Microwave irradiation reaction path

In some cases, modifications in the selectivity, in relation to classical heating, have been observed. These modifications have been ascribed to changes in the reaction path under microwave irradiation the more polar path will be favored. Computational studies have shown that the harder transition state must be favored under microwave irradiation. This result opens new possibilities for the application of micro-wave irradiation to organic and inorganic synthesis as dramatic modifications in the selectivity of competitive reactions can be expected if the transition states are of different hardness. 

Wan et al. [61] also reported the highly effective conversion of methane to aromatic hydrocarbons over Cu, Ni, Fe, and Al catalysts. The effects of the type of catalyst, its configuration, and the microwave irradiation conditions on reaction path and product selectivity were examined under both batch and continuous-flow conditions. 

Path A involves N-formylation of anthranilic acid, condensation of the resultant 2-formaminobenzoic acid with the amine followed by intramolecular amidation of the intermediate amidine to form the product. On the other hand, the amine instead of anthranalic acid may be formylated and go through the known Niementowski reaction (path B). When the reaction of 2-formamidobenzoic acid with aniline and the condensation of formanilide with anthralic acid were conducted under microwave irradiation, the desired 3-phenylquinazolin-4(3 JT)-one was obtained in both cases in a few minutes in 68-87% yield. 

If only a "yes-no" answer Is sufficient, a combination of (1) oxygen-consumption measurements, and (11) analysis of concentration of acceptor A decrease, or AO2 formation (events 1 and 11 can be measured simultaneously) In the absence and In the presence of a compound Q for a given time of constant Irradiation t, completed with (111) oxygenation(s) of A In the presence and In absence of Q with chemically or by microwave discharge generated IO2 should be carried out. In most cases these three simple experiments can either discover side-reaction paths of 02 AO2, or Q, respectively, or deliver quite a reliable "yes-no" answer (79). Providing that no complications occur, reasonable relative quenching efficiencies related to some known quencher Q (Tables 2-11) can be very easily obtained In this way. 

Lourenco et al. (2013) reported N-alkylation reaction of amine functionalized phenylene moieties in crystal-like mesoporous silica. A potassium iodide catalyzed method commonly used for the selective N-monoalkylation of aniline, was adapted and optimized to the N-monoalkylation reactions of the amine functionalized periodic mesoporous phenylene-silica (NH2-PMO) under microwave irradiation with conservation of the ordered mesostructure and the crystal-like molecular scale periodicity of the material. This functionalization opens a path for the preparation of new materials with different amino-alkyl groups specially designed for a desired application. 

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