Amine Basicity
Amine Basicity
Amines, with their negative lone pair of electrons, tend to be basic. This means the negative lone pair of electrons can grab a proton (H+). This turns the amine into amine salt. Salts have both the positive cations and negative anions combined. Salts are soluble in water.
In the lab, we know that amines will react with aqueous HCl to form a salt that can dissolve in water. If we have an unknown compound that we think might be an amine, we can test that hypothesis by trying to dissolve a small amound of our compound in 10% aqueous HCl. If our compound dissolves, we could determine that we have a basic compound – perhaps an amine.
In medicines, it is sometimes preferable to sell the amine as its water-soluble salt. For instance, Benadryl and Sudafed are the hydrochloride salts of the amines.
An interesting example, although illicit, form of amines and amine salts is cocaine and crack. Crack (the free base) is formed when the hydrochloride salt powder form of cocaine is added to boiling water with sodium bicarbonate, NaHCO3, (to deprotonate it). A rock forms. It is broken into smaller pieces and sold as crack.
If an acid like HCl is produced in a reaction, an amine base is often used to soak up the acid that is produced. Pyridine is a common base for this task. We have seen this before in the tosylation of an alcohol. Notice that the H from the alcohol and the Cl from TsCl are not in the product. The pyridine base soaked up the HCl that is produced in this reaction.
