Green metrics in Mechanochemistry

The development of new green methodologies and their broader adoption for promoting sustainable development in chemistry laboratories and industry play a significant role in society, due to the economic importance of chemistry and its and widespread presence in everyday life. Therefore, a sustainable approach to chemistry contributes to the well-being of worldwide population and comply with the United Nations Sustainable Development Goals (UN SDGs) and the European Green Deal. The review highlights how mechanochemical methods in batch and in continuous are an eco-friendly approach for organic synthesis, with a lower environmental footprint in most cases, compared to solution-based procedures. The assessment is objectively based on the use of green metrics (e.g. atom and real atom economy, E-factor, Process Mass Intensity, Material Parameter Recovery, Eco-scale, Stoichiometric Factor, etc.) and indicators (e.g. DOZN tool and Life Cycle Assessment, LCA, studies) applied to organic transformations such as synthesis of amide bond, carbamates, heterocycles, Active Pharmaceutical Ingredients (APIs), porphyrins, Porous Organic Polymers (POPs), metal- or acid-catalysed processes, multicomponent and condensation reactions, rearrangements, etc. The generalized absence of bulk solvents, the precise control over the stoichiometry (i.e., using agents in a stoichiometrically rather than in excess), and the more selective reactions enabling simplified work-up procedures are the distinctive factors marking the superiority of mechanochemical processes over solution-based chemistry.