Rh-based hydroformylation

Fluorous-soluble polymer ligands obtained from copolymerization of p-dipenylphos-phinostyrene and (heptadecylfluoro)decyl acrylate are suitable for the preparation of a Rh-based hydroformylation catalyst. ... 

Catalyst development in hydroformylation started with the discovery of the reaction in 1938 and has led to several major new developments during intensive industrial appUcation of the reaction. Thereby, irmovations in catalyst and process technologies went hand-in-hand. The introduction of Rh-based hydroformylation required, for example, much stricter requirements with regard to catalyst separation, recovery, and recycle compared to Co-based technologies due to the much higher price of the catalytic metal (by about a factor of 1000). 

From 1974 onwards, Rh-based hydroformylation became industrial. The use of a catalyst metal that is about 1000-times more expensive than cobalt was driven by several reasons. First, Rh-hydroformylation is more active and thus requires much lower process pressures (lower energy consumption in compression units) and smaller reactors. Second, Rh-hydroformylation shows a very high selectivity to the aldehyde product with only minimal hydrogenation activity being observed. This is of particular importance for propylene hydroformylation where butyl alcohol is not the principle market use. In contrast, for the desired end-use of w-butyraldehyde in the form of its aldol condensation product 2-ethylhexanol a pure aldehyde feed is required as hemiacetals (formed by reaction of aldehyde and alcohol) complicate product purification and add to operating costs. 

Figure 5.6 Catalytic cycle for Rh-based hydroformylation reaction.

Rh-based hydroformylation reactions, where oidy CO is present as the ligand, have also been studied. In such a situation, a rhodium carbonyl cluster such as Rh CCO), may be used as the precatalyst. Under catalytic conditions, most of the cluster is converted to HRh(CO), and the general mechanism discussed earlier operates. Similarly, other Rh-containing precursors, such as Rh(CO)2(acac), under CO and pressure are also converted to HRh(CO). ... 

Rhodium is an expensive metal, and the commercial viability of the Rh-based hydroformylation process depends on the efficiency of the catalyst recovery process. In the past, this has been achieved either by a complicated recycle process or, more commonly, by energy-requiring distillation. A major advancement in the Rh-based hydroformylation process was the introduction of TPPTS (see structure 5.19) as the ligand. 

The adoption of a second liquid phase has also proved useful in the hydroformylation reaction of propylene for which Ruhrchemie and Rhone-Poulenc have used Rh based water... 

Ligand (136), an analog of PPh3 with amphiphilic character, was used for making [Rh(CO) (136)(acac)]. The rhodium-based hydroformylation of 1-hexene using catalysts formed in situ... 

Rh, are the base of active catalysts for CO hydrogenation and the hydroformylation of olefins. The presence of several promoters modifies their catalytic behavior and synergic effects on the base-metal have been observed Table 8.5 illustrates several examples in which homonuclear or heteronuclear carbonyl compounds have been used in the preparation of Co- or Co-Rh-based catalysts for the CO hydrogenation and/or hydroformylation reactions. 

Following the recommendations of Manassen [18] the history of biphasic hydroformylation began with work on various water-soluble ligands (Table 1). After this preparatory work on various aspects [30], Kuntz [22, 199] expressed the basic idea of a new generation of water-soluble oxo catalysts with triphenyl-phosphine trisulfonate (TPPT S, as the Na salt, as compared with TPPMS and TPPDS, the mono- and disulfonate) as ligands for a Rh-based oxo process, mainly for the hydroformylation of lower olefins such as propene (eq. (5)). 

Research in hydroformylation has also been driven towards a catalyst that may be immobilized on a surface, without losing activity, but is as active as an homogeneous counterpart. Deloxan rhodium (HK I 2 % (Rh))-based catalysts may be used for these reactions. 

The Rh/PPhs hydroformylation catalyst system was developed approximately simultaneously by Geoffrey Wilkinson (and students),Union Carbide, BASF, and Celanese. This catalyst system has been extensively studied, and the key species is HRh(CO)(PPh3)2. Once again the core mechanism is the same as that discussed previously for the cobalt systems and shown in Figure 12. Rhodium catalysts are approximately 1,000 times faster than ones based on cobalt (Rh is also about 1,000 times more expensive). Thus, rhodium catalysts can be run at considerably milder pressures and temperatures (8-10 bar, 125 °C), which dramatically reduces the capital expenditures for industrial plant construction. The increased activity of Rh over Co mainly derives from the stronger electronic preference of... 

It is generally agreed that Roelen s discovery of the hydroformylation reactiont was the birth of the transition metal-catalyzed carbonylation. Initially, Co catalysts were most extensively used, but the Rh-based processes have since been developed as a superior methods. Although Pd may have been tested along with several other metals, such as Fe, Ru, and Ni, it has never been shown to be very useful in the hydroformylation reaction, sometimes called the oxo process. A publication in 1963 by Tsuji et al. on a related but clearly different reaction of alkenes with CO and alcohols in the presence of a Pd catalyst producing esters was one of the earliesL if not the earliesL reports describing a successful and potentially useful Pd-catalyzed carbonylation reaction. This was soon followed by the discovery of another Pd-catalyzed carbonylation reaction of allylic electrophiles with CO and alcohols ° (Scheme 7). 

Proposed mechanism for hydroformylation using a Rh-based catalyst. 

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