Laboratory Experiment pubs.acs.org/jchemeduc
Using Whiskey-Flavoring Compounds To Teach Distillation and IR Spectroscopy to First-Semester Organic Chemistry Students Hayley Wan,* Nada Djokic, Brenna Arlyce Brown, and Yonghoon Kwon Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada S Supporting Information *
ABSTRACT: Laboratory techniques, such as boiling point determination, distillation, and infrared spectroscopy, are commonly taught during first-semester undergraduate organic chemistry courses. This integrated experiment teaches the usefulness of combining these different laboratory techniques for structure elucidation purposes. The idea of whiskey distillation is used as a real-world example to engage organic chemistry students and teach the importance of skills such as boiling point determination, simple and fractional distillation, structure elucidation, IR spectroscopy, and critical thinking. Students do not distill real whiskey samples but rather mixtures containing two different whiskey-flavoring compounds.
KEYWORDS: Second-Year Undergraduate, Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Applications of Chemistry, Food Science, IR Spectroscopy, Separation Science
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point data and IR spectroscopy of the pure fractions to determine the identity of the unknown liquids. Specific combinations of the two flavoring compounds correspond to fictitious whiskies that are detailed in the student handout.
aboratory techniques, such as boiling point determination, distillation, and infrared spectroscopy, are commonly taught in first-semester undergraduate organic chemistry courses.1 It is important that students not only learn how to perform these techniques but also why it is useful to combine different laboratory techniques for structure determination.2 This laboratory experiment aims to couple the teaching of basic laboratory techniques (boiling point determination and distillation) with IR spectroscopy and structure determination. Although a variety of experiments exist that teach these basic and very important techniques, an integrated experiment was designed that would develop critical-thinking skills and at the same time contain “real-life” relevance to better engage the students. Whiskey is a common alcoholic drink consumed throughout the world. Different whiskies from different countries possess their own unique aromas and tastes according to the barrel aging and distillation processes.3 Chemically speaking, whiskies are very complex drinks that contain a vast number of organic compounds responsible for their flavoring and unique taste.4 A variety of aldehydes, ketones, lactones, phenols, alcohols, and esters are found in whiskies, and each produces different flavors. For example, γ-nonalactone produces an apricot or peach-type flavor, whereas 4-hydroxy-3-methoxybenzaldehyde produces a vanilla-type flavor.5,6 This experiment is based on the fact that different whiskies from around the world have different tastes and, therefore, contain different flavoring compounds. During this integrated experiment, students learn how to separate a mixture (containing two unknown whiskey flavoring compounds) using simple and fractional distillation. Then, they use boiling © 2013 American Chemical Society and Division of Chemical Education, Inc.
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EXPERIMENT This experiment is suitable for first-semester undergraduate organic chemistry courses and can be completed within a 2 h and 50 min laboratory period, including a 15−20 min introductory lecture. Students carry out this experiment with a partner to reduce equipment and chemical costs.7,8 Each student pair is provided a vial containing 22 mL of a 1:1 mixture of two unknown liquids for their unknown whiskey extracts sample. In the first part of the experiment, students use simple distillation to separate the compounds within their unknown whiskey extracts mixture. They collect the distillate in a graduated cylinder and record the temperature at every 1 mL of distillate. Students stop distilling once 20 mL has distilled to avoid boiling the distillation flask to dryness. Once the distillate cools, students transfer the distillate back into the distillation flask for fractional distillation. Students use a self-prepared fractionating column comprised of a water condenser packed with copper sponge (this is a replacement for the more expensive Vigreaux column). Students collect 2 mL fractions in premarked test tubes but record the temperature at every 1 mL of distillate. When ∼2 mL of liquid remains in the distillation flask, students stop the distillation. Students Published: December 23, 2013 123
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Laboratory Experiment
Table 1. Structures, Aroma Type, and Boiling Points for Possible Whiskey Flavoring Extracts
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HAZARDS Safety glasses and lab coats are required. Acetone, ethyl acetate, propionaldehyde, ethyl acrylate, 1,1-diethoxyethane, 2-propanol, 1-pentanol, butyraldehyde, 3-methyl-1-butanol, ethyl butyrate, 2-butanone, 2-pentanol, 1-penten-3-ol, heptanal, 2pentanone, and 2-methyl-1-propanol are flammable and irritants. Heptanal is harmful to the environment and corrosive. Dichloromethane (for cleaning IR plates) is carcinogenic. Propionaldehyde, butyraldehyde, 3-methyl-1-butanol, and heptanal possess strong odors. Students are told not to consume or taste any of the samples or distillates.
determine which test tubes contained their two pure components and IR spectra of these “pure” fractions are obtained. Students are provided with a list containing structures, aroma types, and boiling points of potential unknowns (Table 1). They are also given a list showing the names of whiskies, the country of origin, and the organic compounds contained within that particular type of whiskey (Supporting Information). All of the whiskey names, country of origin, and chemical composition of the whiskies are fictional. Students use the data collected to construct two distillation curves, one for simple distillation and another for fractional distillation. Students calculate corrected boiling points using the barometric pressure provided. From the physical and spectroscopic data, students identify the two unknown liquids and the name of the “whiskey” sample.
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DISCUSSION
The unknown liquids chosen for this experiment consisted mostly of aldehydes, ketones, esters, and alcohols to mimic functional groups contained in the flavoring compounds commonly found in whiskies. These functional groups can 124
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compounds. This was not the typical “cookbook” style experiment and involved multitasking, time management, and problem-solving skills. Although students found the experiment to be very involved, they also enjoyed the experience.
also be easily distinguished by IR spectroscopy. The chosen compounds are inexpensive, readily available, and have relatively low toxicity. Students carried out this experiment in pairs and also performed both simple and fractional distillations using the same sample, which helped to cut down on chemical and equipment costs. Reducing costs was an important issue, especially for large class sizes. To further reduce equipment costs, students used a self-prepared fractionating column (consisting of a condenser and copper sponge) instead of a Vigreux column. Note that it is possible (timewise) for this experiment to be completed as an individual lab experiment if equipment and costs permit. Only five out of the sixteen whiskey combinations (Instructor Notes in the Supporting Information) were actually used. The other eleven were “dummy” samples that students had to eliminate as part of the critical-thinking process. The five successful samples used in this experiment were (1) 2propanol/ethyl butyrate (Gatsby Willow), (2) 2-butanone/3methyl-1-butanol (Glen Quidditch), (3) 2-butanone/1-pentanol (Lagascrappie), (4) ethyl acetate/3-methyl-1-butanol (Pedersons), and (5) 1-pentanol/2-pentanone (Tigamory). The “whiskey” samples used were also chosen because of their more pleasant smelling nature. With large class sizes, it was important to use samples that were less odorous as students performed distillations at the same time. This experiment has been run on a trisemester basis since 2012 with students enrolled in first-semester organic chemistry. Each laboratory class accommodated 20 students and was instructed by one teaching assistant. Each student pair distilled and separated the two unknown liquid components using both distillation methods. Representative student data are provided in the Supporting Information. This experiment allowed students to be exposed to both simple and fractional distillations using one whiskey extracts sample. Students were taught that fractional distillation should be used when less than 25 °C boiling point difference existed between two liquids to be distilled. In this experiment, both liquids were unknowns; therefore, it was not possible to decide whether simple distillation or fractional distillation should be used. Students were required to do both simple and fractional distillations regardless of the boiling point difference between the two liquids because (1) it provided them with the experience of using both techniques and (2) students were able to compare both techniques and observe that fractional distillation allowed for more efficient separation. At the end of the experiment, the corrected boiling point and IR spectrum for each “pure” fraction were used to determine the identities of the two unknown liquids. Students deduced from the provided chart (Supporting Information) the unknown “whiskey” sample. The success rate for this experiment was very high. Only 1−2% of student pairs were unable to successfully separate the whiskey sample and obtain good IR spectra. If good IR spectra cannot be obtained (due to unsuccessful separation) or if IR spectrometers are not available for student use, then the instructor can provide copies of the relevant IR spectra. This integrated laboratory experiment was successful in engaging students by using the real-life concept of whiskey distillation. Students learned how to perform simple and fractional distillations as well as combine the use of infrared spectroscopy and problem solving skills to elucidate structures of their unknown compounds from a list of possible
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CONCLUSION This experiment used the idea of whiskey distillation as a realworld example to engage first-semester organic chemistry students. Students did not actually distill real whiskey samples but rather mixtures of different compounds that could be found in whiskey. The experiment coupled important techniques, such as boiling point determination and distillation, with IR spectroscopy and structure elucidation. These techniques are all extremely useful additions to the future chemist’s toolbox, and this experiment allowed students to further develop their critical-thinking skills in the laboratory.
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ASSOCIATED CONTENT
S Supporting Information *
Instructor’s notes, student handout, author data, representative student data, and CAS registry numbers. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*H. Wan. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors would like to acknowledge the help and support from the Chemistry Storeroom staff (A. Yeung, M. Munroe, and M. Kingston) in preparing the lab rooms and the student samples. The authors also thank the 2012 and 2013 teaching assistants, as well as the students, for providing feedback.
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REFERENCES
(1) Martin, C. B.; Schmidt, M.; Soniat, M. A Survey of the Practices, Procedures, and Techniques in Undergraduate Organic Chemistry Teaching Laboratories. J. Chem. Educ. 2011, 88, 1630−1638. (2) Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. A Microscale Approach to Organic Laboratory Techniques; Brooks/Cole: Belmont, CA, 2013; pp 58−62. (3) Gill, V. A. Whiskey Tour. Chem. World 2008, 5 (12), 40−44. (4) Poisson, L.; Schieberle, P. Characterization of the Most OdorActive Compounds in an American Bourbon Whiskey by Application of the Aroma Extract Dilution Analysis. J. Agric. Food Chem. 2008, 56, 5813−5819. (5) Liquor Press. http://www.liquorpress.com/2011/03/01/thechemistry-of-casks-%E2%80%93-part-2/ (accessed June 2013). (6) Lee, K. Y. M.; Paterson, A.; Piggott, J. R. Perception of Whiskey Flavour Reference Compounds by Scottish Distillers. J. Inst. Brew. 2000, 106, 203−208. (7) Neckers, D. C.; Duncan, M. B.; Gainor, J.; Grasse, P. B. Cost effectiveness in the organic laboratory. J. Chem. Educ. 1977, 54, 690− 692. (8) Martin, N. H.; Waldman, F. S. The Three R’s of Resource Management in the Undergraduate Organic Chemistry Laboratory. J. Chem. Educ. 1994, 71, 970−971.
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