Holistic Metrics for Assessment of the Greenness of Chemical

Article pubs.acs.org/jchemeduc

Holistic Metrics for Assessment of the Greenness of Chemical Reactions in the Context of Chemical Education M. Gabriela T. C. Ribeiro†,* and Adélio A. S. C. Machado‡ †

REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Porto 4169-007, Portugal Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Porto 4169-007, Portugal

‡

S Supporting Information *

ABSTRACT: 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. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, High School/Introductory Chemistry, Safety/Hazards, Green Chemistry, Reactions, Synthesis

T

he basic objectives of green chemistry1,2 were incorporated in the 12 principles formulated by Anastas and Warner.1 These principles, of qualitative nature, are focused in the reduction of wastes and the elimination of the use and production of toxic substances. The aim of these principles is to minimize the human health and environmental impact of chemical activities, without compromising the progress of chemistry. The 12 principles may be used as a guide for the development of environmentally benign products and processes. The principles have been used in teaching green chemistry and the importance of their introduction in school curricula has been discussed.3,4 Recently, a review on green chemistry teaching resources5 stressed the importance that the 12 principles acquired in the incorporation of green chemistry in the chemistry curricula, as well as the limited use of green metrics from a teaching perspective. The evaluation of greenness in chemistry is a complex issue and different types of metrics have been used: mass metrics6−9 (required by the first two of the 12 principles), energy metrics10 (required by the sixth principle), toxicity/ environmental metrics11,12 (required by several of the 12 principles) and safety metrics13−15 (required by the twelfth principle). Simple metrics for quickly assessing the greenness of chemistry experiments are desirable. They may facilitate the selection of green experiments by curricula designers and teachers and be used by students at the secondary level or at the first year of college for evaluating their experiments with respect to greenness. Moreover, they may contribute to supporting the incorporation of green chemistry in teaching. For this purpose, holistic metrics that consider simultaneously all the 12 principles of green chemistry are preferable. In fact, alterations of the conditions for performing reactions, when © 2013 American Chemical Society and Division of Chemical Education, Inc.

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.16 Recently, a new semiquantitative holistic metric, the green star, has been developed by us for comparative evaluation of the greenness of reactions in undergraduate teaching laboratories.17−19 Green star was designed to address simultaneously all the principles of green chemistry applicable in each situation (chemical reaction, chemical process, etc.), and it is a systemic metric of global greenness, as expressed by those principles. It has been used by preservice teachers, in their initial teacher education in the university, to assess the improvement of greenness of syntheses performed in the laboratory in succession under altered conditions17−19 and to assess the experiments included in 10th and 11th years of the secondary chemistry curricula in Portugal.20,21 These evaluations showed that green star may be time-consuming and this may discourage teachers from using it in their teaching practice. Therefore, we have decided to look for simpler metrics, as well as metrics with better features for making students more aware of the exploration of opportunities for greenness improvement. The objective of this article is to 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. For the sake of simplicity, these metrics were designed to analyze the accomplishment of each of the 12 principles of green chemistry, with predefined binary criteria (accomplishment/no accomplishment), instead of the more complex three level criteria used in green star.17,18 The Published: March 11, 2013 432

dx.doi.org/10.1021/ed300232w | J. Chem. Educ. 2013, 90, 432−439

Journal of Chemical Education

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results of the assessment are presented either graphically, by pie chart obtained using an Excel spreadsheet (green circle), or by tables, obtained using a strengths, weaknesses, opportunities and threats (SWOT) analysis22 (green matrix). To illustrate the construction of these metrics, they were applied to syntheses experiments whose greenness had been previously optimized and evaluated with the green star, which was used for their validation. The work reported here is summarized in Figure 1.

Table 2. Risks to Human Health and the Environment Because of the Substances Involved Risks Health

Environment

Hazard Symbols C, Corrosive T, Toxic T+, Very toxic Xi, Irritant Xn, Harmful No indication N, Dangerous for the environment No indication

Classification High

Moderate Low High Low

Table 3. Risks of Potential Chemical Accident Because of the Substances Involved Risks

Hazard Symbols

Health

Figure 1. Diagram of the holistic metrics used in the work.

C, Corrosive T, Toxic T+, Very toxic Xi, Irritant Xn, Harmful No indication F, Highly flammable F+, Extremely flammable No indication E, Explosive O, Oxidizing agent No indication

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DESIGN AND CONSTRUCTION OF THE METRICS The metrics involve only the principles that are relevant for the situation under analysis; in teaching experiments, the fourth (designing safer chemicals) and 11th (real-time analysis for pollution prevention) principles are generally excluded, because the laboratory work does not include the preparation of new products. The metrics are constructed accordingly to criteria defined to assess the accomplishment of each principle, listed in Table 1. For this purpose, the protocol of the experiment is analyzed for obtaining information about: • Stoichiometric reagents in excess (information is used to assess the accomplishment of principle P2) • Pressure and temperature conditions (accomplishment of P6) • Risks to human health and to the environment (P1, P3, P5 and P9) and of potential chemical accidents (P12) of all the substances involved (raw materials/feedstocks, products, byproducts, solvents, and other auxiliary substances such as catalytic reagents, solvents, separation agents, etc.) and wastes • Renewability of raw materials/feedstocks and tendency to break down into innocuous degradation products (P7 and P10) • Use of derivatizations (P8) The risks for every substance are classified as high, moderate, or low, according to the criteria defined in Tables 2 and 3. This classification follows the criteria used before for the establishment of the green star,17,18 in which scoring of the risks as 3, 2,

Flammability

Reactivity

Classification High

Moderate Low High Low High High Low

and 1 correspond to high, moderate, and low, respectively. The information about the substances, needed for Tables 2 and 3, can be obtained from material safety data sheets (MSDS), available online at the Web sites of several manufacturers of chemical products. In the case of lack of information (this is often the case for degradability), the worst score is chosen. Using all this information, the accomplishment of each principle by the protocol analyzed is assessed using the criteria in Table 1. For principles P1, P3, P5, P9, and P12, the accomplishment of the principles implies that substances involved have low risks; therefore, these metrics cannot discriminate protocols using substances with moderate instead of high risks.

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GREEN CIRCLE In this metric, the results of the assessment are represented graphically in a circle, obtained using a pie chart in an Excel spreadsheet (green circle).23 The circle is divided in a number of sectors equal to the number of principles used in the greenness evaluation, each filled either in green, if the respective principle is

Table 1. Criteria To Assess the Accomplishment of the Principles of Green Chemistry Green Chemistry Principles P1 P2 P3 P5 P6 P7 P8 P9 P10 P12

Prevention Atom Economy Less hazardous chemical synthesis Safer solvents and auxiliary substances Increase energy efficiency Use renewable feedstocks Reduce derivatives Catalysts Design for degradation Safer chemistry for accident prevention

Criteria for Accomplishment of the Principle No waste is produced or, if produced, has low risk to human health and the environment Reactions without excess of reagents (≤10%) and without formation of byproducts (water not considered) All the substances involved have low risks to human health and the environment Neither solvents nor other auxiliary substances are used or, if used, have low risks to human health and the environment Environmental pressure and temperature All raw materials/feedstocks involved are renewable Derivatizations are not used Catalysts are not necessary or they have low risks to human health and the environment All substances involved are degradable and break down to innocuous products All substances involved have low risks of chemical accident 433



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accomplished, or in red, if it is not. Each principle is considered accomplished if, according with the information gathered, the protocol fulfills the criteria defined in Table 1. A simple visual inspection of the circle provides an indication of the greenness. To check this visual result, a quantitative value, named the accomplishment of principles index (API), may be calculated as the percentage of principles accomplished (100 × number of principles accomplished/total number of principles that apply). When all the principles are accomplished, API = 100, if none, API = 0.

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Figure 2. Scheme of SWOT matrix.

GREEN MATRIX In the case of green matrix, although the assessment is also based in the criteria defined in Table 1, a SWOT analysis is used to acquire a more complete vision of the situation about greenness, or its absence, and possibilities of improving it.

of green chemistry, assessed by the criteria defined in Table 1. For this purpose, the items that reduce the greenness, the difficulties to increase it and the strategies that may be followed to overcome these are identified. For the internal analysis, to turn Table 1 operational, the dimensions of analysis in Table 4 were established: the aspects that allow (strengths) or prevent (weakness) each principle to be accomplished. Each dimension corresponds to a principle (the number indicates which principle it refers to) and, for each principle, strengths and weaknesses are indicated. In the analysis, the number of strengths indicates the number of principles accomplished and the greater the number of strengths identified, the greater the greenness. In revisions and optimizations of protocols to improve greenness, weaknesses must be converted to strengths to increase the number of principles accomplished. Dimensions of external analysis are defined considering the aspects that can change a weakness into strength. They are presented in Table 5. Aspects that may promote the accomplishment of the principles still not achieved configure the opportunities to reduce the weaknesses and increase the strengths. The external circumstances that may bring difficulties to the identified improvements configure the threats. To construct the green matrix, which is the SWOT matrix obtained by this procedure, all the strengths and weaknesses are listed in a table according to the criteria presented in Table 4; the opportunities and the threats are also listed in the table (see Figure 3 as an example).

SWOT Analysis

This type of analysis has been scarcely present in this Journal24,25 and, apparently, only in cases in which SWOT was used as a framework for brainstorming, not as a tool for multidimensional evaluation of complex situations. Therefore it is briefly described here when used for this purpose. The SWOT analysis was created in the 1960s in the United States, and has been mainly used for situation analysis of organizations, but more recently has gone out of management, namely, to technology26,27 and chemistry.23 To implement a SWOT analysis on an object, the objectives of the evaluation task must be well-defined at the beginning before proceeding to assess their accomplishment. The evaluation of strengths and weaknesses of the object to be analyzed refers to the positive and negative aspects that contribute or oppose, respectively, to achieving the objectives defined previously (this is the so-called internal analysis that gathers the strengths and the weaknesses found). In parallel, an external analysis is also implemented, where opportunities (items that may turn the object stronger with respect to the objectives) and threats (items that may compromise the success of the objectives established) are identified. SWOT analysis is a qualitative assessment that intends to facilitate better choices in the implementation of measures to pursuit the objectives defined. These are built upon strengths, eliminate weaknesses, and exploit opportunities or use them to counter the threats. After defining the objectives (e.g., in the present case, obtaining a green protocol for a synthesis based in the accomplishment of the relevant principles of green chemistry), it is necessary to define the items to be used for evaluating the accomplishment of each principle. These items, called dimensions of internal analysis, assess the strengths and weaknesses. To find opportunities for improvements of the protocol, so that the weaknesses found can be eliminated, and to see whether these improvements are feasible, identifying any restraints to its application, the threats, items called dimensions of external analysis are also defined. From the list of dimensions of each type, the strengths and weaknesses are identified, as well as the opportunities and threats. The obtained information is systematically presented in a table, the SWOT matrix, which provides a global view of the appreciation of the object, based on the objectives of the evaluation (Figure 2).

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EVALUATION OF GREENNESS To illustrate the use of these metrics, the syntheses of iron(II) oxalate dihydrate and tetraamminecopper(II) sulfate monohydrate were analyzed. Syntheses of Iron(II) Oxalate Dihydrate

The results of experiments performed in the laboratory, described in the literature,18,28 were used. In a first group of experiments, the iron(II) oxalate dihydrate was prepared from iron(II) sulfate heptahydrate, oxalic acid, and sulfuric acid (procedure 1). These experiments were optimized in alternative procedures, as follows: • First improvement: Sulfuric acid was replaced by ascorbic acid to reduce iron(III), which eventually formed iron(II) (procedure 2) • Second improvement: Experiments were performed at room temperature using this last procedure (procedure 3) • Third improvement: Experiments were performed at room temperature, with an excess of 4% of oxalic acid (procedure 4) The green matrix is presented in Figure 3, and the green circle, together with the green star for comparison, in Figure 4. For the

SWOT Analysis of Greenness

When SWOT analysis is applied to chemical greenness, the objects to be analyzed may be compounds, synthesis reactions (as in the present case), processes, etc. The objective is to evaluate their greenness by the accomplishment of the principles 434



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Table 4. Dimensions for Internal Analysis and Criteria for Computing the Strengths and Weaknesses Dimensions of Analysis 1 2 3 5

6 7 8 9

Strengths

Weaknesses

Risks to human health and the environment of the waste Excess of reagents and formation of byproducts (water not considered) Risks to human health and the environment of all the substances involved Risks to human health and the environment of solvents and/or of other auxiliary substances Pressure and temperature

No waste produced or waste involves a low risk to human health and the environment Reactions without excess of reagents (≤10%) and no formation of byproducts (water not considered) All substances involved have low risks to human health and the environment Neither solvents nor other auxiliary substances are used, or, if used, have low risks to human health and the environment Room pressure and temperature

Utilization of renewable substances (water not considered) Derivatizations Utilization of catalysts

All raw materials/feedstocks involved are renewable (water not considered) Not used Catalysts not necessary or they have low risks to human health and the environment All substances involved are degradable and break down to innocuous products (water not considered)

Waste produced with moderate/high risks to human health and/or the environment Reactions with excess of reagents >10% and/or formation of byproducts At least one of the substances involved with moderate/high risks to human health and/or the environment At least one of solvents/other auxiliary substances used with moderate/high risks to human health and/or the environment Pressure or temperature different from room pressure and temperature At least one raw material/feedstock involved is not renewable (water not considered) Used Catalysts with moderate/high risks to human health and/or the environment are used At least one of the substances involved is not degradable breaking down to innocuous products (water not considered) At least one of the substances involved has moderate/high risks of chemical accident

10

Utilization of degradable substances to innocuous products (water not considered)

12

Risks of potential chemical accident of all the substances involved

All substances involved have low risks of chemical accident

Table 5. Dimensions for External Analysis Opportunities

Threats

Replacement of substances with moderate or high risk by substances with Difficulties in fulfilling the conditions mentioned in the opportunities for economic reasons or low risk because alternatives to the processes used are not known Elimination of solvents/other auxiliary substances or replacement by others with low risk Optimization of the process to increase atom economy (stoichiometric proportions or near) Optimization of the process to reduce energy consumption, looking for conditions at room pressure and temperature Use of catalysts with low risks in place of stoichiometric reagents No use of derivatizations Replacement of not degradable substances by degradable ones that break down to innocuous products Replacement of nonrenewable substances by renewable ones

• In procedure 3, the temperature was also decreased to room temperature and the number of strengths increased as the principle P6 was accomplished. • In procedure 4, the excess of oxalic acid was reduced to 4%, but as byproducts formed, the principle P2 was only partially accomplished and, consequently, the number of strengths remained unchanged. Green circles, in Figure 4, show that the number of principles accomplished increased from procedure 1 to 3 (the principles accomplished turned from red to green), but not for procedure 4. It is instructive to compare the present metrics with the green star. Figure 4 shows that, in contrast with the results of the green circle and the green matrix, the green area of the green star

initial protocol, procedure 1, the green matrix (Figure 3) presents two strengths, corresponding to the accomplishment of principles P8 and P9. The green circle for the same procedure shows that only those principles are accomplished (Figure 4). The opportunities in the matrix suggest several possible changes to increase the greenness. To increase the strengths, the opportunities were explored and the synthesis was performed using the three new procedures mentioned above (procedures 2−4, Box 1). The implications on the green matrix are also presented in Box 1: • In procedure 2, sulfuric acid (C) was replaced by ascorbic acid (lower risk) and the number of strengths increased due to the accomplishment of principle P5. 435



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Figure 3. Green matrix for the syntheses of iron(II) oxalate dihydrate synthesis.

Figure 4. Green stars and green circles for the syntheses of iron(II) oxalate dihydrate.

star became greener. Moreover, the green star provides additional information, as several principles are partially accomplished: P1 in all the procedures; P2 in procedure 4; P3 in procedures 2−4; P6 in procedures 1−2; and P12 in procedures 2−4. This is explained by the criteria used to construct the green star,18 which are presented in the Supporting Information as

increased from procedure 1 to 4, as is visually apparent. The green star area index (GSAI), calculated as the ratio of the area of the green star to the area of maximum possible greenness (all scores equal to 3) expressed as a percentage (GSAI = 100 × area of the green star/area of green star of maximum greenness),19 increased from 20 to 46. The green matrix and the green circle did not respond to the last change (procedure 4), but the green 436



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Figure 5. Green matrix for the syntheses of tetraamminecopper(II) sulfate monohydrate.

Tables 1−4, and involve three levels of accomplishment of the principles. Syntheses of Tetraamminecopper(II) Sulfate Monohydrate

The results of experiments using copper(II) sulfate pentahydrate and ammonia as reagents, described previously in the literature,17 were used. In the initial protocol,29 a large excess of ammonia was used, but the synthesis was optimized to conditions near stoichiometry to increase greenness.17 The green matrix and the green circle, together with the green star, are presented in Figure 5 and Figure 6, respectively. For this case, the green matrix (Figure 5) presents three strengths, corresponding to the accomplishment of principles P5, P8, and P9. The opportunities in the matrix suggest the use of stoichiometric proportions as advisable to increase the greenness, and indeed, when the synthesis was performed near stoichiometric proportions, the number of strengths increased (Box 2). In procedure 2, the excess of ammonia was reduced to 7% (and byproducts are not formed, water not considered), and the principle P2 is accomplished. Principle P1 is also accomplished because ammonia is not considered in waste (because the proportions of stoichiometric reagents are now near stoichiometric ones). The green circle (Figure 6) also becomes greener, with the index API increasing from 30 to 50. All the metrics responded to the changes implemented to increase greenness, but the green star (Figure 6) again provides additional information: the principle P2 was partially accomplished in procedure 1 because byproducts were not formed. This is explained, as in the previous case, by the criteria used to construct the green star, which are presented in the Supporting Information.

Figure 6. Green stars and green circles for the syntheses of tetraamminecopper(II) sulfate monohydrate.

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DISCUSSION

partial accomplishments of the principles. Therefore, a limitation of the green matrix is that it is not possible to discriminate the accomplishment of principles when substances with moderate, instead of high risk, are used. The green star is a graphical representation of greenness and the aspects that led to the partial or complete accomplishment of the principles are not evidenced, although these may be found in detail in the tables required for its construction. By consulting these tables, it is possible to identify what needs to be changed to improve greenness.17,18

Comparison of the Green Matrix with the Green Circle

The green matrix allows identification of the principles accomplished, as well as the aspects that contributed to the accomplishment. Because of the inclusion of opportunities and threats, the aspects that can be changed to improve greenness and their difficulties are also identified. In summary, this metric involves a lot of thinking about the several components of the greenness at play, providing a detailed vision useful to proceed to improved greenness. In the green circle, the information that led to its construction is not evident in the metric; however, by visual inspection, the principles that are accomplished are more easily and quickly identified. As the green matrix and the green circle are based on the same criteria to assess the accomplishment of the principles, when used together, they are mutually complementary; indeed, the green circle, when obtained from the SWOT analysis, provides a compact graphical result of the green matrix, but the compaction means loss of information, as is often the case when compressing data. On the other hand, construction of the green circle may be made by a simpler assessment of the accomplishment of the relevant green principles, by direct application of the predetermined criteria in Table 1. Indeed, the green circle is a summative tool (only the results of the global assessment obtained by direct application of criteria are provided), while the green matrix is a formative tool (the construction of the SWOT table requires that the results of the detailed analysis of different aspects of greenness are expressed in the table, and this extra effort by the user is expected to enhance his or her knowledge about green chemistry). Both metrics have been used by our students, preservice teachers and inservice teachers, as well as in postgraduate courses, when evaluating the greenness of laboratory experiments and improving it. This is one of the lines we have been using to teach green chemistry to train future teachers in our educational MSc degrees. In these experiments, they are asked to assess greenness and suggest improvements in synthetic protocols from the literature and test their suggestions for improvement in the laboratory.17−19 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) for the past few years, by ∼30 people, in small groups. In their opinion, the two metrics responded well to the changes made in the protocols and, because of the simplicity of the evaluation procedure, have been perceived as more friendly to use than the green star. This positive response suggests that these metrics may be useful for curricula designers and teachers in the selection of experiments. The green circle, when constructed directly from the criteria table, is simple enough to be used broadly by students at secondary level, while the use of the green matrix, with its elaboration, may be adequate only to the final year (if enough time is available for discussion of the SWOT analysis) or in the first year of college. However, because of the absence of green chemistry education in the secondary school chemistry curricula in Portugal, we were unable to test this in a real context.

Comparison of the Green Circle with the Green Star

From the results, it was verified that the accomplished principles, colored green in green circle, correspond to the designation of three in the green star, while the principles that are not accomplished, colored red in green circle, are designated with 1 or 2 (not accomplished or partially accomplished, respectively) in the green star. The green star gives a more accurate assessment of the greenness because there are three levels of evaluation of the principles,14−16 as referred to before, while for the green circle the criterion is binary: accomplishment or no accomplishment. Therefore, as with the green matrix, the green circle does not discriminate the accomplishment of principles when substances with moderate, instead of high risk, are used. However, as the green star is more complex and its construction is more time-consuming, the simplicity of the green circle is an advantage.

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CONCLUSIONS The green circle and the green matrix are useful for a quick assessment of the greenness of a chemical reaction or process without performing the experiment from a protocol, if this is detailed enough, or upon experimental execution in the laboratory. If used together, the green circle and the green matrix permit a detailed description of the results of the evaluation: the green circle allows a quick visual identification of the principles accomplished or not accomplished and the green matrix gives details about the aspects that justify the assessment and about those that could be optimized to increase greenness. They are both easy to deliver (although the SWOT analysis, being probably a novelty for most chemists, requires training), as they are based in criteria with only two levels: accomplishment or no accomplishment. However, the green circle and the green matrix do not respond to all improvements that can be implemented to increase greenness: owing to the limitation of using only two levels of discrimination, they do not consider partial accomplishment of the principles. In this respect, the green star previously presented17−19 is superior. Holistic metrics like all 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. In conclusion, the metrics presented here enhance the understanding of the principles of green chemistry and their use, and may be useful to facilitate their incorporation in teaching activities, which is important for the development of practices in chemistry that must be proactively changed to reach sustainable chemistrythe ultimate purpose of green chemistry.

Comparison of the Green Matrix with the Green Star

The green matrix and the green star allow the identification of the principles that are achieved or are not achieved, but the green matrix uses only two levels of accomplishment of the principles, while the green star uses three, which allows discrimination of 438



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(23) Deetlefs, M.; Seddon, K. R. Green Chem. 2010, 12, 17−30. (24) Keller, H.; Cox, J. R. J. Chem. Educ. 2004, 81, 520−522. (25) Brown, M. E.; Cosser, R. C.; Davies-Coleman, M. T.; Kaye, P. T.; Klein, R.; Lamprecht, E.; Lobb, K.; Nyokong, T.; Sewry, J. D.; Tshentu, Z. R.; Zeyde, T.; Watkins, G. M. J. Chem. Educ. 2010, 87, 500−503. (26) Sin, G.; Van Hulle, S. W. H.; De Pauw, D. J. W.; van Griensven, A.; Vanrolleghem, P. A. Water Res. 2005, 39, 2459−2474. (27) Arslan, O.; Er, I. D. J. Hazard. Mater. 2008, 154, 901−913. (28) Pass, G.; Sutcliffe, H. Practical Inorganic Chemistry; Chapman and Hall: London, 1974. (29) Clareen, S. S.; Marshall, S. R.; Price, K. E.; Royall, M. B.; Yoder, C. H.; Schaeffer, R. W. J. Chem. Educ. 2000, 77, 904.

ASSOCIATED CONTENT

S Supporting Information *

Criteria to construct the green star. This material is available via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the preservice teachers M. Salomé O. F. Fernandes, Â ngelo E. R. Neves, and Bruna M. A. Faria for their collaboration in performing the syntheses. M. G. T. C. Ribeiro’s work has been supported by Fundaçaõ para a Ciência e a Tecnologia through grant no. PEst-C/EQB/LA0006/2011. An anonymous reviewer is thanked for calling our attention to the different nature (summative vs formative) of the two metrics.

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REFERENCES

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Holistic Metrics for Assessment of the Greenness of Chemical

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