In the Laboratory
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A Qualitative Organic Analysis That Exploits the Senses of Smell, Touch, and Sound Deborah C. Bromfield-Lee and Maria T. Oliver-Hoyo* Department of Chemistry, North Carolina State University, Raleigh, NC 27695; *
[email protected] Qualitative organic analysis is the identification of organic functional group(s) in a compound. Since some functional groups impart characteristic aromas, this experiment explores how the sense of smell can be used as a discriminating tool in identifying the functional group in an unknown. In addition to describing odors and characterizing functional groups by certain smells, students perform confirmatory tests that rely primarily on the senses of touch and sound. Typical procedures were modified to employ multiple senses taking advantage of all the physical changes that take place in the reaction between the functional group and the test reagent. The use of a light probe (LP) enables students to qualitatively analyze many visual changes as an auditory response. Students “hear” significant changes in color, solution viscosity, and the presence of a precipitate.1 Experimental Overview A variety of compounds were chosen for their distinct odors and were tested to decide the suitability in using them in a teaching laboratory environment. For each functional group one or two safe and easy confirmatory tests were chosen after extensive testing. As written, this experiment was tested by four organic laboratory sections (65 students) and all procedures and instructor’s notes can be found in the Supplemental Material.W In preparation for the lab, students make a chart of various functional groups giving an example molecule of each. In the lab, students use their sense of smell to characterize the aromas by testing known functional groups and formulate descriptive categories of smells for each functional group. Students work in groups of 2 or 3 to compensate for any student who is unable to smell certain chemicals. Students then use their own olfactory classification scheme to determine which functional group their unknown compound has and which confirmatory tests are needed to confirm their assertion (Scheme I). The
chosen confirmatory tests produce distinct changes (1), which are monitored by one or more senses. This approach encourages students to discuss aromas they may have trouble identifying, to use adjectives that truly characterize their groups, and to examine their olfactory findings to decide on confirmatory testing. Confirmatory tests for the different functional groups utilize the senses of touch (generation of heat) or sound (produced in the chemical reaction or via the use of a light probe) promoting the use of senses usually neglected in laboratory procedures. Each group may be given their own set of known chemicals or several workstations may be set up. The more odorous compounds are placed in the hood along with the test reagents. The instructor must show and monitor how to properly smell by wafting and how to use a light probe (Lumitest light probe purchased from the American Printing House for the Blind Inc.) to identify changes in color, viscosity, and formation of a precipitate. Students are expected to write a brief procedure, results, conclusion, and answer post-lab questions. The experiment can be completed in an average of two hours. Characterization by spectroscopic methods such as IR and NMR may be used to supplement this sensorial qualitative analysis. More advanced students may discuss the mechanisms involved in these reactions (see the Supplemental MaterialW). Practical Considerations To avoid contamination, the testing reagents and sample compounds are placed in small glass dropper bottles. Strips of filter paper, similar to smelling strips, are used to allow students to waft the compounds (preventing students from directly inhaling from the bottle). The toxicity of all compounds was evaluated for the effects of inhalation. The known and unknown samples used in this experiment do not exhibit effects on the lungs at
observations skunk
wood
fuel
vinegar
ammonia
wine
animal
sweet
fruity
thiol
aldehyde
alkene
carboxylic acid
amine
alcohol
amide
ketone
ester
Jones’ reagent
see/LP smell
Baeyer’s reagent
see/LP smell
Na2CO3
hear
pH test
see/LP touch smell
CAN
CH3COCl
hydrolysis
2,4-DNP
ferric hydroxamate
see/LP
see/LP smell see/LP see/LP touch smell smell hear Scheme I. Example procedure for olfactory classification and sensorial chemical test confirmation. LP is light probe.
1976 Journal of Chemical Education • Vol. 84 No. 12 December 2007 • www.JCE.DivCHED.org
In the Laboratory
moderate levels. Some of the compounds show only minor effects with contact to skin. It is still advisable to have the students close all bottles tightly after use. Coffee crystals are made available for the students to smell between compound identification. This is a recommended procedure to “clean” the sense of smell. Some students took advantage of this while others did not think it was necessary. However, those that used the coffee crystals to cleanse their nasal passage during the experiment stated it helped to differentiate better the various aromas. Studies have shown that people recall with greater accuracy odors over longer periods of time than things that they see (2). This fact is exploited as students are asked to be creative in describing the compounds and to remember the functional groups by descriptive aromas. As the senses of smell, sound, and touch take priority in this experiment, it is suitable for visually impaired students to perform it in an active and meaningful manner. The use of dropper bottles is also ideal for students with vision disabilities for its ease in dispensing liquids. Visually able students are also stimulated as they engaged in ways not usually employed in laboratory settings. The students are not only using multiple senses to perform the lab, but also devising their own experimentation. The experiment is designed to be an inquirybased lab, in which the students decide on which confirmatory tests are needed based on their classification of aromas and the relationship to functional groups. General Hazards All corrosive reagents used, such as oxidants [CrO 3, K2MnO4, Fe(NO3)3, and CAN2], strong acids and bases (HCl
and NaOH) and acetyl chloride, should be handled with proper care to avoid severe burns. Chromium is carcinogenic. Potentially flammable reagents include the alcohols, ketones, aldehydes, thiols, amines, and alkenes. These should be at safe distances from ignition sources. Owing to the strong aromas some reagents may have (such as aldehydes and thiols), wafting is the only acceptable technique used throughout this experiment. Amines are incompatible with oxidizing agents, may cause burns, and may have strong odors that may cause burning sensation if inhaled directly. Extreme prolonged exposure to thiols may be toxic to the liver and kidneys. Ethanamide is hydroscopic and excessive prolonged exposure may cause damage to the liver. Suggested reagent concentrations, the use of filter paper as smelling strips, and wafting technique permit the safe use of the sense of smell in this experiment. Follow tested procedures (stated in the Supplemental MaterialW) as extreme prolonged exposure to some compounds can be irritating or hazardous. Results Students were able to detect and characterize the known compounds; however, some required a bit of assistance in grouping together the compounds with the same functional groups. Correlations between the functional group and characteristic aromas allowed students to identify the functional groups of their unknowns. Students came up with a wide range of descriptions and used very interesting adjectives in their characterization. Examples of students’ descriptions are shown in Table 1. Students showed differences in opinion about an odor in terms of what smelled good or bad, but were able to identify the variety of functional groups. Only 3 out of 65 students
Table 1. Odor Characterization by Students
Compound
Sample of Students’ Characterizations
Methanol
Bananas, sweet alcohol, wet paint, fresh dirt, wet feet, citrus, weak Pine-Sol.
Ethanamide
Feet, body odor, eggs, old person’s house, wet dog with vinegar, old book.
Formaldehyde
Almond, sesame oil, Fritos chips, latex paint, Target, after effect nostril burning.
Cyclohexanone
Soap in public bathrooms, doctor’s office, paint thinner, cherry cough drops.
Acetic acid
Vinegar, glue, rotten feet, nursing home, urinal tablet, cement.
Butylamine
Bleachy chlorine, ammonia, horse urine, hair perm, rotten fish, tuna.
Butanethiol
Bad garlic, rotten or burned pumpkin seeds, sweetener.
Hexene
Cheap fruity perfume, gasoline, nail salon, paint thinner, rotten vegetables.
n-Propyl acetate
Permanent marker, glue, nail polish remover, onion, mineral spirits.
Ethanol
Disposable lab gloves, hair product (dye), gin, vodka, Pine-Sol or Clorox.
N-methylacetamide
Dirty diaper, stinky boy’s locker room, nursing home, rotten flower.
Butyraldehyde
Vomit, fried plantains, burning Play-Doh, rotten wood, fake cheese.
Acetone
Moldy moth-balls, acetone, permanent marker, cheap vodka, rubber cement.
Citric acid
Weak acid, burning tires, stale, musty old attic, faint cheese, faint sour.
Diethyl amine
Dead animal, urine, awful ammonia, bleach, rotten fish, old antifreeze.
1-Octanethiol
Burned rubber in a field of flowers, onion/garlic/chive/skunk combo, bad chips.
Cyclohexene
Gasoline station, car exhaust, vinyl, burning Legos, department store, death.
Ethyl acetate
Acetone, reminding of salicylic acid, permanent marker, vinegar.
www.JCE.DivCHED.org • Vol. 84 No. 12 December 2007 • Journal of Chemical Education 1977
In the Laboratory
had difficulty characterizing any of their compounds owing to allergies or a pre-disposed condition. More male students than females had difficulty in detecting certain smells. Methanol, Nmethylacetamide, citric acid, and ethanamide were difficult for some of the students to identify. Eleven out of 40 males (28%) reported that methanol had no smell, while no females appeared to be unable to discern this odor. Two out of 25 females (8%) could not detect any aroma from ethanamide, while 10 out of 40 males (25%) did not detect the ethanamide. In general, males had difficulty distinguishing and characterizing particularly sweet or pleasant odors (3–5). Some student comments were enlightening as to their experience in the lab. Examples include
• This lab really surprised me on how accurate using your senses could actually be. I think this was a great lab (even though some of the material offended the senses)… • I liked this lab the most out of all the labs we have had this semester. It was an easy-to-follow procedure and I have a lot of fun trying to figure out the functional groups. Some of the smells were a bit strong, but it was still very interesting and I learned a lot.
• I felt this was a very fun lab. Very interesting and felt that I could relate it to my everyday life. I felt this was the best lab of the semester.
• I thought this was an informative lab experiment to show how important our sense of smell can help in everyday chemistry.
Conclusion Owing to the differences shown by males and females it is recommended that each group be composed of at least one male and one female. It is vital that the students waft the compounds properly so that they do not become saturated with the aromas. Using the filter paper as smelling strips is a good way to decrease the strength of many of the compounds. Students who used the light probe were able to connect an auditory representation to the visual changes observed. Based on the performance of the students in the laboratory as well as on their write-ups, it can be concluded that this sensorial lab can add richness to traditional organic laboratories. Students were able to group compounds by their functional group characteristic smells, utilize their own classification to decide on necessary confirmatory tests, and utilize effectively the senses of touch, sound, and smell to identify their unknowns.
In addition, students’ feedback strongly stated they enjoyed the experiment especially discovering for themselves the functional group involved. Acknowledgments The authors would like to thank Maria Gallardo-Williams for incorporating this experiment into the laboratory schedule and her organic students who enthusiastically tested these procedures. This work has been made possible by the generous support of the National Science Foundation via CAREER Award No. REC-0346906. WSupplemental
Material
Experimental protocols for the students, detailed notes and hazards for the instructors, and proposed mechanisms for each reaction used are available in this issue of JCE Online. Notes 1. For students unable to view changes in color or intensity, a light probe may be used. The light probe can distinguish these changes by detecting changes in light passing through the test tube and emitting different frequencies or sound. 2. CAN is ceric ammonium nitrate, (NH4)2Ce(NO3)6.
Literature Cited 1. (a) Shriner, Ralph L.; Herman, Christine F.; Morrill, Terence C.; Curtin, David Y.; Fuson, Reynold C. The Systematic Identification of Organic Compounds, 8th ed.; John Wiley and Sons, Inc.: Hoboken, NJ, 2004. (b) Griswold, John R.; Rauner, Richard A. J. Chem. Educ. 1991, 68, 418–420. (c) Solomons, T. W. Graham; Fryhle, Craig B. Organic Chemistry, 7th ed.; John Wiley and Sons, Inc.: New York, 2000. (d) Bruckner, Reinhard. Advanced Organic Chemistry: Reaction Mechanisms; Harcourt Academic Press: San Diego, 2002. (e) Silvert, D. J. J. Chem. Educ. 1987, 64, 971–972. 2. Savic, Ivanka. Curr. Opin. Neurobiol. 2002, 12, 455–461. 3. Doty, Richard L.; Kerr, Kara-Lynne. Neuropsychologia 2005, 43, 1749–1753. 4. Doty, Richard L.; Applebaum, Steven; Zusho, Hiroyuki; Settle, R. Gregg. Neuropsychologia 1985, 23, 667–672. 5. Doty, Richard L. Psychophysical Measurement of Odor Perception. In The Human Sense of Smell; Laing, D. G., Doty, R. L., Breipohl, W., Eds.; Springer-Verlag: Berlin, 1992; pp 91–134.
1978 Journal of Chemical Education • Vol. 84 No. 12 December 2007 • www.JCE.DivCHED.org
