Chemistry Reference
In-Depth Information
can either be liquid phase or solid state reactions, but investigation might
be helpful for exploration of chemical differences. With respect to cata-
lytic reactions in ball mills, comparison of TON as well as TOF revealed
strong similarities with solvent-free accomplishment in microwave ap-
paratus. However, it has to be mentioned that similar performance in a
microwave field or under mechanochemical conditions is only possible if
proper mixing is applied. Otherwise the product yield is lower, as dem-
onstrated in Figure 10.14 for aniline oxidation
62
and also for other types
of reactions like Knoevenagel condensation
61
or Suzuki-Miyaura cross-
coupling.
29
Beside comparison with other technologies of energy entry, ball milling
procedures are often compared to simple stirring in a flask
82,110-112
and with
the comminution of reagents using mortar and pestle.
26,28,29,58,59
The last
method in particular is outmoded due to low robustness.
29
Although many
reactions might be realized with this technique, the application of mortar
and pestle for advanced organic synthesis procedure is questionable (Section
10.1.2). However, grindstone chemistry undoubtedly has one big advantage:
its energy eciency, since the energy provided to the reaction mixture is
truly renewable. For all other methods the activation energy is generated
from energy transformation starting, in most cases, with electrical energy.
The energy needed for the production of a defined quantity of product
(n
product
) is defined as molar energy (E
m
, Eq. 10.16):
10,29
E
grid
P
i
n
product
;
i
E
m
ΒΌ
(10
:
16)
Figure 10.14 Comparison of conversion and selectivity for the KMnO
4
-mediated
oxidation of p-toluidine (Scheme 10.3C) carried out with different
methodsofenergyentry.
62
Search WWH ::
Custom Search