Preparation of Alkyl Aryl Ethers
49
indicate that deactivated phenols are more active and selective for O-alkylation
Entry 6). Introduction of an electron-donating substituent on the aromatic ring
(
substantially decreases the reaction rate (Entry 7). Alkyl iodides react more readily
than bromides, with chlorides being still less reactive.
In conclusion, the present procedure using a basic (pH ¼ 9.3) and easily avail-
able ionic liquid [bmIm]OH provides an efficient and convenient procedure for the
O-alkylation of phenols without requiring any other base and organic solvent. This
method offers marked improvements with regard to operational applicability,
high isolated yields of products, and greenness of procedure, avoiding hazardous
organic solvents and toxic catalysts, and thus, it provides a facile and practical
procedure for the preparation of alkyl aryl ethers. In addition, it turned out that
[bmIm]OH could be reused up to six times after recovery with unchanged activity.
Experimental
Yields refer to pure isolated products. All compounds are known and were characterized by compar-
ison of their physical and spectroscopic data with those of authentic samples. The IL [bmIm]OH was
prepared according to Ref. [13].
Preparation of Alkyl Aryl Ethers
ꢁ
Alkyl halide (10 mmol) was added to a mixture 10 mmol phenol in 10mmol [bmIm]OH at 70 C, and
the reaction mixture was stirred for 2 h until completion of reaction (TLC). The reaction mixture was
3
3
extracted with 15 cm ethyl acetate. The extract was washed with 5 cm H O, dried, and evaporated.
2
The crude product was purified by column chromatography over silica gel providing the pure product
3
Table 1). The ionic liquid left in the reaction vessel was mixed with 10cm ether containing 1% HBr,
(
ꢁ
decanted, and heated at 80 C under vacuum for 30min. The resulting ionic liquid, 1-butyl-3-methy-
limidazolium bromide, was converted to the base according to Ref. [13]. The recovered ionic liquid
was reused six times with consistent activity.
References
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1] March J (1992) Advanced Organic Chemistry, 4th edn. John Wiley & Sons Inc
2] Green TW, Wuts PGM (1991) Protective Groups in Organic Synthesis. Wiley, New York
3] Breslow R, Groves K, Mayer MU (2002) J Am Chem Soc 124: 3622
4] Heers J, Bockx LJJ, Mostmans JH, Van Cutsem J (1979) J Med Chem 22: 1003
5] McKillop A, Fiaud JC, Hug RP (1974) Tetrahedron 30: 1379
6] Dehmlow EV, Dehmlow SS (1993) Phase Transfer Catalysis, 3rd edn. Wiley-VCH Verlag GmbH
7] Kornblum N, Berrigan PJ, LeNoble (1963) J Am Chem Soc 85: 1141
8] Kornblum N, Seltzer R, Haberfield P (1963) J Am Chem Soc 85: 1148
9] Welton T (1999) Chem Rev 99: 2071
[10] Hussey CL (1988) Pure Appl Chem 60: 1763
[11] Earle MJ, Seddon KR (2000) Pure Appl Chem 72: 1391
[12] Li J, Peng Y, Song G (2005) Catal Lett 102: 159
[13] Ranu BC, Banerjee S (2005) Org Lett 17: 3049