Containerless reaction monitoring in ionic liquids by means of Raman microspectroscopy

Reaction monitoring by Raman microspectroscopy in levitated room temperature ionic liquid (RTIL) droplets is reported. Due to their non-volatility, RTIL droplets are well-suited to act as wall-less microreactors. The droplets were produced by a piezoelectric flow-through microdispenser connected to an automated flow injection system and were levitated by an acoustic trap. Taking advantage of the flow system versatility, the sequence of reagents was easily changed to study a model organic reaction: the Knoevenagel condensation. The reaction was followed by Raman microspectrometry and the obtained spectra were analysed using multivariate curve resolution to retrieve the concentration profiles and pure spectra of reactants, intermediates and products involved in the reaction. In addition, information about solvation interactions was obtained by monitoring the desolvation process taking place when a volatile co-solvent evaporated from the droplet.