The application of microemulsion systems as switchable reaction media for the rhodium-catalyzed hydroformylation of 1dodecene is being reported. The influence of temperature, phase behavior, and the selected nonionic surfactant on the reaction has been investigated. The results revealed that the structure and the hydrophilicity (degree of ethoxylation) of the applied surfactant can have a strong impact on the performance of the catalytic reaction in microemulsion systems, in particular on the reaction rate. The surfactant determines the boundary conditions for catalysis (interfacial area, local concentrations) and can also interact with the catalyst at the oil−water interface and hinder the reaction. In addition to the discussion of the experimental results, we present a proposal for the impact of surfactantbased reaction media on the reaction mechanism of the catalyst reaction.
Catalysis, particularly metal-catalyzed reactions in microemulsion systems, offers a sustainable approach for organic reactions in water. However, it is still a challenging task because of the complex role of the nonionic surfactant in such a system and the interaction of the phase behavior and reaction performance. To get a profound knowledge of this role and interaction, a systematic study of the palladium-catalyzed hydroxycarbonylation of 1-dodecene in a microemulsion system is reported. The influence of the temperature, additives such as cosolvents, the catalyst concentration, and the hydrophilicity of the surfactant and its concentration has been investigated with regard to both the phase behavior and reaction performance. Interestingly, the investigations reveal that not the phase behavior of the microemulsion system but mainly the dimension of the oil–water interface and the local concentrations of the substrates at this interface, which is provided by the amount and hydrophilicity of the surfactant, control the reaction performance of hydroxycarbonylation in these systems. Moreover, it was found that the local concentration of the active catalyst complex at the interface is essential for the reaction performance. Dependent on the surface active properties of the catalyst complex, its bulk concentration, and the nature and amount of additives, the local concentration of the active catalyst complex at the interface is strongly influenced, which has a huge impact on the reaction performance.
The implementation of homogeneous catalysis in industry is still a challenging task due to the recycling of the mostly expensive catalyst complexes. The application of a liquid two-phase systems provides a viable approach to overcome this issue. Hereof, systematic lab investigations and the transfer to a continuously operated mini-plant for the palladium catalyzed methoxycarbonylation of 1-dodecene are presented (reaction volume scale up factor: 19). Under optimized reaction conditions, a yield of 92% to the corresponding ester was achieved after a reaction time of 20 h in lab-scale experiments. 97% of the product was located in the nonpolar phase and the catalyst was quantitatively immobilized in the polar phase. Subsequently, the proof of concept has been successfully carried out in a mini-plant, which was continuously operated over 100 h. The reaction performance in the mini-plant with a yield of esters of 83.5% and a chemo-selectivity of 91.2% was found to be comparable with the lab experiment. The catalyst leaching was permanently kept below 25 ppb, which validates the previous findings of the lab experiments. The catalyst remains stable and the formation of palladium black was prevented during the entire operation. By comparing lab and mini-plant results, a significant influence of the catalyst preformation process and the mini-plant operation mode on reaction rate and selectivity is identified.
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