11.10 Reactions of Arenes: A Preview

1. 11.10Reactions of Arenes:A Preview 1. Some reactions involve the ring. 2. In other reactions the ring is a substituent.

2. 1. Reactions involving the ring a) Reduction Catalytic hydrogenation (Section 11.4) Birch reduction (Section 11.11) b) Electrophilic aromatic substitution (Chapter 12) c) Nucleophilic aromatic substitution (Chapter 23) 2. The ring as a substituent (Sections 11.12-11.17)

3. H H H H H H H H H H H H H H H H H H H H H H H H H H Reduction of Benzene Rings catalytic hydrogenation (Section 11.4) Birch reduction (Section 11.11)

4. 11.11The Birch Reduction

5. H H H H H H H H H H H H H H Birch Reduction of Benzene Product is non-conjugated diene. Reaction stops here. There is no further reduction. Reaction is not hydrogenation. H2 is not involved in any way. Na, NH3 CH3OH (80%)

6. H H H H H H • + Na+ • Na •• H H H H – H H Mechanism of the Birch Reduction (Figure 11.8) Step 1: Electron transfer from sodium +

7. H • OCH3 • •• Mechanism of the Birch Reduction (Figure 11.8) Step 2: Proton transfer from methanol H H H • •• H H – H

8. H •• • • OCH3 OCH3 • • •• •• Mechanism of the Birch Reduction (Figure 11.8) Step 2: Proton transfer from methanol H H H H H H • • •• H H H H – H H H –

9. H H H • + • Na H H H H Mechanism of the Birch Reduction (Figure 11.8) Step 3: Electron transfer from sodium

10. H H H • + • Na H H H H Mechanism of the Birch Reduction (Figure 11.8) Step 3: Electron transfer from sodium H – H H •• + Na+ H H H H

11. •• • OCH3 • H Mechanism of the Birch Reduction (Figure 11.8) Step 4: Proton transfer from methanol H – H H •• H H H H

12. •• • OCH3 – •• • • OCH3 • •• H H H H H H H H H Mechanism of the Birch Reduction (Figure 11.8) Step 4: Proton transfer from methanol H – H H •• H H H H

13. H H H H H H H H C(CH3)3 H C(CH3)3 H H H Birch Reduction of an Alkylbenzene Na, NH3 If an alkyl group is present on the ring, it ends up asa substituent on the double bond. CH3OH (86%)