Synthesis of Nipagin Esters Using Acidic Functional Ionic Liquids as Catalysts

Abstract

Several Brønsted acidic functional ionic liquids (FILs) with an alkane sulfonic acid group were synthesized. These FILs as dual solvent-catalysts for Nipagin esterification reactions were investigated. The results indicated that [HSO₃-pMIM]HSO₄ has the best catalytic activity and recyclability among the various kinds of FILs investigated, and its structure was characterized by infrared and NMR. The [HSO₃-pMIM]HSO₄ could be easily separated from the reaction mixture and reused without noticeably decreasing the catalytic activity.

Keywords:

• Acidic functional ionic liquids
• catalysis
• Nipagin ester
• synthesis

ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China (30571463) and the Natural Science Foundation of Shandong Province (Y2005B07).

Notes

^a Benzene as water-segregated reagent.

^b Double the amount of reactants.

^a Double the amount of reactants.

^a Ester 1 = ethyl Nipagin, the reaction condition: n _acid:n _alcohol: n _cat = 1:3.0:0.15, 85–100 °C, 3 h.

^b Ester 2 = butyl Nipagin, the reaction condition: n _acid:n _alcohol: n _cat = 1:3.0:0.10, 125–135 °C, 3 h.

^c Ester 3 = octyl Nipagin, the reaction condition: n _acid:n _alcohol: n _cat = 1:3.0:0.10, 130–140 °C, 3 h.