EXPERIMENTAL-STUDY OF THE GAS-PHASE KINETICS OF REACTIONS WITH HYDRATED H3O+ IONS (N=1-3) AT 298-K

Flowing afterglow experiments are reported which follow the influence of stepwise hydration on the kinetics of proton transfer from the hydronium ion to H2S, CH2O, HCOOH, CH3OH, CH3CHO, C2H5OH, CH3COOH, HCOOCH3, (CH3)2O, (CH3)2CO, and NH3at 298 ± 2 K. Rate constants have been measured for the reactions of these molecules with H3O+-H2O, H3O+-(H2O)2, and H3O+-(H2O)3. The reactions were observed to proceed according to the general equation H3O+.(H2O)n+ B ⟶ BH+-(H2O)m+ (n — m + 1)H2O with 0≤m≤n, albeit product distributions could not be unraveled. Comparisons are made with the rate constants for the “nude” reactions involving H3O+. The reversal in the relative basicity of H20 and H2S upon hydration which can be deduced from known energetics of solvation is manifested by a sharp drop (by k 103) in the observed reaction rate constant for n = 1,2, and 3. For B = CH2O, equilibrium-constant measurements are reported which indicate a trend toward the equalization of the basicities of H2O and CH2O upon hydration with up to three water molecules. All of the hydrated H30+ ions are observed to react rapidly and irreversibly with the remaining, somewhat stronger, oxygen bases with k k 10-9cm3molecule-1s-1and decreasing slightly and monotonically with increasing hydration. Comparisons with calculated capture rate constants indicate that these reactions proceed with approximately unit probability. The intriguing possibility of generating polymeric water molecules from the reactions investigated is discussed briefly. © 1979, American Chemical Society. All rights reserved.