Novel solid base catalysts for Michael additions
Synthesis, Characterization and Application

DISSERTATION

zur Erlangung des akademischen Grades
doctor rerum naturalium(Dr. rer. nat.)
im Fach Chemie

eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät I
Humboldt-Universität zu Berlin

von
M.Sc. (Chemistry) Zhijian Li

geboren am 27.04.1977 in Fujian, P.R. China

Präsident der Humboldt-Universität zu Berlin

Prof. Dr. Jürgen Mlynek

Dean: Dekan der Mathematisch-Naturwissenschaftlichen Fakultät I
Prof. Thomas Buckhout, PhD

Approvals:
1. Gutachter: Prof. Dr. Erhard Kemnitz
2. Prof. Dr. Heiner Lieske

Tag der mündlichen Prüfung: 18.08.2005

Abstract

In contrast to solid acid catalysts, much fewer efforts have been made to study solid base catalysts. In this thesis, preparation, characterization and application of oxides and modified oxide as solid basecatalysts were studied. The catalysts include MgO prepared by different methods, potassium-modified ZrO₂, calcined Mg-Al hydrotalcites, and a novel catalyst system Mg(O,F), which was prepared by sol-gel method for the first time. The catalysts were studied by N₂ adsorption/desorption measurement, XRD, FTIR, XPS, TG-DTA-DTG and NMR. Acid-base properties of the catalysts were investigated by TPD, FTIR spectroscopy and microcalorimetry to correlate with the catalytic behavior. Calcined Mg-Al hydrotalcite and Mg(O,F) are found to be highly active and selective catalysts for liquid-phase Michael additions of CH-acid compounds with methyl vinyl ketone.

Keywords: Solid base catalyst, Michael addition, acid-base properties, heterogeneous catalysis, MgO, ZrO₂ , Hydrotalcite, Mg(O,F), sol-gel

Abstrakt

Im Gegensatz zu „festen Säuren“ sind „feste Basen“ wesentlich seltener Untersuchungsgegenstand in ihrer Anwendung als Katalysatoren in der heterogenen Katalyse.

In der vorliegenden Promotionsarbeit wurden entgegen diesem Trend die Herstellung, Charakterisierung und Anwendung basischer Oxide sowie modifizierter Oxide in ihrer Eignung als feste Basen in der Katalyse untersucht. Zu diesen Katalysatoren gehören MgO, hergestellt nach unterschiedlichen Methoden, Kalium modifiziertes ZrO₂, calcinierte Mg-Al Hydrotalcite und ein neuartiges Katalysatorsystem auf der Basis von Mg(O,F)-Kompositionen, die zum ersten Mal nach einem Sol-Gel-Fluorierungsverfahren hergestellt wurden.

Die Katalysatoren wurden mittels N₂ Adsorptions/Desorptionsuntersuchungen (BET), XRD, FTIR, XPS, TG-DTA-DTG und MAS NMR untersucht. Die Säure-Basen-Eigenschaften der Katalysatoren wurden durch TPD, FTIR Spektroskopie und Mikrokalorimetrie charakterisiert und mit den katalytischen Eigenschaften korreliert. Calcinierte Mg-Al Hydrotalcite und Mg(O,F) waren in diesem Zusammenhang am stärksten aktiv und auch selektiv wie für die Flüssigphasenreaktion der Michael-Addition von CH aciden Verbindungen mit Methylvinylketon gezeigt wurde.

Eigene Schlagworte: „Feste Basen“-Katalysator, Michael-Addition, Säure-Basen-Eigenschaften, heterogene Katalyse, MgO, ZrO₂ , Hydrotalcite, Mg(O,F), Sol-Gel -Fluorierung

“Chemistry without catalysis would be like a sword without a handle, a light without brilliance, a bell without sound……”--- Alwin Mittasch

Table of contents

• 1     Introduction
  • 1.1 General introduction – from catalyst to solid base catalyst
  • 1.2 Types of solid base catalysts
  • 1.3 Application of solid base catalysts in liquid-phase reactions
  • 1.4 Main reactions investigated in this thesis: Michael additions
  • 1.5 Scope and outline of this thesis
• 2 Experimental Section
  • 2.1 Chemicals
  • 2.2 Catalyst preparation
  • 2.3 Characterization
  • 2.4 Reaction
• 3 MgO as solid base catalysts in Michael addition
  • 3.1 Introduction
  • 3.2 Preparation and characterization of MgO prepared by different methods
  • 3.3 Catalytic behavior of MgO catalysts
  • 3.4 Conclusions
• 4 Characterization and catalytic behavior of potassium-modified ZrO₂ base catalysts
  • 4.1 Introduction
  • 4.2 Preparation and characterization of potassium-modified ZrO₂
  • 4.3 Catalytic behavior of potassium-modified ZrO₂
  • 4.4 Conclusions
• 5 Application of calcined Mg-Al hydrotalcites for Michael additions
  • 5.1 Introduction
  • 5.2 Preparation and characterization of calcined Mg-Al hydrotalcites
    • 5.2.1 Catalyst preparation
    • 5.2.2 Characterization of calcined hydrotalcites
    • 5.2.3 TG-DTA
  • 5.3 Catalytic behavior of calcined Mg-Al hydrotalcites
  • 5.4 Acid-base properties of calcined hydrotalcites
    • 5.4.1 FTIR study of pyridine adsorption
    • 5.4.2 FTIR study of CO₂ adsorption
    • 5.4.3 Microcalorimetric measurements
  • 5.5 Correlation of catalytic behavior and the acid-base properties
  • 5.6 Conclusions
• 6 Sol-gel preparation, characterization and catalytic behavior of Mg(O,F)
  • 6.1 Introduction
  • 6.2 Sol-gel preparation
  • 6.3 Characterization of Mg(O,F) samples
  • 6.4 Catalytic behavior of Mg(O,F)
  • 6.5 Conclusions
• 7 Summary and conclusion
• Acknowledgements
• List of Abbreviations, Acronyms and Symbols
• References
• Lebenslauf
• Selbständigkeitserklärung

Tables

• Table 1.1  Types of solid base catalysts
• Table 1.2  Types of solid superbase catalysts []
• Table 1.3 Possible solid acid-base bifunctional catalysts
• Table 1.4TheE factor (kg by-product/kg product) [121]
• Table 1.5Michael additions of different donors to methyl vinyl ketone (MVK) catalyzed by solid catalysts in liquid phase.
• Table 1.6  Catalysts in the literatures used for the Michael additions
• Table 3.1 Preparation and characteristics of MgO catalysts
• Table 3.2 The results of the Michael addition using different MgO as catalysts
• Table 4.1 Characteristics of different potassium-modified zirconia catalysts (I)
• Table 4.2 The results of double-bond isomerization of 1-butene at 150 °C over calcined catalysts
• Table 4.3The results of Michael addition and leaching tests at room temperature
• Table 5.1Textural properties of hydrotalcites, calcined hydrotalcites, MgO and Al₂O₃
• Table 5.2Total and irreversible adsorption of CO₂ at p = 0.2 Torr at 40°C
• Table 6.1 Preparation conditions, elemental analysis results and texture properties of the samples
• Table 6.2Texture properties of the samples
• Table 6.3 Assignment of the FTIR absorption bands
• Table 7.1
  Summary of the behavior of catalysts in Michael addition
• Table 7.1 Zusammenfassung der katalytischen Eigenschaften verschiedener Katalysatoren

Images

• Fig.1.1 Number of the solid catalysts in the industrial processes [12]
• (1.1)
• (1.2)
• (1.3)
• (1.4)
• (1.5)
• (1.6)
• (1.7)
• (1.8)
• (1.9)
• (1.10)
• Scheme 1.1 Michael additions of 2-methylcyclohexane-1,3-dione (1), 2-acetylcyclopentanone (2a), and 2-acetylcyclohexanone (2b) to methyl vinyl ketone (3) to obtain Michael adducts: 2-methyl-2-(3-oxo-butyl)-cyclohexane-1,3-dione (4), 2-acetyl-2-(3-oxo-butyl)-cyclopentanone (5a), and 2-acetyl-2-(3-oxo-butyl)-cyclohexanone (5b).
• Fig. 3.1 Ions in low coordination on the surface of MgO [174]
• Fig. 3.2 XRD patterns of MgO. MgO-1 (a), MgO-2 (b), MgO-3 (c), MgO-4 (d), MgO-5 (e), MgO-6 (f), MgO-7 (g), Mg(OH)₂ (h)
• Fig. 3.3 N₂ adsorption/desorption isotherms of MgO catalysts
• Scheme 3.1 Possible reaction procedure in the reaction of 2-methylcyclohexane-1,3-dione (1) with methyl vinyl ketone (2) using MgO as catalyst
• Fig. 4.1XRD patterns of the catalysts after calcinations, a) ZR; b) KAC-ZRH; c) KN-ZRH; d) KAC-ZRO
• Fig. 4.2 Pore size distributions of the indicated catalysts
• Fig. 4.3 TG-DTG-DTA profiles of KHC-ZRH (above) and KHC-ZRO (below) dried at 80 °C before calcination
• Fig. 4.4 Temperature-programmed desorption of CO₂
• Scheme 5.1 The hydrotalcite-type structure (up) and formation process of the hydrotalcite-related materials (down)
• Fig. 5.1 XRD patterns of hydrotalcites (A) and hydrotalcites calcined at 550 °C (B) with Mg/Al molar ratios of 3.0 (a), 2.2 (b), 1.4 (c), and 0.6 (d). The sample in A: d was further calcined at 700 °C to give the XRD pattern B: d1. The MgO reference material is shown after calcination in B: f. The Al₂O₃ reference oxide is shown before (boehmit in A: e) and after calcination (-Al₂O₃ in B: e).
• Fig. 5.2 ²⁷Al MAS NMR spectra of Al₂O₃ and calcined hydrotalcites
• Fig. 5.3 TG-DTA profiles of hydrotalcites with Mg/Al molar ratios of 0.6 (a) and 3.0 (b)
• Fig. 5.4 Results of the Michael addition of 2-methylcyclohexane-1,3-dione (15 mmol) to methyl vinyl ketone (22.5 mmol) in 10 mL methanol over the hydrotalcites (A) and over the calcined hydrotalcites, Al₂O₃ and MgO (B). Catalyst amounts were 0.225 g for the hydrotalcites, Al₂O₃, and MgO and the amount remaining after calcination of 0.225 g hydrotalcite at 550 °C
• Fig. 5.6 Dependence of Michael adduct yield on Mg/Al ratio of catalyst after 24 h
• Fig. 5.7 Results of the solvent-free Michael additions of 2-acetylcyclopentanone (15 mmol) (A) and 2-acetylcyclohexanone (15 mmol) (B) to methyl vinyl ketone (22.5 mmol) on CHT0.6 and CHT3.0 (0.225 g)
• Fig. 5.8 Pyridine adsorption on Al₂O₃ (a), calcined hydrotalcites with Mg/Al molar ratios of 0.6 (b), 1.4 (c), 2.2 (d) and 3.0 (e) and MgO (f). Spectra were measured after adsorption and evacuation at 40 °C
• Fig. 5.9 Temperature programmed desorption of pyridine. Effect of the evacuation temperature on the intensity of the band of adsorbed pyridine around 1440 cm^–1
• Scheme 5.1 Bicarbonate species
• Scheme 5.2 Carbonate species
• Fig. 5.10 CO₂ adsorption on Al₂O₃ (a), calcined hydrotalcites with Mg/Al ratios of 0.6 (b), 1.4 (c), 2.2 (d) and 3.0 (e), and MgO (f). Spectra were measured after adsorption and evacuation at 40 °C
• Fig. 5.11 TPD of CO₂ adsorbed on Al₂O₃, spectra taken in vacuum at 40, 100, 150, 200 and 250 °C
• Fig. 5.12 TPD of CO₂ adsorbed on MgO, spectra taken in vacuum at 40, 100, 150, 200, 250 and 300 °C.
• Fig. 5.13 TPD of CO₂ adsorbed on CHT0.6 (left) and CHT3.0 (right), spectra taken in vacuum at 40, 100, 150, 200, 250 and 300 °C
• Fig. 5.14 Intensity of band around 1220 cm^–1 after evacuation at40 °C
• Fig. 5.15 Differential heat of CO₂ adsorption at 40 °C as a function of CO₂ uptake
• Fig. 5.16 Differential heat (up) and integral heats (down) of adsorption of benzoic acid in toluene measured by microcalorimetry at 70 °C, except for that of MgO (at 40 °C)
• Scheme 5.3 Plausible mechanism of Michael addition of 1,3-dione to methyl vinyl ketone over acid-base pairs on calcined hydrotalcites
• Scheme 6.1 Sol-gel preparation of the Mg(O,F) samples
• Fig. 6.1 N₂ adsorption/desorption isotherms of calcined Mg(O,F) samples
• Fig. 6.2 Pore size distributions of calcined Mg(O,F) samples
• Fig. 6.3 XRD patterns of Mg(O,F) samples (b-f) and reference materials MgO-s (a) and MgF₂-s (g) before calcination (A) and after calcination at 350 °C (B) and 550 °C (C) in Ar
• Fig. 6.4 TG- DTA profiles of uncalcined MOF-1.6
• Fig. 6.5 FTIR spectra of calcined MOF-0.4–MOF-1.6 (b–e), MgO-s (a), MgF₂-s (f), and commerical Mg(OH)₂ (g) and MgF₂-c (h)
• Fig. 6.6 ¹⁹F MAS NMR spectra of MOF samples after calcination at 350 °C: (a) MOF-0.4, (b) MOF-0.8, (c) MOF1.2, (d) MOF-1.6, (e) MOF-2.0, (f) MgF₂-s, and (g) MgF₂-c
• Fig. 6.7 Typical ¹⁹F chemical shifts of octahedral aluminum environments with oxygen and fluorine in the first coordination sphere, AlO_{6- x} F _x , versus x [274]
• Fig. 6.8 ¹⁹F MAS NMR spectra of MOF-1.6 after calcination at 550 °C
• Fig. 6.9 XPS results of Mg(O,F) samples after calcination at 350 °C in Ar
• Fig. 6.10 TEM of calcined MOF-1.6
• Fig. 6.11 Michael addition of 2-methyl-cyclohexane-1,3-dione to methyl vinyl ketone with the MOF samples calcined at 350 °C. Yield (A) and selectivity (B) of Michael adduct versus reaction time. Reaction temperature: room temperature (RT)
• Fig. 6.12 Michael addition of 2-methyl-cyclohexane-1,3-dione to methyl vinyl ketone with the MOF-1.6 at RT, 50 and 75 °C. Yield of Michael adduct (A) and bridged ketol (B) versus reaction time
• Scheme 6.2 Michael additions of 2-methylcyclohexane-1,3-dione (1), 2-acetylcyclopentanone (2a), 2-acetylcyclohexanone (2b) and 2-methoxycarbonyl cyclopentanone (3) to methyl vinyl ketone (4). Michael adduct: 2-methyl-2-(3-oxo-butyl)-cyclohexane-1,3-dione (5), 2-acetyl-2-(3-oxo-butyl)-cyclopentanone (6a), 2-acetyl-2-(3-oxo-butyl)-cyclohexanone (6b) and 2-oxo-1-(3-oxo-butyl)-cyclopentanecarboxylic acid methyl ester (7)
• Fig. 6.13 Michael addition of 2-acetylcyclopentanone (pK _a = 7.8), 2-acetylcyclohexanone (pK _a = 10.1) and 2-methoxycarbonyl cyclopentanone (pK _a = 10.3) to methyl vinyl ketone with calcined MOF-1.6. Yield of Michael adduct versus reaction time. Reaction temperature: room temperature (RT).
• Scheme 7.1
• Schema 7.1