3- Methyl pentane, isomerization

An industrial example of a eonseeutive reversible reaetion is the eatalytie isomerization reaetions of n-hexane to 2-methyl pentane and 3-methyl pentane and is represented as ... 

Barusch and Payne (6), in 1951, were successful in stabilizing a cool flame in a straight tube, and used this device to investigate the relationship between the octane number of the fuel and its tendency to form cool flames. Using a similar device Ober-dorfer (30), working in the author s laboratory was able to study the cool flames of the isomeric hexanes. In this manner, n-hexane, 2-methyl pentane, 3-methylpentane, and 2,2-dimethylbutane were readily brought to cool-flame combustion. The fuel-air ratio... 

As a comparison of the enthalpies of formation of isomeric aldehydes and ketones shows, the disubstituted carbonyl compounds (ketones) are more stable than the monosubstituted carbonyl compounds (aldehydes), analogous to the stability order for the corresponding 1,1-disubstituted ethenes and the 1-n-alkenes. For the three aldehyde/methyl ketone isomeric pairs (nc = 3-5), initially it seems that the enthalpies of isomerization are fairly constant. However, if the interpolated value for pentanal is used, the trend is clearly that of more negative enthalpy of isomerization with increasing c(g) —31.7, —33.9, —34.5 kJmol-1. The non-constant enthalpies are expected because the slopes, ag, in Table 4 are quite different for aldehydes and ketones. The greater contribution to the isomerization enthalpy differences comes from the methyl ketone which is more stabilized than the aldehyde by an additional —CH2— group. The enthalpies of isomerization of the corresponding alkenes are much less exothermic (—6.1 0.8 kJmol-1) than those of the carbonyl compounds. 

In connection with the research on destructive hydrogenation at the Institute of High Pressures, Maslyanskii (224) passed benzene at 475° under 200 atm. hydrogen over molybdenum oxide (1 mole CeH6 16 moles Ha) to produce 58% methylcyclopentane, 14% cyclohexane, 8% 2-methyl-pentane, 5% n-hexane, and 8% unreacted. Over molybdenum sulfide the product distribution was similar. The preparation of these catalysts was described by him in 1940 (223). Isomerization and other conversions accompanying destructive hydrogenation were also pointed out by Prokopets and by others (257,311,314). 

A simple naphtha isomerization process has a feed of 10,000 barrels per day (bpd) of a 50 wt% mixture of n-hexane and methyl pentane. The feed is heated and sent to a reactor, where it is brought to equilibrium at 1300 kPa and 250°C. The reactor products are cooled to the dew point and fed to a distillation column operated at 300 kPa. The bottoms product of the distillation is rich in n-hexane and is recycled to the reactor feed. An overall conversion of n-hexane of 95% is achieved. 

The simulation was converged to achieve the target conversion of n-hexane with a recycle of 19.35 metric tons/h. The recycle composition is 50.0 mol% n-hexane, 21.1 mol% 2-methyl pentane, 25.1 mol% 3-methyl pentane, 3.6mol% 2,3-methyl butane, and 0.2 mol% 2,2-methyl butane. This is a converged solution, but it is only one of many possible converged solutions. No attempt has yet been made to optimize the design. The optimization of this process is examined in problem 4.14. For more realistic information on isomerization process conditions, consult Meyers (2003). 

The cyclic mechanism was demonstrated by comparing the initial product distributions in the hydrogenolysis of methylcyclopentane and in isomerization of methylpentanes and -hexane. For instance, the ratios 3-methyl-pentane/n-hexane, extrapolated to zero conversion, are the same in hydrogenolysis of methylcyclopentane and in isomerization of 2-methylpentane. Since cyclic type isomerization involves first carbon-carbon bond formation and then carbon-carbon bond rupture, one does not expect hydrocracking of alkanes to occur by this mechanism. In contrast, as suggested early on (55), if bond shift isomerization involves first carbon-carbon bond rupture and then carbon-carbon bond recombination, a common intermediate should exist, leading to both the isomerization and the hydrocracking products. 

Skeletal rearrangements of saturated hydrocarbons on CePd3 were studied by Le Normand et al. (1984). Hydrogenolysis of methylcyclopentane, isomerization of 2-methyl-pentane and aromatization of 3-methylhexane were performed at 350 or 360°C. The results were compared with those of classical Pd/Al203, Pd/Si02 or Pd/Ce02 catalysts. The activity of CePd3 itself was very low and palladium atoms seemed to play a minor role. For example, the initial reaction of methylcyclopentane was the selective formation of isopentane, which is not observed on classical palladium catalysts. Air treatment at... 

This isomerization reaction is also seen to occur in the gas phase at ordinary temperatures. For example, when 3-methyl pentane is ionized, the 70-eV spectra of partially deuterated molecules have shown that, even at high energies, the only butyl ions formed in primary fragmentations are sec-butyl ions " ... 

In the case of 1-pentene as the olefin hexanoylcobalt tetracarbonyl, 2-methyl-pentanoylcobalt tetracarbonyl, hexanal, and 2-methyl-pentanal are formed as the carbonylated products (99), and especially in reactions started under dinitrogen atmosphere a large part of the olefin excess is isomerized to 2-pentene (100). 

Three isomeric alkanes have the molecular formula C5H12 The unbranched isomer is as we have seen n pentane The isomer with a single methyl branch is called isopen tane The third isomer has a three carbon chain with two methyl branches It is called neopentane... 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Polymerization/lsomerization. The polymerization of 5-methyl-1,4-hexadiene (>99% pure) was carried out in n-pentane with a (5-TiCl3/Et2AlCl catalyst at 0°C according to the procedure described previously (14). To assess monomer disappearance and identify isomerization products, samples were withdrawn at specified intervals from the reaction mixture for GLC analysis (14). The final polymer conversion was determined by precipitation in excess methanol. 

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... 

Skeletal ring contraction steps of primary C7 and Cg rings are more probable than bicyclic intermediates (132b). Aromatization of methylcyclo-pentane indicated no carbonium mechanism with a nonacidic catalyst. Instead, Pines and Chen (132b) proposed a mechanism similar to that defined later as bond shift. This is a methyl shift. Two additional isomerization pathways characteristic of chromia have also been demonstrated vinyl shift (94) and isomerization via C3 and C4 cyclic intermediates (90a). These were discussed in Section III. 1,1-Dimethylcyclohexane and 4,4-dimethyl-cyclohexene gave mainly toluene over various chromia catalysts. Thus, both skeletal isomerization and demethylation activities of chromia have been verified. The presence of an acidic almnina support enhances isomerization dual function effects are thus also possible. 

The idea of the evidence is rather simple and can be elucidated by means of the following experiment. Let us consider, for example, a molecule of 2-methylpentane labeled in a branched position by 13C 2-methyl- 13C(2)-pentane. If the consecutive reactions in the adsorbed state are with a given metal of low extent, and this is certainly true for Pt or Pd, then the appearance, among the product, of 3-methyl-l3C(3)-pentane is very strong evidence of the operation of the 5C (cyclic) intermediates. Only via a ring closure at one place and an opening at another place of the molecule can a label move simultaneously with the branch. On the other hand, when the branch and labeled atom become separated by isomerization, this is evidence of the operation of the 3Cay complexes (see Fig. 5). 

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 rules governing this type of isomerism appeared, therefore, to be fairly clear but certain glaring exceptions soon became apparent. Thus, Idelson and Karady91 converted the 1 1 chromium complex (129) of l-phenyl-3-methyl-4-(2-hydroxy-4-sulfonaphth-l-ylazo)-5-pyrazolone into the sulfopiperidide and treated the product with pentane-2,4-dione. Chromatography of the reaction... 

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