Acid-base Reactions Induced by a Plasma Phase on Liquid Targets : Bronsted Acidity and Oxo Synthesis

The interactions between liquid targets and plasmas provided by a d.c. point-to-plane corona device operated under p = 1 atm. are considered in terms of both Bronsted and Lewis acid-base reactions. The treatments of aqueous solutions by the chargeless species of air or NH3 plasmas increase the Bronsted acidity of the target, and for an air plasma, the pH decrease is a linear function of the quantity of electricity involved in the discharge. The simplified model proposed for these water-plasma interactions involves water vapour and singlet oxygen. Analytical applications are also developped to determine the area treated by the activated neutrals, with respect to the operating conditions. The treatment of liquid olefins by a CO + H2 plasma under corona conditions illustrates the Lewis acid-base character of the relevant plasma, and leads to the formation of carbonylated compounds.