Alkane pyrolysis reaction mechanism

The reaction mechanism used for this study was the alkane pyrolysis scheme of Edelson and Allara. [10] This consists of 98 reactions involving 38 chemical species. It is not so large that it overburdens the computers used yet is of a size sufficient to yield meaningful timing of the program modules. 

One of the early controversies in the field of pyrolysis revolved about the question of the importance of concerted, molecular elimination reactions of hydrocarbons to give olefins and alkanes as products. Numerous experiments (51) have given a decisive answer to this problem in favor of the completely radical mechanism for alkane pyrolysis. At the same time, ironically, very clear cut evidence has been elicited to show that both mono- and polyolefins can react quite readily in concerted, molecu-... 

Edblom, E. C. Orban, M. Epstein, I. R. 1986. A New lodate Oscillator The Landolt Reaction with Ferrocyanide in a CSTR, J. Am. Chem. Soc. 108, 2826-2830. Edelson, D. Allara, D. L. 1980. A Computational Analysis of the Alkane Pyrolysis Mechanism Sensitivity Analysis of Individual Reaction Steps, Int. J. Chem. Kinet. 12, 605-621. 

In spite of the extremely high reaction temperatures, a purely heterogeneous mechanism was originally proposed to explain the formation of olefins on the Pt-surface." " " " Only in the case of C5+ alkanes, was a non-negligible contribution of homogeneous pyrolysis reactions supposed. 

Other examples of such protocols exist in pyrolysis and combustion, where again a whole range of gas-phase organic mechanisms may be present depending on the starting fuel. An example of the likely reaction classes for alkane pyrolysis is given in Table 3.1 and for alkane oxidation in Fig. 3.2. A more detailed discussion of the... 

Edelson, D., Allara, D.L. A computational analysis of the alkane pyrolysis mechanism sensitivity analysis of individual reaction steps. Int. J. Chem. Kinet. 12,605-621 (1980)... 

The addition reactions take place at a carbon-carbon multiple bond, or carbon-hetero atom multiple bond. Because of this peculiarity, the addition reactions are not common as the first step in pyrolysis. The generation of double bonds during pyrolysis can, however, continue with addition reactions. The additions can be electrophilic, nucleophilic, involving free radicals, with a cyclic mechanism, or additions to conjugated systems such as Diels-Alder reaction. This type of reaction may explain, for example, the formation of benzene (or other aromatic hydrocarbons) following the radicalic elimination during the pyrolysis of alkanes. In these reactions, after the first step with the formation of unsaturated hydrocarbons, a Diels-Alder reaction may occur, followed by further hydrogen elimination ... 

The use of computer generation systems in modelling the pyrolysis of large hydrocarbons is no longer considered simply an alternative to manual mechanism construction. It has become a necessity. The quantity of species and reactions becomes enormous, increasing molecular weight. This is particularly true if the focus is not merely on linear alkanes but also on other typical components of naphthas and gasoils, such as Bo-alkancs or cyc/o-alkanes, where the number of possible isomers increases exponentially with the number of carbon atoms in the molecule. 

A similar computational modelling approach has been shown to be useful, for example, in studying the mechanism of low-temperature oxidation of alkanes (4), pyrolysis of alkanes (5-7), other gas-phase reactions (8), the formation of photochemical smog (9,10), and peroxide decomposition (11), among others. It is not uncommon to begin with all possible species and by permutation and combination derive a complete set of reactions, and then eliminate a subset by chemical... 

The pyrolysis of 3,8-bis(TMS)-l,2,5,6-tetrathiocane (47) was studied by pulse pyrolytic GC/MS. Compound (47) undergoes thermal decomposition via two mechanisms. The first pathway involves the formation of S2 and trimethylvinylsilane, which reacts further to give CSj, SiS2, and lower alkanes. The second pathway involves loss of three sulfur atoms to form TMS-substituted thiophenes <85JOM(289)23l>. Compound (47) also undergoes reaction with Fc3(CO)i2 to give a variety of sulfur-iron carbonyl complexes <86ZOK1540>. 

We have seen that alkanes undergo chemical transformations when subjected to pyrolysis, and that these processes include the formation of radical intermediates. Do alkanes participate in other reactions In this section, we consider the effect of exposing an alkane (methane) to a halogen (chlorine). A chlorination reaction, in which radicals again play a key role, takes place, producing chloromethane and hydrogen chloride. We shall analyze each step in this transformation to establish the mechanism of the reaction. 

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