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.

We present a crystallographic and computational study of three hydantoin-based active pharmaceutical ingre-dients�nitrofurantoin, furazidin, and dantrolene�aimed at identifying factors resulting in different propensities of these compounds to form polymorphs, hydrates, solvates, and solvatehydrates. This study is a continuation of our research toward understanding how small structural differences in closely related compounds affect their propensity to form different crystal phases, as all three compounds contain an imidazolidine-2,4-dione scaffold and a N-acyl hydrazone moiety and all form multiple crystalline phases. Crystallographic and computational analysis of the already known and newly obtained nitrofurantoin, furazidin, and dantrolene crystal structures was performed by dissecting the properties of individual molecules and searching for differences in the tendency to form hydrogen bonding patterns and characteristic packing features. The propensity to form solvates was found to correlate with the relative packing efficiency of neat polymorphs and solvates and the ability of molecules to pack efficiently in several different ways. Additionally, the differences in the propensity to form solvate-hydrates were attributed to the different stability of the hydrate phases.