Metrics for green syntheses

Despite being introduced approximately 30 years ago, green metrics are still not widely implemented in the practice of Green Chemistry. Nowadays, there is a general desire and fashion for Green Chemistry considering the modern global concerns of climate change and resource scarcity. However, the scientific literature reveals a confusing array of definitions and methodologies related to green metrics, particularly in both organic and inorganic chemistry. In this review we want to focus on organic synthesis, namely new reaction pathways that employ organic and inorganic catalysts, grounded in fundamental chemistry. The application of rigorous green metrics must go along with the experimental validation of synthetic procedures. This is essential to establish clear guidelines for defining truly green synthetic approaches, and to prevent misunderstandings or overreaching claims that are based on subjective rather than objective assessments. This work originated from an IUPAC project aimed at providing standardized guidance for the use of green metrics. Accordingly, we present a list of green metrics and related terminology currently employed to assess material usage, energy efficiency, and environmental impact in individual reactions and synthetic strategies.