Titanium dioxide photocatalysis: An assessment of the environmental compatibility for the case of the functionalization of heterocyclics

The environmental burden associated with some functionalization reactions of nitrogen-heteroaromatics via TiO2 (solar) photocatalysis is compared with the same reactions under thermal conditions. Two methods, LCA (Life Cycle Assessment) and EATOS (Environmental Assessment Tool for Organic Synthesis), both based on a detailed analysis of the experiments, are used for the assessment. The thermal processes are consistently evaluated to give a better environmental performance. Photocatalysis is disfavored by the required management of a large amount of excess reagent and solvent involved. Still the good yield and simplicity of the photocatalytic method are promising (and are positively evaluated by a third assessment, EcoScale). The precautions for making photocatalytic syntheses environmentally viable are discussed.