the production of thymoquinone from thymol and carvacrol

such as diethylenetriamine (dien) and triethylenetetramine (trien). Adding four -
CH2CO2 - groups to an ethylenediamine framework gives a hexadentate ligand, which
can single-handedly satisfy the secondary valence of a transition-metal ion (Figgis
1966).
Figure 3.4. Typical polydentate ligands
(Source: Keim et al. 2002)
In the catalyst synthesis, the encapsulation of metal complexes into the zeolites
method is known as a ship in a bottle procedure. Encapsulation of metal complexes is
occurred in the super cages of the zeolite. Ship in a bottle approach involving the
entrapments of a bulky complex in a zeolite cage, has been widely used to immobilize
metal complexes of phthalocyanines, porphyrin and Shiff’s base type ligands as seen in
Figure 3.5 (Arends et al. 2001).
Ligands bond with transition metal using the electron pairs. With this bonding
ligand give electrons to the transition metal. Electropositive metal ion enters a second
interaction with ligand to give accepted electrons from ligand to ligand. With this
interaction metal gives electron and the bond between the metal and oxygen weakens.
The weak bond between them causes the increasing susceptibility of reaction entrance
of reactant. That is why transition metal complexes are used as catalysts. Transition
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