- Kinetics of the Reactions of Partially Halogenated Methyl Radicals (CH2Cl, CH2Br, CH2I, and CHCl2) with Molecular Chlorine
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The gas-phase kinetics of the reactions of four partially halogenated methyl radicals (CH2Cl, CH2Br, CH2I, and CHCl2) with Cl2 have been studied as a function of temperature using a tubular reactor coupled to a photoionization mass spectrometer.Radicals were homogeneously generated by pulsed 193- and/or 248-nm laser photolysis.Decays of the radical concentrations were monitored in time-resolved experiments as a function of to obtain bimolecular rate constants for the R + Cl2 -> RCl + Cl reactions studied.The following Arrhenius expressions (k = A exp(-E/RT)) were obtained (the numbers in brackets are log(A/(cm3 molecule-1 s-1)), E/(kJ mol-1); the temperature ranges are also indicated): R = CH2Cl ; R = CH2Br ; R = CH2I ; R = CHCl2 .Errors are 1?, including both random and an estimated 20percent systematic error in the individual bimolecular rate constants.The Arrhenius parameters of these and two other R + Cl2 reactions are compared with theoretical determinations based on semiempirical AM1 calculations of transition-state energies, structures, and vibration frequencies.The calculations qualitatively reproduce the observed trends in both the Arrhenius A factors and in the activation energies.The use of molecular properties to account for reactivity differences among all the R + Cl2 reactions which have been studied to date are also explored using free-energy correlations with these properties.
- Seetula, J. A.,Gutman, D.,Lightfoot, P. D.,Rayes, M. T.,Senkan, S. M.
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- Visible-Light-Mediated C-I Difluoroallylation with an α-Aminoalkyl Radical as a Mediator
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Herein, we report a protocol for direct visible-light-mediated C-I difluoroallylation reactions of α-trifluoromethyl arylalkenes with alkyl iodides at room temperature with an α-aminoalkyl radical as a mediator. The protocol permits efficient functionalization of various α-trifluoromethyl arylalkenes with cyclic and acyclic primary, secondary, and tertiary alkyl iodides and is scalable to the gram level. This mild protocol uses an inexpensive mediator and is suitable for late-stage functionalization of complex natural products and drugs.
- Yue, Fuyang,Dong, Jianyang,Liu, Yuxiu,Wang, Qingmin
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supporting information
p. 7306 - 7310
(2021/10/01)
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- Catalytic Interconversion of Alkyl Halides by Gas-liquid Phase-transfer Catalysis
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High halogen exchange conversions are achieved when a gaseous mixture of alkyl halides (chlorides, bromides, iodides) is passed over a solid bed consisting of porous inorganic supports bearing a phase-transfer catalyst under gas-liquid phase-transfer catalysis (g.l.-p.t.c.) conditions.The process is catalytic since the bed undergoes no changes once it reaches operating conditions.For example, a methylene dichloride and bromoethane mixture is converted into all the halogen-exchange products, and their statistical distribution at equilibrium depends on the original ratio of the halogens in the organic reagents.Catalytic activity is high: 200 ml of such a mixture can be converted in 1 h by passage through 200 g of alumina coated with 10 percent tetrabutylphosphonium bromide.The catalytic process is promoted by the halide anions present as Q(1+)X(1-) in the liquid phase constituted by the molten catalyst and as Na(1+)X(1-) in the solid inorganic support; the halide anions partition themselves between the liquid and solid phases as a function of their respective affinities.This catalysis depends on the diffusion, partition, and adsorption of the alkyl halides between the gaseous, liquid, and solid phases, as well as on their intrinsic nucleophilic reactivity.Mechanistic aspects and industrial applicability are discussed.
- Tundo, Pietro,Venturello, Paolo,Angeletti, Enrico
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p. 485 - 492
(2007/10/02)
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- Carbon-Halogen Bonding Studies. Halogen Redistribution Reactions between Alkyl or Acetyl Halides and Tri-n-butyltin Halides
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The equilibrium positions have been determined for the halogen redistribution reactions of tri-n-butyltin halides with a variety of structurally different types of alkyl halides and with acetyl halides.These have been related through the reaction ΔGo values to carbon-halogen bond dissociation energy differences.It is suggested that the trends observed in the latter may provide evidence for the existence of a small steric bond weakening effect in the order C-I > C-Br > C-Cl bonds on going from methyl to primary, secondary, and tertiary alkyl halides.On the other hand, with the 2,3-? bond containing allyl, benzyl, and propargyl halides , α-haloacetones, and haloacetonitriles, there may be some type of electronic carbon-halogen bond strengthening effect which lies in order C-I > C-Br > C-Cl.Finally, for the acetyl halides, the data are in agreement with increases in bond strengths resulting from ? contributions being in the order C-Cl > C-Br > C-I.
- Friedrich, Edwin C.,Abma, Charles B.
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p. 1367 - 1371
(2007/10/02)
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