Why does aniline dissolve in HCl, where acetanilide does not?
Aniline is somewhat basic. It is not as basic as ammonia, since protonation destroys the interaction between the ring and the lone pair on the nitrogen atom, but even still, it is sufficiently basic (pKb ~ 9.4) to dissolve in hydrochloric acid. On the other hand, in acetanilide, the nitrogen atom is located right next to a ketone functionality. Because of the electronegativity of the oxygen atom, the ketone is strongly electron-withdrawing – and this makes the positive charge of the conjugate acid much less readily tolerable, hence, acetanilide is a very weak base and is not affected by HCl to an appreciable extent.
