Synthesis of Alkylphenyl Ethers in Aqueous Surfactant Solutions by Micellar Phase-Transfer Catalysis. 1. Single-Phase Systems

Abstract

Phase-transfer catalysis and micellar catalysis are two conventional methods of promoting reactions between lipophilic and hydrophilic reactants. Phase-transfer catalysis employs organic solvents that may be undesirable for both economic and environmental reasons, while application of micellar catalysis is limited by the relatively low solubilization capacities of surfactant solutions. Micellar phase-transfer catalysis is a process that combines the best aspects of both conventional methods while avoiding some of the associated problems. Reaction systems consist of reactants, water, surfactant and a phase-transfer catalystno organic solvent is used. The surfactant acts to solubilize and emulsify the lipophilic reactant, while the role of phase-transfer catalyst is to shuttle the hydrophilic reactant from the aqueous phase into the micellar environment where the reaction primarily takes place. Alkylation of phenol with 1-bromobutane was studied under phase-transfer, micellar, and micellar phase-transfer conditions in single-phase solutions at relatively high reactant loadings. Cationic (dodecyltrimethylammonium bromide), anionic (sodium dodecyl sulfate), and nonionic (dimethyldodecylamine oxide) surfactants were compared. Higher conversions with micellar phase-transfer catalysis over conventional micellar and phase-transfer catalysis were observed in nonionic and anionic surfactant systems. For cationic surfactant systems, no significant advantage was observed for micellar phase-transfer catalysis in comparison to conventional micellar catalysis. The effect of cationic surfactant concentration was studied and an optimum surfactant concentration was observed. Effects of initial reactant concentrations and two types of mixing were also studied. Mixing effects were significant, suggesting that mass transport rates of components between the aqueous and micellar pseudophases in these microheterogeneous systems at high reactant concentrations may affect reaction kinetics.