3-Hydroxy-1,2,3-benzotriazin-4-one, 1, was prepared by diazotization of o-aminob-enz-hydroxamic acid, 2. 3-Methoxy-1,2,3-benzotriazin-4-one, 5a, was obtained by reaction of 1 with dimethyl sulphate and was found to be stable to thermolysis. Acetylation and benzoylation of 1 yielded the N-acetoxy-5b and benzoyloxy-5c derivatives respectively. The N-benzoyloxy derivative 5c is converted into the acetate 5b by a novel 'acyl-exchange' reaction in acetic anhydride. Acid hydrolysis of 1 gives anthranilic acid, and thermolyses of 1 in amyl alcohol and aniline afford amyl anthranilate and N-phenylanthranilamide, respectively. The ketenimine 11 is postulated as an intermediate in the thermal breakdown of 1, and this is confirmed by the isolation of the Diels–Alder adduct 12 from reaction of 1 with phenyl isocyanate. Thermolysis of 1 in inert solvents affords a novel compound, 3-(o-aminobenzoyloxy)-1,2,3-benzotriazin-4-one, 6, which polymerizes when 1 is subjected to prolonged thermolysis in diglyme. 6 resisted methylation and acid hydrolysis, but underwent acyl-oxygen cleavage when diazotization of 6 was attempted and suffered 'acyl-exchange' when acylation was attempted. The formation of 6 from 1 also involves the ketenimine 11. The importance of these observations to an understanding of previously reported reactions of benzotriazinones is discussed. The o-aminobenzoyloxy derivative 6 shows potential as an o-aminobenzoylating agent.

Die aus der Hydroxamsäure (I) erhältliche Titelverbindung (II) wird durch Methylierung bzw. Acylierung in die Derivate (III) bzw. (IV) übergeführt.

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