Photochemical Nitration by Tetranitromethane. Part XXVII. Adduct Formation in the Photochemical Reaction of 4-Methylanisole. Solvent and Temperature Effects on the Regiochemistry of Reaction of the Radical Cation of 4-Methylanisole.

The photolysis of the charge-transfer complex of 4-methylanisole and tetranitromethane in dichloromethane gives four isomeric nitro-trinitromethyl adducts, including the epimeric 1-methoxy-4-methyl-3-nitro-6-trinitromethylcyclohexa-1,4- dienes 3 and 4 and the epimeric 1-methoxy-3-methyl-6-nitro-3-trinitromethyl-cyclohexa-1,4-dienes 5 and 6, 4-methyl-2-trinitromethylanisole 1,4-methyl-2-nitroanisole 2, nitrophenols 7 and 9, and 4-methyl-4-nitrocyclohexa-2,5-dienone 8. Similar reaction in acetonitrile also gives these products, with the exception of two of the adducts (3 and 4). The effect of reaction temperature on the yields of the various products indicates that they are formed either by attack of trinitromethanide ion on the radical cation of 4-methylanisole vicinal to the methoxy group at C2 (1, 3 and 4), or by attack of trinitromethanide ipso to the methoxy group (2, 5, 6 and 8). By conducting the photolysis in dichloromethane with trifluoroacetic acid present, the trinitromethanide pathway is eliminated, and the products formed are derived from reaction between 4-methylanisole and/or its radical cation and NO2. The effects of added Baits Bu(4)N(+)ClO(4)(-) (TBAP) or Bu(4)N(+)C(NO2)(3)(-) (TBAT) to reactions in dichloromethane are seen as the consequences of changes in the polarity of the solvent and nor to competition between ion-pair and radical-pair collapse during the reactions. By analogy with adducts 3 and 4, two adducts 16 and 17 derived from similar photolysis reactions of 4-chloroanisole are shown to be the epimeric 4-chloro-1-methoxy-3-nitro-6-trinitromethylcyclohexa-1,4-dienes 16 and 17 rather than nitrito(or hydroxy)-trinitromethyl adducts. The X-ray crystal structure of 1-methoxy-4-methyl-r-3-nitro-c-6-trinitr diene 3 is reported.