Phthalic anhydride Schmidt reaction

Treatment of phthalic acid (145) with sodium azide under acidic conditions has been reported" to give various products anthranilic acid (147) and a trace of o-phenylenediamine (148) in concentrated sulfuric acid and anthranilazide (149) and benzimidazol-2-one (150) in 90% sulfuric acid. Analogously, phthalic anhydride (146) gives the following products anthranilic acid (147), benzimidazol-2-one (150) and some 3,l-benzoxazine-2,4(l//)-dione (isatoic anhydride) (151) in sulfuric acid and benzimidazol-2-one (150) in acetic acid. A recent report" has revealed that Ae Schmidt reaction of phthalic acid (145) in 90-98% sulfuric acid gives anthranilic acid (147) and anthranilazide (149) (major products) by a process thought to involve 3,l-benzoxazine-2,4(l//)-dione (151) as an intermediate. Benzimidazol-2-one (150) is produced in this reaction by a secondary process from anthranilazide (149). Photolysis of (149) also produces (150). 

Phthalide and phenolphthalein appear to be the only lactones which have been subjected to the Schmidt reaction, and both proved to be unreactive. Acetic anhydride gives a yield of 85% of methyl amine. Phthalic anhydride yields isatoic anhydride, benzimidazolone, and an-thranilic acid. ... 

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