A green chemical synthesis of coumarin-3-carboxylic and cinnamic acids using crop-derived products and waste waters as solvents

Abstract

Crop-derived products, like juices obtained from edible fruits and vegetables, and waste waters deriving from agricultural and industrial processing have been recently exploited to efficiently promote several ‘classic’ and innovative synthetic organic reactions. Such a green chemical approach prevented the use of toxic, polluting, and hazardous materials and in the mean time allowed to increase the commercial values of crop products and industrial byproducts. Coumarin-3-carboxylic and cinnamic acids represent classes of naturally occurring and semi-synthetic compounds with interesting and promising pharmacological activities. In this Letter a new and improved methodology for the Knoevenagel condensation yielding the title compounds using juices from edible fruits and vegetables (lemon, grapefruit, carrot, pomegranate, kiwi, vinegar, tomato), liqueurs (limoncello), and waste waters (buttermilk and residues of olive processing) as solvents is described. Coumarin-3-carboxylic and cinnamic acids have been synthesized in excellent yields by ultrasound irradiation from differently substituted 2-hydroxybenzaldehydes, 2-hydroxyacetophenones, and benzaldehydes, and Meldrum’s acid as starting substrates. The findings described herein enforce the concept of the usefulness of products and byproducts derived from agriculture and food industry to accomplish green chemical processes.