Alkylation dealkylation

Examples of alkylation, dealkylation, homologation, isomerization, and transposition are found in Sections 1,17,33, and so on, lying close to a diagonal of the index. These sections correspond to such topics as the preparation of alkynes from alkynes carboxylic acids from carboxylic acids and... 

It can be seen in Figure 16 that the non-participating methyl group for each of the disproportionation transition states has enough room to avoid steric constraints with the zeolite wall. The activation energies are -i- 164 kJ/mol, -i-174 kJ/mol, and -i- 187 kJ/mol for an alkylation/dealkylation to the ortho, meta, and para position respectively. 

The aromatization of propane and butanes is a thermodynamically feasible endothermic reaction (35-45 Kcal/mole). Aromatization in the Cyclar process includes a series of distinct reaction steps, including dehydrogenation, olefin oligomerization, cyclization, hydrogen transfer, alkylation, dealkylation, and cracking. 

We knew, however, that we could do Sn2 chemistry at this position because we had converted diol 48 to dinitrile 57. Therefore, we capitalized on this conversion, elaborating dinitrile 57 kingianin J by a series of steiicaUy undemanding reactions. Thus, reduction to the dialdehyde and then to the diol 62 was followed by mesylation, malonic ester alkylation, dealkylative decarboxylation, and hydrolysis (Scheme 24). 

A hydrocarbon pool mechanism via alkylation/dealkylation of hydrocarbon scaffolds. Olefins interconversion via methylation, oligomerization, and cracking. 

So, the ethylene production does correlate with coke presence, in particular with aromatics formation as far as the diffusion limitations are not significant. However, it seems that the majority of ethylene is not always formed directly from MeOH [115]. The aromatics and other coke species could be the products of the conversion of primary carbenium ions, which are mobile and could equilibrate each other [28]. This may explain the isotopic distribution in products and retained coke molecules and the coexistence of aromatics and carbenium ions [28], In addition to the coproduction of ethylene with aromatics in olefins interconversion cycle, formation of ethylene via alkylation-dealkylation of methyl aromatics with heavy olefins or with the equivalent carbenium ions like ethyP, propyP, and butyP could be an option. The alkyl aromatics with the side chain length of two carbons or longer are not stable in the pore and dealkylates on the acid sites due to too long residence time and steric hindrances. This may lead to formation of ethylene, other olefins, and alkylaromatics with different structure, namely PMBs [129]. In other words, the ethylene is formed via interaction of the carbenium ions like ethyP, propyP, and butyP formed from MeOH or heavy olefins with aromatics and other coke precursors followed by cracking and in a less extent by a direct alkylation of PMBs with methanol. The speculation is based properly on analysis of the prior arts and is not contradictory with the concept of the aromatic cycle for ethylene formation. 

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