In the Laboratory
Triboluminescent Crystals from the Microwave Oven
W
Bruce W. Baldwin* Chemistry Department, Spring Arbor University, Spring Arbor, MI 49283;
[email protected] David M. Wilhite Pharmacia Corporation, Kalamazoo, MI 49001
For undergraduate students in the laboratory, a constant frustration is the lack of interesting uses for synthesized chemical products. Some notable exceptions are the bouncing putty experiment (1) and synthesis of soap from common vegetable oils (2). These experiments derive their immense appeal from producing a product that students find interesting. The present report deals with another example of a compound that will dazzle students and introduce them to performing experiments in the microwave oven. Following the basic reagent combinations introduced by Erikson (3), the amidation of anthranilic acid with acetic anhydride to produce 1 was carried out in one minute in a microwave oven (1,000 W):
lubricants that would supply an answer to this ubiquitous question (6 ). A plastic coating activated by mechanical grinding was engineered using a triboluminescent carbazole derivative in combination with an attached polymerizable vinyl group. When crystals of 9-ethyl-3-vinyl carbazole 2 were included in a ball-bearing lubricant, the sparks resulting from normal friction in the ball-bearing race induced polymerization of the vinyl groups. This produced polymers of 1,000,000 molecular weight, acceptable as protective lubricants. The resulting protective sheath could lengthen the life of the grinding surfaces and, thus, reduce bearing replacement needs.
O
NH2
N
O
O OH
1. Microwave
+ H3C
O
CH3
2. H2O, Microwave
O OH NH 1
O
CH3
The average student yield is 60% (~1.0 g), more than enough to observe the triboluminescent effect. This project provides the instructor an opportunity to give the students background on microwave oven amidation (4 ), recrystallization, and triboluminescence (5). The ease of synthesis and ability to check crystal quality with a 360-nm mineral lamp permits concentration on improving recrystallization technique. Because crystal quality is critical for the success of this experiment, fast microwave oven synthesis allows extra time for discussing how to obtain crystals of excellent quality. Many students repeat the experiment once or twice after consultation to see if crystal quality can be improved. The highest quality crystals for triboluminescence appear to be those that glow yellow under irradiation with long-wave UV light (360 nm). The fluorescing color is usually purple if the crystals form too quickly or incorporate large amounts of solvent into the structure. Either type of crystal will spark when crushed in a darkened room, but the yellow glowing crystals give the most intense sparking. Because triboluminescence depends on crystal quality, the instructor can point out factors involved in crystal growth, including, but not limited to, factors such as slowness of cooling and solvent incorporation into the crystal, which is indicated by lack of sheen when the crystals are dried. Although the triboluminescence effect is spectacular by itself, students inevitably ask “What good is it?” A search of the literature revealed an application to self-activating protective 1344
2
In summary, amidation was carried out conveniently and quickly in the microwave oven (one minute) using inexpensive glassware. The target product provided a compound with the interesting ability to triboluminesce when crushed. Hence, a procedure requiring good recrystallization technique yielded a fascinating product for the students to observe. Hazards Because anthranilic acid is an irritant, be sure not to breathe the powder. Acetic anhydride is corrosive, reacts violently with water, and is a lachrymator. Methanol is a toxic, flammable liquid; therefore, care should be taken in its use. WSupplemental
Material
A handout for students and notes for the instructor are available in this issue of JCE Online. Literature Cited 1. Armitage, D. A.; Hughes, M. N.; Sinden, A. W. J. Chem. Educ. 1973, 50, 434. 2. Phanstiel, O. IV; Dueno, E.; Wang, Q. X. J. Chem. Educ. 1998, 75, 612–614. 3. Erikson, J. J. Chem. Educ. 1972, 49, 688. 4. Mirafzal, G. A.; Summer, J. M. J. Chem. Educ. 2000, 77, 356–357. 5. Hardy, G. E.; Baldwin, J. C.; Zink, J. I.; Kaska, W. C.; Liu, P.-H.; Dubois, L. J. Am. Chem. Soc. 1977, 99, 3552– 3558. A more recent review is Sweeting, L. M. Chem. Mater. 2001, 13, 854–870. 6. Inoue, T.; Tazuke, S. Chem. Lett. 1981, 589–592.
Journal of Chemical Education • Vol. 79 No. 11 November 2002 • JChemEd.chem.wisc.edu
