Interaction continuous catalyst regeneration

The added nucleophiles also interact with other electrophilic species, such as Lewis and protonic acids. In contrast to protonic acids which are consumed in the initiation step, Lewis acids act as catalysts and are not consumed during the polymerization. Because they are continuously regenerated, they may form complexes with the added nucleophiles through-... 

Reversible deposits (nitrogen, coke) are removed during regeneration. If we assume that the poisoning effect increases with the concentration of the deposits, then the poisoning effect is inversely proportional to the catalyst-to-oil ratio, and therefore is dependent on the coke selectivity of the catalyst. Irreversible catalyst poisons (metals), on the other hand, build up and continue to interact with the catalyst. 

For continuous processing it is necessary that the catalyst does not deactivate and that it is possible to regenerate the catalyst for reuse. If not, catalyst disposal will lead to waste production and other solid-acid catalysts, e. g. zeolites, might be more attractive. This aspect must still be investigated in detail, as must the reproducibility of the production of the composites. Finally, it should be mentioned that the selectivity of the reactions can be affected by reducing the acidity of the acid sites, because of an interaction between the silica matrix and the polymer backbone. 

Related cyclopropanations have also been reported using sulfonium and telluronium ylides as intermediates. In particular, the cyclopropanation of enones has been carried out employing an allyl bromide as the cyclopropa-nating reagent and sulfonium and telluronium salts 134 and 135 as pre-catalysts (Scheme 7.84). These species, in the presence of a base, generated the corresponding ylide which underwent the cascade Michael/intramolecular nucleophilic substitution and it is in this second step that the real catalytically active species is released, able to interact with another molecule of the allyl bromide and thus regenerating the sulfonium or telluronium salts pre-catalysts, which can afterwards continue in the catalytic cycle. The substitution at the... 

---