Metal−Acetylacetonate Synthesis Experiments: Which Is Greener?

ARTICLE pubs.acs.org/jchemeduc

Metal
Acetylacetonate Synthesis Experiments: Which Is Greener? M. Gabriela T. C. Ribeiro*,† and Ad
elio A. S. C. Machado‡ †

REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ci^encias da Universidade do Porto, Rua do Campo Alegre 687, Porto 4169-007, Portugal ‡ Departamento de Química e Bioquímica, Faculdade de Ci^encias da Universidade do Porto, Rua do Campo Alegre 687, Porto 4169-007, Portugal.

bS Supporting Information ABSTRACT: 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. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Analytical Chemistry, Chemoinformatics, Safety/ Hazards, Green Chemistry, Microscale Lab, Reactions, Synthesis he basic objectives of green chemistry1,2 as defined in the 12 principles formulated by Anastas and Warner1 have been used in the teaching of green chemistry. Later, the second 12 principles of green chemistry3 and the 12 principles of green chemical engineering were formulated.4 However, chemistry is an activity of great complexity and a variety of situations need evaluation to ensure greenness when chemical processes are scaled to industrial practice. The importance of the introduction of green chemistry in school curricula has been discussed.5
7 One way to incorporate green chemistry in chemical education as suggested by Braun and co-workers6 is through laboratory activities that allow students to experience (i) the importance of reducing or eliminating the use or production of hazardous substances that involve risks to health and to the environment and (ii) the advantage of applying the concepts of residue prevention and atom economy that appear in the first two of the 12 principles.8,9 However, the 12 principles of green chemistry1,3,4 are qualitative in nature, whereas quantitative evaluations are important, especially in the world of industrial chemistry. For this purpose, green mass metrics10
15 and environmental metrics16,17 have been used to assess quantitatively products and processes in industrial practice. Although the field of green metrics is complex, some green chemistry mass metrics are simple enough to be used in chemical education and examples of their inclusion in undergraduate chemistry experiments have been reported, namely, the environmental factor,18,19 mass intensity,20 atom economy,18,19,21
24 and relative mass efficiency21,24 (see Table 1 for definitions). However, each of these metrics has been utilized by itself and the global importance of green chemistry metrics, as well as their

T

Copyright r 2011 American Chemical Society and Division of Chemical Education, Inc.

relative merits assessed by direct comparison, do not appear to have been stressed in educational context. The main objective of this article is to present the methodology that we have been using for training future chemistry teachers who graduate with the chemical education degree to be mindful of green chemistry. This seems an effective way to achieve the transformation of chemistry into green chemistry. An important feature of our work is to make the students understand that the evolution from traditional chemistry toward establishing greener chemistry requires a persistent effort toward greener laboratory procedures, especially synthesis experiments, and that such efforts must be evaluated carefully by tools that confirm the increase of global greenness when changes are introduced in laboratory protocols. The basic outline of our procedure is (i) students are asked to perform synthesis experiments as described in the literature, (ii) they are challenged to review these experiments from the point of view of the twelve principles of green chemistry and modify the protocols as necessary to achieve greener synthetic procedures, and finally (iii) they are asked to evaluate the suggested changes in the laboratory to obtain experimental confirmation of their efforts through the calculation of green metrics. For this purpose, a global graphic metric has been devised, the green star,25 which is used in this work together with traditional green chemistry numerical mass metrics.10
13 A lateral objective of our methodology is to acquaint students with green chemistry metrics, their variety, the difficulties of the choice of metrics, and their calculation.

Published: April 11, 2011 947

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Table 1. Green Chemistry Mass Metrics Abbreviation

Metric

E factor

Environmental factor

MI

Mass intensity

AE

Atom economy

AU

Atom utilization

RME

Relative mass efficiency

XEE

Element efficiency

Expression E factor ¼

mass of waste mass of the product

10, 11

total mass of all the reagents mass of the product

13

molar mass of the product sum of the molar masses of all the stoichiometric reagents

12

MI ¼ AE ¼

Reference

mass of the product total mass of all the substances produced

10, 11

mass of the product total mass of all the stoichiometric reagents

13

mass of the element in the product total mass of the element in the stoichiometric reagents

13

AU ¼ RME ¼ XEE ¼

The methodology presented in this article involves optimization of a green experiment for synthesis of a metal
acetylacetonate. The synthesis of this type of complex has been used often in the undergraduate inorganic laboratory26
33 but was suggested for the present purpose by a recent publication,32 in which a new protocol for the syntheses of iron(III)
acetylacetonate was claimed to be greener than previous ones.33 These protocols32,33 were implemented in the laboratory and their relative greenness was assessed by metrics. The results were explored to identify possible green improvements and these were included in revised protocols. Experiments following these green improvements were performed and their green success or failure was evaluated again by metrics. The changes pursuant to green improvements were of two types: (i) the ratio of acetylacetone/iron(III) was decreased to values closer to stoichiometry and (ii) as the improvement in greenness was found to be limited, other metals were used to obtain a greener experiment. A roadmap of the experiments, shown in Figure 1, provides the main details of the strategy of the laboratory work. The synthesis were performed at microscale, as reducing the scale improves safety, shortens reaction times, and cuts costs of reagents and treatment and deposition of wastes, allowing the use of more expensive reagents.34 Moreover, as the amounts of reagents used and reaction times are reduced, the exposure to hazardous substances is reduced and therefore risk (= hazard  exposure) decreases.

’ EXPERIMENTAL WORK Synthesis of Iron(III)
Acetylacetonate

A number of experiments were initially performed following a published protocol33 in which the product was prepared from iron(III) chloride hexahydrate and acetylacetone, utilizing a large excess of the ligand (procedure A in Figure 1). To increase the greenness, the experiment was optimized by looking for proportion of reagents closer to stoichiometry. Instead of a large excess of acetylacetone (55%), the ratio acetylacetone/Fe(III) was decreased to a value closer to stoichiometry (excess 7%) to reduce waste and favor a more complete incorporation of atoms of the reagents into the product. The value of 7% was obtained after some trial experiments and corresponds to an excess that did not affect the yield. For instance, a lower excess of 5% decreased the yield by 1.6%. In addition, the more benign reagent

Figure 1. Roadmap providing the main details of the laboratory work.

iron(III) citrate (procedure B) was used in place of iron(III) chloride hexahydrate. Another protocol32 claimed to be greener and therefore a number of experiments were performed for assessment of its advantages. Under this protocol, a solution of aqueous potassium hydroxide solution (20%) was added to a proportion of an aqueous solution of iron(III) chloride hexahydrate, to produce iron(III) hydroxide. After isolation of the latter by filtration, acetylacetone was added to produce the iron(III) 948

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of green chemistry (on a scale from 1 to 3, minimum to maximum value of perceived greenness); criteria for attributing the scores are presented in the Supporting Information. The set of values is represented graphically by a star in an Excel spreadsheet in which each dimension of the graphic describes a principle. The number of dimensions of the chart is the number of principles used in the greenness evaluation, which may be less than 12 if some of the principles of green chemistry are not relevant. In the present case, the green star charts have only 10 corners as the fourth and 11th principles were not considered because teaching experiments do not include the preparation of new products (Figure 2). As the score length represented in each dimension of the plot is the degree of accomplishment of the corresponding principle, the area of the chart is a visual holistic metric of greenness. Thus, the chart is the green star: the larger its area, the greener is the reaction, synthetic pathway, and so forth. A quantitative value, the green star area index (GSAI), may also be calculated as the ratio of the area of the green star to the area of maximum possible greenness (all scores equal to 3) and expressed as a percentage. The green star area index varies from 0% (no greenness at all) to 100% (maximum greenness, full star). The Supporting Information includes an Excel spreadsheet for easy drawing of the green star with an example of the construction and the calculation of the green star area index.

Figure 2. A green star chart. Each principle is represented by its own radial line, which is labeled P1 through P12 (P4 and P11 are not included). The rating corresponding to each principal is reflected by a distance from the center of the star and can be 1, 2, or 3. Each principle and rating forms a point; each point is connected to its neighbor by a line; the collection of lines forms a green star whose area gives an indication of a holistic metric of greenness. In this example, each principle has a rating of 2.

acetylacetonate. However, the filtration of iron(III) hydroxide was time-consuming and caused the loss of a considerable quantity of intermediate product; therefore, the protocol was changed. Acetylacetone was added directly to the reaction flask after the formation of the hydroxide (procedure C). In this way, isolation was bypassed and the greenness of the procedure was further increased.

Green Chemistry Mass Metrics

At this first stage of development of the green star,25 its use has been accompanied by the calculation of several mass metrics. This has a double purpose: first, to assess the scope and validity of green star, and second, to investigate how the joint use of green star and other metrics improves the evaluation of greenness. The metrics used are listed in Table 1. The mathematical expressions for the calculations are presented in detail in the Supporting Information, but a few remarks on the procedures used for them as well as the aims of the utilization of each metric are provided next.

Synthesis of Acetylacetonates of Bivalent Metals

For further exploration of improved greenness, the acetylacetonates of three other metals were prepared following published protocols.35 For the preparation of manganese(II)
and magnesium
acetylacetonates, the protocols indicated the use of sodium acetate as a buffer. However, it was not possible to precipitate the products this way as the pH had to be increased, and therefore, potassium hydroxide was used instead. However, the synthesis was less green than intended, as evaluated by green star (see below) because potassium hydroxide is corrosive. For the preparation of calcium
acetylacetonate, the protocol35 proposed the use of calcium nitrate, potassium hydroxide, and acetylacetone. When calcium nitrate was substituted by calcium hydroxide and no potassium hydroxide was used, a greener synthesis was achieved.

Waste Minimization

Waste production has been evaluated by calculation of the environmental factor10,11 or of the mass intensity.13 The environmental factor (E factor) is the ratio of the total waste mass (calculated as the total mass of reagents less the mass of product) to the mass of product. The mass intensity (MI) is the ratio of the total mass of materials used (stoichiometric reagents, solvents, other auxiliary reagents, etc.) to the mass of product. In this case, the waste is calculated by difference, E factor, = MI
1, assuming there are no losses.

’ HAZARDS The hazards of each reagent are included in Tables 5 and 7 presented in the Supporting Information.

Incorporation of Atoms of Stoichiometric Reagents into the Product

’ METRICS FOR EVALUATION OF GREENNESS

Four metrics have been used for evaluation of this feature. Atom economy (AE) is the ratio, expressed as percentage of the mass of atoms of stoichiometric reagents that are incorporated in the final product to the mass of total atoms of stoichiometric reagents (this assumes that there were no losses in the process and that all stoichiometric reagents were converted to product and byproducts).12 Atom utilization (AU) is the ratio (%) of the mass of the product to the mass of all the substances produced in the chemical reaction (product and byproducts) calculated as the sum of the masses of all reagents.10,11 Relative mass efficiency (RME) is the ratio (%) of the mass of product to the mass of stoichiometric reagents.13 Element efficiency (XEE, X = symbol of the element) is the ratio (%) of the mass of the main element in

Green Star

The metric green star25 was designed to consider simultaneously all of the principles of green chemistry applicable in each situation (a reaction, a synthetic pathway, or a chemical process, etc.) when pursuing greenness and to provide a holistic assessment that is intended to be a systemic metric of the inherent benignness of the procedure. In the construction of green star, for each intervening substance, information about risks to human health and the environment, potential chemical accidents, as well as renewability and tendency to break down into innocuous degradation products, are collected. Using predefined criteria,25 a score is attributed to the accomplishment of each of the principles 949

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Table 2. Evaluation of Greenness of the of Iron(III)
Acetylacetonate Synthesisa

Values of metrics:number of replications for each procedure = 3, value ( standard deviation provided. b Abbreviated versions, with labels removed, of the annotated example in Figure 2. a

twelfth principles increase, respectively, GS1 f GS3 and GS2 f GS4; and (iii) using potassium hydroxide to form iron(III) hydroxide as an intermediate compound reduces the area of the star because potassium hydroxide is a corrosive substance and the scores of the third, fifth, and 12th principles are reduced to 1 (GS1
4 f GS5). The values for the green star area index included in Table 2 confirm the visual evaluation of the green star. However, the maximum green area (GSAI = 51.25 for GS4) is far from the desirable value of 100.

the product to the total mass of the element present in the stoichiometric reagents.13 The RME and XEE metrics have been used in industrial processes as useful ways to evaluate the incorporation of atoms from the reagents into the product because the data needed for these calculations are often available in industrial practice.13 In the present case, the values of RME and AU are the same because AU was calculated considering the mass of the waste and not the mass of byproducts.

’ EVALUATION OF GREENNESS OF THE SYNTHESIS OF FE(III)
ACETYLACETONATES

Comparison of Mass Metrics and Green Star

Using numerical data from the experiments, yields and the values of green chemistry metrics were calculated (water was not considered in calculations). The results are included in Table 2 and show some features that are interesting to stress before discussing their relationships with the green star values. In procedure A, the yield was found to be similar (increased slightly) when experiments were performed with large excess of acetylacetone and a ratio closer to stoichiometric, but the E factor and MI decreased and RME/AU increased owing to a decrease in the mass of stoichiometric reagents. In procedure B, the yield decreased when experiments were performed closer to stoichiometry and, because of the decrease in yield, the E factor and MI increased and RME/AU and FeEE decreased. Moreover, the comparison with procedure A shows that the E factor and MI were larger and RME/AU and FeEE smaller, owing mainly to the lower yield. The comparison with both procedures A and C (see next) shows that, in procedure B, AE is the largest, which is due to the smaller contribution of the

Green Star

From data on properties, the risks to human health and environment of all substances involved were collected, from which the scores to construct the green star were obtained (data provided in Tables 5 and 6 of the Supporting Information). The green star of the experiments of iron(III)
acetylacetonate performed under different conditions are presented in Table 2. The visual comparison of the five green stars shows that (for the meaning of GS1
GS5, see Table 2 and Figure 1) (i) for both procedures A and B, under conditions closer to stoichiometric, the area of the green star increases as the score of the first principle increased from 2 to 3 (there is less excess of acetylacetone in the waste) and the score of the second principle increases from 1 to 2 (the incorporation of atoms from the reagents into the product increases); that is, the area increases GS1 f GS2 and GS3 f GS4; (ii) when iron(III) citrate was used instead of iron(III) chloride (procedure B vs procedure A), the area of the green star increases, as the scores of the third and 950

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Table 3. Evaluation of Greenness of the Bivalent Metal
Acetylacetonate Synthesisa

a Values of metrics:number of replications for each procedure = 3, value ( standard deviation provided. b Abbreviated versions, with labels removed, of the annotated example in Figure 2.

anions and hydration water in the case of the iron(III) citrate relative to iron(III) chloride hexahydrate. In procedure C, the comparison with procedures A and B shows the lowest E factor and MI, owing mainly to the decrease of the mass of auxiliary reagents (18 mg of potassium hydroxide for procedure C and 500 mg of sodium acetate trihydrate for the other two procedures). FeEE was larger for procedure C than for procedure B, but smaller than for procedure A owing to increase or decrease of yield, respectively. The values of RME/AU were not influenced by the mass of auxiliary reagents, but varied positively when the yield increased and negatively when the mass of stoichiometry reagents increased. Therefore, the results for RME/AU values may be interpreted as follows: (i) they were smaller than those from procedure A when the excess of acetylacetone was 7%, owing to the lower yield for procedure C, although the excess of acetylacetone was smaller (the effect of low yield predominates); (ii) they were larger than those for procedure A when the excess of acetylacetone was 55%, because of a smaller excess of acetylacetone, albeit the yield was lower (in this case, the effect of the low excess of acetylacetone predominates); (iii) they were larger than those for procedure B when the excess of acetylacetone was 62%, owing to a smaller excess of acetylacetone (the yield is similar for both); and (iv) when the excess of acetylacetone was 3%, they were larger for C than for B, owing to a larger yield (the excess of acetylacetone is similar for both). FeEE (XEE with X = Fe) changed in all procedures owing only to yield, because the excess of acetylacetone had no direct effect on this metric since there is no iron in its composition. In summary, this study helps to elucidate the relationships between the different mass metrics, which are complex and have not been discussed often in the literature.

When the green star and mass metrics (Table 2) are considered together, their comparison shows a contradiction: procedure B (iron(III) citrate as reagent), with reagent ratio closer to stoichiometry, shows the fullest green star and the most favorable value for AE, but the best E factor and MI correspond to procedure C (potassium hydroxide used) and the most favorable RME/AU and FeEE to procedure A (iron(III) chloride used, with stoichiometric ratio closer to stoichiometry). This situation results because green chemistry mass metrics provide an incomplete assessment of greenness, as they do not account for health or environmental risks. Environmental metrics16,17 are essential to complement a green evaluation but they are complex to use. Therefore, green star, in which all the principles of green chemistry at play are accounted for, seems to be a useful metric for the evaluation of greenness, owing to its holistic nature, although so far it has been applied only for assessments in the educational context.25,36,37

’ EVALUATION OF GREENNESS OF THE SYNTHESIS OF ACETYLACETONATES OF BIVALENT METALS Green Star

The green star of the experiments for preparation of manganese
, magnesium
, and calcium
acetylacetonates, as well as their mass metrics, are presented in Table 3. The visual comparison of the six green stars (GS) shows that (for the meaning of GS6
GS11, see Table 3 and Figure 1) (i) under conditions closer to stoichiometry, the area of the green star increases with respect to procedures involving large excess of reagents, owing to effects on the first principle (less excess of acetylacetone in the waste) and the second principle (incorporation of atoms from the reagents into the product), for comparisons GS6 f GS7, GS8 f GS9, and GS10 f GS11; 951

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characteristics: (i) it allows the easy and intuitive comparison of the greenness of different alternative experimental procedures by simple visual analysis, and it can also be easily expressed by a number between 1 and 100 (green star area index) when required for more precise comparisons; (ii) it allows immediate identification, by direct visual analysis, of the aspects that require optimization to improve greenness, as well as assessment of progress along the optimization procedure; and (iii) it is easy to construct, although sometimes it may be difficult to obtain all the information needed regarding the toxic and environmental properties of the substances involved, especially concerning degradability. The present work shows that, when used simultaneously, green star and mass metrics may provide results that are not totally consistent. This is a consequence of the differences in the nature of the assessment they involve (holistic vs reductionist). Mass metrics such as atomic productivity,38 which emphasize concentrating the atoms of the reagents in the product and minimizing their loss in wastes, evaluate only the efficient use of atoms in a chemical reaction. In contrast, green star allows a fuller evaluation of the green quality of a synthesis process, because it includes toxicity and environmental aspects of the substances and conditions of reaction. These differences are shown in Table 4, which, although probably not exhaustive, compares the scope of the two types of metrics with respect to aspects involved in the assessment. This discussion explains why the optimization of a reaction when green star is used may yield procedures with less favorable green chemistry mass metrics, as found in the case of the iron(III)
acetylacetonate. The latter ignore toxicological and environmental implications and may provide a distorted picture of the global greenness. Greenness is a difficult concept to measure because of the intrinsic complexity of the chemistry and its multiple connections with the environment, the biosphere, and society itself. Holistic metrics are preferable but they are difficult to devise and to handle, and therefore, in practice, reductionist metrics are often sought in evaluating greenness, despite the fact that the interplay between some of these is sometimes complex. This work suggests that a more complete evaluation of reactions and procedures is provided by the simultaneous use of both types of metrics. Green star provides a broad view, whereas mass metrics a more restricted assessment addressing only the productivity of atoms. Another tool for holistic assessment of greenness, iSUSTAIN,39 has been recently introduced, but we have not yet compared its use in parallel with green star. Finally, the present study shows that the synthesis of calcium
acetylacetonate should be preferred among the metal
acetylacetonates as an example of green chemistry. However, this choice may not be suitable, for instance, if the synthesis is included in the laboratory course to illustrate the chemistry of transition-metal ions—which shows that the concept of greenness is relative, a natural consequence of the extreme complexity of chemistry!

Table 4. Factors that Influence Green Star and Green Chemistry Mass Metrics Effects on Green

Effects on Mass

Factor

Star

Metrics

Nature of the waste Nature of solvents

Yes Yes

No No

Mass of the waste

No

E factor, MI

Mass of solvents, including

No

E factor, MI

water Yield

No

E factor, MI, AU, RME, XEE

Energy efficiency

Yes

No

Use of renewable feedstocks Reduction of derivatizations

Yes Yes

No No

in chemical reactions Nature of catalysts

Yes

No

Degradation of the substances

Yes

No

Risks to human health

Yes

No

Risks to the environment

Yes

No

Risks to cause chemical accident

Yes

No

involved

and (ii) for calcium
acetylacetonate, the green star presents a larger area than for the other complexes because all the substances used were milder with respect to environmental and safety characteristics and no byproducts were produced (excluding water); therefore, the scores of second, third, fifth, and 12th principles increased, for comparisons GS7, GS9 f GS11. The values for green star area index included in Table 3 confirm the visual evaluation of the green star. The value for the calcium complex (GSAI = 57.50 for GS11) is the highest that it was possible to obtain in the present greenness optimization. Yield and Green Chemistry Mass Metrics

Near stoichiometry, the E factor and MI decreased and RME/ AU increased. This is due to a decrease in the masses of the stoichiometric reagents, although in the cases of the synthesis of magnesium
and calcium
acetylacetonates close to stoichiometry the yield decreased. In this case, the positive effect of the decrease of the excess of the acetylacetone predominated over the negative effect of the decrease of the yield. XEE (X = Mn, Mg, Ca) changed owing only to variation of yield, as in the element efficiency of iron(III)
acetylacetonate synthesis. The E factor and MI were the smallest and RME/AU, XEE, and AE the largest for the synthesis of calcium
acetylacetonate. There are three main reasons for this situation: (i) the E factor and MI decreased owing to a larger yield and the absence of auxiliary reagents (except water); (ii) RME/AU and XEE increased owing to a larger yield; and (iii) AE increased owing to a larger ratio of the molar mass of the product to the molar mass of calcium hydroxide when compared with the similar ratios for manganese and magnesium cases (chlorides) (see formula for the calculation of AE in Supporting Information).

’ DISCUSSION Green star, because it is a holistic green chemistry metric that considers all the relevant 12 principles in a global and systemic way, is useful in evaluating the greenness of a specific chemical reaction. This usefulness is a consequence of the main green star

’ CONCLUSIONS Hjeresen7 refers to the importance of using green chemistry to involve young people in the preservation of the planet for future generations, by explicitly connecting green chemistry teaching with the promotion of sustainable development. It is indeed crucial for achieving sustainability to incorporate green chemistry 952

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in the teaching of chemistry, and in this context, students should be made aware of the importance and difficulties of optimizing the greenness of chemical reactions. The strategy proposed in the present work is useful for this goal: the students become familiar with the 12 principles of green chemistry and green metrics and gain some experience in considering aspects to be changed to improve the greenness of chemical reactions. For complete and reliable evaluation of the greenness of a synthetic pathway, procedure, or chemical process, several characteristics of the compounds involved in the reactions and the reactions themselves, environment, safety, efficiency, energy, economy, and so forth40 have to be considered. Green chemistry mass metrics provide useful indications about greenness, but in some cases, the results of these calculations may be contradictory. Moreover, they provide only an incomplete picture of greenness, as environmental metrics,16,17 complex and difficult to use as they are, are required to complement this information. In contrast, green star responds holistically to the many features that have to be considered when the greenness of a chemical reaction is under discussion, as it involves in its global and systemic assessment all the relevant 12 principles of green chemistry. Although the information it provides may not be complete, its parallel use with mass metrics gives a fuller accountancy of greenness.

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’ ASSOCIATED CONTENT

bS

Supporting Information Three files are provided: (i) experimental procedures for synthesis of acetylacetonates; formula to calculate the green chemistry mass metrics for a chemical reaction; information for construction of green star (criteria for attributing scores and scores for the construction of green star for the acetylacetonates); (ii) Excel file to obtain the green star and to calculate green star area index; and (iii) green star animations to visualize the increase in greenness along with the optimization of procedures. This material is available via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT The authors wish to thank the preservice teacher Olga M. S. Martins for her support in the laboratory work. ’ REFERENCES (1) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: London, 1998. (2) Lancaster, M. Green Chemistry
An Introductory Text; The Royal Society of Chemistry: Cambridge, 2002. (3) Winterton, N. Green Chem. 2001, 3, G73–G75. (4) Anastas, P. T.; Zimmerman, J. B. Environ. Sci. Technol. 2003, 37, 95A–101A. (5) Anastas, P.; Wood-Black, F.; Masciangioli, T.; McGowan, E.; Ruth, L., Ed.; Exploring Opportunities in Green Chemistry and Engineering Education: A Workshop Summary to the Chemical Sciences Roundtable; The National Academy Press: Washington DC, 2007. (6) Braun, B.; Charney, R.; Clarens, A.; Farrugia, J.; Hitchens, C.; Lisowski, C.; Naistat, D.; O0 Neil, A. J. Chem. Educ. 2006, 83, 1126–1129. 953

dx.doi.org/10.1021/ed100174f |J. Chem. Educ. 2011, 88, 947–953