REACTIONS OF PROTONATED ACETIC-ACID CLUSTERS (CH3COOH)(N)H+ (N=1-3)

Reactions of(CH3COOHH+ (n = 1-3) with a series of base molecules B were studied using a selected ion dow tube. All the reactions observed proceed at near gas kinetic collision rates for bases having higher proton affinities than acetic acid. Different reaction channels are observed with increasing proton affinity of the neutral: association and proton transfer for the proton-bound monomer; association, ligand switching and proton transfer for the dimer; association, ligand switching, switching with solvent evaporation and proton transfer for the trimer. A thermochemical comparison of the appearance enthalpy and free energy for proton transfer from (CH3COOHH+ and (C2H5OHH+ established that both sets of reactions take place by forming BH+ with evaporation of three monomeric units (of acetic acid or ethanol, respectively) rather than evaporation of neutral dimers. Proton transfer from (CH3COOHH+ is fast provided that the reaction is exothermic; proton transfer from (CH3COOHH+ is fast even if the reaction is endothermic (but exergonic).