LIGHT-INITIATED AND THERMAL NITRATION REACTIONS DURING PHOTOLYSIS OF NAPHTHALENE TETRANITROMETHANE OR 1-METHOXYNAPHTHALENE TETRANITROMETHANE IN DICHLOROMETHANE

The photolysis of naphthalene or 1-methoxynaphthalene together with tetranitromethane in dichloromethane, using light with a cutoff at lambda < 435 nm, has been investigated. It is shown that naphthalene, a representative of less reactive aromatics, predominantly (85-90%) reacts to give nitro compounds with a low alpha/beta-ratio (ca. 1.5) via a photochemical addition/elimination mechanism, the remaining part being formed via thermal, N02-promoted nitration (alpha/beta-ratio ca. 20). The adducts am formed by photochemical excitation of the CT complex between naphthalene and tetranitromethane, resulting in formation of the triad [ArH.+ NO2(NO2)3C-] from which the observed chemistry develops by attack of trinitromethanide upon the radical cation. For 1-methoxynaphthalene, a representative of more highly reactive aromatics, the reaction is again photochemically initiated and again adducts seem to be responsible for the further development of thermal nitration reactions, apart from the N02-induced reaction. Elimination of HN02 from one of the 1,4-adducts induces a novel HNO2/tetranitromethane-dependent nitration process, shown separately to operate in the dark on reactive substrates. The aryltrinitromethane formed in this step is ''hydrolyzed'' to the corresponding carboxylic acid, 4-methoxy-1-naphthoic acid, under the anhydrous conditions prevailing during photolysis. Nitrous acid is a likely candidate as the proton source for this reaction. With an alcohol present, moderate yields (up to almost-equal-to 50%) of alkyl 4-methoxy-l-naphthoates are obtained. From other adducts, nitro compounds are formed by elimination of nitroform. Trinitromethanide ion was shown to possess greatly differing reactivity (ratio > 10(3)) toward a model radical cation, tris(4-bromophenyl)aminium ion, in dichloromethane and acetonitrile, respectively.