Membrane-Supported Recovery of Homogeneous Organocatalysts: A Review

Abstract

As catalysis plays a significant role in the development of economical and sustainable chemical processes, increased attention is paid to the recovery and reuse of high-value catalysts. Although homogeneous catalysts are usually more active and selective than the heterogeneous ones, both catalyst recycling and product separation pose a challenge for developing industrially feasible methods. In this respect, membrane-supported recovery of organocatalysts represents a particularly useful tool and a valid option for organocatalytic asymmetric synthesis. However, catalyst leaching/degradation and a subsequent decrease in selectivity/conversion are significant drawbacks. As the effectivity of the membrane separation depends mainly on the size of the catalyst in contrast to the other solutes, molecular weight enlargement of small organocatalysts is usually necessary. In the last few years, several synthetic methodologies have been developed to facilitate their recovery by nanofiltration. With the aim of extending the possibilities for the membrane-supported recovery of organocatalysts further, this contribution presents a review of the existing synthetic approaches for the molecular weight enlargement of organocatalysts.

Asymmetric Organocatalysis and Continuous Chemistry for an Efficient and Cost-Competitive Process to Pregabalin

“…Furthermore, the nanofiltration can be made continuous and it has been demonstrated on scale under GMP conditions. OSN relies on the differences in molecular size and geometry of the solutes and has already been demonstrated to recycle organocatalysts; ,, based on the reported precedents, and given the difference in molecular weights between the starting materials and products with the catalyst (Figure ), OSN seemed one of the best options with the highest chances of success.…”

Organic Solvent Nanofiltration in Pharmaceutical Applications

“…88 Compared with other catalyst recovery techniques, OSN can selectively separate the catalyst from the product without phase transition and biphasic operation, which makes the recovery and reuse of homogeneous catalysts easier and greener. 87,89 A technological evaluation showed that significant energy and cost savings of up to 85% and 75%, respectively, can be achieved by OSN, compared to that of distillation. 90 Catalyst recovery/recycling via OSN is also a typical purification process (Figure 3c) to separate the catalyst from the product.…”

Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions

“…There is increasing interest in applying OSN for the purification of pharmaceutically relevant compounds [33][34][35][36], as well as for solvent recovery [37,38]. OSN has also been proposed for the recovery of enlarged metal catalysts [39], and organocatalysts [40]. As an alternative recycling method to precipitation, Livingston et al demonstrated the OSN enabled recovery of C 3 -symmetric quinidine-based organocatalysts [41].…”