Advancements in Photochemistry and Flow Systems for Synthesis and Analysis

Abstract

This dissertation explores the integration of photochemistry with flow systems, demonstrating significant advancements in organic synthesis, nanomaterial production, and quantitative analysis. The research encompasses four key areas: reduction of nitro compounds with a heterogeneous catalyst in a flow system, development of a flow actinometer, scalable synthesis of silver nanoparticles (AgNPs) in flow, and selective semi-oxidation of tetrahydroisoquinoline (THIQ). The second chapter investigates the catalytic reduction of nitro compounds to amines using palladium nanoparticles supported on glass wool (Pd@GW) under flow conditions. This work demonstrates the potential of heterogeneous catalysis in flow systems for efficient and selective organic transformations, highlighting the advantages of continuous-flow processes in terms of reaction control and scalability. The third chapter addresses a critical gap in flow photochemistry by developing a simple Norrish Type II actinometer based on valerophenone photochemistry. This tool enables accurate measurement of light absorption in flow systems, a parameter often overlooked in photochemical reactions. The actinometer's design allows for easy implementation in organic chemistry laboratories, facilitating more rigorous and comparable studies in flow photochemistry. The fourth chapter focuses on the scalable synthesis of AgNPs using flow photochemistry. Various Norrish Type I photoinitiators are evaluated for their efficiency in reducing silver ions to nanoparticles. The flow system allows for rapid, continuous production of AgNPs with controlled size and morphology, demonstrating the potential for industrial-scale synthesis of nanomaterials through photochemical methods. In the fifth chapter, the selective oxidation of THIQ to dihydroisoquinoline (DHIQ) is achieved through a singlet oxygen-mediated process. Utilizing both homogeneous (Ru(bpy)₃Cl₂) and heterogeneous (RuB@GW, MoCo@GW) catalysts, the reaction demonstrates exceptional selectivity due to the vastly different singlet oxygen quenching rates of THIQ and DHIQ. The use of glass wool-supported catalysts facilitates easy separation and reusability while being compatible with flow systems. Collectively, these studies display the synergistic benefits of combining photochemistry with flow systems and heterogeneous catalysis. They demonstrate improved reaction efficiency, enhanced control over reaction parameters, and potential for scalability across various chemical processes. The use of visible light, recyclable catalysts, and in some cases molecular oxygen as an oxidant aligns with green chemistry principles. These advancements open new pathways for more sustainable and efficient chemical manufacturing processes, from organic molecule synthesis to nanomaterial production.