The separation, post-reaction, of ionic liquids and catalysts from reaction products is an unresolved challenge in the application of ionic liquids to organometallic catalysis. This paper addresses this challenge using organic solvent nanofiltration technology. Suzuki reactions were carried out in a homogeneous solution, comprising 50 : 50 wt% ethyl acetate and ionic liquid. The post reaction mixture was diluted further with ethyl acetate and then separated by nanofiltration into a permeate fraction and a retained (retentate) fraction. The product was recovered in the nanofiltration permeate, while the ionic liquid and palladium catalyst were retained by the membrane and recycled into subsequent consecutive reactions. Thus, the organic solvent nanofiltration was able to separate the Suzuki reaction product from both catalyst and ionic liquid. Three ionic liquids were tested: cocosalkyl pentaethoxi methyl ammonium methosulfate (ECOENG 2 500), tetrabutylammonium bromide (TBAB) and trihexyl(tetradecyl)phosphonium chloride (CyPhos 1 101). All the ionic liquids screened showed positive effects on the catalytic stability, significantly reducing the formation of palladium black and providing high reaction yields over consecutive recycles. The best performance was observed for the CyPhos 1 101 system. Additional investigations employing this ionic liquid showed that the reaction-recycle process can be successfully performed at lower catalyst-substrate ratios, leading to higher catalyst turnover numbers.

Due to potentially toxic contamination of pharmaceutical products, effective removal of palladium from post-reaction solutions is of great importance, especially in the pharmaceutical industry. This work addresses this challenge by combining organic solvent nanofiltration (OSN) with adsorbents in a hybrid process. Post-reaction solutions resulting from acylation and Suzuki reactions were subjected to OSN, the catalyst was retained by the membrane, and the product was collected in the permeate. Palladium levels in the permeate were reduced further by using adsorbents. This technique achieved ultralow palladium concentration (<10 mg Pd kg product−1) for post-reaction solutions with toluene and ethyl acetate as solvents. The results obtained using the hybrid OSN−adsorbent process were compared to those using selected adsorbents only. When palladium was removed from a post-Suzuki reaction solution, using polystyrene-bound trimercaptotriazine as the adsorbent, the hybrid process, while using 10 times less adsorbent than the adsorbent-only process, was able to reduce the product contamination to an 8.5 times lower level. It is thought that the membrane stage of this technique removes bulky ligated palladium along with palladium nanoparticles, species that are hard to remove by adsorption only. The residual palladium in the permeate stream comprises well-dissolved, smaller molecules, and these are removed very effectively by the adsorbent. This allows high-purity products to be achieved by treatment of the OSN permeate with low amounts of absorbents. Therefore, this hybrid process is recommended for separations where adsorbent-only treatment can result in significant product losses, or where strong ligand−palladium interactions compete with adsorbent active sites, keeping palladium in solution.

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