Isopentane, isomerization

There are three isomeric pentanes, ie, saturated aHphatic hydrocarbons of molecular formula C H 2- They are commonly called / -pentane [109-66-0] isopentane [78-78-4] (2-methylbutane), and neopentane [463-82-1] (2,2-dimethylpropane). 

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 isopentane. The third isomer has a three-carbon chain with two methyl branches. It is called neopentane. 

Anderson and Avery s bond shift mechanism has the consequence of predicting that a quaternary carbon atom cannot be generated in the hydrocarbon product. In fact, Anderson and Avery (24) showed that in the isomerization of isopentane over platinum films, only a very small amount (<1%) of neopentane was produced (although the equilibrium constant for isopentane <= neopentane is 0.16 at 278°C). Furthermore,... 

The rise in this ratio with the increasing number of tertiary C—H bonds in the molecule is explained by the increased probability of peroxyl radical undergoing isomerization. The experiments indicate that oxidized PP contains mainly block hydroperoxyl groups [12,88]. Hydrocarbons with tertiary C—H bonds (for example, isobutane, isopentane, and cumene) are oxidized in the liquid phase to stable molecular products, mainly hydroperoxides and A[02] = [ROOH], The recombination of tertiary peroxyl radicals gives rise to small amounts of dialkyl peroxide and alcohol (see Chapter 2). 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

One important application of analysis of variance is in the fitting of empirical models to reaction-rate data (cf. Section VI). For the model below, the analysis of variance for data on the vapor-phase isomerization of normal to isopentane over a supported metal catalyst (Cl)... 

An augmented central composite design was used in obtaining reaction-rate data in a flow differential reactor the reaction occurring was the isomerization of normal pentane to isopentane in the presence of hydrogen (Cl). Using the subscripts 1, 2, and 3 for hydrogen, normal pentane, and isopentane respectively, an empirical rate equation can be written... 

The isomerization process is utilized to convert light paraffins such as butane, pentane, and hexane into higher-octane isoparaffins. Isoparaffins have higher octane numbers than normal paraffins of the same carbon number. For example, n-pentane has a research octane number of about 61, and isopentane has an octane number of approximately 92. 

Butane isomerization and pentane-hexane isomerization are the two most important isomerization processes. Isobutane is utilized primarily as alkylate feedstock. Isopentanes and isohexanes have become valuable high-octane blending components in gasoline. 

From isopentane we get three isomeric alkenes but none has geometric isomers. 

Pentane isomerization was carried out on a much smaller scale. Isopentane, because of its high octane number and good lead response, was blended directly into aviation gasoline. It also served to increase the volatility of blends containing such high-boiling components as alkylate. 

Equilibria. The equilibrium distributions of butane, pentane, and hexane isomers have been experimentally determined (5, 16) and are diagrammed in Figure 2. In each case, lower temperatures favor the more highly branched structures. At the approximately 200° F. temperature usually employed for isomerization, the butane equilibrium mixture contains about 75% isobutane. That for pentane contains about 85% isopentane.. In the case of hexane, the equilibrium product contains about 50% neohexane and has a Motor octane rating of about 82. In all cases, of course, the yield of the desired isomers can be increased by fractionation and recycle. 

The other commercialized pentane isomerization process is that of the Standard Oil Co. (Indiana) (20). This process differs from the Indiana-Texas butane process in that the aluminum chloride is introduced as a slurry directly to the reactor and that about 0.5% by volume of benzene is added continuously in the feed to suppress side reactions. Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The Pan American Refining Co. operated the Indiana pentane isomerization process commercially during the last nine months of the war and produced about 400 barrels of isopentane per calendar day. 

Napththa Isomerization. The only commercial isomerization of light naphtha was carried out in two plants employing the isomate process developed by the Standard Oil Co. (Indiana) (20). In this process, a feed containing normal pentane and low octane number hexanes is converted to isopentane and to hexanes of higher octane number. Pentanes and hexanes in any ratio may be processed. By recycle of selected fractions of the product, concentrates of isopentane or of neohexane and diisopropyl can be obtained as the ultimate products. 

In order to interpret the remarkably high activity of platinum to promote isomerization of neopentane to isopentane, the direct formation and involvement of metalla-cyclobutane intermediate 18 was suggested.152,158 This a,y diadsorbed species bonded to a single platinum atom is in accordance with the existence of platinum complexes and the ability of platinum to catalyze a-y exchange.156,159... 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction ... 

It was found244 that a tertiary hydride ion source (isoalkanes formed under reaction conditions through isomerization) is necessary to yield the products. However, when isopentane and hydrogen pressures greater than 14.6 atm are used, the reduction becomes catalytic. The function of hydrogen under such conditions is to reduce the formed isopentyl cation, thereby regenerating isopentane and yielding a proton. 

Isomerization—A refining process which alters the fundamental arrangement of atoms in the molecule, Used to convert normal butane into isobutane, as alkylation process feedstock, and normal pentane and hexane into isopentane and isohexane, high-octane gasoline components,... 

The carbides and nitrides of the early transition metals have attracted considerable attention. Much of this can be attributed to the catalytic properties of these materials. Levy and Boudart1 were the first to note the Pt-like catalytic behavior of WC, which for many reactions is more catalytically active than metallic tungsten.2 Others have noted that the early transition metal carbides and nitrides, in general, are excellent catalysts for reactions characteristic of the more expensive noble metals.3,4 For example, WC has been found to catalyze the isomerization of neopentane to isopentane,1 a reaction that previously had been known to be catalyzed only by iridium and platinum.5... 

The formation of C6 and C7 acids along with some ketones was reported in the reaction of isopentane, along with methylcyclopentane and cyclohexane with CO in HF-SbF5 at ambient temperatures and atmospheric pressure.406 Yoneda et al.407 have also found that other alkanes can be carboxylated as well with CO in HF-SbF5. Tertiary carbenium ions, which are produced by protolysis of C—H bonds of branched alkanes in HF-SbF5, undergo skeletal isomerization and disproportionation before reacting with CO. Formation of the tertiary carboxylic acids in the... 

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