Hydrogenolytic demethylation

Figure 10 Reaction pathways of mono-functional hydrogenolytic demethylation ( methanolysis ). a = probability to remain adsorbed and be demethylated again...

Figure 11 Theoietieal earbon-number distribution of product from hydrogenolytic demethylation ( methanolysis ) of n-Ci4 ealculated with a probability for demethylation eompared to desorption of a = 0.5in every successive step...

Additionally, certain metals, notably Ni [13] but also Co [12] show a tendency to promote successive hydrogenolytic demethylation ( methanolysis ). This reaction proceeds via a specific C-C bond cleavage mechanism (Figure 10) such that the terminal C-C bond of the adsorbed hydrocarbon radical cleaves with preference. While some of the higher fragments desorb, others remain adsorbed and undergo a subsequent demethylation step, etc. 

Figure 12 Carbon-number distribution of product from hydrogenolytic demethylation of n-Ci4, derived from experimentally observed Ci / Cb molar ratios by application of the methanolysis model. Experimental data refers to Figure 1 and reaction conditions of p=80 bar, LHSV—0.2 1/h, H2/n-Ci4 116...

On the other hand, a kinetic investigation had been reported on thermal hydrogenolytic demethylation of propylene by Amano, A. and Uchiyama, M. ( ) The reaction can be expressed by the stoichiometry. 

The free radical chain mechanism, which also could be successfully applied to the hydrogenolytic demethylation of toluene, (, 7, ) is, to our understanding, essentially as follows. 

The kinetic isotope effect observed on the overall rates of hydrogenolytic demethylation of propylene in the presence of deuterium was successfully interpreted in terms of a free radical chain mechanism. Little differences were inferred to exist between the rates of addition of H or D- to propylene and also between those of unimolecular decomposition of the produced hot n-propyl radicals, and thus the kinetic isotope effect was ascribed mainly to the difference between the steady state concentrations of [H-] in the presence of hydrogen and the concentrations of [D ] + [H ] in the presence of deuterium. In more detail, conversion of rather inactive allyl radical by metathesis with deuterium into an active D is relatively slow. This was concluded to be the main cause of the observed kinetic isotope effect, which agrees well with the calculated... 

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