A Scalable Membrane Pervaporation Approach for Continuous Flow Olefin Metathesis

The translation of olefin metathesis reactions from the laboratory to process scale has been challenging with traditional batch techniques. In this contribution, we describe a continuous membrane reactor design that selectively permeates the ethylene byproduct from metathetical processes, thereby overcoming the mass-transport limitations that have negatively influenced the efficiency of this transformation in batch vessels. The membrane sheet-in-frame pervaporation module yielded turnover numbers of >7500 in the case of diethyl diallylmalonate ring-closing metathesis. The preparation of more challenging, low-effective-molarity substrates, a cyclooctene and a 14-membered macrocyclic lactone, was also effective. A comparison of optimal membrane reactor conditions to a sealed tubular reactor revealed that the benefits of ethylene removal are most apparent at low reaction concentrations.