Nucleophilic Opening of the Oxirane Ring with Tetraalkylammonium Salt Anions in the Presence of Proton Donors

The behavior of tetraethylammonium salts in nucleophilic opening of the oxirane ring of epichlorohydrin (ECH) in the system ECH–proton donor–Et4N+ X–, where proton donor is benzoic acid or 4-nitrophenol and X = PhCOO or NO3, was studied by the kinetic and spectrophotometric methods. The order of the reaction in tetraethylammonium salt, benzoic acid, and 4-nitrophenol was estimated as first, zero, and less than zero, respectively. The mechanism of nucleophilic opening of the oxirane ring of ECH was elucidated on the basis of monitoring of the accumulation of 4-nitrophenoxide ion in the system ECH–4-nitrophenol–Et4NX upon variation of the initial concentrations of both tetraethylammonium salt and proton donor (4-nitrophenol) itself. The anion X of the initial tetraethylammonium salt was found to be irreversibly consumed as a result of its attack on the oxirane ring with participation of the proton donor, which led to generation of tetraethylammo­nium 4-nitrophenoxide, and the latter catalyzed the subsequent formation of the final product. An increase in the concentration of 4-nitrophenol was accompanied by reduction of both the rate of formation of 4-nitrophenoxide ion and the overall reaction rate, which corresponds to a mechanism involving nucleophilic attack of the anion X on the oxirane ring that is not activated by the proton donor.