Question

Are anhydrides highly reactive?

Answer 1

Anhydride:

1. In organic chemistry, anhydrides are organic compounds that contain a functional group $(-\mathrm{CO}-\mathrm{O}-\mathrm{CO}-)$.
2. Example: Acetic anhydride $({\mathrm{CH}}_3-\mathrm{CO}-\mathrm{O}-\mathrm{CO}-{\mathrm{CH}}_3)$.

Explanation:

1. Anhydrides come under the class of carbonyl compounds.
2. Carbonyl compounds are electrophilic.
3. Since in the carbonyl moiety, carbon is attached to oxygen and oxygen is more electronegative than carbon, so oxygen withdraws electron density from carbon, thus carbon becomes electron-deficient, so it's susceptible to nucleophilic attack.
4. So, carbonyl compounds can be easily attacked by nucleophiles.
5. Anhydrides consist of two carbonyl groups linked via an oxygen atom.
6. When lone pair of electrons on oxygen is delocalized over one of the carbonyls, then oxygen has a positive charge and it withdraws electron density from the other carbonyl group attached to it via inductive effect making it much more electrophilic.
7. Also when the lone pair of electrons on oxygen is delocalized towards one carbonyl group and so the lone pair is not available for delocalization towards the second carbonyl group, then the second carbonyl group becomes much more electrophilic, thus enhancing the reactivity of anhydride towards nucleophiles.
8. So, yes, anhydrides are highly reactive.