Syngas pressure

The use of the sulfoxantphos ligand (compound (b) in Figure 7.8) in the biphasic hydroformylation of 1-octene with [BMIM][PF6] has been studied by Dupont and coworkers [58], The ligand allowed recycling of the catalyst solution up to four times with no loss in activity or selectivity. Flighly regioselective hydroformylation (n/iso = 13) was reported for a Rh/phosphine-ratio of 4 (100°C, 15 bar syngas pressure). 

The influences of the ligand-to-metal ratio, reaction temperature and syngas pressure on the enantioselectivity and regioselectivity were also studied. A multi-substrate screening approach has recently been used by Dow Chemical Company to identify the best catalyst for the hydroformylation of vinyl acetate. Here, the chiral phosphite Kelliphite, 5 (Fig. 1) gave enantioselectivity up 88% ee and excellent regioselectivity for the branched isomer [24,25]. 

All the preliminary measurements of the Rh-3/5/Si02 (denoted as Rh-3-SILP) catalyst discussed so far were initially studied at 100 °C and 10 bar syngas pressure (H2 CO 1 1) over a period of up to 36 h. This time on stream was further extended to 180 hours to test the long-term stabihty of the Rh-3-SILP dehydroxylated catalyst system (Fig. 3). 

Year Catalyst Syngas pressure fbar) H2/CO ratio Temp. rc> Time (h> Methanol conv. m Ethanol selectivity (%) Ref. 

Electron-transfer processes can give rise to substitution-labile 17-electron complexes . A 17-electron species prepared by electrochemical methods favors CO reaction with ( -Cp)2TiCl2. Electron-transfer catalysis has been proposed for the conversion of FcjfCO), 2 to FefCO) . A possibly related process is the transformation of Rh4(CO), 2 into [Rh(CO)4] under syngas pressure. This may be an important step in the synthesis of ethylene glycol from CO and H2. 

In contrast to its organic-soluble derivative, HRh(CO)(TPPTS)3 does not take up a second molecule CO to form HRh(CO)2(TPPTS)2, even at syngas pressures of 20 MPa. As has been shown, the latter compound generates by dissociation of either carbon monoxide or TPPTS the unsaturated species HRh(CO)(TPPTS)2 or HRh(CO)2(TPPTS), which is responsible for the formation of linear and branched aldehydes (Scheme 4). As HRh(CO)(TPPTS)2 is formed by TPPTS dissociation from the starting compound HRh(CO)(TPPTS)3, and HRh(CO)2(TPPTS) is only obtained by an equilibrium reaction from HRh(CO)2(TPPTS)2, the observed increased n/i selectivity for water-soluble rhodium oxo catalysts becomes comprehensible. 

Detailed studies by Bourne on the hydroformylation of propene [106] in the temperature range 110-150 °C and at syngas pressures of up to 10 MPa confirmed partly the earlier results of Natta. Although they were not obtained under real industrial (i.e. commercial) hydroformylation conditions T = 150-180 °C, p = 20-35 MPa), these data give insight into the major trends. 

At high syngas pressure, physical solvent-based processes become increasingly attractive, for example, the Rectisol and Selexol processes. There are more than 55 Selexol plants worldwide, treating natural and syngas.51 The Selexol process solvent is a mixture of dimethyl ethers of polyethylene glycol, and has the formulation... 

Sections 1.3.1-1.3.3 discuss representative hydroformylation processes in water, ILs and SCCO2. Unfortunately, strict comparison between the efficiencies of the alternative solutions proposed is not possible due to the number of reaction parameters syngas pressure, ligand/metal ratios, catalyst loading, olefin/metal ratio, temperature and so on. Moreover, catalysts performances are expressed in different studies in different terms. For clarity, we anticipate that the activity and selectivity of a hydroformylation catalyst can be expressed either in terms of its turnover number (TON) and the ratio of linear to branched aldehyde (n/Z) in the product mixture, or in terms of the yield of -butyraldehyde, which is the combination of the nji and the TON. In other studies a comparison between TOF values is reported. 

If the conditions of the Ruhrchemie/Rhone-Poulenc process are applied to linear a-alkenes (LAOs) with 5-12 carbon atoms, the space-time yield of the hydroformylation reaction decreases with increasing chain length of the substrate. Table 1 summarizes the results of the batchwise hydroformylation of LAOs different at 30-80 bar syngas pressure. 

Two-phase hydroformylation of alkenes is an example of the development of a low-pressure oxo process operating at a syngas pressure of 20-50 bar. As can be seen in Table 2, the conversion rate seems to reach a maximum between 30 and 80 bar in the hydroformylation of n-l-hexene. By increasing the syngas pressure from 25 to 270 bar the n/iso-ratio decreases from 98 2 to 92 8. Whereas the increase of... 

Highly viscous triazine-based ionic liquids have been recently applied for the rhodium catalyzed hydroformylation of l-octene [179]. Hydroformylation was carried out at 69 bar syngas pressure and total l-octene conversion was achieved... 

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