Chapter 23: Aryl Halides

Addition Reactions of Benzyne

Summary

• The strained triple bond in benzyne makes it reactive towards addition reactions.
• Additions of H₂O and NH₃ are commonly encountered are a result of the methods of formation (see above).
• Substituted benzynes can also be formed, where the subsequent addition reaction typically gives mixtures of products:

• Diels-Alder reactions of Benzyne
• Addition reactions of Alkynes and Alkenes

MECHANISM OF THE ADDITION OF AMMONIA TO BENZYNE
Step 1: The N in amide functions as the nucleophile and attacks the reactive triple bond C in benzyne creating the new C-N bond and an intermediate carbanion.
Step 2: An acid/base reaction. Rapid protonation of the reactive carbanion from the ammonia forms the aniline and anotheer molecule of the amide ion.

© Dr. Ian Hunt, Department of Chemistry