Stability of Quaternary Onium Salts under Phase-Transfer Conditions in the Presence of Aqueous Alkaline Solutions

Article abstract of DOI:10.1021/jo00366a022

The parameters that affect the stability of a series of quaternary ammonium and phosphonium salts R4M⁺Y^- under phase-transfer catalysis (PTC) conditions in a chlorobenzene-aqueous NaOH two-phase system have been defined.Quaternary ammonium salts are much more stable than phosphonium derivatives.When the quaternary cation R4M⁺ is the same, the stability is in the order I > Br^- >> Cl^-.It dramatically increases either by diminishing the concentration of the base in the aqueous phase (from 50percent to 15percent aqueous NaOH) or by adding to the heterogenous system a molarexcess of the corresponding inorganic salt NaY.In all cases the degradation reactions are found to proceed in the organic phase via extraction of OH^- as R4M⁺OH^-, interfacial phenomena being unimportant.As a consequence quaternary onium salts are stable in the presence of aqueous alkaline solutions provided that the extractability and/or the reactivity of OH(-) in the organic phase are minimized.