Aqueous two phase hydroformylation

In aqueous two-phase hydroformylation of 1-octene and 1-dodecene the amphiphilic ligands of type 25 (n = 10, 12) have been shown to form Rh catalysts that are superior to Rh/TPPTS systems [129]. The bicyclic ligands 26 were considered to be of interest as substitutes for TPPMS in the new oxo process developed by Union Carbide for the hydroformylation of higher olefins using N-methylpyrroli-done or polyalkylene glycols as solvents [7, 51, 52], Rh(I) complexes [Rh(26)2]+ [96] showed, however, a very poor performance as catalysts in biphasic systems for hydrogenation and hydroformylations in contrast to non-functionalized 1-phospha-norbornadiene [98], This was explained by formation of P,P(0) chelates blocking... 

The most severe dra wback in homogeneous catalysis is the separation of the catalyst from the reaction mixture. The industrial success of the aqueous two-phase hydroformylation ofpropene to n-butanal [1] in Ruhrchemie AG in 1984 represents the considerable progress in this field. However, aqueous/organic biphasic catalysis has its limitations when the water solubility of the starting materials proves too low, as in hydroformylation of higher olefins (see Chapter 1). To solve this issue, a variety of approaches have been attempted. Additions of co-solvents [2] or surfactants [3, 4] to the system or application of tenside ligands [5, 6] and amphiphilic phosphines [7, 8] are ways to increase the reaction rates. Other approaches such as fluorous biphase system (FBS see Chapter 4) [9], supported aqueous phase catalysis (SAPC see Section 2.6) [10], supercritical CO2 (cf. Chapter 6) [11] and ionic liquids (cf Chapter 5) [12] have also been introduced to deal with this problem. 

We vrill describe the basics of aqueous two-phase hydroformylation with TPPTS and rhodium complexes thereof [1] as they apply to C3 and C4 olefins according to the Ruhrchemie/Rhone-Poulenc process. Emphasis will be put on the commercial applications and the basic description of the processes. 

An aqueous two-phase hydroformylation went on stream at Ruhrchemie AG in 1984 (fourth generation) at their site in Oberhausen/Germany with an annual capacity of 100 kt/a [1]. The current capacity is 500kt/a. The Rh catalyst is immobilized in the aqueous phase. A sulfonated phosphine ligand (TPPTS, trisodium salt of 3,3, 3 Lphosphinidynetris(benzenesulfonic acid) confers the metal catalyst with high solubility in water. The catalyst is removed into the aqueous phase before distillation of the product, which avoids thermal stress. The loss of rhodium is in the range of parts per billion. 

Scheme 2.27 Methods for sulfonation of aryl phosphines and a selection of sul-fonated aryl mono- and diphosphines tested for rhodium-catalyzed aqueous two-phase hydroformylation.

Unfortunately, to date only TPPTS is available in quantities useful for scale-up purposes, which may be explained by the rather unpleasant synthetic protocol required. The hydroformylation with TPPTS is the only aqueous two-phase hydroformylation used in industry to date [98]. Up to now, the use of BINAS and related sulfonated diphosphines is limited to academic hydroformylation studies [85, 99,100]. 

A Rh(TPPTS) catalyst generated by this protocol may form with TPPTSO a colloidal dispersion, which has to be considered in the interpretation of the catalysis results [167]. The oxidation of TPPTS is slower than that of PPhj, which accounts for the aqueous two-phase hydroformylation protocol. 

A remarkable stabilizing effect of rhodium on the hydrolysis rate of a cage monophosphite derived from sulfonated calix[4]arene was observed by Cobley and Pringle [175]. The phosphite has a life in water of only 5 h. However, coordination to Rh enhanced its stability toward hydrolysis to 4 months. Consequently, it survived even the conditions of an aqueous two-phase hydroformylation. 

Aqueous two-phase hydroformylation of methyl oleate and a technical linseed oil was conducted by anchoring the Rh(TPPTS) catalyst either on silica [2] or on activated carbon (Nuchar WV-B) [47]. Especially, the latter proved highly efficient as a mass transfer promoter. 

There are several methods to enhance the reaction rate and selectivity of the aqueous two-phase hydroformylation of higher olefins [14]. Besides classical measures, such as proper adjustment of catalyst concentration, metal/ligand ratio. 

Scheme 7.5 Aqueous two-phase hydroformylation with a water-soluble rhodium catalyst and an additional promoter ligand.

Cationic phosphine ligands containing guanidiniumphenyl moieties were originally developed in order to make use of their pronounced solubility in water [72, 73]. They were shown to form active catalytic systems in Pd-mediated C-C coupling reactions between aryl iodides and alkynes (Castro-Stephens-Sonogashira reaction) [72, 74] and Rh-catalyzed hydroformylation of olefins in aqueous two-phase systems [75]. 

Taking all criteria into consideration, aqueous two-phase techniques are very sound methods for homogeneously catalyzed processes such as hydrogenations or hydroformylations. Of the various alternatives to the conventional (and solvent-free) processes most progress in terms of ecological impact and economics has been attained by the aqueous biphasic approach (Figure 5.20). 

Aqueous two-phase hydrogenation may be a method of choice for synthetic purposes when no incompatibility problems between water and the substrates, products, or catalyst arise. It has already been proven by the success of the Ruhrchemie-Rhone-Poulenc hydroformylation process, that the catalyst can be retained in the aqueous phase with very high efficiency, and that aqueous-organic biphasic processes using organometallic catalysts are suitable for indus-... 

The history of aqueous industrial two-phase catalysis began in 1984 when the hydroformylation of propene in water was first carried out in the plants of Ruhrchemie AG. The development of the aqueous two-phase process was completely atypical in that the initial research work was done by Rhone-Poulenc but the development work was done by the former Ruhrchemie (today part of Hoechst AG). A rather long time elapsed before further fundamental work was begun in academic laboratories. 

On the industrial level, aqueous two-phase systems are used more often than nonaqueous two-phase systems. The Kuraray Co. operates a pilot plant for the hydrodimerization of 1,3-butadiene in a two-phase system with a Pd/tppms catalyst (140). The reaction is carried out in sulfolane-water, from which the products, the octadienols, separate. The final products can be octanol or nonanediol made by subsequent isomerization and hydroformylation. The capacity of the Kuraray process is about 5000 tons/year. 

Aqueous, two-phase catalysis is also utilized industrially in several other processes apart from hydroformylation. The hydrodimerization of butadiene and water, a... 

As noted above, the addition of alcohols improves the reaction activity in the two-phase hydroformylation of higher olefins with Rh/TPPTS catalysts. Reaction selectivity, however, is diminished if the operating conditions are otherwise similar. This is illustrated in Figure 1, which compares the conversion and selectivity of 1-octene hydroformylation over the (acac)Rh(CO)2/TPPTS catalyst in water alone and 50% aqueous methanol as the solvent [10, 11], Selectivity can be improved in the aqueous methanol system when ligands other than TPPTS are used, as for example with ionic phosphites of the type 1 cited above. These ligands differ significantly from TPPTS in that they are expected to be amphiphilic in character the ionic portion is hydrophilic while the rest of the ligand is relatively hydrophobic. 

The concept of TRPTC provides a reasonable explanation for the satisfactory catalytic reactivity of Rh/nonionic phosphine complexes in the case of the two-phase hydroformylation of higher olefins. At a temperature lower than the cloud point, a nonionic phosphine-modified rhodium catalyst would remain in the aqueous phase since the partition of the catalyst between water and a nonpolar aprotic organic solvent strongly favors the aqueous phase. On heating to a temperature higher than the cloud point, however, the catalyst loses its hydrate shell, transfers into the organic phase and then catalyzes the transformation of alkenes to aide-... 

There have been many approaches to overcome the problem of low space-time yields in biphasic reaction systems with rhodium and other metals, such as the Ruhrchemie/Rhone-Poulenc process. Concerning two-phase hydroformylation of higher alkenes in an aqueous-organic reaction system, the different approaches can be categorized as follows ... 

Non-aqueous approaches toward two-phase hydroformylation have been demonstrated by Horvath et al. [16] with the use of a fluorous biphasic system containing a rhodium catalyst bearing partially fluorinated ponytail ligands, and Olivier and Chauvin [17] with TPPMS and TPPTS dissolved in nonaqueous ionic liquids (see Sections 7.2 and 7.3). 

In this section, we will report on investigations in the two-phase hydroformylation of higher alkenes with aqueous Rh-TPPTS catalyst systems. The overview on the present state of the art in two-phase hydroformylation will be confined to those investigations which are not covered by the respective original authors in this book. 

New and efficient routes to modify phosphines with phosphonic acid groups have been developed. Phosphonate-phosphines showed high solubilities in water and were used to immobilize rhodium catalysts in the aqueous phase of biphasic systems. In the two-phase hydroformylation of propene, some of the novel catalysts showed activities and regioselectivities similar to those of Rh/TPPTS. Amphiphilic Rh/phosphonate-phosphine catalysts were found widely superior to Rh/TPPTS in the hydroformylation of 1-octene (see Section 3.2.1) [67]. 

It was not until the work at Ruhrchemie AG (and thus the occupation of a skilled and experienced team in industry) that development led to the first large-scale utilization of the aqueous, homogeneous catalysis technique at the beginning of the 1980s, viz. in hydroformylation (the oxo process) [11]. The generally used embodiment of two-phase catalysis, for example as practised in Shell s SHOP method [12], was thus extended to aqueous two-phase catalysis. These (and the other industrial applications see Chapter 6) have led to the literature concerning these particularly attractive aqueous variants being dominated by publications from industry, particularly patent literature, rather than from academia, for virtually a decade. 

Aqueous, two-phase catalysis is also utilized industrially in a number of other processes apart from hydroformylation. The hydrodimerization of butadiene and water, a telomerization variant yielding 1-octanol or 1,9-nonanediol (cf. Section 6.9), is carried out at a capacity of 5000 tonnes per annum by the Kuraray Corporation in Japan. Rhone-Poulenc is operating two-phase, aqueous, catalytic C—C coupling processes (using TPPTS obtained from Ruhrchemie) for small-scale production of various vitamin precursors such as geranylacetones. Moreover, TPPTS-modified Ru catalysts have been proposed for the homogeneously catalyzed hydrogenation to convert unsaturated ketones into saturated ones. 

One focus of the book is the hydroformylation process, the process involved in the first commercial implementation of aqueous-phase catalysis with its detailed descriptions of fundamental laws, special process features, and the present state of the art. Further focal points of the book are basic research on the complex catalysts (central atoms, ligands) and on the influence of the reaction conditions, solvents, and co-solvents, and a survey of other aqueous two-phase concepts and of proposed applications, with experimental examples and details. Environmental aspects are also considered. 

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