Lactic acid as an invaluable bio-based solvent for organic reactions

Lactic acid was used, for the first time, as a bio-based green solvent to promote some organic reactions, such as three-component reactions of styrenes, formaldehyde and an active phenolic compound or N,N-dialkylacetoacetamides, three-component reactions of diethyl acetylenedicarboxylate, anilines and aromatic aldehydes, aniline-catalyzed condensations between salicylaldehydes and diethyl acetylenedicarboxylate, and the synthesis of substituted quinolines through Friedländer annulation between 2′-aminoacetophenone and 1,3-dicarbonyl compounds. In these reactions, lactic acid solvent exhibited many advantages including bio-based origin, superior synthetic efficiency, ease of isolating the product and good recyclability of the reaction medium. The concept of using lactic acid as a green solvent not only enriches the diversity and versatility of bio-based green solvents, but also offers us an effective means for designing environmentally benign synthetic systems.