the production of thymoquinone from thymol and carvacrol
the production of thymoquinone from thymol and carvacrol
the production of thymoquinone from thymol and carvacrol
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forming in <strong>the</strong> reaction mixture due to <strong>the</strong> association <strong>of</strong> <strong>thymoquinone</strong>, as<br />
<strong>thymoquinone</strong> has a tendency to polymerize.<br />
For Fe(salpn)-NaY catalyst, <strong>carvacrol</strong> conversion increased much higher than<br />
<strong>the</strong> o<strong>the</strong>r catalysts as seen in Figure 7.9. This increase in <strong>carvacrol</strong> conversion could be<br />
explained by hydrogen peroxide decomposition data. According to this data, Fe(salpn)-<br />
NaY catalyst reached equilibrium in a longer time. Fe-based catalyst has shown a good<br />
activity <strong>and</strong> <strong>carvacrol</strong> conversion increased <strong>from</strong> 12.7% to 27.6% after increasing <strong>the</strong><br />
hydrogen peroxide amount. Reaction continued with more available hydrogen peroxide.<br />
Carvacrol conversion increased <strong>from</strong> 14.2% to 23.5% for Cr(salpn)-NaY catalyst after<br />
increasing <strong>the</strong> hydrogen peroxide amount. The Zn <strong>and</strong> Ni-based catalysts, except Bi<br />
based catalyst (4.9%), have shown smaller conversion values <strong>of</strong> 6.75% <strong>and</strong> 5.9%,<br />
respectively compared to when <strong>carvacrol</strong>-to-hydrogen peroxide ratio was 3.<br />
In <strong>the</strong> literature, <strong>the</strong> oxidation <strong>of</strong> <strong>carvacrol</strong> with hydrogen peroxide was studied<br />
by using Mn(III) porphyrin complexes (Martin et al. 1999). Fe(III) meso-<br />
tetraphenylporphyrin or Fe(III) phthalocyanines (Milos et al. 2001) <strong>and</strong> keggin-type<br />
tungstoborates (Santos et al. 2003) under homogeneous conditions. Mn(III) porphyrin<br />
complexes showed high <strong>carvacrol</strong> conversion with a selectivity range 70-99.6%.<br />
Oregano essential oil containing mainly 47.6% <strong>thymol</strong> <strong>and</strong> 25.1% <strong>carvacrol</strong> were<br />
transformed to oil containing <strong>thymoquinone</strong> (20-66%) using Fe(III) meso-<br />
tetraphenylporphyrin or Fe(III) phthalocyanines complexes (Milos et al. 2001). Keggin-<br />
type tungstoborates showed <strong>carvacrol</strong> conversion values <strong>of</strong> 35-40% providing mainly<br />
mixtures <strong>of</strong> benzoquinones, with a small amount (2.5%) <strong>of</strong> TQ (Santos et al. 2003).<br />
With heterogeneous catalyst which was zeolite encapsulated Mn(III) tetra porphyrin<br />
complexes, <strong>the</strong> oxidation <strong>of</strong> <strong>carvacrol</strong> (