A Greener Organic Chemistry Course Involving Student Input and

Chapter 4

A Greener Organic Chemistry Course Involving Student Input and Design Downloaded by UNIV OF IDAHO on November 22, 2016 | http://pubs.acs.org Publication Date (Web): November 16, 2016 | doi: 10.1021/bk-2016-1233.ch004

Loyd D. Bastin* and Kaitlyn Gerhart Departments of Chemistry and Biochemistry, Widener University, One University Place, Chester, Pennsylvania 19013, United States *E-mail: [email protected]

When greening an organic chemistry laboratory, redesigning the course to educate students about green chemistry rather than simply greening the individual experiments is crucial. This chapter describes a process of redesigning the organic chemistry I laboratory from a microscale course into a green chemistry lab. An organic chemistry I laboratory course where the students learn key organic chemistry techniques, the principles of green chemistry, and to apply green chemistry concepts was developed. A feedback mechanism was designed to involve students in the development and greening of experiments. As a capstone experiment, a three step inquiry-based, green synthesis was devised. The capstone experiment requires the students to search the literature and find methods for performing a carbonyl reduction, alcohol dehydration, and alkene bromination. The student-researched methods are analyzed as a class exercise before the experiments are performed, and the class chooses the best method for each reaction.

© 2016 American Chemical Society Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Downloaded by UNIV OF IDAHO on November 22, 2016 | http://pubs.acs.org Publication Date (Web): November 16, 2016 | doi: 10.1021/bk-2016-1233.ch004

Introduction One of the major challenges facing society in the 21st century is environmental sustainability. How do we as a society continue to meet our demands and needs without compromising the ability of future generations to meet their needs (1)? Since a key component of an environmentally sustainable future is to decrease the amount of pollution and use of natural resources by chemical industries, chemists and engineers will play a key role in addressing the sustainability challenge. In order to combat the pollution and overuse of our natural resources, the chemical industry will need to develop new processes and products that use starting materials from renewable sources, develop new products that are biodegradable, and develop processes that generate less hazardous waste and use less hazardous substances. In order to provide scientists and engineers with the tools necessary to address these challenges, we must educate future generations about sustainability, green chemistry, and green engineering. Students need to understand the importance of environmental sustainability, the principles of sustainability (triple-bottom line and life cycle analysis), and how green chemistry can be a tool to address the challenge. Therefore, it is important for chemistry faculty to infuse sustainability and green chemistry into the curriculum. While there are a variety of textbooks available for organic chemistry courses (2–5) and multitudes of experiments published in the Journal of Chemical Education for organic chemistry courses, there are only two textbooks for a green organic chemistry laboratory course (6, 7). A number of green organic chemistry laboratory experiments have been published in the Journal of Chemical Education, but there are substantially fewer green experiments found in the Journal of Chemical Education than traditional organic chemistry experiments. However, the number of published green organic experiments is increasing and were recently summarized by Dicks (8) in a supplemental textbook for chemists who wish to incorporate green chemistry into the organic chemistry lecture and laboratory curriculum. Here we describe the design of an organic chemistry sequence that immerses the students in a laboratory experience where they learn to apply the principles of green chemistry (9). This goal is accomplished through a sequential and deliberate introduction to environmental contamination and chemical exposure, introduction to sustainability and green chemistry, and laboratory experiments that have been revised to be greener. Additionally, the students are asked to analyze the experiments using the twelve principles of green chemistry and several green chemistry metrics. Finally, the students are asked to provide suggestions to improve the greenness of each experiment. These suggestions were then investigated by a group of undergraduate research students for incorporation into the subsequent offering of the course. Widener University is a private, primarily undergraduate, regional metropolitan university with ~2900 undergraduate students. The chemistry department is an undergraduate only, ACS-approved department consisting of nine tenured and two non-tenure track faculty. The department graduates three to six chemistry majors per academic year, and many of our upper level courses are populated by of students majoring or minoring in chemistry, chemical engineering, 56 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


biochemistry, environmental science, and biology. The organic chemistry I course discussed here is taken by about 60 second year biology, chemical engineering, chemistry, biochemistry, and environmental science students each year. The four-credit lecture portion of the course consists of four 50 minute class periods each week. The laboratory portion is an additional one-credit course consisting of a 50 minute lab lecture and three hour laboratory session each week. The lab lecture hour convenes all 60 students at the same time and introduces the students to the experiments, techniques, lab notebook expectations, and green chemistry. There are five laboratory sections of organic chemistry I offered each fall semester with an enrollment between 14-16 per section. Since our revision of the course eight years ago, approximately 460 students have participated in the greening process described.

Design Process Previous to our redesign, the organic chemistry I laboratory experiments at Widener were performed on the microscale. While the microscale techniques successfully reduce waste and minimizes risk by reducing the chemist’s exposure to hazardous chemicals, this approach does not address the larger problems of hazardous waste disposal in industry and the potential large scale exposure of the environment to hazardous chemicals. Rescaling a reaction does not truly address the issue of hazardous waste disposal or the need for more environmentally friendly solvents, reagents, and reactions. Therefore, we transformed the organic chemistry I laboratory into a green organic chemistry laboratory. The redesign was guided by the goal to educate students about green chemistry rather than simply greening the individual experiments. Also, it was imperative to design the laboratory to incorporate the principles of green chemistry throughout the course regardless of whether the experiments have been completely “greened”. Our approach involved assessing the pedagogical value of current experiments performed in the organic chemistry I laboratory. We then interviewed science faculty to determine the skills/knowledge that students should obtain from the laboratory course. Using this information, we searched the current literature for green organic chemistry experiments that met revised course goals. As we found suitable experiments, the experiments were performed and evaluated for pedagogical value. We selected the experiments that met the revised course goals and included green chemistry concepts. Greening the organic chemistry laboratory accomplished several goals: (1) The experiments utilize safer starting materials, reagents, and products, (2) the students learn about renewable resources and recycling of reaction products, (3) the experiments use safer solvents, and (4) the waste generated is less hazardous.

Immersion of Students in the Greening Process When the experiments were implemented eight years ago, we intentionally designed a feedback loop into our course design. Hence, the experiments are continually evaluated and some have been improved based on student suggestions 57 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


over the past eight years. This feedback mechanism (Figure 1) requires the organic chemistry students to suggest modifications to the experiments as part of their laboratory reports. Although others have greened their organic chemistry lab courses (6, 10–13), our approach to the course offers a learning experience that ask the students to suggest modifications and be involved in the greening of the course and individual experiments. These modifications are then evaluated and researched by undergraduate students in the research lab. If these improvements are greener than the current experimental procedure, the experiment is modified and the students the following year use the modified procedure. As a result of these experiences, students are challenged to apply their knowledge, and in so doing, feel a sense of accomplishment and involvement far beyond what a typical lab provides.

Figure 1. Feedback mechanism to involve students in the greening process.

Experiments Solventless Aldol Condensation The first experiment of the organic chemistry I laboratory is a solventless aldol condensation (Figure 2) adapted from published experiments by Doxsee et al. (14) and Thompson (15). The experiment is used to introduce the concepts of solubility, recrystallization, filtration, melting point, and mixed melting point. Additionally, this experiment introduces the Twelve Principles of Green Chemistry (9). The experiment exhibits three green chemistry principles: atom economy, waste reduction via a solventless reaction, and catalysis. The experimental procedure is very green and we have not significantly modified the experimental procedure. Over the years, several students recommended a 58 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


multitude of suggestions for reducing our water usage during filtrations for this and subsequent labs in our course. Recently, we purchased two recirculating water aspirator systems to reduce our water usage in the organic laboratories.

Figure 2. Solventless aldol condensation.

Acid-Base Extraction The second experiment is a modified version of a traditional three component acid-base extraction (16). The students separate and purify 9-fluorenone, benzoic acid, and ethyl 4-aminobenzoate from a solid mixture containing the components (Figure 3). Diethyl ether is used as the extraction solvent instead of methylene chloride. The students are exposed to acid/base chemistry, liquid-liquid extraction, solubility, recrystallization, melting point, and mixed solvent recrystallization. The experiment highlights two green chemistry principles: safer solvents and safer organic components. In addition to using a less hazardous extraction solvent, the original procedure used p-dibromobenzene as the neutral component in the mixture. The p-dibromobenzene is more hazardous than 9-fluorenone if inhaled.

Figure 3. Components of mixture in acid-base extraction. 59 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Biosynthesis of Ethanol The third experiment is an adapted distillation experiment (17, 18). The experiment involves fermentation of molasses using Baker’s yeast followed by simple and fraction distillations to purify the ethanol product. The students learn simple distillation, fractional distillation, and gas chromatography. The experiment highlights three green chemistry principles: benign reagents, renewable feedstocks, and atom economy. Additionally, the ethanol can be used for later experiments.


Friedel-Crafts Acylation

Figure 4. Friedel-Crafts acylation of ferrocene.

The fourth experiment of the semester is a Friedel-Crafts Acylation of ferrocene (Figure 4) adapted from Mohrig (19). The experiment was adapted to include small-scale column chromatography. The students learn column chromatography, thin-layer chromatography, melting point, and IR spectroscopy. The experiment highlights four green chemistry principles: atom economy, greener reagents, catalysis, and energy efficiency. This experiment can also be performed using recrystallization as the purification technique (18) to reduce waste from the chromatography solvents. However, the experiment requires an increase in scale (1.5g vs 200mg). We chose to use column chromatography so that the students are introduced to column and thin-layer chromatography using colored materials. As the students analyze the greenness of the first three experiments, they become more comfortable with the analysis and their suggestions for experiment modification start to improve around this point in the semester. Therefore, the fourth experiment provides an excellent example of how the students were involved in further greening of our initial experiment. Over the years, several students suggested the use of microwave heat rather than thermal heating. Initially, we were reluctant to incorporate the change into the laboratory because Widener does not own a reaction-grade microwave system. However, after learning of several successful experiments utilizing a household microwave, we tested the use of a household microwave as the heating source for the reaction. For the last six years, we have been able to safely perform the reaction in a 1000W household microwave with short 10-second heating cycles. The reaction typically requires three heating cycles. This change reduces the heating time from 30 minutes to 30 seconds. 60 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Spearmint Oil Separation

Figure 5. Components of spearmint oil mixture separated by column chromatography.

The fifth experiment was adapted from an experiment by Davies and Johnson (20). The experiment involves the separation of the colorless components of spearmint oil (Figure 5) via column chromatography. Since the components are colorless, the students are exposed to the monitoring of a column by thin-layer chromatography. Additionally, the students learn to use IR spectroscopy and TLC to determine the effectiveness of a column separation. The experiment exemplifies the use of greener solvents, but also provides an example of a greener experiment that needs further improvement. Our experiment uses a larger column in order to increase the yield of each component. The use of a larger column increases the amount of solvent and adsorbent thus generating more waste than the Davies’ procedure. The students suggested the replacement of ethyl acetate with 2-methyltetrahydrofuran as the polar component in the eluent. This change was made and a 5% 2-methyltetrahydrofuran in hexane eluent resulted in better separation than the original 5% ethyl acetate in hexane eluent. Unfortunately, 95% of the eluent remains hexane.

Synthesis As a capstone experiment for the organic chemistry I laboratory, we developed a three step inquiry-based, green synthesis. While there have been numerous inquiry-based experiments published (21–27), it is difficult to find multi-step green syntheses for the organic laboratory (28, 29). Since synthesis is a fundamental part of organic chemistry, we thought it was necessary to develop a multi-step green synthesis. This first semester capstone experiment requires the students to search the literature and find methods for performing a series of organic reactions. The student-researched methods are then analyzed for greenness as a class exercise before the experiments are performed, and the class chooses the best method for each reaction.

61 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 6. General reaction scheme for the synthesis of 1,2-dibromo-1phenylpropane. During the course of this experiment, students are required to search organic textbooks, the Journal of Chemical Education, and the ACS website for procedures that accomplish each step of the synthesis (Figure 6). Only after the students have provided a procedure from the literature are they shown the default procedure developed for each reaction. When the students bring in their suggested procedures, the class reviews the cost effectiveness, safety, and greenness of each proposed method using the twelve principles of green chemistry and several metrics (percent yield, atom economy, E-factor, effective mass yield) as guides. By highlighting these different factors, the professor emphasizes the overall effectiveness of green methodologies and the students learn to analytically review procedures for a synthesis. If a student proposes a greener method that has not been previously investigated, the materials are ordered so that the student can perform their procedure the following week.

Experimental Details The instructor should view these experimental designs with flexibility. In order for this synthetic sequence to be effective, students need to be given the opportunity to experiment and research alternative methods for carrying out each step. It is strongly recommended that the laboratory have one rotary evaporator for every eight students. Each step should take the students no more than a three-hour lab period. Ideally, the students will obtain high yields so that several methods of characterization are possible. In our laboratory, students characterize the products by boiling point, melting point, and IR. By the end of the first semester organic laboratory, most students do not have a strong comprehension of IR. However, the spectra obtained during this experiment show very clear differences and allow the students to easily verify if their procedure is successful. 1H-NMR and 13C-NMR analysis could easily be introduced, if desired. 62 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Reduction


The students find a number of suitable methods for the reduction of a ketone to a secondary alcohol. These methods include the use of carrots (30) and Baker’s yeast (31) as natural sources of reductases (Figures 7 and 8). These examples provide an excellent opportunity to discuss the advantages and disadvantages of enzymatic catalysis in synthesis. We have allowed students to try these two methods to demonstrate that the reductases are extremely selective and only catalyze the reduction of molecules with similar structural features.

Figure 7. Carrot-based enzymatic reduction of benzofuran-2-yl methyl ketone.

Figure 8. Baker’s yeast enzymatic reduction of ethyl acetoacetate.

The students also occasionally find a reduction method reported by O’Brien and Wicht using poly(methylhydro)siloxane (Figure 9) as the reducing agent (32). We have found this reagent effective for this reduction scheme in the research laboratory, but less effective in the teaching laboratory. Instead, we have opted for a revised sodium borohydride reduction (Figure 10) of the ketone (31). While the atom economy is much lower for this reaction compared to the enzymatic reductions, the percent yield is much greater than the O’Brien and Wicht procedure. This procedure also allows for the reuse of the ethanol produced in the fermentation of molasses experiment earlier in the semester, if desired. Additionally, the students suggested a couple of modifications to the experiment over the years. The students suggested using diethyl ether instead of methylene chloride as an extraction solvent to purify the reduction product. Therefore, they were allowed to attempt the work-up using diethyl ether. Overall, product yield shows that this solvent was not as effective as methylene chloride. In a later iteration of the course, a student suggested the use of cyclopentyl methyl ether (CPME) to replace methylene chloride as the extraction solvent. The students performed the experiment using CPME as the extraction solvent and found that the solvent produced similar yields and purity to methylene chloride extractions. While CPME is a greener solvent, there is an additional energy cost to remove CPME after extraction compared to methylene chloride. 63 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 9. Polymethylhydrosiloxane (PMHS) reduction of citronellal with catalytic fluoride provided tetrabutyl ammonium fluoride (TBAF) in tetrahydrofuran (THF).

Figure 10. Results of various reduction methods for propiophenone.

The reduction of propiophenone with sodium borohydride takes approximately fifteen minutes. However, the work up is time consuming. Neutralization of the sodium borohydride with hydrochloric acid is difficult and generates a fair amount of waste. This step produces copious amounts of hydrogen gas and the contents of the flask can easily overflow if the addition is not done slowly. Despite the lengthy work-up time, students can complete this step of the synthesis in a three-hour lab period. The percent yields obtained for this step average 80%. During the development of the synthesis, the identity of the product was verified by IR, refractive index, boiling point, and 1H-NMR. Students can see the difference between the alcohol product and the ketone by the disappearance of the carbonyl peak at 1680 cm-1 and the appearance of the hydroxyl peak at 3300 cm-1.



Elimination Once students have obtained 1-phenyl-1-propanol, their next task is to eliminate the alcohol and form a double bond, creating trans-β-methylstyrene (Figure 11). The students typically find four procedures for this transformation. The most common method is the use of sulfuric acid (33, 34) as an aqueous catalyst for the dehydration reaction (Figure 11b). This procedure is the most familiar to the students since it is the reagent found in most organic chemistry textbooks. Many students also find a procedure using phosphoric acid (34–36) as the catalyst (Figure 11a) and typically have a sense that it is the greener reagent since it appears in Doxsee and Hutchison’s laboratory textbook (6). Occasionally, the students find the sulfuric/phosphoric acid mixture procedure (Figure 11c) in Pavia (37). The discussion of these three options typically revolves around a comparison of atom economy, percent yield, and reagent hazards. The atom economies are similar with the phosphoric acid version having a slightly higher atom economy. The percent yields of each method are also similar with the sulfuric acid version producing a slightly higher yield. With those two points in mind, there is no reason to choose the procedure that uses a mixture of the two acids. Thus, the choice is made largely based on a comparison of the acid hazards. Occasionally, a student will find Doyle and Plummer’s procedure that uses Nafion NR50 (Figure 11d), a recyclable solid phase acid catalyst (38). The recycling process adds substantial waste to the reaction; therefore, we opted to use the phosphoric acid procedure.

Figure 11. Elimination reagents. We use a modified version of the phosphoric acid catalyzed (Figure 11a) dehydration driven by distillation published by Doxsee and Hutchison (35). Our procedure has been modified in two ways to improve energy efficiency and reduce waste. Instead of using fractional distillation to drive and purify the alkene from the alcohol, we use simple distillation. This change reduces our distillation time by about one hour thus reducing our energy usage. Additionally, the simple distillation results in water being distilled with the alkene product. Since we have distilled a product/water mixture, there is no need to add additional water for the work-up used by Doxsee and Hutchison, thus we reduce our waste by about 5 mL per student. The product is sufficiently pure (determined by 1H-NMR) to carry out the final reaction, so we also eliminated the simple distillation used by Doxsee and Hutchison. The percent yield of trans-β-methylstyrene is around 80%. The 65 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

IR spectrum after this step shows the disappearance of the alcohol peak at 3300 cm-1 and a strengthening of double bond character in the 3080 cm-1 to 2850 cm-1 region.


Bromination The final step of the synthesis calls for adding bromine across the alkene. The students typically find three procedures to accomplish this transformation (Figure 12). A nice green analysis of these bromination procedures was published by McKenzie et al. (39). McKenzie analyzes the atom economies, experimental atom economies, E-factor, effective mass yields, and hazards of the bromine in methylene chloride (Figure 12a), pyridinium tribromide in ethanol (Figure 12b), and hydrobromic acid with hydrogen peroxide in ethanol (Figure 12c) methods. Our class discussions also focus on these metrics, and we concluded, as does McKenzie et al. that the hydrobromic acid with hydrogen peroxide method is the greenest alkene bromination method.

Figure 12. Bromination reagents.

We developed a bromination procedure for trans-β-methylstyrene that was adapted from the McKenzie et al. procedure (Figure 12c). The procedure uses a combination of 49% hydrobromic acid in water and 30% hydrogen peroxide in water to release bromine into the ethanol solvent system. Students can clearly monitor the progress of the bromination through the solution’s color changes. Once the product is brominated, the excess acid is neutralized using sodium bicarbonate. The original procedure uses filtration to remove the product because the product is insoluble in ethanol and water. However, 1,2-dibromo-1-phenylpropane is soluble in both ethanol and water. Thus, we developed an extraction procedure using ethyl acetate and water to purify the product. The resulting oil can then be characterized. The IR spectra for this step can be distinguished by the weakening of double bond character in the trans-β-methylstyrene IR from the region of 3080 cm-1 to 2850 cm-1 and the appearance of a carbon-bromine peak at 575 cm-1. 66 Fahey and Maelia; Green Chemistry Experiments in Undergraduate Laboratories ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Conclusion The organic chemistry I laboratory described here provides a contemporary green organic chemistry laboratory experience. The lab gradually introduces students to the principles and metrics of green chemistry while exploring the technical skills of purification and characterization typically found in an organic chemistry I laboratory course. The laboratory design provides a framework for students to contribute to the development and redesign of green chemistry experiments. This approach has sparked interest in green chemistry research among chemistry, chemical engineering, and biology majors at our institution. The capstone synthesis experiment provides students with a chance to explore green methods for three reactions commonly discussed in organic chemistry lecture courses. Under the guidance of their professor, students learn to apply green chemistry principles by picking appropriate, safe, and green reagents for the synthetic steps.

Acknowledgments We would like to thank the following Biology and Chemistry faculty members from Widener University for their input on the topics and techniques that are important for their respective students to obtain from the organic chemistry laboratory: David Coughlin, Kelly Davis, Louise Liable-Sands, Scott Van Bramer, and Fran Weaver. Special thanks to Chris Annunziato, Kevin Blattner, Brandon Driscoll, Wayne Karnas, Andrew Montgomery, Alysha Moretti, Cassandra Pelton, and Michael Polen for their help testing and revising several experiments. Brandon Driscoll, Kristen Anderson, and Irina Knyazeva of the Chemistry Stockroom were also essential in the development and testing of several of the labs by helping us find chemicals, glassware, yeast, etc. Another special thanks to Irina Kynazeva and Krishna Bhat for their many suggestions and revisions to the experiments. We thank the Widener University Faculty Development Grant program and the Widener University Arts and Sciences Student Summer Research Housing Fellowship for funding.

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A Greener Organic Chemistry Course Involving Student Input and

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