In the Laboratory
Caring for the Environment While Teaching Organic Chemistry Elvira Santos Santos,* Irma Cruz Gavilan Garcia, and Eva Florencia Lejarazo Gomez Environmental Division, School of Chemistry, Universidad Nacional Autonoma de México, Ciudad Universitaria 04510, Coyoacan, México D. F.; *
[email protected] It is accepted worldwide that the treatment and proper disposal of hazardous wastes1 is the responsibility of the generator; that means, it is in the responsibility of those people who handle chemical reagents and products (pure and mixed) in large or small quantities to dispose of the wastes. The increasing deterioration of the environment demands an acceptance of this responsibility. Through ignorance of the hazards or lack of the proper methods for handling and treating chemical products and residues, past generations have contributed in polluting the environment (air, water, and soil). For this reason, the Organic Chemistry Department at the School of Chemistry of the National Autonomous University of Mexico (UNAM) is teaching an environmentally conscious organic chemistry lab structured with not only the goal of obtaining a product with a high yield and quality, but also awareness of the environmental impact the products, byproducts, and residues generated during the different stages of the experiment will have. Therefore it is important to know the physical, chemical, and toxicological properties, as well as how to apply an appropriate treatment to dispose of the wastes to conclude a successful experiment. Students acquire knowledge and develop the basic abilities needed to solve different types of problems related to synthesis, separation, purification, and analysis in the laboratory. Often, the students are so interested in these objectives that they do not pay attention to the wastes generated during the experiments. It is well known that lab experiments usually generate small quantities of a large variety of wastes. The complexity of the wastes generated in educational labs is diverse. Thus, detailed studies of their treatment have been undertaken (1–3). In U.S. universities, according to their national and local legislation (4–7), the waste problem has been solved by preliminary handling, followed by accumulation processes (8) in order to send these wastes to specialized companies for treatment and disposal. In Mexico, there are no specific regulations for the wastes generated in academic institutions. In addition there are not many hazardous waste treatment companies. Therefore, we have developed an holistic program towards green chemistry, focusing on the treatment and handling of wastes generated during experimental lab sessions and broader educational issues. The program objective is environmental awareness in chemistry teaching. This program has been useful as an educational method particularly when conducting experiments in the organic chemistry lab (9, 10). In Mexico there are very few people prepared to organize, guide, and follow a plan designed to solve the waste problems in an integral way. For this reason, we believe that the experimental chemistry labs would be an ideal location for students to determine possible solutions to the waste problems. The Organic Chemistry Department has been working since 1990 on programs that make students conscious of the environment while learning organic chemistry. The name of one these programs is called “Taking Care of the Environment in the Experimental Organic Chemistry Teaching”. 232
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Program Objective The main objective of this program is for chemistry students to learn about waste treatment methods and microscale and semi-microscale (0.1–10 g) experiments. This gives us an opportunity to introduce students to process optimization, waste minimization, nonpolluting processes (green processes), recycling of residues, reusing of products and residues, conversion of toxic wastes to nonhazardous wastes, and stabilization and conditioning of toxic residues. When these procedures are not possible, the last option is incineration or confinement at a site approved by Mexican environmental authorities. This knowledge creates an environmental conscience in the students that will be retained when they finish their studies and start working. Ultimately, the students may influence the decisions that industry managers make regarding their responsibilities to society on environmental issues. This program energized instructors to seek an environmental quality improvement through education. However, global markets mandate that environmental problems are not matters of a single country, as pointed out by the United Nations Environment Programme’s Chairman (11), but are everyone’s problem for future generations. As we have begun to educate students, they have become more environmentally conscious and have been able to participate in solving environmental problems. Since this program has been permanently incorporated into their experimental work, a separate lab called “Environmental Management Unit” was established. This lab allowed the implementation of the methodology described in this article for teaching experimental chemistry. Currently we are collaborating with all departments at the School of Chemistry (approximately 5000 undergraduate students) and with professors and researchers of 26 different branches of the UNAM 2 through a second program called “Ecological Control of the University’s Campus”. Our hope is that future generations of UNAM graduates will have a “caring-forthe-environment” attitude. Program Description
Ecological Diagrams The first aspect of the program is to teach students to identify the wastes generated in each experiment. The second is to quantify the wastes (volume or weight) to establish the relationship between quantity of raw materials versus quantity of wastes. When analyzing experiments in chemistry handbooks (12–14), we found that the procedures3 generally are limited to a small paragraph in which the only instructions are about how and when reagents are added, energy provided, or unitary operations are developed that lead to isolation and, in some cases, purification of the desired product. There are
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In the Laboratory
few experiments that consider characterization and waste treatment (14). We cite below the traditional procedure of a classical experiment in organic chemistry, the synthesis of 3,5dimethylisoxazole (10), as an example: To a hydroxylamine hydrochloride solution (3.5 g) in water (7 mL) contained in a round-bottom flask, is added acetylacetone (5.1 mL). The mixture is heated with reflux until the ferric chloride test is negative (approximately 45 min). Empty the reacting mixture right away in cold water (30 mL) and extract the product with dichloromethane (2 × 15 mL). Collect both extracts. Dry with anhydrous sodium sulfate. Once the organic phase is dry, separate the sodium sulfate by filtration. Distill the solvent, transfer the residual brown oil to a 25-mL flask and distill, eliminating the first fraction. Collect the 3,5-dimethylisoxazole, which distills as colorless oil at a temperature from 142 ⬚C to 144 ⬚C at 760 mm Hg (128–132 ⬚C, 585 mm Hg).
When students read the procedure, their attention is only focused on generating the product. Even if they try, the students may have problems identifying the quantities of residues4 or byproducts5 they generate when following the reaction. For this reason, we developed a diagram named the “ecological diagram” (Figure 1) that was added to the classical procedure. In this diagram we show in a simplified and clear manner each step of the procedure and, more importantly, the generated residues are marked with symbols that point out the different wastes (R1, R2, R3, R4, R5) in a sequential way indicating the order of their generation. The method currently used at UNAM to obtain the 3,5dimethylisoxazole follows the traditional procedure while using the ecological diagram developed for this experiment. Thus, the student can identify the steps where each waste residue is generated, as well as the treatment for each waste. The ecological diagrams for the experiments of all the courses given in the School of Chemistry at UNAM for the different majors (chemist, chemical engineer, pharmacobiological chemist, food chemist) have been developed. To date, 150 ecological diagrams and 570 waste residues had been identified. For each residue, a treatment method has been developed, tested, and incorporated into the class manuals.
Classification and Identification of Residues Once the number of generated residues in each experiment is known, we established its nature based on degree of damage and, according to the Mexican regulations, as innocuous or toxic. In order to classify wastes as innocuous, we had to know the theoretical and actual chemical composition of each waste. The theoretical composition is obtained by following the reactions of the procedure. To obtain the actual composition, we had to make qualitative and quantitative chemical tests, using different techniques and instruments, for example, pH meter, thin layer chromatography, gas chromatography–mass spectrometry, high-performance liquid chromatography, or atomic absorption spectroscopy, depending on the residue’s nature. After determining waste residue composition, we proceed to investigate the innocuous or toxic nature of the waste, consulting reference sources (1–8). One of the most valuable sources was the MSDS (Material Safety Data Sheets), www.JCE.DivCHED.org
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hydroxylamine hydrochloride, acetylacetone 1) mix and reflux 45 min
reaction mixture test with FeCl3 for absence determination of acetylacetone
R1
reaction mixture 2) add water (30 mL) 3) extraction with dichloromethane (2 × 15 mL) 4) phase separation
organic layer
aqueous layer
raw material, product traces, water
3,5-dimethylisoxazole, dichloromethane 5) dry with anhyd Na2SO4 6) filter, wash CH2Cl2
solid
R2
liquid
sodium sulfate wet
3,5-dimethylisoxazole, dichloromethane
R3
7) distill
distillate
residue
dichloromethane R4
crude product 8) distill, recover the fraction between 128–132 °C
residue
distillate
distillation residue
3,5-dimethylisoxazole
R5
incineration
treatment
recycling
Figure 1. Ecological diagram of the synthesis of 3,5-dimethylisoxazole.
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but owing to the lack of these written in Spanish, we had to adapt (and in some cases elaborate) them for academic purposes according to the OSHA’s Hazard Communication Standard, 29 CFR 1910. 1200. Consolidating this information, a student reference source, Handbook of Handling Toxic and Hazardous Substances Used in Experimental Work, was published. This manual contains the material safety data sheets used in all the organic chemistry courses and of most products used in the labs. Currently, we are creating a database to add the information in the manual to our Web site for Spanish speaking users.
Waste Recycling, Reusing, and Treatment After the toxic nature of the residues has been ascertained, the following possibilities exist for disposal: i. Recycling: When a waste contains one or more of the raw materials that were not consumed during the process, studies are made to find out whether or not it is possible to reuse the wastes as raw materials in the same experiment for subsequent courses. If purification is needed, the cost of this must be evaluated (cost–benefit balance). When there is a solvent in high concentration in the residue, it can be purified by distillation and reused.
instructor selects the residue; the instructor usually collects 6–10 residues during the semester. This exercise assures the students that the residues are really being studied and treated and that they are not just collected and then thrown away. Additionally, it shows the students that the analysis and treatment of the residues represents many difficulties, which, under the supervision of their teachers, can be solved. Process Optimization: Residues Minimization, A New Educational Strategy To illustrate one of the optimization strategies, synthesis of anthraquinone is discussed because it is a special type of ketone, a quinone, as well as a raw material for several dyes. Also, there are several synthetic routes that are simple and adequate to obtain the same product. By studying the different synthetic routes it is possible to minimize the ecological impact.
Synthesis of Anthraquinone from Anthracene The traditional method for anthraquinone synthesis involves the use of chromium salts and starts from anthracene, O
ii. Reusing: When a waste is a byproduct, it is determined if it could be used in another experiment as a raw material or if it could be transformed into another compound that could be useful. iii. Treatment: When a waste cannot be recycled or reused, and it has dangerous properties, it must be treated by an appropriate method to obtain: a. Nontoxic product: This can be done through one or many reactions (if during this process no more toxic waste is generated). These nontoxic products can be thrown into the garbage if solid, down the drainage if liquid, or into the air if gaseous. b. Reduced to a better handling form: If the waste is, for example, a solution we can precipitate it. In other cases, the solution, if it is an organic solution or an inorganic–organic mixture, can be concentrated and thus transported in a safer and less costly way to an incinerator,6 or to confinement7 when it is a toxic inorganic or a polyhalogenated product. This technology must be in accordance with all the Mexican federal regulations.
Once these residues are collected, they can be transported to the “Environmental Handling Unit” in the School of Chemistry, where they will undergo several procedures (i, ii, or iii above). Social Service8 students of all majors (chemistry, chemical engineering, pharmacobiological chemistry, and food chemistry) conduct these procedures designed by teachers and students that participate in the program.
Introduction of an Experiment for Recycling, Reusing, and Treatment of Hazardous Residues We introduce as the last experiment of each organic course the development of procedures i, ii, or iii. The students develop a waste treatment method for one of the residues they generated during one of their experiments. The lab 234
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CrO3 AcOH
O anthracene
anthraquinone
and is described below: Place 2.0 g of powdered anthracene and 30 mL of glacial acetic acid in a 250-mL, two-necked round-bottomed flask with a reflux condenser and a dropping funnel. Mix the flask contents thoroughly by a swirling action and heat the mixture to reflux when most of the anthracene dissolves. Dissolve 10 g of chromium trioxide in 7–8 mL of water, add 25 mL of glacial acetic acid and pour the well-stirred mixture into the dropping funnel. Remove the heat source from the flask and add slowly the oxidizing reagent at such a rate that the mixture continues to reflux (7–10 min); then reflux for another 10 min until the anthracene has completely reacted. Cool down the solution and pour it into 250 mL of cold water. Stir the mixture vigorously, filter off the precipitated anthraquinone under gentle suction, wash it thoroughly on the filter with hot water, then with 50 mL of hot 1 M NaOH solution and finally with an excess of cold water; drain well. Dry the anthraquinone by pressing it between several sheets of filter paper and leave it overnight in a desiccator over CaCl2. The yield is 5.5 g (94%). Purify the anthraquinone by either of the following methods: i. Crystallize the crude product from boiling glacial acetic acid with the aid of decolorizing charcoal, wash the resulting crystals on the Buchner funnel with a little cold rectified petroleum ether and dry in the air. ii. Sublime the dry solid; the purified anthraquinone is obtained as yellow crystals having a mp of 286 ⬚C.
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The ecological diagram is shown in Figure 2. As can be seen residues R1 and R2 are generated. Their predominate hazardous characteristics are described in Table 1. Anthraquinone synthesis is no longer synthesized from anthracene and chromium salts and is only used for comparative experiments.
Optimization of the Synthesis of Anthraquinone from o-Benzoylbenzoic Acid Another synthetic route for the synthesis of anthraquinone uses o-benzoylbenzoic acid and has been used worldwide for several years. As a first step, a reference search of the reported techniques was made. In different sources several conditions for the synthesis are described (from 100 ⬚C to 150 ⬚C; from 5 min to 120 min; and using between 3 and 5 mL of H2SO4 for 1, 2, or 5 grams of o-benzoylbenzoic
acid). These syntheses show noncorrelating results (yields) and in some cases they do not include a reported yield. We show some of these results in Table 2. As a result of the variation in experimental conditions, the students were given as a problem the optimization of this synthesis. While optimizing the synthesis the students were to deduce the influence of the selected independent variables on product yield and to find a value for each of these variables that would give the highest yield and minimize the residues generated. We conducted some initial experiments, modifying the reaction conditions (H2SO4 volume, time, and temperature) to establish the maximum and minimum limits of each variable in which each student could obtain congruent results. Ultimately, the optimization problem considered only the ef-
Table 1. Components of Residues R1 and R2 from the Anthraquinone Synthesis
anthracene, glacial acetic acid
CrO3, CH3CO2H, H2O
1) reflux dropping
Component
Characteristic
Cr(VI); Cr (III)
Toxic
CH3COOH
Corrosive
Anthracene
Toxic
NaOH
Corrosive
2) reflux (10 min)
Table 2. Traditional Routes for the Synthesis of Anthraquinone
reaction mixture 3) water 4) filter
liquid
Cr(III), Cr(VI), acetic acid, H2O
solid
o-Benzoylbenzoic acid/g
Acid/ (ml, g)
Temp/ ºC
5
H2SO4
150
Time/ min
Yield/ g
Ref
5
---
15
150
60
---
16
100
120
1.8
17
100
30
4–4.5
18
5, 9.1
anthracene, anthraquinone, AcOH
1
H2SO4 3, 5.5
5) wash (hot water)
R1
7) wash (cold water)
liquid
H3PO4
2
6) wash (1 M NaOH)
25, 42.1
solid
5
H2SO4 5, 9.1
NaOH, AcONa, H2O, pH > 9
crude anthraquinone recrystallization
Table 3. Anthraquinone Yield at Different Reaction Conditions
sublimation
Experiment
R2
incineration
pure anthraquinone
treatment recycling and confinement
Figure 2. Ecological diagram of the anthraquinone synthesis from anthracene.
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Time/min
Temp/⬚C
H2SO4/g
Yield(%)a
A1
60
62
5.7
1.12
A2
60
62
7.6
14.04
A3
60
62
9.5
38.03
B1
60
90
5.7
45.68
B2
60
90
7.6
61.37
B3
60
90
9.5
75.85
C1
60
120
5.7
98.65
C2
60
120
7.6
94.50
C3
60
120
9.5
96.08
a
Average value from several experiments done by students during six semesters.
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100
Table 4. Compounds Found in Residues A1 and C1
9.5 g H2SO4 7.6 g H2SO4
80
Yield (%)
5.7 g H2SO4 60
Exp
H2SO4/ g
Yield (% )
Residues (R2, R3)
A1
5.7
1.12
90% raw material, Na2SO4a, H2O
C1
5.7
98.65
1.2% raw material, Na2SO4a, H2O
a
40
Innocuous (approximately 8 g of Na2SO4).
20
0 0
20
40
60
80
100
120
140
Temperature / °C Figure 3. Yield versus temperature at constant time (60 min) for the synthesis of anthraquinone from o-benzoylbenzoic acid.
fect of the temperature and the quantity of acid and was presented to the students as: Deduce the reaction conditions (temperature and quantity of sulfuric acid) necessary to obtain anthraquinone with a yield higher than 90% and a purity of 99% starting with o-benzoylbenzoic acid in 60 minutes of total reaction time. O
O H2SO4
C o-benzoylbenzoic acid, conc H2SO4
OH O
O o-benzoylbenzoic acid
anthraquinone
1) heat
Weigh 1 g of o-benzoylbenzoic acid in a test tube, add cautiously, drop by drop, while stirring the concentrated sulfuric acid; heat the reaction in a constant temperature bath the indicated time, stir occasionally. At the end of this period let the mixture reach room temperature and pour over 50 g ice兾water contained in a 250-mL Erlenmeyer flask. Add a 30% NaOH solution until pH = 10.0, filter, wash with water until pH = 7.0. Dry the obtained product. Determine its melting point and the purity of the product with thin layer chromatography (take an infrared spectrum of the product), and determine the yield.
reaction mixture 2) pour over 50 g ice/water 3) filter
liquid
solid
anthraquinone, raw material, H2SO4 (trace)
H2SO4(aq) R1
4) wash (30% NaOH)
liquid
solid
o -benzoylbenzoic sodium salt, Na2SO4, NaOH, H2O
anthraquinone, alkaline 5) wash (H2O)
liquid
R2
solid
o-benzoylbenzoic salt, NaOH, sodium traces
incineration
treatment
anthraquinone
recycling
Figure 4. Ecological diagram of anthraquinone synthesis from o-benzoylbenzoic acid.
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If it is desired, time can be a variable too but the number of experiments increases considerably as does the total time that each student must spend to solve the problem. The results obtained in several experiments at different temperatures (60, 90, and 120 ⬚C) using 5.7 g, 7.6 g, and 9.5 g of concentrated H2SO4, with a fixed reaction time at 60 min are shown in Table 3. At 120 ⬚C with any quantity of H2SO4 the yield is always above the 90% required by the problem. The highest yield is obtained with the minimum quantity of acid, which also generates less residual acid. It can be clearly seen that in order to obtain a good yield of the anthraquinone the determining variable is the temperature. The quantity of H2SO4 is also important but not in the same magnitude as the temperature, which is clearly observed by plotting a graph of “yield versus temperature” with different quantities of H2SO4 (Figure 3). If we compare experiment A1 with C1 (Table 3), we find that more product is formed in the latter than in the former. With these results students can easily deduce that obtaining the maximum yield minimizes the generation of residues (Table 4). The ecological diagram for this experiment is shown in Figure 4.
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In the Laboratory
Synthesis of Anthraquinone from o-Benzoylbenzoic Acid Using Microwave Technology
Table 5. Results from the Microwave Synthesis of Anthraquinone
Anthraquinone starting from o-benzoylbenzoic acid and using a microwave technology (19) was examined as a green experiment. The synthetic problem was presented to the students as:
Time/min
Determine the necessary reaction time in order to obtain anthraquinone with an 80% yield and 99% purity starting with o-benzoylbenzoic acid using an acidic clay (K-10) as a catalyst, and microwaves as the source of energy.
a
Yield (% )a
15
20
20
50
25
80
40
85
In all cases the purity is 100%.
A Petri dish with 0.5 g activated clay (K-10) and 0.1 g of obenzoylbenzoic acid well mixed is placed inside a Pyrex container containing iron tetroxide–aluminum oxide (50%–50%). A filtration funnel (previously weighed) is used to cover the reaction mixture. A test tube is placed over the funnel stem (Figure 5). The whole system is placed inside an adapted commercial 900 W microwave oven. Examine different reaction times until the desired yield is achieved. Once the reaction time has been reached the Pyrex container is carefully taken out of the oven and left until it reaches room temperature. The funnel containing the anthraquinone crystals that have sublimed is weighted. The mass of product is determined by subtraction. The melting point is determined and the purity is determined by thin layer chromatography, FTIR, or HPLC; the yield is calculated for each selected reaction time (Table 5).
Figure 5. Microwave oven containing the apparatus for the synthesis of anthraquinone.
This technique gives the opportunity to reuse the acidic clay (K-10) catalyst 15–20 times. It allows the production of a pure product without further purification owing to the in situ sublimation (Figure 6). In this way, the production of any residue is eliminated, which is a clean process (Figure 7).
This project was extended to the Ecological Improvement of the University’s Campus Program (information pamphlet: Campus’ Ecological Control, first edition, May 1994) and is being implemented in 18 different branches of the university as an educational project. This program stimulates students, researchers, teachers, and the authorities to become responsible for the adequate handling of the wastes generated. Our main goal is to encourage Mexican institutions to assume their responsibilities in taking care of the environment as well as modifying habits and attitudes to develop an environmental culture among the future professionals in chemistry. We developed a methodology that joins teaching of chemistry and the care for environment in which students gain insight onto the concepts of pollution, health care, environment care, hazardous materials, hazardous wastes generation and minimization, processes optimization, clean processes, and social responsibility.
80
Yield (%)
Conclusions
100
60
40
20
0 0
5
10
15
20
25
30
35
40
45
Time / min Figure 6. Yield versus reaction time for the synthesis of anthraquinone using microwave technology.
o-benzoylbenzoic acid, activated clay (K-10) 1) heat (microwave)
solid
sublimed solid
Acknowledgments This work would not have been possible without the support and collaboration of the organic chemistry professors and lab heads on each of the courses in which this methodology was used, as well as the heads of departments. We wish to extend our special recognition to the Social Service www.JCE.DivCHED.org
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raw material (trace), activated clay (K-10)
pure anthraquinone
Figure 7. Ecological diagram of anthraquinone synthesis from obenzoylbenzoic acid using microwave technology.
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students that have participated in this project and to those who have unconditionally contributed their knowledge, energy, and enthusiasm to work on a common cause for the benefit of all members of the University.
4.
Notes
5.
1. Hazardous waste is defined as any material that, because of its quantity, concentration, chemical, physical, or infectious characteristics, represents a health risk or a threat to an ecosystem. 2. The organizational structure of the UNAM is different from U.S. universities; UNAM is composed of schools (i.e., medicine, law, etc.) and institutes (immunology, materials, etc.). 3. Each experiment protocol contains in its format: objectives, reaction, material, substances, procedures, comments, questions, and references. 4. Residue is defined as any material generated during a transformation or process that by its nature can not be reused in the same process. 5. A byproduct is defined as material obtained from a transformation or a process that differs from the desired product. 6. An incinerator is an oven that operates at high temperatures, performing the combustion of organic residues decomposing them until inorganic residues are obtained (salts, ashes, etc.). 7. Controlled confinement is the work of engineering for the storage or final disposal of hazardous wastes that will guarantee its isolation. 8. Social service is an activity developed by Mexican students that is related to their field and provides a community benefit. It must last 460 hours and students can receive scholarships for the service.
6.
1. Arkansas Guide for Small Quantity Generator of Hazardous Waste; Department of Pollution Control and Ecology: Little Rock, AR, April 1988. 2. Waste Disposal in Academic Institutions; Kaufman, J. A. Ed.; Lewis: Chelsa, MI, 1990. 3. Understanding the Small Quantity Generators of Hazardous Waste
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8. 9.
10.
11. 12. 13.
14.
15. 16.
Literature Cited
238
7.
•
17. 18. 19.
Rules: A Handbook for Small Business; EPA/530-SW-86-019; U.S. Environmental Protection Agency: Washington, DC, 1986. Prudent Practices for Disposal of Chemicals from Laboratory; National Academy Press: Washington, DC, 1983. Prudent Practices in the Laboratory, Handling and Disposal of Chemicals; National Academy Press: Washington, DC, 1995. Lunn, G.; Sansone, E. Destruction of Hazardous Chemicals in the Laboratory; Wiley-Interscience Publication: New York, 1990. Armour M. Hazardous Laboratory Chemicals Disposal Guide; CRC/Lewis Publishers: Boca Raton, FL, 1996. Zimmer S. W. J. Chem. Educ. 1999, 76, 808–811. Santos, S. E.; Gavilán, G. I.; Korkowski, P. I.; Lomeli, T. V.; Medina, D. G. Handling of Waste Chemicals in Educational Laboratories; Fourth Chemical Congress of North America: New York, 1991; pp 25–30. Química Orgánica; Experimentos con Enfoque Ecológico; Dirección General de Publicaciones y Fomento Editorial: UNAM: México, 2001. UNEP Helmsman Topfer Addresses Environmental Challenges, Environ. Sci. Technol. 1999, 33, 18A–23A. Mayo, D. W.; Pike, R. M.; Trumper, P. K. Microscale Organic Laboratory, 3rd ed.; John Wiley & Sons: New York, 1994. Pavia, D. L.; Lampman, G. M.; Kriz. G. S. Introduction to Organic Laboratory Techniques, 3rd ed.; Saunders College Publishing: Philadelphia, PA, 1998. Mohrig, J. R.; Noring, C. H. Experimental Organic Chemistry, A Balanced Approach: Macroscale and Microscale; W. H. Freeman and Company: New York, 1998; pp 186–202. Fieser, L. F.; Fieser, M. Organic Experiments; Chapman & Hall, LTD: London, U. K., 1956; pp 761–765. Anderson, L. C; Elderfield, R. C.; Bachmann, W. E. A Manual for the Organic Chemistry Laboratory; John Wiley & Sons, Inc.: New York, 1960; pp 157–159. Vogel, A. I. Practical Organic Chemistry, 3rd ed.; Longmans Publishers: London, 1956; pp 728–740. Adams, R. Laboratory Experiments in Organic Chemistry, 5th ed.; McMillan Company: New York, 1970. Bram, G.; Loupy, A. Chem. & Ind. 1991, 396–397.
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