Ether synthesis from activated aromatic halides and alkali-metal carbonates

Abstract

Aromatic halides activated by an electron-withdrawing group at the ortho or para position has been found to react with alkali-metal carbonates or hydrogencarbonates at elevated temperatures to form ethers. The ether yield is markedly enhanced by catalysts such as silica and aluminium silicate. The rate of the etherification is dependent on the kind of activating groups 2Y–Ar–X + M₂CO₃→ Y–Ar–O–Ar–Y + 2MX + CO₂(Y = NO₂ > CN > ArSO₂ > ArCO), halides (X = F > Cl ≈ Br ≈ I) and alkali metals (M = K > Na > Li). Cuprous and cupric compounds act as cocatalysts with silica and further promote the reaction. The reaction of p-chlorobenzophenone with potassium carbonate or sodium carbonate to bis(4-benzoylphenyl) ether in the presence of silica or silica–cuprous oxide catalyst was investigated in detail and the reaction mechanism is proposed. The silyl ether formed from an aromatic halide and the silanol group on the surface of silica is presumed to be the intermediate of the etherification.