Thermoregulated Phase-separable Catalysis

It has been reported that the rates of hydroformylation decrease in the order 1-hexene 1-octene 1-decene in the classical aqueous/organic two-phase system, whereas the rates are almost identical in the homogeneous organic system [23], Interestingly, in the hydroformylation of a mixture of equimolar 1-hexene and 1-decene in the presence of Rh/1 (N = 25) complex as the catalyst, roughly the same reaction rates at various conversion levels have been observed [19]. This phenomenon further verified the conclusion that the organic phase is the reaction site of TRPTC. 

Critical Solution Temperature (CST) of PETPP in Organic Solvents 

Till now, there have been many studies on the solubility of nonaqueous solutions of ionic surfactants. On the other hand, information on nonionic surfactant solutions is still scarce. Kon-no et al. [27] studied the effect of temperature on the solubility of a-monoglycerol esters of Qi Q7 fatty acids in benzene. Such solubility behavior has also been observed by Matin and Pink [28] for zinc soaps in various organic solvents. The solubility increases slowly as the temperature is raised. Within a narrow temperature range, the solubility begins to increase very rapidly. The temperature at which the abrupt change in the solubility occurs is called the critical solution temperature (CST). 

It is known that in conventional homogeneous catalysis, one usually has to abandon the advantages of phase separation in catalyst recovery and product puri- 

The strategy of TPSC (using nonionic phosphines with the property of CST as ligand to separate, recover and reuse a homogeneous catalyst) was firstly applied in the hydroformylation of higher olefins [30] (Table 3). 

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The opposite temperature-dependent solubility of ligands in organic solvents is applied in the thermoregulated phase-separable catalysis (TRPSC) first published by Jin and coworkers [17] in 2000. The general principle is shown in Fig. 2 [10]. 

Fig. 2 The general concept of thermoregulated phase-separable catalysis (TRPSC)...

Thermoregulated Phase-transfer and Thermoregulated Phase-separable Catalysis... 

Yu, F. Zhang, R. Xie, C. Yu, S. (2010). Polyether-substituted thiazolium ionic liquid catalysts - a thermoregulated phase-separable catalysis system for the Stetter reaction. Green Chem. Vol. 12, No. 7, pp. 1196-1200, ISSN. 1463-9262... 

Thermoregulated phase-transfer and phase-separable catalysis are attractive catalyst recycUng techniques complementing other approaches of multiphase catalysis. They utilize temperature-dependent solubility or miscibiUty phenomena to switch between homogeneous reaction and heterogeneous separation stages. 

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. 

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