that have been reserved internationally for the use of radio frequencies employed
for ISM purposes other than communications [35]. Examples of applications in
these bands include radio frequency process heating, microwave heating source,
and medical diathermy machines. The powerful emissions of these devices can
create electromagnetic interference and disrupt radio communications that
use the same frequency. Accordingly, these devices have been limited only
to certain frequency bands. The ISM bands are defined by the International
Telecommunication Union – radio communications sector (ITU-R).The globally
used frequencies are 2.45, 5.8, and 24GHz; other frequencies are established by
each country (Table 1.2) [14].
For several years, the microwave (MW) frequency response and impact on
chemical reactions have been examined in only but a few cases. Research reports
regarding frequency effects in microwave-assisted organic syntheses have tended
to be rather scarce. In the field of inorganic chemistry, Möller and Linn [36]
used 5.8GHz microwaves to calcine ceramics, and Takizawa and coworkers [37]
utilized 28 GHz microwaves for the rapid synthesis of (In0.67Fe0.33)2O3, whereas
5.5GHz microwaves were used [38] in the rapid syntheses of cryptomelane-type
manganese oxides for catalysis. In the field of organic chemistry, Gedye and
Wei [39] used a variable-frequency microwave oven to effect the Knoevenagel
reaction of acetophenone with ethyl cyanoacetate in the presence of piperidine
(no solvent; microwave frequency, 8.1 GHz); with anisole as the solvent, the
reaction was carried out at 12.2GHz. Séguin and coworkers [40] reported a new
IR reactor cell built with a microwave cavity operating at a frequency of 5.8GHz;
this equipment allowed efficient and time-resolved heating of the catalyst. The
authors also showed that the 5.8GHz microwave frequency is the optimal
frequency for catalyst heating. Microwave-induced oligomerization of methane