Kinetics of UV-laser induced dehydrochlorination of 1-chloro-1,1-difluoroethane

The decomposition of 1-chloro-1,1-difluoroethane by a radical chain reaction has been studied in a flow reactor in the temperature range from 503 to 773 K. For the initiation of the chain small amounts of added chlorine were photolyzed with a XeCl laser (λ = 308 nm). The formation of the dehydrochlorination and chlorination products, vinylidene fluoride, and 1,2-dichloro-1,1-difluoroethane respectively, is described by a kinetic model. Arrhenius parameters for the two abstraction reactions and were determined by a competition method: Experimental and modeling results are discussed with respect to former studies on the thermal reaction of 1-chloro-1,1-difluoroethane.     

Kinetics and mechanism of the pyrolysis of 1-Chloro-1, 1-difluoroethane in the presence of chlorine

The first stage thermal reactions of CF₂CICH₃ in the presence of chlorine have been studied between 554 and 614 K. These are and Rate equations derived from a radical mechanism are shown to fit the experimental results. Values of Arrhenius parameters for the decomposition of the CF₂ClCH₂. radical and its reactions with Cl₂ and Cl are given.     

Pyrolysis of 1-chloro-1,1-difluoroethane in the absence and in the presence of CCl4 and mixtures of CCl4 + HCl

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′, L^½ /mol^½ · 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.     

Theoretical calculations of product percentage yields for the thermal decomposition of 2-chloro-1,1-difluoroethane

Theoretical calculations of the product percentage yields for the thermal decomposition of CHF₂CH₂Cl are consistent with the experimental percentage product yields supporting the proposal that the unexpected formation of 1,2-difluoroethene can be explained by a 1,2-FCl interchange converting CHF₂CH₂Cl into CHFClCH₂F, which then undergoes a 2,1-HCl elimination. Thermal activation rate constants and threshold energy barriers for dominant reactions in this system were calculated. Theoretical product percentage yields varied greatly because different basis sets produced a wide range of threshold energy barriers, but the computational results were generally consistent with a recent experimental report.     

The mechanism of thermal dehydrochlorination. Pyrolysis of 1-Chloro-1-fluoroethane and 1-chloro-1, 1-difluoroethane

The thermal decompositions of 1-chloro-1-fluoroethane and 1-chloro-1,1-difluorethane at atmospheric pressure have been studied in the temperature range 500–600°C in a flow system. The dehydrochlorinations are homogenous in a carbonaceous reactor and unimolecular. The rate constants are given by and The criteria for molecular or chain processes in thermal dehydrochlorinations are discussed.     

Kinetics and mechanism of the pyrolysis of pentachloroethane

The rate of the inhibited pyrolysis of pentachloroethane was studiedover the temperature range of 820 to 865°K using the toluene-carrier technique in a stirred-flow reactor. The pyrolysis rate was found to be first order in reactant, and the rate constant is described by k=10^11.6±0.7 exp [(?48,200±2600)/RT] sec^?1. An increase by a factor of 6.6 in the surface/volume of the reactor had a negligible effect on the rate. This observation, in addition to a reevaluation of earlier kinetic data for the pyrolysis of pentachloroethane, lead to the following conclusions concerning the pyrolysis mechanism. The initiation and termination as well as the propagation reactions were homogeneous, the termination involved both Cl and C₂Cl₅ radicals (crosstermination), and autocatalysis was caused by interaction between chlorine and pentachloroethane rather than by dissociation of molecular chlorine.     

1,2-二芳基取代-1,1''-二氟乙烷的合成

1,2 二芳取代 1,1’ 二氟乙烷主要用作混合液晶添加剂以达到降低粘度增加响应速度的作用,同时也可以增加混晶的工作温度范围和抗紫外辐照的能力,并且能够实现低压驱动,文献报道的4种合成方法(硫缩醛的氟化、炔的氟化加成、酮的氟化以及腙的氟化[1,2])或反应条件苛刻,或转化率低,作者参考文献[3,4,5]对反应改进后发现,当在80℃、DAST(二乙胺基三氟化硫络合物)与乙二醇二甲醚的混合溶剂(体积比为3∶1)中进行酮的氟化反应时可达到95%的转化率。合成路线如下。1　实验部分1 1　仪器与试剂美国Nicolet60XR型红外光谱仪,日本JEOL公司FX …     

Recalculation of data on the thermal decomposition of 1,1-difluoroethane and 1,1,1-trifluoroethane

Disagreements in rate constants and parameters between published results on the decomposition of 1,1-difluoroethane and 1,1,1-trifluoroethane are shown to originate from incorrect specification and setting of reaction conditions in one of the studies. When corrected, applicable results are in excellent agreement.     

The kinetics and mechanism of the reaction between 1-chloro-2,3-epoxypropane and p-cresol in the presence of basic catalysts

Rate constants for the reaction of 1-chloro-2,3-epoxypropane with p-cresol in the presence of basic catalysts were studied at the temperature range of 71–100°C. It was found that in the presence of sodium p-cresolate, three consecutive reactions proceeded giving the following products: 1-chloro-3-(tolyloxy)-2-propanol (CTP), 1-(p-tolyloxy)-2,3-epoxypropane (TEP) as a main product, and 1,3-di(p-tolyloxy)-2-propanol (DTP). Their rate constants at 71°C were: k₁ = 0.030 ± 0.009, k₂ = 1.58 ± 0.02, and k₃ = 0.033 ± 0.005 dm³/mol · min, respectively. In the presence of quaternary ammonium salts, this process consisted of 5 reactions which led to CTP as a main product as well as TEP and 1,3-dichloro-2-propanol (DCP). The rate constant of CTP formation at 71°C was established, k₁ = 0.130 ± 0.030 dm³/mol · min, as were the ratios of the other rate constants k₂/k₋₄ = 1.5 ± 0.2, k₅/k₋₄ = 20.0 ± 5.0, and k₄/k₁ = 0.6 ± 0.7. Based on the changes in Cl⁻ ion concentration during the reaction, the catalystic activity of quaternary ammonium salts was explained. The kinetic model of these reactions in the presence of basic catalysts has been proposed and appropriate kinetic equations have been presented. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 73–79, 1997.     

Kinetics and mechanism of the reaction of 1-chloro-2,4,6-trinitrobenzene with the N,N-dimethylaminohydrazone of furfural in acetonitrile

Kinetics of the arylation of the N,N-dimethylaminohydrazone of furfural with picryl chloride in acetonitrile at 298 K has been studied. The reaction is not catalyzed by nucleophiles. The mechanism includes the rapid equilibrium formation of σ-adduct with its slow unimolecular decomposition. Rate and equilibrium constants for the individual steps were calculated. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 173–176, May–June, 2000.     

A gas-phase electron diffraction study of the molecular structure of 1,1-difluoroethane

The molecular structure of 1,1-difluoroethane has been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. Effective least-squares refinement of the geometry was achieved with fixed values for vibrational amplitudes transferred from normal coordinate calculations on related molecules. In subsequent calculations, in which several amplitudes were also allowed to refine, only minor changes were noted. The refinements yielded the following main geometrical parameters (r_avalues with e.s.d. in parentheses): C—C = 1.498(4) Å, C—F = 1.364(2) Å, C—H(mean) = 1.081(3) Å, ∠CCH(mean) = 111.0(7)°, ∠CCF = 110.7(3)°, ∠FCF = 107.4(5)°. Dependent angles are ∠FCH = 108.5(8)° and ∠HCH = 107.9(7)°.     

Shock tube study of dissociation and relaxation in 1,1-difluoroethane and vinyl fluoride

This paper reports measurements of the thermal dissociation of 1,1-difluoroethane in the shock tube. The experiments employ laser-schlieren measurements of rate for the dominant HF elimination using 10% 1,1-difluoroethane in Kr over 1500-2000 K and 43 < P < 424 torr. The vinyl fluoride product of this process then dissociates affecting the late observations. We thus include a laser schlieren study (1717-2332 K, 75 < P < 482 torr in 10 and 4% vinyl fluoride in Kr) of this dissociation. This latter work also includes a set of experiments using shock-tube time-of-flight mass spectrometry (4% vinyl fluoride in neon, 1500-1980 K, 500 < P < 1300 torr). These time-of-flight experiments confirm the theoretical expectation that the only reaction in vinyl fluoride is HF elimination. The dissociation experiments are augmented by laser schlieren measurements of vibrational relaxation (1-20% C(2)H(3)F in Kr, 415-1975 K, 5 < P < 50 torr, and 2 and 5% C(2)H(4)F(2) in Kr, 700-1350 K, 6 < P < 22 torr). These experiments exhibit very rapid relaxation, and incubation delays should be negligible in dissociation. An RRKM model of dissociation in 1,1-difluoroethane based on a G3B3 calculation of barrier and other properties fits the experiments but requires a very large DeltaE(down) of 1600 cm(-1), similar to that found in a previous examination of 1,1,1-trifluoroethane. Dissociation of vinyl fluoride is complicated by the presence of two parallel HF eliminations, both three-center and four-center. Structure calculations find nearly equal barriers for these, and TST calculations show almost identical k(infinity). An RRKM fit to the observed falloff again requires an unusually large DeltaE(down) and the experiments actually support a slightly reduced barrier. These large energy-transfer parameters now seem routine in these large fluorinated species. It is perhaps a surprising result for which there is as yet no explanation.     

Solvent effects in the fluorination of 1,2-dichloro-1,1-difluoroethane (R-132b) to 2-chloro-1,1,1-trifluoroethane (R-133a)

Trichloroethylene has been found to act as a rate enhancing co-factor in the liquid phase, tantalum (V) halide catalyzed, fluorine-for-chlorine exchange reaction of 1,2-dichloro-1,1-difluoroethane (R-132b) to 2-chloro-1,1,1-trifluorethane (R-133a). Several trifluoromethyl substituted benzenes have also been found to be rate-enhancing solvents.     

IR and visible luminescence studies in the infrared multiphoton dissociation of 1,2-dibromo-1,1-difluoroethane

The infrared multiphoton dissociation of 1,2-dibromo-1,1-difluoroethane gives rise to IR and visible luminescence. Vibrationally excited parent molecules dissociate via two primary channels yielding bromine and vibrationally excited HBr. The strong visible emission observed between 350 to 750 nm has been assigned to electronically excited carbene CF₂Br H.     

The CW-CO2 laser induced reaction of 1,1-difluoroethane with chlorine

The CW–CO₂ laser induced reaction of CF₂HCH₃ (1) with Cl₂ yields vinylidene fluoride (2) as the main product; other products are CH₃CF₂Cl (3), CF₂ClCH₂Cl (4), CF₂ = CHCl (5), CF₂ = CCl₂ (6) and CF₂ Cl₂ (7). The yield dependence of 2 on the CF₂HCH₃/Cl₂ ratio, the laser irradiation time, the laser power and the pressure of the gaseous reactants have been investigated. Furthermore, the TEA–CO₂ laser induced reaction of 1 with Cl₂. the CW–CO₂ laser induced reaction of 2 and 2 with Cl₂ have also been studied in order to gain more mechanistic insights for this complicated reaction system. Apparently, CF₂ClCH₃ but not CF₂HCH₂Cl. is the main precursor to 2. Interestingly, it has been found that the relatively strong double bond of CF₂ = CH₂ can be broken by laser irradiation. The possibility of applying this laser methodology to the production of vinylidene fluoride has been discussed.     

连续CO2激光引发的1,1-二氟乙烷与氯的反应

本文报道了CW-CO2激光引发的CF2HCH3与Cl2的反应.除主要产物CF2=CH2外,还有CF2ClCH3. CF2ClCH2Cl. CF2=CHCl. CF2=CCl2和CF2Cl2.为了探索应用激光方法合成CF2=CH2的可能性,研究了激光输出功率. 照射时间. 反应体系中CF2HCH3与Cl2的比例及样品压力对CF2=CH2得率的影响.同时为了探讨反应机理,还进行了TEA-CO2激光引发CF2HCH3加Cl2实验和CW-CO2激光作用下CF2=CH2. CF2=CH2加Cl2的反应研究,令人感兴趣的是在激光照射CF2=CH2时,发现了双键的断裂.     

Neighboring group participation in the pyrolysis kinetics of 4-chloro-1-butanol in the gas phase

The pyrolysis of 4-chloro-1-butanol has been studied in a static system, seasoned with allyl bromide, and in the presence of the free radical suppressor toluene. The working temperature and pressure ranges were 400–450°C and 43–164 Torr, respectively. The reaction is homogeneous, unimolecular, and follows a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k₁(s^?1) = (13.34 ± 0.50) ? (221.1 ± 6.7) kJ mol^?1 (2.303RT)^?1. The products tetrahydrofuran, formaldehyde, and propene, arise by the participation of the neighboring OH group in 4-chloro-1-butanol pyrolysis. The reaction is best explained in terms of an intimate ion pair type of mechanism.