the production of thymoquinone from thymol and carvacrol

conversion (wt.%)
45
40
35
30
25
20
15
10
5
0
0 100 200 300 400 500
time (min.)
thymol oxidation
carvacrol oxidation
Figure 7.15. The percentage of thymol and carvacrol conversion (reaction conditions:
thymol or carvacrol/H2O2 molar ratio=1, 0.2 g Cr (salpn)-NaY catalyst,
60ºC)
7.5. Oxidation of Thyme Essential Oil
There were several reports in the literature about the chemical composition of
essential oil. The summary of these studies were also given in Chapter 5. Most reports
indicated that thymol or carvacrol were the major component in the essential oil
(Dorman et al. 1995). In this study, essential oil which was purchased from Arifo ulları
Company was analyzed in HPLC.
Essentail oil contains many monoterpenes. However, in HPLC analyses only
carvacrol and thymoquinone were observed and no other components were identified
such as thymol, p-cymene, α -terpinene for three different wavelengths (254 nm, 280
nm, 295 nm).
In the literature for oxidation reactions, large differences have been observed
between GC and HPLC analysis results. Using GC for the analysis of reaction mixtures
in the presence of residual H2O2, products were oxidized by H2O2 at elevated
temperature in the GC system (Ma et al. 2002). Hence, lately HPLC was preferred
technique for the oxidation reactions.
As shown in Figure 7.16 carvacrol was the major component and it was
converted to BQ, THQ, TQ (with 33.6% yield), unknown products with 70% conversion
65