Phase Transfer Catalyzed Wittig Reaction in the Mitrotube Reactor under Liquid-Liquid Slug-Flow Pattern

摘要

Phase transfer catalysis (PTC) is an important method in synthetic two-phase chemistry. Stable liquid-liquid hydrodynamic flow in a microtube reactor offers considerable benefits over the conventional batch reactors. In this work, we attempted to conduct a two-phase organic solvent/aqueous sodium hydroxide solution PTC Wittig reaction of benzyltriphenylphosphonium bromide and o- and p-methoxybenzaldehydes in a microtube reactor under reproducible slug-flow pattern. Stable operating conditions and a defined specific interfacial area are crucial to study the interaction between kinetics and mass transfer effects. A strong impact of aqueous-to-organic (AO) phase volumetric flow ratio on the specific interfacial area and consequently on mass transfer between phases was observed. The increase of the specific interfacial area causes a higher overall reaction rate at the same residence time when 0.1 M sodium hydroxide solution was used, which confirms that mass transfer has an influence.on the overall reaction rate. Increasing the aqueous sodium hydroxide solution concentration at the organic-Water interface increased mass transport. At defined conditions, when the surface-to-volume ratio and concentration of OH- ions were adequate, reaction kinetics came to be the rate-limiting step.