Phthalimido‐nitren I. Bleitetraacetat‐Oxydation von N‐Aminophthalimid in inerten Lösungsmitteln. Bildung und Eigenschaften von trans‐1,4‐Bisphthaloyl‐2‐tetrazen

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Abstract
Lead tetraacetate oxidation of N‐aminophthalimide (11) in inert solvents gives as major products phthalimide (15) or trans‐1,4‐bisphthaloyl‐2‐tetrazene (12), the former (15) on slow, the latter (12) on fast addition of the oxidizing agent. As by‐products are found: (a) in the presence of acetic acid: N‐acetylamino‐phthalimide (14), and (b) in its absence (especially at higher temperatures): benzocyclobutenedione (13) along with N‐phthalimido‐phthalimide (16) as well as traces of phthalic anhydride (17).The tetrazene 12 and phthalimide (15) are considered to be formed by oxidation and fragmentation, respectively, of the intermediate 1,4‐bisphthaloyl‐tetrazane (18). Phthalimido‐nitrene (22), or its conjugated acid 23, is postulated to be the species which initiates the major reactions, namely: (a) addition to the educt 11 to give the tetrazane 18 and (b) fragmentation with loss of N2 to give the dione 13. The minor by‐products 16 and 17 may be the result of cross‐amidation of 11 with 15 and rearrangement‐oxidation via phthalazine‐1,4‐dione (30), respectively.The structure of the tetraacyltetrazene 12 follows from its properties, among others a comparison of its UV. spectrum with that of the known 1,4‐dimethoxycarbonyl‐1,4‐dimethyl‐2‐tetrazene (32). Methanolysis of 12 affords 1,4‐di‐(o‐methoxycarbonyl‐benzoyl)‐2‐tetrazene (33). The diacyltetrazene 33 is converted to methyl N‐methoxycarbonyl‐anthranilate (36), N2 and phthalimide (15) on thermolysis, or to methyl N‐acetylphthalamate (35), methyl N, N′‐carbonyldianthranilate (37) and methyl N‐acetyl‐anthranilate (38) on acetylation in pyridine. The intermediate in these reactions, leading to 36, 37 and 38, probably is o‐methoxycarbonyl‐phenylisocyanate (34), itself the result of a Curtius‐type rearrangement. Acetolysis of the tetrazene 12 gives phthalimide (15), N2 and N‐carboxyanthranilic anhydride (42) by a mechanism analogous to that of the methanolysis of 12.In the preparation of 1,4‐dimethoxycarbonyl‐1,4‐dimethyl‐2‐tetrazene (32), required for the above mentioned comparison, by zinc reduction of methyl N‐methyl‐N‐nitro‐carbamate (43), followed by bromine oxidation of methyl N‐amino‐N‐methylcarbamate (44), a deamination of 43 to methyl N‐methyl‐carbamate (45) was observed both in the reductive and in the oxidative step. Both formations of 45 can be formulated via a nitrene and a tetrazane, namely via 47 and 48.

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