Electron impact studies. CXXII. A comparison of reactivities and decompositions of benzoate anions and cations.

The benzoate anion reacts with acetic anhydride to yield an intermediate which decomposes by loss of ketene with accompanying proton transfer. The proton transfer is involved in the rate- determining step of the elimination reaction. The abundance of the product ion in the reaction of RC6H4CO2- with acetic anhydride increases as the electron-donating properties of R increase. Collision-induced charge stripping of the ions RC6H4CO2- yields the corresponding cations which fragment primarily by elimination of CO2 (or O+CO). Fragmentation through the carboxyl centre precedes the fragmentation of R (e.g. when R = Me, MeO, Cl or Br).