Isomerization 2-pentenes

The loss of a proton from suitably substituted carbocations can provide both the trans- and ds-isomers of the resulting alkene, but the frans-isomer normally predominates. For example, deprotonation at C3 of the 2-pentyl carbocation produces mainly trans-peniene. By analyzing the relative energies of the conformational isomers of the carbocation that lead to the two isomeric 2-pentenes, explain why the fr s-isomer is formed preferentially. This analysis is aided by the use of Newman projections based on the partial structure shown. 

Beller and Krauter [63] found that by the effect of a Co(TPPTS) (TPPTS = trisodium salt of 3,3, 3"-phosphinidynetris(benzenesulfonic acid)) catalyst on a mixture of isomeric 2-pentenes, almost exclusively aldehydes were formed at a syngas pressure of 30-100bar and 130-150 C (Scheme 5.8). The Hb regioselectivity was 2 1. 

Scheme 5.8 Isomerization-hydroformylation of isomeric 2-pentenes in an aqueous two-phase system.

Figure 14. Variation with relative kinetic energy of cross sections for the formation of product ions resulting from the interaction of Co+ with isomeric pentenes. Symbols represent products corresponding to elimination of H2 (open circle), CH4 (solid square), C2H4 (open triangle), and C3H6(solid circle). Data from reference 50.

Olefins dissolved in aqueous acid are in rapid reversible equilibrium with a carbonium ion formed by addition of a proton.288 This rapidly and reversibly formed carbonium ion has to be a non-classical one in view of the behavior of the isomeric pentenes XLVI and XLVII.28 Both pentenes react with dilute nitric acid to give the same tertiary carbinol. If the reaction is interrupted when half of the olefin has been converted to carbinol, the remaining olefin has its original structure in both cases. The first product of protonation of the olefin is therefore of such a structure that loss of a proton gives only the original olefin. The reversibly formed carbonium ion can not therefore be the classical one. 

Most of the product distils at 36-37°. The product may contain a small amount of the isomeric pentene-i. By redistilling it through a 25-cm. (10-in.) fractionating column containing small pieces of glass rod, the pure hydrocarbon can be readily obtained. Pentene-2 boils at 36.3g° o.o4°/76o mm., melts at —138° 2° has the density d 0.6555, and 1.3839. 

Harmer and co-workers996,997 tested various Nafion-based samples in the dimerization of a-methylstyrene to form isomeric pentenes and a cyclic dimer, which are of industrial interest 13% and 40% Nafion-silica nanocomposites exhibited near-complete conversion and gave the cyclic dimer 300 with high selectivity [Eq. (5.360)], whereas compound 299a was the main product over Nafion NR50. In sharp contrast, isomeric pentenes 299 could be obtained in a continuous process (86% selectivity at conversion >95%). Similar findings were reported with Nafion immobilized in MCM-41 mesoporous silica. In kinetic studies, 13% Nafion-silica and the catalyst with... 

The dehydration of tert-amyl alcohol gives at least two isomeric pentenes (amylenes) ... 

Other isomeric pentenes may be formed by isomerization of the two olefins. If the heating is slow and careful the main product is 2-methyl-2-butene. 

Isomeric Pentenes and Quantitative Analysis of Two Mixtures by Means of the Raman Effect. 

It should be noted that all of the above complexes (except N4) either contain heavy atoms such as Br and I or are formed from reactants containing several double bonds. It has also been found that all of the isomeric pentene ions and cyclopentene ions form dimeric ions as one of the products of reactions with corresponding neutral molecules in the pressure range of 1—10 microns [132]. Recently, saturated hydrocarbons, ethane and propane, have also been found to form dimeric ions under certain conditions (see Sections 6.1.2 and 6.1.3). 

Draw structural formulas and give lUPAC names for all the isomeric pentenes (C5H10) that are ... 

Pentavitin . See Saccharide isomerate Pentene, homopolymer. See Polypentene 4-Pentenoic acid... 

Isomeric pentenes, hexenes, and octenes have been used frequently in academic research to study the properties of new catalytic systems [38, 39]. Kragl and coworkers [40] have screened the hydroformylation of a series of terminal olefins (1-pentene until 1-dodecene) with a rhodium catalyst based on BIPHEPHOS and achieved excellent n-regioselectivities and TOFs (turnover frequencies) between 1895 and 8200 h (Scheme 4.7). 

In a similar manner, Packett at Union Carbide realized a one-pot rhodium-catalyzed version of the methodology by using diols (ethylene glycol, 1,4-butane-diol, or 2,3-butanediol) as acetalization reagents and pyridinium tosylate as co-catalyst [12]. As ligands, bidentate diphosphites and diphosphines were utilized. Under these conditions, the main products were the corresponding diacetals (up to 55%), whereas in the absence of diols mainly isomeric pentenals ( 80%) and valeraldehyde ( 10%) were obtained. 

Duffy L M, Keister J W and Baer T 1995 Isomerization and dissociation in competition. The pentene ion story J. Phys. Chem. 99 17 862-71... 

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... 

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

The same reaction that gave 2 4 4 trimethyl 2 pentene also yielded an isomeric alkene This second alkene produced formaldehyde and 4 4 dimethyl 2 pentanone on ozonolysis Identify this alkene... 

Predict the preferred conformation of the isomeric (Z- and E-) 3-penten-2-ones, A R — CH3. How would you expect the conformational picture to change as R becomes progressively larger ... 

Unimolecular reactions that take place by way of cyclic transition states typically have negative entropies of activation because of the loss of rotational degrees of freedom associated with the highly ordered transition state. For example, thermal isomerization of allyl vinyl ether to 4-pentenal has AS = —8eu. ... 

Isomerization of fluoroolefins by a shift of a double bond is catalyzed by halide 10ns [7] The presence of crown ether makes this reaction more efficient [74] Prolonged reaction time favors the rearranged product with an internal double bond (equations 3-5) Isomerization of perfluoro-l-pentene with cesium fluoride yields perfluoro-2-pentenes in a Z ratio of 1 6 [75] Antimony pentafluoride also causes isomenzation of olefins leading to more substituted products [76]... 

The extent of double-bond isomerization over homogeneous catalysts is influenced by choice of solvent. Saturation of the double bond in 4-(4-me-thoxyphenyl)-3-(2 nitro-4-methoxyphenyl)-l-pentene was achieved smoothly by reduction over RhCl(Ph3P)j in benzene wiihout any hydrogenation of the nitro function. If the solvent were benzene-ethanol, isomerization of the double bond to a conjugated position also occurred ihis styryl bond was inert to reduction under these conditions (77). 

The next step is the isomerization of 2-methyl-1-pentene to 2-methyl-2-pentene using an acid catalyst. 

Finally, metalated epoxides undergo isomerization processes characteristic of traditional carbenoids (Scheme 5.2, Path C). The structure of a metalated epoxide is intermediate in nature between the structures 2a and 2b (Scheme 5.2). The existence of this intermediacy is supported by computational studies, which have shown that the a-C-O bond of oxirane elongates by -12% on a-lithiation [2], Furthermore, experimentally, the a-lithiooxycarbene 4a (Scheme 5.3) returned cydo-pentene oxide 7 among its decomposition products indeed, computational studies of singlet 4a suggest it possesses a structure in the gas phase that is intennediate in nature between an a-lithiocarbene and the lithiated epoxide 4b [3],... 

Kennedy, J. P. and Johnston, J. E. The Cationic Isomerization Polymerization of 3-Methyl-1-butene and 4-Methyl-l-pentene. Vol. 19, pp. 57—95. 

Another difference between the two mechanisms is that the former involves 1,2 and the latter 1,3 shifts. The isomerization of 1-butene by rhodium(I) is an example of a reaction that takes place by the metal hydride mechanism, while an example of the TT-allyl complex mechanism is found in the Fe3(CO)i2 catalyzed isomerization of 3-ethyl-l-pentene. " A palladium acetate or palladium complex catalyst was used to convert alkynones RCOCSCCH2CH2R to 2,4-alkadien-l-ones RCOCH= CHCH = CHCHR. ... 

Mordenite Isomerization of 2-methyl-2-pentene Higher activity [78]... 

Sandelin, F., Salmi, T., and Murzin, D. (2006) Dynamic modelling of catalyst deactivation in fixed bed reactors skeletal isomerization of 1-pentene on ferrierite. Ind. Eng. Chem. Res., 45, 558-566. 

Hence, the rate depends only on the ratio of the partial pressures of hydrogen and n-pentane. Support for the mechanism is provided by the fact that the rate of n-pentene isomerization on a platinum-free catalyst is very similar to that of the above reaction. The essence of the bifunctional mechanism is that the metal converts alkanes into alkenes and vice versa, enabling isomerization via the carbenium ion mechanism which allows a lower temperature than reactions involving a carbo-nium-ion formation step from an alkane. 

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