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1.
The thermal dehydrochlorination CCl2FCH3 → CClFCH2 + HCl has been studied in a static system between 610 and 700 K at pressures ranging from 14 to 120 torr. The experiments were performed in the absence and presence of an added inhibitor (0.5 to 7 torr of C3H6) or catalyst (2 to 8 torr of CCl4). The evolution of the reaction was followed by measuring the pressure rise in the quartz reaction vessel and analyzing the products by gas chromatography. All the experimental results can be explained quantitatively in terms of a reaction model both radical and molecular. The molecular dehydrochlorination has an activation energy of 57.05 kcal/mol and a preexponential factor of 1014.02 s−1. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 191–197, 2001 相似文献
2.
The thermal dehydrochlorination CF2ClCH3→CF2(DOUBLEBOND)CH2+HCl has been studied in a static system between 597 and 664 K in the presence of CCl4, C2Cl6, CF2(DOUBLEBOND)CH2, HCl, and CF3CH3. A kinetic radical and molecular reaction model has been developed. In addition to describing earlier results on the acceleration of the pyrolysis by CCl4 and the further acceleration by HCl, this model describes quantitatively up to conversions of 20% (i) the dependence of the catalytic effect of CCl4 at low concentrations, (ii) the stronger catalytic effect of C2Cl6, and (iii) the inhibitory effect of added CF2CH2 and CF3CH3 when CCl4 is used as a catalyst. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 359–366, 1998 相似文献
3.
NICOLÁS D. GÓMEZ VIOLETA D'ACCURSO FRANCISCO A. MANZANO JORGE CODNIA M. LAURA AZCÁRATE 《国际化学动力学杂志》2014,46(7):382-388
The rate constant of the reaction between CCl2 radicals and HCl was experimentally determined. The CCl2 radicals were obtained by infrared multiphoton dissociation of CDCl3. The time dependence of the CCl2 radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4 and to the reaction with HCl to form CHCl3. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10?13 cm3 molecule?1 s?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10?14 cm3 molecule?1 s?1. 相似文献
4.
Jean Olbregts 《国际化学动力学杂志》1993,25(2):125-135
Although hydrogen abstraction from 1,1,1,2-tetrachloroethane should produce only one kind of radical, CCl3CHCl, the presence of small amounts of trichloroethene, as impurity as well as product of reaction, induces the formation of the a priori unexpected CHCl2CCl2 radicals. The importance of this radical in the reaction pathways of the chlorination and the chlorine induced dehydrochlorination of CCl3CH2Cl, under different experimental conditions, is computed and discussed. For example, at 380 K, and for small partial pressures of chlorine (2 torr), the CHCl2CCl2 radicals account for more than 70% of the formation of the reaction products after only 2% reaction. The major role of trace quantities in long chain radical reactions is emphasized. © 1993 John Wiley & Sons, Inc. 相似文献
5.
The thermal dehydrochlorination CF2ClCH3 → CF2 ? CH2 + HCl has been studied in a static system between 637 and 758 K. It is a homogeneous, molecular first-order reaction and its rate constant is given by This reaction has also been studied in the presence of CCl4 and mixtures of CCl4 and HCl between 585 and 662 K. It is then accelerated and the initial rate increase is given by with log10 (k′, L½ /mol½ · s) = ?(41,650 ± 180)/4.576T + (10.84 ± 0.06) and log10 k″ = (7900 ± 180)/4.576T ? (0.59 ± 0.06). A radical chain mechanism is shown to be consistent with these latter results. 相似文献
6.
Ismat A. Abu-Isa 《Journal of polymer science. Part A, Polymer chemistry》1972,10(3):881-894
The degradation of two chlorinated polyethylene compounds CPE 25 (45% chlorine) and CPE 16 (36% chlorine) was studied by following their rates of dehydrochlorination at two temperatures, 150°C and 180°C in pure nitrogen and pure oxygen atmospheres. Studies on the powdered polymers showed that the dehydrochlorination rate of CPE 25 is about fourteen times faster than that of CPE 16 in nitrogen atmospheres and only three to four times faster in oxygen. The molded polymers gave a lower rate of dehydrochlorination than when in the powdered form. This effect is attributed to diffusion factors. The antimony oxide brought about an induction period in the dehydrochlorination reaction during which only a small amount of HCl is evolved, followed by a very fast rate of dehydrochlorination both in oxygen and nitrogen atmospheres. The duration of the induction period increases with increase in the Sb2O3 concentration, but is followed by an accelerated HCl loss which is faster when Sb2O3 concentration is higher. This work provides supporting evidence that SbCl3 was formed and lost during degradation. Mechanisms of dehydrochlorination are suggested for the reaction in the case of pure chlorinated polyethylene and for the polymer containing antimony oxide. 相似文献
7.
The rate coefficient for the reaction of CCl3 radicals with ozone has been measured at 303 ± 2 K. The CCl3 radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl3 concentration was monitored with a photoionization mass spectrometer. Addition of the O3–O2 mixture to this system caused a decay of the CCl3 concentration because of the reactions of CCl3 + O3 → products (5) and CCl3 + O2 → products (4). The decay of signals from the CCl3 radical was measured in the presence and absence of ozone. In the absence of ozone, the O3–O2 mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl3 + O2 could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10?13 cm3 molecule?1 s?1 and was also found to be independent of the total pressure (253–880 Pa of N2). This result shows that the reaction of CCl3 with O3 cannot compete with its reaction with O2 in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003 相似文献
8.
Linda Nelson Imelda Shanahan Howard W. Sidebottom Jack Treacy Ole J. Nielsen 《国际化学动力学杂志》1990,22(6):577-590
The reaction mechanisms for oxidation of CH3CCl2 and CCl3CH2 radicals, formed in the atmospheric degradation of CH3CCl3 have been elucidated. The primary oxidation products from these radicals are CH3CClO and CCl3CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH3CCl3 have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH3CCl3) = (5.4 ± 3) 10?12 exp(?3570 ± 890/RT) cm3 molecule?1 s?1. A value of this rate constant of 1.3 × 10?14 cm3 molecule?1 s?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH3 CCl3 reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH3CCl3) = (1.09 ± 0.35) × 10?14, ??(OH + CH3CClO) = (0.91 ± 0.32) × 10?14, ??(OH + CCl3CHO) = (178 ± 31) × 10?14, ??(OH + CCl2O) < 0.1 × 10?14; all in units of cm3 molecule?1 s?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed. 相似文献
9.
J. Czarnowski 《国际化学动力学杂志》1996,28(7):489-495
The thermal gas-phase reaction of CF3OF with CCl2CCl2 has been studied between 313.8 and 343.8 K. The initial pressure of CF3OF was varied between 10.8 and 77.5 torr and that of CCl2CCl2 between 3.7 and 26.8 torr. CF3OF was always present in excess, varying the initial ratio of CF3OF to that of CCl2CCl2 from 1.3 to 10. Three products were formed: CF3OCCl2CCl2F, CCl2FCCl2F, and CF3O(CCl2CCl2) 2OCF3. The yields of CF3OCCl2CCl2F were 98–99.5%, based on the sum of the products. The reaction was a homogeneous chain reaction not affected by the total pressure. In presence of O2 the oxidation of CCl2CCl2 to CCl3C(O)Cl and COCl2 occurred. The proposed basic reaction steps are: generation of the radicals CF3O˙ and CCl2FCCl2˙ (κ1) in a biomolecular process between CF3OF and CCl2CCl2, formation of the radical CF3OCCl2CCl2˙ by addition of CF3O˙ to CCl2CCl2, chain generation of CF3O˙ by abstraction of fluorine atom from CF3OF by CF3OCCl2CCl2˙ (κ4), and chain termination by recombination of the radicals CF3OCCl2CCl2˙. The expressions obtained for the constants κ1 and κ4 are κ1 = 3.16 ± 0.6 × 107 exp(−15.2 ± 1.7 Kcal mol−1/RT) dm3 mol−1 s−1, κ4 = 3.7 ± 0.5 × 109 exp(−6.0 ± 1.1 Kcal mol−1/RT) dm3 mol−1 s−1. © 1996 John Wiley & Sons, Inc. 相似文献
10.
Phosphines are inhibitors of thermal degradation of 4-chloro-2-hexene because they form strong complexes with either HCl or ZnCl2, which cause catalysis of the dehydrochlorination. Aliphatic phosphines are more efficient than aromatic phosphines. Aliphatic phosphites also act as stabilizers; they react with HCl, and may be substituted for allylic chlorine in the presence of ZnCl2 as catalyst; the resulting phosphonate may be destroyed by HCl if phosphite is not in excess. Aromatic phosphites do not react at 60°; they only form a complex with HCl and, in the presence of ZnCl2, they cause an increase of the dehydrochlorination rate. This effect is due to the reverse reaction, catalysed by a complex HCl-hexadiene, being slowed down because of the competing phosphite-HCl complex. 相似文献
11.
The reaction of methyl radicals with CCl4 and CCl3Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH3CCl3, formed via the combination of methyl and trichloromethyl radicals. From these investigations Arrhenius parameters for the reactions have been determined: Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl4 and CCl3Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C2Cl6, and the HCl precursor CH3CCl3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl3Br and a chloromethane. Arrhenius parameters were obtained for the reactions and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes. 相似文献
12.
Thermal degradation of PVC treated with alkylaluminum compounds has been studied. Four PVC samples of different molecular weights have been treated with Me3Al, and Et3A1, and the dehydrochlorination rates of the polymers were determined at 190 and 220°C under a nitrogen atmosphere. The alkylaluminum-treated low molecular weight samples show marked increase in thermal stability, i. e., slower rate of dehydrochlorination right from the beginning of degradation, whereas with the higher molecular weight samples stabilization becomes pronounced only after a few percent of dehydrochlorination. The color of R3Al-treated samples was much lighter (yellowish) than those of controls (dark brown) at 1% HCl loss. The average polyene sequence lengths formed during the early stages of dehydrochlorination are found to be much shorter with RsAl-treated PVC than with virgin samples. It appears as though polyene sequences which arose by zipping- initiation from allylic and/or tertiary chlorine sites are longer than those which form by random initiation along the chain. The autocatalytic (i. e., HC1-catalyzed) dehydrochlorination observed with virgin PVC disappears after treatment with R3A1. The HCl-catalyzed dehydrochlorination is minimized when thin films are used instead of powdery samples, which may be due to higher rates of HC1 diffusion through thin films. Autocatalysis of dehydrochlorination is affected by the concentrations of double bonds and HCl and the length of polyene sequences. Interaction between polyenes and HC1 by hydrogen transfer may lead to the re-initiation of unzipping, thus lengthening the polyene sequences. 相似文献
13.
Bla Ivn Joseph P. Kennedy Tibor Kelen Ferenc Tüds Tibor Tams Nagy Bla Turcsnyi 《Journal of polymer science. Part A, Polymer chemistry》1983,21(8):2177-2188
Thermal and thermo-oxidative degradation of poly(vinyl chloride)s (PVCs) containing increased concentrations of allylic chlorines, PVC(A)s, prepared by controlled chemical dehydrochlorination with potassium-t-butoxide (t-BuOK) have been studied. The introduction of small amounts of internal allylic chlorines into PVC significantly decreases the thermal and thermo-oxidative stability of the resin. A linear relationship exists between the initial rates (VHCl)0 of thermal and thermooxidative dehydrochlorination of solid PVC(A)s and the concentration S of internal allylic chlorines. Both the slope and the intercept of the thermo-oxidative (VHCl)0 vs. S plot are higher in oxygen than those obtained in nitrogen at the same temperature; this finding is attributed to fast oxidation of polyenes, and to peroxy radicals formed during polyene oxidation, which initiate subsequent HCl loss by attacking normal repeat units in PVC. The extent of HCl loss as a function of time during thermal degradation of PVC(A)s in intert solvent shows a rapid initial phase followed by a slower stationary phase. The first phase is due to dehydrochlorination involving the labile chlorines, while the stationary phase indicates random initiation of HCl loss at normal? CH2? CHCl? repeat units. Initial rates of HCl loss increase with S, while the rates of HCl loss during the stationary phase are independent of S. The rate constant of initiation of HCl loss at internal allylic chlorines is almost four orders of magnitude higher than that of random initiation; however, the former is still orders of magnitude lower than that of chain propagation. Quantitative analysis of UV-visible spectra of PVC(A)s degraded in solution suggests geometric polyene distribution. The average length of polyenes decreases as the extent of HCl loss increases and reaches a constant value of ca. 3 at ca. 1% HCl loss for all the investigated PVC(A) samples. 相似文献
14.
The reactions of [CCl3]+ with ethylene, 1-hexene, cyclopentence, cyclohexene and styrene have been studied in a field-free, high-pressure ion source by time-resolved ion collection following a short ionizing pulse of electrons. Ethylene is completely unreactive, while addition of [CCl3]+ to the olefinic bond of the other compounds is followed by loss of one or more HCl molecules to give unsaturated cations. Only styrene forms a stable adduct [MCCl3]+ which is an arenium ion produced by addition to the aromatic ring. Rate constants for the reaction of [CCl3]+ have been determined and show that whereas reaction with styrene occurs at almost every ion-molecule collision, with 1-hexene and cyclopentene only 15% of the collisions lead to reaction. 相似文献
15.
《Polymer Degradation and Stability》1987,18(3):213-224
Chain-chlorinated polystyrene samples have been prepared and characterised, containing from 2·5 to 34·3% chlorine by weight (from 0·1 to 1·3 chlorine atoms per styrene unit). Chlorination has been found to involve mainly substitution of the tertiary hydrogen atoms, followed by methylene substitution at reactant concentrations of more than 1 mole Cl2 per styrene unit. Reaction with chlorine is quantitative in CCl4 in the absence of air and the amount of ring-chlorination as a side reaction is very small.Chlorination in the backbone destabilises the polymer, which first loses hydrogen chloride on heating. The double bonds formed provide points of weakness for chain scission, which occurs at lower temperatures than for PS. Under programmed heating, the dehydrochlorination and chain scission reactions overlap to some extent in temperature range, but highly conjugated partially degraded polymer can be made from extensively chain-chlorinated PS. At more than 1 Cl per styrene unit, HCl is almost the sole volatile product, although the conjugated polymer breaks up to chain fragments above 300°C. 相似文献
16.
B. B. Troitskii L. S. Troitskaya 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):75-81
The dehydrochlorination of different samples of PVC under vacuum with continuous removal of HCl by freezing, has been studied at 180–210°C. The comparison of the kinetic curves of the dehydrochlorination of various samples of PVC which were obtained by us and other investigators, with the theoretical curves for the thermal degradation of idealized PVC in the absence of HCl has been carried out. This had made it possible to evaluate the influence of unstable fragments present in the original polymer on the initial rate of PVC degradation quantitatively. It has been shown that the distinction between the stationary rates of the dehydrochlorination of various samples of PVC is determined by the difference of the values of the average length of dehydrochlorination chain, lav. The most probable interval of the values of lav has been ascertained to be 4–12. It is established that the most probable value of the constant of the rate of dehydrochlorination of normal links of PVC, k0, is 2.1 × 10?7?2.5 × 10?7 s?1 at 200°C. © 1993 John Wiley & Sons, Inc. 相似文献
17.
The main characteristics of the evolution of HCl and SbCl3 during the thermal degradation of chloroparaffin-Sb2O3 mixtures, which are typical fire retardant additives for polymers, have been studied.Sb2O3 reacts with HCl evolved from the chloroparaffin without any apparent effect on the dehydrochlorination process itself. Evolution of SbCl3 occurs at a maximum rate between 300 and 350°C and is somewhat delayed in the earlier stage of reaction, depending on the composition of the mixture. 相似文献
18.
Nicolás D. Gómez Violeta D'Accurso V. Mariana Freytes Francisco A. Manzano Jorge Codnia M. Laura Azcárate 《国际化学动力学杂志》2013,45(5):306-313
An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl2, in an Ar bath. The CCl2 radicals were generated by IRMPD of CDCl3. The time dependence of the CCl2 radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k0 = (2.23 ± 0.89) × 10?29 cm6 molecules?2 s?1 and k∞ = (6.73 ± 0.23) × 10?13 cm3 molecules?1 s?1, respectively. 相似文献
19.
The rate constant for the combination of 2,2-dichloro-1,1,1-trifluoroethyl radicals has been measured by applying the rotating sector technique to the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane at 315°K. The observed value is 6.89 × 1012 cc/mole.sec. This value is in excellent agreement with measurements by Wampler and Kuntz which yielded a temperature-independent value of 6.6 × 1012 cc/mole.sec. The measurement by Wampler and Kuntz was determined from the photochemical system (CF3CCl3 + C-C6H12 + hν). The Arrhenius parameters for the reaction CF3CCl2· + Cl2 → CF3CCl3 + Cl were found to be given by the expression log k3 = 12.10 ? 5830/2.3RT (units in mole, cc, and sec). This is a relatively high activation energy for a chlorination reaction and makes the reaction ever slower than the chlorination of chloroform. 相似文献
20.
The kinetics of hydrogen abstraction from cyclohexene by CCl3 radicals were studied in CCl4 solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl3 radicals were produced both by radiolysis of CCl4 and by photolysis of CCl3Br. The rate constant for the reaction was found to be given by the equation where θ = 2.303 RT kcal/mol. This activation energy leads to C? H bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C-C6H11 radical. 相似文献