Summary
In this paper two new semiquantitative green chemistry metrics, the green circle and the green matrix, for quick assessment of the greenness of a chemical reaction or process, even without performing the experiment from a protocol if enough detail is provided in it, are presented.
The evaluation of greenness in chemistry is a complex issue and different types of metrics have been used, but simple metrics for quickly assessing the greenness of chemistry experiments are still desirable. Moreover, holistic metrics that consider simultaneously all the 12 principles of green chemistry are preferable. In fact, alterations of the conditions for performing reactions, when seeking greenness, may have different consequences with respect to different principles: the greenness may improve with reference to some of them, but worsen with reference to others.
The authors have previously developed a semiquantitative holistic metric, the green star, for comparative evaluation of the greenness of reactions in undergraduate teaching laboratories. In this paper, they describe two other holistic metrics, the green circle and the green matrix, which are easier to construct than the green star, and may be used to incorporate green chemistry in chemical education.
First, the design and the metrics used are analyzed. After that, the Green Circle and the Green Matrix are described. Moreover, a SWOT analysis which is used to acquire a more complete vision of the situation about greenness, or its absence, and possibilities of improving it, is presented.
The performance of these metrics was evaluated for several syntheses made in the laboratory, under different sets of conditions. These activities have been developed in three disciplines of different Master’s degree programs for chemistry teachers (pedagogy of green chemistry education for sustainability; chemistry laboratory project; and didactics of chemistry).
To illustrate the use of these metrics, the syntheses of iron(II) oxalate dihydrate and tetraamminecopper(II) sulfate monohydrate are analyzed. For these experiments, the Green Circle, the Green Matrix and the Green Star (for comparison) are used for the evaluation of greenness.
In the discussion section, the three semiquantitative holistic metrics, are compared with each other and the advantages as well as the limitations of each one are presented.
In conclusion, the green circle and the green matrix, if used together, permit a detailed description of the results of the evaluation: the green circle allows a quick visual identification of the principles accomplished (or not) and the green matrix gives details about the aspects that justify the assessment and about those that could be optimized to increase greenness.
Relevance for Complex Systems Knowledge
This paper deals with green chemistry and complex systems and proposes an approach to reimagine higher education. The two holistic semiquantitative green chemistry metrics, the green circle and the green matrix, have been designed to analyze the accomplishment of each of the principles of green chemistry, with predefined binary criteria (accomplishment/no accomplishment). Holistic metrics like these, which are based on systems thinking, present several benefits for teaching green chemistry: familiarization with the 12 principles of green chemistry and their implications as a whole, multidimensional evaluation of the greenness of chemical reactions and processes, identification of aspects that could be optimized to improve greenness, and assessment of the effects on the greenness of the changes implemented, and so forth.
