Double bond isomerization, olefins

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

This process accounts for most of the observations relating to product stereochemistry, double bond isomerism, deuterium exchange and other features encountered in the hydrogenation and deuteration of olefins. 140-142,144 addition of hydrogen to the double bond proceeds in... 

The stereoisomers of olefin saturation are often those derived by cis addition of hydrogen to the least hindered side of the molecule (99). But there are many exceptions and complications (97), among which is the difficulty of determining which side of the molecule is the least hindered. Double-bond isomerization frequently occurs, and the hydrogenation product is the resultant of a number of competing reactions. Experimentally, stereochemistry has been found to vary, sometimes to a marked degree, with olefin purity, reaction parameters, solvent, and catalyst 30,100). Generalizing, it is expedient, when unwanted products arise as a result of prior isomerization, to avoid those catalysts and conditions that are known to favor isomerization. 

Not only the linear Cl0-Cl8 a-olefins but also the linear C10-Cl8 olefins with internal double bonds, the so-called -v /-olefins, are of great importance in surfactant chemistry, n-a-Olefins and n-y-olefins have the same suitability for the manufacture of linear alkylbenzenes, the most important synthetic anionic surfactants, by alkylation of benzene. Nowadays medium molecular weight n- /-olefins are industrially produced by two processes the catalytic dehydrogenation of the corresponding n-alkanes [4,28] and the cometathesis of low and high molecular weight n-v /-olefins, obtained by double-bond isomerization of the isomeric n-a-olefins [29]. 

Table 9 shows the composition of /i-i /-olefin mixtures obtained by the double-bond isomerization cometathesis reaction sequence of the SHOP process. 

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

Included are the dimerization, codimerization, oligomerization, double-bond isomerization, and cyclization of olefins. 

An olefin metathesis/double bond isomerization sequence can be promoted by the catalysis of in situ generated ruthenium hydride species from ruthenium complex 1 (Scheme 41 ).68... 

Double bond isomerization using molecular sieves (5A) was reported in the patent literature by Fleck and Wight of Union Oil Company [34] only a few years after synthetic zeolites became commercially available. More recently [35] ferrierite has also been claimed. The major initial uses were to convert a-olefins (1-olefins) into mixtures of internal olefins for further conversion, usually by oligomerization into various products-lube oil base stocks predominating. Inevitably, patents were issued noting the ability to convert internal olefins into mixtures containing greater concentrations of 1-olefins (e.g., [36]), but few practical processes have resulted. 

Double-bond isomerization reaction of simple olefins requires strong basic catalysts. Various catalyst systems have been reported for this reaction. They include sodium-organosodium catalysts prepared in situ by reacting an excess of sodium with a reactive organic compound, such as o-chlorotoluene or anthracene as reported by Pines and co-workers 5-8). 

An efficient synthesis of functionalized carbazoles was developed by the palladium-catalyzed annulation of a variety of internal alkynes. This reaction involves arylpalladation of the alkyne, followed by intramolecular Heck olefination, and double bond isomerization. The iodoindole 588 reacts with the alkyne 589 in the presence of a catalytic amount of palladium(O) to give substituted carbazoles 590. In this reaction two new C-C bonds are formed in a single step. Higher reaction temperatures were necessary due to the low reactivity of the iodoindole (566) (Scheme 5.29). 

In general the rates of hydrogenation of steroidal double bonds can be roughly classified as follows (a) readily hydrogenated A1, A2, A3, A4, A6, A14, A15 A14 16 diene, A16, A17(20), A20 and 19-vinyl (b) moderately difficult A5 > A22 and (c) difficult to hydrogenate A8 > A9(11) > A7 > A8(14). The data for the hydrogenation of A7-steroids is obscurred by the fact that this olefin is isomerized readily to the 8(14) position. Double bond isomerization does not occur with A7-9/ -steroids.18,23,39,54... 

The hydrogenation of 7 over the catalyst prepared by the reduction of 3 in the absence of any added ligand gave a cis/trans product ratio of 4.0. In addition, a rather large amount of the endo olefin, 10, was also formed. When the catalyst was prepared by the reduction of 3 in the presence of triphenylphosphine (6), a saturated isomer ratio of 2.0 was observed with no double bond isomerization. The same product stereochemistry and lack of double bond isomerization was also found using pre-hydrogenated 1 in the reduction of 7 (3). Thus, one might assume that the catalytic species in these latter two reactions are quite similar, if not identical. 

The hydrogenation of 2 occurred reasonably well in benzene-ethanol to give a rather poor catalyst for the hydrogenation of 1-heptene. The reduction of 2 in the presence of 6 gave a catalyst which was almost twice as reactive for this hydrogenation (Table II). In both cases though, double bond isomerization occurred almost as rapidly as did hydrogenation of 7 over these reduced 2 catalysts. But in this case, the catalyst prepared from 2 in the absence of 6 was almost completely unreactive, presumably because of the increased bulk of the olefin (Table III). 

The reactions using the three NO-containing complexes all showed equilibrium conversion to 2-butene and 3-hexene in 1 hr. The cis/trans ratios for all olefins were also at their equilibrium values (the initial 2-pentene was 48% trans, 52% cis). With the complex Mo(CO)4(bipy) there was observable disproportionation although the conversion was quite small. Some double-bond isomerization was observed with this system (1.2% 1-pentene present). The last complex of Table III also gave a trace of disproportionation, some double-bond isomerization (1.6% 1-pentene), and cis/trans isomerization (equilibrium ratio of cis/trans 2-pentene). 

Indirect evidence for this conclusion lies in the fact that as the alkylating/reducing power of the organoaluminum is increased, the extent of olefin double-bond isomerization accompanying disproportionation... 

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