The Interaction of Methyl Formate with Proton-Bound Solvent Clusters in the Gas Phase and the Unimolecular Chemistry of the Reaction Products

Ion–molecule reactions between neutral methyl formate (MF) and proton-bound solvent clusters W2H+, W3H+, M2H+, E2H+, and E3H+ (W = water, M = methanol, and E = ethanol) showed that the major reaction product is a solvent molecule loss from the initial encounter complex, followed by the formation of protonated methyl formate (MFH+). Collision-induced dissociation breakdown curves of the initially formed solvent-MF proton-bound pairs and trimers were obtained as a function of collision energy and modeled to extract relative activation energies for the observed channels. Density functional theory calculations (B3LYP/6-311+G(d,p)) of the solvent loss reaction were consistent with barrierless reactions in each case. The MF(M)H+ ion also exhibited loss of CH4 at higher collision energies. The reaction was calculated to proceed via the migration of the MF methyl group to form a loosely bound complex between neutral CH4 and an ion comprising (CH3OH)(CO2)H+. Overall, the results indicate that the interaction of methyl formate with atmospheric water can form stable encounter complexes that will dissociate to form protonated methyl formate.