Kinetics of single- and two-phase synthesis of the ionic liquid 1-butyl-3-methylimidazolium chloride

The kinetics of the synthesis of the ionic liquid 1-butyl-3-methylimidazolium chloride (IL) from 1-methylimidazole (MIM) and 1-chlorobutane (Cl-Bu) were studied in a batch reactor. For a MIM-conversion >8%, neat synthesis leads to two phases either rich in IL or Cl-Bu, whereby MIM is soluble in both phases. Addition of ethanol (>20 vol%) leads to a single-phase synthesis and to an increase of the effective rate constant by IL-formation (salt effect). The agreement of the measured and calculated synthesis progress is sufficient in both cases; modelling is based on the experimentally determined thermodynamic and kinetic data. Surprisingly, the rates of single-phase (20 vol% ethanol) and (stirred) two-phase synthesis are almost the same which is the result of the counterbalance of the salt effect (favouring single-phase synthesis) and the higher reactant concentrations (favouring neat synthesis). So for industrial production, the latter synthesis mode is advantageous, as solvent separation is not required. Finally, with respect to a continuous synthesis, the (neat) synthesis was successfully conducted in a tubular reactor.