chemchemical
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Are dry solvents and inert atmo necessary? (NaBHOAc3 red amin))
I'm still new to synthesis, 2nd year grad student with one focus on synthesis. Now we always do stuff under argon to be safe and only use dry solvents
when needed.. however I am on a project that will require large amount of solvents and time to set up the argon lines, so I want to get around that.
Since dry solvents are expensive and this will be made in the grams I don't think the residual water will be an issue. I really only see argon as a
satey measure to things that can easily be oxidized, so I should be clear.
I will be doing a reductive amination using sodium triacetoxyborohyride (STAB) in situ. I've accomplish before with Na borohydride and acetic acid, I
forget if it was dichloromethane or dichloroethane, e-EROS recommends DCE for some reason but I dont see how there could be a big enough difference?
(Any suggestions? DCM is cheaper than DCE). So would residual water eat up the STAB, it will be in excess? Now since the STAB will react with the
schiff base it will drive the reaction forward, preventing hydrolysis back to the ketone and amine, my favorite part because distilling or dean stark
sucks. Then a secondary nitrogen will be protected through acylation by an acid chloride.
I feel this should work
Now, I dont see why we use argon so much, when its water sensitive I use it to get atmospheric water out, or if O2 ill oxidize it, but I dont see any
of these problems in big enough concern.
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Nicodem
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Thread Moved
23-9-2011 at 06:16 |
BromicAcid
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You should be grateful that you get to use Argon as much as you do, it's a privilege you don't often get in the real world. Take advantage of it
while you can especially since in grad school it's always good procedure to get the most pure compound you can.
How much solvent are you talking? Dry solvents come in anything from 50mL units to 200 L pure packs and everything in between. They do not cost much
more than regular solvents in my experience unless you need the 6 9's semiconductor grade or the like. Most retailers will have a spec sheet
available online for their solvents. Look at the amount of water listed for the anhydrous listing and compare to the other listings. Some may have
the same or even less and not be listed as anhydrous. But you always want to use dry solvents for anything that is moisture sensitive. Do not rely
on a reagent chewing up the water because you never want to be on the wrong side of a failed reaction wondering 'what if'. Get it right the first
time and then go back and change the solvent to something more readily available.
With regards to solvent changes, that depends on the reaction conditions. Even if their ability to solvate the reaction medium is similar
dichloroethane could greatly affect the reaction or workup due to its higher boiling point.
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Nicodem
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The fact that you are asking questions which are already covered in the seminal JOC article is demonstration enough that you never even bothered
reading it. Do that first and that come back with more elaborate questions.
Referenceless threads should only be opened in the Beginnings section!
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