The synthesis of various amides has been realised avoiding the use of any organic solvent from activation of carboxylic acids with CDI to isolation of the amides. Mechanochemistry was the key point of the process allowing rapid formation of the amide bond and efficient water-based purification of the final products.
Acylation reactions are ubiquitous in the synthesis of natural products and biologically active compounds. Unfortunately, these reactions often require the use of large quantities of volatile and/or toxic solvents, either for the reaction, purification or isolation of the products. Herein we describe and discuss the possibility of completely eliminating the use of organic solvents for the synthesis, purification and isolation of products resulting from the acylation of amines and other nucleophiles. Thus, utilisation of N,N'-carbonyldiimidazole (CDI) allows efficient coupling between carboxylic acids and various nucleophiles under solvent-free mechanical agitation, and water-assisted grinding enables both the purification and isolation of pure products. Critical parameters such as the physical state and water solubility of the products, milling material, type of agitation (vibratory or planetary) as well as contamination from wear are analysed and discussed. In addition, original organic-solvent-free conditions are proposed to overcome the limitations of this approach. The calculations of various green metrics are included, highlighting the particularly low environmental impact of this strategy.
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