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.

A procedure for teaching green chemistry through laboratory experiments is presented in which students are challenged to use the 12 principles of green chemistry to review and modify synthesis protocols to improve greenness. A global metric, green star, is used in parallel with green chemistry mass metrics to evaluate the improvement in greenness. The methodology is exemplified with the search for the greenest metal−acetylacetonate synthesis experiment commonly included in the teaching laboratory literature. Green star responds holistically to a large number of features that have to be considered when the greenness of a process is under discussion because it involves an assessment of all the relevant twelve principles of green chemistry in a systemic way. The advocated procedure allows students to become familiar with both the 12 principles and green chemistry mass metrics and to gain experience in changing synthetic chemistry to improve its greenness.

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Two new semiquantitative green chemistry metrics, the green circle and the green matrix, have been developed 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. The evaluation is based on the 12 principles of green chemistry. The performance of these metrics was evaluated for several syntheses made in our laboratory, under different sets of conditions. They were compared with a more complex set of metrics, assembled previously in our work, the green star, which was used to validate these new tools. These new metrics are useful for curricula designers and teachers in the evaluation and selection of green chemistry experiments. They are also appropriate for students to use in the context of chemical education for evaluating their experiments. These new metrics seem adequate to stimulate the incorporation of green chemistry in the teaching environment.

Two graphic holistic metrics for assessing the greenness of synthesis, the "green star" and the "green circle", have been presented previously. These metrics assess the greenness by the degree of accomplishment of each of the 12 principles of green chemistry that apply to the case under evaluation. The criteria for assessment were based on the hazards symbols used in the system established by the European Union, directive 67/548/EEC, obtained from the safety data sheets of chemicals. Meanwhile, the Globally Harmonized System of Classification and Labeling of Chemicals (GHS) replaced that system and introduced a new classification of hazards and new symbols. The objective of this work is to present new criteria for the construction of the metrics based on the GHS system. A brief presentation of this system is included. The present upgrade also includes an improvement of the graphic presentation of the green star to facilitate the visual assessment of the degree of accomplishment of each green chemistry principle.

The influence of reaction conditions (yield, excess of stoichiometric reagent, molecular weights of reagents, and mass of auxiliary materials and solvents) on the values of several green chemistry mass metrics (E-factor, mass intensity, atom utilization, relative mass efficiency, and element efficiency), for reactions with 1:1 and 1:3 stoichiometries, has been analyzed, as well as relationships between the metrics. The theoretical behavior of these, when visualized by three-dimensional graphic representations, e.g. surfaces of metric 0 f(yield, excess), together with the experimental values, facilitates the management of its improvement Á changes in conditions in successive experiments should follow the directions shown by the graph. The study shows that there are practical limitations to the greenness increase due to the complex nature of the chemistry but confirms that it is worthwhile to pay more attention to the effort of obtaining quantitative details of the laboratory syntheses to acquire information to assess greenness.

A procedure to improve the greenness of a synthesis, without performing laboratory work, using alternative protocols available in the literature is presented. The greenness evaluation involves the separate assessment of the different steps described in the available protocolsreaction, isolation, and purificationas well as the global process, with the tool green star. This proved to be adequate to assess separately the microgreenness of the steps. Two case studies, the syntheses of ethyl acetate and manganese(III) acetylacetonate, are presented. The results show how the different steps limit the global greenness of the synthesis and suggest that the workup may be more problematic than the reaction itself. Moreover, the study showed that the green star can be used for comparing in detail the alternative protocols proposed for a synthesis, finding the best alternative for each step and allowing the design of a greener protocol by combining them.

The different ways microscale and green chemistry allow reducing the deleterious impacts of chemistry on human health and the environment are discussed in terms of their different basic paradigms: green chemistry follows the ecologic paradigm and microscale the risk paradigm. A study of the synthesis of 1-bromobutane at macro- → microscale (109.3 → 10.9 g of the limiting reagent, butan-1-ol) showed that green chemistry mass metrics (AE, atom economy; RME, reaction mass efficiency; MI, mass intensity; E-factor, environmental factor; CEE, carbon efficiency) are unsuitable for evaluating the advantages of micro- versus macroscale. Poorer values of mass metrics at the microscale and the same green star at both scales showed that green metrics do not recognize that microscale improves safety. As so far no metrics have been proposed for evaluating this purpose, a new risk index (scale risk index, SRI) was developed for assessing the improvement of safety on downsizing the scale of synthesis experiments in chemistry teaching laboratories. The performance of SRI to show the benefits of microscale was assessed for syntheses of 1-bromobutane, tetramminecopper­(II) sulfate monohydrate, and dibenzalacetone.