Hydroformylation of 1‐Octene in Supercritical Carbon Dioxide and Organic Solvents using Trifluoromethyl‐Substituted Triphenylphosphine Ligands

Abstract

AbstractTwo different in situ prepared catalysts generated from Rh(CO)2acac and trifluoromethyl‐substituted triphenylphosphine ligands have been evaluated for their activity and selectivity in the hydroformylation of 1‐octene. The solvents used were supercritical carbon dioxide, hexane, toluene, and perfluoromethylcyclohexane. The highest value for the turnover frequency, 9820 mol1‐octene molRh−1 h−1, has been obtained in supercritical carbon dioxide using ligand I, P[C6H3‐3,5‐(CF3)2]3. For both supercritical carbon dioxide and hexane employing ligand II, P(C6H4‐3‐CF3)3, a selectivity towards the linear aldehyde product, nonanal, and an n:iso ratio of 79.3 % and 4.6–4.8 have been obtained, respectively. These values are significantly higher than those obtained with triphenylphosphine as ligand (nonanal: 74–76 %, n:iso: 3.1–3.3). An increase in trifluoromethyl substitution on the triphenyl ligand results in an increase in the 1‐octene conversion rate, an increase in the n:iso ratio and a decrease in the overall selectivity towards aldehydes. In terms of turn‐over frequency and selectivity the three ligands give comparable results in supercritical carbon dioxide and hexane. This leads to the conclusion that the properties of supercritical carbon dioxide as a solvent for hydroformylation can be better compared with those of hexane rather than with those of toluene.