Alkylcyclopentanes, reactions

The isomerization reaction, which is acid-site controlled, includes the conversion of alkylcyclopentanes into alkylcyclohexanes, which, in turn, are quickly converted to aromatics by dehydrogenation. In addition, isomerization also includes the conversion of feed n-paraffms into higher octane I-paraffins. 

Most multipromoted catalysts have been described for the catalytic reforming of petroleum. For this process it is typical, that several reactions take place simultaneously dehydrogenation of cyclohexanes, dehydroisomerization of alkylcyclopentanes and dehydrocyclization of alkanes. Isomerization, hydrogenolysis, and hydrocracking are also involved in the process. 

Kazanskii and co-workers have described an interesting special case, double cyclization of -octane at 310°C over platinum-on-charcoal catalyst at 0.2 liquid hourly space velocity. The reaction product contains about 0.25% m-octahydropentalane and 2.2-4.5% alkylcyclopentanes (an approximately l lmixture of trans-l-methyl-2-ethylcyclopentane and n-pro-pylcyclopentane) (39, 40). Indirect evidence suggests that most of the octahydropentalane is formed from l-methyl-2-ethylcyclopentane, which cyclizes significantly faster than w-propylcyclopentane. 

Section 1.1.3.1 Formation of 1-vinyl-2-alkylcyclopentanes from 1,6-dienes. Nakai and coworkers found that (207) undergoes an ene reaction on heating in toluene for 20 h at 200 C to give 97% of (208). The stereochemistry of the enophile does not affect the stereochemistry of the product. The isomer with an ( ) double bond in the ene component gives mixtures of stereoisomers. 

Weisz and Prater 28) have pointed out that, while on platinum reforming catalysts alkylcyclohexanes will proceed rapidly to aromatics, the conversion of alkylcyclopentanes to aromatics becomes the key dualfunctional reforming reaction in the neighborhood of 98 (R.O.N. with 3 ml. 

Main reactions in CR processes are dehydrogenation of cyclohexane and alkylcylohexanes, cyclization of alkanes, isomerization of n-parafines, alkylcyclopentanes and alkylaromatics, and hydrocracking. Secondary reactions are the demethylation and cracking of cyclic compounds. 

Figure 5.1 Major reactions in catalytic reforming illustrated with specific examples (a) dehydrogenation of cyclohexanes to aromatic hydrocarbons (b) dehydroisomerization of alkylcyclopentanes to aromatic hydrocarbons (c) dehydrocyclization of alkanes to aromatic hydrocarbons (d) isomerization of n -alkanes to branched alkanes (e) fragmentation reactions (hydrocracking and hydrogenolysis) yielding low carbon number alkanes.

The mode of transport of olefin intermediates between metal and acidic sites must be considered in this type of reaction scheme. In the isomerization of alkanes or dehydroisomerization of alkylcyclopentanes, a reaction sequence involving transport of olefin intermediates from metal to acidic... 

The ring-opening reaction of methylcyclopentane (Scheme 3) is the reverse reaction of the dehydrocyclization of methylpentanes (Scheme 2). Reactions of alkylcyclopentanes on supported and unsupported transition metal catalysts are also very important in naphtha reforming processes . ... 

Effect on Gasoline Properties. The naphtha fed to the reforming reactor contains alkylcyclopentanes. These compounds can be isomerized, and then almost immediately they undergo dehydrogenation to an aromatic. One example is the conversion of methylcyclopentane (MCP) to benzene (B). The overall reaction is shown in (Scheme 3). 

Two types of reactions were observed with alkylcyclopentanes. A nonse-lective ring opening would cleave each C—C bond (in positions a, b, and c. Fig. 3) in a random way. This was reported for Pt/Al203 with high dispersion (7). A selective splitting, on larger Pt particles, would break di-secondary C—C bonds (6 and c) only (7,20). The splitting close to the tertiary (or quaternary) C atom is hindered to different extent over various metals in most cases, but the total inactivity of this bond is rare (8). A third, partially selective mechanism (7) was also considered, but its possible mechanism was not elucidated sufficiently. 

In the aromatization of alkylcyclopentanes, the Pt-BaK-L catalyst is nearly as active and selective as the acidic commercial catalysts. It is proposed that the efficiency of this catalyst in this reaction is related to the nonselective cyclic mechanism proposed by Gault and associates [36] which is also consistent with the nonequilibrium distribution of methylheptane isomers from the conversion of n-octane in the presence of the Pt-BaK-L catalyst (Table VI). 

Similarly to alkanes, cycloalkanes can also undergo catalytic transformations in the presence of bimetallic catalysts. For instance, decalin (D) is transformed into a mixture of its skeletal isomers, ring-opening products (ROPs), ie, Cio-alkylcyclohexanes and CiQ-alkylcyclopentanes, and CPs, ie, hydrocarbons having fewer than 10 carbon atoms in the molecule, on acidic zeolites. The transformation of decalin on zeolites is of consecutive nature isomers are the primary products and are converted in the course of reaction further into ROPs, which ultimately yield CPs (Fig. 8.10). 

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