Octenes hydroformylation

Figure 5.2-5 Recycling experiments - Rh-catalyzed, biphasic 1-octene hydroformylation in...

The ligands synthesized were also apphed to the isomerizing hydroformylation of more reactive 2-pentene. At 120 °C/ 20 bar quantitative conversion of olefin to aldehydes was achieved within 40 min. Trends similar to those described for internal octene hydroformylation were found. The regioselectivity obtained for the individual ligands tends to be 5% higher compared to that for the octenes. Thus, in the presence of 10 75% of n-hexanal were determined, compare Table 3. Obviously, 2-pentene is able to react more smoothly to the terminal isomer compared to olefins having the double bond in an more internal position. Illustrative for this effect are also literature results obtained for 2- and 4-octene.4,5... 

Si02-tethered RhI-thiolate complex catalysts Rh-S/Si02 and Rh-S-P/Si02 were prepared which exhibit high activity for 1-octene hydroformylation.238... 

Liquid Recycle is practical for octene hydroformylation. 1-Octene is readily soluble in organic based catalyst solutions, and product aldehyde and its condensation products can be separated by vaporization. 

Induced Phase Separation is also a good choice for octene hydroformylation. Octene can easily dissolve in the organic based catalyst solution, and with addition of small amounts of water, nonanal and its condensation products will readily separate from the sodium salt of a monosulfonated phosphine. To choose between Liquid Recycle and Induced Phase Separation would require a detailed technical and economic study that is outside the scope of this chapter. 

NAPS is also a possibility for octene hydroformylation, but again a detailed technical and economic comparison would be required in order to chose among it, Liquid Recycle and Induced Phase Separation. 

The use of a water-soluble phosphine based catalyst is not a preferred choice for octene hydroformylation. Although separation of nonanal and its condensation products from an aqueous catalyst should be facile, forming nonanal at a commercially viable rate could be challenging. In order to react, octene needs to be in the same phase as the catalyst, and octane has very low solubility in water. 

TABLE 3.9. Specifications of different units in the 1-octene hydroformylation process as shown in Figure... 

The same types of catalyst have been employed in 1-octene hydroformylation, but with the substrates and products being transported to and from the reaction zone dissolved in a supercritical fluid (carbon dioxide) [9], The activity of the catalyst is increased compared with liquid phase operation, probably because of the better mass transport properties of scC02 than of the liquid. This type of approach may well reduce heavies formation because of the low concentration of aldehyde in the system, but the heavies that do form are likely to be insoluble in scC02, so may precipitate on and foul the catalyst. The main problem with this process, however, is likely to be the use of high pressure, which is common to all processes where supercritical fluids are used (see Section 9.8). 

As mentioned earlier, in the Ruhrchemie-Rhone Poulenc process for propene hydroformylation the pH of the aqueous phase is kept between 5 and 6. This seems to be an optimum in order to avoid acid- and base-catalyzed side reactions of aldehydes and degradation of TPPTS. Nevertheless, it has been observed in this [93] and in many other cases [38,94-96,104,128,131] that the [RhH(CO)(P)3] (P = water-soluble phosphine) catalysts work more actively at higher pH. This is unusual for a reaction in which (seemingly) no charged species are involved. For example, in 1-octene hydroformylation with [ RhCl(COD) 2] + TPPTS catalyst in a biphasic medium the rates increased by two- to five-fold when the pH was changed from 7 to 10 [93,96]. In the same detailed kinetic studies [93,96] it was also established that the rate of 1-octene hydroformylation was a significantly different function of reaction parameters such as catalyst concentration, CO and hydrogen pressure at pH 7 than at pH 10. 

The technically most important biphasic process in the Ruhrchemie/Rhone-Poulenc hydroformylation of propene using the in situ Rh(I) catalyst HRh(CO)-(TPPTS)3 [6, 37]. Its formation from Rh(CO)2(acac) and TPPTS in a syngas atmosphere has been studied in detail [38, 39]. The BINAS-Na (ll)/Rh catalyst showed an outstanding performance in propene hydroformylation [15]. Binudear thiolato bridged rhodium complexes 12 have been used in 1-octene hydroformylation as precatalysts [41], For details of the hydroformylation, cf. Section 6.1 [15, 40, 41],... 

Catalysis of 1-octene hydroformylation in biphasic systems by [Rh(cod)Cl]2-TPPTS can be dramatically enhanced by addition of lipophilic phosphines, e.g., Ph3P. The rate enhancement by the promoter ligands is believed to be the result of an increasing local concentration of the catalytic species at the interface [57]. Mixed-ligand complexes HRh(CO)(TPPTS)3 x(Ph3P)x prepared separately from HRh(CO)(TPPTS) and Ph3P are likely not to be catalyst precursors. 

Kinetics of the 1-octene hydroformylation in aqueous biphasic media with the complex catalyst [RhCl(l,5-cod)Cl]2/TPPTS was also reported in [7]. Thereby, the reaction rate was also described by a mechanistic model (Eq. 14) assuming the addition of the olefin to the active catalyst to be the rate limiting step. 

Fig. 1 Comparison of 1-octene hydroformylation in water and aqueous methanol. The reaction time in water was 24 h the reaction time in 50% aqueous methanol was 5 h [10, 11],...

As noted above, the addition of alcohols improves the reaction activity in the two-phase hydroformylation of higher olefins with Rh/TPPTS catalysts. Reaction selectivity, however, is diminished if the operating conditions are otherwise similar. This is illustrated in Figure 1, which compares the conversion and selectivity of 1-octene hydroformylation over the (acac)Rh(CO)2/TPPTS catalyst in water alone and 50% aqueous methanol as the solvent [10, 11], Selectivity can be improved in the aqueous methanol system when ligands other than TPPTS are used, as for example with ionic phosphites of the type 1 cited above. These ligands differ significantly from TPPTS in that they are expected to be amphiphilic in character the ionic portion is hydrophilic while the rest of the ligand is relatively hydrophobic. 

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]. 

In an application for continuous biphasic, liquid-liquid 1-octene hydroformylation using a SILP Rh-NORBOS catalyst containing [BMIMJfPFe], a steady catalyst performance (TOP of 44 h and n/iso ratio of 2.6) was achieved after 3-4 h of reaction. Furthermore, no leaching of rhodium metal could be detected by ICP-AES analysis of outlet samples, at least after this relatively short reaction time. 

Figure 5 Effect of catalyst concentration on 1-octene hydroformylation rate at different pH values.

---