Nitration of Polycyclic Aromatic Hydrocarbons by Dinitrogen Tetraoxide. II. Synthetic and Mechanistic Aspects.

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Abstract
Treatment of polycyclic aromatic hydrocarbons by dinitrogen tetraoxide in dichloromethane solution leads to the clean production of mononitro derivatives with high positional selectivity in almost quantitative yields. For substrates less reactive than chrysene the addition of catalytic amounts of acid is required for the reaction to proceed at convenient rates. Being very easily performed, the method should be regarded as the best yet found for the synthesis of small amounts of these, in many cases, mutagenic mononitro compounds. From studies on relative reactivities, isomer distributions and the effect of acid, base and nitrosonium ion on the reaction, a mechanism involving initial attack of a novel electrophile, nitrosated dinitrogen tetraoxide, is proposed. The initially formed .sigma.-complex is suggested to be transformed into the nitro .sigma.-complex via a pathway involving radical pairs, thus explaining the observation by others of CIDNP effects on the reaction path of nitrous acid catalyzed nitration, a reaction proposed to follow the same rection scheme.

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