2268-31-7Relevant academic research and scientific papers
Organocatalytic C?F Bond Activation with Alanes
Jaeger, Alma D.,Ehm, Christian,Lentz, Dieter
supporting information, p. 6769 - 6777 (2018/04/02)
Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z≈2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me4Al2(μ-H)2?THF by nucleophilic vinylic substitution (SNV)-like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminum hydride bond, lower the barrier for HDF significantly, and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me2AlH?THF via SNV and formation of a stable intermediate, from which elimination is unselective, which results in a loss of selectivity.
Pulse-Duration Effects on Competitive Reactions in Infrared Multiple-Photon Decomposition of CH2ClCHClF and CHClFCHClF
Ishikawa, Yo-ichi,Sugita, Kyoko,Arai, Shigeyoshi
, p. 5067 - 5071 (2007/10/02)
Vibrationally excited 1,2-dichlorofluoroethane and 1,2-dichloro-1,2-difluoroethane have been observed to dissociate competitively via two channels to form vibrationally excited HCl and HF.The fluence dependences of the branching ratio have been measured for both "short"-pulse (80-ns fwhm) and "long"-pulse (80-ns fwhm with 1-μs-fwhm tail) irradiations.The branching ratio shows not only fluence dependence but also pulse-duration dependence, that is, intensity dependence.When the reactant pressure is 1.0 Torr, collisional deactivation is expected to occur to a considerable extent under long-pulse irradiation while it can be ignored under short-pulse irradiation.The experimental results are interpreted by using the exact stochastic method based on the energy-grained master equations, which take into account collisional deactivation.
CO2 Laser-induced Decomposition of 1,2-Dichloro-1-fluoroethane
Ogura, Hiroo,Yano, Takayuki
, p. 1239 - 1250 (2007/10/02)
CH2ClCHFCl was photolyzed with a TEA CO2 laser at 1033.5 cm-1.The infrared multiphoton dissociation mechanism of CH2ClCHFCl was investigated under various conditions: Sample gas pressure, additive gas presure, pulse number, pulse energy, and pulse duration.It is concluded that primary process of the IRMPD is direct eleimination of molecular HCl and HF, HCl elimination being predominant channel.Primary HCl elimination products cis-and trans-CHF=CHCl, and CH2=CFCl are formed at high vibrational levels, from which additional photon absorption occures in the secondary photolysis to give rise to CH=CCl, CH=CF, and CH2=CHF.All of the secondary products are concluded to be derived from mainly CH2=CFCl among the chlorofluoroethene isomers.CH2=CFCl decomposes via HF and HCl elimination channels together with the C-Cl bond repture channel. appears to be generated by the H atom abstraction reaction of C2H. radical, which may result from further decomposition of and/or .The neat IRMPD at higher pressures gives quite similar primary product distribution, but markedly different secondary product distribution from those in shock tube pyrolysis.
Infrared Laser Multiphoton Dissociation of CF2ClCH2Cl
Yano, T.,Ozaki, S.,Ogura, H.,Tschuikow-Roux, E.
, p. 1108 - 1116 (2007/10/02)
The infrared multiphoton decomposition (IRMPD) of CF2ClCH2Cl was studied with focusing geometry using the P(34) line of the 9.6-μm CO2 band (1033.6 cm-1).The principal reaction product is CF2CHCl.Other products of significance include CFClCHCl, CF2CH2, and CFCH.It is concluded that the primary processes of photodecomposition involve the molecular elimination of HCl and HF and, to a very minor extent, C-C bond rupture.The relative importance of the primary steps is approximately 1000:30:1, respectively.From a series of diagnostic experiments in the presence of hydrogen donors and D2, it is shown that CF2CH2 derives from the secondary photolysis of CF2CHCl.The decomposition yield, the HF/HCl ratio, and the CF2CH2/CF2CHCl ratio were investigated as a function of reactant and argon pressure, the latter serving as a buffer gas.From the dependence of the decomposition yield on pulse number at different pulse energies, E0, the specific rate of decomposition, b, was found to be proportional to b E01.8, the power dependence being somewhat higher than the standard 3/2 power law for focusing geometry.These phenomena are interpreted in terms of a simple geometric fluence model which includes contributions from collisionally induced reactions in the outermost (lower fluence) irradiated region.The nonresonant photodecomposition of C2H6 and C2H4 at 1033.6 cm-1 observed in auxiliary, diagnostic experiments is interpreted in terms of photosensitization processes.
