FireLion3
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Why do people go out of their way to gas organic bases when forming salts?
As opposed to just pouring in the aq. acid?
Crystals do not precipitate in water, but the base is still neutralized by the acid. A great majority of bases that can be turned into acid-salts do
not decompose except at temperatures much higher than the boiling point of water.
Every synthesis I have ever performed that involved forming a HCl salt, I would just add HCl acid, stir for a short period, and then heat it on a
temperature controlled hot plate to boil the water away, or simply vacuum distill the water away with mild heat. HCl salts tend to be very stable and
have much higher boiling/decomposition temperatures than the base alone, so why is this much simpler lab-technique so often overlooked? A lack
temperature controlled hot plates? Ignorance?
Gassing is messy, potentially dangerous, and can sometimes require elaborate set ups, as well as the consuming of a dry-compound that either has to be
thrown out or tediously redryed following the gassing.
[Edited on 17-6-2014 by FireLion3]
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forgottenpassword
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Because ethereal HCl does not cause hydrolysis. Many non-trivial molecules have hydrolysable groups which would react with the conditions that you
describe, but not so if precipitated with ethereal HCl.
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FireLion3
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Can you please give a specific example of what you are talking about? I'm confused. Do you mean the aqueous HCl would cause hydrolysis, or the
dissolved HCl-salt refluxing in water would cause hydrolysis? For the example can you give a specific molecule/group/features that would have an
influence in this said hydrolysis? Electron donating, withdrawing groups near by, for instance? Conjugation, resonance, etc?
To clarify, by ethereal, do you mean gaseous HCl?
[Edited on 18-6-2014 by FireLion3]
Oh, or do you mean HCl-Salt based molecules that will naturally hydrolyze in the presence of water no matter what, just because of their structure?
I.E. Molecules that are unstable in water and cannot be dissolved in it? Like when water was more acidic or basic than the formed HCl salt?
[Edited on 18-6-2014 by FireLion3]
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forgottenpassword
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I mean HCl in ether. There are many hydrolysable groups. Esters, nitriles etc. Boiling them in Hydrochloric acid to dryness will destroy that
functional group, whereas precipitating from ether will leave it intact. Most organic amines are non-trivial, with more than one functional group to
consider.
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FireLion3
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Quote: Originally posted by forgottenpassword  | | I mean HCl in ether. There are many hydrolysable groups. Esters, nitriles etc. Boiling them in Hydrochloric acid to dryness will destroy that
functional group, whereas precipitating from ether will leave it intact. Most organic amines are non-trivial, with more than one functional group to
consider. |
When adding hydrochloric acid in an aqueous solution I always thought it important to never add too much. If I'm boiling it away or distilling it, I
don't want it to get into my vacuum, or boil away into the air. Adding the correct amount isn't too difficult.
Thanks for clarifying though. I just wasn't sure what sort of hydrolyze groups you were referring to. Simple amines I imagine are pretty stable.
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