the production of thymoquinone from thymol and carvacrol

7.4. Oxidation of Thymol
Carvacrol and Thymol are aromatic monoterpenes, which can be found in the
essential oils of many aromatic plants. They are geometrical isomers. Their chemical
structures are very similar as seen in Figure 7.14 (Martin et al. 1999).
(a) (b)
Figure 7.14. Structure of (a) Thymol and (b) Carvacrol (Milos et al. 2001).
From the leaching (heterogeneity test) results and catalyst activity tests for
carvacrol conversion reactions, Cr (salpn)-NaY was found to be relatively more
efficient and stable catalyst than the others. So thymol oxidation and essential oil
oxidation reactions were carried out with Cr (salpn)-NaY catalyst.
The conversion of carvacrol and thymol values was in the 35-39% range. Their
conversion vs time profiles given in Figure 7.15 were very similar because of
similarities between their structures. Oxidation of carvacrol and thymol provided mainly
mixture of TQ, THQ and BQ with a 31.2%, 34.5% TQ yield respectively. The yields of
thymol and carvacrol were very close to each other.
In literature, TQ was produced only in small amount as a result of carvacrol and
thymol oxidation reactions by using different type of catalyst (Santos et al. 2003).
However in our study, a relatively higher TQ formation was yielded for both thymol
and carvacrol oxidation reactions.
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