Question

Are amides acidic or basic?

Answer 1

Definition of acid:

1. A chemical compound that can release proton$\left({\mathrm{H}}^{+}\right)$ in aqueous solution or can accept lone pair of electrons.
2. Example: Acetic acid$\left({\mathrm{CH}}_3\mathrm{COOH}\right)$, hydrogen chloride$\left(\mathrm{HCl}\right)$.

Definition of base:

1. A chemical compound that can release hydroxide$\left({\mathrm{OH}}^{-}\right)$ ion in aqueous solution or can donate lone pair of electrons.
2. Example: Sodium hydroxide$\left(\mathrm{NaOH}\right)$, potassium hydroxide$\left(\mathrm{KOH}\right)$.

Explanation:

1. Since $\mathrm{N}-\mathrm{H}$ bond in amides has a Ka of about ${10}^{-16}$, which is very low, so they are considered to be weak acids.
2. Amides are very weak bases in comparison to amines.
3. Because in the case of amine lone pair of electron on nitrogen$\left(\mathrm{N}\right)$ can be easily donated to electron-deficient species like proton, but for amides, lone pair on nitrogen is in conjugation with adjacent carbonyl, so its less available for donation, and hence amides are less basic than amines.
4. Hence amides are much more acidic than amines
5. However, when compared with esters, aldehydes and ketones, amides are much stronger bases.
6. Because in the case of esters lone pair of electrons are on oxygen which is more electronegative than nitrogen and hence esters have less tendency to donate lone pair.
7. So, amides are more basic than esters. In the case of aldehydes and ketones, no lone pair is available for donation and hence are less basic than amides.
8. Reaction where amide behaves as an acid: Reaction of acetamide$\left({\mathrm{CH}}_3{\mathrm{CONH}}_2\right)$ with sodium.

9. Reaction where amide behaves as a base: Reaction of acetamide$\left({\mathrm{CH}}_3{\mathrm{CONH}}_2\right)$ with hydrogen chloride$\left(\mathrm{HCl}\right)$

10. Thus we can say that amides can behave as acid as well as a base depending on the substrate we have.