“Green Star”: a holistic Green Chemistry metric for evaluation of teaching laboratory experiments

Abstract

This paper presents a new semi-quantitative metric, Green Star (GS), for evaluation of the global greenness of chemical reactions used in teaching laboratories. Its purpose is to help choose the more acceptable reactions for implementing Green Chemistry (GC) and to identify suitable modifications of protocols to improve the greenness of the chemistry practiced by students. GS considers globally, in principle, all the Twelve Principles of GC. The metric consists in the evaluation of the greenness of the reaction for each principle by pre-defined criteria, followed by graphical representation of the results in an Excel radar chart Á the fuller the chart, the higher degree of greenness. To illustrate the construction and the scope of the metric, a case study is presented Á the iron(II) oxalate dihydrate synthesis performed under several sets of conditions to pursue the implementation of greenness.

Greenness of chemical reactions – limitations of mass metrics

“…Green Chemistry Letters and Reviews 3 coefficients. The greenness was also evaluated considering all the 12 Principles of Green Chemistry by calculation of the Green Star, as reported elsewhere (16,19).…”

“…The experimental values of the metrics used in the present discussion were obtained in the studies reported before (16,19). Table 4 presents a road map of the present study, showing for each case the conditions that were changed in successive synthesis experiments and the metrics influenced by them, as described below.…”

“…Although the systemic nature of green chemistry has been recognized almost since its inception (15), its exploration has been limited, probably due to the traditional reductionist attitude of the chemical education and academic practice of chemistry, in which its different aspects are considered separately, often ignoring their inter-relationships Á this situation creates difficulties to the scale-up of reactions and industrial process development, which are systemic tasks. We have recently devised a holistic green chemistry metric, the Green Star (16), which has been applied in our efforts to teach green chemistry in this Department (17Á19) and is currently under further evaluation for improvement. In this effort, for comparison purposes, a lot of data on several other metrics described in the literature (3Á6) has been calculated in experiments of syntheses of several compounds which were repeated under different conditions to increase greenness.…”

“…Thereafter, it was investigated how to use mass metrics to identify the main aspects which need improvement to increase the greenness of chemical reactions of different types. To accomplish these tasks, data collected in previous laboratory studies (16,19) were used in two case studies, the syntheses of iron(III) tris(acetylacetonate) ( Table 4, case study 1) and of iron(II) oxalate dihydrate (case study 2). In the laboratory studies, syntheses were repeatedly performed under several sets of different conditions to improve their greenness (16,19), with careful registration of masses of reagents, solvents, etc.…”

“…To accomplish these tasks, data collected in previous laboratory studies (16,19) were used in two case studies, the syntheses of iron(III) tris(acetylacetonate) ( Table 4, case study 1) and of iron(II) oxalate dihydrate (case study 2). In the laboratory studies, syntheses were repeatedly performed under several sets of different conditions to improve their greenness (16,19), with careful registration of masses of reagents, solvents, etc. and products, as advised by the second 12 Principles of Green Chemistry proposed by Winterton (21), and the most common mass metrics described in the literature (see Table 1) were calculated and used to assess the progress toward greenness in each case.…”