Aromatic Substitution Reactions between Ionized Benzene Derivatives and Neutral Methyl Isocyanide

Aromatic substitution reactions of selected ionized benzenes derivatives (chlorobenzene, nitrobenzene, dimethylphtalates) and phenoxy cation using neutral methyl isocyanide as a nucleophile are shown to efficiently occur in the gas phase. Nitrilium ions are produced in high abundance during these processes. These reactions have been performed in the hexapole collision cell of a large-scale hybrid tandem mass spectrometer. Computed 298 K enthalpy diagrams at the B3LYP/6-31+G(d,p) level of theory confirm the exothermic formation of the N-methylbenzonitrilium ions starting with ionized chloro- and nitrobenzene molecular ions. In this last case, two other exothermic processes are also detected: (i) an oxygen atom transfer yielding ionized nitrosobenzene and neutral methyl isocyanate and (ii) a loss of carbon monoxide from the ion/molecule reaction product generated when metastably generated phenoxy cations (produced in the hexapole collision cell) react with methyl isocyanide. Using extended theoretical calculations, several reaction pathways have been derived. The behavior of the three isomeric dimethyl phthalates has been investigated in the same way.