the production of thymoquinone from thymol and carvacrol

The data on complexes prepared by flexible ligand method, ligand synthesis
method, zeolite synthesis method for heterogeneous catalysts are given in Table 4.1. In
the case of inorganic matrices, zeolites are an interesting choice because the pore
diameters and geometry can introduce shape selectivity in the catalytic reaction.
In all reactions as seen in Table 4.1, acetonitrile is used as solvent. Solvents
effect the reaction rate through competitive sorption and adsorption in the zeolite
cavities. In addition, polarities, hydrophilicity, size of solvent molecule also play a role
on reaction rate. Among the solvents CH3CN, CCl4, C2H5OH and pyridine used,
CH3CN has shown the best result in many oxidation reactions (Maurya et al. 2002b).
These oxidation reactions proceed better in acetonitrile. The reason might be that
reactant and hydrogen peroxide could reach active sites more easily than others.
Oxidation reactions with hydrogen peroxide have strongly hydrophilic character. Most
of substrates, such as monoterpenes have hydrophobic character. This causes a
mismatch between them. To overcome this situation, bridging solvents such as
acetnitrile, methanol are used (Sanderson et al. 2000).
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