Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: joe955 on May 06, 2010, 07:14:58 AM
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Will Hydrochloric acid (Muriatic Acid) convert any and all amine's to HCl or do amine's only convert to HCl by bubbling Hydrogen Chloride through the freebase?
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Do you mean ammonium hydrochlorides.
Do all bases react with strong acids?
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I'm not understanding your response with a question. I was under the impression that an amine free base can be converted to a salt form by reacting the amine free base with HCl. But I'm a little confused if the gas Hydrogen Chloride (HCl) is needed to convert the amine free base to a salt form or if Hydrochloric Acid (HCl) can be used to convert the amine free base to a salt form?
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One of the challenges with using muriatic/concentrated HCl is that they are a maximum of 37% HCl. The rest is water, so if you use that you're mostly adding water, which will dissolve any salt you might have (although somebody has probably precipitated a salt using this and will tell me I'm dumb, but I haven't ever done it that way). That's the reason people bubble pure HCl gas into a reaction, you don't have to deal with that issue.
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You can use HCl in ether or dioxane to get the salt as a precipitate, these can be bought as 1M solutions.
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Ok I do believe that the gas is needed more so than using the acid that makes more sense.
Can the gas be substituted with just Hydrogen or does it for sure have to be Hydrogen Chloride?
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Since when hydrogen is an acid strong enough to protonate anything?
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You're getting confused now, it has nothing to do with whether it's aqueous or gaseous. The most important property is the acidic proton, which as Borek pointed out, hydrogen does not have.
Pure HCl gas is pretty easy to generate and it works real well to avoid the issue I mentioned with the aqueous HCl so that's why people use it, not because it's more effective in the gas form. If you could concentrate HCl to 100% then people would use it.
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Ok so then it is that the acid has the acidic proton present but as you said the acid has mostly water which is not going to help the salt form and since the gas is pure HCl with the acidic proton present and no water that is good.
Now I no you said that you have not really tried to use the acid over the gas but does it seem possible that if the acid was to be used and the water evaporated would the free base form into a salt as it dries and be considered HCl?
I'm not sure but it seems like maybe this is similar to what helenn said "You can use HCl in ether or dioxane to get the salt as a precipitate, these can be bought as 1M solutions".
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Since when hydrogen is an acid strong enough to protonate anything?
I thought that this was true. Good thing I checked. I was told that using hydrochloric acid with aluminum was the process for converting to HCl. But when I checked what this was creating "Hydrogen" I got a little weary about making a "Hindenburg" bomb to convert amines to HCl. I also read what Hydrogen reacts and don’t react with and it read "doesn't react with acid or base". I just wanted to confirm that I was reading the right things before I made the 6 O'clock news.
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if the acid was to be used and the water evaporated would the free base form into a salt as it dries and be considered HCl?
Yes, we do this all the time in our lab.
If you have an amine in aqueous HCl and then concentrate the solution to dryness you are left with the corresponding ammonium chloride.
The acid-base reaction is always: acid + base -> salt, regardless of whether the solvent is water or something else (assuming the solvent is inert under the reaction conditions).
HCl gas and other alternative HCl sources are used when you want a solvent other than water - often in cases where water would not be inert under the reaction conditions.
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Is there a formula used to determine how much of the aqueous HCl to add per volume?
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Of course! But it is not related to your initial volume, it is related to initial molar quantity of amine!
Gaseous HCl is used because your amine will be soluble in some organic solvent. Bubbling HCl gas forms the salt that is insoluble in organic so it precipitates. Depending on how that amine was initially prepared, precipitating the amine hydrochloride may purify it from non-basic organic components.
If you add aqueous HCl a couple things may happen:
1. you may get two phases depending on the organic solvent, your hydrochloride would end uup in the organic layer.
2. You get one phase that is now "wet" and your hydrochloride precipitates as a sticky mess, in poor yield, or not at all.
but your use of the phrase "freebase" makes me think I should not have bothered typing this..
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Does anyone else get the vibe we're helping someone start up a coke mill? :P
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Is there a formula used to determine how much of the aqueous HCl to add per volume?
It depends on the amine used:
eg: methylamine - 1:1 molar ratio
ethylenediamine (1,2-diaminoethane) 2:1 (HCl to amine)
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There is one more thing that you may want to consider.
If you use aqueous HCl and then remove/evaporate the water afterwards,
there is a risk that the residual HCl salt will be in the form of a gum or oil.
That may be ok if you are going directly into the next step,
but it may be useless if you need to isolate the amine hydrochloride by filtration.
Also, there are several ways to generate gaseous HCl if you need it. For example,
if you add sulfuric acid to NaCl it will react and form sodium sulfate and gaseous HCl.
Of course, the gaseous HCl thus liberated will not be perfectly dry. But if you bubble it
through a washing flask containing conc sulfuric acid, and then into your amine solution,
it will come out pretty dry.
I am sure there are procedures (including descriptions of the apparatus setup)
that describe this old-school method.
Good luck and best regards,
/Markov
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joe955 - Were you able to successfully convert the amine free base to a salt by bubbling HCl gas up through the solution containing the free base?
I'm looking to carry out the same reaction, and it would be my first time doing so. So after finding this thread, I'm very curious as to what your results were - since you didn't post any! :P
Also - I apologize for replying to an old thread, but I figured it was senseless to create a new thread on the same topic when I was looking for an update on this specific topic (from joe955, if possible).
Thank you!