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80 Conversion, % 100 80 60 40 Y =83 - 0.19 X Hydrogen pressure 10 bar 2 bar 70 60 50 40 Actual enantiomeric excess, % 20 30 0 20 0 50 100 150 200 250 300 Time, min Y =44 - 0.07 X Figure 4-14. Effect of hydrogen pressure. Experiment 1: 5 mg (13 μmol Pt) D- type of catalyst, [EP 0 ] =2.571 mol l -1 , no free cinchonidine, P H2 = 2 bar. Full squares (left axis) – ethyl pyruvate conversion, crossed squares (right axis) – actual EE, line – linear approximation of actual ee decrease. Experiment 2: 4 mg (13 μmol Pt) D- type of catalyst, [EP 0 ] = 2.571 mol l -1 , no free cinchonidine, P H2 = 10 bar. Full triangles (left axis) – ethyl pyruvate conversion, crossed triangles (right axis) – actual ee, line – linear approximation of actual EE decrease. Type of [EP ], Table 4-4. Details of catalysts and reaction parameters. Exp. P H2 , Pt surf. ee * max, Cinchonidine, Time slope Initial 0 N. bar Atoms, catalyst % concentration, ee * max, min -1 mol l - rate b , μmol a and mmol l -1 1 min min -1 loading, mg 1 2 5.8 D, 4 36 0 110 0.07 2.571 14 2 10 5.8 D, 4 78 0 30 0.07 2.571 140 3 c 10 5.8 D, 4 76 0 20 0.19 0.514 99 4 c 10 29 D, 20 65 0 9 0.22 0.514 37 5A c 10 1.11 Pt/Al 2 O 3 , 76 1 - 0.24 0.257 128 20 5B c 10 0.56 Pt/Al 2 O 3 , 10 76 1 - 0.21 0.257 132 45
6A c 10 19.5 B, 20 61 0 3 0.18 0.514 24 6B c 10 3.9 B, 4 76 0 - - 0.514 - 7A d 10 2.2 D, 1.5 79 1 30 - 0.514 e 130 7B 10 2.2 D, 1.5 78 1 30 - 0.514 120 8 c 10 5.8 D, 4 76 1 55 0.04 0.514 121 9 c 10 3.9 B, 4 74 1 34 0.07 0.514 42 Comments: a – The number of Pt surface atoms was estimated from the medium particles size according to “full shell” model of Pt nanoclusters and from chemisorption on conventional Pt/Al 2 O 3 , b – Initial rate values [min -1 ] were calculated as normalization a reaction rate [mmol min -1 ] on number of Pt surface atoms [mmol] in the reaction mixture, c – The graph is not shown; important parameters of reaction are presented, d – The purified EP was used. Effect of catalyst loading The decrease of initial rate from 99 min -1 to 37 min -1 with an increase of catalyst loading from 4 mg (13 μmol Pt) to 20 mg (65 μmol Pt) was found in Exp. 3 and 4. Also, the maximum of actual enantiomeric excess (ee* max ) has also decreased from 76 % to 65 %. A possible explanation for this is that the time necessary to reach the maximum enantioselective activation level may not be the same for various catalyst loadings and the full conversion of ethyl pyruvate has already been accomplished. In other words, the number of chiral sites (π-bonded cinchonidine) did not reach the maximum possible value under the 10 bars of hydrogen pressure. It should be noted, that this effect can not be explained as mass transport phenomena in liquid phase, since according to Minder, Baiker and co-workers [183] the kinetically controlled region lays below 15 g l -1 of catalyst concentration while in the Exp. 3 and 4 the maximum catalyst concentration is 0.28 g l -1 . In fact, we performed the reactions with 20 mg (Exp. 5A, ee max = 76 %, initial rate = 128 min -1 ) and 10 mg (Exp. 5B, ee max = 76 %, initial rate = 132 min -1 ) with conventional Pt/Al 2 O 3 and concluded that in our experiments mass transport effect in liquid phase does not limit the reaction. The rate of migration of hydrogen from gas to the liquid phases was the same, since both experiments were performed under the same hydrogen pressure (10 bar). A similar decrease of ee max with an increase of catalyst loading was found for the B type catalyst (see Exp. 6A and 6B in Table 4-4). By comparing these results with those reviewed by Studer, Blaser and Exner in 2003 [44] we can see that there are intrinsic differences between the colloids stabilized by chiral ligands and the conventional Pt/Al 2 O 3 heterogeneous catalysts which are unmodified prior to introduction to the reaction vessel. In fact, decrease of initial rate and maximum enantiomeric excess with an increase of catalyst loading are in contradiction to the results observed for the conventional Pt/Al 2 O 3 system which may be attributed to the fact, that our catalysts have adsorbed cinchonidine already on them, whereas the catalyst systems reviewed in the literature are exposed to cinchonidine during the reaction (in situ). Role of the ethyl pyruvate in nature of ITP The ITP time was found to be almost independent of the initial concentration of ethyl pyruvate (Exp. 2 and 3). The ITP was found to be 20-30 min in Exp. 2 (20 ml EP) and 20-25 min in the case of Exp. 3 (4 ml EP). Ee* max is almost the same value (76-78 %) in both experiments, but initial rate increased by ≈ 30 % with an increase of the initial concentration of ethyl pyruvate. 46
Page 1 and 2: Preparation and Characterization of
Page 3 and 4: 5.4 Summary 66 Chapter 6 Cinchonidi
Page 5 and 6: Abstract Studies of the interaction
Page 7 and 8: many compounds are biologically act
Page 9 and 10: Fig. 1-7. Hexahelicene [3]. 7. Chir
Page 11 and 12: R H COOH C OH CH 3 H COO - Bricine-
Page 13 and 14: Catalyst activity, expressed in the
Page 15 and 16: In fact, there are only two heterog
Page 17 and 18: similar way as relative abundance o
Page 19 and 20: surface concentration of cinchonidi
Page 21 and 22: site on Pt surface formed by a adso
Page 23 and 24: Chapter 2 Introduction to the nanos
Page 25 and 26: Triangular prism 5 4 Comments: A -
Page 27 and 28: precursors and building-up. This me
Page 29 and 30: 2.3 Preparation of nanoclusters on
Page 31 and 32: Paris Marseille Ljubljana Synphos Q
Page 33 and 34: Chapter 4 Cinchonidine modified Pt
Page 35 and 36: dihydrocinchonidine (355 mg or 1.2
Page 37 and 38: Table 4-1. Comparison between 5 % P
Page 39 and 40: widening can be used in estimation
Page 41 and 42: 1 Absorbance 0.1 2 1600 1400 1200 1
Page 43 and 44: the focus of these prior experiment
Page 45 and 46: Fig. 4-11. Tilted adsorbed cinchoni
Page 47 and 48: sci., QL. comp. 768 (str) 756 (str)
Page 49: Conversion, % 100 80 60 40 ITP time
Page 53 and 54: pressure, exposing time, cinchonidi
Page 55 and 56: Fig. 4-16. Linear relationship betw
Page 57 and 58: 1 , 1209 cm -1 and 1382 cm -1 remai
Page 59 and 60: Our results are in line with previo
Page 61 and 62: eaction. The stability of the catal
Page 63 and 64: Table 5-1. Ee and reaction rate ind
Page 65 and 66: Enantiomeric excess, % 85 80 75 A2
Page 67 and 68: 35 30 Before After Percent of parti
Page 69 and 70: catalyst activation seems to indica
Page 71 and 72: Table 5-3. Assignment of some vibra
Page 73 and 74: 6.2 Experimental Materials Cinchoni
Page 75 and 76: Fig. 6-3. TEM image of cinchonidine
Page 77 and 78: From the results of EP and EB hydro
Page 79 and 80: enhancement. However the exact fact
Page 81 and 82: Further, this family of man-made li
Page 83 and 84: Fig. 7-2. TEM of quiphos modified P
Page 85 and 86: of quiphos adsorbed on Pt and Pd an
Page 87 and 88: Fig. 7-8 Flat adsorbed quiphos via
Page 89 and 90: comp., H 11,12,13,14 2 C b., 2 P 11
Page 91 and 92: Chapter 8 “Quiphos-spider” modi
Page 93 and 94: flat crystal surface due to the hig
Page 95 and 96: Chapter 9 Diphos and diop modified
Page 97 and 98: Table 9-1. Average crystal size of
Page 99 and 100: Fig. 9-4. Conformation of diphos mo
Page 101 and 102:
ings. Due to these reasons we can n
Page 103 and 104:
Fig. 9-9. Proposed orientation of a
Page 105 and 106:
The model of adsorption of diop on
Page 107 and 108:
The calculation of energy of formin
Page 109 and 110:
For the preparation of synphos modi
Page 111 and 112:
1 2 20 40 60 80 2Θ Fig. 10-3. XRD
Page 113 and 114:
The DRIFT spectra of synphos (Fig.
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peaks which can be used for analysi
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References [1] G.E. Tranter, J. Che
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[64] A. Szabo, N. Kunzle, T. Mallat
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[128] J.D. Aiken III, R.G. Finke, J
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[189] K. Umezawa, T. Ito, M. Asada,
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I declare that the current Ph.D. th
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