Substitution reactions nitrate catalysis

Zeolites offer possibilities for both catalysis and selectivity enhancement in aromatic substitution reactions, where such effects are much needed to overcome the many problems caused by the traditional methods. Two reaction types where superior methodologies are particularly needed, namely selective nitration of simple benzenoids and 2,6-dialkylation of naphthalene, have been addressed in the present study. 

Today microemulsions are used in catalysis, preparation of submicron particles, solar energy conversion, extraction of minerals and protein, detergency and lubrication [58]. Most studies in the field of basic research have dealt with the physical chemistry of the systems themselves and only recently have microemulsions been used as a reaction medium in organic synthesis. The reactions investigated to date include nucleophilic substitution and additions [59], oxidations [59-61], alkylation [62], synthesis of trialkylamines [63], coupling of aryl halides [64], nitration of phenols [65], photoamidation of fluoroolefins [66] and some Diels-Alder reactions. 

Zaraisky. A.P. Kachurin. O.I. Velichko, L.I. Shur. V.B. Tikhonova. LA. Furin. G.G. Phase transfer catalysis in reactions of electrophilic substitution. VIII. Phase transfer catalytic nitration of arenes with sodium nitrite in an acidic medium. Zh. Org. Khim. 1999, 35. 1063-1067. 

Though aromatic, pyridine is very resistant to electrophilic aromatic substitution and undergoes reaction only under drastic conditions. For example, nitration or bromina-tion requires high temperatures and strong acid catalysis. 

In the last years, only some examples of multicomponent pyrrole syntheses have been published, but those are highly interesting in terms of reaction conditions and substitution patterns of the obtained pyrroles. One example is the conversion of a-iodoketones 594 in a Hantzsch pyrrole synthesis under high-speed vibration milling conditions (HSVM) and CAN catalysis, with silver nitrate as scavenger for the produced hydroiodic acid (Scheme 13.149) [269]. 

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