Ionic liquids are finding a wide range of applications from reaction media to separations and materials processing. In order to provide larger quantities of ionic liquids, a sustainable synthesis method is needed which includes optimization of the separation of the reaction mixture, possibly using thermal methods. Here, the experimental vapor-liquid equilibrium (VLE) involved in the synthesis of a model ionic liquid, 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) from 1-bromohexane and 1-methylimidazole in acetone has been performed at 1.01325 bar using a modified Othmer still. The binary systems involving solvent and reactants, acetone/1-bromohexane and acetone/1 -methylimidazole, possessed fairly wide equilibrium envelopes. The binary systems involving the ionic liquid, acetone/[HMIm][Br], and 1-methylimidazole/[HMIm][Br],were also measured and found to have no detectable trace of ionic liquid in the vapor phase (dew points) as expected. Isobaric liquid-liquid equilibrium (LLE) was performed for the partially miscible system of 1-bromohexane/[HMIm][Br] where 1-bromohexane was found to be moderately soluble in the IL-rich phase, but the IL is virtually insoluble in the 1-bromohexane phase. As the binary system, 1-bromohexane/1-methylimidazole reacts rapidly under the temperatures of interest, the UNIFAC activity coefficient model was used to predict the binary VLE data. All experimental data were well-correlated by the Peng-Robinson equation of state with van der Waals one-parameter mixing rule (PR-EoS VDW-1) and the non-random two liquid (NRTL) activity coefficient method. (C) 2013 Elsevier B.V. All rights reserved.