In the Laboratory
A New Investigative Sophomore Organic Laboratory Involving Individual Research Projects1 Gregory B. Kharas Department of Chemistry, DePaul University, 1036 West Belden Avenue, Chicago, IL 60614
In the reports in this Journal on laboratory instruction, one focus of attention is the application of the problem-solving approach to the introductory-level organic chemistry laboratory (1–4). These courses are often offered to a large and varied group of students, ranging from science majors to sophomores of marginal skill, most of whom will not major in chemistry. The problem-solving approach calls for a laboratory curriculum that provides a greater intellectual challenge and a resemblance to a research experience. In the Department of Chemistry at DePaul University, we have designed a curriculum that involves individual research projects for the nine laboratories of the Spring quarter of a three-quarter introductory organic chemistry course. These projects integrate the instructor’s research and learning experiences for the students via interdisciplinary approaches of classic organic chemistry and polymer chemistry. The foundations for the individual projects are laid out during the first and second quarters of laboratory instruction when students are introduced to classic synthetic, separation, and purification techniques. In the third quarter of the lab sequence, in carrying out the individual projects, emphasis is shifted towards obtaining and interpreting data for compounds that are not described in the laboratory manual (5) rather than making representative compounds. The individual research projects carried out during the last three years involved syntheses of various trisubstituted ethylenes (TSE), their radical polymerization, and copolymerization with styrene. The TSE compounds were prepared via a piperidine-catalyzed Knoevenagel condensation of substituted aromatic aldehydes and active methylene according to general reaction RCHO + NC–CH 2–R′ → RCH=C(CN)R′ R in most projects was a substituted phenyl, with substituents such as Cl, Br, F, OCH3, alkyl, CN, in ortho, meta, or/and para positions, and R′ was CO 2 CH 3 (methyl cyanoacetate) or CONH2 (cyanoacetamide). A Knoevenagel condensation is an example of aldol-like condensations, which are very useful reactions in organic chemistry and are described in most organic chemistry textbooks (e.g., 6). The Knoevenagel reaction (7) and its modifications (8, 9) are simple in both procedure and equipment needed, and have considerable synthetic and pedagogic value. Several key concepts, usually included in the sophomore organic course, are illustrated by this one-step reaction: (i) carbon–carbon bond formation, (ii) the acidity of active methylene compounds (specifically, malonic esters and nitriles) containing electron-withdrawing groups, (iii) the ease of dehydration to extend conjugation, (iv) formation of (E) and (Z) isomers, and (v) the relevance of alkene formation for polymer synthesis. Once the TSE compounds are prepared, students attempt homopolymerization in the presence of a typical radical initiator, 2,2′- azobisisobutyronitrile (AIBN), R–CH=C(CN)R′ → –[–RCH–C(CN)R′–]n–
followed by copolymerization of the TSE compounds with styrene (ST) nR–CH=C(CN)R′ + nC6H 5–CH=CH2 → –[RCH–C(CN)R′–(C6H5)CH–CH2–] n– Polymerization and copolymerization of alkenes are major reactions from the perspective of plastics, coatings, and rubber technology, as they provide our society with a variety of useful materials. Interest in polymerization experiments in introductory chemistry courses is growing (10, 11). It is important that students gain some knowledge of polymers, their chemical structures, preparation, and physical properties. These reactions illustrate such concepts as chain initiation, propagation and termination; the stability of peroxides and azonitriles; and the high molecular weight nature of polymers that are included in the first-year organic course. Experimental Procedures
Microscale TSE Synthesis In a dry conical reaction vial (5 mL) equipped with a Teflon spin vane, place the active methylene compound (0.01 mol methyl cyanoacetate), the appropriate aldehyde (0.01 mol), and dimethyl formamide (1 mL). Attach a Claisen head adapter to the vial and fit an air reflux condenser to the side arm of the head adapter. Add a drop of piperidine to the mixture in the vial through the straight arm of the head adapter. Let the mixture stir at room temperature for one hour. If no solid product forms, heat the mixture at 70–80°C for 2 hours, and then allow it to cool to room temperature. Remove the head and condenser, cap the vial, and store the vial until the next period. For isolation of the product, cool the vial in ice and collect the product on a Hirsch funnel with suction filtration. Select a solvent or mixed solvents for recrystallization by applying a Craig tube–microscale crystallization technique (5). Recrystallize the solid and dry it under vacuum at room temperature. Determine the melting point and percentage yield of the recrystallized product. Use a TLC plate (silica gel, chloroform) for a qualitative analysis of the product. If the compound is not pure, repeat recrystallization. Macroscale TSE Synthesis In a scaled-up synthesis use appropriate glassware (5), a fivefold increase of reagents, and 1–2 drops of piperidine. For product purification use a semimicroscale crystallization technique (5) with a Hirsch funnel.
TSE Polymerization Into a dry 16 × 150-mm test tube place 1 g of the TSE, 0.1 g of AIBN, and 10 mL of appropriate solvent (ethyl acetate, chloroform, DMF). Cap the tube with a rubber septum and insert a hypodermic needle to release any pressure generated during the reaction. Place the tube in a preheated oven at 70 °C and leave it there until the next pe-
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In the Laboratory how to search printed Chemical Abstracts (CA). They have to prepare and submit a literature review report for grading, which Period Activity contains a printout of their on-line and 1. Introduction to the project, hand-out materials distributed, individual TSE printed CA search strategy. We have found target structures assigned. The science librarian gives a presentation on that students enjoy literature searches for how to conduct both a manual and on-line computer literature search. their compounds. It was exciting to see 2. Microscale synthesis of the assigned TSE compound with an objective to students realize that information and check the feasibility of the synthesis. learning are a continuum and transcend an immediate need imposed by the indi3. Literature searches are discussed with the instructor. Isolation and vidual research projects. purification of the product by recrystallization. Characterization of the TSE The TSE synthesis procedure worked compound (solubility, melting point, TLC, IR spectrum). well (with yields 20–90 wt %) in the case 4. Macroscale TSE synthesis of the assigned compound. of phenyl-substituted methyl α5. Purification and characterization of the TSE macroscale product (melting cyanocinnamates and α-cyanocinnamides point, TLC, C, H, N elemental analyses, IR spectrum, proton NMR). prepared from 4-nitro-, 2-, 3-, 4-methoxy-, 6. Homopolymerization of TSE and its copolymerization with styrene. 4-ethoxy-, 4-propoxy-, 4-butoxy-, 2-, 3-, 4Discussion of molecular modeling results. methyl-, 4-ethyl-, 4-isopropyl-, 2-cyano-, 37. Isolation and purification of the polymer. cyano-, 4-cyano-, 2-, 3-, 4-Cl-, 4-Br-, 4-F-, and many other phenyl-substituted ben8. Characterization of polymer products (solubility, nitrogen elemental zaldehydes (12–15). Some of the aldehydes analysis, IR spectrum, and proton NMR). (e.g., 2-nitrobenzaldehyde, 2- and 49. Complete laboratory work, clean up. Submission of the monomer and pyridinecarboxyaldehyde) did not form copolymer samples, and final project reports for grading. methyl α-cyanocinnamates. Based on the yield of the individual microscale synthesis, a procedure for the macroscale reaction is modified to riod. Take the tube out of the oven, record the time, and cool insure that enough of the TSE compound is prepared (2–3 the tube to room temperature. Add the contents of the tube g) to carry out the polymer and copolymer syntheses. Very dropwise with stirring into a beaker with 200 mL of iceoften purification of the scale-up TSE product requires cold methanol. Separate any precipitated product by sucmodification of recrystallization procedure (i.e., a change of tion filtration using medium filter paper (#2) and a Buchner mixed solvent composition). Students see for themselves funnel. Rinse the product on the paper with cold methanol. that scale-up is more than a simple increase in quantities Dry the product in a vacuum oven at 60 °C. Determine mass of reagents and size of glassware. and percentage yield. Contrary to the copolymerization experiments with styTSE Copolymerization with Styrene rene, none of the TSE polymerization experiments produced homopolymer. Previous studies have shown that trisubstiPlace into a dry 16 × 125-mm test tube 0.02 mol of the tuted alkenes containing substituents larger than fluorine TSE, 0.02 mol of styrene, and 0.002 mol of AIBN. Add apon the double bond exhibit no tendency to undergo polymerpropriate solvent to make 20 mL. Continue the procedure ization, owing to steric difficulties (16). Nevertheless, stufor TSE polymerization above. Purify the copolymer by disdents are asked to attempt the experiment and explain why solving it in 10 mL of an appropriate solvent and precipihomopolymerization of the TSE does not proceed, whereas tate the copolymer by adding the solution dropwise to 200 its copolymerization with styrene readily results in formamL of ice-cold methanol. Repeat the copolymer dissolution– tion of a copolymer. Again, students can recognize the conprecipitation if the copolymer still contains unreacted TSE nection between chemical structure and reactivity. as determined by IR analysis. Filter the precipitated copolyStudents are required to do molecular modeling of their mer by suction using filter paper and a Buchner funnel. TSE compounds using HyperChemTM software (assisted by Transfer the copolymer into a tared, labeled vial, and dry it a teaching assistant) and to attach optimized structure and under vacuum at 70 °C to constant weight. Determine the charge-distribution data to the research report. yield based on the weight of both monomers. Calculate the The project is conducted under supervision and guidcomposition of the copolymer from the results of nitrogen ance of the instructor and teaching assistants. One of the analysis. unique attractions of the approach is the possibility of discovery—the preparation of a new polymer. Since the inDiscussion structor does not test in advance the assigned structure, reactions, or products, both student and instructor are parEach student is assigned a target TSE compound with ticipating in the quest in a close relationship, making rea particular combination of the functional groups. The stusearch in the instructional laboratory a valuable personal dent follows the project’s schedule (see below), which inand intellectual experience. In addition, the approach advolves nine 5-hour lab periods. Students receive handouts dresses the failure to make a targeted TSE compound or/ that present an introduction and background, the research and a polymer, which is also an important part of scientific strategy, specific objectives, a tentative schedule, proceevidence. Students see for themselves that exploratory dures, safety guidelines, and requirements of the grading projects yield valuable information even when the results policy as it applies to experimental work, weekly reports, are negative. Based on experimental observations and and the final project report. mechanistic considerations, students are asked to attempt An integral part of the individual research project is to explain why a specific reaction does not work. Several an on-line and printed Chemical Abstracts literature search. steps are taken to minimize this frustrating experience: (i) The objective is to find information on the assigned comthe student is advised about possible modifications of reacpound and its polymers. Students are instructed on how to tion conditions; (ii) a discussion meeting is set up to consearch on-line with a chemical compound name, formula, sider all relevant factors and a reasonable explanation is and a registry number using DialogTM Database, as well as Spring Quarter Organic Laboratory Schedule
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In the Laboratory worked out; and (iii) the student is assigned another targeted compound. Upon completion of the project students submit a detailed printed report that includes a literature review, an experimental part, results, discussion, and conclusions, in the same manner as the reports done by research chemists. Grades are assigned on the basis of performance of syntheses and characterization, persistence, manipulative skills, demonstration of understanding of the theory behind the chemistry and techniques, attention to safety guidelines, the notebook, weekly reports (graded by the TA), and a final report (graded by the instructor). Perhaps one could argue that individual research projects covering one third of the academic year deprive students of a breadth of experience in organic chemistry. On the contrary, we believe that students need to develop some experiences in depth at this stage in their training, and our program provides this. We needed to know how this nontraditional lab exercise appealed to the majority of students, and so we conducted an anonymous survey. Students were asked to rate the following statement: “I would rather continue normal lab exercises than participate in a research project.” Based on the rating scale of 1 (strongly agree), 3 (neutral), 5 (strongly disagree), with 2 and 4 in between, the responses averaged 4.6. Planning future individual research projects is accomplished by reviewing a variety of commercially available aldehydes, active methylene compounds, styrene derivatives, etc. We believe that, owing to diversity of functional groups and substitution, “families” of trisubstituted ethylenes can be utilized to personalize the research experience of undergraduates in an intellectually stimulating environment. For the instructor, the planning process is not too burdensome, since the main concern is to identify target chemical structures, reactions, and experiments in a clear, accessible, and practical way so the students can do the exploration. Individual research projects were assigned to 16 students during Spring quarter, 1993, 17 students during Spring 1994, and 39 students in Spring 1995. During the last three years more than 50 trisubstituted ethylenes, methyl a-cyanocinnamates and a-cyanocinnamides were prepared. None of the prepared TSE-ST copolymers had been reported in the chemical literature, thus making each individual research project a genuine discovery experience. Some individual projects from 1993 and 1994 were repeated, expanded, and subsequently presented and published by two graduate students (12–15).
proach integrates genuine research experience with laboratory instruction in an accessible but nontrivial manner. This is provided by the variety of experiences in the interdisciplinary areas of organic chemistry as it is applied to polymer synthesis. Second, this approach works in the framework of a mainly teaching university that allows little time for faculty to be involved in research. Two groups of institutions for whom the organic laboratory with individual research projects might be particularly appropriate are liberal arts colleges and universities and community colleges. These institutions, like DePaul, are focused on undergraduate education and student development. The curriculum has been designed in a way that should make it relatively easy to adopt at other institutions, as it does not require unusual facilities or equipment. Acknowledgment I am indebted for many helpful discussions with the students participating in the projects and the teaching assistants, Julie Eaker, Regan Theiler, and Sandra Armatys. I am grateful to my colleagues Thomas J. Murphy, Fred W. Breitbeil, III, and Avrom A. Blumberg for very fruitful discussions, and to Sara Steck Melford for her support of this curriculum development. Many thanks go to Marilyn M. Browning and Robert L. Acker for instruction and supervision of students to do on-line and printed Chemical Abstracts literature searches for individual research projects. Gratitude is extended for the partial support of the DePaul University Research and Quality of Instruction Councils, the National Science Foundation’s DUE Course and Development Grant (No. 9455681), and the College of Liberal Arts and Sciences, DePaul University matching funds. Note 1. Presented at the 210th ACS National Meeting in Chicago, IL, August 1995.
Literature Cited 1. 2. 3. 4. 5. 6. 7.
Conclusion The individual research projects idea worked quite well here at DePaul. We found that the elements of the unknown and discovery are very stimulating and motivating for most students. This approach focuses, at the undergraduate level, both on organic laboratory curriculum reform and on the development of faculty. The key to revitalization of the organic lab curriculum is the uniting of each instructor’s personal knowledge of the subject and skill in the craft of teaching. It would motivate faculty members who are primarily teachers to seek opportunities to deepen their knowledge, while those engaged in discipline-based research would connect their research with learning experiences for their students and would develop expertise in innovative teaching. Two features make the sequence described above unique and of interest to other institutions. First, the ap-
8. 9. 10. 11. 12.
13. 14. 15. 16.
Fife, W. K. J. Chem. Educ. 1968, 45, 416–418. Pickering, M. J. Chem. Educ. 1991, 68, 232–234. Cooley, J. H. J. Chem. Educ. 1991, 68, 503–504. Hathaway, B.A. J. Chem. Educ. 1987, 64, 367–368. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G.; Introduction to Laboratory Techniques; Saunders: New York, 1990. Solomons, T. W. G. Organic Chemistry, 5th ed.; Wiley: New York, 1992; pp 901–902. Reeves, R. L. In The Chemistry of the Carbonyl Bonds; Patai, S., Ed.; Interscience: New York, 1966; Chapter 12. Kolb, K. E.; Field, K. W.; Schatz P. F. J. Chem. Educ. 1990, 67, A304. Rowland, A. T. J. Chem. Educ. 1995, 72, 548–549. Andrews-Henry, H. J. Chem. Educ. 1994, 71, 357–358. Slough, G. A. J. Chem. Educ. 1995, 72, 1031–1032. Blaine, D. A.; Brtek, L. M.; Flood, R. M.; Krubert, C.; Rizzo, A. T.; Sterner, E. A.; Kharas, G. B. Abstracts of Papers, 210th National Meeting of the American Chemical Society, Division of Chemical Education, Chicago, IL; American Chemical Society: Washington, DC; Abstract No. 186 and Nos. 187–192, 1995. Kharas, G. B.; Eaker, J. M.; Dian, B. C.; Elenteny, M. E.; Kamenetsky, M.; Provenza, L. M.; Quinting, G. R. Macromol. Rep. 1995, A32, 13–23. Kharas, G. B.; Eaker, J. M.; Armatys, S. A.; Fehringer, J. A.; Gehant, R. M.; Glaser, E. C.; Johnson, K. A.; Moy, P. S.; Quinting, G. R. Macromol. Rep. 1995, A32, 405–414. Lindquist, N. A.; Camenisch, D. R.; Eremine, D. A.; Kharas, G. B.; Engelbrecht, K. M.; Quinting, G. R.; Polymer Preprints, 1995, 36(2), 229–230. Alfrey, T., Jr.; Bohrer, J. J.; Mark, H. Copolymerization; Interscience: New York, 1952.
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