- Is Water the Best or the Worst Solvent for Cycloadditions of Singlet Oxygen to Aromatic Compounds?
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An accelerating effect of water, greater than two orders of magnitude, is observed for the photo-oxygenation of disodium 3,3'-(1,4-naphthylidene)dipropionate at variance with the current assumption on the constancy of the rate constant of 1O2 cycloadditions in various solvents.
- Cazin, Bernadette,Aubry, Jean-Marie,Rigaudy, Jean
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- Kinetic studies of singlet oxygen [4 + 2]-cycloadditions with cyclic 1,3-dienes in 28 solvents
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The [4 + 2]-cycloaddition of singlet oxygen with 1,4-dimethylnaphthalene (DMN) and derivatives has been studied in 28 solvents by laser flash photolysis and steady state photolysis. The bimolecular rate constants of singlet oxygen quenching by DMN, via a physical process (kq) and via a chemical reaction (kr), are solvent-dependent and increase by more than 2 orders of magnitude from cyclohexane to formamide. This significant solvent dependence is in contrast with previous investigations conducted in six or seven solvents. It is discussed in terms of the solvatochromic properties of the different solvents. Moreover, for seven water-soluble 1,3-dienes, the overall rate constant k0 (= kr + Kq) is much higher in water than in methanol. Our results are consistent with a two-stage mechanism implying as a first step an equilibrium producing an exciplex with charge transfer character. A shift toward the formation of this exciplex leading to the cycloaddition product occurs by an increase (i) in the Hildebrand solubility parameter δH, (ii) in the dipolarity-polarizability parameter π* of the solvent, and (iii) in the solvophobicity of the diene.
- Aubry, Jean-Marie,Mandard-Cazin, Bernadette,Rougee, Michel,Bensasson, René V.
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- Search for Singlet Oxygen in the Decomposition of Hydrogen Peroxide by Mineral Compounds in Aqueous Solutions
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The possibility of singlet oxygen (1O2) occurrence in the decomposition of H2O2 by mineral compounds in aqueous basic solutions was examined.Tetrapotassium rubrene-2,3,8,9-tetrcarboxylate was used as a trap, giving an endoperoxide detected by HPLC.We found that four families of mineral compounds lead to the formation of the endoperoxide: the oxides of the alkaline earths Ca, Sr, and Ba; the derivatives of elements of groups 3A, 4A, 5A, and 6A in d0 configuration (expect niobium); the oxides of actinides and lanthanides; and finally the oxidizers ClO-, BrO-, Au3+, IO3-, and IO4-.One compound in each family was selected for further investigation in order to strengthen the 1O2 hypothesis.Thus, the yield of the endoperoxide of potassium 9,10-diphenylanthracene-2,3,6,7-tetracarboxylate was enhanced when the parent compound was introduced in a mixture of H2O2 + (ClO-, Nd2O3, MoO42-, Ca(OH)2 + deuterated water instead of light water.
- Aubry, J. M.
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p. 5844 - 5849
(2007/10/02)
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