Supported Liquid-phase Hydroformylation

Supported Liquid-phase Hydroformylation. - A potentially attractive alternative to chemically anchored hydroformylation catalysts is the use of supported liquid-phase catalyst (SLPC) systems for gas-phase hydroformyl-ations. The homogeneous catalyst is dissolved in a non-volatile solvent and then condensed in the pores of a support, where the strong negative capillary forces effectively immobilize the catalyst, thereby preventing metal loss. In addition one might expect that the environment of the homogeneous system 

studies on the catalyst showed v(CO) bands at 2070, 2002, 1993, and 1947cm . While these do not correspond to any known Rh carbonyl species, the authors suggest that the predominant species contain at least three triphenylphosphine groups. 

The activity of this system is highly dependent on the type of support and pore filling where the surface area of the gas-triphenylphosphine boundary and also the degree of adsorption of Rh onto the surface of the 

A number of phosphines have been investigated as solvents in SLPC systems and the catalytic performance of these are summarized in Table 2. 

A kinetic study has been carried out for the SLPC hydroformylation of propene using [RhH(CO)(PPh3)3] in triphenylphosphine. The reaction orders were 1.0, 1.03, and 0.09 in Rh concentration, p(propylene) and pCHj). For p(CO) the reaction order was pressure dependent and at pressures above 

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Hjortkjaer, J., Scurrell, M.S., and Simonsen, P. (1979) Supported liquid-phase hydroformylation catalysts containing rhodium and triphenylphosphine. J. Mol. Catal., 6 (6), 405 20. 

Table 4.4 Supported ionic liquid phase hydroformylation in ionic liquids...

Figure 4.6 Silica-supported ionic liquid phase hydroformylation...

Adsorption of a high-boiling solvent onto a high-surface-area microporous solid yields a supported liquid phase that can be removed from the sohd only by extraction with a second solvent or by distillation at high temperature under vacuum. Under typical reaction conditions, a solid that contains a supported liquid phase looks and behaves as a solid, yet it can dissolve small quantities of a metal complex into the supported phase. One of the first examples of this arrangement was achieved with the immobilization of Rh(CO)(PPh3)2Cl in benzyl butyl phthalate on silica. The supported complex was successfiilly used to effect the gas-phase hydroformylation of propene. 

The application of zeolite-entrapped rhodium carbonyl clusters [prepared by exchanging Rh(NH3)6Cl3 into NaY zeolite followed by reduction in (CO H2) mixtures] as catalysts for the liquid-phase hydroformylation of alkenes has been discussed. More recently, infrared spectra of Rh6(CO)i6, supported on NaY zeolite by sublimation and treated with carbon monoxide at 100 C, have been found to be virtually identical to those obtained in the hydroformylation experiments. ... 

Hydroformylation of Olefins in Supported Liquid-phase Catalysis... 

Supported liquid-phase catalysis,in which the catalyst is dissolved in a small volume of solvent, adsorbed on, usually, a hydrophilic solid, seeks to resolve issues associated with substrate solubility in multi-phase catalysis and performance/catalyst leaching in supported catalysis reports on the hydroformylation of long-chain alkenes under both supported aqueous phase and supported ionic liquid-phase regimes have been reported. 

L. A. Gerritsen, Hydroformylation with Supported Liquid Phase Rhodium Catalysts , Delft University Press, 1979. 

For instance substitution chlorination of organic compounds produces hydrogen chloride which must simultaneously desorb back in the gas phase to prevent supersaturation of the liquid phase. Another industrially important process involves "supported liquid phase catalyst", where the reactants have to be transferred from a bulk gas to a liquid reaction phase while the products are released back into the gas phase. Here the catalyst is in the form of a melt on a solid support and it finds applications in alkylation, carbonylation, hydroformylation and oxidation of inorganic and organic compounds. The subject matter was recently reviewed delicately by Villadsen and Liv-berg (11,12). Other examples of these interesting systems are shown in Table 6. 

The rhodium pre-catalyst was formed by reacting [Rh(acac)(CO)2] with excess of the appropriate phosphine ligand (10 equiv.) in acetonitrile. This acetonitrile solution was combined with the IL and the modified support Evaporation of the acetonitrile in vacuo resulted in a free-flowing powder. This catalyst was subsequently evaluated in suspension for the liquid phase hydroformylation of 1-hexene [5]. It was observed that the IL, especially [BMIMJfBF ], partially leached into the organic phase, accompanied by rhodium leaching, at high aldehyde concentrations. Most probably, the covalently bound IL remained on the support while the multilayers of additional IL, having cross-solubility with the polar hydroformylation products, were removed from the support [31]. 

Solid-Supported Ionic Liquid Phase Hydroformylation... 

Gerritsen, L.A., Herman, J.M., Klut, W., and Scholten, J.J.F. (1980) Hydroformylation with supported liquid phase rhodimn catalysts. Part II. The location of the catalytic sites. J. Mol. Catal, 9 (2), P 157-168. 

In another interesting area in the study of hydroformylation, Davis developed the concept of supported aqueous phase (SAP) catalysis.175 A thin, aqueous film containing a water-soluble catalyst adheres to silica gel with a high surface area. The reaction occurs at the liquid-liquid interface. Through SAP catalysis, the hydroformylation of very hydrophobic alkenes, such as octene or dicyclopentadiene, is possible with the water-soluble catalyst [HRh(CO)(tppts)3]. 

SLPC or SAPC (supported liquid [or aqueous] phase catalysis [9,10,62,64] see also Section 5.2.5) provide no improvement, probably because of the tremendous stress on the support/transition metal bond during the repeated change between tetrahedral and trigonal-bipyramidal metal carbonyls over the course of a single catalyst cycle. Only recent publications [11,21,26b,28h] report on successful realization of supported homogeneous hydroformylation catalysts, but so far there is no confirmation by practise-soriented tests -not to mention by commercial applications. 

Rhodium Catalysed Hydroformylation Using Supported Ionic Liquid Phase SILP) Catalysis... 

The term Supported Ionic Liquid Phase (SILP) catalysis has recently been introduced into the literature to describe the heterogenisation of a homogeneous catalyst system by confining an ionic liquid solution of catalytically active complexes on a solid support [68], In comparison to the conventional liquid-liquid biphasic catalysis in organic-ionic liquid mixtures, the concept of SILP-catalysis offers very efficient use of the ionic liquid. Figure 7.10 exemplifies the concept for the Rh-catalysed hydroformylation. 

Figure 7.10. Supported ionic liquid phase (SILP) catalysis exemplified for the Rh-catalysed hydroformylation reaction...

The scope of SILP was extended by investigating charged monophosphine ligands, as well as liquid-phase CF hydroformylation. The latter was demonstrated on 1-octene using the SILP Rh-(NORBOS-Cs3)/ [bmim][PF6]/silica catalyst. The authors recognize that the supported catalyst-phihc phase offers the significant advantage of very efficient ionic liquid use. 

SILP hydroformylation catalysts were prepared by dissolving appropriate amounts of Rh(CO)2 (acac) and ligand in dried methanol followed by stirring for 30 min. Afterwards, the ionic liquid was added to the solution. After stirring for another 30 min, the support was added and the solution stirred for 60 min. Finally, the methanol was removed in vacuo and a pale red powder was obtained. The supported ionic liquid-phase catalyst was stored imder argon for further use. 

The first fixed-bed application of a supported ionic liquid-phase catalyst was hydroformylation of propylene, with the reactants concentrated in the gas phase (265). The catalyst was a rhodium-sulfoxantphos complex in two ionic liquids on a silica support. The supported ionic liquid phase catalysts were conveniently prepared by impregnation of a silica gel with Rh(acac)(CO) and ligands in a mixture of methanol and ionic liquids, [BMIMJPFg and [BMIM][h-C8Hi70S03], under an argon atmosphere. 

Industrial problems have, in some instances, been solved either by a proper choice of construction materials and suitable process design or by development of heterogeneous catalytic systems using supported complexes or by generating active complexes in situ on a support material which avoid some of the problems of liquid-phase operation. For example, a number of the problems in liquid-phase vinyl acetate processing have been overcome by development of supported Pd catalysts (106). Vapor-phase hydroformylation has been carried out on supported rhodium complexes (107). 

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