Green Star metric

The Metrics Green Star, Green Circle and Green Matrix... 

Figure 8.7 Holistic metrics based on the principles of green chemistry. The graphic metrics refer to an optimization experiment of the syntheses of tetram-minecopper(ii) sulfate monohydrate 16 (only ten of the twelve principles were used in the evaluation, principles 4 and 11 being excluded). When the excess of ammonia was deceased from 300% (top metrics) to 7% (bottom metrics), the green area in the graphics increased and the indexes API (green circle) and GSAI (green star) increased respectively from 30 to 50 and from 40 to 55.

Although the first versions of these metrics were developed from SDS that used risk phrases (R-phrases) and safety phrases (S-phrases), the metrics have been revised to adapt them to GHS, which required a new definition of the criteria to score the hazards and assess the accomplishment of the GC principles. As in GHS the systemization of the hazards in classes and categories, to which hazard statements are assigned (hazard codes or H codes), is more detailed than in the system of the R- and S-phrases, the change provided a finer evaluation of hazards and made easier the construction of the metrics. The revision included also an improvement of the graphic look of the green star to increase the facility of reading the individual scores of the principles. These new versions of the metrics are those discussed in this text. 

The strategy for construction of the metrics will be exemplified here very briefly for the case of the green star when used to evaluate a synthesis reaction. A tool for its implementation can be accessed in the net, in a specific site. The tool calculates the metric automatically upon introduction of the data, by applying the criteria defined in two tables mentioned below (table H codes/score of hazards and table score of hazards/scores of principles ), that are included in it. The site provides also an example of the use of green star that shows the results along the construction of the metric. 

The green circle is obtained by a similar procedure, the only difference being a simpler binary criterion (accomplishment/no accomplishment) for evaluation of the principles, where the intermediate level in the 1/3 scale of green star is included in the lower level (no accomplishment). The metric is presented as an Excel pie chart, where the colours green/red in the sectors are used to identify the accomplishment/no accomplishment of the principles. For comparison of different green circles, an accomplishment of principles index (API) may be calculated as the percentage of principles accomplished (API = 100 X number of principles accomplished/total number of principles that apply). 

In more recent activities, the green star is being used in a broader study of the synthesis experiments used in the 1st and 2nd years organic and inorganic laboratories of chemistry BSc courses of Portuguese universities. This study showed that the metric is adequate to evaluate separately the three stages of the synthesis process, the reaction step (with ten corner stars), and the two post-reaction steps, isolation and purification (six corner stars). This assessment of the micro-greenness of the steps shows that the post-reaction... 

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