Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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CHAPTER 2 using Au/TiO2 and Au/Al2O3 as catalysts for the oxidation of phenols with hydrogen peroxide found that the arene is not hydroxylated but biaryls are formed [193]. The authors suggest the reaction to occur via coupling of free aromatic radicals. MeOH as a solvent gave the best results suggesting that HO∙ radicals – which are scavenged by alcohols – play no major role; interestingly, the reaction did not proceed with TBHP which was ascribed to the specific formation of a Au‐H2O2 intermediate. As another example, Au supported on TiO2 and different carbons converted 2‐methyl‐1‐naphthol to 2‐ methyl‐1,4‐naphtoquinone with molecular oxygen [194]. While gold catalysts gave high conversions, the selectivity to the quinone was low and thus higher yields were obtained in the absence of any catalyst as gold was promoting the overoxidation. 2.3.6 <strong>Oxidation</strong> of amines The oxidation of amines to (mainly) imines or amides over heterogeneous catalysts is a young field of research. Catalysis with gold has evolved quickly after the first reports in 2007 [119]. The oxidation of a broad range of different amines [195] is now well‐established. Successfully applied catalysts are Au/graphite (Table 2‐7, entry 1 and 2) [195, 196], Au/CeO2 (entry 3 and 4) [197‐199], Au/Al2O3 (entry 5a) [200], Au/hydroxylapaptite [195] and Au/TiO2 (entry 6) [196, 201]; TiO2 alone is also catalytically active even in the absence of light [201]. The oxidation is usually carried out in non‐polar solvents at elevated temperatures (≥100 °C), the TOFs of all cited nano‐catalysts are comparable being in the range of 1 h ‐1 to 10 h ‐1 for the oxidation of dibenzylamine. The group of Corma showed that at least for Au/TiO2 smaller Au nanoparticles afforded a more active catalyst [196]. On the other hand, the oxidation of amines is a rare example where bulk gold also shows considerable catalytic activity (entry 5b) [119, 200]. This might explain why heterogeneous catalysts prepared in situ giving rather large Au NPs on CeO2 were highly active [197] which would, however, limit the scope of the very straightforward in situ catalyst synthesis (Figure 2‐12) as for many oxidation reactions small nanoparticles are beneficial. The high activity of bulk gold for the oxidation of amines offers an intriguing opportunity for the design of catalysts chemoselective only for the oxidation of amine groups in multifunctional molecules, a feature rarely found for heterogeneous oxidation catalysts. Tertiary amines can also be oxidized to the corresponding N‐oxides [202] in aqueous systems with higher TOFs (e.g. 500 h ‐1 for triethylamine with Au/C, entry 7). Primary anilines not bearing an oxidizable α‐C‐atom can be selectively oxidized with O2 by Au/TiO2 and Au/CeO2 catalysts to the corresponding azo compounds offering a very attractive and environmentally benign alternative to industrial procedures (Table 2‐7, entry 8) [199]. This reaction is furthermore catalyzed by dissolved Cu(I)halides in the presence of pyridine [203]. In combination with ascorbic acid, homogeneous Cu(I) compounds also oxidized primary amines to imines with molecular oxygen at significantly lower 48
Table 2-7: Aerobic oxidation of amines. 2 R NH 2 catalyst [Ox] R N R 2 R 1 NH 2 catalyst [Ox] catalyst Entry Catalyst Substrate Product Solvent T (°C) Rct. Time (h) Conversion Selectivity TOF (h -1 ) Ref. 1 Au/graphite dibenzyl amine BB a toluene 110 17 100% 95% 1.2 [195] 2 Au/graphite benzyl amine BB a toluene 100 1 99% 100% 100 [196] 3 Au/CeO2 aniline diazobenzene toluene 100 6 98% 91% 75 [199] 4 Au/CeO2 b benzyl amine BB a toluene 108 8 >99% 91% 7.2 [197] 5a Au/Al2O3 benzyl amine BB a toluene 100 24 92% c - 0.2 [200] 5b gold powder benzyl amine BB a toluene 100 24 92% c - 0.001 [200] 6 Au/TiO2 n-hexylamine n-hexyl caproic amide - 130 20 60% 91% 15 [201] 7 Au/C triethyl amine triethyl amine- N-oxide aq. NaOH 70 2 100% 100% 500 [202] 8 Au/TiO2 aniline diazobenzene toluene 100 9 100% 90% 15 [199] a b c N-benzylidenbenzyl amine. Formed in situ. Yield. R 1 R 2 N N R 1 N R 2 R 2 [Ox] R 2 O N R 2 R 2
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TECHNICAL UNIVERSITY OF DENMARK (DT
Page 3 and 4:
Preface The present dissertation su
Page 5 and 6:
the carboxylic acid, ceria inhibite
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Resume Denne afhandling giver indle
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hvorimod mængden af katalysator ku
Page 11 and 12: 2.3.8 Oxidation of sulfides .......
Page 13 and 14: 5.3.5 Macroscopic mass transport in
Page 15 and 16: Chapter 1 Introduction With its gre
Page 17 and 18: 1. Introduction Scheme 1‐1: High
Page 19 and 20: 1. Introduction Figure 1‐2: Phase
Page 21 and 22: 1. Introduction [28] S. Bawaked, N.
Page 23 and 24: 2.1 Introduction 2.1 Introduction E
Page 25 and 26: 2.2.1 Synthesis of gold catalysts 2
Page 27 and 28: 2.2 Catalyst synthesis for oxidatio
Page 29 and 30: 2.2 Catalyst synthesis for oxidatio
Page 31 and 32: 2.3 Selective liquid‐phase oxidat
Page 33 and 34: Table 2-1: Overview over alcohol ox
Page 45 and 46: Ph O O Ph (4) (5) 2.3 Selective liq
Page 51 and 52: Table 2-4: Side-chain oxidation of
Page 53 and 54: 2.3.4 Oxidation of cyclohexane 2.3
Page 55 and 56: Table 2-5: Oxidatin of cyclohexane.
Page 59 and 60: Table 2-6: Ring hydroxylation of ar
Page 61: 2.3 Selective liquid‐phase oxidat
Page 65 and 66: Table 2-8: Oxidation of hydroquinon
Page 69 and 70: Table 2-9: Oxidation of silanes wit
Page 71 and 72: Table 2-10: Oxidation reactions cat
Page 73 and 74: 2.4 Strengths and opportunities of
Page 81 and 82: 2.6 References 2.6 References [1] M
Page 83 and 84: 2.6 References [56] H. Tumma, N. Na
Page 85 and 86: 2.6 References [113] C. Keresszegi,
Page 87 and 88: 2.6 References [169] Q. Zhu, Y. Lia
Page 89 and 90: 2.6 References [223] M. Fetizon, M.
Page 91 and 92: Chapter 3 Selective Liquid-Phase Ox
Page 93 and 94: 3.2 Experimental 3.2.1 Catalyst pre
Page 95 and 96: 3.3 Results Scattering amplitudes a
Page 97 and 98: Absorption (a.u.) 1.2 1.0 0.8 0.6 0
Page 99 and 100: Conversion (%) 100 90 80 70 60 50 4
Page 101 and 102: 3.3 Results Figure 3‐5: In situ X
Page 103 and 104: 3.3 Results Table 3‐2: Conversion
Page 105 and 106: 3.3 Results In order to gain insigh
Page 107 and 108: 3.3 Results the cost of selectivity
Page 109 and 110: 3.4 Discussion synergetic interacti
Page 111 and 112: 3.5 Conclusions to corroborate the
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3.6 References [29] T. Mitsudome, Y
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Chapter 4 Selective Side-Chain Oxid
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4.2 Experimental single‐step flam
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4.2 Experimental alcohol (Aldrich,
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4.3 Results Scheme 4‐1: Oxidation
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4.3 Results Figure 4‐2: Formation
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4.3 Results oxidation by either 2,6
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Absorption (a.u.) Absorption (a.u.)
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4.3 Results atomic mixing of Ag and
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4.3 Results Figure 4‐7: Influence
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4.4 Discussion and mechanistic cons
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4.5 Conclusions heterogeneous radic
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4.6 References [29] S.I. Zabinsky,
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Chapter 5 Experimental Determinatio
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5.2 Experimental The most important
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5.2 Experimental Eurotherm 2216e te
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Figure 5-1: Schematic view of the e
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(Eq. 5‐5) AB i j ε AB i j β 5.2
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(a) (b) (c) (d) (e) (f) (g) (h) (i)
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5.3 Results two association sites o
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Pressure (bar) 150 145 140 135 5.3
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5.3 Results Figure 5‐7: Oxidation
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Weight (g) 5.3 Results Figure 5‐8
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5.4 Discussion catalytic reactions
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5.4 Discussion corresponding CO2‐
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5.5 Conclusions 5.5 Conclusions The
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5.6 References [29] I. Tsivintzelis
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6.1 Introduction 6.1 Introduction A
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6.2 Experimental [38]. In a typical
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6.3 Results out in 1 mm quartz tube
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6.3 Results Figure 6‐2: Structure
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6.3 Results Figure 6‐4: Epoxidati
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6.3 Results Figure 6‐6: Compariso
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6.3 Results Figure 6‐8: Influence
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6.3 Results investigated the epoxid
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6.3 Results Figure 6‐10: Co‐epo
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6.3 Results Figure 6‐11: EXAFS an
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6.4 Discussion would need to be for
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6.5 Conclusions Formation of the ep
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6.6 References [28] J. Perles, N. S
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Chapter 7 Concluding Remarks 7.1 Co
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7.2 Final remarks and outlook speci
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Acknowledgements Acknowledgements T
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Curriculum Vitae Matthias Josef Bei
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