Laboratory Experiment pubs.acs.org/jchemeduc
A Two-Step Synthesis of the Laundry Detergent Perfume Additive β‑Citronellyl Tosylate Cheryl M. Mascarenhas* Department of Chemistry, Benedictine University, Lisle, Illinois 60532, United States S Supporting Information *
ABSTRACT: A two-step synthesis of the compound β-citronellyl tosylate is described. The final product, synthesized by the reduction of β-citronellal with sodium borohydride followed by a solvent-free tosylation, is used as a perfume precursor and additive to laundry detergent. This project can be performed in two weeks in a typical second-year organic chemistry teaching laboratory. It exposes students to perfume chemistry, a topic not typically discussed in an organic chemistry course. Moreover, the solvent-free tosylation step of the reaction leads pedagogically to a discussion about green chemistry. KEYWORDS: Second-Year Undergraduate, Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Alcohols, Aldehydes, Green Chemistry, NMR Spectroscopy, Thin Layer Chromatography, Synthesis Scheme 1. Synthesis of β-Citronellyl Tosylate
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t has been a tradition in chemical education to use examples of compounds in “real-world” applications to illustrate esoteric concepts.1 Although many of the applications in textbooks and the chemical educational literature are biological and medicinal in nature, examples using soaps,2 essential oils, perfumes, and cosmetics can be traced back to the 1940s. There are several earlier articles published in this Journal that describe the chemical composition of essential oils,3 whereas more recent lab experiments focus on the synthesis of perfumes.4,5 Sulfonates of several compounds are used as additives in the perfume industry, especially for laundry and other cleaning detergents. One such sulfonate used as an additive to perfume laundry detergents is β-citronellyl tosylate. The actual perfume is not the tosylate but rather β-citronellol, whose perfume is redolent. The mechanism of the perfume release involves gradual hydrolysis of the β-citronellyl tosylate over time in the laundry cycle to form β-citronellol, thereby generating the fragrant compound during the laundry cycle.6 A two-step synthesis of the additive β-citronellyl tosylate is described for a second-year undergraduate organic chemistry laboratory course. The general public is well acquainted with citronella oil,7 and thus students are able to make a connection with a “real-world” experience. Using natural citronella oil as the starting material for the synthesis is not practical because citronella oil contains many components. Hence the synthesis uses pure β-citronellala major component of citronella oil as the starting material. The two-step synthesis of β-citronellyl tosylate is outlined in Scheme 1 and can be synthesized over the course of two consecutive weeks in two 3 h lab periods. The project is straightforward for second-year organic chemistry students, and there are no special equipment requirements other than an NMR, thereby making it accessible to a broader audience. The project was run on two occasions (spring semester 2011 and spring semester 2012) in a second-semester second-year organic chemistry lab course designed for students © 2013 American Chemical Society and Division of Chemical Education, Inc.
who are chemistry and biochemistry−molecular biology majors. This particular lab course incorporates projects with the goal to prepare chemistry and biochemistry majors for future research, expose them to new ideas, and highlight practical synthetic applications.8 Students who performed this project worked mostly in pairs; a total of twenty-five second-year organic chemistry students completed the experiment (13 students in spring 2011 and 12 students in spring 2012).
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PEDAGOGICAL CONSIDERATIONS Although the focus of this experiment is the two-step synthesis of the tosylate, there are several pedagogical features that enrich the project: first, this experiment correlates well with the corequisite lecture course in which reductions with reagents, such as sodium borohydride, and nucleophilic additions to carbonyls are heavily emphasized.9 Additionally, this perfume synthesis is rigorous enough to be implemented in a chemistry majors lab course, rather than a non-chemistry majors lab course: the theory (nucleophilic hydride additions to carbonyls, tosylations) and the techniques utilized (synthesis, column chromatography, NMR characterization) elevate the rigor of Published: August 9, 2013 1231
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should not be looked into and should be pointed away from the user. Sodium bicarbonate has no known OSHA hazards.
the experiment. Students are expected to read the Proctor and Gamble patent in order to answer questions associated with the experiment. Second, there are few tosylations reported in the undergraduate chemical educational literature,10 and there is scant emphasis placed on the tosyl group; thus, this experiment provides exposure to an alcohol protecting group that is used frequently in modern organic synthesis.11 Third, although this is only a two-step synthesis, students gain the experience of carrying a product from one step to the next in order to reach a target molecule; should the β-citronellal reduction fail, the intermediate compound β-citronellol is commercially available and can be provided to the students to allow them to proceed with the synthesis. Finally, the use of methanol as the solvent for the reduction and the solvent-free tosylation12 allow for a discussion on green chemistry principles13 and sustainability. It should be noted, however, that both the workup and purification steps of the project are not solvent-free, a drawback that that should be addressed with students.
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DISCUSSION Both steps of the two-step synthesis were performed by students with relative ease. For the first step, the aldehyde reduction of β-citronellal, complete conversion to alcohol was observed in the 1H NMR; only one group was unable to reduce the β-citronellal to β-citronellol, but, given a commercial sample of β-citronellol on day 2, the group obtained the tosylate with a 53% purified yield. The most challenging aspect to the second, tosylation step involved purification to separate the desired product from residual reactants. However, as long as the student handout was methodically followed, students were successful in purifying β-citronellyl tosylate via column chromatography. There were, however, diminished yields for two groups of students who self-reported that they spilled their compounds and were not careful with the column, leading to rejection of coeluted fractions. This highlighted for students the importance of careful hands and planning while carrying out a multistep synthesis. Students obtained overall yields between 19 and 31% for the two-step synthesis and column purification.18 Given that this experiment required students to carry 0.1 mL of compound through two steps, a reaction on solid support, and tricky column purification, the overall product yields are satisfactory. Representative student TLC plates and 1H NMR spectra are in the Supporting Information. The 1H NMRs for both the β-citronellol and the tosylate were assigned by students without much difficulty.
EXPERIMENTAL PROCEDURE
Day 1
The first step of the synthesis is a classic sodium borohydride reduction in methanol of β-citronellal to the perfume βcitronellol.14 The product is extracted and concentrated. The crude product is verified by TLC, and a sample is prepared for NMR analysis. Day 2
The tosylation of the intermediate alcohol is a solvent-free reaction adapted from the literature that involves mixing together potassium hydroxide, potassium carbonate, βcitronellol, and excess tosyl chloride in a mortar with a pestle.15 Potassium carbonate is proposed to serve as a basic solid support for the reaction, whereas potassium hydroxide helps deprotonate β-citronellol, thereby leading to the desired synthetic target, β-citronellyl tosylate.16 After filtration, purification, and isolation via pipet column chromatography, a sample is prepared for NMR analysis.17 Detailed experimental procedures for the syntheses of βcitronellol and β-citronellyl tosylate are in the Supporting Information.
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ASSESSMENT AND ANALYSIS OF THE MERIT OF THE EXPERIMENT All students were required to write a formal lab report upon completion of the experiment. The lab report grades reflected the overall performance of students in the class. The first time this experiment was performed (spring 2011), students were given an unannounced pre-test, and a post-test on the final exam that posed the same questions as the pre-test.19 Average student scores (Table 1) on the post-test questions significantly improved in comparison with the pre-test questions, with a post-test average score of 24.6 points, in comparison with 13.3 points on the pre-test. Finally, as a third form of assessment, students from spring 2011 filled out an anonymous survey on the day of their final lab exam (detailed in the Supporting Information). Students self-reported that their knowledge about sulfonations and perfumes increased after the completion of the project and that their attitudes toward the experiment improved after its completion. An unexpected consequence was that students’ self-confidence in performing column chromatography decreased, most likely because they were exposed to column separation conditions in which the compounds had closer Rf values than what they had previously experienced with column chromatography.
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HAZARDS Students are required to work exclusively in the hood and to wear personal protective equipment: full lab coats, gloves, and safety goggles. Potassium hydroxide is corrosive and can cause severe skin burns. It must be ground with the pestle in a mortar in a hood, using the full personal protective equipment listed above. Dichloromethane and deuterated chloroform are suspected carcinogens. Hexanes comprises a mixture of isomers including n-hexane, a neurotoxin. It must be used in a hood with the full personal protective equipment listed above. Magnesium sulfate and silica gel have a target organ effect and may be harmful if absorbed through skin, inhaled, or ingested. β-Citronellal, tert-butyl alcohol, diethyl ether, ethanol, ethyl acetate, and methanol are irritants, toxic by ingestion, and flammable liquids. β-Citronellol, p-toluenesulfonyl chloride, and brine are irritants. Potassium carbonate is an irritant, harmful if absorbed through skin or ingested. Sodium borohydride is water reactive, corrosive, and toxic by skin absorption and ingestion. β-Citronellyl tosylate has no reported safety information. Phosphomolybdic acid hydrate is corrosive and an oxidizer. UV light can sunburn eyes and skin. The UV lamp
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SUMMARY
In summary, a successful two-step synthesis of β-citronellyl tosylate was performed. The project exposed students to both solvent-free reactions and the tosylate functional group. It also illustrated a perfume synthesis, thereby highlighting a useful practical application to organic chemistry. 1232
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C. The Chemistry of Flavor. J. Chem. Educ. 1945, 22, 567−569. (g) Magnus, J. B. Essential Oils as Strategic Materials. J. Chem. Educ. 1944, 21, 256−258. (4) For simple, nonsynthetic J. Chem. Educ. lab experiments that involve perfumes, see: (a) Logan, J. L.; Rumbaugh, C. E. The Chemistry of Perfume: A Laboratory Course for Nonscience Majors. J. Chem. Educ. 2012, 89, 613−619. (b) Lavoie, J.-M.; Chornet, E.; Pelletier, A. Identification of Secondary Metabolites in Citrus Fruit Using Gas Chromatography. J. Chem. Educ. 2008, 85, 1555−1557. (c) Mowery, K. A.; Blanchard, D. E.; Smith, S.; Betts, T. A. Investigation of Imposter Perfumes Using GC-MS. J. Chem. Educ. 2004, 81, 87−89. (d) Duprey, R.; Sell, C. S.; Lowe, N. D. The Chemistry of Fragrances: A Group Exercise for Chemistry Students. J. Chem. Educ. 2003, 80, 513−515. (e) Lynch, M. A.; Gloffke, W.; Rauner, R. A. An Undergraduate Thin-Layer Chromatography Experiment. Olfactory Delights. J. Chem. Educ. 1995, 72, 1137−1138. (5) Cunningham, A. D.; Ham, E. Y.; Vosburg, D. A. Chemoselective Reactions of Citral: Green Syntheses of Natural Perfumes for the Undergraduate Organic Laboratory. J. Chem. Educ. 2011, 88, 322−324. (6) (a) Hartman, F. A.; Sivik, M. R. Sulfonate derivatized perfumes. U.S. Patent 5,710,122, January 20, 1998. (b) Sivik, M. R.; Hartman, F. A. Sulfonate Derivatized Perfumes. Int. Pat. WO 97/22580, June 26, 1997. (7) Ritter, S. What’s That Stuff? Citronella Oil. Chem. Eng. News. 2006, 84 (44), 42. (8) For other projects used in this lab course, see: (a) Mascarenhas, C. M. The Comparative Nucleophilicity of Naphthoxide Derivatives in Reactions with a Fast-Red TR Dye. A Discovery-Oriented Capstone Project for the Second-Year Organic Laboratory. J. Chem. Educ. 2008, 85, 1271−1273. (b) Lazarski, K. E.; Rich, A. A.; Mascarenhas, C. M. A One-Pot, Asymmetric Robinson Annulation in the Organic Chemistry Majors Laboratory. J. Chem. Educ. 2008, 85, 1531−1534. (9) For second-year organic chemistry textbook references to aldehyde reductions, see: (a) Brown, W. H.; Foote, C. S.; Iverson, B. L.; Anslyn, E. V. Aldehydes and Ketones. Organic Chemistry, 6th ed.; Brooks/Cole: Belmont, CA, 2012; Chapter 16, pp 616−620. (b) Carey, F. A.; Giuliano, R. M. Aldehydes and Ketones: Nucleophilic Addition to the Carbonyl Group. Organic Chemistry, 8th ed.; McGraw Hill: New York, NY, 2011; Chapter 17, pp 734−735. (c) Bruice, P. A. More about Oxidation-Reduction Reactions. Organic Chemistry, 6th ed.; Prentice Hall: Boston, 2011; Chapter 20, pp 890−892. (d) Smith, J. G. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction. Organic Chemistry, 3rd ed.; McGraw Hill: New York, NY, 2011; Chapter 20, pp 726−730. (e) Fox, M. A.; Whitesell, J. K. Nucleophilic Addition and Substitution at Carbonyl Groups. Organic Chemistry, 2nd ed.; Jones and Bartlett: Sudbury, MA, 1997; Chapter 12, pp 597−599. (f) Wade, L. G., Jr. Ketones and Aldehydes. Organic Chemistry, 7th ed.; Prentice Hall: Upper Saddle River, NJ, 2010; Chapter 18, p 831. (10) (a) Norris, P.; Fluxe, A. Preparation of a D-Glucose-Derived Alkene. An E2 Reaction for the Undergraduate Organic Chemistry Laboratory. J. Chem. Educ. 2001, 78, 1676−1678. (b) Cabay, M. E.; Ettlie, B. J.; Tuite, A. J.; Welday, K. A.; Mohan, R. S. The DiscoveryOriented Approach to Organic Chemistry. 5. Stereochemistry of E2 Elimination: Elimination of cis- and trans-2-Methylcyclohexyl Tosylate. J. Chem. Educ. 2001, 78, 79−80. (c) Norris, P.; Freeze, S.; Gabriel, C. J. Synthesis of a Partially Protected Azidodeoxy Sugar. A Project Suitable for the Advanced Undergraduate Organic Chemistry Laboratory. J. Chem. Educ. 2001, 78, 75−76. (d) Howell, B. A.; Kohrman, R. E. Preparation of 2-Bromopentane. J. Chem. Educ. 1984, 61, 932−934. (e) Bartlett, P. A.; Marlowe, C. K.; Connolly, P. J.; Banks, K. M.; Chui, D. W.-H.; Dahlberg, D. S.; Haberman, A. M.; Kim, J. S.; Klassen, K. J.; Lee, R. W.; Lum, R. T.; Mebane, E. W.; Ng, J. A.; Ong, J.-C.; Sagheb, N.; Smith, B.; Yu, P. Synthesis of Frontalin, the Aggregation Pheromone of the Southern Pine Beetle. A Multistep Organic Synthesis for Undergraduate Studies. J. Chem. Educ. 1984, 61, 816− 817. (f) Smith, L. R.; Williams, H. J. Glutamic Acid in Pheromone Synthesis. A useful chiral synthon. J. Chem. Educ. 1979, 56, 696−698. (g) Wiseman, P. A.; Betras, S.; Lindley, B. Conversion of a Primary
Table 1. Comparison of Student Scores on Pre- and PostTests
No.
Question
1
Mechanism for conversion of βcitronellal to β-citronellol The purpose of KOH in the tosylation step The purpose of the K2CO3 in the tosylation step The purpose of the TsCl in the tosylation step What was the solvent used for the tosylation step What was the solvent used for the reduction step Which compound is the actual perfume for the laundry Identify the 1H NMR shown (βcitronellal, β-citronellol, or the β-citronellyl tosylate) Identify the correct structure of the tosylate Totals
2 3 4 5 6 7 8 9
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Total Points Assigned per Question
Pre-Test Average Score
PostTest Average Score
6
0.6
4.6
3
2.8
3.0
3
1.0
2.0
3
2.5
3.0
3
1.3
2.5
3
1.8
2.5
3
0.0
2.0
3
1.8
2.0
3
1.8
3.0
30
13.3
24.6
ASSOCIATED CONTENT
S Supporting Information *
The initial student handout; questions for the students; instructor notes; NMR data; assessment information. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The author gratefully acknowledges the Department of Chemistry at Benedictine University for funding and the students who participated in the assessment surveys.
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REFERENCES
(1) Franklin, S.; Pienta, N. J.; Fry, M. D. 8:31 a.m. Belly Flop: Attitude Adjustment through Weekly Feature Molecules. J. Chem. Educ. 2005, 82, 847−850. (2) For recent J. Chem. Educ. lab experiments involving the synthesis of soaps and cosmetics, see: (a) Liao, W. C.; Lien, C.-Y. Facial Toner Preparation Using Distilled Fragrant Compounds of Natural Herbal Plants. J. Chem. Educ. 2011, 88, 470−472. (b) Mabrouk, S. T. Making Usable, Quality Opaque or Transparent Soap. J. Chem. Educ. 2005, 82, 1534−1537. (c) de Mattos, M. C. S.; Nicodem, D. E. Soap from Nutmeg: An Integrated Introductory Organic Chemistry Laboratory Experiment. J. Chem. Educ. 2002, 79, 94−95. (3) For early J. Chem. Educ. articles that identify essential oils as a topic of pedagogical interest and describe the structures of these compounds, see: (a) Fortineau, A.-D. Chemistry Perfumes Your Daily Life. J. Chem. Educ. 2004, 81, 45−50. (b) Runquist, O. The Essential Oils. A Series of Laboratory Experiments. J. Chem. Educ. 1969, 46, 846−847. (c) Roderick, W. R. Current Ideas on the Chemical Basis of Olfaction. J. Chem. Educ. 1966, 43, 510−519. (d) Sterrett, F. A. The Nature of Essential Oils II. Chemical Constituents, Analysis. J. Chem. Educ. 1962, 39, 246−251. (e) Sterrett, F. A. The Nature of Essential Oils I. Production. J. Chem. Educ. 1962, 39, 203−206. (f) Crocker, E. 1233
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Alcohol to an Alkyl Halide via a Tosylate Intermediate. J. Chem. Educ. 1974, 51, 348−349. (11) For brief references to tosylation in second-year organic chemistry textbooks, see: (a) Brown, W. H.; Foote, C. S.; Iverson, B. L.; Anslyn, E. V. Alcohols. Organic Chemistry, 6th ed.; Brooks/Cole: Belmont, CA, 2012; Chapter 10, pp 403−405. (b) Brown, W. H.; Foote, C. S.; Iverson, B. L.; Anslyn, E. V. Functional Group Derivatives of Carboxylic Acids. Organic Chemistry, 6th ed.; Brooks/Cole: Belmont, CA, 2012; Chapter 18, p 708. (c) Carey, F. A.; Giuliano, R. M. Nucleophilic Substitution. Organic Chemistry. 8th ed.; McGraw Hill: New York, NY, 2011; Chapter 8, pp 347−350. (d) Solomons, T. W. G.; Fryhle, C. B. Alcohols and Ethers. Organic Chemistry, 7th ed.; upgrade; John Wiley & Sons, Inc.: New York, 2002; Chapter 11, pp 495−498. (e) Bruice, P. A. Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds. Organic Chemistry, 6th ed.; Prentice Hall: Boston, 2011; Chapter 10, pp 416−419. (f) Smith, J. G. Alcohols, Ethers, and Epoxides. Organic Chemistry, 3rd ed.; McGraw Hill: New York, NY, 2011; Chapter 9, pp 338−340. (g) Fox, M. A.; Whitesell, J. K. Substitution by Nucleophiles at sp3-Hybridized Carbon. Organic Chemistry, 2nd ed.; Jones and Bartlett: Sudbury, MA, 1997; Chapter 8, pp 398−399. (h) Jones, M. J., Jr.; Fleming, S. A. Substitution and Elimination Reactions: The SN2, SN1, E1 and E2 Reactions. Organic Chemistry, 4th ed.; W. W. Norton & Company: New York, NY, 2010; Chapter 7, pp 283−285. (i) Wade, L. G., Jr. Reactions of Alcohols. Organic Chemistry, 7th ed.; Prentice Hall: Upper Saddle River, NJ, 2010; Chapter 11, pp 472−475. (12) For examples of other organic solvent-free organic chemistry lab experiments reported in this journal, see: (a) Rosatella, A. A.; Afonso, C. A. M.; Branco, L. C. Oxidation of Cyclohexene to trans-1,2Cyclohexanediol Promoted by p-Toluenesulfonic Acid without Organic Solvents. J. Chem. Educ. 2011, 88, 1002−1003. (b) Gregor, R. W.; Goj, L. A. Solvent-Free Synthesis of 2,2′-Dinitrobiphenyl: An Ullmann Coupling in the Introductory Organic Laboratory. J. Chem. Educ. 2011, 88, 331−333. (c) Young, D. M.; Welker, J. J. C.; Doxsee, K. M. Green Synthesis of a Fluorescent Natural Product. J. Chem. Educ. 2011, 88, 319−321. (d) Aktoudianakis, E.; Chan, E.; Edward, A. R.; Jarosz, I.; Lee, V.; Mui, L.; Tahatipamala, S. S.; Dicks, A. P. Comparing the Traditional with the Modern: A Greener, Solvent-Free Dihydropyrimidone Synthesis. J. Chem. Educ. 2009, 86, 730−732. (e) McKenzie, L. C.; Huffman, L. M.; Hutchison, J. E.; Rogers, C. E.; Goodwin, T. E.; Spessard, G. O. Greener Solutions for the Organic Chemistry Teaching Lab: Exploring the Advantages of Alternative Reaction Media. J. Chem. Educ. 2009, 86, 488−493. (f) Phonchaiya, S.; Panijpan, B.; Rajviroongit, S.; Wright, T.; Blanchfield, J. T. A Facile Solvent-Free Cannizzaro Reaction. An Instructional Model for Introductory Organic Chemistry Laboratory. J. Chem. Educ. 2009, 86, 85−86. (g) Nguyen, K. C.; Weizman, H. Greening Wittig Reactions: Solvent-Free Synthesis of Ethyl trans-Cinnamate and trans3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester. J. Chem. Educ. 2007, 84, 119−121. (h) Sobral, A. J. F. N. Synthesis of meso-Diethyl-2,2′dipyrromethane in Water. An Experiment in Green Organic Chemistry. J. Chem. Educ. 2006, 83, 1665−1666. (i) Dintzner, M. R.; Wucka, P. R.; Lyons, T. W. Microwave-Assisted Synthesis of a Natural Insecticide on Basic Montmorillonite K10 Clay. Green Chemistry in the Undergraduate Organic Laboratory. J. Chem. Educ. 2006, 83, 270−272. (j) Esteb, J. J.; Hohman, J. N.; Schlamadinger, D. E.; Wilson, A. M. A Solvent-Free Baeyer-Villager Lactonization for the Undergraduate Organic Laboratory: Synthesis of γ-t-Butyl-ε-caprolactone. J. Chem. Educ. 2005, 82, 1837−1838. (k) Cave, G. W.; Raston, C. L. Green Chemistry Laboratory: Benign Synthesis of 4,6-Diphenyl[2,2′]bipyridine via Sequential Solventless Aldol and Michael Addition Reactions. J. Chem. Educ. 2005, 82, 468−469. (l) Esteb, J. J.; Gligorich, K. M.; O’Reilly, S. A.; Richter, J. M. Solvent-Free Conversion of αNaphthaldehyde to 1-Naphthoic Acid and 1-Naphthalenemethanol: Application of the Cannizzaro Reaction. J. Chem. Educ. 2004, 81, 1794−1795. (m) Leung, S. H.; Angel, S. A. Solvent-Free Wittig Reaction: A Green Organic Chemistry Laboratory Experiment. J. Chem. Educ. 2004, 81, 1492−1493. (n) Palleros, D. R. Solvent-Free Synthesis of Chalcones. J. Chem. Educ. 2004, 81, 1345−1347.
(13) (a) Costa, N. E.; Pelotte, A. L.; Simard, J. M.; Syvinski, C. A.; Deveau, A. M. Discovering Green, Aqueous Suzuki coupling Reactions: Synthesis of Ethyl (4-Phenylphenyl)acetate, a Biaryl with Anti-Arthritic Potential. J. Chem. Educ. 2012, 89, 1064−1067. (b) Eby, E.; Deal, S. T. A Green, Guided-Inquiry Based Electrophilic Aromatic Substitution for the Organic Chemistry Laboratory. J. Chem. Educ. 2008, 85, 1426−1428. (c) Haack, J. A.; Hutchison, J. E.; Kirchhoff, M. M.; Levy, I. J. Going Green: Lecture Assignments and Lab Experiences for the College Curriculum. J. Chem. Educ. 2005, 82, 974−976. (d) Jones-Wilson, T. M.; Burtch, E. A. A Green Starting Material for Electrophilic Aromatic Substitution for the Undergraduate Organic Laboratory. J. Chem. Educ. 2005, 82, 616−617. (e) McKenzie, L. C.; Huffman, L. M.; Hutchison, J. E. The Evolution of a Green Chemistry Laboratory Experiment: Greener Brominations of Stilbene. J. Chem. Educ. 2005, 82, 306−310. (f) Goodwin, T. E. An Asymptotic Approach to the Development of a Green Organic Chemistry Laboratory. J. Chem. Educ. 2004, 81, 1187−1190. (g) Reed, S. M.; Hutchison, J. E. Green Chemistry in the Organic Teaching Laboratory: An Environmentally Benign Synthesis of Adipic Acid. J. Chem. Educ. 2000, 77, 1627−1629. (14) There is a literature report of a solvent-free reduction of βcitronellal, but it was not adopted because of its lengthy experimental time. See: O’Brien, K. E.; Wicht, D. K. A greener organic chemistry experiment: reduction of citronellal to citronellol using poly(methylhydro)siloxane. Green Chem. Lett. Rev. 2008, 1, 149−154. (15) Kazemi, F.; Massah, A. R.; Javaherian, M. Chemoselective and scalable preparation of alkyl tosylates under solvent-free conditions. Tetrahedron 2007, 63, 5083−5087. (16) It should be noted that potassium hydroxide must be added to the basic potassium carbonate solid support for complete tosylation of β-citronellol. See ref 15 for details. (17) For literature values of the 1H NMR of β-citronellyl tosylate, see: Doan, N. N.; Le, T. N.; Nguyen, H. C.; Hansen, P. E.; Duus, F. Ultrasound Assisted Synthesis of 5,9-Dimethylpentadecane and 5,9Dimethylhexadecane − the Sex Pheromones of Leucoptera cof feella. Molecules 2007, 12, 2080−2088. (18) The overall yield obtained after two steps and column purification was 29−33% by an experienced chemist. (19) Detailed information and questions on the pre-test and post-test can be found in the Supporting Information. As a general rule, the author runs assessment surveys, pre-tests, and post-tests the first year a project is performed in a teaching lab, in order to evaluate the pedagogical merit of the project. Given the clearly positive outcomes from the spring 2011 semester, the assessment was not repeated in spring 2012.
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