2-Pentene isomerization

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. 

As shown in Fig. 13, a variety of metal carbonyls upon sonication will catalyze the isomerization of 1-pentene to cis- and tram-2-pentene (186). Initial turnover rates are about 1-100 mol 1-pentene isomerized/mol of precatalyst/hour, and represent rate enhancements of 102 5 over thermal controls (174). The relative sonocatalytic and photocatalytic activities of these carbonyls are in general accord. An exception is Ru3(CO)12, which is... 

C5 Pentesom [Pentene isomerization] A process for isomerizing linear pentenes to isopentenes, catalyzed by a zeolite. The isopentenes are intended for use as intermediates in the production of ethers for use as fuel additives. Developed by UOP in 1992 and offered for license in 1993. See also C4 Butesom. 

Kinetics and Mechanism of w-Butene and w-Pentene Isomerization over Na-Y Zeolites... 

Figure 2. Arrhenius plot for 1-butene and 1-pentene isomerization...

The oxidation and double bond isomerization are competitive reactions, and the extents of these reactions are influenced by solvents. DMF is good for the oxidation, whereas use of acetic acid facilitates the isomerization. Both reactions proceed in alcoholic solvents. Acetonitrile and DMSO retard oxidation by complex formation with the catalysts. The double bond migration is facilitated by high temperatures. The oxidation of 1-octene in n-propyl alcohol yielded 2-octanone to the extent of 62% at 90 °C, 85% at 60 C, and more than 97% at 30 °C. 4-Methyl-1-pentene isomerized to the 2- and 3-alkenes, which formed ir-allylic complexes in ethanol, but normal oxidation to the methyl ketone took place in DMF and y-butyrolactone. ... 

Under the test conditions of table 1, catalyst life for 1-pentene isomerization exceeded 24 hours but in the same period conversion of 1-butene decreased to - 30%. The catalyst was regenerated at 450°C by air (15 min) then H2/H20 (1 hour). Repeated regenerations were successful. 

A post-exposure isomerization reaction was observed in which 2-methyl-l-pentene isomerized to 2-methyl-2-pentene. We propose that this reaction proceeds via S02-olefin charge transfer complexes. 

In the first instance a catalyst running in l-butene/H /H O at 360°C for 4 hrs and giving <30% branched product was exposed to l-pentene/Hg/H O at 360°C. The resultant branching of 1-pentene was excellent 63%. Other runs in which the reaction temperature was lowered to 300°C prior to admission of 1-pentene agreed with the above result. It is concluded that a catalyst inactive for 1-butene isomerization may still have activity for 1-pentene isomerization. 

Pentene isomerization and hydrosilylation have also been induced by irradiation of phosphinated polystyrene-bound FeCCO) complexes. ... 

The isomerization of 1-hexene to cis- and tra 5-2-hexene was performed with [RuAu( M-H)2(CO)(PPh3)4](PF6)J l Isomerization of 1-pentene was studied in the presence of [H3Ru4 Au(PPh3) (CO)i2] and [H2Ru4 Au(PPh3) 2(CO)i2]. These two clusters are clearly more active for 1-pentene isomerization than the parent [H4Ru4(CO)i2], in marked contrast to the behavior of the ruthenium-copper analogs. 

Fig. 4. Effect of pretreatment temperature on the activities of KF/AI2O3 for the isomerization of 1-pentene and Michel reaction between nitromethane and 2-hutanone 43 1-pentene isomerization at 273 K, Q Michael reaction at 273 K.

The analogous states involved in pentene isomerization in mordenite are illustrated in Fig. 4.10a and b. Pentene isomerization occurs via the secondary rather than the primary carbenium ion. 

FIGURE 9.23 Transient experiments in the gas phase. Case study pentene isomerization on a ferrierite catalyst (Figure 9.22). 

In this context, it is notable that while solutions of 1-pentene and Co2(CO)8 proved to be essentially unreactive when irradiated, solutions of Co2(CO)g, 1-pentene and HSiEt3 were active for pentene isomerization with small concentrations of silylalkenes also found as an end product [75]. However, a chain reaction appears unlikely for the hydrosilation pathway the apparent fate of the cobalt radicals is to form 18 e species such as HCo(CO)4 and Et3SiCo(CO)4 which themselves are photo or thermal catalysts for pentene isomerizations. The silyl alkene products appear to result from the formation of Et3SiCo(CO)3( 1-pentene) followed by insertion of pentene into the Si-Co bond, then P-hydride elimination. 

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. 

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