ABSTRACT
The microwave region of the electromagnetic spectrum lies between l cm and l m and in order to avoid interfering with radar and telecommunication activities that operate within this region, most domestic and commercial microwave instruments operate at 2.45 GHz. The heating effect utilized in microwave-assisted organic
8.1 Background to Microwave Chemistry .......................................................... 163 8.1.1 Solvents ............................................................................................. 165 8.1.2 Domestic Microwave Ovens ............................................................. 165 8.1.3 Modi ed Domestic Microwave Ovens ............................................. 166 8.1.4 Commercial Systems ........................................................................ 166 8.1.5 Multimode Reactors ......................................................................... 166 8.1.6 Single-Mode Reactors....................................................................... 166 8.1.7 Batch Reactors .................................................................................. 167 8.1.8 Continuous Flow Reactors ................................................................ 167 8.1.9 Vessels .............................................................................................. 167
8.2 Microwave Irradiated Pericyclic Reactions .................................................. 168 8.2.1 1,3-Dipolar Cycloaddition of Nitrile Imine and
Azomethine Imines/ or Ylides........................................................... 168 8.2.2 1,3-Dipolar Cycloaddition of Nitrile Oxides, Nitrones, or Azides ..... 171 8.2.3 Hetero-Diels-Alder [4 + 2] Reactions .............................................. 175 8.2.4 Miscellaneous Pericyclic Reactions ................................................. 178
8.3 Nucleophilic Substitutions under Microwave Irradiation ............................. 184 8.4 Alkylation Reactions under Microwave Irradiation ..................................... 186
8.4.1 C-Alkylation ..................................................................................... 187 8.4.2 O-Alkylation ..................................................................................... 190 8.4.3 N-Alkylation ..................................................................................... 191
8.5 Microwave Irradiated Radical Reactions ..................................................... 193 8.5.1 Rearrangements under Microwave Irradiation ................................. 196
8.6 Microwave Irradiated Ring Opening ............................................................ 201 References ..............................................................................................................206
transformations is due in the main, to dielectric polarization, although conduction losses can also be important particularly at higher temperatures. When a molecule is irradiated with microwaves, it rotates to align itself with the applied eld. The frequency of molecular rotation is similar to the frequency of microwave radiation and consequently the molecule continually attempts to realign itself with the changing eld and energy is thus absorbed.
