Ionic liquid-phase asymmetric catalytic hydrogenation: hydrogen concentration effects on enantioselectivity

A Comparison of Ruthenium‐Catalysed Arene Hydrogenation Reactions in Water and 1‐Alkyl‐3‐methylimidazolium Tetrafluoroborate Ionic Liquids

“…[15] Based on the above results it seems likely that the improvement is also due to increased solubility of the benzene substrate in the [bmim] [BF 4 ] ionic liquid, although other factors such as viscosity, which is higher for the ionic liquid, are important. The effect of the increased solubility of benzene in the ionic liquid has been confirmed by comparing the effect of stirrer speed on turnover in the two solvents.…”

Hydrogenation in Ionic Liquids

“…1.12 [15] 219 c, [15] [10,16] [bmim] [PF 6 ] b,c 6.6 x 10 2 (5.38 x 10 2 ) 0.73 d (0.88) 1.363 [15] 450 c, [15] [10,16] [bmim] [21] 314.0 b, [22] [ [20] 90 b, [20] [10] [P(C 6 H 13 ) 3 Table 1 shows that H 2 solubility in ionic liquids is typically much lower than in molecular solvents, which can lead to low reaction rates. Mass transfer effects associated with low gas solubility play a key role in hydrogenation, and may be critical when processes such as catalytic asymmetric hydrogenation are carried out in ionic liquids.…”

“…For other reactions requiring high H 2 concentrations, low solubility problems can be solved by carrying out reactions at elevated pressures, which raises the H 2 solubility. [16] Interestingly in many cases product selectivities are achieved due to solubility differences between the intermediate and fully hydrogenated products. [24] For example, in the partial hydrogenation of 1,3-butadiene using Pd(0) nanoparticles in [bmim] [BF 4 ], it was observed that 1,3-butadiene is at least three times as soluble in the ionic liquid as the intermediate butenes, inhibiting further hydrogenation and leading to product selectivity.…”

“…Zhou et al have proposed a mechanism for this reaction. (Figure 35) Figure 34 www.intechopen.com When Dupont et al [16] carried out asymmetric hydrogenation of (Z)--acetamido cinnamic acid using Ru-(tolyl-BINAP) in [bmim] [BF 4 ] and IPA mixture at RT, they observed that the reduction was accompanied by kinetic resolution of the substrate…”

“…Redel et al [117] prepared metal nanoparticles (Co, Rh and Ir) in ILs by decomposition of their corresponding metal carbonyls (Co 2 (CO) 8 , Rh 6 (CO) 16 4 ] as reaction solvent, the iridium nanoparticles demonstrated the best catalytic activity (1940 mol product (mol metal) -1 h -1 after 1 hour at 97 % conversion) in comparison to the rhodium nanoparticles (380 mol product (mol metal) -1 h -1 after 2.5 hours at 95 % conversion), with the cobalt nanoparticles being particularly poor (0.16 mol product (mol metal) -1 h -1 after 3 hours at 0.8 % conversion). The superior activity of the iridium in comparison with rhodium was postulated to be due to the smaller particle size of the Rh nanoparticles and therefore their accompanying larger surface-to-volume ratio.…”