Hydroformylations temperature-influence

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]. 

The influence of process variables such as the temperature, pressure of H2 and CO on the hydroformylation reaction is well recognized by all researchers. However, other aspects, such as stirring speed, the shape and size of the stirrer, relative amounts of the aqueous and organic phases, etc. are usually overlooked by people working in laboratories far from the actual chemicals production. A few papers in the open literature deal with these questions, of which perhaps the most important concerns the location of the chemical reaction. Does it takes place in the bulk phases or at the interphase region ... 

The influence of temperature and carbon monoxide partial pressure on the optical purity of the products is different, depending on the type of ligand used and on the molar ratio between ligand and metal. In the hydroformylation of styrene by [Rh(CO)2Cl]2 and (R)-BzMePhP the effect of the Pco was studied 34) at 110 °C and at 50 atm pH. For ratios L /M of 2 and 3, the optical yield shows a maximum at about 70 atm pOT in the range 0-100 atm, and at higher L /M ratio, the maximum appears at higher pressures for a L /M ratio of 4 there is practically no difference in the optical yield observed in experiments carried out at pco of 30 and 70 atm 34). 

At room temperature the Rh-catalyzed hydroformylation of butadiene [22] and of 1-pentene is possible (eq. (2)) [10 a]. In the latter case, [Rh(CO)2(acac)] in the presence of triphenylphosphine achieves slightly higher turnover frequencies (TOF) as compared to reactions in toluene. The product ratio of Ao-aldehyde was not influenced by the solvent. The use of the monosulfonated triphenylphosphine (tppms), however, reduced the activity of the catalyst drastically although its use allowed a more efficient recycling of the catalyst [10 a]. 

Hydroformylation with platinum complexes proceeds as described in Scheme 5 when a Lewis acid, e.g., SnCl2, is added. The Lewis acid removes the chloride from the platinum center to afford a vacant coordination site to which the olefins can coordinate. Asymmetric induction occurs during the formation of alkyl intermediates via olefin insertion into the Pt-H bond [8]. Most importantly, the re-gio- and enantioselectivities are strongly influenced by the reaction temperature in the Pt(II)-catalyzed asymmetric hydroformylations [10, 70, 71, 72, 73]. Re-... 

Kinetics of the hydroformylation of propylene using RhCl(CO)(TPPTS)2/TPPTS complex catalyst in aqueous system was studied by an orthogonal experimental design analyzing the influence of temperature total pressure, molar ratio H2/CO, partial pressure of propylene, molar ratio Rh TPPTS, and the catalyst concentration on the initial reaction rate [33],... 

Compilations of early results are available in several reviews45. Relatively good optical yields have been obtained in the rhodium-catalyzed hydroformylation of terminal and some internal alkenes45. Reaction conditions of the rhodium-catalyzed hydroformylation of styrene have been intensively studied. The influence of temperature and carbon monoxide partial pressure differs with ligand and ligand-to-metal ratio45. 

Certain amines, when linked to TPPTS, form ionic solvents liquid at quite low temperature. Bahrman [34] used these ionic liquids as both ligands and solvents for the Rh catalyst for the hydroformylation of alkenes. In this otherwise interesting approach, however, the ligand/rhodium ratio, which influences the selectivity of the reaction, is difficult to control. 

Table 2. Influence of the Partial Pressure of Carbon Monoxide and the Temperature on the n/iso Ratio in Hydroformylation of Selected Substrates...

Although the conventional solvents such as aliphatic and aromatic hydrocarbons and ethers does not influence the n/iso ratio in hydroformylation (30), in supercritical carbon dioxide higher n/iso ratio was found for propene (44,45) and for 1-octene (46,47). In perfluoroalkane-toluene mixture, practically the same product composition is obtained as in toluene alone, but the former solvent combination allows a one-phase catalysis coupled with a temperature-dependent effective biphase catalyst separation (48-51). For the review of fluorous biphasic hydroformylation, see Ref (52). 

Systematic studies on the influence of temperature on the regioselectivity in the hydroformylation of vinyl substrates in the presence of unmodified rhodium-hased precursors have been carried out only in few cases. In particular the investigations reported in literature concern the hydroformylation of styrene, ethyl- and allyl ethers and 1-hexene, with RJi4(CO)i2 over temperatures, ranging from 20 °C to 100 °C. 

Figure 2. Influence of temperature on the hydroformylation regioselectivity of selected substrates in the presence of Rli4(CO)i2 as catalyst precursor...

As described above, both the nature of the substrate and the reaction conditions strongly influence the regioselectivity in the hydroformylation of vinyl substrates. The above results clearly demonstrate that, by raising the reaction temperature, and decreasing the CO and Hi partial pressures, the amount of linear aldehydes increases. Indeed, this is a general trend in the hydroformylation of different substrates and constitutes a fundamental starting point for a rationahzation of the influence of experimental parameters on the reaction selectivity. 

Palladium-mediated hydroformylation of several terminal and internal olefins was also investigated by the Beller group (Scheme 5.30) [138]. Rapid isomerization already took place when 1-octene was stirred at room temperature in the presence of the catalyst without any hydrogen pressure. Within 1 h, 1-octene was almost completely equilibrated to produce a mixture of internal olefins. Hydroformylation trials at 40 or 80 bar syngas pressure and at 80 or 100 °C revealed the strong influence of these parameters on the success of the reaction. 

In a similar manner, a modified Rh(PPh3) catalyst was able to convert camphene under neat conditions at 200 bar into the aldehydes [77, 78]. This protocol was carried out in a >400 g scale. When the syngas pressure and temperature were lowered (90 bar, 100 °C), the linear aldehydes were formed in nearly quantitative yields [7 6]. In the presence of phosphorus ligands, the formation of the endo isomer was favored (exo/endo 1 1.5), whereas in immodified systems both exo and endo compounds were formed in nearly equal amounts. Neither steric nor electronic parameters of the Ugands were found to influence significantly the diastereose-lectivity of the rhodium-catalyzed hydroformylation. The reaction was likewise performed in a toluene/water biphasic system employing TPPTS to immobilize the rhodium catalyst in the aqueous phase [84]. A mixture of exo and endo isomers of the linear aldehyde (exo/endo 1/1.5) was obtained in nearly 100% chemoselectivity and 71% yield [Rh(COD)(OAc)]2, TPPTS, CO/Hj (1 1, 8 MPa), 80 C, toluene/water (2.5 1 v/v), 48 h. ... 

As Monflier and coworkers [48] have shown, the rhodium-catalyzed hydroformylation of triglycerides in water pressure can be supported by the addition of randomly methylated P-cyclodextrines (RAME-P-CDs). Syngas pressure (20-80 bar), temperature (50-80 °C), nature of the sulfonated phosphine ligand, and the amount of R AME-P-CD had a profound influence of the catalytic results. 

The catalyst concentration in technical operations may vary from 0.1 to 5.0 wt-% as metal, based on olefin [125], although concentrations higher than 2 % are very seldom used (e. g. if low temperatures are applied in the hydroformylation). V. L. Hughes and I. Kirshenbaum reported that the catalyst concentration has a strong influence on the ratio of isomeric aldehydes formed in the hydroformylation reaction [126]. According to their publication heptene-1 will give 75% of n-alcohol plus 25% of iso-alcohol... 

Pressure and temperature exhibit a strong influence on the isomer distribution of the hydroformylation products. Thus, in the case of straight chain olefins, higher CO partial pressure favors the formation of straight chain aldehydes at constant reaction temperatures [62, 196]. 

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