Ullmann Diaryl Ether Synthesis in Ionic Liquids

Abstract

Copper-catalyzed Ullmann diaryl ether synthesis has been successfully demonstrated in ionic liquids as reaction media. The copper catalysts immobilized in ionic liquid media can be reused. Product isolation can be achieved via simple extraction using organic solvents.

Key words

Ullmann diaryl ether synthesis - copper catalysts - ionic liquids - aryl halides - phenols

References

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• 4b

  See ref. [2a]

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• 7b

  Presumably, tetraalkylammonium salts, tetraalkyl-phosphonium salts and 1-alkylpyridinium salts with melting points below the reaction temperature can also be used.

• Recently the in situ formation of N-heterocyclic carbene complexes of palladium were identified when 1-n-butyl-3-methylimidazolium-based ionic liquids (bmiX, X = Br, BF₄) were employed in Heck reaction. See:
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11

Representative Experimental Procedure: In a sealed vial, a mixture of phenol (188.2 mg, 2 mmol), p-iodobenzonitrile (458 mg, 2 mmol), NaO-t-Bu (192.2 mg, 2 mmol) and CuI (38.2 mg, 0.2 mmol) in 1 mL of bmiI ionic liquid was heated at 110 °C with vigorous stirring overnight. The reaction mixture gave light brownish color. The product was extracted using 2:1 hexanes/EtOAc (3×) and was purified through a short silica gel column.

12

Investigations on recylcing of bmiX ionic liquids are in progress.