Photonitration of aromatic compounds by tetranitromethane
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes the photochemical reactions of aromatic substrates with tetranitromethane. These reactions are known to proceed via the initial formation of a triad of species; the aromatic radical cation, trinitromethanide ion, and nitrogen dioxide. The chemistry of these systems involves the recombination of this triad. This thesis consists of five major parts. In the first (Chapter 2), the photochemical reactions of 1,5-dimethylnaphthalene with tetranitromethane are described. The initial step in the recombination of the triad is the reaction of trinitromethanide ion with the aromatic radical cation and this work highlights the importance of the resultant carbon radical stability to the reaction pathway. The isolation of a number of nitro-trinitromethyl adducts 221-224, 228-229, and hydroxy-trinitromethyl adducts 225-227, in addition to the thermal allylic rearrangement of adduct 228 to adduct 221 is documented. The second part (Chapter 3), discusses the photochemical reactions of 1-methoxynaphthalene with tetranitromethane. The effect of the methoxy substituent on the aromatic substrate is examined and the likely mode of formation of the trinitromethyl aromatic compound 309 and the nitro aromatic compound 306 via highly unstable intermediate adduct species is described. The identification of two labile nitro-trinitromethyl adducts 314 and 315 is also documented. The third part of this thesis (Chapter 4) describes the photochemical reactions of 4-methylanisole with tetranitromethane. A solvent induced change in the regiochemistry of trinitromethanide ion attack on the radical cation is rationalised in terms of the stabilisation of the trinitromethanide ion by more polar solvent environments. Evidence was obtained indicating that the nitrotrinitromethyl adducts 423 and 424 are formed via an allylic rearrangement of initially formed adducts 435 in competition with the formation of the observed nitro aromatic compound 420. The fourth part of this thesis (Chapters 5 and 6) describes the photochemical reactions of 2-methylanisole, 2,4-dimethylanisole, 4-fluoroanisole, and 4-fluoro-3-methylanisole with tetranitromethane. The effect of substitution of the aromatic substrate was explored and nitro-trinitromethyl adducts 518-519, 521-522, 617-623, and 634-636 identified. The final section of this thesis (Chapter 7) examines the effect of ethanol in the photolysis medium. The photochemical reactions of tetranitromethane with 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,2-methylenedioxybenzene are described in addition to re-examination of the photochemical reactions of tetranitromethane with 1-methoxynaphthalene and 2-methylanisole in the presence of ethanol in the photolysis solution. Ethanol solvation of the trinitromethanide ion appears to retard nucleophilic attack on the aromatic radical cation in addition to introducing a sterically mediated change in the regiochemistry of trinitromethanide ion attack on the radical cation. A final feature of interest, the identification of highly labile nitro-trinitromethyl adducts 724 and 725 in the photolysis product mixtures of 1,4-dimethoxybenzene and tetranitromethane is also documented.