In an article titled "Industrial Suzuki chemistry" in the "Special Publication" section of the September 2016 issue of Speciality Chemicals (always a good read), the authors (John C. Parks and Eric L. Williams of Albemarle) mention an interesting technique I have not heard of yet:
Suzuki reactions are prone to catalyst poisoning. This means that it is wise to clean reaction equipment diligently and maintain a dedicated reactor for the Suzuki step. For very high value chemicals, Albemarle will run a reactor seasoning batch before starting the campaign.
A seasoning batch is typically the desired Suzuki reaction run at one-tenth the normal concentration. If the seasoning batch runs to ~90% completion, we generally consider the reactor seasoned.I've never heard of this, has anyone else? I'm not quite sure what they mean by "seasoned." This usually makes me think of "seasoning" a cast-iron pan, i.e. polymerizing a protective oil coating on the surface. In this case, I suspect that it is a test to see whether or not there are catalyst poisons (sulfur compounds, etc) on the reactor wall? It'd be interesting to know if there was a difference between different reactor materials (glass, stainless steel, Hastelloy.)
If the purpose of this step is mainly a test run, 'seasoning' might be misleading. Maybe they assume that the first batch will catch any catalyst poisons that are present. In that case, running that step contributes to the successful run of the main batch. Then 'seasoning' in the sense of 'preparing' would work. Oh, semantics.
ReplyDeletePd II is a pretty strong oxidizing agent, with an Eo of +0.987V, about the same as elemental bromine. The activation barrier is low and it's unscrupulous about what it deposits on, just like silver. Presumably you're working at much lower catalyst loadings than the academic versions, which are already low,
ReplyDeleteThis is the same idea as running a conditioning batch for hydrogenations. Conditioning the reactor for a sensitive hydrogenation reaction as a technique has been around for a long time.
ReplyDeleteAlso, if your hydrogenation stalls, it is advisable to filter off the heterogenous catalyst and re-submit the filtrates to fresh hydrogenation catalyst, rather than adding more and more catalyst.
DeletePd-catalysed coupling reactions often proceed through Pd-nanoparticles generated from Pd pre-catalyst, and a parasitic process like their agreggation of the active Pd species into Pd black can derail it. (For this reason Heck high-temp reactions in particular are sensitive to catalyst overload, they work better with lower catalyst loading.)
I thought cast iron pots/pans needed to be seasoned before you cooked in them?
ReplyDeleteYou can cook in them at any point, even if they're rusty, I just don't think I would eat the food coming out of that pan...
DeleteI suspect that the seasoning batches consume whatever compounds would poison the catalyst. We sometimes need to do this where I work.
ReplyDelete