TRPTC

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

Based on the inversely temperature-dependent solubility of phosphines modified with polyoxyethylene chains, TRPTC has been proposed, and applied to the aqueous/organic two-phase reaction system [11], The general principle of TRPTC is depicted in Figure 1. 

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-... 

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. 

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). 

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. 

TRPTC system based on the Cp of TRLs has been proposed [13]. The general principle of TRPTC is depicted in Figure 2. The TRPTC process can be described as follows at a temperature lower than the cloud point, the catalyst is soluble in the aqueous phase. On heating to a temjjerature higher than the cloud point, however, the catalyst transfers from the aqueous phase into the organic phase. Thus, the catalyst and the substrate are in the same phase and the reaction proceeds in the... 

TRPTC has already been applied successfully in the hydroformylation of higher olefins and the CO selective reduction of nitroarenes, both on a laboratory scale. 

Indeed, high activity was obtained in the biphasic hydroformylation of higher olefins in the presence of Rh/PETPP complexes as catalysts, which demonstrated that the water solubility of the substrate did not influence the effectiveness of the TRPTC system. Some TRPT catalysts such as PETPPs 17, P-N bidentate (PEDPA... 

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