Photochemical nitration by tetranitromethane. Part VI. Predominant nitro/trinitromethyl addition to naphthalene in dichloromethane and acetonitrile

Abstract

The photochemical reaction between naphthalene and tetranitromethane in dichloromethane or acetonitrile gave predominantly (85–95%) products of nitro/trinitromethyl addition to the aromatic system, namely cis- and trans-1-nitro-4-trinitromethyl-1,4-dihydronaphthalene and trans-2-nitro-1-trinitromethyl-1,2-dihydronaphthalene. A small amount of trans-2-hydroxy-1-trinitromethyl adduct was also formed, presumably originating from an initial nitrito/trinitromethyl adduct.

The minor reaction pathway directly gave product(s) of nitro substitution, the ratio of 1- to 2- nitronaphthalene being high ( 25) in dichloromethane and in the beginning of the acetonitrile runs (up to ≈ 40% conversion). The temperature dependence of this process suggests that coupling between (napthalene)⁺˙ and nitrogen dioxide is the major pathway leading directly to nitro products. 2-Nitronaphthalene, formed after long reaction periods in acetonitrile runs, was presumably formed via elimination of nitroform from the 1,2-adduct.

cis-1-Nitro-4-trinitromethyl-1,4-dihydronaphthalene was isolated in pure form and shown to undergo facile base-catalysed elimination of nitroform in dichloromethane and acetonitrile to give 1-nitronaphthalene. It also underwent a slow spontaneous elimination in acetonitrile. It was stable under acidic conditions. GLC of the pure adduct gave exclusively 1-nitronaphthalene at a low injector-port temperature, whereas at higher temperatures a mixture of products was formed (naphthalene, 1- and 2-nitronaphthalene and 1-naphthonitrile).