A procedure for the assessment and optimization of the greenness of solvents in synthesis was developed. It involves two optimization components, aiming at the optimization of both the intrinsic greenness of the solvents and their efficiency to improve the overall green performance of the synthesis, evaluated with mass, energy and time greenness metrics. The procedure was tested in a study with educational purpose for assessing and improving the greenness of solvents used in the workup step of a ionic liquid synthesis that involves a solventless reaction step (1-hexyl-3-methylimidazolium chloride) and proved useful to systematize the aspects that should be considered to choose the solvents used in the workup. The results show that there may be a competition in the solvent choice between a safer solvent and a more hazardous solvent with better performance of the overall synthesis process, which requires optimization for reaching a balanced solution. The study illustrates the problems of the substitution of solvents in synthetic processes to improve greenness, as well as the importance of the utilization of a battery of greenness metrics for evaluation of the overall synthesis outcomes.

This article reports a study, performed in educational context, to increase the greenness of the extraction of R-(+)-limonene from orange peels. Protocols from the literature were evaluated with the green star (GS)metric and new protocols, based in them, were designed to increase the overall greenness. These were tested in the laboratory and their greenness was assessed by traditional greenness metrics and metrics inspired in the industrial activity. Results showed that the steam distillation technique presents the largest overall greenness when evaluated by the GS, because organic solvents are not involved, but mass and energy metrics indicate that the extractions by solvent techniques are greener. This conflict denotes the complexity of the concept of chemical greenness and the need of using several types of metrics when greenness evaluation is at stake. The results show that the inclusion of experiments on the R-(+)-limonene extraction in the educational laboratory is efficient to show the difficulties of assessing the greenness of chemistry and of implementing Green Chemistry.

This article reports a study to increase the overall greenness of chemical syntheses for first-year university laboratories. The separate evaluation of the micro-greenness of the three stages of synthesis (reaction, isolation and purification) using the Green Star (GS) was implemented and their respective contribution to overall greenness was investigated for two examples: syntheses of cobalt (III) tris(acetylacetonate) and potassium nitrilosulfonate. Results showed that the post-reaction (work-up) steps are the most problematic for overall greenness. Greenness optimization can be achieved by combining the greenest procedures for each step obtained from different protocols available in the literature.

New semi-quantitative metrics for simple evaluation of global greenness of chemical reactions used in teaching laboratories, namely, the Green Circle (GC) and Green Matrix (GM), were developed. These metrics globally consider all Twelve Principles of Green Chemistry. To illustrate their construction, the greenness of several syntheses performed in the laboratory under different sets of conditions was assessed. The tools were validated by comparing the results with another metric, the Green Star (GS), developed in our previous study. Results showed these new metrics were useful for the intended purpose, having the advantage of being simpler than the GS.