Aminocatalysts are More Environmentally Friendly than Hydrogen-Bonding Catalysts

The importance of asymmetric organocatalysis in contemporary organic synthesis is widely acknowledged. However, there are practically no data on the environmental safety of organocatalysts, although this aspect is crucial for the sustainability of all new materials, chemicals, and technologies. To start to fill this data-gap, a library of 26 organocatalysts containing hydrogen-bonding catalysts [(thio)ureas and squaramides] and aminocatalysts (primary or secondary amines) was evaluated for their toxicity using the naturally luminescent Vibrio fischeri bacteria (ISO assay; one of the most widely used ecotoxicity tests). Thioureas and squaramides were shown to be relatively toxic: none of them was ranked as "not harmful" (i. e., half maximal effective concentration EC₅₀ >100 mg L^-1 ), whereas the presence of the trifluoromethyl moiety increased their toxic effect. Importantly, the aminocatalysts, whose EC₅₀ values ranged from 25 to >300 mg L^-1 , could be considered remarkably more environmentally safe or green alternatives.