil for the stnictural characterization of isomeric species. An example of this is the work of Flanison and co-workers [17]. They probed the reactions of CH. NHVions with isomeric butenes and... 

Figure Bl.7.10. Tliree mass spectra showing the results of reactive collisions between a projectile ion C H. NH, isomeric butenes. (Taken from Usypchiik L L, Harrison A G and Wang J 1992 Reactive...

Usypchuk L L, Flarrison A G and Wang J 1992 Reactive collisions in quadrupole cells. Part I. Reaction of [CFl3NFl2] with the isomeric butenes and pentenes Org. Mass Spectrom. 27 777-82... 

Prior to 1975, reaction of mixed butenes with syn gas required high temperatures (160—180°C) and high pressures 20—40 MPa (3000—6000 psi), in the presence of a cobalt catalyst system, to produce / -valeraldehyde and 2-methylbutyraldehyde. Even after commercialization of the low pressure 0x0 process in 1975, a practical process was not available for amyl alcohols because of low hydroformylation rates of internal bonds of isomeric butenes (91,94). More recent developments in catalysts have made low pressure 0x0 process technology commercially viable for production of low cost / -valeraldehyde, 2-methylbutyraldehyde, and isovaleraldehyde, and the corresponding alcohols in pure form. The producers are Union Carbide Chemicals and Plastic Company Inc., BASF, Hoechst AG, and BP Chemicals. 

In an effort to further support the proposed mechanisms for the Y+propene reaction, we have examined the reactions of Y with four isomeric butenes, which are essentially propene molecules with one additional methyl group (Fig. 31). Based on estimated potential energy barrier heights22 and thermodynamics (Fig. 32))22-31-34,i56,i57 q js eXpected that analogous product channels to those observed for propene should be seen for the butenes. Therefore, a comparison of reactions of butene isomers to reactions with propene should allow us to further test the validity of the proposed mechanisms. Here we briefly summarize our most notable conclusions from this work. 

BLISS [Butylene isomerization system] A process for isomerizing / -butenes to isobutene. Piloted by Texas Olefins Company in Houston, TX, 1990 to 1992. 

Polyethylene glycols (PEG) have been employed as phase transfer agents (and as solvents) in a number of reactions(11). Application of PEG-400 to the Wacker reaction results in the oxidation of both terminal and internal olefins (e.g., isomeric butenes to butanone) (12). 

Cyclohexene was shown to react partly by a radical mechanism when chlorinated in the absence of oxygen even in the dark.247 The reaction is slightly less stereoselective than the ionic process (96% trans-1,2-dichlorocyclohexane vs. 99%). Isomeric butenes under similar conditions give products nonstereoselec-tively.248 Branched alkenes are less prone to undergo free-radical halogenation. 

The hydrogenation of 1,3-butadiene, in contrast, yields a mixture of the isomeric butenes with product distributions highly depending on reaction conditions (nature of solvent, cyanide cobalt ratio) 134-136... 

Superacid-catalyzed alkylation of adamantane with lower alkenes (ethene, propene, isomeric butenes) has been investigated by Olah et al.151 in triflic acid and triflic acid-B(0S02CF3)3. Only trace amounts of 1 -ferf-butyladamantane (37) were detected in alkylation with 1- and 2-butenes, whereas isobutylene gave consistently relatively good yield of 37. Since isomerization of isomeric 1-butyladamantane under identical conditions did not give even traces of 37, its formation can be accounted for by (r-alkylation, that is, through the insertion of the ferf-butyl cation into the C—H bond (Scheme 5.22). This reaction is similar to that between ferf-butyl cation and isobutane to form 2,2,3,3-tetramethylbutane discussed above (Scheme 5.21). In either case, the pentacoordinate carbocation intermedate, which may also lead to hydride transfer, does not attain a linear geometry, despite the unfavorable steric interactions. 

Scheme 9.17 Product distributions from the reaction of isomeric d6-2,3-dimethyl-2-butenes with N-methyltriazolidinedione. Products a, b, c and d arise form H or D transfer from sites a, b, c and d in the isomeric butenes.

With the data in Figure 17.7, oxidation numbers can be assigned to the C atoms of the two isomeric butenes of Figure 17.8. Hence, 1-butene possesses the oxidation number -3 at one C atom, the oxidation number -2 at two C atoms, and the oxidation number -1 at one C atom. On the other hand, 2-butene consists of two sets of two C atoms with oxidation numbers -3 and -1, respectively. 

Draw the formulae of all the possible isomeric butenes and determine their symmetry elements and point groups. Use the flow chart in the appendix to assist you. 

In addition to the locations of the double bonds, another difference of alkenes is the molecule s inability to rotate at the double bond. With alkanes, when substituent groups attach to a carbon, the molecule can rotate around the C-C bonds in response to electron-electron repulsions. Because the double bond in the alkene is composed of both sigma and pi bonds, the molecule can t rotate around the double bond (see Chapter 6). What this means for alkenes is that the molecule can have different structural orientations around the double bond. These different orientations allow a new kind of isomerism, known as geometrical isomerism. When the non-hydrogen parts of the molecule are on the same side of the molecule, the term cis- is placed in front of the name. When the non-hydrogen parts are placed on opposite sides of the molecule, the term trans- is placed in front of the name. In the previous section, you saw that the alkane butane has only two isomers. Because of geometrical isomerism, butene has four isomers, shown in Figure 19.12. 

The thermal structural isomerization of methylcyclopropane has been studied by Chesick. The products are the four isomeric butenes... 

The aldehyde derived from the next higher hydrocarbon of the ethylene series, viz., the four carbon hydrocarbon, butene, is known as crotonic aldehyde because on oxidation it yields an acid known as crotonic acid. As there are two isomeric butenes due to the position of the double bond there will likewise be possible two isomeric aldehydes or butenals. 

Methylallyl Chlorides with K3Co(CN)dH. An aqueous solution of K3Co(CN)5 (200 ml., 0.15M cobalt, 0.15M KOH) was prepared in a hydrogen atmosphere, 300 ml. hydrogen being absorbed. A total of 0.0144 mole y-methylallyl chloride was injected in 0.004-mole increments. Each addition resulted in the rapid evolution of approximately 50 ml. gas, followed by a slow absorption of about 40 ml. gas. A gas sample was taken for analysis. Similar reductions of this substrate and of a-methylallyl chloride carried out at cyanide to cobalt ratios of 5.1 and 7.0 resulted in the formation of the isomeric butenes listed in Tables II and III under excess CoH. ... 

In another study, 1-butene was deuterated and the resulting butane and isomeric butenes were subjected to microwave spectroscopic analysis to determine the position of the deuterium atoms in each material. On the basis of these findings mechanistic proposals were presented for reactions considered to take place over each of the three different types of sites shown in Fig. 3.8.59-62... 

Fig. 11. The exchange of cts-2-butene and the deuterium content of the isomerized butenes as a function of percentage hydrogenation, over palladium-alumina at 18° (31).

In the reactions of 1-butene with deuterium at 30-60°, the two 2-butenes are almost equally deuterated but in each case 2-butene-do constitutes 50-60yo of the product. The isomerized butenes are rather less deuterated at higher temperatures. The general pattern of the high-temperature exchange results is very similar to that described for palladium in Section II, G, 2. Hydrogen exchange is, however, much more marked. 

Poutsma, M. L., Chlorination Studies of Unsaturated Materials in Nonpolar Media. 3. Competition between Ionic and Free radical Reactions During Chlorination of Isomeric Butenes and Allyl Chloride, J. Am. Chem. Soc. 1965, 87, 2172 2183. 

There are other significant differences between the ene reactions using these auxiliaries. For example, in the ene reaction with the isomeric butenes, /rn .v-2-phenylcyclohexanol affords a higher level of antijsyn selectivity than with the Z-isomer, although lower than observed with the oxoacetate of 5-methyi-2-(l-methyl-1 -phenylethyl)cyclohexanol (see Table 4. entries 3, 4 see also 8, 9). Furthermore, and again in contrast to the reactions using the oxoacetate of... 

A more sophisticated technique is necessary in the case of those reactions which lead to more than one olefin. Thus s-butyl halides (Maccoll and Stone, 1961) pyrolyse to yield three isomeric butenes... 

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