- Infrared Multiphoton Dissociation of Heptafluoropropane
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The dissociation yield and branching ratio in CO2-laser-induced multiphoton dissociation (MPD) of CF3CF2CHF2 were studied as a function of irradiation frequency (979.7, 1037.4, and 1081.1 cm-1) and laser fluence (focal fluence 2).Br2 was successfully employed to reveal the dissociation mechanisms by scavenging a number of primary and secondary dissociation fragments produced in the MPD.At low laser fluences the distributions of scavenged products were the same regardless of irradiation frequencies.The primary dissociation of CF3CF2CHF2 was found to proceed mainly via the higher activation energy channels (i.e., C-C ruptures: CF3CF2CHF2 -> C2F5 + CHF2, and CF3CF2CHF2 -> CF3 + C2HF4) rather than via HF elimination (CF3CF2CHF2 -> C3F6 + HF) in our experimental conditions.The observed branching ratio between the two C-C rupture channels (ca. 2:1) agreed with the results obtained by RRKM calculation.A remarkable difference in product distribution with respect to the irradiation frequency was observed at higher laser fluences.This indicates that the secondary photolysis of primarily produced radicals within the laser pulse occured significantly at higher fluences (i.e., C2F5 -> CF3 + CF2, CHF2 -> CF2 + H, CF3 -> CF2 + F, and C2HF4 -> CF2 + CHF2), depending strongly upon the irradiation frequencies.
- Kato, Shuji,Makide, Yoshihiro,Tominaga, Takeshi,Takeuchi, Kazuo
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- Fluorinated phosphonium ylides: Versatile in situ Wittig intermediates in the synthesis of hydrofluorocarbons
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A simple and convenient technique has been developed for the synthesis, characterisation and isolation of hydrofluoro/hydrohalofluorocarbons such as chlorodifluoromethane (CF2ClH), difluoromethane (CF2H2), bromodifluoromethane (CF2BrH) and dibromofluoromethane (CFBr2H) as possible chlorofluorocarbon (CFC) alternatives. The Wittig reaction of carbonyl compounds with in situ generated triphenylphosphonium ylides in DMF forms terminal fluoroolefins. However, in the absence of the carbonyl moiety these ylides undergo decomposition. The high reactivity of fluoromethylene triphenylphosphonium ylides in DMF in the absence of the carbonyl moiety has been exploited for the first time to design the synthesis of hydrofluorocarbons.
- Bhadury, Pinaki S.,Palit, Meehir,Sharma, Mamta,Raza, Syed K.,Jaiswal, Devendra K.
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- Experimental and computational studies on the gas-phase reaction of CBrF3 with hydrogen
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Gas-phase hydrogen dehalogenation of halon 1301 (bromotrifluoromethane, CBrF3) has been studied experimentally in a tubular alumina reactor operating at atmospheric pressure. It is found that hydrogen can accelerate the decomposition of halon 1301 and that conversion levels of CBrF3 and H2 increase with temperature and residence time. CBrF3 conversion increases with decreasing input volume ratio of CBrF3 to H2. The species produced are a complex mixture of halogenated hydrocarbons including CHF3, CH2F2, C2HF3, C2F6, C2H2F4, C2HF5, CHBrF2, CH3Br, CH2Br2, CHBr2F, and CH2BrF in addition to HBr and HF. The production yield of CHF3, the major product, increases with temperature to 1023 K, after which CHF3 levels decrease with increasing temperature. Conversely, CHF3 selectivity decreases with increasing temperature, residence time, or input ratio of CBrF3 to H2. The initiation reaction is believed to be the rupture of the C-Br bond in CBrF3, and the radical species CF3 then reacts with H2 to produce H and CHF3. The key step in the process is the attack of H radical on CBrF3 to produce CF3 and HBr. Experimental data are compared with the model predictions, and good agreement between experimental and modeling prediction is obtained for CHF3 production. However, the existing mechanism does not predict the formation of CHBrF2, which is detected during the experimental study, and the concentrations of CH2F2 and C2F6 measured experimentally are significantly different from those predicted. Modifications to the existing NIST mechanism are suggested to improve the prediction of the quantity of these species produced. Gas-phase hydrogen dehalogenation of halon 1301 (bromotrifluoromethane, CBrF3) has been studied experimentally in a tubular alumina reactor operating at atmospheric pressure. It is found that hydrogen can accelerate the decomposition of halon 1301 and that conversion levels of CBrF3 and H2 increase with temperature and residence time. CBrF3 conversion increases with decreasing input volume ratio of CBrF3 to H2. The species produced are a complex mixture of halogenated hydrocarbons including CHF3, CH2F2, C2HF3, C2F6, C2H2F4, C2HF5, CHBrF2, CH3Br, CH2Br2, CHBr2F, and CH2BrF in addition to HBr and HF. The production yield of CHF3, the major product, increases with temperature to 1023 K, after which CHF3 levels decrease with increasing temperature. Conversely, CHF3 selectivity decreases with increasing temperature, residence time, or input ratio of CBrF3 to H2. The initiation reaction is believed to be the rupture of the C-Br bond in CBrF3, and the radical species CF3 then reacts with H2 to produce H and CHF3. The key step in the process is the attack of H radical on CBrF3 to produce CF3 and HBr. Experimental data are compared with the model predictions, and good agreement between experimental and modeling prediction is obtained for CHF3 production. However, the existing mechanism does not predict the formation of CHBrF2, which is detected during the experimental study, and the concentrations of CH2F2 and C2F6 measured experimentally are significantly different from those predicted. Modifications to the existing NIST mechanism are suggested to improve the prediction of the quantity of these species produced.
- Li, Kai,Kennedy, Eric M.,Moghtaderi, Behdad,Dlugogorski, Bogdan Z.
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- Continuous Process for Preparing the Difluoromethylating Reagent [(DMPU)2Zn(CF2H)2] and Improved Synthesis of the ICHF2Precursor
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Complex [(DMPU)2Zn(CF2H)2] 1 is a crystalline organometallic reagent with utility in various catalytic difluoromethylation reactions under mild conditions. Unfortunately, this reagent is not commercially available and the procedure for the preparation of this air- and moisture-sensitive zinc complex has only been reported on a small scale. Herein, we report the development of a continuous process for the preparation of reagent 1 on >100 g scale by using a continuous stirred-tank reactor. The key to success is the design of a continuous reactive crystallization process in which the precipitation of the zinc complex 1 is driven by its low solubility in the reaction solvent. The improved synthesis of the iododifluoromethane precursor 2 from readily available bromodifluoroacetic acid further enables the synthesis of complex 1 on a larger scale.
- Monfette, Sebastien,Fang, Yuan-Qing,Bio, Matthew M.,Brown, Adam R.,Crouch, Ian T.,Desrosiers, Jean-Nicolas,Duan, Shengquan,Hawkins, Joel M.,Hayward, Cheryl M.,Peperni, Nikita,Rainville, Joseph P.
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p. 1077 - 1083
(2020/05/19)
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- Alternative synthetic routes to hydrofluoroolefins
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A series of hydrofluoroolefins with -CF=CH2, -CH=CHF and -CH=CF2 groups were designed and prepared via various synthetic routes, including HX or BrF elimination, Wittig-type olefination or fluorination using SF4.
- Yagupolskii, Yu. L.,Pavlenko,Shelyazhenko,Filatov,Kremlev,Mushta,Gerus,Peng, Sheng,Petrov,Nappa, Mario
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p. 134 - 141
(2015/11/10)
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- Selective reduction of halopolyfluorocarbons by organosilicon hydrides
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It is demonstrated that silicon hydrides can be used for reduction of polyfluorinated halocarbons. For example, the reaction between CF3CCl2F and excess triethylsilane, catalyzed by benzoyl peroxide, leads to the formation of a mixture containing CF3CHClF (major), CF3CH2F, and ClSi(C2H5)3. On the other hand, the reaction of chlorofluoroalkanes, containing an internal -CCl2- group readily proceeds with reduction of both chlorines, leading to compounds such as (CF3)2CH2 and CF3CH2C2F5. In contrast to chlorofluoroalkanes, bromofluoroalkanes are much more reactive and reaction with hydrosilane rapidly proceeds without the catalyst at elevated temperature.
- Petrov, Viacheslav A.
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p. 7294 - 7297
(2007/10/03)
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- Preparation of and fluoroalkylation with (chlorodifluoromethyl)trimethylsilane, difluorobis(trimethylsilyl)methane, and 1,1,2,2-tetrafluoro-1,2-bis(trimethylsilyl)ethane
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CF2BrCl reacts with aluminum/N-methylpyrrolidinone in the presence of chlorotrimethylsilane to give Me3SiCF2Cl in high yield. Similarly, CF2Br2 gives Me3SiCF2Br with bromotrimethylsilane. Chlorodifluoromethylation of aldehydes using Me3SiCF2Cl and a catalytic amount of TBAF in polar solvents occurs at room temperature, providing difluoromethylated alcohols in two steps. Electroreduction of Me3SiCF2Cl in the presence of chlorotrimethylsilane gives Me3SiCF2SiMe3 (anion-derived product) and Me3SiCF2CF2SiMe3 (radical-derived product). Using THF/HMPA strongly favors the former, whereas THF/TDA-1 (tris(3,6-dioxaheptyl)amine) the latter. Me3SiCF2SiMe3 difluoromethylates aldehydes acting as a difluoromethylene dianion ('CF22-'/equivalent), whereas Me3SiCF2CF2SiMe3 acts at room temperature as an in situ source for the perfluorovinyl anion (due to β-elimination of fluorotrimethylsilane). However, at low temperature the elimination pathway is suppressed and tetrafluoroethylene dianion ('-CF2CF2-'/equivalent) behavior is observed. The structure of Me3SiCF2CF2SiMe3 was analyzed by X-ray diffraction. All of the studied fluoroalkylating reagents are moisture- and air-stable and can be readily obtained from a single convenient precursor (CF2BrCl).
- Yudin, Andrei K.,Prakash, G. K. Surya,Deffieux, Denis,Bradley, Michael,Bau, Robert,Olah, George A.
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p. 1572 - 1581
(2007/10/03)
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- Thermal Gas Phase Hydrodehalogenation of Bromochlorodifluoromethane
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The thermal hydrodehalogenation of bromochlorodifluoromethane (Halon-1211; CBrClF2) in the gas phase has been studied using a plug flow alumina reactor at atmospheric pressure over the temperature range 400-900 degC with residence times of 2-3 s and CBrClF2/hydrogen molar intake ratios of ca. 10.Conversion of CBrClF2 starts at ca. 400 degC with C-Br bond homolysis followed by reaction with HX (X being Br, Cl or H) to yield CHClF2.At higher temperatures other products arise and complete conversion of CBrClF2 is achieved at ca. 600 degC.At temperatures above 850 degC complete dehalogenation to mainly methane (yield 80percent) is attained.In the temperature range 450-550 degC the (pseudo) first-order rate constant for the overall reaction (F) was found to obey: log (kF/s-1) = (9.4 +/- 1.5) - (150 +/- 25) kJ mol-1/2.303RT.The thermolysis of CBrClF2 was also studied using an excess of 2-phenylpropane (cumene) as a radical scavenger, resulting in the following Arrhenius expression for reaction (G): log (kG/s-1) = (15.1 +/- 0.5) - (262 +/- 9) kJ mol-1/2.303RT.From these parameters the bond dissociation energy for the C-Br bond in CBrClF2 was calculated to be 268 +/- 8 kJ mol-1, leading to a heat of formation of the CClF2-radical of -279 +/- 17 kJ mol-1.Kinetic analysis and separate experiments with H2O2 as an initiator for making H-radical showed that attack by H-radical is the main route for decomposition of CBrClF2.At temperatures higher than 500 degC HBr rather than H2 acts as a hydrogen transfer agent resulting in a fast radical chain (reactions G and L-O) with the observed Arrhenius parameters as a consequence.
- Lijser, Huub J. P. de,Louw, Robert,Mulder, Peter
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p. 139 - 146
(2007/10/02)
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- Kinetics and Mechanism of the Gas-phase Thermal Bromination of Difluorochloromethane
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We have studied the kinetics of the gas-phase thermal bromination of difluorochloromethane in the dynamic regime at 613-693 K.The form of the kinetic equation has been established for conversions of the difluorochloromethane not greater than 20percent.The absolute value of the rate constant of the bromination reaction has been determined.The energy of the C-H bond in difluorochloromethane has been calculated.
- Zhdanov, G. F.,Poluektov, V. A.,Belevtsev, E. G.,Orlov, G. D.
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- Infrared Multiphoton Dissociation of Pentafluoroethane: Two-Channel Dissociation Process and Secondary Photolysis of Radical Products
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The dissociation yield and branching ratio in CO2 laser-induced multiphoton dissociation (MPD) of C2HF5 were investigated.In order to distinguish the two primary dissociation pathways (C2HF5 -> C2F4 + HF, Ea=71.6 kcal/mol; C2HF5 -> CF3 + CHF2, Ea=93.5 kcal/mol), Br2 was employed as an excellent scavenger of radicals and C2F4.The scavenged products were CBrF3, CHBrF2, CBr2F2, and C2Br2F4.The yield of C2Br2F4 originating from HF elimination was much smaller than those of CBrF3 and CHBrF2 from C-C bond rupture.The pulse energy dependence of the product distribution demonstrates that the primarily produced radicals were further photolyzed within the laser pulse (CF3 + nhν -> CF2 + F, and CHF2 + n'hν -> CF2 + H) to yield CBr2F2.The secondary photolysis of the radicals was also confirmed by real-time monitoring of infrared emission from HF* and DF* generated in the MPD of C2DF5 in the presence of H2 as an F atom scavenger.In the MPD of neat C2HF5, the formation of C2F4 was unexpectedly enhanced with increasing pulse energy; this was explained by assuming that C2F4 was mainly formed via recombination of CF2 radicals originating from the secondary photolysis of primarily produced radicals.
- Kato, Shuji,Makide, Yoshihiro,Takeuchi, Kazuo,Tominaga, Takeshi
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p. 3977 - 3981
(2007/10/02)
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- THE HYDROLYSIS OF BROMODIFLUOROMETHYLTRIPHENYLPHOSPHONIUM BROMIDE
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Hydrolysis of +Br- afforded a high yield of bromodifluoromethane and triphenylphosphine oxide.Hydrolysis in the presence of a radioactive isotope of bromine or sodium iodide gave unequivocal evidence that the mechanism for this reaction proceeds through a difluorocarbene intermediate.
- Flynn, R. M.,Manning, R. G.,Kessler, R. M.,Burton, D. J.,Hansen, S. W.
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p. 525 - 532
(2007/10/02)
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- CYCLOPROPANE CHEMISTRY. PART 5 . HEXAFLUOROCYCLOPROPANE AS A SOURCE OF DIFLUOROCARBENE
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Thermolysis of hexafluorocyclopropane in the presence of ethylene, propene, vinyl chloride, and vinyl bromide gives good yields of the corresponding 1,1-difluorocyclopropanes, formed by addition of difluorocarbene to the olefin.The tetrafluoroethylene formed dimerises to octafluorocyclobutane, co-dimerises with the olefin, or survives, depending on the reaction conditions.With allene, hexafluorocyclopropane gives 1-(difluoromethylene)cyclopropane, 2,2,3,3-tetrafluorospiropentane, and products derived from tetrafluoroethylene and allene.
- Birchall, J. Michael,Fields, Roy,Haszeldine, Robert N.,McLean, Reginald J.
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p. 487 - 496
(2007/10/02)
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- Silicon-substituted derivatives of trifluoro(trifluoromethyl)silane. Some chemistry of the silicon-iodine bond in a polyhalo system
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The fluoroiodosilane CF3SiF2I has been utilized to generate a series of compounds of formula CF3SiF2X, where X = Br, Cl, F, and OSiF2CF3; all but X = F are new compounds. Conversion of Si-I bonds to Si-X is effected by antimony(III) halides or, for oxygen, mercury(II) oxide. Each of the halodifluoro(trifluoromethyl)silanes undergoes pyrolytic decomposition at 100° to generate SiF3X and CF2, although the thermal decomposition of CF3SiF2I is quite complex. Each of the CF3SiF2X species (other than CF3SiF3) reacts with water vapor to generate CF3SiF3 and, for X = Br or I, CF2HX. The halodifluoromethanes evidently result from the reaction of CF2 with HX - the CF2 in turn resulting from the interaction of water vapor and CF3SiF3 at room temperature. Correlations of fluorine chemical shifts and directly bonded silicon-fluorine coupling constants between CF3SiF2X species and the corresponding SiF3X species are presented.
- Sharp, Kenneth G.
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p. 1241 - 1244
(2008/10/08)
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