Hydroformylation ionic liquids

Of course, there is still a large amount of research to be done to develop further the very preliminary character of the above described economic evaluation of an ionic liquid hydroformylation process. Only on the basis of more detailed data it will be possible to decide whether we will see an industrial hydroformylation plant using ionic liquids in the future. 

Since the solubility of long-chain alkenes is higher in ionic liquids than in water, there is much interest in finding effective ionic liquid catalysts for the hydroformylation reaction. Bis-phosphines have proved to be particularly useful in hydroformylation reactions and a bis-phosphine with a charged cobaltocenium backbone, analogous to l,l/-bis(diphenylphosphino)ferrocene (dppf), has been developed specifically for use in ionic liquid hydroformylation reactions [26], In combination with [Rh(CO)2(acac)], the 1, I -bis(diphenylphosphino)cobaltocenium hexafluorophosphate ligand dissolved in [bmim][PF6] effectively catalyses the hydroformylation of 1-octene as shown in Scheme 8.11. 

The POP-Xantphos ligand, which at the present affords the best turnover frequencies and l b ratios is considerably more expensive than the rather simple TPPTS ligand employed in aqueous biphasic hydroformylation. Compared to the classical rhodium-phosphine process, manufacturing costs in the aqueous biphasic process are about 10% lower. Accordingly, requirements for a fairly expensive catalyst will be exceptional if it should be considered in an industrial process, especially if one bears the additional costs for the required ionic liquid in mind. Nevertheless, the prospect of biphasic ionic liquid hydroformylation looks very promising. 

Supported Ionic Liquid Hydroformylation Systems (SILCs)... 

Alternative Media for Chemical Reactions and Processing, M.A. Abraham L. Moens (Eds.), Chap. 4, 34-49, ACS, Washington, D.C. ISBN-13 9780841237797 Sen, D.J. (2006). Reflection of Green Chemistry, Pharma Times, 38(7), pp. 35-39 Sharma, A. (2009). Catalytic Reaction Engineering Using Ionic Liquids Hydroformylation of 1-Octene, PhD Thesis, University of Toulouse, France. 

Gompared to other wide-bite-angle diphosphine ligands, xantphos-type ligands can be modified easily while retaining their favorable properties, especially in hydroformylation, and as a result many derivatives have been synthesized by several groups and used in fluorous-phase hydroformylation catalysis, aqueous phase catalysis, one-phase hydroformylation and catalyst extraction, catalysis in ionic liquids, hydroformylation with immobilized catalysts, and catalysis in supercritical G02. ... 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

In this context, the use of ionic liquids with halogen-free anions may become more and more popular. In 1998, Andersen et al. published a paper describing the use of some phosphonium tosylates (all with melting points >70 °C) in the rhodium-catalyzed hydroformylation of 1-hexene [13]. More recently, in our laboratories, we found that ionic liquids with halogen-free anions and with much lower melting points could be synthesized and used as solvents in transition metal catalysis. [BMIM][n-CgHi7S04] (mp = 35 °C), for example, could be used as catalyst solvent in the rhodium-catalyzed hydroformylation of 1-octene [14]. 

Obviously, the use of a nonvolatile ionic liquid simplifies the distillative workup of volatile products, especially in comparison with the use of low-boiling solvents, where it may save the distillation of the solvent during product isolation. Moreover, common problems related to the formation of azeotropic mixtures of the volatile solvents and the product/by-products formed are avoided by use of a nonvolatile ionic liquid. In the Rh-catalyzed hydroformylation of 3-pentenoic acid methyl ester it was even found that the addition of ionic liquid was able to stabilize the homogeneous catalyst during the thermal stress of product distillation (Figure 5.2-1) [21]. This option may be especially attractive technically, due to the fact that the stabilizing effects could already be observed even with quite small amounts of added ionic liquid. 

As early as 1972 Parshall described the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate melts [1]. [NEt4][SnCl3], the ionic liquid used for these investigations, has a melting point of 78 °C. Recently, platinum-catalyzed hydroformylation in the room-temperature chlorostannate ionic liquid [BMIM]Cl/SnCl2 was studied in the author s group. The hydroformylation of 1-octene was carried out with remarkable n/iso selectivities (Scheme 5.2-13) [66]. 

Moreover, these experiments reveal some unique properties of the chlorostan-nate ionic liquids. In contrast to other known ionic liquids, the chlorostannate system combine a certain Lewis acidity with high compatibility to functional groups. The first resulted, in the hydroformylation of 1-octene, in the activation of (PPli3)2PtCl2 by a Lewis acid-base reaction with the acidic ionic liquid medium. The high compatibility to functional groups was demonstrated by the catalytic reaction in the presence of CO and hydroformylation products. 

Olivier-Bourbigou s group, for example, has recently shown that phosphite ligands can be used in Rh-catalyzed hydroformylation in ionic liquids as well as the well loiown phosphine systems [81]. Since phosphite ligands are usually unstable in aqueous media, this adds (apart from the much better solubility of higher olefins in... 

Another interesting recent development is the continuous, Rh-catalyzed hydroformylation of 1-octene in the unconventional biphasic system [BMIM][PF6]/scC02, described by Cole-Hamilton et al. [84]. This specific example is described in more detail, together with other recent work in ionic liquid/scC02 systems, in Section 5.4. 

In the author s group, much lower-melting benzenesulfonate, tosylate, or octyl-sulfate ionic liquids have recently been obtained in combination with imidazolium ions. These systems have been successfully applied as catalyst media for the biphasic, Rh-catalyzed hydroformylation of 1-octene [14]. The catalyst activities obtained with these systems were in all cases equal to or even higher than those found with the commonly used [BMIM][PF6]. Taking into account the much lower costs of the ionic medium, the better hydrolysis stability, and the wider disposal options relating to, for example, an octylsulfate ionic liquid in comparison to [BMIM][PF6], there is no real reason to center future hydroformylation research around hexafluorophosphate ionic liquids. 

When water-miscible ionic liquids are used as solvents, and when the products are partly or totally soluble in these ionic liquids, the addition of polar solvents, such as water, in a separation step after the reaction can make the ionic liquid more hydrophilic and facilitate the separation of the products from the ionic liquid/water mixture (Table 5.3-2, case e). This concept has been developed by Union Carbide for the hydroformylation of higher alkenes catalyzed by Rh-sulfonated phosphine ligand in the N-methylpyrrolidone (NMP)/water system. Thanks to the presence of NMP, the reaction is performed in one homogeneous phase. After the reaction. 

Certain amines, when linked to TPPTS, form ionic solvents liquid at quite low temperatures. Bahrman [33] used these ionic liquids as both ligands and solvents for the Rh catalyst for the hydroformylation of alkenes. In this otherwise interesting... 

In the rhodium-catalyzed hydroformylation of 1-hexene, it has been demonstrated that there is a correlation between the solubility of 1-hexene in ionic liquids and reaction rates (Figure 5.3-4) [28]. 

Many organic chemical transformations have been carried out in ionic liquids hydrogenation [4, 5], oxidation [6], epoxidation [7], and hydroformylation [8] reactions, for example. In addition to these processes, numerous synthetic routes involve a carbon-carbon (C-C) bond-forming step. As a result, many C-C bondforming procedures have been studied in ambient-temperature ionic liquids. Among those reported are the Friedel-Crafts acylation [9] and allcylation [10] reactions, allylation reactions [11, 12], the Diels-Alder reaction [13], the Heck reaction [14], and the Suzuld [15] and Trost-Tsuji coupling [16] reactions. 

Room temperature ionic liquids (RTILs), such as those based on A,A-dialkylimidazolium ions, are gaining importance (Bradley, 1999). The ionic liquids do not evaporate easily and thus there are no noxious fumes. They are also non-inflammable. Ionic liquids dissolve catalysts that are insoluble in conventional organic chemicals. IFP France has developed these solvents for dimerization, hydrogenation, isomerization, and hydroformylation reactions without conventional solvents. For butene dimerization a commercial process exists. RTILs form biphasic systems with the catalyst in the RTIL phase, which is immiscible with the reactants and products. This system is capable of being extended to a list of organometallic catalysts. Industrial Friedel-Crafts reactions, such as acylations, have been conducted and a fragrance molecule tra.seolide has been produced in 99% yield (Bradley, 1999). 

Hydroformylation of alkenes can be carried out in a few minutes under microwave activation at a relatively low pressure (2.7 bar) employing the rhodium(I)/XANTPHOS catalyst. The presence of the ionic liquid butyl-methylimdazolium tetrafluoroborate ([bmim][BF4]) was crucial. Unfortu-... 

In contrast, we intend to demonstrate the principle aspects of catalyst recycling and regeneration using the ionic liquid methodology. These aspects will be explored in more detail for the example of Rh-catalysed hydroformylation (see Section 7.2). First, however, we will briefly introduce important general facts concerning transition metal catalysis in ionic liquids (see Section 7.1.2). This will be followed by a consideration of liquid-liquid biphasic reactions in these media from an engineering point of view (see Section 7.1.3). 

Liquid-liquid Biphasic, Rh-catalysed Hydroformylation Using Ionic Liquids... 

The first investigations of the rhodium-catalysed hydroformylation in room temperature ionic liquids were published by Chauvin et al. in 1995 [44], The hydroformylation of 1-pentene with the neutral catalysts [Rh(CO)2(acac)]/triarylphosphine was carried out in a biphasic reaction using [BMIM][PF6] as the ionic liquid (see Scheme 7.2). 

Scheme 7.2. First example of Rh-catalysed hydroformylation with room temperature ionic liquid as published...

---