What is the structure of the precipitate that forms after the sulfuric acid has been added?

Question

During an experiment when I created benzocaine by direct esterification of p-aminobenzoic acid with ethanol what is the structure of the precipitate that forms after the sulfuric acid has been added???

Answer 1

I have actually taught this lab several times, so you're in good hands!

The precipitate that you see after acidification is actually a zwitterion (the chapter in your text book on amines should have more information about zwitterions if you're interested).

Because the nitrogen in an amine has a lone pair of electrons it can act as a Lewis base and p-aminobenzoic acid is both an amine and an acid, so its acid portion donates H+ and its amine portion accepts it.

The structure of the ion would be exactly like the original acid but with the hydrogen missing from the carboxyl group and a negative charge on the oxygen that it was bonded to and the amine will gain a hydrogen (becoming NH3) and a positive charge.

Hope this helps!