A very simple procedure was described recently by David Knight and coworkers for the removal of ruthenium after metathesis reactions. The process involves simply stirring the crude metathesis reaction solution with excess 15% hydrogen peroxide for 1h at room temperature as a biphasic mixture. At low catalyst loadings (0.37 mol%) a single peroxide wash was needed to get the Ru levels down to 2 ppm. At higher catalyst loadings (1.37 mol%) two washes were necessary to reach the same level of Ru. The fact that the process is biphasic and brief make this method in theory compatible with many common organic functional groups. Typically, no peroxides are present in the product after treatment.
The ruthenium dioxide formed can be recovered and reused. One disadvantage of the method is that a large excess of peroxide has to be used, because it decomposes rapidly in the presence of ruthenium oxide. But hydrogen peroxide is cheap.
The reactions were run on relatively small scale, but it sure looks promising. No chromatography required!
Typical procedure: After the completion of the metathesis reaction in DCM, water and 37% aq hydrogen peroxide were added and the mixture was stirred for 1h. The mixture started to effervesce and a black precipitate was formed. The layers were separated and the aqueous was extracted with DCM. The peroxide test for the organic phase is usually negative; if positive, a single sulfite wash was sufficient. After filtering through a silica plug the solvent was removed to yield the product as colorless oil.
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Looks like it’s a process that would be relatively easy to scale-up, e.g. for use in industry. Did the university in question get a patent on this (and if not, why not)?
Looks like they did patent it, although they foolishly dropped it, see WO2007091085 at espacenet…….
my understanding is that patents get quite expensive later one once you move into the national patent stage. Perhaps their technology transfer office figured there wasn’t much money to be made in such use / process methodology patent. It is much easier to enforce patent on a particular compound (drug, catalyst, etc) as a “composition of matter” than on general way of using something in the process. Even if some company scaled up a key metathesis step and used peroxide quench in it to get the Ru out – how do you find out what they are putting into their reactor? And it is not a critically-important step, they could have used something else, like perborate or percarbonate or Oxone or bleach wash if necessary, or scavenge Ru with metal-binding resins.
There are no problems in patenting processes, it has been done many many times! Also, any good patent attorney would make sure that hydrogen peroxide would be covered in the broader sense i.e. perborates, percarbonates etc. Also, I am sure that you realise all chemical processes have to be disclosed in the synthesis of pharma compounds and the like, enforced by the European “REACH” legislation, I’m sure the US has similar measures.