Hydroformylations aqueous biphasic system

A wide variety of new approaches to the problem of product separation in homogeneous catalysis has been discussed in the preceding chapters. Few of the new approaches has so far been commercialised, with the exceptions of a the use of aqueous biphasic systems for propene hydroformylation (Chapter 5) and the use of a phosphonium based ionic liquid for the Lewis acid catalysed isomerisation of butadiene monoxide to dihydrofuran (see Equation 9.1). This process has been operated by Eastman for the last 8 years without any loss or replenishment of ionic liquid [1], It has the advantage that the product is sufficiently volatile to be distilled from the reactor at the reaction temperature so the process can be run continuously with built in product catalyst separation. Production of lower volatility products by such a process would be more problematic. A side reaction leads to the conversion of butadiene oxide to high molecular weight oligomers. The ionic liquid has been designed to facilitate their separation from the catalyst (see Section 9.7)... 

As outlined in Chapter 5, Section 5.2.3.2 various approaches to overcoming the low rates of the hydroformylation of long chain alkenes in aqueous biphasic systems have been proposed. Some of these, such as the use of microemulsions [24-26] or pH dependent solubility [27], have provided improvements often at the expense of complicating the separation process. Perhaps the most promising new approaches involve the introduction of new reactor designs where improved mixing allows for... 

For the rhodium-catalyzed hydroformylation of propylene in an aqueous biphasic system. Cents et al. have shown that the accurate knowledge of the mass transfer parameters in the gas-liquid-liquid system is necessary to predict and optimize the production rate [180]. Choudhari et al. enhanced the reaction rate by a factor of 10-50 by using promoter Ugands for the hydroformylation of 1-octene in a biphasic aqueous system [175]. 

The OATS concept was tested on the catalytic hydroformylation of 1-octene, a hydrophobic substrate. This reaction was selected because it has previously been shown to be inactive for traditional aqueous biphasic systems (18). The catalyst used was a Rh/TPPTS complex, an industrial water soluble catalyst (22). The application of the OATS concept increased catalytic efficiency by a factor of 65 (TOP increased from 5 h for biphasic to 325 h for monophasic). 

A major improvement in both catalytic activity and selectivity of propene hydroformylation in the organic-aqueous biphasic system was achieved by using the newly synthesized BINAS-Na ligand 10 in combination with rhodium(III) acetate (65). 

The latest development in industrial alkene hydroformylation is the introduction by Rurhchemie of water-soluble sulfonated triphenylphosphine ligands.94 Hydroformylation is carried out in an aqueous biphasic system in the presence of Rh(I) and the trisodium salt of tris(m-sulfophenyl)phosphine (TPPTN). High butyraldehyde selectivity (95%) and simple product separation make this process more economical than previous technologies. 

An example of a large scale application of this concept is the Ruhrchemie/ Rhone Poulenc process for the hydroformylation of propylene to n-butanal, which employs a water-soluble rhodium(I) complex of trisulfonated triphenyl-phosphine (tppts) as the catalyst [103]. The same complex also functions as the catalyst in the Rhone Poulenc process for the manufacture of the vitamin A intermediate, geranylacetone, via reaction of myrcene with methyl acetoacetate in an aqueous biphasic system (Fig. 1.35) [104]. 

Kuntz subsequently showed that the RhCl (tppts) 3 catalyzed the hydroformylation of propylene in an aqueous biphasic system [29]. These results were further developed, in collaboration with Ruhrchemie, to become what is known as the Ruhrchemie/Rhone-Poulenc two-phase process for the hydroformylation of propylene to n-butanal [18, 19, 22, 30]. Ruhrchemie developed a method for the large scale production of tppts by sulfonation of triphenylphosphine with 30% oleum at 20 °C for 24 h. The product is obtained in 95% purity by dilution with water, extraction with a water insoluble amine, such as tri(isooctylamine), and pH-controlled re-extraction of the sodium salt of tppts into water with a 5% aqueous solution of NaOH. The first commercial plant came on stream in 1984, with a capacity of 100000 tons per annum of butanal. Today the capacity is ca. 400000 tpa and a cumulative production of millions of tons. Typical reaction conditions are T=120°C, P=50bar, CO/H2 = 1.01, tppts/Rh = 50-100, [Rh] = 10-1000 ppm. The RhH(CO) (tppts)3 catalyst is prepared in situ from e.g. rhodium 2-ethylhexanoate and tppts in water. 

What about when the substrate and product are water soluble The problem of catalyst recovery in this case can be solved by employing inverse aqueous bi-phasic catalysis. An example is the hydroformylation of N-allylacetamide in an aqueous biphasic system in which the catalyst is dissolved in the organic phase and the substrate and product remain in the water phase. This formed the basis for an elegant synthesis of the natural product, melatonin, in which the aqueous solution of the hydroformylation product was used in the next step without work-up (Fig. 7.6) [32]. 

Hydroformylation and Carbonylation Reactions in Aqueous Biphasic Systems... 

For example, 1-octene can be hydroformylated in the interfacial organic/ water region with a considerably enhanced rate compared to the classic biphasic hydroformylation. This approach involves the use of both TPPTS and triphenylphosphine. Interaction of triphenylphosphine and the TPPTS-based catalyst takes place at the liquid-liquid interface (Scheme 1.21). A new catalytic species containing two TPPTS and one triphenylphosphine ligand is formed in the liquid/liquid boundary layer, where it can access the reactants present in the organic phase in significantly higher concentrations with respect to the aqueous phase. This new version of the hydroformylation reaction in aqueous biphasic systems resulted in a 10-50-fold increase in overall reaction rate. ... 

Hydroformylation is one of the mildest and most efficient methods of producing aldehydes and hence it has a wide range of applications in the petrochemical industry. The cleanest, industrially important hydroformylation process is the aqueous biphasic system developed by Ruhrchemie/Rhone-Poulenc [63]. However, the applicability of this system is limited to substrates which have a low solubility in water, such as propene and 1-butene. It is advantageous to use scC02 because there is no gas-liquid phase boundary and because of the ability of scC02 to dissolve gases in high concentrations, combined with effective product and catalyst separation [64]. 

Rhodium complexes modified with polyether phosphine oxides according to the Structure 30 were used as catalysts for the hydroformylation of 1-decene and oleyl alcohol in micellar aqueous-biphase systems [56, 57]. 

Additional data on hydroformylation of 1-pentene, 1-octene and ethyl acrylate are provided in Table 1. In all the runs, the solutions became clear and yellow after a period of 10 minutes, which indicated the formation of the microemulsion with the catalyst formed in situ inside the water droplets. The solutions were clear and homogeneous during the entire run, which definitely excludes reaction via a biphasic pathway. Because of equipment limitations, the highest reaction temperature we investigated was 87.1 C. The stability of the W/CO2 microemulsion system at such a high temperature is remarkable. At the conditions employed, conversions ranged from 6 to 75%. The increase of temperature and the addition of NaOH were found to increase the reaction rate. The initial reaction rate for 1-pentene is about two times higher than that of 1-octene. In studies on hydroformylation of different olefins in aqueous biphasic systems, Brady et al. [2/] found that there is a marked dependence of the reaction rate on the solubility of the terminal olefins in water. The data shown in... 

The separation of catalysts and products in a liquid/liquid biphasic system is a scheme that has the advantage of demonstrated practicality. Aqueous biphasic catalysis is used in hydroformylation and biphasic separations are important parts of several other commercialized processes [86,142,143]. Recent reports using low molecular weight catalysts in aqueous biphasic systems, in fluorous systems, and in ionic liquids are indicative of the growing interest in this general area - chemistry that has been summarized in a number of recent reviews [8,144-150]. 

Rhodium(I) and cobalt(O) complexes of AMPHOS, [(nbd)Rh(AMPHOS)2] , and [Co(CO)3(AMPHOS)]2(PF6)2, were already being used in the early 1980s for the hydrogenation and hydroformylation of maleic and crotonic acid or styrene and 1-hexene in water or aqueous biphasic systems [49]. The lower effectiveness of the Co catalyst was attributed to the lighter metals proclivity to oxidation and phosphine... 

Biphasic hydroformylation is a typical and complicated gas-liquid-liquid reaction. Although extensive studies on catalysts, ligands, and catalytic product distributions have appeared, the reaction mechanism has not been understood sufficiently and even contradictory concepts of the site of hydroformylation reaction were developed [11, 13, 20]. Studies on the kinetics of hydroformylation of olefins are not only instructive for improvement of the catalytic complexes and ligands but also provide the basic information for design and scale-up of novel commercial reactors. The kinetics of hydroformylation of different olefins, such as ethylene, propylene, 1-hexene, 1-octene, and 1-dodecene, using homogeneous or supported catalysts has been reported in the literature. However, the results on the kinetics of hydroformylation in aqueous biphasic systems are rather limited and up to now no universally accepted intrinsic biphasic kinetic model has been derived, because of the unelucidated reaction mechanism and complicated effects of multiphase mass transfer (see also Section 2.4.1.1.2). 

Hydroformylation of ethylene using a water-soluble Rh-TPPTS catalyst has been investigated [27] using a toluene-water solvent system at 353 K. The effect ofTPPTS concentration on rate shows a maximum at a P/ Rh ratio of 8 1. The rate of reaction first increases with catalyst concentration, and above a certain value it remains constant. The effect of aqueous-phase hold-up shows a maximum in the rate at = 0.4. The apparent reaction orders for the partial pressures of hydrogen and ethylene were found to be one and zero respectively. A strong inhibition in the rate with an increase in Pqq was observed. An interesting example of tandem synthesis of methacrolein in an aqueous biphasic system has been reported by Deshpande et al. [28], in which hydroformylation of ethylene and aldol condensahon reactions occur in two immiscible liquid phases with a high yield of the product Use of a two-phase system prevents contact of the hydroformylation and aldol catalysts, the interaction of which leads to deactivation. 

Several ligands were screened for the liquid-liquid bip basic hydroformylation with ionic liquids. Some of them were particularly constructed for the reaction in these solvents by the modification of known structures. Others were derived from the hydroformylation in aqueous biphasic systems (TPPTS, TPPMS, Sulfoxantphos) [100]. Common phosphorus ligands (e.g., PPhj) may result in a significant leaching of the rhodium catalyst into the product phase. Steinriick and... 

The rhodium/TPPTS-catalyzed hydroformylation of 1-octene and other higher olefins in an aqueous biphasic system was studied at pressures from 40 to 90 bar and temperatures of up to 120 °C. Nonionic amphiphiles of the alkoxyethylene type were applied to promote the contact between the reacting species by enlargement of the interfacial area. The highest reaction rates were obtained at a surfactant concentration of about 1 wt% [109]. 

The rhodium/TPPTS-catalyzed hydroformylation of higher olefins in organic/ aqueous biphasic system in the presence of double long-chain cationic surfactants (37) was studied at 100 °C and 20 bar CO H2 = 1 1 pressure. The reaction rate was comparable with that in homogeneous catalysis system [111]. 

The rhodium-based process for propylene hydroformylation is distinctly superior. Here the regioselectivity is high (-95%), and the reaction conditions are less severe (-50 bar, 120°C). An additional and significant advantage of the modern Rh-based process is that, by using a water-soluble phosphine in an aqueous biphasic system, the catalyst can be easily separated from the product. 

Internal olefins could be converted into linear aldehydes if a suitable catalyst is in hand. BeUer and Krauter [26] reported that Co-1 catalyzed hydroformylation of 2-pentene in an aqueous biphasic medium, furnishing the desired aldehydes in good yields with an njiso ratio up to 70 30 at an elevated temperature and pressure. The same group also demonstrated the hydroformylation of internal olefins catalyzed by Rh-2 in an aqueous biphasic system, which afforded the aldehydes with significantly higher regioselectivities (n/iso>99 1), compared to similar catalysts in organic solvents [27]. The control of pH and CO partial pressure was shown to be important for a successful reaction in this case. 

Nevertheless, few examples of successful catalysts showing acceptable results for the hydroformylation of internal olefins in the biphasic catalytic systems have been reported to date. This is due to many causes. First, the suUbnation of ligands could be a difficulty. Moreover, the high temperature is a positive factor for the isomerization reaction of internal olefins but may be a cause for the rhodium loss and leaching into the organic phase in the biphasic hydroformylation. Seller and Krauter studied the hydroformylation of 2-pentene in an aqueous biphasic system with a Co/TPPTS catalyst in 1999. A linear to branched ratio (n/i) of up to 75 25 was obtained at 100 °C and 100 bar CO/Hj [83]. The catalyst was reused up to four times without loss of activity. Inspirationally, they reported for the first time... 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

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