Xylenes reflux, 30 mins Anthracene Maleic anhydride until 9,10-dihydroanthracene-9,10-a,B-succinic anhydride Melting point 260°C
The Correct Answer and Explanation is:
Correct Answer:
The reaction described is a Diels–Alder reaction between anthracene and maleic anhydride in xylene under reflux to form 9,10-dihydroanthracene-9,10-α,β-succinic anhydride, which has a melting point around 260°C.
Explanation
This is a classic example of a Diels–Alder cycloaddition reaction, which is a [4+2] cycloaddition between a conjugated diene and a dienophile. In this case, anthracene acts as the diene. Anthracene is an aromatic hydrocarbon made of three fused benzene rings. The 9 and 10 positions of anthracene are the most reactive for Diels–Alder reactions because forming a new six-membered ring at these positions preserves aromaticity in the outer rings while allowing temporary loss of aromaticity in the central ring.
Maleic anhydride is a strong dienophile due to the presence of two electron-withdrawing carbonyl groups. These groups pull electron density away from the double bond, making it more reactive towards electron-rich dienes such as anthracene.
The reaction typically takes place in a non-polar solvent such as xylene, and refluxing the mixture for about 30 minutes provides the energy needed to drive the reaction to completion. Under these conditions, the diene and dienophile react to form 9,10-dihydroanthracene-9,10-α,β-succinic anhydride, where a new six-membered ring is formed and the central ring of anthracene becomes non-aromatic.
The product is a bicyclic compound with an attached succinic anhydride group. It is a solid at room temperature and has a relatively high melting point around 260°C, indicating strong intermolecular forces and stability due to its rigid structure and potential for hydrogen bonding through the anhydride group.
This reaction is widely used in organic synthesis to form complex cyclic systems in a predictable and stereospecific manner, and it is commonly demonstrated in undergraduate chemistry labs.
