Communication pubs.acs.org/jchemeduc
Photochemistry Is Back in the Undergraduate Organic Laboratory Douglass F. Taber* and Craig M. Paquette Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States S Supporting Information *
ABSTRACT: A commercial four-foot display ultraviolet fluorescent tube works well both for the photodimerization of trans-cinnamic acid and for the photochemical dimerization of benzophenone to benzopinacol. These procedures were designed for the undergraduate organic chemistry laboratory course.
KEYWORDS: Second-Year Undergraduate, Laboratory Instruction, Organic Chemistry, Hands-On Learning/Manipulatives, Laboratory Equipment/Apparatus, Photochemistry
P
sunlamps were withdrawn from the market several years ago. Since that time, undergraduate laboratory experiments using photochemistry have relied3 on specialized equipment. A commercial display ultraviolet fluorescent tube4 can efficiently promote both of these photodimerizations. Substantial conversion is observed after just 2 h of irradiation, and a total of 4 h is more than sufficient, in both cases. The lamps are about 4 ft long, so many students can be accommodated simultaneously. Using this ultraviolet fluorescent lamp, the benzophenone dimerization−pinacol experiment was reinstituted in the undergraduate organic laboratory course and has been used successfully for several years.
hotochemical transformations, such as the solid-state dimerization of trans-cinnamic acid 1 to the cyclobutane 2 (Scheme 1)1 and the dimerization2 (Scheme 2) of
Scheme 1. Dimerization of trans-Cinnamic Acid 1 to the Cyclobutane 2
■
HAZARDS Looking at the UV light can cause severe eye damage. These lamps do not put out very much visible light, but they do emit a lot of ultraviolet light. A wooden box was constructed to go around the light to protect the students.
benzophenone 3 to benzopinacol 4 with subsequent rearrangement to benzopinacolone 5, have in the past commonly been used in the undergraduate organic laboratory course. The light source for these photodimerizations was sometimes sunlight, but usually commercial sunlamps were used. Such
■
Scheme 2. Dimerization of Benzophenone 3 to Benzopinacol 4 with Rearrangement to Benzopinacolone 5
ASSOCIATED CONTENT
S Supporting Information *
Copies of 1H and 13C NMR spectra for the dimethyl ester of diacid 2. This material is available via the Internet at http:// pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
© XXXX American Chemical Society and Division of Chemical Education, Inc.
A
dx.doi.org/10.1021/ed3004287 | J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
■ ■
Communication
ACKNOWLEDGMENTS We thank Federico Cruz for his able assistance with these experiments. REFERENCES
(1) Hein, S. M. An Exploration of a Photochemical Pericyclic Reaction Using NMR Data. J. Chem. Educ. 2006, 83, 940−942. (2) (a) Zaczek, N. M.; Ruff, J. C.; Jackewitz, A. H.; Roswell, D. F. Migratory Aptitudes, an Organic Chemistry Experiment. J. Chem. Educ. 1971, 48, 257−259. (b) Churio, M. S.; Greia, M. A. Photochemistry of Benzophenone in 2-Propanol. J. Chem. Educ. 1997, 74, 436−438. (3) (a) Bernard, E.; Britz-McKibbin, P.; Gernigon, N. Resveratrol Photoisomerization: An Integrative Guided-Inquiry Experiment. J. Chem. Educ. 2007, 84, 1159−1161. (b) Romero, A.; Hernàndez, G.; Suárez, M. F. Photocatalytic Oxidation of Sulfurous Acid in an Aqueous Medium. J. Chem. Educ. 2005, 82, 1234−1236. (c) Gano, J. E.; Gao, A. J.; Garry, P.; Sekher, P. Small Scale Reactor for Ultraviolet Photochemistry. J. Chem. Educ. 2002, 79, 1361. (d) Danylec, B.; Iskander, M. N. 1H NMR Measurement of the Trans-Cis Photoisomerization of Cinnamic Acid Derivatives. J. Chem. Educ. 2002, 79, 1000−1001. (e) Magner, J. T.; Selke, M.; Russell, A. A.; Chapman, O. L. A New Photochemistry Experiment: A Simple 2 + 2 Photocycloaddition that Poses an Interesting NMR Problem. J. Chem. Educ. 1996, 73, 854−856. (4) We use a Spectroline XX-40, 4 ft long, 40 W, 365 nm fluorescent tube http://www.gardco.com/pages/labapp/uv/bench_display_lamp. cfm, accessed May 2013. This is suitable for at least 40 students at a time. For a smaller group of students, a personal face tanner, which is less expensive, might work well also.
B
dx.doi.org/10.1021/ed3004287 | J. Chem. Educ. XXXX, XXX, XXX−XXX
