Phenol alkylation under phase transfer catalysis conditions: Insights on the mechanism and kinetics from computations

Abstract

• Additional phenol improves the partition equilibrium. • The RN4+PhO−(PhOH) complex reacts in the organic phase. • Higher aggregates may be involved for Et4N + and Pr4N+. Experiments reported in the literature involving alkylation of the phenol under phase transfer catalysis conditions support the formation of the RN 4 + PhO ― (PhOH) complex in the organic phase. This complex could be directly involved in the transition state. In the present theoretical study, the phase transfer catalyzed alkylation of phenol was investigated using M06-2X calculations and solvent effect using the SMD model combined with reliable experimental single-ion solvation free energy data in aqueous solution. The analysis was done for tetraethylammonium, tetrapropylammonium and tetrabutylammonium phase transfer catalysts. In the case of tetrabutylammonium ion, the calculations have predicted a reaction kinetics compatible with experimental data. In addition, the BuN 4 + PhO ― (PhOH) complex is calculated to be the active species in the catalysis. For the tetraethylammonium and tetrapropylammonium cations, both the RN 4 + PhO ― and RN 4 + PhO ― (PhOH) complexes are not able to explain the catalysis, suggesting that another more complex aggregate can be involved in the process.