Multiphase Homogeneous Catalysis - Hardcover

Cornils, Boy

Hardcover

ISBN 10: 3527307214 ISBN 13: 9783527307210

Verlag: Wiley-VCH Verlag & Co, 2008

Inhaltsangabe

This long-awaited two-volume handbook is the one-stop reference for everybody working in the field of multiphase catalysis. Covering academic and industrial applications, it will set the standard for future developments.
All editors are top scientists with an industrial or academic background, and have put together an international team to present every facet of this fascinating methodology -- including aqueous phase catalysis, ionic liquids, flourous phase chemistry, supercritical solvents and catalysis with polymer bound ligands -- in a compact and competent manner.

Über diesen Titel

Über die Autorin bzw. den Autor

Boy Cornils has worked at the former Hoechst AG in Germany, where he was the director of the reasearch. He is the editor of several bestselling titles.

Wolfgang A. Herrmann is president of the Technical University of Munich and has received several awards for his work in organometallic chemistry, like the Otto-Bayer Medal, the ACS Award in Organometallic Chemistry, the Werner-Heisenberg Medal of the Alexander von Humboldt foundation and many more. He has authored a plethora of publications and is the editor of numerous bestselling books.

Istvan Horvath is Professor at the Eötvös Universitiy in Budapest. He is the Editor-in-Chief of the "Encyclopedia of Catalysis" and has chaired many meetings and symposia in the areas of green chemistry and catalysis.

Walter Leitner holds the chair of Technical Chemistry and Petrochemistry at RWTH Aachen (successor to Prof. Keim). In November 2003 he became external scientific member of the Max-Planck-Institut für Kohlenforschung.

Stefan Mecking was research associate at the Freiburg Materials Research Center and Institute of Macromolecular Chemistry of Albert-Ludwigs-University Freiburg. Since March 2004 he is full professor at Konstanz University, Chair of Chemical Materials Science. He has received the BASF Catalysis Award and the Otto-Roelen-Medaille.

H. Olivier-Bourbigou is research associate at the Ecole du Petrole et du Moteurs and her research interest are ionic liquids and green chemistry.

Dieter Vogt is full professor in inorganic chemistry and catalysis. He received his Ph.D. from Aachen University of Technology in 1992 with prof. W. Keim as supervisor. He did his Habilitation at the Institute of Industrial Chemistry and Petrochemistry of the RWTH Aachen. End of 1998 he was appointed as full professor of Inorganic Chemistry and Coordination Chemistry at Eindhoven University of Technology. His main research interest are in the field of homogeneous catalysis, catalyst recycling and new materials for application in catalysis.

Von der hinteren Coverseite

This long-awaited two-volume handbook is the one-stop reference for everybody working in the field of multiphase catalysis. Covering academic and industrial applications, it will set the standard for future developments.
All editors are top scientists with an industrial or academic background and have put together an international team to present every facet of this fascinating methodology -- including aqueous-phase catalysis, ionic liquids, fluorous-phase chemistry, supercritical solvents, and catalysis with polymer-bound ligands -- in a compact and competent manner.

From the Contents:

Organic Chemistry in Water
Homogeneous Catalysis in the Aqueous Phase
Technical Solutions
Technical Applications of Supercritical Fluids
Organic-Organic Biphasic Catalysis on a Laboratory Scale
Enantioselective Catalysis in the Fluorous Phase
Catalysis in Nonaqueous Ionic Liquids
Commercial Applications and Aspects of Ionic Liquids
Catalysis using Supercritical Solvents
Soluble Polymer-Bound Catalysts
Polymer-Bound Metal Complexes as Catalysts for C-C and C-N Coupling

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Multiphase Homogeneous Catalysis, 2 Volumes

John Wiley & Sons

Copyright © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
All right reserved.
ISBN: 978-3-527-30721-0

Chapter One

Introduction

Boy Cornils, Wolfgang A. Herrmann, Istvn T. Horvth, Walter Leitner, Stefan Mecking, Hlne Olivier-Bourbigou, and Dieter Vogt

"Sipping a cup of decaffeinated coffee the reader may wonder on the somewhat unusual classification of solvents as 'alternative': alternatives to what? And why would we need alternative media for doing chemistry or for any other purpose? These may be the first questions for those who are just starting to discover the existing new developments on using solvents other than volatile and often toxic organics for synthesis and especially for catalytic reactions. Yes, indeed, ...".

Yes, indeed, similarly to an opening cornucopia, the arsenal of methods and techniques in homogeneous catalysis has offered remarkable progress in recent years. Above all, these improvements concentrate on the modification and the handling of homogeneous catalysts in general and the removal and subsequent recycling of catalysts in particular. The progress to be dealt with in this book has been rendered essentially possible by the introduction of separate phases in the context of "homogeneous" catalysis: an apparent contradiction with far-reaching consequences. For the first time, this book reviews all the realistic possibilities described so far using multiphase operation of homogeneous catalysis: processes with organic/organic, organic/aqueous, or "fluorous" solvent pairs (solvent combinations), nonaqueous ionic solvents, supercritical fluids, and systems with soluble polymers. In Figure 1, the family tree of homogeneous catalysis proves that this recent research extends considerably the scope of the work.

Following the logic of this tree, the multiphase processes on the left-hand side belong among the operations with "immobilized catalysts" but on "liquid supports". The topics of this book are the processes with the liquid supports water, supercritical fluids, ionic liquids, organic liquids, soluble polymers, and fluorous liquids; among these, only two processes (Ruhrchemie/Rhne-Poulenc and Shell SHOP) are operative industrially so far. The more important "leaves" of the family tree are shaded in gray.

In Figure 2, demonstrating the genesis of homogeneous and heterogeneous catalysis, the topical processes are on the borderline between heterogeneous and homogeneous catalysis (and catalysts).

Why multiphase systems? This goes back to the 1980s and the enormous impetus which was given to the homogeneous catalysis community by the first realization of Ruhrchemie/Rhne-Poulenc's oxo process at the Oberhausen plant site. Astonishingly, it was this development (and not the earlier SHOP process of Shell) that sensitized the scene to the possibilities of multiphase action: only on the basis of the "aqueous" activities that so much widespread and multi-faceted research work, with effects on the newer areas mentioned has been accomplished successfully. There was earlier work and proposals to imitate the decisive advantage of heterogeneous catalysis: the immediate separation of catalyst and substrates/ products just after reaction which makes it possible to avoid additional separation steps post-reaction, such as distillations and other thermally stressing procedures. All proposals have the same target: to enable the homogeneous catalyst to be bound to a suitable "support", i.e., another phase, without losing its superior homogeneous catalytic activity and selectivity. Within the scope of this book the editors define "phases" not only thermodynamically (as uniform states of matter of one substance which are separated (and separable) from each other by unequivocal phase boundaries; for example, water-ice or normal-supercritical states) but also as different states of aggregation of different compounds, such as systems consisting of water-organic liquids. Thus this book deals with homogeneous catalysts on liquid supports. Additionally, the processes described imply two- or three-phase reactions (the latter is the case if gaseous reactants complete the reaction scheme, e.g., hydrogen in hydrogenations or syngas in hydroformylations).

The use of liquids in homogeneous catalysis thus means not only a liquid support and from there a basic intervention in the handling and the operation of the catalyst, but also a modern separation technique for efficient work-up in organic synthesis. Figure 3 illustrates the enormous importance of the biphasic technique for homogeneous catalysis: the catalyst solution is charged into the reactor together with the reactants A and B, which react to form the solvent-dissolved reaction products C and D. The products C and D have different polarities than the catalyst solution and are therefore simple to separate from the catalyst phase (which may be recycled in a suitable manner into the reactor) in the downstream phase separation unit.

This double meaning of the multiphasic approach is specially visible in the case of fluorous liquids, where organic chemists are at least as interested as the catalytic community in the use of these fluids.

The ability of different combinations of solvent pairs to enable biphasic operation can be estimated on the one hand according to the principle of "like dissolves like" ("similia similibis solvuntur", as the old alchymists used to say) in respect to the solvent for the catalyst and, on the other hand, with the help of diagrams as shown in Figure 4 and of fundamental investigations.

The fundamentals of miscibility (solvation power, [E.sup.N.sub.T]) of various solvents from nonpolar, aprotic tetramethylsilane (TMS; with [E.sup.N.sub.T] = 0 as defined) to polar water ([E.sup.N.sub.T] = 1) are given by the solvent polarity scale in Figure 5.

This graph gives a selection of 14 (out of approximately 360) of the usual solvents above the baseline and seven more exotic solvents (supercritical C[O.sub.2] and ionic liquids included) below. The 14 compounds, from left to the right with increasing solvent polarity, include apolar, aprotic (such as TMS, cyclohexene, or benzene), bipolar (such as acetone or DMF), and eventually bipolar, protic solvents (cyclohexanol, ethanol, phenol). Using the [E.sup.N.sub.T] values, numerous solvent-dependent processes may be correlated with each other. Other measures that can be used for the estimation of miscibility/solvent power are the cohesive pressures, solubility parameters, dispersive forces, Kamlet-Taft parameters, etc. Solvent combinations of exotic members and systems with more than two members are known and have been recommended, but their application has been concentrated in the lab because of economic disdavantages with their handling and recyclability/ separability.

A recent proposal concerns mixed organic-aqueous tunable solvents (OATS) such as dimethyl ether-water, the solubility of which for substrates can be influenced by a third component such as carbon dioxide. C[O.sub.2] acts as a "antisolvent" and as a switch to cause a phase separation and to decant the phases from each other (preferably under pressure). This behavior makes the operation of bi- or multiphase homogeneous catalytic processes easier and more economic: the preferential dissolution at modest pressure of carbon dioxide causes phase separation which results in large distribution coefficients of target molecules in biphasic organic-aqueous systems. This extraordinary behavior lead to a sophisticated flow scheme (Figure 6).

This operation, which needs at least two internal recycles, may be economic for special purposes (e.g., highly prized applications) such as enzyme-catalyst conversions. Indeed, it has been tested for the ADH-catalyzed reduction of hydrophobic ketones coupled with regeneration of the cofactor NADH. Another possibility discussed recently is the use of surface polarity-modified (heterogeneous) catalysts and their distribution between two immiscible solvents which occurs against gravity.

It might be added that the multiphase operation offers more than the decisive separation between desired products and catalyst, although there are differences between the various multiphase liquids. It cannot be emphasized enough that the use of polar multiphase liquids also separate the byproduct "heavy ends" from the catalyst in the system, thus avoiding a build-up in the catalyst recycle. In other processes (and probably also if very apolar fluorous liquids are used) an additional purge is needed to remove the high boilers from the catalyst, which then requires a further (and costly) separation or purification.

It is also worth mentioning that the multiphase approach has been used as a strategy to avoid undesired consecutive reactions or even to segregate two different and incompatible catalysts in one-pot or in tandem syntheses. In a typical example, Chaudhari et al. described the combination of a hydroformylation step - catalyzed by phosphine-modified rhodium complexes - with the Mannich reaction of the oxo aldehydes formed, catalyzed by tertiary amines. Thus the manufacture of methacrolein according to Figure 7 proceeds best in two different phases: the organic phase for hydroformylation and the aqueous phase in which the Mannich reaction is achieved (Figure 8).

Our definitions of phases or multiphases, respectively, include interfacial events, but it must be emphasized that the engineer's definition of "interphases" or "interfacial engineering" concentrates more on solid-solid phase boundaries such as in the manufacture of chips, photographic films, polymer composites, advanced ceramics, etc., or on processes with heterogeneous catalysts and other phases. Last, but not least, the possibility of placing the emphasis on "greener" techniques and thus so-called "sustainable" operations may be mentioned in passing.

Although they also are "biphasic", this book does not include immobilized, modified homogeneous catalysts on solid supports ("anchored catalysts"). There is little mileage in looking for ostensibly more and more effective ligands and better and better optimization of the solid support and/or catalyst precursor to ensure, on the one hand, adequate immobilization on the support (sufficient stability of the covalent bond between the support matrix and the central atom) and, on the other, adequate mobility for the catalytically active catalyst constituents (sufficient lability of the modified ligand sphere). All the results so far allow only the conclusion that with the heterogenizing techniques used significant problems remain to be solved. The reason for this is that the various catalyst species undergo changes in spatial configuration as they pass through the catalytic cycle typical of a homogeneous process.

The constant "mechanical" stress on the catalyst's central atom <-> ligand bonds and the constant change in the bond angles and lengths ultimately lead also to a weakening of the central atom <-> support bond. In hundreds of publications this is conveniently demonstrated using the hydroformylation reaction catalyzed by heterogenized cobalt or rhodium carbonyls as an example. The catalyst passes through the two forms of a trigonal-bipyramidal and a tetrahedral metal carbonyl, which overstresses and weakens the heterogenizing bond between the metal and the support - ending up with a considerable "leaching" of the catalysts's active components. This leaching always affects not only the usually costly central atoms but also the (frequently more costly) ligands of homogeneous metal complex catalysts. Therefore, it might be no coincidence that - apart from lab or pilot plant work and apart from enzymatic techniques - no homogeneously catalyzed reaction attained large-scale, commercial status. Processes including the reaction in biphasic operation but on heterogeneous catalysts (as, for example, in) are also not included.

According to our definition, homogeneous catalysis includes catalysts which, inter alia,

are molecularly dispersed "in the same phase" or between two suitable phases (see above),

are unequivocally characterized chemically and spectroscopically and can be synthesized and manufactured in a simple and reproducible manner,

can be tailor-made for special purposes according to known and acknowledged principles and based upon a rational design, and

permit unequivocal reaction kinetics related to each reactant catalyst molecule, in general each metal ion.

These definitions allow the well-known compilation of the advantages/disadvantages of both catalytic regimes (Table 1).

Entry 7 of Table 1 is the reason for the application of the idea to use multiphase techniques, probably first articulated and systematized by Manassen and Jo. In 1972, Manassen suggested

"... the use of two immiscible liquid phases, one containing the catalyst and the other containing the substrate ..."

and hence the general form of biphase catalysis, which constitutes a logical development of the work in "molten salt media" (further developed and known today as "ionic liquids"; this term used to refer to high-melting, inorganic or organic/ inorganic salts or salt mixtures; cf. Chapter 5). The inventors of Shell's SHOP process, who had already worked on soluble, homogeneous complex catalysts in a biphase system some years earlier, cited the special method without particular emphasis. Some years later, Jo concentrated on hydrogenations and Kuntz published his work on aqueous-phase hydroformylation, i.e., reactions of commercial interest. Other historical roots may be found in.

Looking back, it must be stated that Manassen and Beck/Jo's ideas were developed independently of each other. Remarkably, the fundamental papers of Jo and Kuntz created little interest and only found a wider echo in academic research once Shell and Ruhrchemie had managed to achieve industrial scale-up of their biphase catalyses in organic/organic or in aqueous systems. In a drastic departure from the normal pattern, here basic research lagged considerably behind industrial research and application. This has changed with the introduction of other liquid phases such as ionic liquids (as defined today), supercritical liquids, polymeric fluids, and fluorous liquids.

As a last definition the book concentrates on organometallic catalysts as one of the bases of homogeneous catalysis, although the introduction of strange additives like water and other immiscible ingredients such as other organic liquids, carbon dioxide, nonaqueous ionic liquids, solvent-miscible polymers, or even perfluorinated compounds was originally regarded as disturbing if not poisoning. So Cintas wrote in respect of the "additive" water:

"At first, the idea of performing organometallic reactions in water might seem ridiculous, since it goes against the traditional belief that most organometallics are extremely sensitive to traces of air and moisture and rapidly decompose in water".

Other statements voice people's doubts about the same fact. Acid-base catalysts, the other well developed category of homogeneous catalysts, are mentioned when their action is typical or decisive for the demonstration of the respective multiphase action.

Besides one book summarizing Chemistry in Alternative Reaction Media, which concentrates more on physical aspects rather than applications, the above-mentioned multiphase media have so far been dealt with only in monographs such as

Aqueous-Phase Organometallic Catalysis,

Applied Homogeneous Catalysis with Organometallic Compounds,

Handbook of Fluorous Chemistry,

Ionic Liquids in Synthesis,

Chemical Syntheses Using Supercritical Fluids,

Emulsion Polymerization and Emulsion Polymers.

(Continues...)

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Details zur Ausgabe

• Verlag: Wiley-VCH Verlag & Co
• Erscheinungsdatum: 2008
• Sprache: Englisch
• ISBN 10: 3527307214
• ISBN 13: 9783527307210
• Einband: Tapa dura
• Anzahl der Seiten: 905
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar