N-Acetylanthranilic Acid: A Highly Triboluminercent Material Triboluminemence. the emission of lieht when a crvstal is broken. has been known far mme time but remains an l though rnwly itmrga~irand orgmiv 1nnrerix1.i xrr rrlrorred rn exhil~itrt.is pmperty.' ol,wurr p l w m n r n ~ s wru The effevr hu. I w w rxplninrd hg exelrarim d rhr r d e r ilr try an elrrtric dischnrpe between the surfneb of the fmrtured crystal and subsequent fluorescence. I n the eouee of the laboratory preparation of 2-methylbenzisoxaeinone,'.s we have found that its hydrolysis product, N-acetylanthranilic acid, is highly triboluminescent and that this serves to make the experiment more intriguing than the normal synthetic preparation. In the experiment, anthranilic acid is converted t o Zmethylbenzisoxrtzinone by the action of acetic anhydride. This compound may be isolrtted (a good exercise in that the benzisoxszinane is readily hydrolyzed by stmaspheric moisturel) or converted directly t o N-acetylanthrmilic acid by a mild hydrolytic reaction.
Experimental Preparation of N-acetylanthranilic acid: Place 10 g (0.072 mole) of snthranilic acid in a round-bottom flask equipped with a reflux condenser. Add 30 ml (32 g, 0.32 mole) of acetic anhydride, bring the mixture slowly t o the reflux temperature and maintain heat for 15 min. Allow the solution t o cool and add 10 ml water through the condenser. Bring the mixture t o a soft boil once more and allow to cool slowly. Isolate the crystals of N-acetylanthranilic acid ( m . ~ 183-5'C) . by suction filtration in the hood and wash the ~ r o d u c with t a small amount of cold methanol. If the intermediate henzisoxazinone is isolated according t o Helmkamp and JohnsonPit may readily be converted to N-acetylanthranilic acid by dissolving in a hot mixture of 35 ml of acetic acid and 10 ml of water (assuming approximately 10 g of the benaisoxaainone) and allowing the solution to stand. Theseprocedures usually yield well-formed crystals but the material may be recrystallized from acetic acid/water mixtures. To demonstrate the property of triboluminescence, the crystals should be well-formed, and it is vital that they he completely free of solvent. The triboluminescence is best demonstrated by placing several crystals of the compound between two watch glasses and gently grinding. Thelight emitted is readily obeerved in a. darkened room.
and Company, 1968, p. 155. a BOGERT M. T., AND Smi,, H. A., J. Amer. Chem. Soe., 29, 517 (1907).
688
/
Journal of Chemical Education
