the production of thymoquinone from thymol and carvacrol

Figure 4.1. Flexible ligand method: (a) diffusion of flexible ligand (b) formation and
encapsulation of complex in zeolite Y supercage
(Source: Velde et al. 2000)
The encapsulated metal complexes, which are prepared by flexible ligand
method, are active catalysts for the decomposition of hydrogen peroxide, for the
oxidation of phenol and selective oxidation reactions as seen in Table 4.1 by using H2O2
as oxidant.
Cr(III), Fe(III), Bi(III), Ni(II) and Zn(II) complexes of N,N-bis(salicylidene)
propane-1,3-diamine (H2 salpn as seen in Figure 4.2) encapsulated in Y-zeolite were
prepared by flexible ligand method (Maurya et al. 2002). As H2salpn has better flexible
backbone, so its insertion into the cavity of the zeolite was better and hence, formation
of metal complexes was enhanced. These encapsulated complexes are active catalysts
for the decomposition of hydrogen peroxide and for the oxidation of phenol to catechol
and hydroquinone with good selectivity.
Figure 4.2. Structure of H2salpn
(Source: Maurya et al. 2002)
Copper and manganese salens complexes encapsulated in the cavities of zeolites
NaX and NaY to be used in selective oxidation reactions (Chandra et al. 1998). Salens
carrying bulky substituents are retained to greater extent in the zeolite. The
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