The Synthesis of Asymmetrical Tertiary Alkyl Ethers Catalyzed by Ionic Liquids with and without CO2.

The synthesis of a series of asymmetrical tertiary alkyl ethers from the etherification of tertiary alkyl alcohols with corresponding alcohols was investigated. Ionic liquids (ILs) with Brønsted acidity, [BsMIm][HSO4] (1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate) and [BMIm][HSO4] (1-butyl-3-methylimidazolium hydrogen sulfate), were found to be suitable catalysts for the reactions. Tertiary alkyl ethers including MTBE (methyl tert-butyl ether), ETBE (ethyl tert-butyl ether), IPTBE (isopropyl tert-butyl ether), TAME (tert-amyl methyl ether), and TAEE (tert-amyl ethyl ether) could be produced. Effects of reaction temperature, reaction time, and amount of the catalyst used on the synthesis of the MTBE were investigated. The conversion of TBA (tert-butyl alcohol) and the selectivity of MTBE could reach 69.9 % and 77.4 %, respectively at 393 K as the molar ratio of TBA: Methanol: [BMIm][HSO4] was 20:20:1. The reaction mixture splited into two phases after reaction, and the IL could be separated from the products simply by decantation and could be reused. CO2 could enhance the conversion of TBA and the selectivity of MTBE significantly at suitable pressures.