Thermoregulated Phase Transfer Catalysis

2 Thermoregulated Phase Transfer Catalysis - A conceptual advance in the field of biphasic hydroformylation of higher olefins is the use of rhodium catalysts generated from nonionic tenside phosphines, such as ethoxylated tris(4- 

Other examples of the application of this concept in the hydroformylation of 

Virtually quantitative conversions were observed in the hydroformylation of 1-tetradecene with rhodium complexes generated from the lithium salt of tppms or the lithium (sodium) salts of 21 (Table 2 R=Ph n=3,4) and 22 (Table 2) in methanol as solvent.127,334 Catalyst recycling involved evaporation of methanol and addition of water to form a two phase system, separation of the aqueous phase, evaporation to dryness and addition of MeOH. 

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. 

Recently, a new aqueous biphasic catalytic system based on the cloud point of nonionic tensioactive phosphine, termed thermoregulated phase-transfer catalysis (TRPTC) has been developed [13]. The concept ofTRPTC as a missing link could not only provide a meaningful solution to the problem of catalyst/product separation, but also extricate itself from the limitation of low reaction rates of water-immiscible substrates. 

Thermoregulated Ligands and Thermoregulated Phase-Transfer Catalysis 

Applications oT Thermor ulated Phase-Transfer Catalysis 

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Jin Z, Zheng X (1996) Thermoregulated Phase-transfer Catalysis. In CornUs B, Hermann WA (eds) Aqueous-Phase Organometallic Catalysis, Chap. 4, Sect. 6.3. Wiley, Weinheim, p 233... 

Fig.1 The general concept of thermoregulated phase-transfer catalysis (TRPTC)...

Thermoregulated Phase-transfer Catalysis with Nonionic Water-soluble Phosphines... 

Thermoregulated phase-transfer catalysis, however, could be successfully put into effect for the hydroformylation of higher olefins in aqueous/organic two-phase media [11], As shown in Table 2, various olefins have been converted to the corresponding aldehydes in the presence of nonionic phosphine-modified rhodium complexes as catalysts. An average turnover frequency (TOF) of 250 h-1 for 1-do-decene and 470 Ir1 for styrene have been achieved. Even the hydroformylation of oleyl alcohol, an extremely hydrophobic internal olefin, would give a yield of 72% aldehyde [19]. In comparison, no reaction occurred if Rh/TPPTS complex was used as the catalyst under the same conditions. 

The principle of thermoregulated phase-transfer catalysis (TRPTC), originally developed by Bergbreiter et al. [12], which has been applied to two-phase hydro-formylation by Fell, Jin and co-workers [13], which is based on a temperature-controlled switch of the catalyst system from the aqueous phase to the organic phase (see Section 4.6.3). 

Two novel methodologies termed assymmetric phase transfer catalysis and thermoregulated phase transfer catalysis have been developed readily in the past decade and have broadened greatly the scope of application of PTC. Therefore, it is worthwhile briefly discussing these two techniques. 

FIG. 8 Thermoregulated phase transfer catalysis hydroformylation of higher olefins (Cg-C ). 

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