3-Methylheptan

A complete synthesis of di-heliotridane has been effected by Prelog and Zalan, 2 using Prelog s general method for the synthesis of dicyclic amines, the proximate, primary material in this case being 1 7-dibromo-4-amino-3-methylheptane hydrobromide,... 

For n-decane isomerization, when a good balance between the metal phase and the acidic phase of the catalysts is reached, the isomerization and cracking yield curves of the catalysts are a unique function of the conversion, meaning that these yields do not depends on the porosity nor the acidity of large pore materials. Formation of the most bulky isomers, such as 4-propylheptane and 3-ethyl-3-methylheptane was favored in mesoporous solids (figure 1). Criteria based on the formation of these particular isomers are linked with mesoporosity and could be useful to discriminate between zeolites catalysts with and without mesopores. 

Figure 1 (a) Approach to the Thermodynamic Equilibrium (ATE) of the 4-propylheptane (4PC7) distribution in the n-decane (nCIO) monobranched isomers, (b) distribution of the 3-ethyl-4-methylheptane (3E4MC7) and 3-ethyl-3-methylheptane (3E3MC7) in the nCIO dibranched isomers as a function of the nCio conversion. 

Methylenecyclopropanes, 50, 30 3-Methylheptan-4-ol, 52, 22 Methyl iodide, with triphenyl phosphite and cyclohexanol,... 

Since there are two different connections possible for n-octane, 1,6 or 3, 8, which could lead eventually to ethylbenzene, there is a statistical entropy factor involved here which is not part of the o-xylene route. Therefore, if both closures were equally possible from an enthalpy perspective, one would predict a 2 1 ethylbenzene to o-xylene ratio. The formation of the m- and p-xylene requires prior isomerization of n-octane to 2- and 3-methylheptane, respectively. 

In our calculations we will first discuss our results starting with both the 2-and 3- octyl cations (the 4- octyl cation cannot form a 1,6-p-H-structure). The n-octane conversion to aromatics, as described by Davis (8), is a good test of our proposed mechanisms, for several reasons (1) his experimental observation would require the formation of approximately equal amounts of 1,2-dimethylcyclohexane (o-xylene) and ethylcyclohexane (ethylbenzene), even though in our mechanism the structure of the needed 1,6-p-H cation intermediates are quite different, and (2) the formation of to- and p-xylene requires a prior isomerization of n-octane to 2- and 3- methylheptane, and this must be a faster reaction than the dehydrocyclization (or at least competitive with it). If our mechanisms are valid, we should be able to reproduce some aspects of the above results. 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

We have not carried out calculations starting with secondary cations derived from the title alkanes because at a computational level, these will have ground-states and transition-states similar to heptane itself (previously discussed). This will be true even though the most stable carbocations in these branched alkanes will be the corresponding tertiary ions, which in themselves will not be directly involved in dehydrocyclization processes. However, one has to keep in mind that the thermodynamic ground-states in these real catalytic reactions will be the alkanes themselves, and in this regard secondary cations formed from n-octane or 2- (or 3-) methylheptane will not differ much in absolute energy. As shown earlier, a 1,6-closure of 2-methylheptane leads eventually to m-xylene, while 3-methylheptane has eventual routes to both o- and p-xylene. 

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