1 -Hexene biphasic hydroformylation

Hydroformylation of Mid Range Olefins - Rhodium/tppts catalysts exhibit low catalytic activity in the hydroformylation of mid range olefins (C5-Cg) in a two phase system due to the much lower solubility of such olefins in water. In the Rh/tppts catalysed biphasic hydroformylation of 1-hexene, for example the conversion is only 11-22% with a n/i ratio of aldehydes of 98/2.353,373 The rate of 1-hexene hydroformylation catalysed by Rh/tppts increased by a factor 2.3 when subjected to ultrasound (35 kHz) and high stirring rates.360,361... 

Table 9 summarizes further biphasic hydroformylation reactions of various mid range terminal and internal olefins such as 1-hexene, 1-octene and 2-hexene catalysed by different water soluble systems. 

Kalck et /.96,359,362 studied the biphasic hydroformylation of 1-hexene using water soluble dinuclear species such as Rh2(m-S-lBu)2(CO)2(tppts)2 and C0/H20 where H20 acts both as a solvent and hydrogen source according to the water gas shift reaction (Equation 2). The turnover frequency (TOF) obtained was 40 h 1 and the n/i ratio of the aldehyde 96/4.96 Using RhH(CO)(tppts)3 catalysts lower rates were obtained under the same conditions.96... 

The prototype industrial process based on this concept is the Ruhrchemie-Rhone Poulenc process for the hydroformylation of propylene to butanal94,219,220 (see Section 7.3.1). Because of the use of appropriately modified water-soluble ligands, the catalyst resides and operates in the aqueous phase. The particular features of this process are the positive energy balance and easy catalyst recovery, namely, the simply circulation of the aqueous catalyst solution. New types of water-soluble Ir and Rh complexes with tris(hydroxymethyl)phosphine222 were described, and the biphasic hydroformylation of 1-hexene was accomplished in ionic liquids.223 A cationic sugar-substituted Rh complex displays high regioselectivity to branched aldehydes.224... 

In the biphase hydroformylation of 1-hexene the conversion rate strongly depends on the phosphorus to rhodium ratio (P/Rh ratio). An increase of the P/Rh ratio from 50 1 to 100 1 and to 150 1 results in a decrease of the conversion from 33% to 18% and to 9% respectively (Table 3). This may be due to the shift of the 1, 2 and 3 (Scheme 1). At higher phosphine concentrations the formation of the catalytically active species is suppressed. Furthermore the salt effect is much more pronounced in the aqueous catalyst solution than in homogeneous organic systems. 

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). 

The biphasic hydroformylation of 1-hexene with carbon dioxide (4 MPa)/hydrogen (4 MPa) can also be catalyzed by Ru3(CO)i2 in ILs/toluene giving high yields and good chemoselectivity in heptanols with relatively low amounts of hexane (11%) (Scheme 17). ... 

The organic-organic biphasic hydroformylation of hexene-1 in poly(ethylene glycol) as a polar phase, in which higher olefins are somewhat more soluble than in water, resulted in high yield, but the reaction gave rather low n / i ratio (0.75) (57). The ionic-liquid based hydroformylation of octene-1 succeeded with remarkable nii selectivities (19 1) using 7z-butyl-3-methyl-imidazolium (BMIM) trichlorostannate as the reaction medium (58). 

Hexene was transformed into -heptanal with a relatively low Hb ratio of 2 1. Noteworthy, up to a thiophene concentration of 500 ppm no intoxication effect was observed in the catalytic reaction. Alternatively, for the aqueous biphasic hydroformylation of 1-hexene, the complex RuCl2(DMS0)2(PyS03Na)2 was utilized. Remarkably, it converted cleanly also technical naphtha containing thiophene impurities of up to 50 ppm [31]. 

Hydroformylation of 1-hexene using water soluble rhodium catalysts modified with such tenside ammonium salts of tppts afforded up to 55% C7-aldehydes (n/i=94/6). Similarly, Rh/tppts catalysts in the presence of tenside phosphonium salts e.g. Me(CH2)i3P Et3 gave 74% yield to aldehydes (TOF=186 h ) in the biphasic hydroformylation of l-tetradecene. ... 

A particular advantage of SAP catalysis is that reaction with hydro-phobic substrates occurs at the aqueous/organic interface allowing water insoluble higher olefins to be hydroformylated using the RhH(CO)(tppts)3 system. In the biphasic hydroformylation using RhH(CO)(tppts)3 the reaction rates decrease in the order 1-hexene > 1-octene > 1-decene. In contrast, using the same catalyst in a silica supported aqueous phase similar activities and selectivities were obtained in the hydroformylation of these olefins. The low n/i ratio observed in... 

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. 

In the quest for suitable solvent systems the [Rh(CO)2(SULPHOS)] complex (SULPHOS = 31) was found to catalyze the hydroformylation of 1-hexene in water-methanol/isooctane (1/1/1, v/v/v) yielding heptanal and 2-methylhexanol in a ratio of 2.2 (80 °C, 30 bar syngas) [83]. An important point here is in that the biphasic micture becomes homogeneous above 60 °C, but phase separation occurs again upon cooling to room temperature. This kind of solvent behaviour may lead to fast reactions at higher... 

Similar to the above case, hydroformylation of 1-hexene using a water-soluble rhodium catalyst [RhH(CO)(TPPMS)3] gave lower yields when a-cyclodextrin was added to the biphasic reaction system [14]. Again, the reason was suspected in the interaction between the cyclodextrin and the rhodium catalyst. 

An ionic liquid was fully immobilized, rather than merely supported, on the surface of silica through a multiple-step synthesis as shown in Fig. 15 (97). A ligand tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium) salt (tppti) was prepared so that the catalyst, formed from dicarbonylacetylacetonate rhodium and the ligand (P/Rh = 10), could be soluble in both [BMIMJBFq and [BMIM]PF6. The supported ionic liquid-catalyst systems showed nearly three times higher rate of reaction (rate constant = 65 min ) that a biphasic system for the hydroformylation of 1-hexene at 100°C and 1500 psi in a batch reactor, but the n/i selectivity was nearly constant the same for the two ( 2.4). Unfortunately, both the supported and the biphasic ionic liquid systems exhibited similar metal leaching behavior. 

The synthesis of cobalt carbonyl-boimd silanetriol, Coa(CO)9CSi(OH)a (11) was originally reported by Seyferth et al. (34) by careful hydrolysis of Si—Cl bonds present in Coa(CO)9CSiCla (Scheme 8B). The X-ray crystallographic measurement (35) reveals a cage structure for compound 11. The OH groups present in 11 can be used further for the buildup of a number of heterosiloxanes. The cobalt carbonyl-boimd silanetriol 11 exhibits very high catalytic activity in the hydroformylation of 1-hexene in a biphasic vide infra) system (35). 

The hydroformylation of 1-hexene by supported ionic liquid catalysis (SILC) was recently reported by researchers at ExxonMobil. In this system, the active catalyst HRh(CO)(tppti)3 (tppti = tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium)) is contained within the ionic liquid phase while excess tppti ligand is immobilized in the support material. TOP values of 65 min" were obtained with silc while an unsupported biphasic ionic liquid medium gave TOP values of 23 min. ... 

CH2(OCH2CH2)nOCH3]QH6 (n = 30-160) has been prepared [63] and exhibited comparable catalytic activity in the hydroformylation of 1-hexene in a single-phase or in a biphasic system. 

The cavitron device was used to study the conversion rate of n-l-hexene hydroformylation under biphasic conditions. Under standard reaction conditions, but at a lower pressure of lObar, a conversion of 17% (n/iso ratio 99 1) was reached in this unit compared with 12% in a regular stirred autoclave. 

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