Adil A. Jarrar University of Jordan Arnrnon, Jordan
Photolysis of a Heterocyclic Compound A n advanced undergraduate experiment
~ b n s i d e r a h l e interest in photochemical reactions is a prominent feature of recent organic chemistry research. There is consequently a growing need for photochemical preparations t h a t would fit into the general organic chemistry course. A novel photochemical rearrangement was recently discovered ( 1 ) and later studied in some detail (2). In this reaction various auinoxaline-1.4-dioxideswith a variety of suhstituents in positions two and three were found t o rearrange by irradiation with uv light. The products were invariablv benzimidazolones with acvl and arovl e r o u ~ in s - ~ one and three positions (see eqns. (1)-"(3)). T h e radiation source used was a 450-W Hanovia mercury lamp, h u t the reactions can he carried out in sunlight provided prolonged irradiation periods are allowed. This article describes the preparation and photolysis of
2-phenyl-3-henzoylquinoxaline-l,4-dioxide(III~. The experiment is adapted t o suit a n organic chemistry introductory course and may he introduced near the final stages when the students have acquired the ability t o speculate about t h e mechanisms of the reactions involved. It was given t o students in our lahoratories and was found to appeal t o them. They appreciated working with small quantities of beautifully crystalline solids. The yields they ohtained ranged from 50-90% of those reported in the experimental section below. Experimental Benzafurazan oxide (BFO)' is known to be prepared from o-nitroaniline by oxidation with chlorine in alkaline alcoholic solution. The present procedure uses commercial bleach (5% NaOCl(aq)z and eliminates the difficulty of using chlorine gas as reported in an organic synthesis preparation (31.
o-Nitroaniline (1, 41 g, 0.3 mole) was dissolved in 95% ethanol (250 ml) containing potassium hydroxide (21 g) and treated over 1 hr with 5% aqueous sodium hypochlorite (about 800 ml) a t about (t1O"C. The resulting precipitate was collected and recrystallized from ethanol (the solution was acidified with acetic acid to keep the orange o-nitroaniline in solution). Yield 15%, mp 7112'C. 2-Phenyl-3-benzoylquinoxaline-1,4-dioxide (ID)(4) is prepared by the reaction of BFO with dibenzoylmethane(I1) in diethylamine.
' Several students may share in r h ~ spreparation and divide the product. BCO is also comrnerrinllg available lrnm Aldrich Chemical Co. 2Available under a variety of trade names as a household blench. A suegested mechanism is given in ref. 4 'A iurersted mechanism ispven in refs I I , and 0, 5 Alternat~rrlv the d u t i o n msv be e x ~ u s e dto runliaht for ahuut six hours or for longer time if thk experiment is to heeontinued in a following laboratory meeting.
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BFO (3.4 g, 0.025 mole) was dissolved in warm diethylamine (25 ml) and a solution of (II) (5.6 g, 0.025 mole) in diethylamine (25 ml) was added. The product starts to form within 15-20 min.3 After 1-2 hr the yellow precipitate was thinned with the solvent and filtered (3.4 g, 40%). A second mop may he obtained if the mother liquor is left at room temperature for 24 hr, raising the total yield to above 70%. However, the first crop is sufficient for the continuation of the experiment. It is recrystallized from methanol as thin yellow needles mp 234% Compound (m)(1 g) was dissolved in warm ethanol (150 ml) in a round bottom flask, Erlenmeyer flask, or a long, wide test tube, fitted with a cork and a 50-em glass tubing. Several flasks or tubes were arranged around a 450-W Hanovia mercury lamp (any other equivalent uv source may he used). Irradiation for 3 hr led to the formation of a voluminous white fluffy
twi
TLC was used to follow the progress of the reaction and showed progressive disappearance of the starting material. The colorless 1,3-dihenzoylhenzimidazolone(N) was filtered (0.5 g, 50% yield) and recrystallized from methanol mp 217-218'C. An extra 0.2 g of the product could be obtained hy further irradiation of the mother liquor (1 hr) and later concentration to about 25 ml (an extra 3 hr in the sun accomplishes the same result). In our laboratory mns only the primary product was collected. Additional Experiments Although the color, melting points, ir spectra (if available) and tlc behavior are sufficient to establish the differences between (III) and (IV), the students may be asked t o devise experiments to answer the following 1) If o-phenylenediamine and urea can be fused together at 140'C to produce henzimidazolone-2 151, how can the structure of
(IV) be proved by an unambiguous synthesis? 2) How can henzoic acid and henzimidazalane-2 he obtained from
(N)? Acknowledgment The author thanks Prof. C. H. lssidorides and Prof. M. J. Haddadin of the American University of Beirut for their encouragement. Literature Clted (11 Haddadin, M.J., sndluidaidea, C. H., TeIrohadronLett., 8,153 (19671. (21 (a) Haddadin. M. J.. Agopian. G., and ksidorides, C. H.. J. Or8 Chem.,5 4 514 (19711;(blJarrer,A.A., Ph.D.theai%.ArnerieanUniuemityaf Beirut, Aup. 1971. (3)Maiimy, F. B., '.Organic Synthesis," Vol. 37. (Editor: Casan, J.1. John Wiley & Sons, he., New York, 1957. p. I. (4) Isaidorido~,C. H., and Haddadin, M. J.. J Olg. Chsm.,3l.4W7 (19661. (51 Ahmad. Y..Habib. M. S.. Mahammady, A . Bakhtiari. B., and Shamsi. S. A,, J. org. Chem U.201 (19681.
VolurneSl. Number 11. November 1974
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