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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: derekb.lowe@gmail.com Twitter: Dereklowe

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August 31, 2010

Nanopowders?

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Posted by Derek

Here's a lab question for everyone. I have a bottle of Aldrich copper oxide nanopowder on my lab bench; I've been meaning to try it out for some Ullmann reactions. I note that Aldrich (and others) are now selling a variety of such nanopowders, mostly metals and insoluble metal compounds.

And that makes sense, because these are the things that tend to react at their surfaces, and you'd have to think that a real nanopowder would have a tremendous surface area. My question is: does this really work out? Has anyone noticed a difference between the nanopowder form of a particular reagent and its more traditional one? I can imagine there being one - but I can also imagine the particles clumping up under some conditions and giving you back the equivalent of the cheaper stuff, too. Any hands-on experience out there?

Comments (10) + TrackBacks (0) | Category: Life in the Drug Labs


COMMENTS

1. AlchemistOrganique on August 31, 2010 8:15 AM writes...

My experiences thus far: Mg turnings worked better than nanopowder for generating Grignards. However, reductive dehalogenation (sonicated)worked well with nanopowder zinc than unactivated powder. Although this might be overkill, I try to keep nanoparticulate metals as air-free as possible. Greater surface area may facilitate the formation of the troublesome oxide coating.

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2. processchemist on August 31, 2010 9:13 AM writes...

Worked on quite a lot of Ullmann reactions over the years, and copper oxide in general has been screened and discarded. No experience with nanopowders, but usually a good mass transfer (stirring) is one of the essential features to have good results. Obviously this means a minimum reactor size of 250 ml and mechanical stirring (I remember for a Rosenmund cyanation a 40% of difference in yeld between mechanical and magnetical stirring in a 250 ml flask). You don't need only surface, you need a good rate of exchange between products absorbed on the surface and reactants in solution. And good stirring prevents clumping too, in general.

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3. barry on August 31, 2010 9:53 AM writes...

I can't speak to the Ullman, but certainly Rieke's finely divided metals (used to be just Magnesium, now it's many more) are dramatically more reactive than conventional bulk metal or powder--if they're fresh. All that surface area also means that they degrade faster too.

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4. milkshake on August 31, 2010 10:05 AM writes...

I worked with Cu metal "nanopowder" from Aldrich about 6 years ago and I used it as a stoechiometric reagent for Wurtz-like coupling of 2,6-difluoroiodobenzene with ethylester of bromodifluoroacetic acid. I think it was done in anyhrous DMSO ot 70C under Ar and it worked beautifully. The procedure called for activated copper powder, I bought the activated Cu nanopowder from Aldrich as a matter of curiosity and the reaction was very clean. I did not try the traditional activated copper (which is made from CuSO4 and Zn dust, followed by acid wash and drying), I presume it would work about the same. Funny thing, the Cu nanopowder was listed in the catalog as a slurry in hexanes but what I got from Aldrich was a brown free-flowing powder. Also, a colleague tried to repeat the procedure on a similar substrate recently and I gave him the procedure - but he was unable to buy the Cu nanopowder, apparently Aldrich had discontinued it in the meantime.

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5. jay on August 31, 2010 11:48 AM writes...

check out the recent publication from John Porco at BU. http://pubs.acs.org/doi/pdf/10.1021/ja102482b

they utilize Ag Nanoparticles and observe a significant increase in conversion for their highlighted transformation as opposed to standard catalytic Ag conditions.

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6. Scripps Florida on August 31, 2010 2:13 PM writes...

Well, not exactly nanopowder, but....a little while ago, I was trying to make the mono-organozinc from dibromomethane, and found that the STREM grade zinc (98%, 100-200 um) did not work beyond 10% conversion, even when activated and heated +10 deg higher.
However, ALD

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7. Scripps Florida on August 31, 2010 2:15 PM writes...

(continued) 10 um powder, prewashed with acid, worked like a shot, completing the reaction in under 1 h

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8. AMD on September 1, 2010 11:17 AM writes...

A question:

Do any of these nano-powders allow you to do something you couldn't do before? Or are they just variants on existing reagents?

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9. Phil on September 1, 2010 11:59 AM writes...

I'm not an expert in nanoscience, but from what I know about nanoparticles from preparing a literature seminar is that you can't prevent them from recombining to bulk metal without some kind of dispersant or stabilizer. If you have tiny metal particles in suspension, they will eventually precipitate as the bulk metal. So I don't really understand the idea of a nanopowder, unless "nano" is being misused. It should mean particles in the 1-100 nm range, not just a finely powdered material. If you can see them, they aren't nanoparticles (you can see emission from nanoparticles in quantum dots, but not the particles themselves).

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