Improving process efficiency of gold-catalyzed hydration of alkynes: merging catalysis with membrane separation†
In this report, we investigate the integration of a membrane separation protocol in line with the gold-catalyzed hydration of alkynes. The catalytic reaction is optimised towards that end and subsequently merged with membrane technology via the development of an organic solvent nanofiltration (OSN) procedure. The protocol is investigated over both ceramic and polymeric membranes. Several gold catalysts were screened in the hydration of diphenylacetylene 1, and high rejection was observed in all cases using Borsig-type polymeric membranes. Catalyst recycling was also achieved up to 4 times using [Au(OTf)(IPr)] (3). In addition, the retained catalyst in the last catalytic cycle was analyzed and readily converted into [Au(Cl)(IPr)] (synthetic precursor to 3), using a straightforward treatment. The sustainability of the process was improved by using a green solvent, 2-methyltetrahydrofuran (Me-THF), and by reducing the amount of solvent used via the implementation of a second membrane.