Octane isomers

Zeohte 5A is used because its pores can size-selectively adsorb straight-chain molecules while excluding branched and cycHc species. The normal hydrocarbon fraction has better than 95% purity, and the higher octane isomer fraction contains less than 2% normal hydrocarbons (64). 

In contrast to this mechanism, the one proposed in our work operates direct from the oxidation state of the alkane feedstock. The same alkyl cation intermediate can lead to both alkane isomerization (an alkyl cation is widely accepted as the reactive intermediate in these reactions) and we have shown in this paper that a mechanistically viable dehydrocyclization route is feasible starting with the identical cation. Furthermore, the relative calculated barrier for each of the above processes is in accord with the experimental finding of Davis, i.e. that isomerization of a pure alkane feedstock, n-octane, with a dual function catalyst (carbocation intermediate) leads to an equilibration with isooctanes at a faster rate than the dehydrocyclization reaction of these octane isomers (8). 

Catalytic cracking was performed by a conventional pulse technique. The catalyst was pretreated with helium at 723 K for 2 hr. 0.8 mm of octane isomers mixture was injected, and the products were analyzed using a liquid paraffin column operating at room temperature to 373 K. Na-mordenlte was converted into the decationlzed form before the cracking. 

The ring opening of l,8,8-trimethyl-3-azatricyclo[3.2.1.02,4]octane isomers by 70% hydrogen fluoride/pyridine has also been studied. A series of y-fluoroamines and nonfluorinated amines, isomers of the starting aziridines, was obtained but no /Mluoroamincs were isolated.165... 

Table II. Predicted Composition of Octane Isomers Compared with Values Observed in Two Crude Oils, Mole Percent Predicted, C Alkanes Crude Oils f = 0.1 East Ponca Texas (2) City (4) ...

Seitz and East selected five isomeric protonated octane isomers (CgH "1"), all featuring C—H—C or C—H—H 3c-2e bonds for their theoretical studies (ab initio calculations at the MP2/6-3 lG(d) level of theory).847 In most cases, dissociation into ion-molecule complexes was found to be again barrierless. Proton affinities of C—C and C—H bonds are in the range 154—187 kcal mol 1 and 139-150kcalmol-1, respectively. 

Tetramethylbutane 36 was not formed when n-butane and. sec-butyl cation were reacted. The isomer distribution of the octane isomers for typical butyl cation-butane alkylations is shown in Table 5.7. 

Finally, these carbenium ions suffer rapid hydride transfer from isobutane, leading to the different octane isomers and regenerating the fert-butyl cation to perpetuate the chain sequence ... 

Isomerization of C5 and Q paraffins is a refinery process that generates high octane for the gasoline pool, while contributing no olefins or aromatics (11). Branched C5 and C6 paraffins have much higher octanes than normal pentane and normal hexane, as shown in Table 4.9 (5). Furthermore, C5 and C6 isomers can be separated by distillation, and flow schemes can be employed to recycle lower-octane isomers to the isomerization reactor. 

The following facts are the basis for butene isomerization (I) There is a basic similarity in the composition of alkylates produced from all four butene isomers. (2) Alkylate molecules, once formed, are relatively stable under alkylation conditions and do not isomerize to any appreciable extent alkylate fractions having the same carbon number ore not equilibrated (see Table I). (3) Thermodynamic equilibrium between the butene olefins highly favors isobutene formation at alkylation temperatures. (4) Normal butenes p>roduce only small and variable amounts of normal butane, thus indicating only a small and variable amount of chain initiation from normal butenes. Yet the alkylate composition shows a high concentration of trimethylpentanes and a low concentration of dimethylhexanes. (5) A few of the octane isomers can be explai.ned only by isomerization of the eight-carbon skeletal structure this isomerization occurs while isobutene dimer is in ionic form. For example, 2,3,3- and 2,3,4-trimethylpentanes... 

Use of Catalysts Containing Transition Metal Cations. Ethyl -ene being alkylated over certain zeolite catalysts reacts specifically. Ethylene can not, however, be alkylated with Isobutane In the presence of H2SO., because of the formation of stable ethylsulphates. We examined the Isobutane - ethylene alkylation over crystalline aluminosilicates and found that those catalysts containing RE and/or Ca In combination with transition metal cations were most active. The alkylation has resulted In not hexanes as would be expected, but an alkylate containing octane Isomers as the major product (about 80%). Moreover, the product composition was similar to that obtained from n-butene over CaREY. The TMP-to-DMH ratios were 7.8 and 7.1 respectively. 

Similarly, in Figure 6.4.4, the compound has the molecular formula CgHig and is one of the octane isomers. It is plainly not the straight chain octane, since the eight carbon atoms are not joined in a single chain. The longest chain is the one shaded - the two alternatives are given. Use a model kit if necessary to appreciate this structure. 

The accelerating action of ozone was also observed in a homogeneous gaseous system—i.e., in the slow oxidation of saturated hydrocarbons, such as propane, butane, hexane, heptane, and several octane isomers (9). 

Because octane can exist as a liquid or vapor at normal temperature and pressure, exposure could occur by either dermal contact or inhalation (Ippm air = 4.67 mg m ) oral exposure would most likely be either incidental or accidental. Isooctane, an octane isomer, can comprise up to 1% of the total hydrocarbons emitted from the exhaust of diesel and gasoline engines. 

The evolution of the systems with increasing temperature or reaction time indicates that bicyclo[3.2.1]octane structures, rather stable in the medium range of temperatures (160-200°) are irreversibly converted to bicyclo[3.3.0]octane isomers at higher temperatures (250°). They act as unstable intermediates whenever a temperature higher than 200° is required to pass from the bicyclo[2.2.1]heptane to the bicyclo[3.2.1]-octane, and this happens in the Gg and Cio series. 

Under more drastic conditions, with aluminum chloride, the main products at 50° are methylbicyclo[3.2.1]octane isomers, while nor-bornane structures are absent, whatever the starting hydrocarbon. The mixtures include 1-, 2-, and 3-methylbicyclo[3.3.0]octane, 1- and 2-methylbicyclo[2.2.2]octane, 1-, 2-, 3-, and 6-methylbicyclo[3.2.1]-octane, bicyclo[4.3.0]octane and bicyclo[3.2.2]octane and give evidence for the passage to the perhydrindane. 

Methylated and unmethylated methoxyazocine appear, on the basis of their chemistry and spectroscopy, to exist in the tub conformation (39), similar to cyclooctatetraene. These compounds react with dienophiles and potassium f-butoxide to give Diels-Alder adducts and benzonitriles, respectively, presumably via an azabicyclo[4.2.0]octane isomer (40). The properties of 39 indicate that the methoxy group is attached to the imino and not an olefinic carbon. This has been confirmed by recent ab initio calculations.69... 

Table C2 Some Hosoya-type indices for the data set of 18 octane isomers (Appendix C - Set 1) calculated on the unweighted molecular graph and the following graph-theoretical matrices A, adjacency matrix D, distance matrix L, Lapiacian matrix D , reciprocal distance matrix % matrix C reciprocal geometry matrix.

Table S5 Molecular path/walk indices obtained by summing atomic path/walk inidces for octane isomers (C8, Appendix C — Set 1).

Kuanar, M., Kuanar, S.K., Mishra, B.K. and Gutman, 1. (1999b) Correlation of line graph parameters with physico-chemical properties of octane isomers. Indian J. Chem., 38, 525-528. 

Fig. 16. The diagram showing positions of various octane isomers in the coordinate system (P2, P3)...

It is evident from the data of Table 1 that dependence of catalytic performance of SAPO-31 on reaction temperature has the same trends as for SAPO-11, but exhibiting better characteristics than its coimterpart at the same time. The latter state is illustrated by higher content of octane isomers in the products, higher content of methylheptanes in Cg fraction and lower concentration ratios of... 

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