2396-00-1Relevant academic research and scientific papers
Magnetic Field Effects on the Photodissociation Reaction of Triarylphosphine in Nonviscous Homogeneous Solutions
Sakaguchi, Yoshio,Hayashi, Hisaharu
, p. 3421 - 3429 (2007/10/03)
The magnetic field effects (MFEs) on the photodecomposition reactions of triphenylphosphine and its halogen and methyl derivatives are investigated in fluid solutions. The yield of diarylphosphinyl radicals decreased with increasing magnetic field from 0.1 to 5 T but was stationary below 0.1 T and above 5 T. The MFE becomes larger by the substitution of halogen atoms and the 3- or 4-methyl group. In cyclohexane, the yields of the escaped diarylphosphinyl radicals at 1 T are reduced to 0.69, 0.55, 0.59, and 0.56 of those at 0 T for triphenylphosphine and its tris(4-chloro), tris(3-methyl), and tris(4-methyl) derivatives, respectively. This magnetic field dependence was ascribed to originate from the deactivation process of the excited triplet state, which is a variant of the d-type triplet mechanism originally proposed by Steiner. The interaction between the closely lying nπ* and ππ* states makes their solvent dependence complicated.
Chromium(ii)-mediated reactions of iodonium tetrafluoroborates with aldehydes: Umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates
Chen, Da-Wei,Ochiai, Masahito
, p. 6804 - 6814 (2007/10/03)
The method described herein allows us, for the first time, to perform umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates. The method involves generation of organochromium(III) species via reaction of iodonium salts with anhydrous chromium dichloride, followed by their nucleophilic addition to aldehydes to yield alcohols. In contrast to the reaction of aryl and alkenyl halides with chromium dichloride, these iodonium salts are so active that organochromium(III) could be generated without using a nickel catalyst. Substituent effects of unsymmetrically substituted diaryliodonium salts on the product profiles are in good agreement with the reported mode of decomposition of the intermediate unsymmetrical diaryliodanyl radicals. Alkenyl(mesityl)iodonium tetrafluoroborates undergo exclusive alkenylation of aldehydes with no signs of the formation of an arylation product.
Is Selective Monosubstitution of Dihalides via SRN1 Reaction Feasible? An Electrochemical Approach for Dichloroarenes
Amatore, Christian,Combellas, Catherine,Lebbar, Nour-Eddine,Thiebault, Andre,Verpeaux, Jean-Noel
, p. 18 - 26 (2007/10/02)
1,4-Dichlorobenzene and dichloropyridines undergo SRN1 reaction with various nucleophiles upon electrochemical initiation.Substitution can compete with reduction only when indirect electrolyses at low current are performed.Selective formation of monosubstitution products is observed when the nucleophiles used behave as electron-donating groups when attached to the aromatic moiety, a situation which is just the opposite of what had been observed when the same reactions were initiated photochemically.This surprising difference in behavior can be rationalized in terms of different capabilities of both activation methods to generate the key monosubstitution anion radical, ArNuX(.-).Kinetic and thermodynamic data concerning the reactivity of dichloroarenes in such processes are presented and discussed.
Free-Radical Reductions of Arenediazonium Ions in Aqueous Solution. V. Pulse-Radiolytic Determination of Rate Constants for Some para-Substituted Benzenediazonium Ions
Packer, John E.,Moenig, Joerg,Dobson, Brian C.
, p. 1433 - 1441 (2007/10/02)
Some rate constants for the reduction of para-substituted benzenediazonium ions by the radicals eaq-, .CH2OH, (CH3)2.COH and some semiquinone radical anions have been measured.The substituent group has no effect on the rates with eaq-, but as the reduction potential of the reducing radical becomes more positive, the substituent effect increases, electron-withdrawing groups enhancing the rates.No free halide is formed on reduction of p-BrC6H4N2+ or p-IC6H4N2+ by eaq- or .CH2OH.
Free-Radical Reductions of Arenediazonium Ions in Aqueous Solution. IV. Kinetics of Reactions of para-Substituted Diazonium Ions with Benzyl Alcohol, Isopropyl Alcohol And Methanol
Packer, John E.,Heigway, Christopher J.,Miller, Helen M.,Dobson, Brian C.
, p. 965 - 977 (2007/10/02)
Electron-withdrawing substituents are shown to increase the chain length of free-radical hydrodediazoniation reactions, but the actual reaction step causing the substituent effect depends on the relative rates of propagation and termination reactions.With benzyl alcohol as reducing agent the rate of the slow propagation step is increased, while with isopropyl alcohol the rate of the termination step is decreased.Rate constants for some reactions of radicals with diazonium ions are reported, and the nature of some of these reactions and their implication foran understanding of the homolysis of aromatic diazo compounds are discussed.
