Butane isomerism

Initially, aluminum chloride was the catalyst used to isomerize butane, pentane, and hexane. Siace then, supported metal catalysts have been developed for use ia high temperature processes that operate at 370—480°C and 2070—5170 kPa (300—750 psi), whereas aluminum chloride and hydrogen chloride are universally used for the low temperature processes. 

The two isomeric butanals, n- and isobutyraldehyde, C HgO, are produced commercially abnost exclusively by the Oxo Reaction of propylene. They also occur naturally ia trace amounts ia tea leaves, certain oils, coffee aroma, and tobacco smoke. 

As the number of carbon atoms increases, the number of possible isomers becomes larger. Whereas there are only two isomeric butanes, there are three isomeric pentanes. With hve carbons, in addition to the open-chain compounds shown, a stable ring compound known as cyclopentane is also possible. Five- and six-membered carbon rings are very stable because the bonds between carbon atoms in these size rings are close to the 109° angle preferred by carbon. Three- and four-membered hydrocarbon rings are also known, but they are less stable because of the required distortion of the bond angle. 

Butomerate A catalytic process for isomerizing //-butane to isobutane. Developed by the Pure Oil Company. 

The kinetics of the thermal isomerization of methylcyclopropane to four isomeric butanes have been determined from rate-constant measurements over a wide range of temperatures 695-1154 K. The kinetic parameters are consistent with the formation... 

The epoxidation of propylene is discussed in Chapter 10, Section 2. Some isobutane can be made by isomerizing -butane. The isomerization of -butenes to isobutylene is also being commercialized. 

Isomerization Butane C4H10 Isobutane C4H10 Rearrangement... 

The skeletal isomerization of butane to isobutane is a typical reaction catalyzed by superacidity. Early in the history of this work, S04/Fe203, S04/Ti02, and S04/Zr02, were termed superacids owing to their ability to isomerize butane at room temperature or below [32, 37, 39] The formation of isobutane from butane, however, does not necessarily require superacidic strength. A bimolecular reaction pathway based on the intermediacy of butane is energetically lower than a monomolecular mechanism [129-133]. The monomolecular and bimolecular mechanisms are shown in Schemes 17.1 and 17.2, respectively, using pentane as a model. 

Synthesis of the Two Butanes.—The two isomeric propyl iodides, by means of the Wurtz and Frankland reactions, yield the two isomeric butanes, the constitution of which must, therefore, be as shown in the following reactions ... 

The isomeric propyl iodide yields the isomeric butane... 

The question now arises, how may we determine which one of the various formulas, in the case of the five hexanes for instance, is to be assigned to each individual compound of definite physical properties To which one of the butanes, pentanes and hexanes do we assign the straight chain formula or the name normal In the case of the butanes the answer and the reason for it are found in a new synthesis of one of the butanes. We have given one synthesis of the two butanes, viz., from propyl iodide and methyl iodide. As one propyl iodide yields one butane and the other yields the isomeric butane, we know that one of the two isomeric butanes must have the straight chain or normal formula. But we do not know whether the propyl iodide from which the butane boiling at + i is prepared, is really the one possessing the normal or the iso formula. Therefore, it will be seen that the relationship between the isomeric propyl iodides and the isomeric bu-... 

Isomerism of Alkyl Halides.—In discussing the question of isomerism in connection with the butanes and pentanes (pp. 21-29), we found that, while the two isomeric butanes really yield four methyl substitution products, i.e., pentanes, two of them possess the same... 

As we shall see, there are several different types of structural isomer. Isomers have to be named so that you can tell the difference between them. Consider the first member of the alkane series that shows structural isomerism, butane. 

Problem 3.2 Could we assign structures to the isomeric butanes on the h-iis of the number of Isomeric monochloro derivatives ... 

A crucial difference between solid and liquid acids is the ability of certain solids with strong Bronsted sites to isomerize -butane to i-butane via a bimolecular mechanism. A Cg carbocation is formed which isomerizes and undergoes p-fission. In this fission, the formation of two M0-C4 units is apparently preferred. Only if fission is preceded by extensive isomerization of the Cg carbocation can isotopic scrambling reach the randomization predicted by the binomial law. 

Binary coencapsulation of ethane, cyclopropane, and isomeric butanes together with larger organic guest (e.g., p-xylene, naphthalene, and anthracene) was observed for nanoscale cylindrical capsule 26 (50). Note that these gases alone could not be trapped (Fig. 12). 

The supply of branched alkenes from cracking processes is limited and there is a need for catalytic isomerization processes to increase the supply. One method is to isomerize butane and then to dehydrogenate the isobutane (ref. 5). 

Variation in the ratio of isomeric butanes with sediment temperature in the Camavon Basin of Western Australia. In Bjor0y, M. (ed.) Advances in Organic Geochemistry 1981, Wiley, 76-79. 

Figure 1.12 Space-filling models of the isomeric butanes.

The names for the two isomeric butanes (n-butane and isobutane) illustrate the important features of the common nomenclature system used for alkanes. The stem but-indicates that four carbons are present in the molecule. The -ane ending signifies the alkane family. The prefix n- indicates that all carbons form an unbranched chain. The prefix iso- refers to compounds in which all carbons except one are in a continuous chain and in which that one carbon is branched from a next-to-the-end carbon, as shown ... 

Hydroformylation of Aliphatic Olefins In 1997, Herrmann and coworkers [25] were the first to use NHCs and imidazohum salts, respectively, as hgands or preligands in rhodium-catalyzed hydroformylation. The isolated NHC-rhodium complexes 1 and 2 (Figure 2.55) and the complexes prepared in situ from the water-soluble imidazolium salts 3a-c and rhodium(lll)acetate were tested in the homogeneous and biphasic hydroformylation of propene. The catalyst derived from 1 produced >99% yield of isomeric butanals (CO/H2 = 1 1,10 MPa S/C = 100 000 1, toluene, 60 h). In the biphasic system, after 20 h of reaction time and S/C = 10000 1 in water, rhodium catalysts derived from 2 or based on hgands 3a-c allowed up... 

Butenes are usually obtained from Crack C via naphtha steam cracking (Scheme 4.4) [31]. After the removal of butadiene and isobutene from the crude stream, the so-called Raffinate II contains 1-butene, cis/trans-2-hutene, and the isomeric butanes. Alternatively, it has been produced for a subsequent hydroformylation by dehydrogenation of n-butane on a Cr on alumina... 

In isomerizing butane with aluminum chloride, only a small amount of catalyst-hydrocarbon complex is formed, but pentane and especially hexane produce more complex. Both pentane and hexane tend to crack during treatment and this is the cause of the extensive side reactions. The formation of sludge is inhibited in pentane isomerization by the use of 0.3 to 1.3 weight per cent benzene, and in hexane isomerization, hydrogen is used as an inhibitor. 

We can see the obvious conclusion that more carbon means more heat, but the differences between the isomeric butanes and the isomeric pentanes are instructive. In each case, the more branched the isomer, the less energy we get on burning it. Since the products are identical each time, this means that the branched isomers are lower in energy than the linear ones. This is quite general for alkanes and indeed quite a number of other compound classes. 

Butenes are usually derived from Crack-C4 from naphtha steam cracking [27]. After the removal of butadiene (by extraction) and isobutene (by conversion into methyl t-butylether) from the crude stream, the so-called Raffinate II contains 1-butene (50-65%), cis/trons-2-butene, and the isomeric butanes. Raffinate II is the cheapest source of butenes, and their most valuable hydroformylation product is n-pentanal, whereas the isomers 2-methylbutyraldehyde and 3-methylbutyraldehyde are less in demand and lower in value. The main application for -valeraldehyde is its transformation into 2-propylheptanol (2-PH) by aldolcondensation and subsequent hydrogenation of the product (Scheme 14.4) [28, 29]. like 2-EH, 2-PH is also an important plasticizer alcohol. n-Valeraldehyde is also used as an ingredient in flavoring mixtures. w-Valeraldehyde can be converted into -valercarboxylic ester by subsequent oxidation and esterification with tertiary valeric alcohol, providing a useful lubricant and a substitute for Freon. 

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