14477-72-6Relevant articles and documents
Efficient Photocatalysis of the irreversible One-Electron and Two-Electron Reduction of Halothane on Platinized Colloidal Titanium Dioxide in Aqueous Suspension
Bahnemann, Detlef W.,Moenig, Joerg,Chapman, Rita
, p. 3782 - 3788 (1987)
The irreversible one- and two-electron reductions of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) by conduction band electrons, eCB-, photogenerated in aqueous colloidal suspensions of platinized titanium dioxide (TiO2/Pt) have been investigated.Both bromide and fluoride ions, i.e., the respective products of the one-electron and two-electron transfer to halothane, are formed with high quantum yields Φ (ΦF- = ΦBr = 0.43 for photoplatinized TiO2) provided efficient hole scavengers, e.g., methanol, are present.The intermediacy of a carbon-centered radical, CF3C.HCl, resulting from the initial reaction of halothane with eCB-, is strongly indicated.However, this radical is apparently well stabilized on the oxide surface and does not diffuse into the aqueous phase to an appreciable extent since typical product distributions for homogeneous free-radical reactions are not observed.Adsorption of the parent molecule halothane onto TiO2/Pt also,appears to be an efficient process as deduced from several experimental results.Induction periods between 15 and 35 min, apparent in the concentration vs. illumination time profiles, are explained by photoinduced rearrangements of the Pt deposits resulting in better electron relay properties of the metal.Implications of the observed results on the design of suitable catalysts for synthetic organic photochemistry are discussed.
Kinetics of radical heterolysis reactions forming alkene radical cations
Horner, John H.,Bagnol, Laurent,Newcomb, Martin
, p. 14979 - 14987 (2007/10/03)
Rate constants for heterolytic fragmentation of β-(ester)alkyl radicals were determined by a combination of direct laser flash photolysis studies and indirect kinetic studies. The 1,1-dimethyl-2-mesyloxyhexyl radical (4a) fragments in acetonitrile at ambient temperature with a rate constant of khet > 5 × 109 s-1 to give the radical cation from 2-methyl-2-heptene (6), which reacts with acetonitrile with a pseudo-first-order rate constant of k = 1 × 106 s-1 and is trapped by methanol in acetonitrile in a reversible reaction. The 1,1-dimethyl-2-(diphenylphosphatoxy)hexyl radical (4b) heterolyzes in acetonitrile to give radical cation 6 in an ion pair with a rate constant of khet = 4 × 106 s-1, and the ion pair collapses with a rate constant of k ≤ 1 ± 109 s -1. Rate constants for heterolysis of the 1,1-dimethyl-2-(2,2- diphenylcyclopropyl)-2-(diphenylphosphatoxy)ethyl radical (5a) and the 1,1-dimethyl-2-(2,2-diphenylcyclopropyl)-2-(trifluoroacetoxy)ethyl radical (5b) were measured in various solvents, and an Arrhenius function for reaction of 5a in THF was determined (log k = 11.16-5.39/2.3RT in kcal/mol). The cyclopropyl reporter group imparts a 35-fold acceleration in the rate of heterolysis of 5a in comparison to 4b. The combined results were used to generate a predictive scale for heterolysis reactions of alkyl radicals containing β-mesyloxy, β-diphenylphosphatoxy, and β-trifluoroacetoxy groups as a function of solvent polarity as determined on the ET(30) solvent polarity scale.
Electron transfer as a possible initial step in nucleophilic addition elimination reactions between (radical) anions and carbonyl compounds in the gas phase
Staneke, Paul O.,Ingemann, Steen,Nibbering, Nico M. M.
, p. 179 - 184 (2007/10/03)
The reactions of the HO-, CH3S-, CH2S- and CH2=C(CH3)-CH2- ions with three ketones (CF3COR; R=CH3, CF3, C6H5) and three esters of trifluoroacetic acid (CF3CO2R; R=CH3, C2H5 and C6H5) have been studied with use of Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry. All four negative ions react exclusively by proton transfer with CF3COCH3. With the other substrates, the HO- ion reacts by various pathways, such as proton transfer, SN2 substitution, E2 elimination and attack on the carbonyl group. The CH3S- ion is unreactive towards CF3COC6H5 but is able to react by hydride transfer, SN2, E2 and/or carbonyl attack with the remaining neutral species. The CH2S- radical anion reacts by electron transfer to afford stable molecular radical anions of CF3COCF3 and CF3COC6H5, whereas the main reaction with the two esters, CF3CO2CH3 and CF3CO2C2H5, is dissociative electron transfer leading to CF3CO2- and CF3- ions. The CH2=C(CH3)-CH2- anion displays a more complex reactivity pattern involving electron transfer, SN2, E2 as well as attack on the carbonyl group. Direct evidence for the occurrence of electron transfer as the initial step in an overall BAC2 type process has not been obtained for the systems studied. The reaction of the CH2S- ion with CF3CO2C6H5 was observed, however, to yield exclusively a CF3COCHS-. radical anion. Based upon the absence of a BAC2 process in the reaction of CH2S- with the methyl and ethyl esters of trifluoroacetic acid in combination with the facile occurrence of electron transfer from this radical anion, it is suggested that the CF3COCHS-. ion is formed by an initial electron transfer followed by coupling between the CH2S molecule and the CF3CO2C6H5- radical anion and subsequent loss of C6H5OH from the collision complex.
