Reaction scheme isobutane

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

The Horiuti-Polanyi reaction scheme shows that in the case of isobutane, the reaction scheme involves isobutyl and adsorbed olefin intermediates. Cremer et al. (49) identified 2-propyl, r-bonded propylene, and di-a-bonded propylene surface species on platinum during propylene hydrogenation. 

Kinetic Parameters for the Horiuti-Polanyi Reaction Scheme for Isobutane Dehydrogenation and Isobutylene Hydrogenation... 

The surface chemistry involved in the conversion of isobutane on solid acids is shown schematically in Fig. 17. The conversion takes place according to a surface chain reaction scheme involving initiation, propagation, and... 

Fig. 17. Schematic representation of surface chain reaction scheme for isobutane conversion on solid acid catalysts (99).

The reaction scheme for isobutane conversion is expanded by allowing each adsorbed species to be formed from adsorption of the corresponding olefin on a Brpnsted acid site, as illustrated here for isobutyl and n-butyl species ... 

The reaction scheme for isobutane conversion also includes 73 steps representing hydride transfer for each surface species (with the exception of isobutyl species) with isobutane ... 

Finally, the reaction scheme is expanded to include two initiation steps representing activation of isobutane to form surface isobutyl species or surface propyl species ... 

The photolysis of isobutane has been studied by Okabe and Becker at 1470 and 1236 A, by Tschuikow-Roux and McNesby at 1470 A and by Lias and Ausloos at 1470,1236 and 1048-1067 A. The products of reaction are hydrogen, propene, methane, ethane, iso-butene, propane, neopentane, isopentane and ethylene, with smaller amounts of cis- and traiu-butene-2, butene-1, and methyl-cyclopropane the first five of these are the main products. The following reaction scheme accounts for the products. 

More recent work on the generation of global reaction schemes for the combustion of alkane hydrocarbons up to isobutane in flames, has been carried out by Jones and Lindstedt [207]. Their global model included two fuel consumption steps ... 

Figure 1. Reaction scheme of the acid-catalyzed two-step condensation of phenol with formaldehyde (a) and isobutanal (b), and dehydration and cyclization of the primary phenol/isobutanal product (c).

We have recently shown that metal-exchanged zeolites give rise to carbocationic reactions, through the interactions with alkylhalides (metal cation acts as Lewis acid sites, coordinating with the alkylhalide to form a metal-halide species and an alkyl-aluminumsilyl oxonium ion bonded to the zeolite structure, which acts as an adsorbed carbocation (scheme 2). We were able to show that they can catalyze Friedel-Crafts reactions (9) and isobutane/2-butene alkylation (70), with a superior performance than a protic zeolite catalyst. 

In this work, the goal is to design a control function in such a manner that neither the reaction heat nor kinetic nor mass transfer terms are required for stabilizing temperature. The scheme provides an estimated value of the heat generation from energy balance. Alkylation isobutane/propylene using sulfuric... 

The presence of tin atoms regularly distributed on the platinum surface isolates the platinum atoms by increasing the distance between two adjacent platinum atoms, as does the copper atoms on a nickel surface [108] or the tin atoms on a rhodium, platinum or nickel surface [106, 109-111]. The presence of tin would thus avoid the hydrogenolysis reaction, leading to a more selective catalyst (Figure 3.37). Indeed, the formation of isobutene from isobutane involves only one platinum atom, with the reaction passing through a simple mechanism of P-H elimination after the first step of C-H bond activation (Scheme 3.26). 

Under photo-stimulation, isoindolyloxyl radical (5) abstracts primary, secondary, or tertiary hydrogens from unactivated hydrocarbons including cyclohexane, isobutane, or n-butane (Scheme l).23 The nitroxide (5) traps the resultant carbon-centred radical (R ) and so afford the A -aI koxyisoindo les (6). Blank photolysis experiments with no added hydrocarbon have shown some unprecedented / -fragmentation of (5) to afford the nitrone (7). A number of C60 nitroxide derivatives have been synthesized and characterized by ESR spectroscopy which show features common to nitroxide radicals.24 Reaction of nitroxide and thionitroxide radicals with thiyl radicals have been observed, from which sulfinyl, sulfonyl, and sulfonyloxy radicals were generated.25 The diisopropyl nitroxide radical was generated in the reaction of lithium diisopropylamide with a-fluoroacetate esters.26... 

When isobutane (2) is contacted with HF-SbF5 at 10°C in the presence of carbon monoxide, analysis of the reaction products both from the gas phase and from the liquid phase can be rationalized by the two pathways described in Scheme 5.4.30 54 55... 

Because the reaction is catalytic in ferf-butyl cation and the deprotonation/ reprotonation steps are very fast, extensive regioselective deuteriation of the isoalkane is observed at room temperature as shown by GC-MS analysis. The absence of mass 68 (d10-isobutane) and the presence of mass 64 due to S02 formation in the oxidative process are typical features in accord with the oxidative activation of the alkane and the Markovnikov-type addition of deuterons on the intermediate isobutylene (14). However, the exchange process does not take place in the presence of carbon monoxide, which traps the ferf-butyl cation and prevents deprotonation (Scheme 5.7). 

The alkylation of alkanes by olefins, from a mechanistic point of view, must be considered as the alkylation by the carbenium ion formed by the protonation of the olefin. The well-known acid-catalyzed isobutane-isobutylene reaction demonstrates the mechanism rather well (Scheme 5.18). 

Similar reactions were observed with the CH3CH2F-SbF5 complex (Scheme 5.19). When the complex was treated with isobutane or isopentane, direct alkylation products were observed [Eq. (5.59)]. 

The strong competition between alkylation and hydride transfer appears in the alkylation reaction of propane by butyl cations, or butanes by the propyl cation. The amount of C7 alkylation products is rather low. This point is particularly emphasized in the reaction of propane by the terf-butyl cation, which yields only 10% of heptanes. In the interaction of isopropyl cation 31 with isobutane 2 the main reaction is hydride transfer from the isobutane to the isopropyl ion followed by alkylation of propane by the isopropyl ions (Scheme 5.20). 

Even the alkylation of isobutane by the ferf-butyl cation 4 despite the highly unfavorable steric interaction has been demonstrated142 by the formation of small amounts of 2,2,3,3-tetramethylbutane 36. This result also indicates that the related five-coordinate carbocationic transition state (or high-lying intermediate) 35 of the degenerate isobutylene-terf-butyl cation hydride transfer reaction is not entirely linear, despite the highly crowded nature of the system (Scheme 5.21). 

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