1- Pentene, isomerization studies

Additional evidence for the greater stability of the cis conformation of allylic anions is provided by other base catalyzed isomerization studies of 1-butene and 1-pentene. It was found that the thermodynamically less stable cis isomers of 2-butene and 2-pentene were the major products of the reaction182-186). Furthermore, m-2-butene isomerizes, under the same conditions, faster than the tram isomer to give 1-butene. 

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. 

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

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],... 

Ligand screening experiments were conducted on the alkenes 1-pentene and pent-4-en-l-ol, because such substrates were inert to 3a-3c (15). Pentene lacks any polar or protic group and pentenol contains the alkene and OH separated by 3 carbons. The preliminary studies involved phosphines with both imidazol-2-yl and pyrid-2-yl substituents on P as well as t-Bu, i-Pr, Ph, and Me groups (16). From the screening, complex 1 derived from the phosphine ligand 4 (17) was identified as the most capable (in terms of both reaction rate and final yield) of promoting isomerization of both 1-pentene and pent-4-en-l-ol. 

Microwave activation of alkane transformations was studied in detail by Roussy et al., who summarized their results in several papers [2, 28, 29, 79]. Isomerization of hexane, 2-methylpentane, 2-methyl-2-pentene, and hydrogenolysis of methylcydo-pentane have been investigated, and the diversity of possible effects has been specified [2]. The course of 2-methylpentane isomerization on a 0.3% Pt/Al203 catalyst depended on the mode of heating - the distribution of hexane products was different... 

Karapinka and Orchin (18) made an extensive study of the isomerization of 1-pentene under stoichiometric hydroformylation conditions. 

Most of the work with alumina was done, however, attempting to elucidate the nature of the catalytically active sites in dehydrated alumina. The catalytic activity of alumina is enhanced by treatment with hydrofluoric acid. Oblad et al. (319) measured a higher activity in the isomerization of 1- and 2-pentene. Webb (339) studied the effect of HF treatment on ammonia adsorption by alumina. There was no difference in the capacity. However, the ammonia was more easily desorbed at a given temperature from the untreated sample. Apparently, the adsorption sites grew more strongly acidic by the treatment. No NH4+ ions, only NHj molecules were detected by their infrared spectra, indicating that the ammonia was bound by Lewis acids rather than Bronsted acids. 

The isomerization of light olefins is usually carried out to convert -butenes to isobutylene [12] with the most frequently studied zeolite for this operation being PER [30]. Lyondell s IsomPlus process uses a PER catalyst to convert -butenes to isobutylene or n-pentenes to isopentene [31]. Processes such as this were in larger demand to generate isobutene before the phaseout of MTBE as a gasoline additive. Since the phaseout, these processes often perform the reverse reaction to convert isobutene to n-butenes which are then used as a metathesis feed [32]. As doublebond isomerization is much easier than skeletal isomerization, most of the catalysts below are at equilibrium ratios of the n-olefins as the skeletal isomerization begins (Table 12.5). 

In the case of alkenes, 1-pentene reactions were studied over a catalyst with FAU framework (Si/Al2 = 5, ultrastable Y zeoHte in H-form USHY) in order to establish the relation between acid strength and selectivity [25]. Both fresh and selectively poisoned catalysts were used for the reactivity studies and later characterized by ammonia temperature programmed desorption (TPD). It was determined that for alkene reactions, cracking and hydride transfer required the strongest acidity. Skeletal isomerization required moderate acidity, whereas double-bond isomerization required weak acidity. Also an apparent correlation was established between the molecular weight of the hard coke and the strength of the acid sites that led to coking. 

The preparation of acyclic allylic hydroperoxides has been described before (3, 7, 9), but it is not clear how the reactivities differ from the better known saturated hydroperoxides and cyclic allylic hydroperoxides. Dykstra and Mosher prepared allyl hydroperoxide by the reaction of allyl methanesulfonate with hydrogen peroxide and alcpholic potassium hydroxide and purified the hydroperoxide by gas chromatography. It detonated on heating and decomposed on exposure to light but was relatively stable in the cold and dark. The isomeric allylic hydroperoxides formed from the autoxidation of the branched olefin, 4-methyl-2-pentene, have also been isolated and were not abnormally reactive (3). In the present study, cis- and trans-2-butene were photooxidized in the presence of methylene blue as a sensitizer (14), and the product, l-butene-3-hydro-peroxide, was isolated by preparative chromatography. 1-Butene proved unreactive and 2-butene-l-hydroperoxide could be formed only by isomerization of the secondary hydroperoxide. 

In this work we extend our study to the hydrogenation and isomerization of a series of a,p-unsaturated alcohols, such as 2-propen-l-ol (A2), (E -2-buten-l-ol (EB2), (" -2-penten-l-ol (ZP2), (E -2-penten-l-ol (EP2), (" -2-hexen-l-ol (ZH2), (E -2-hexen-l-ol (EH2), carried out in the presence of RhCl(PPh3)3, with and without triethylamine (NEts), at 303 K, using ethanol as solvent. The major targets of our research are to investigate the influence of the unsaturated alcohol structure on the product distribution and to verify the possibility of extending the results, previously obtained with (" -2-butene-1,4-diol, to other analogous substrates. 

Yang144 has reported a study of 3-methyl-2-pentene (30), which undergoes isomerization and oxetane formation when irradiated with benzophenone or benzaldehyde. The quantum yields for these processes are shown in Table V. 

Similar observations were made by Saltiel in a study of the isomerization of 2-pentene.14S In contrast to the stilbene system, a single decay ratio could not account for the results with different sensitizers (Table VI). This implies that different intermediates were produced with different sensitizers. 

Section I1,D,1 The kinetics have been studied for competitive formation of 3//-pyrazoles and cyclopropenes thermally from the isomeric vinyldiazo compounds 2,3-dimethyl-l-phenyl-l-diazo-2-butene and 4-methyI-3-phenyl-2-diazo-3-pentene. The higher (12 kJ/mol) ground state energy of the latter accounts almost entirely for its larger (x68) rate of cyclization to a 3H-pyrazole, relative to its isomer.172... 

Skeletal isomerization requires higher temperature and stronger acid catalysts than do double-bond migration and cis-trans isomerization. Butylenes, for example, are transformed to isobutylene over supported phosphoric acid catalysts.98 The equilibrium mixture at 300°C contains approximately equal amounts of straight-chain and branched butenes. Similar studies were carried out with pentene isomers.99 Side reactions, however, may become dominant under more severe conditions.100... 

This paper concerns the cationic isomerization polymerization of 3-methyl-1-butene and 4-methyl-1-pentene. Specifically, the microarchitecture (composition) of poly(3-methyl-l-butene) and poly(4-methyl-1-pentene) has been investigated, and the effect of synthesis conditions on polymer composition, polymer molecular weight and polymerization rate of 4-methyl-1-pentene has been studied. 

According to Ketley (7), who studied the infrared spectra of poly(4-methyl-1-pentene) samples prepared with A1C13, AlBr3, and EtAia2 in n-pentane and ethyl chloride diluent in the range — 78 to —130°, isomerization polymerization increases with decreasing temperature and increasing dielectric constant. 

The cationic isomerization polymerization of 4-methyl-l-pentene is of interest because the completely isomerized structure can be viewed as a perfectly alternating copolymer of ethylene and isobutylene, a structure which cannot be synthesized by conventional techniques. One of the difficulties encountered in the study of this polymer was the lack of an accurate structure determination method necessary for a detailed correlation of synthesis conditions and polymer microstructure. The work described in this paper attempts to provide such a correlation. 

The results of the study of the effect of synthesis conditions on the composition of poly(4-methyl-l-pentene) have shown that even under conditions most favorable for the successful competition of isomerization with propagation, i.e., —120° C, using EtAlCl2, in ethyl chloride, the polymer contains only 50% of the desired 1,4-structure. It appears that in the series (n— l)-methyl-l-alkenes as n increases the likelihood of obtaining completely isomerized products via cationic isomerization polymerization is decreased. This is supported qualitatively by results obtained in the cationic polymerization of 4-methyl-l-hexene, an (n—2)-methyl-1-alkene (17). 

At the conditions of the study, it was postulated that the isomerization of the n-pentenes on the acid sites was the rate-limiting step, so that the rate is given by... 

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... 

Prior to Takegami s studies, the effect of isomerization of acylcobalt carbonyls on the products of the reaction between cobalt hydrocarbonyl and olefins had received little attention. Terminal olefins had been found to give a mixture of linear and branched products at low temperatures under carbon monoxide, and this was taken as reflecting the mode of addition of cobalt hydrocarbonyl (62, 73, 147). In view of the slow rate of isomerization of acylcobalt carbonyls this seems justified. However, it is worth noting that branched products predominated in the reaction of 1-pentene with hydrocarbonyl under nitrogen even when the olefin had isomerized only to the extent of 50% (73). Both isobutylene and alkyl acrylates had been found to produce branched products. It was suggested that isobutylene, with an... 

Olefin isomerization has also been mediated by the photolysis of Fe(C0)s.144 Recently, a detailed study of alkene isomerization by photolysis of Fe(CO)5 has shown that the reaction is truly photocatalytic.14S The very high quantum yields ( 1.0), Table 24, and the fact that the pentenes are ultimately equilibrated to the thermodynamic ratio support the notion that the role of the light is to generate a thermally active catalyst. A mechanism similar to that in reactions (53)-(57) involving Fe(CO)3 as the repeating unit can be used to account for the results. 

Studies by Lapidus and coworkers 33) of the isomerization of w-butenes on nickel-zeolite catalysts indicate that some zeolite catalysts are active for the disproportionation of butenes to propylene and pentenes. 

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