# Can amines in acidic medium last for long?

I have been thinking of a situation where amines are kept in moderately-to-highly acidic media. In such a case, the amines would assume the protonated forms:

$$\ce{RNH2 + H3O+ <=>> RNH3+ + H2O}$$

However, I don't think that the protonated amine would remain as it is. I feel that thermal agitations may cause the protonated amine to remove an ammonia molecule as a leaving group:

$$\ce{RNH3+ <=>[K] R+ + NH3}$$

The fact that a positively charged nitrogen is highly electron withdrawing, and might tug at the $\ce{C-N}$ $\sigma$-pair, seems to aid in the removal of an ammonia molecule, along with the fact that gaseous ammonia can easily remove itself from the medium, enhancing the reaction's equilibrium towards the forward direction. However the rather unstable carbocation that forms as a result of the deammoniation may prove to hinder this reaction, although the forming carbocation may be immediatly suppressed by the conjugate base of the acid used (like $\ce{Cl-}$, etc.) The overall reaction for an anime placed in conc.$\ce{HCl}$ could be:

$$\ce{RNH2 + HCl <=> RCl + NH3}$$

I have no lab equipments, nor the ability to access sources that confirm or reject my thoughts, so I decided to ask for help here. So, Can amines in an acidic medium remain as such for long periods, or release ammonia? If this doesn't happen at room temperatures, may this happen at a higher temperature?

• I suspect it would depend on what the nature of R was (i.e. whether it was able to stabilise a carbocation). In general, quaternary ammonium salts of amines are stable, and indeed isolable (often as nice crystalline solids). – NotEvans. Jul 14 '17 at 9:32
• I don't know of that word, aminium, but I'm assuming you mean salts of $\ce{NR3}$, where R could be H or some other group, in that case, often, yes, but it would, as stated above, depend on the exact nature of the groups – NotEvans. Jul 14 '17 at 9:35
• Alkyl ammonium ions are generally stable and more stable than the ammonium one due to inductive effects. You get a salt, which is often the way amines are commercially distributed. K is very small in the second reaction you draw. I want be surprised to get some ammonia smell opening whatever contains amines, tough. – Alchimista Jul 14 '17 at 13:47
• Note that according to Wikipedia, "many hydrochlorides of amines have a longer shelf-life than their respective free bases", which, along with making amines more bioavailable, is why so many amine-based medications are delivered as the hydrochloride (or other acid) salt. – airhuff Jul 14 '17 at 14:47
• Obligatory IUPAC Gold Book reference. The $\ce{NH4+}$ cation is called ammonium and so are the various substitutions of $\ce{R}$ for $\ce{H}$. – Ben Norris Jul 16 '17 at 13:44