Benzoxazinone Syntheses
David R. Eckroth Jamaica,
York College N e w York 11432
A n organic chemistry experiment
There are five compounds which can easily he converted to 2-methyl-4H-3,l-benzoxain-4one (VI) by acetic anhydride.' There is evidence to suggest that the reactions2 proceed via an anthranil-type intermediate which gives rise to the formation of VI by further reaction with acetic anhydride. The experiment is presented as a class problem, each student being impressed with the fact that his particular reaction yields the same product as that of every other student. The first-year student in organic chemistry is little exposed to reactive intermediates which are commonly encountered in more advanced study of organic chemistry. The five compounds are o-nitrophenylacetic acid (I), o-azidobenzaldehyde (II), anthranil (1111, anthroxanic acid (IV), and anthranilic acid (V). They are converted to VI apparently in the following ways /-OAc
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VII Experimental Preporofion of 2-Methyl-4H-3,1-benzoxozin-4-one ( V I )
The general procedure for conversion of I-V to VI is described. Under the hood, a mixture of 2.33 g (0.0144 mole) of anthroxanic hcid and 20 ml of acetic anhydride in a 100-ml round-bottom flesk fitted with a reflux condenser is warmed gradually to the boiling point. A bunsen burner may be used. There is no visible reaction as the mixture approaches the boiling point, but a. clear yellow solution is formed. I t gradually becomes light red (and from I and IV carbon dioxide is evolved). After 4.5 hr of reflux, either (1) the acetic anhydride is evaporated from the reaction mixture on the rota-vac and the resulting gum is recrystallized from anhydrous ether to give colorless crystals, mp 80-81°C (lit.' mp 80-8l0C), infrared peeks st 1755, 1637, 1605, and 156.5 cm-1, or (2) the reaction mixture is cooled in a water bath, then further cooled in an ice-acetone bath (-20°C) and 10 ml of water is added to induce hydrolysis and sdting out of N-acetyl anthranilic add which is filtered and recrystallized from glaoial acetic acid to give colorless crystals, mp 185'C. Preparation of 2(2'-Methoner~lfonamido)~henyl-4H-3,1-benzoxadn-4-one ( V I I I ) The general procedure for the conversion of 111 and IV to VII is described. Under the hood, 8. solution of 5.0 g (0.042 mole) of 111 and 20 ml of methane sulfonyl chloride in s. 100-ml round-bottom flesk fitted with a reflux condenser is warmed gradually to the boiling point. A bunsen burner may be used. The reaction mixture turns brown on warming. After 4.5 hr of reflux, the brown reaction mixture is cooled to room temperrtture and the excess methane sulfonyl chloride is evaporated on a rota-vac a t 0.1 mm Hg. The brown crystals and tar are recrystallized twice from chloroform to give pale yellow crystals, mp 210-13'C. The infrared spectrum shows characteristic peaks a t 3077, 1765, 1608, 1565, 1339, 1153, and 969
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An interesting addition to this experiment is the conversion of I11 and IV to 2(2'-methanesu1fonamido)phenyl-4H-3,1-benzoxazin-4-one (VII) by methane sulfonyl ~hloride.~
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ECKROTH, D. It., unpubli~bedresults. ZExcept, of course, the reaction of anthranilic aoid (V) with acetic anhydride. a L o v ~ .G. M.. Master's Thesis, Wake Forest University, August, 1968, pp.46-47. "ANSCHUTZ, R., AND SCHMIDT, O., Ber., 35,3470 (1902).
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-0Ae Journal of Chemical Education
