Extraction of phenolic compounds with [omim] BF₄ ionic liquid

[omim] BF₄ ionic liquid synthesized with water-bath microwave method was selected as extractant to extract separately seven kinds of phenolic compounds, such as phenol, o-cresol and others. The effects of extraction time and temperature, phase ratio and pH of the aqueous solution of phenolic compounds on the extraction equilibrium were discussed. Results show that extraction equilibrium can reach within 10 minutes, and with increasing extraction temperature or decreasing the volume ratio of [omim] BF₄ ionic liquid to aqueous phase, the distribution coefficient decreases gradually. The extraction efficiency is higher when phenolic compounds are in molecular form which happens when the pH value of the aqueous solution of phenolic compound is smaller than its pKα value. The distribution coefficients of phenolic compounds between water and [omim] BF₄ are in the same order of that between water and [bmim] PF₆ or other conventional organic solvents. Meanwhile, the extraction mechanism of phenolic compounds with [omim] BF₄ ionic liquid was investigated. It was found that during extraction, hydrogen bonds are formed between the fluorine of the [omim] BF₄ and the hydroxy of the phenolic compounds.