Rhodium-catalyzed biphasic hydroformylation

Rhodium-catalyzed biphasic hydroformylation of olefins. The Ruhrchemie-Rhone Poulenc process for manufacturing... 

Shirakawa S, Shimizu S, Sasaki Y. Rhodium-catalyzed biphasic hydroformylation of 4-oc-tene using water-soluble calix[4]arene-phosphine ligands. New J Chem 2001 25(6) 777-9. 

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]. 

In 1975 Kuntz has described that the complexes formed from various rhodium-containing precursors and the sulfonated phosphines, TPPDS (2) or TPPTS (3) were active catalysts of hydroformylafion of propene and 1-hexene [15,33] in aqueous/organic biphasic systems with virtually complete retention of rhodium in the aqueous phase. The development of this fundamental discovery into a large scale industrial operation, known these days as the Ruhrchemie-Rhone Poulenc (RCH-RP) process for hydroformylation of propene, demanded intensive research efforts [21,28]. Tire final result of these is characterized by the data in Table 4.2 in comparison with cobalt- or rhodium-catalyzed processes taking place in homogeneous organic phases. 

The first investigations of rhodium-catalyzed hydroformylation in room-temperature Hquid molten salts were published by Chauvin et al. in 1995 [6, 67]. The hydroformylation of 1-pentene with the neutral Rh(CO)2(acac)/triarylphosphine catalyst system was carried out as a biphasic reaction with [BMIM][Pp6] as the ionic liquid. 

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. 

Interfacial kinetics of biphasic hydroformylation of 1-dodecene catalyzed by water-soluble rhodium complex have been studied by a combined numerical and experimental approach [54]. 

Two new phosphines, tris[p-(10-phenyldecyl)phenyl]phosphine and 2,2 -bis di [p-(10-phenyldecyl)phenylphosphinomethyl]-l,T-biphenyl were successfully synthesized and sulfonated in H2S04. The resulting water soluble surface active phosphines were applied to the rhodium catalyzed hydroformylation of higher alkenes. It is found that these two ligands are not only excellent for octene hydroformylation, but catalyze tetradecene hydroformylation under biphasic conditions as well. Rates and selectivities are superior to TPPTS-modified rhodium catalysts under the same reaction conditions [68]. 

Table 4.6. Rhodium-catalyzed hydroformylation in aqueous-organic biphasic media with polymeric phosphine ligands ...

The thermal instability of rhodium-based hydroformylation catalysts has already been overcome commercially in the Ruhrchemie/Rhone-Poulenc process for propene hydroformylation in which the sodium salt of a sulfonated triphe-nylphosphine ligand (TPPTS, la) is used to solubilize the catalyst in the aqueous phase. In this process, the second phase is toluene and the reaction is carried out as a batch process with rapid stirring to intimately mix the two immiscible phases. After reaction, the system is allowed to separate and the organic phase is simply decanted from the aqueous catalyst phase. Both water-soluble polymers and PAMAM dendrimers have been reported as supports for rhodium-catalyzed hydroformylation under aqueous biphase conditions, but reactivities and regioselec-tivities were only comparable to or worse than those obtained with the reference TPPTS ligand. The aqueous biphase approach has found limited application for the hydroformylation of longer-chain alkenes, because of their very low solubility in water leading to prohibitively slow reaction rates, but there have been a variety of approaches directed at the solution of this problem. 

Finally, water-soluble phosphorylated BlNAPs were tested as ligands in aqueous biphasic rhodium-catalyzed hydroformylation of vinyl acetate. Compared with catalysts prepared with the parent ligand in a homogeneous medium, the chemo-, regio- and enantioselectivities were markedly lower [24]. 

When using a solvent in catalysis it is important to understand its mixing behavior with potential solutes or other solvents that may be used with it in biphasic reaction systems. For example, it has been shown that the rate (TOF) of the rhodium-catalyzed hydroformylation of 1-hexene in a range of ILs is generally well correlated with the solubility of the 1-hexene [22]. If, as in this example, a particular material is of great interest, its miscibility with the solvent should be studied in detail. However, it is also useful to be able to gain some capacity to predict how a wide range of different materials will interact with the solvent. Both approaches have been used with ILs. 

Epoxidation of oleic and linoleic acid was readily achieved by treatment with the acetonitrile complex of hypofluorous acid (55). Phase-transfer-catalyzed biphasic epoxidation of unsaturated triglycerides was accomplished with ethylmethyldioxirane in 2-butanone (56). The enantioselective formation of an a,P-epoxy alcohol by reaction of methyl 13()S)-hydroperoxy-18 2(9Z,llfi) with titanium isopropoxide has been reported (57). An immobilized form of Candida antartica on acrylic resin (Novozyme 435) was used to catalyze the perhydrolysis and the interesterification of esters. Unsaturated alcohols were converted with an ester in the presence of hydrogen peroxide to esters of epoxidized alcohols (e.g., epoxystearylbutyrate) directly (58). Homoallyl ethers were obtained from olefinic fatty esters by the ethylaluminium-in-duced reactions with dimethyl acetals of formaldehyde, acetaldehyde, isobutyralde-hyde, and pivaldehyde (59). Reaction of 18 2(9Z, 12Z) with 50% BF3-methanol gave monomethoxy and dimethoxy derivatives (60). A bulky phosphite-modified rhodium catalyst was developed for the hydroformylation of methyl 18 1 (9Z)and 18 1(9 ), which furnished mixtures of formylstearate and diformylstearate (61). 

Hydroformylation of Aliphatic Olefins In 1997, Herrmann and coworkers [25] were the first to use NHCs and imidazohum salts, respectively, as hgands or preligands in rhodium-catalyzed hydroformylation. The isolated NHC-rhodium complexes 1 and 2 (Figure 2.55) and the complexes prepared in situ from the water-soluble imidazolium salts 3a-c and rhodium(lll)acetate were tested in the homogeneous and biphasic hydroformylation of propene. The catalyst derived from 1 produced >99% yield of isomeric butanals (CO/H2 = 1 1,10 MPa S/C = 100 000 1, toluene, 60 h). In the biphasic system, after 20 h of reaction time and S/C = 10000 1 in water, rhodium catalysts derived from 2 or based on hgands 3a-c allowed up... 

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