LIQUID PHASE - Startseite · 2013. 7. 23. · 4 Selective Oxidations Catalyzed by Mesoporous Metal Silicates 127 Oxana A. Kholdeeva 4.1 Introduction 127 4.2 Synthesis and Characterization

LIQUID PHASEOXIDATION VIAHETEROGENEOUSCATALYSIS

LIQUID PHASEOXIDATION VIAHETEROGENEOUSCATALYSIS

Organic Synthesis andIndustrial Applications

Edited by

MARIO G. CLERICI

Formerly with Enitecnologie (ENI Group)

San Donato Milanese, Italy

OXANA A. KHOLDEEVA

Boreskov Institute of Catalysis

Novosibirsk, Russia

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Library of Congress Cataloging-in-Publication Data:

Liquid phase oxidation via heterogeneous catalysis : organic synthesis and industrial applications / edited

by Mario G. Clerici, formerly with Enitecnologie (ENI Group) ; San Donato Milanese, Italy, Oxana A.

Kholdeeva, Boreskov Institute of Catalysis, Novosibirsk, Russia.

pages cm

Includes index.

ISBN 978-0-470-91552-3 (cloth)

1. Oxidation. 2. Oxidation–Industrial applications. 3. Heterogeneous catalysis.

4. Heterogeneous catalysis–Industrial applications. I. Clerici, Mario G. II. Kholdeeva, Oxana A.

QD281.O9L57 2013

5410.393–dc23

2012047247

Printed in the United States of America

ISBN: 9780470915523

10 9 8 7 6 5 4 3 2 1

http://www.copyright.com

http://www.wiley.com/go/permission

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CONTENTS

Preface xi

Contributors xiii

Abbreviations xv

1 Environmentally Benign Oxidants 1

Giorgio Strukul and Alessandro Scarso

1.1 Introduction 1

1.2 Oxygen (Air) 3

1.3 Alkylhydroperoxides 5

1.4 Hydrogen Peroxide 9

1.5 Conclusions 16

References 17

2 Oxidation Reactions Catalyzed by Transition-Metal-Substituted

Zeolites 21

Mario G. Clerici and Marcelo E. Domine

2.1 Introduction 21

2.2 Synthesis and Characterization of Zeolites 22

2.2.1 Isomorphous Metal Substitution 23

2.2.2 Synthesis of Titanium Silicalite-1 (TS-1) 24

2.2.3 Characterization of Titanium Silicalite-1 (TS-1) 26

2.2.4 Ti-Beta, Synthesis and Characterization 30

v

2.2.5 Other Ti Zeolites 32

2.2.6 Other Metal Zeolites 33

2.3 Catalytic Properties 34

2.3.1 Hydroxylation of Alkanes 34

2.3.2 Hydroxylation of Aromatic Compounds 40

2.3.3 Oxidation of Olefinic Compounds 47

2.3.4 Oxidation of Alcohol and Ether Compounds 59

2.3.5 Reactions of Carbonyl Compounds 60

2.3.6 Oxidation of N-Compounds 63

2.3.7 Oxidation of S-Compounds 65

2.4 Mechanistic Aspects 66

2.4.1 The Nature of Active Species 66

2.4.2 Hydroxylation 69

2.4.3 Epoxidation 71

2.4.4 Oxidation of Alcohols 72

2.4.5 Ammoximation 73

2.4.6 Decomposition of Hydrogen Peroxide 74

2.4.7 Active Species, Adsorption and Catalytic Activity 74

2.5 Stability of Metal-Substituted Zeolites to Reaction Conditions 77

2.6 Conclusions 78

References 80

3 Selective Catalytic Oxidation over Ordered NanoporousMetallo-Aluminophosphates 95

Parasuraman Selvam and Ayyamperumal Sakthivel

3.1 Introduction 95

3.2 Synthesis 100

3.2.1 Microporous Aluminophosphates 100

3.2.2 Mesoporous Aluminophosphates 102

3.3 Characterization 103


3.4.1 Oxidation of Hydrocarbons 106

3.4.2 Oxidation of Olefins 110


3.4.4 Oxidation of Phenols 113

3.4.5 Ammoximation and Ammoxidation 114

3.4.6 Baeyer–Villiger Oxidation 116

3.4.7 Oxidation of Heterocycles 116


3.6 Catalysts Stability 118

3.7 Conclusion 119

References 120

vi CONTENTS

4 Selective Oxidations Catalyzed by Mesoporous Metal Silicates 127

Oxana A. Kholdeeva

4.1 Introduction 127

4.2 Synthesis and Characterization 128

4.2.1 General Synthetic Approaches 128

4.2.2 Characterization Techniques 129

4.2.3 Sol-Gel Synthesis of Amorphous Mixed Oxides 132

4.2.4 Thermolytic Molecular Precursor Method 136

4.2.5 Templated Synthesis of Ordered Metal Silicates 136

4.2.6 Postsynthesis Modifications 156

4.2.7 Organic–Inorganic Hybrid Materials 162


4.3.1 Oxidation of Alkanes 163

4.3.2 Oxidation of Aromatic Compounds 167



4.3.5 Oxidation of Ketones and Aldehydes 183

4.3.6 Oxidation of S-compounds 185

4.3.7 Oxidation of Amines 188


4.5 Stability 194

4.5.1 Mechanisms of Deactivation 194

4.5.2 Solving Problem of Hydrothermal Stability 197

4.5.3 Hydrothermally Stable Catalysts: Scope and Limitations 199

4.6 Conclusions and Outlook 200

References 201

5 Liquid Phase Oxidation of Organic Compounds by SupportedMetal-Based Catalysts with a Focus on Gold 221

Cristina Della Pina, Ermelinda Falletta, and Michele Rossi


5.2 Catalyst Preparation and Characterization 222


5.3.1 Oxidation of Hydrocarbons 224

5.3.2 Oxidation of Alcohols and Phenols 228

5.3.3 Oxidation of Carbohydrates: The Case of Glucose 241

5.3.4 Oxidation of Amines and Aminoalcohols 244

5.3.5 Oxidative Polymerization of Aniline and Pyrrole 245

5.4 Reaction Mechanisms 250

5.5 Catalyst Stability 254

5.6 Conclusions 256

References 256

CONTENTS vii

6 Selective Liquid Phase Oxidations in the Presence of Supported

Polyoxometalates 263

Craig L. Hill and Oxana A. Kholdeeva



6.2.1 Choice of POM 266

6.2.2 Embedding POM into Silica and Other Matrixes 267

6.2.3 Adsorption on Active Carbon 271

6.2.4 Electrostatic Attachment 273

6.2.5 Dative and Covalent Binding 283






6.3.5 Oxidation of Aldehydes 298

6.3.6 Co-Oxidation of Alkenes and Aldehydes 299

6.3.7 Oxidation of S-containing Compounds 301


6.5 Stability 307

6.6 Conclusions 309

References 311

7 Selective Oxidations Catalyzed by SupportedMetal Complexes 321

Alexander B. Sorokin



7.2.1 General Synthetic Strategies 324

7.2.2 Metal Porphyrins 329

7.2.3 Metal Phthalocyanines 331

7.2.4 Complexes with Other Macrocyclic Ligands 336

7.2.5 Chiral Complexes 337

7.3 Catalytic Properties and Stability 338



7.3.3 Oxidation of Aromatic Hydrocarbons 352

7.3.4 Oxidation of Substituted Phenols 353


7.3.6 Miscellaneous Oxidations 359

7.4 General Remarks on Stability 362

7.5 Conclusion and Perspectives 364

References 365

viii CONTENTS

8 Liquid Phase Oxidation of Organic Compounds by Metal-Organic

Frameworks 371

Young Kyu Hwang, G�erard F�erey, U-Hwang Lee, and Jong-San Chang


8.2 Characteristics and Structures 372

8.2.1 Characteristics 372

8.2.2 Structures 374

8.2.3 Syntheses 378

8.2.4 Active Sites 380


8.3.1 Oxidation of Cycloalkanes 388



8.3.4 Oxidation of Alcohols and Phenols 398

8.3.5 Oxidation of Sulfides 399


8.5 Stability 402

8.5.1 Thermal and Chemical Stability 402

8.5.2 Leaching of Active Metal Components 404

8.6 Conclusion 405

References 405

9 Heterogeneous Photocatalysis for Selective Oxidations

with Molecular Oxygen 411

Andrea Maldotti, Rossano Amadelli, and Alessandra Molinari


9.2 Catalysts Preparation and Mechanistic Aspects 413

9.2.1 Titanium Dioxide 413

9.2.2 Highly Dispersed Oxides 416

9.2.3 Polyoxotungstates 418






9.4 Stability 438

9.5 Conclusions 443

References 444

10 Industrial Applications 451

10.1 The Hydroxylation of Phenol to Hydroquinone and Catechol 451

Ugo Romano and Marco Ricci

10.1.1 The Discovery of TS-1 451

CONTENTS ix

10.1.2 The Hydroxylation of Phenol 452

10.1.3 The Industrial Process 456

10.1.4 Other Processes Exploiting TS-1 460

References 461

10.2 The Greening of Nylon: The Ammoximation Process 462

Franco Rivetti and Roberto Buzzoni

10.2.1 Nylon-6 and e-Caprolactam, Outlook

and Industrial Production 462

10.2.2 TS-1 Catalyzed Ammoximation 466

10.2.3 Eni Cyclohexanone Ammoximation Process 467

10.2.4 Salt-Free Caprolactam Production 470

10.2.5 Other TS-1-Catalyzed Ammoximation Reactions

and Related Processes of Industrial Relevance 470

10.2.6 Conclusion 471

References 472

10.3 Production of Propylene Oxide 474

Anna Forlin, Massimo Bergamo, and Joerg Lindner

10.3.1 Propylene Oxide Production via Ethylbenzene

Hydroperoxide Route 476

10.3.2 Propylene Oxide Production via Cumene

Hydroperoxide Route 480

10.3.3 Propylene Oxide Production via Hydrogen Peroxide Route 483

10.3.4 Conclusions 487

References 494

10.4 Engineering Aspects of Liquid Phase Oxidations 496

Bruce D. Hook

10.4.1 Heterogeneous Liquid Phase Systems 496

10.4.2 Temperature-Control Requirements 499

10.4.3 Packed-Bed Reactors 500

10.4.4 Three-Phase Systems – Gas, Liquid, Solid 501

10.4.5 Oxidant Selection 503

10.4.6 Summary 505

References 506

Index 507

x CONTENTS

PREFACE

Liquid phase oxidation finds widespread application in the chemical industry for the

manufacture of a variety of chemicals ranging from the commodities to fine chemi-

cal specialties. About half of the overall capacity of oxidation processes, in fact, are

liquid phase ones. Until not long ago, however, heterogeneous catalysis did not play

a major role in this area, if compared to homogeneous catalysis. The prospects

started to change at the beginning of the 1980s with the synthesis of Titanium

Silicalite-1 (TS-1), even though the new processes based on it had to wait until the

2000s. Actually, the need to use hydrogen peroxide was initially felt to be a serious

obstacle to the development of large volume processes for which TS-1 appeared to

be suited. On the other hand, research activities, both in academia and industry,

received a great stimulus with papers and patents growing exponentially on the syn-

thesis, characterization and application of a large variety of new metal-substituted

molecular sieves, catalytically active for oxidation reactions. At the same time,

other families of catalysts, namely supported transition-metal complexes, noble

metal nanoparticles and photoactive materials benefited from major development.

On the whole, the area of catalysis related to liquid phase oxidations has experi-

enced an impressive progress in the last two to three decades, from both a scientific

and industrial perspective.

Books and journal reviews of excellent quality dealing with the above-mentioned

catalysts are available. Liquid phase oxidation, however, is in most cases covered by

single chapters, inevitably providing a partial picture of a multifaceted topic. The

second aspect is that the point of view and the needs of chemists looking for novel

synthetic routes generally remain in the background. This new book has the aim to

overcome these limitations, giving a comprehensive picture of promising materials,

privileging their application to organic synthesis and illustrating industrial

xi

realizations. Sections on synthesis and characterization provide essential informa-

tion on the different classes of materials. Stability under reaction conditions and

reusability are specifically stressed in each chapter.

The book is mainly oriented to an audience composed of faculty members,

researchers of both academia and industry, and R&D managers directly or indirectly

involved in organic synthesis and catalysis. To facilitate the desired approach, all

chapters are organized in a similar fashion, with the exception of the first and last

ones. Trying to adhere to the style of organic chemistry textbooks, catalytic propert-

ies are organized per class of compounds.

Typical oxidants, illustrated in the first chapter, are molecular oxygen, organic

hydroperoxides and, especially, hydrogen peroxide, while oxidants more or less dis-

tant from “green chemistry” are extraneous to the book. Inorganic molecular sieve

catalysts, namely, transition-metal-substituted zeolites, aluminophosphates and

mesoporous silicates are the subjects of the next three chapters. Supported catalysts

of gold, polyoxometalates and metal complexes are dealt with in chapters five

through seven and are followed by a novel class of functional materials, metal-

organic frameworks, and by heterogeneous photocatalysts. Industrial applications

in the last chapter, from early POSM process to recent ones for the hydroxylation of

phenol, production of caprolactam and of propylene oxide, are contributed by

authors directly involved in their development. A section on engineering aspects of

liquid phase oxidations dealing with issues that could facilitate subsequent scale up

of lab results closes the last chapter. Each chapter contains an extensive bibliogra-

phy covering most of the recent literature up to the beginning of 2012.

We would like to thank the authors that accepted to contribute to the book for

their nice work and their adhering to a uniform style. Finally, we thank Jonathan T.

Rose, Senior Editor of Wiley for his help and assistance from the initial preparation

of the book project through to its realization.

MARIO G. CLERICI

OXANA A. KHOLDEEVA

October 2012

Milan and Novosibirsk

xii PREFACE

CONTRIBUTORS

Rossano Amadelli, CNR-ISOF, U.O.S, c/o Dipartimento di Chimica Universit�a di

Ferrara, Ferrara, Italy.

Massimo Bergamo, Dow Deutschland Anlagengesellschaft mbH, Stade, Federal

Republic of Germany.

Roberto Buzzoni, Eni S.p.A., Green Chemistry - Research Center Novara, Catalysis,

Novara, Italy.

Jong-San Chang, Research Group for Nanocatalyst and Biorefinery Research

Group, Korea Research Institute of Chemical Technology (KRICT), Daejeon,

Republic of Korea.

Mario G. Clerici, formerly with ENI Group, San Donato Milanese, Italy.

Cristina Della Pina, Universit�a degli Studi di Milano, Dipartimento di Chimica e

ISTM-CNR, Milano, Italy.

Marcelo E. Domine, Instituto de Tecnolog�ıa Qu�ımica, ITQ (UPV - CSIC), Valencia,

Spain.

Ermelinda Falletta, Universit�a degli Studi di Milano, Dipartimento di Chimica e

ISTM-CNR, Milano, Italy.

G�erard F�erey, Universit�e de Versailles Saint-Quentin-en-Yvelines, Institut

Lavoisier (UMR CNRS 8180), Versailles cedex, France.

Anna Forlin, Dow Italia S.r.L., Correggio (Reggio Emilia), Italy.

Craig L. Hill, Emory University, Department of Chemistry, Atlanta - GA, USA.

xiii

Bruce D. Hook, The Dow Chemical Company, Performance Materials R&D,

Freeport - TX, USA.

Young Kyu Hwang, Research Group for Nanocatalyst and Biorefinery Research

Group, Korea Research Institute of Chemical Technology (KRICT), Daejeon,

Republic of Korea.

Oxana A. Kholdeeva, Boreskov Institute of Catalysis, Novosibirsk, Russia.

U-Hwang Lee, Research Group for Nanocatalyst and Biorefinery Research Group,

Korea Research Institute of Chemical Technology (KRICT), Daejeon, Republic

of Korea.

Joerg Lindner, Dow Deutschland Anlagengesellschaft mbH, Stade, Federal

Republic of Germany.

Andrea Maldotti, Dipartimento di Chimica Universit�a di Ferrara, Ferrara, Italy.

Alessandra Molinari, Dipartimento di Chimica Universit�a di Ferrara, Ferrara,

Italy.

Marco Ricci, Eni S.p.A., Centro Ricerche per le Energie non Convenzionali -

Istituto Eni Donegani, Novara, Italy.

Franco Rivetti, formerly with ENI Group, Milano, Italy.

Ugo Romano, FEEM - Fondazione Eni Enrico Mattei, Milano, Italy.

Michele Rossi, Universit�a degli Studi di Milano, Dipartimento di Chimica e ISTM-

CNR, Milano, Italy.

Ayyamperumal Sakthivel, University of Delhi, Department of Chemistry, Delhi,

India.

Alessandro Scarso, Universit�a Ca’ Foscari, Dipartimento di Scienze Molecolari e

Nanosistemi, Venezia, Italy.

Parasuraman Selvam, Indian Institute of Technology - Madras, National Centre

for Catalysis Research and Department of Chemistry, Chennai, India.

Alexander B. Sorokin, Institut de Recherches sur la Catalyse et l’Environnement

de Lyon, IRCELYON, UMR 5256, CNRS, Universit�e Lyon 1, Villeurbanne,

France.

Giorgio Strukul, Universit�a Ca’ Foscari, Dipartimento di Scienze Molecolari e

Nanosistemi, Venezia, Italy.

xiv CONTRIBUTORS

ABBREVIATIONS

(FePctBu4)2N N-bridged di-iron phthalocyanine complex

2,6-AQDS anthraquinone-2,6-disulfonate

2,6Cl2pyNO 2,6-dichloropyridine-N-oxide

2-pymo 2-hydroxypyrimidinolate

2R, RR-L (R,R)-(-)-1,2-cyclohexanediamino-N,N’-bis(3-tert-butyl-5-

(4-pyridyl)salicylidene)

2S, SS-L (S,S)-(-)-1,2-cyclohexanediamino-N,N’-bis(3-tert-butyl-5-

(4-pyridyl)salicylidene)

ACP acetophenone

AO anthraquinone process

APO aluminophosphate

AZY azoxybenzene

AZO azobenzene

BDC 1,4-benzenedicarboxylate

BDPB 1,4-bis[(3,5-dimethyl)pyrazol-4-yl]-benzene

BIPY 2,2’-bipyridine

bpdc biphenyldicarboxylate

BPED meso-1,2-bis(4-pyridyl)-1,2-ethanediol

bpy 4,4’-bipyridine

BQ benzoquinone

BT benzothiophene

btb 1,3,5-benzene-tri-benzoic acid

xv

BTC 1,3,5-benzenetricarboxylate

BTEC 1,2,4,5-benzenetetracarboxylic acid

BV Baeyer–Villiger (oxidation reaction)

CD colloidal dispersion

CHP cumyl hydroperoxide

CHPO chlorohydrin process

CMOF isoreticular chiral metal-organic framework

CSTR continuous stirred-tank reactior

CT charge transfer

CUM coordinatively unsaturated metal

CVD chemical vapor deposition

DBT dibenzothiophene

DEF diethylformamide

DFT density functional theory

DHBDC 2,5-dihydroxybenzenedicarboxylate

DHTP dihydroxyterephtalate

DMDBT 4,6-dimethyl dibenzothiophene

DMF N,N’-dimethylformamide

DOPO direct oxidation of propylene with oxygen

DP deposition-precipitation

DPM diphenylmethane

DR UV-vis diffuse reflectance UV-vis

DTBP 2,6-di-tert-butylphenol

EB ethylbenzene

EBHP ethylbenzene hydroperoxide

ES-40 ethyl silicate 40

EXAFS extended X-ray absorption fine structure

FAMEs fatty acid methyl esters

FDMS 1,10-ferrocenediyl-dimethylsilane

FePcS iron tetrasulfophthalocyanine

FePctBu4 iron tetra-tert-butylphthalocyanine

GA glutaraldehyde

H2tea triethanolamine

H2TMPyP 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin

HDS hydrodesulfurization

Hmdea N-methyldiethanolamine

HMDS hexamethyldisilazane

HOPO hydro-oxidation of propylene with oxygen and hydrogen

xvi ABBREVIATIONS

HP/HPPO HPPO with H2O2 from direct synthesis

HPPO hydrogen peroxide to propylene oxide (PO process)

Hpz pyrazole

HQ hydroquinone

HR TEM high-resolution transmission electron microscopy

IBA isobutyraldehyde

Im imidazole

IWI incipient wetness impregnation

KIE kinetic isotope effect

L1 and L2 1,2,4,5-tetrakis(4-carboxyphenyl) benzene and 5,15-dipyridyl-

10,20-bis(pentafluorophenyl)-porphyrin

LDH layered double hydroxide

L-lac L-lactic acid

MAPO metal-substituted APO

MAS NMR magic-angle spinning nuclear magnetic resonance

MBA methylbenzylalcohol

MIL Materials of Institut Lavoisier

MIL-101 mesoporous chromium terephthalate, abbreviation derives from

“Mat�eriau de l’Institut Lavoisier”

MMO methane mono-oxygenase

MN 2-methylnaphthalene

Mn(acac) Mn(II) acetylacetonate complex

MNQ 2-methyl-1,4-naphthoquinone

MOF(s) metal-organic framework(s)

MPc metal phthalocyanine complex

MPc(NO2)4 metal tetranitrophthalocyanine complex

MPcCl16 metal hexadecachlorophthalocyanine complex

MPcF16 metal phthalocyanine perflorinated complexes (M ¼ Fe, Ru).

MPcS metal tetrasulfophthalocyanine complex

MPS methyl phenyl sulfide

MTBE methyl-tert-butyl ether

MTDCPP metal 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin complex

MTMP metal tetamesytilporphyrin complex

MTMPyP metal tetra(4-N-methylpyridyl)porphyrin complex

MW microwave

NDS naphthalene disulfonate

NHPI N-hydroxyphthalimide

NP(s) nano-particle(s)

NSB nitrosobenzene

ABBREVIATIONS xvii

ODS oxidative desulfurization

PANI polyaniline

PDMS polydimethylsiloxane membrane

PILC pillared clay

PMO periodic mesoporous organosilicas

PO propylene oxide

POM polyoxometalate

POSM propylene oxide – styrene monomer (PO process)

POSS polyhedral oligomeric silsesquioxane

PSD pore-size distribution

PVA polyvinylalcohol

PVDF polyvinylidene fluoride

PVP polyvinylpyrrolidone

Py pyridine

PYZ pyrazine

PZ pyrazole

PZDC pyrazine-2,3-dicarboxylate

RPM(s) robust porphyrinic material(s)

SAPO silicoaluminophosphate

SAXS/SANS small-angle X-ray/neutron scattering

SBU(s) secondary building unit(s)

SCD supercritical drying

SEM scanning electron microscopy

SDA structure-directing agent

TBAOH tetrabutylammonium hydroxide

TEAOH tetraethylammonium hydroxide

TBHP tert-butyl hydroperoxide

TBOT tetra-n-butyl orthotitanate

TBSIB 2-(tert-butylsulfonyl)iodosylbenzene

TCPP tetra(4-carboxyphenyl)porphyrin

TDCPP 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin

TEMPO 2,2,6,6-tetramethylpiperidyl-1-oxyl

TEOS tetraethyl orthosilicate

TEOT tetraethyl orthotitanate

TIE template ion exchange

TMA trimethylacetaldehyde

TMOS tetramethyl orthosilicate

TMBQ 2,3,5-trimethylbenzoquinone

xviii ABBREVIATIONS

TMP 2,3,6-trimethylphenol

tmtacn 1,4,7-trimethyl-1,4,7-triazacyclononane ligand

TOF turnover frequencies

TON(s) turnover number(s)

TPAOH tetrapropylammonium hydroxide

TPABr tetrapropylammonium bromide

TPD temperature-programmed desorption

TPM triphenylmethane

TS-1 titanium silicalite-1

UHP urea hydroperoxide

XANES X-ray absorption near-edge structure

XPS X-ray photoelectron spectroscopy

XRD X-ray diffraction

ZMOF(s) zeolite-like metal-organic framework(s)

ABBREVIATIONS xix

1ENVIRONMENTALLY BENIGNOXIDANTS

GIORGIO STRUKUL�

AND ALESSANDRO SCARSO

1.1 INTRODUCTION

The arsenal of possible oxidants available to the organic chemist to carry out oxida-

tion reactions is very wide. It ranges from the simplest one, naturally occurring, air

(oxygen) to other common synthetic ones like, e.g., hydrogen peroxide and bleach,

to more sophisticated ones, often requiring relatively complex synthetic procedures,

e.g., organic peroxides and hydroperoxides, peroxy acids, iodoso benzenes, and

dioxiranes. At variance with other catalytic reactions involving simple molecules

like hydrogenation or hydroformylation, oxygen activation and transfer is a much

more complex, more difficult to control process and has not witnessed similar

extreme degrees of efficiency in terms of activity and selectivity. In fact, while the

synthesis of sophisticated complex molecules, like some fine or chiral chemicals

involved in pharmaceutical or natural product synthesis is still dominated by the

use of homogeneous catalysts, often with the use of toxic oxidants, generating large

amounts of waste, implying complex process procedures for the separation of

products from unreacted reagents and catalysts, in oxidation even some large indus-

trial processes (e.g., the Wacker and Oxirane processes, the synthesis of adipic and

terephthalic acids) still rely on the use of soluble catalysts.

Nowadays, sustainability issues are also becoming important economic

factors so, even this area is being strongly influenced by the implementation of

the current binding twelve principles of Green Chemistry [1]. Replacement of

�Corresponding author

1

Liquid Phase Oxidation via Heterogeneous Catalysis: Organic Synthesis and Industrial Applications,First Edition. Edited by Mario G. Clerici and Oxana A. Kholdeeva.� 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.

technologies based on soluble catalysts wi th heterogeneous ones is intrinsically

more likely to lead to important technic al improve ment s in te rms o f cata lys t

design, process simplification, milder or more sustainable r eaction conditions ,

use of cheaper or more environmentally friendly oxidants. In the overall process

the latter represents a key i ssue.

Going green im plies an eva luation o f t he properties of c ommon oxidant s.

Table 1.1 reports an anal ysis of the byprod uct formed , the atom efficiency and the

cost for a seri es of them [2, 3]. Two oxida nts sta nd ou t in terms of envir onme ntal

acceptability: oxygen ( air) and hydrogen peroxide giving either no byproduct or

wat er as by pro duc t an d an ato m ef ficie n cy c lose to or ab ove 50 %. An anal y sis of

their E-facto r leads to similar conclusi ons (Table 1.1) [4, 5]. Althoug h the E-facto r

refers to a specifi c reaction, it is strongly influenced by the choice of the oxidant. As

an example, in Table 1.1 the E-fa ctor is cal cula ted for the epoxi datio n of p ropen e

with differ ent oxidants . As shown, water is n ot consider ed a waste and its E-facto r

is assumed to be zero. For all the othe r oxidan ts repor ted, the amount o f waste com-

pa re s t o a n d in s om e c as es la rgel y exce ed s th e a mo un t o f u s ef ul p r od u ct. A t hir d

class can be include d in this restri cted list of environm entally benign oxida nts, i.e.

alky lhydrop eroxides, even if the justific ation of this cho ic e is not related to th eir

intrinsic propert ies but relies on differ ent grounds, as will be clear in the foregoing.

In th e n ext s ec ti o ns th e g en e ral pr op er ti e s, met ho d s o f p ro du c ti o n, envi ro nme n tal

impact and som e consider ations relat ed to the u se of oxygen, alkyl h ydroperoxid es

and hydrog en perox ide will be criti cally pres ented with the aim of providing some

general guidelines for their use in cat alytic oxida tion reactions.

TABLE 1.1 Comparison between Different Terminal Oxidants in Terms of Green

Character

Oxidant ByproductaAtom

efficiency (%)a E-factorbCost (D /kg)

or (D /l)c

O2 H2O (none) 50 (100) 0 35

H2O2 H2O 47 0 63

CH3C(O)OOH CH3C(O)OH 27 1.03 390

t-BuOOH t-BuOH 22 1.27 150

NaClO NaCl 21 1.01 16

Pyridine-N-oxide Pyridine 17 1.36 450

CumOOH CumOH 12 2.34 110

KMnO4 MnO2þH2O 10 1.50 89

2KHSO5þKHSO4þK2SO4 (Oxone1)

3 KHSO4þK2SO4 10d 10.03 73

m-CPBA m-CBA 9 2.70 460

PhIO PhI 7 3.52 e

aOne O atom transfer, in parentheses two O atoms transfer.bCalculated for the epoxidation of propene.cData from www.sigmaaldrich.com for the most concentrated sold version of the oxidant, May 2012.dTwo O atoms are transferred to products.eNot sold.

2 ENVIRONMENTALLY BENIGN OXIDANTS

http://www.sigmaaldrich.com

1.2 OXYGEN (AIR)

Air is the cheapest possible oxidant and the most desired for large industrial cata-

lytic operations. However, in most cases for an effective catalytic reaction pure oxy-

gen is preferred. The reasons are many: (i) faster reactions and greater reactor

productivity; (ii) improved yield and better energy efficiency by avoiding dilution

of reaction gases with nitrogen; (iii) smaller, lower capital cost plants; (iv) lower

energy consumption; (v) environmental improvements due to significant reduction

in the amount of purge gas. This implies a separation process from the other air

components generally accomplished via fractional distillation of liquid air.

Air is first condensed through a series of compression/expansion cycles and sub-

sequently separated in a double distillation column. The original Hampson–Linde

process exploiting the Joule–Thomson effect has been modified and improved sev-

eral times over the years in order to increase the efficiency and reduce energy con-

sumption [6]. Even with these improvements the process remains quite energy

intensive and the optimum economic balance requires that oxygen is manufactured

on very large scale plants and then distributed to users as piped gas, as liquid oxy-

gen in road tankers or as compressed gas in cylinders [6]. Distribution costs are very

high in relation to the fairly low ex-factory cost of oxygen so that the price per unit

can vary more than one order of magnitude depending on distribution facility. The

consequence is that the cost of oxygen as oxidant for laboratory or small scale

organic syntheses (gas cylinders used) is not much lower than other common oxi-

dants (Table 1.1).

By contrast with many other simple diatomic molecules such as N2 or H2, the

oxygen molecule (or dioxygen) is paramagnetic as it has two unpaired electrons in

the ground state. The highest occupied molecular orbitals (HOMOs) are a pair of p�

orbitals of identical energy, so that the two highest energy electrons have no reason

to spin-pair [7]. The diradical nature of the oxygen molecule is very useful in under-

standing its chemistry. In fact, most of its reactions proceed in one-electron steps:

electrons added to the O2 molecule populate antibonding (p�) orbitals and weaken

the O�O bond (Scheme 1.1) [8]. This effect is evident in both the O�O bond length

and its dissociation energy making the resulting superoxo (O2��) and peroxo (O 2�

2 )

species more reactive and kinetically more easy to control.

As rationalized by Sheldon and Kochi [9], metal catalyzed oxidations can be

conveniently divided into two types: homolytic and heterolytic. Homolytic oxida-

tions involve free-radical intermediates and, in solution, are catalyzed by first-row

transition metals characterized by one-electron redox steps (e.g., CoII/CoIII,

O2 O2

eO2

2

bond energy (kcal/mole)

length (Å)

e

1181.21

881.26

461.49

SCHEME 1.1 Basic data on the dioxygen molecule and the superoxo and peroxo anions.

OXYGEN (AIR) 3

MnII/MnIII, CuI/CuII). In homolytic reactions the hydrocarbon to be oxidized is gen-

erally not coordinated to the metal and is oxidized outside the coordination sphere

via a radical chain. The main role of the metal is generally to decompose organic

hydroperoxides, formed in solution either spontaneously or by action of an initiator,

generating radicals to sustain the radical chain. This behavior is also known as the

Haber–Weiss mechanism (Scheme 1.2). These radical processes are common and

constitute the basis for several very important industrial applications (e.g., the

synthesis of adipic [10] and terephthalic [11] acids). However, radical chains are

difficult to control, they do not often preserve the configuration of the substrate and

typically lead to the formation of a wide variety of products as a consequence of a

series of consecutive reactions because the reaction product is generally more easily

oxidizeable than the reactant itself. It should be pointed out that the triggering of

radical chains is not an exclusive property of certain metal ions in solution but can

be effected also by the surface of a heterogeneous catalyst, especially when

reactions are carried out in the liquid phase. The general consequence is that

reactions involving one-electron processes with dioxygen as the oxidant are gener-

ally carried out at low conversion per pass and normally show only moderate to low

selectivities towards the desired product.

In the activation of dioxygen on the surface of a heterogeneous catalyst (particu-

larly in gas phase reactions) the formation of surface oxo species is generally

invoked. Oxygen is chemisorbed on Group 8–10 metals in this way, even at

relatively low temperatures. Indeed these surface oxo species are often repre-

sented as single bonded to the surface (Scheme 1.3A) to indicate their high

reactivity once adsorbed on defective, coordinatively unsaturated surface sites.

This chemisorbed oxygen can be exploited for the oxidation of, e.g., ethylene to

ethylene oxide [12–14], CO to CO2 [15, 16] or in catalytic combustion [17–20],

i.e. in reactions where selectivity is either not a problem or poor selectivity can be

economically tolerated. In the same way, metal-oxide or mixed-metal-oxide cata-

lysts generally employ their already existing surface oxo species (lattice oxygen)

for the high temperature oxidation of hydrocarbons. This is typical for n-type

semiconductor oxides (e.g., Ti, V, and Mo) where a lower oxidation state is easily

accessible to the central metal atom (Scheme 1.3B). Oxygen vacancies are subse-

quently replenished by dioxygen. This two-step process is known as the Mars–Van

Krevelen mechanism [21]. Because lattice oxygen is more tightly bound than

chemisorbed oxygen, it can be delivered in a more controlled fashion opening the

way to selective oxidation and this mechanism is involved in processes like, e.g.,

the synthesis of acrolein or acrylonitrile [22–24].

CoII Co + ROOH III + RO• + OH–

CoIII Co + ROOH II + ROO• + H+

SCHEME 1.2 Cobalt-catalyzed decomposition of hydroperoxides (Haber-Weiss mechanism).


For the reasons described above the use of oxygen as oxidant in heteroge-

neously catalyzed organic reactions is always associated, to a variable extent,

with substrate total oxidation and/or with the formation of byproducts. Therefore,

one of the main efforts in catalyst design is to keep these problems to a minimum,

because the advantage of using a cheap and environmentally benign oxidant can

be outweighed by loss of starting reagent and the need to dispose significant

amounts of unwanted byproducts. Moreover, oxygen is a gas and its use for

reactions in the liquid phase generally requires medium to high pressures to

increase the solubility in the reaction medium. It forms explosive gas mixtures

with the vast majority of volatile organic compounds requiring adequate safety

control in the apparatus to stay out of the explosion limits (extra capital invest-

ment). In other words, despite oxygen being a very cheap and practical oxidant,

its environmental sustainability may become a questionable concept that should

be evaluated only a posteriori.

1.3 ALKYLHYDROPEROXIDES

Hydroperoxides represent a reduced and easier to control form of dioxygen. As is

clear from Scheme 1.1, in peroxides the O�O bond is longer and its energy lower

than in free dioxygen. Therefore, it is easier to deliver one of the oxygen atoms of

hydroperoxides in a controlled manner under mild conditions.

They can easily react with suitable transition-metal precursors to give a variety

of species (some of which are stable enough to be isolated) involved in oxygen

transfer to hydrocarbons. The different oxygenated species that are liable to play a

M

O2, subs

M

O O subs

M

O + subs(O)

chemisorbedoxygen

OMn+

O

OMn+

O

O

O subs

OMn+

O

OMn+

O

O

Osubs

OMn-1+

O

OMn-1+

O

O subs(O)O2

latticeoxygen

Mars-van Krevelen

(A)

(B)

SCHEME 1.3 Oxygen activation on the surface of heterogeneous catalysts. (A) Through

chemisorption; (B) by replenishing consumed lattice oxygen.

ALKYLHYDROPEROXIDES 5

role in oxidation processes are schematically represented in Scheme 1.4. The first

step consists of the formation of a hydroperoxide adduct from which all other spe-

cies can form in a cascade of reactions. Among the different species shown in the

scheme, only hydroxo (G) are not directly involved as the oxidizing species in oxy-

gen transfer processes. With the exception of oxo species, where hydroperoxides

operate as mono-oxygen donors to the metal, in the other cases the O�O moiety

remains intact. In all cases, only one of the peroxy oxygens is utilized in oxygen

transfer, the other one is used to make alcohols (water).

Their behavior in oxidation is largely dependent on the type of metal used as

catalyst. With one-electron redox systems homolytic oxidation prevails and hydro-

peroxides are simply decomposed in the catalytic system to generate radical species

according to the Haber–Weiss mechanism (Scheme 1.2).

With two-electron redox systems heterolytic oxidations are generally involved

and the metal can selectively transfer one oxygen atom to a suitable substrate. This

is the basis for a wide variety of catalytic oxidation reactions, some of which have

found applications in industry like, e.g., the Halcon and Shell processes for the pro-

duction of propylene oxide [25, 26] or the synthesis of Esomeprazole [27, 28] and

Indinavir [29, 30] in the pharmaceutical industry that are based on enantioselective

sulfoxidation and epoxidation respectively.

Alkylhydroperoxides can be prepared in many different ways [31], however,

only the most stable ones have been used in practice as oxidants for organic trans-

formations. Bulk hydroperoxides are intrinsically unsafe materials as they can

decompose violently by homolytic or heterolytic fission hence proper care must be

taken to handle them safely. Their stability follows the well-known order, tertiary>secondary> primary, that also parallels the ease with which they can form from the

corresponding hydrocarbons via radical autoxidation.

Mn+1 O Mn+1

Mn+2OO

Mn

Mn+1 OH

H+

OMn+2

ROOH

- H2O

Mn+1 OOR

Mn

H2O2

R+

Mn+1 OOH

H+H2O2

(A)

(D)

(B)

(F)

ROOHH2O

(C)

H2O2

oxo µ-oxo

hydroxoperoxo

hydroperoxo

(E)alkylperoxo

ROOH, H2O2 Mn(ROOH)

Mn(H2O2)

- ROH

- H2O

- Mn+1OH

(G)

- H2O

- H2O

- H+

- H+

SCHEME 1.4 Schematic network connecting the metal-oxo and -peroxo species involved

in metal-promoted oxidations.


Stable alkylhydroperoxides that have been extensively used in catalytic

oxidations are t-butyl hydroperoxide (TBHP), cumyl hydroperoxide (CHP) and eth-

ylbenzene hydroperoxide (EBHP). Their major application is in the synthesis of

propene oxide (PO) according to different technologies. They are produced by the

autoxidation of the corresponding hydrocarbons containing a tertiary or a benzylic

C�H bond. In the industrial practice their synthesis is carried out in one section

of the plant.

The use of hydroperoxides implies that one molecule of alcohol is released per

molecule of propylene oxide in the epoxidation stage. Indeed, much more alcohol is

coproduced, owing to the less than 100% selectivity in both the autoxidation and

epoxidation reactions. The choice of the peroxide is dictated also by the economics

of the process that is strongly bound to the possibility to convert the large amounts

of the alcohol coproduct into commercially valuable chemicals. Generally,

ethylbenzene or isobutane are used, and the corresponding 1-phenyl ethanol and

t-butanol are transformed into polymer-grade styrene or isobutene for octane

enhancers in gasoline (MTBE, ETBE) [26]. The end of pipe recycling or commer-

cialization of the coproduct is a key issue to justify the environmental acceptability

of processes based on alkylhydroperoxides. Nonetheless, the presence of a

coproduct implies that the value of propylene oxide is significantly affected by the

demand/pricing of the coproduct and difficulties can arise in balancing two different

markets that may occasionally experience diverging dynamics of growth.

In all cases the alkylhydroperoxide oxidant is produced on site and the synthesis

unit is integrated in the main PO process. A simplified view of the main integrated

process operations is shown in Scheme 1.5.

RH

O2ROOH

O

ROH

Ph

H

Ph

OHMeOH

O

Ph OH Ph H

H

Ph OH

peroxidesynthesis

POsynthesis

catalyst

R =

MTBE

- H2O

H2

to recycling

styrene

- H2O

- H2O

SCHEME 1.5 A simplified view of the operations taking place in the different propene

oxide technologies, including the transformation of the alcohol coproducts into valuable

chemicals.

ALKYLHYDROPEROXIDES 7

The process originally developed by Halcon/ARCO, with a current market share

of ca. 13%, is based on the use of TBHP as the oxidant. Isobutane is oxidized with

air at ca. 120–140 �C and 25–35 bar in a typical autoxidation reaction yielding com-

parable quantities of TBHP and t-butyl alcohol (TBA) with conversions around

40%. The epoxidation of propylene is a liquid phase homogeneous reaction carried

out in TBA as the solvent at 110–120 �C, under pressure (ca. 40 bar), in the presence

of a soluble MoVI catalyst. Yields on propylene are ca. 90% at 10% conversion. The

ratio of the coproduced TBA to propylene oxide is in the range 2.4 to 2.7. TBA is

mostly dehydrated to isobutene and etherified with methanol or ethanol for the pro-

duction of octane boosters [32].

Alternatively, EBHP is used in two other processes, developed by Hal-

con/ARCO and by Shell, with a whole market share of ca. 35%. EBHP is pro-

duced by the autoxidation of ethylbenzene at 140–160 �C, limiting the conversion

to somewhat below 15% to minimize the decomposition of the hydroperoxide.

The selectivity to EBHP is in the range 80–85%, with the balance being a mixture

of 1-phenylethanol and acetophenone. The epoxidation of propylene, catalyzed in

the Shell process by TiIV supported on silica (Ti/SiO2) and by a soluble organic

salt of MoVI in the Halcon/ARCO process, is operated in the liquid phase at ca.

100–120 �C. In both cases, the 1-phenylethanol coproduct is dehydrated to styr-

ene. The yields of propylene oxide are 91–92%, with a styrene to propylene oxide

ratio close to 2.2 [32].

An advanced version of the hydroperoxide process, in which the alcohol is

transformed back into the starting hydrocarbon, was commercialized by Sumitomo

in 2003 (market share ca. 4%). As the end use of the coproduct is no longer a dis-

criminating issue for the choice of oxidant, the preference was for CHP over other

hydroperoxides, on the grounds of its higher stability and superior performance

in the epoxidation stage. Cumene is regenerated at the end of the process by the

dehydration–hydrogenation of cumyl alcohol and recycled to the autoxidation

reactor. In practice, hydrogen and oxygen are consumed to yield equimolar amounts

of epoxide and water; in this aspect the process resembles the monooxygenase type

of reactions [32].

The above examples clearly show that despite unfavorable atom efficiency and

E-factor the sustainable use of alkylhydroperoxides as oxidants is possible,

although it strongly depends on the profitable conversion of the corresponding

alcohol. This is possible in large scale plants where process integration is easy to

practice, it does not constitute a problem for small applications in fine chemistry

because the amount of hydroperoxide necessary can be easily bought on the mar-

ket and the alcohol disposed of, but it becomes complicated in medium scale

operations where neither of the above conditions apply (easy hydroperoxide sup-

ply and alcohol conversion), posing economic constraints that may suggest other

oxidant systems. This is why, as reported above, commercial applications of

alkylhydroperoxides other than propylene oxide are mainly in the synthesis of

pharmaceuticals where the large added value of the final product compensates

for the cost of disposal of all the byproducts produced along the complex syn-

thetic procedure.


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LIQUID PHASE - Startseite · 2013. 7. 23. · 4 Selective Oxidations Catalyzed by Mesoporous Metal Silicates 127 Oxana A. Kholdeeva 4.1 Introduction 127 4.2 Synthesis and Characterization