Studies of quinone monooximes derived from dihydroxyphenylalanines

Khozam, Mahmoud Mohamed (2007) Studies of quinone monooximes derived from dihydroxyphenylalanines. Doctoral thesis, London Metropolitan University.


This thesis is concerned with the nitrosation behaviour of 1,5-, 1,6- and 2,7-dihydroxynaphthalenes towards equimolar and excess sodium nitrite/acid. The direct and indirect methods of nitrosations have been used to prepare mono- and di-nitrosated products. Under all experimental conditions examined, only the mono-nitrosation products were isolated. No di-nitrosation products were observed even in the reaction involving excess sodium nitrite/acid. The direct nitrosation of 1,6-dihydroxynaphthalene afforded 6-hydroxy-1,2-naphthoquinone 2-oxime as the main product together with some 6-hydroxy1,4-naphthoquinone 4-oxime as the 4-nitrosated compound, which were separated by using the chelating technique. For the 1,5- and 2,7-dihydroxynaphthalenes only one product resulted, 5-hydroxy-1,2-naphthoquinone 2-oxime and 7-hydroxy-1,2-naphthoquinone 1-oxime, respectively. In both cases no nitrosation at the 4-position occurred. The tendency of the dihydroxynaphthalenes investigated in this work to undergo only mono-nitrosation might reflect the deactivation of the naphthalene rings by the introduction of the CO and NO groups. In order to check this hypothesis compounds 5-hydroxy-, 6-hydroxy-1,2-naphthoquinone 2-oximes and 7-hydroxy-1,2-naphthoquinone 1-oxime were treated with excess sodium nitrite/acid, but in all cases no reaction was observed. All the new organic compounds of 1,2- and 1,4-oximes obtained from these studies were characterised by elemental analysis, IR and NMR spectroscopy, mass spectrometry and X-ray crystallography. The quinone oximic character of all 1,2-oximes was also supported by their acetylation behavior. The indirect nitrosation of the 1,6-dihydroxynaphthalene with sodium nitrite/acid in the presence of metal salts afforded the metal complexes of the 2-nitrosated compound as the main product together with some uncomplexed 4-nitrosated isomer. In contrast, nitrosation of 1,5- and 2,7-dihydroxynaphthalenes in the presence of metal salts gave only the metal complexes and no 4-nitrosated compounds were obtained. During this study, a slightly modified procedure was used to prepare the uranium complexes. The method consists of reacting 6-hydroxy-1,2-naphthoquinone 2-oxime, 7-hydroxy-1,2-naphthoquinone 1-oxime or 6-hydroxy-1,4-naphthoquinone 4-oxime with uranyl nitrate hexahydrate in the presence of triethyl amine as base. The nickel, copper and uranium complexes were characterised by elemental analysis and IR spectroscopy. Nickel and copper were determined by atomic absorption spectrometry (AAS) while, uranium was determined by inductively coupled plasma mass spectrometry (ICP-MS).

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