Control of the formation and reaction of copper-oxygen/nitrogen monoxide adduct complexes in multiphase streams
Modern catalytic processes rely on efficient activation of gases such as oxygen for the atom-economic insertion into organic substrates which thus are further refined. The velocity of the mass transfer through the phase boundary is an essential key parameter for the efficiency of the whole reaction. Since the gas reacts on the liquid side, a competition between mass transfer and reaction can occur leading to a local depletion in reactand. In best case, the mass transfer is enhanced by the reaction consuming the gas. Until now, we have investigated the reactivity of copper bis(pyrazolyl)methane complexes with dioxygen and their catalytic oxygen transfer to phenols only in milligram scale in presence of excess oxygen. For the transfer to technical conditions, any information about the kinetics with equivalent amounts of oxygen and complicated substrate-mixing conditions are missing yet. Hence, for up-scaling of this mild and atom-economic catalysis reaction, a comprehensive analysis of all steps as well as a deeper understanding of the mass transfer through the boundary layer gas-liquid is required. A reaction-dependent mass transfer enhancement overlays the pure mass passage. This term has not yet been determined as well as the intrinsic kinetics which shall be analysed up to the millisecond regime in close collaboration with the research group Schindler who runs a stopped-flow-setup.For transferring of our model system into bubble-containing systems, we envision a stepwise transfer from the lab vessel via the T-channel and the superfocusmixer (mass passage liquid-liquid) to the Taylor-flow and the bubble swarm for the fundamental understanding of the mass transfer gas-liquid.In this project, we plan the further development of our consecutive reaction system as model reaction. By variation of the substituents (with feedback information from kinetic measurements) we adjust the reaction speed such that we can separately address different Hatta regimes. In the collaboration with the research groups Hlawitschka, Kraume, Schlüter and Rinke/Simon, a multidimensional analysis of the reaction with the working gas (oxygen, nitrogen monoxide) and the subsequent reaction is accomplished by measuring the concentration of starting compounds and products. Fluorescence spectroscopy is sensitive for the copper(I) complexes whereas the product complexes can be monitored by high-resolution high-speed shoots (intense purple colour) and Raman techniques. Raman spectroscopy enables the detection of all consecutive products. This allows to monitor the reaction in the bubble stream as well as the intrinsic kinetics within this lead experiment.