Comparison of greenness and whiteness of selected mechanochemical and solution-based reactions using a new RGBsynt model

Abstract

In analytical chemistry, the idea of assessing the “whiteness” of a method, which refers to the RGB model used in colour coding, has gained significant popularity in recent years. Whiteness represents the overall evaluation, which includes greenness (environmental impact) and functional features, represented by redness (analytical efficiency), and blueness (practicality). This work presents the first whiteness assessment model dedicated to chemical synthesis, called “RGBsynt”, inspired by the metrics used in analytics. The assessment may be applied to a set of 2–10 methods, described by parameters such as yield, product purity, E-factor, ChlorTox, time-efficiency and energy demand, which refer to the three primary colours. The model is implemented in an easy-to-use Excel spreadsheet where users input the values of the mentioned parameters, and then data analysis, evaluation and results visualization are carried out fully automatically. The RGBsynt model was employed to compare 17 solution-based procedures for O- and N-alkylation, nucleophilic aromatic substitution, and N-sulfonylation of amines with their corresponding 17 mechanochemical alternatives. The selection of synthesis processes was preceded by a thorough literature review to ensure representative examples and reliable comparison of methods. The evaluation results clearly indicate the superiority of mechanochemistry, both in reducing environmental impact (greenness), and in overall potential (whiteness). The RGBsynt model might be considered as a simple and useful tool for evaluating synthesis methods, allowing comparison of various reactions based on empirical data.