Tuning catalyst performance in the SILP-catalyzed gas-phase hydroformylation of but-1-ene by choice of the ionic liquid

For the industrially relevant hydroformylation of but‑1-ene the concept of supported ionic liquid phase (SILP) has been applied previously. In this work, we have studied the influence of the type of ionic liquid (imidazolium and phosphonium based cations, various anions) on the solubility of the three reagents but‑1-ene, carbon monoxide and hydrogen. For the olefin, the predicted solubility values were determined using the COSMO-RS software tool. These data were compared to the experimentally determined values. A correlation between the predicted solubility and the observed activity within similar ILs could be observed. The highest activity could be obtained with the IL [N₁₈₈₈][NTf₂]. A variation of the olefin chain length supported the observed correlation between solubility and activity. With increasing chain length, the activity of the SILP catalyst also increased. For the undesired consecutive reaction leading to aldols it was found that the substrate solubility does not significantly influence the activity or hydrocarbon accumulation under the used reaction conditions. The anion had a more pronounced effect on the accumulation of aldols, with hydrophilic Cl⁻ and [EtOSO₃]⁻ showing lowest accumulation as well as aldol formation activity, while [NTf₂]⁻ showed highest values for both accumulation and formation activity. It was shown that the Kamlet-Taft-parameter β is a suitable value to be correlated with activity and accumulation for different ILs.