the production of thymoquinone from thymol and carvacrol

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shared oxygen atoms with various regular arrangements, to form hundreds of different three-dimensional crystal frameworks (Kaduk et al. 1995). The framework structure encloses cavities containing pores of molecular dimensions. Their frameworks are made up of 4-connected networks of atoms. One way of thinking about this is in terms of tetrahedra, with a silicon atom in the middle and oxygen atoms at the corners. These tetrahedra can then link together by their corners as seen in Figure 2.1. Zeolite Y has a faujasite type framework structure, with three different cavities or cages which are the large supercage, the sodalite cage and the double 6-ring. The structural formula of a zeolite for a crystallographic unit cell is: Mx/n((AlO2)x(SiO2)y).wH2O Where M is the cation of valance of n, w is the number of water molecules. The ratio y/x (Si/Al ratio) usually has values of 1-5 depending upon the structure. The sum (x+y) is total number of tetrahedral in the unit cell (Breck 1974). Figure 2.1. Framework structure of zeolite Y (Source: Kaduk et al. 1995) The replacement of SiO4 tetrahedra by the (AlO4) - tetrahedral in the zeolite framework causes excess negative charge. Cations are needed to neutralize. Compensation of negative charge by associated cations such as; H + , Na + , K + , Ca +2 , 5
NH4 +2 generates the acid sides. Catalytic activity of the zeolites is attributed to the presence of these acidic sites. The most commonly encountered faujasites are zeolites X (higher Al) and zeolite Y (lower Al). Zeolite Y is the most important catalytic zeolite, and is generally synthesized in the Na form (Richardson 1989). There are 70 known different kinds of building arrangements, each resulting in a distinct structure. Some of these occur as natural minerals; some are synthetic. Catalytically important zeolites are listed in Table 2.1 (Sen et al. 1999, Richardson 1989). Table 2.1. Catalytic zeolites (Source: Richardson 1989) Zeolite Pore type Dimensions(Å) Faujasite, X, Y Modernite Zeolite beta ZSM –5 Zeolite A 2.4 Properties of Zeolite interconnected spheres interconnected channels interconnected channels interconnected channels interconnected spheres 4.1 Å diameter pore 11.4 Å diameter cavity 6.5x7.0 Å channels 2.6x5.7 Å channels 7.6x6.4 Å channels 5.5x5.5 Å channels 5.3x6 Å channels 5.1x5.5 Å channels 4.1 Å diameter pore 11.4 Å diameter cavity A large-pore zeolite such as zeolite Y, whose structure consists of almost spherical 13 Å supercages interconnected tetrahedrally through smaller apertures of 7.4 Å in diameter. This is limited regarding the size of guest molecules by the space available in these cavities (Hoelderich et al. 2000). Zeolite properties can be changed with modification of cation exchange, impregnation. These techniques are used to introduce metal into zeolites. Impregnation 6
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: advantages compared to homogeneous
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 and 66: carvacrol conversion (%) 16 14 12 1
Page 67 and 68:
e 11.6% with a small amount of THQ.
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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the production of thymoquinone from thymol and carvacrol

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