the production of thymoquinone from thymol and carvacrol

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Figure 7.10. Typical HPLC chromatograms of oxidation of carvacrol reaction recorded for before and after for low and high conversions With Cr-based catalyst 13% of TQ was observed along with small amounts of THQ and BQ. On the other hand, using Fe-based catalyst, TQ formation was found to 55
e 11.6% with a small amount of THQ. Zn, Ni and Bi catalysts were more selective for the TQ formation compared to Fe and Cr based catalysts. However, the leached metal ions detected by ICP technique in the reaction medium catalyzed the carvacrol oxidation reaction homogeneously. Therefore, it was difficult to call these catalysts as complete heterogeneous catalysts due to significant metal ion leaching from catalysts to reaction medium. For Zn, Ni and Bi, Fe, catalysts the presence of metal ions in the reaction mixture after 5 hours was detected by ICP analysis. The percentage of leached metal ions to the reaction medium was 25.2%, 19%, 64%, 10% for Zn, Ni and Bi, Fe catalysts respectively (reaction conditions: carvacrol/H2O2 molar ratio=3, 0.1 g catalyst, 60 ºC). For Cr catalyst no metal ion was detected by ICP technique. Since Cr and Fe-based catalysts have shown better catalytic activity than the others we decided to examine the heterogeneities of these catalysts (in section 7.2.3) by hot filtration technique further and the results were presented later in the text. As seen from Figure 7.8 conversion of carvacrol increased with time for all catalysts, but reached a steady state at different times. The maximum conversion of about 14.2% was observed with Cr(salpn)-NaY after a period of 1.5 hours. For Fe(salpn)-NaY 12.7% carvacrol conversion was observed within 2 hours. Rest of the catalysts recorded lower conversions than Fe(salpn)-NaY, Cr(salpn)-NaY catalysts. As seen from Table 7.6, maximum conversions were achieved by using Cr(salpn)-NaY and Fe(salpn)-NaY catalyst for both carvacrol-to-hydrogen peroxide molar ratios of 3 and 1. When the carvacrol-to-hydrogen peroxide molar ratio was decreased to 1 (i.e.; increasing hydrogen peroxide) again, the oxidation of carvacrol gave thymoquinone with close to 100% selectivity for Zn, Ni and Bi catalysts. The selectivity towards thymoquinone decreased with increasing carvacrol conversion for Fe(salpn)-NaY and Cr(salpn)-NaY catalysts. The decrease in selectivity was due to the two more components observed in the reaction mixture and no attempts were made to identify them. Some of them were probably higher molecular weight compounds (7.1) 56
Page 1 and 2:
THE PRODUCTION OF THYMOQUINONE FROM
Page 3 and 4:
ACKNOWLEDGEMENTS I would like to ac
Page 5 and 6:
ÖZET Bu tezde, genel esnek ligand
Page 7 and 8:
5.4. Catalytic Monoterpene Oxidatio
Page 9 and 10:
LIST OF FIGURES Figure Page Figure
Page 11 and 12:
LIST OF TABLES Table Page Table 2.1
Page 13 and 14:
of thymoquinone are limited only to
Page 15 and 16: advantages compared to homogeneous
Page 17 and 18: NH4 +2 generates the acid sides. Ca
Page 19 and 20: homogeneous internal structures whi
Page 21 and 22: CHAPTER 3 TRANSITION METALS AND COO
Page 23 and 24: not determined by orbital energy al
Page 25 and 26: 3.3.1. Oxidation State The transiti
Page 27 and 28: it surrounds the metal, forms very
Page 29 and 30: metal complexes catalyze the reacti
Page 31 and 32: Figure 4.1. Flexible ligand method:
Page 33 and 34: included in the synthesis mixture.
Page 35 and 36: CHAPTER 5 OXIDATION OF MONOTERPENES
Page 37 and 38: In the GC-MS analysis of the oil of
Page 39 and 40: There are few studies on monoterpen
Page 41 and 42: Homolytic Pathways: Heterolytic Pat
Page 43 and 44: 6.1. Materials CHAPTER 6 EXPERIMENT
Page 45 and 46: inductively coupled plasma spectrom
Page 47 and 48: These tests were performed in detai
Page 49 and 50: Table 7.1. Metal content of encapsu
Page 51 and 52: 7.1.3. X-ray Diffraction (XRD) Anal
Page 53 and 54: Figure 7.2 (cont.) 42
Page 55 and 56: ands observed in the region 1200-16
Page 57 and 58: Figure 7.5. IR spectra ligand (H2 s
Page 59 and 60: Figure 7.6. DSC analysis result sho
Page 61 and 62: 7.2. Catalytic Activities 7.2.1. De
Page 63 and 64: eaction products, among which TQ wa
Page 65: carvacrol conversion (%) 16 14 12 1
Page 69 and 70: during the oxidation process and th
Page 71 and 72: leaching of Cr (salpn) complexes fr
Page 73 and 74: 7.3.2. Effect of Temperature Four d
Page 75 and 76: 7.4. Oxidation of Thymol Carvacrol
Page 77 and 78: at 60 o C. Essentail oil contained
Page 79 and 80: REFERENCES Anthony, F., 1999. Advan
Page 81 and 82: Martin, R.R.L., Neves, G. 2001. “
Page 83 and 84: APPENDIX A DETERMINATION OF HYDROGE
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