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Author: Subject: Powder addition in reflux?
Fyndium
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[*] posted on 27-11-2020 at 15:57
Powder addition in reflux?


How do you add powder reagents in reflux reactions? If they are applied through column, they tend to stick to the walls and form clogs easily at the reflux level.
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CharlieA
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[*] posted on 27-11-2020 at 17:37


One way is to use a 2-neck flask for the reaction/refluxing apparatus ("pot"). The powder to be added is in a separate flask (need not be a standard-taper neck) of any shape. The "powder flask" is connected with a flexible hose that fits over its neck at one end and over the the second neck of the pot at the other end. The hose should be long enough for the flasks to be roughly parallel to each other. With the flask holding the solid "hanging down", the hose will close off the flasks from each other so that the vaporizing liquid will be prevented from wetting the dry solid. The flask of solid is tilted/raised up to allow the solid to be added to the pot. This is a fairly standard and classical way of adding a solid to a reaction pot. (If you can mentally envision this description you surely have a vivid imagination!
If necessary, I could U2U a sketch...or maybe post it in this thread.
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SHADYCHASE54
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[*] posted on 28-11-2020 at 05:09


Dr. Bob helped me with this issue and sold me a large pressure equalized powder addition funnel, well worth the cost and for what it was a very reasonable deal. I don't know if he has any more but for sensitive reactions that require intermittent powder addition they are awesome. I tried the way of adding powder by connecting a flask buy a large diameter flex. tube I found the addition often became difficult to control as the reaction progressed especially if the reaction was heated. The powder would become stuck together and as I said controlling addition when the powder is no longer free flowing is like tossing acetic acid in a jar of baking soda, much more fun to watch than to clean up.
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Heptylene
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[*] posted on 28-11-2020 at 07:10


Perhaps addition of the powder as a slurry in the reaction solvent is possible?
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[*] posted on 28-11-2020 at 13:57


Quote: Originally posted by SHADYCHASE54  
Dr. Bob helped me with this issue and sold me a large pressure equalized powder addition funnel, well worth the cost and for what it was a very reasonable deal. I don't know if he has any more but for sensitive reactions that require intermittent powder addition they are awesome. I tried the way of adding powder by connecting a flask buy a large diameter flex. tube I found the addition often became difficult to control as the reaction progressed especially if the reaction was heated. The powder would become stuck together and as I said controlling addition when the powder is no longer free flowing is like tossing acetic acid in a jar of baking soda, much more fun to watch than to clean up.


A powder addition funnel sounds awesome, I never knew you could buy them.

I usually use a two neck with a stopper in the side joint. When addition is required I remove the stopper and place a glass funnel in and add the powder through that.




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Fyndium
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[*] posted on 28-11-2020 at 15:40


I ended up using a vigreux column on one neck with jointed funnel on top of it and having a dimroth in the middle. If I had a straight glass column, I'd used that, but dimroth got almost instantly clogged so I had to make a compromise. Some powder had to be scraped twice during the addition, but otherwise it worked decently.

If there were, I'd think of using a gunpowder type funnel to add powders into a reaction. It should have a similar rotating dosage valve which when turned upwards, picks up more powder, and when turned down, will administer it into the reaction. Another one would be just axially sliding dosier with spring loading, this would add a dose of powder with single push of a finger. This could be 3d-printed from PP or machined from teflon.

[Edited on 29-11-2020 by Fyndium]
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