Zeul Mos
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How much time does it take for ammonia to condense?
Note: this is my first post here, so if I do or say anything wrong, please don't get mad at me.
I want to run a birch reduction of benzene, saw that on Nile Red's video and it seems quite interesting. The thing is, when I tried to run it, ammonia
didn't condense. I let the apparatus run for 10 minutes and eventually gave up. I want to try it again, but this time with more dry ice and
isopropanol. Any idea why couldn't I get ammonia?
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BromicAcid
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Please provide links if you're referencing something you can find online. Please provide a description of your setup, even if you just say it's the
same or similar to the one in the video. Please describe additional details of your condenser and the amount/form of dry ice you used (pellets,
powder, chunks, prills). Was the addition sub-surface or were you trying to condense neat ammonia? Did you have your flask in dry ice too? Were you
just using dry ice or a dry ice bath with a solvent (you mention trying more isopropanol, did you have any this run)? Did you have any temperature
monitoring, how long did you let things cool down before introducing the ammonia? How were you creating your ammonia (are you sure you were making
ammonia to being with) and at what rate (do you have any idea)? There are plenty of variables. The more time on the front end you take crafting your
post and including details the easier you can be helped out from other forum members.
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Zeul Mos
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My setup was made out of a Liebig condenser, with a drying tube attached to it, the tube was filled with sodium hydroxide, so that the ammonia would
not react with it ( the desiccant). The drying tube had a hose attached to it that lead to a small flask that was kept in a dry ice/isopropanol bath.
I let the setup cool down for a minute or two before starting the reaction. Then, to the flask attached to the condenser I added an equal amount of
sodium hydroxide and ammonium nitrate, 30 g of each, then added dropwise a few mililiters of water to give the reaction a boost.
That's quite everything.
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BromicAcid
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I'm not sure I understand, it sounds like you were using a Liebig condenser on your flask but where were you putting the dry ice?
Okay, is this the video you were talking about?
<iframe sandbox width="560" height="315" src="https://www.youtube.com/embed/gHokrNS1ask" frameborder="0" allowfullscreen></iframe>
If so your description for your setup is all on the ammonia generation side, correct? What were you trying to condense your gas into? Depending on
the flow rate and the temperature of the gas, the amount of cooling you have and the size of the flask it can take quite a bit of time to get those
first couple drops of liquid. Once you get enough gas condensed so that your tubing would be sub-surface you condense much faster/easier. That might
be covered in the video, I only watched the first minute or so but that's just a general observation from condensing gasses.
[Edited on 3-5-2016 by Polverone]
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Zeul Mos
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The dry ice/isopropanol bath was put where the ammonia should get out, so that it would condense. Just like in the video.
[Edited on 6-2-2016 by Zeul Mos]
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BromicAcid
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Again if your gas is coming out too fast you might not have the contact time to get material condensing on the walls of your flask. To give it the
best chance load up the bath with plenty of dry ice and give the setup a good 15 minutes to cool to temperature before attempting to condense ammonia.
Once you see droplets try to get them to coalesce and get the tubing below the liquid droplets. This will help the bas to better condense. If you
can do anything to pre-cool the gas before entering the setup even better. If you can put a dry ice condenser on your receiver flask then all your
problems would be solved. It's a specialized piece of glassware but if you're thinking of condensing gasses a lot it would be worth the investment.
I am talking about something like this:
http://www.sigmaaldrich.com/catalog/product/aldrich/z103098?...
Although the ones I usually use have straight walls instead of the bubble looking walls. The center section is filled with dry ice and solvent, the
vapors in the setup then have to travel past and over this cooled area before exiting.
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Zeul Mos
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So if I install the setup correctly, much like in the video, after a good 15 minutes I'd have ammonia condensing through, right?
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BromicAcid
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Not necessarily, again, it's going to be a combination of your flow rate and cooling capacity that is going to determine how long it will take this
material to condense, too fast and you might not condense anything no matter how long you go since you'll blow it all away (not likely but possible).
If your setup is engineered well and you have plenty of cooling area and a good flow rate then you could see droplets within a minute. The bottom
line is I cannot say exactly how long it will take to see anything. Obviously if you're generating a ammonia quickly, and you've been running for a
few minutes and you see nothing then you should probably adjust some parameter of your setup and not just stay your course.
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Zeul Mos
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Can I use sodium chloride as a desiccant for the reaction? It is quite hygroscopic and I won't have sodium hydroxide too soon.
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JJay
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It is hard to say for sure, but it will certainly not work as well as sodium hydroxide.
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Loptr
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Some sources of ammonia have changed to different chemicals, such as with some cooler packs changing over to urea.
Are you sure that ammonia was actually being generated and allowed to enter the condensation vessel? Are you sure you actually have ammonium nitrate?
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Zeul Mos
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I didn't get my ammonium nitrate through cold packs but from a chemical source.
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chemrox
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What is the heavy water/ammonia connection? The heavy water plant in WWII Norway was an ammonia plant. I'd like to know more than what's on wiki..
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Loptr
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Good to hear. It's best to start off with a single unknown (the reaction), than several (reactants and reaction) and wonder what went wrong.
Quite a few on this forum get their supplies from more available places, which means more variability in the mundane aspects of synthesis.
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