Development of a scalable photochemical reactor for syntheses of fine chemicals.

This study is in the area of sustainable chemical technology and is ultimately aimed at developing a novel generic approach towards efficient, clean, safe and scalable synthesis of important intermediates for pharmaceutical applications and catalysis using non-thermal activation of chemical bonds. Current study is focused on molecular activation by light, specifically addressing the class of singlet oxygen reactions. A laboratory-scale annular recirculating photoreactor and a scalable microreactor unit were designed, assembled and tested in oxygenation of α-pinene and stereoselective oxygenation of homoallylic alcohols by the photogenerated singlet oxygen. Efficiencies of light utilization and the quantum yields of the reactions for different sources of light in various lamp-reactor geometries were quantified using actinometry. It was shown that optimal thickness of the reaction layer, high intensity of light and elevated oxygen pressures in continuous gas-liquid segmented flow are crucial for both safe and efficient oxygenation. This study proved the viability of a novel concept of compact reactors with embedded light emitting diodes. Finally, a methodology of efficient oxyfunctionalization of allylic compounds was developed. Following the developed methodology, the applicability of functional nanomaterials based on pure and dye-modified porous silicon as heterogeneous photo sensitizers of singlet oxygen was studied in detail. It was demonstrated that the photosensitizing efficiency of all the samples is much lower than that of conventional dye photosensitizers. Low activity of the novel photosensitizers was attributed to quenching of the photogenerated singlet oxygen by the surface quenching groups of porous silicon, low quantum yield of photoluminescence in the case of pure porous silicon and to thermodynamically favorable quenching of the photoexcited porphyrin states due to energy/electron transfer to silicon nanocrystals in the case of dye modified porous silicon