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

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.