Electron induced reactions of unsaturated hydrocarbons in water clusters

The reactions of gas-phase hydrated electron (H2O)n−, n < 75, with acrylic acid, methyl acrylate and vinyl acetate monomers are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The first reaction step is uptake of the reactant molecule with formation of a hydrated radical anion. The subsequent reaction steps, however, are remarkably different. With acrylic acid, products of the composition (C2H3COOH)m−, m ≤ 6, are observed, which are evidence for oligomerization. With methyl acrylate, uptake of a second molecule is followed by elimination of methanol, which is rationalized with the formation of a five-membered ring. Formation of hydrated hydroxide OH−(H2O)n happens to a small extent, which is evidence for the reduction of methyl acrylate to C2H4COOCH3. Only one molecule of vinyl acetate is taken up by the clusters. After longer reaction delays, cleavage of the molecule with formation of C2H3O−(H2O)n is observed, which occurs preferentially at n ≈ 10.

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► Hydrated electrons induce specific reactions in the gas phase.
► Hydrated acrylic acid radical anion initiates oligomerization of acrylic acid.
► Hydrated methyl acrylate radical anion undergoes radical addition to neutral methyl acrylate and subsequent 5-exo-trig cyclization with methanol elimination.
► Hydrated vinyl acetate radical anion undergoes cleavage of the central CO bond.
► Cleavage of vinyl acetate radical anion strongly depends on size of hydration shell.