Kinetics and thermochemistry of the R + HBr ⇌ RH + Br (R = CH2Cl, CHCl2, CH3CHCl or CH3CCl2) equilibrium
Kinetics and thermochemistry of the R + HBr ⇌ RH + Br (R = CH2Cl, CHCl2, CH3CHCl or CH3CCl2) equilibrium
复制标题
DOI：
10.1039/ft9969203069
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
J. A. Seetula
中科院分区：
文献类型：
--
作者：
J. A. Seetula
在可加热管式反应器中研究了CH_2Cl、CHCl_2、CH_3CHCl和CH_3CCl_2与HBr的反应动力学。的自由基，R，均匀地产生在反应器中通过脉冲248 nm激基复合物激光光解。在准一级反应条件下，监测R随HBr浓度变化的衰减，以确定随温度和压力范围变化的速率常数。在宽的温度范围内分别研究了反应，在这些温度范围内测定的速率常数符合Arrhenius表达式（所述误差限为1σ+ Student t值，单位为cm 3 molecule-1 s-1）：k（CH2Cl）=（6.6 ± 1.7）× 10-13 exp[-（4.1 ± 0.2）kJ mol-1/RT]，k（CHCl2）=（4.1 ± 1.0）× 10-13 exp[-（9.8 ± 1.0）kJ mol-1/RT]，k（CH3CHCl）=（3.0 ± 0.9）× 10-13 exp[+（3.0 ± 0.2）kJ mol-1/RT]，k（CH3CCl 2）=（4.4 ± 0.9）× 10-13 exp[-（5.9 ± 0.7）kJ mol-1/RT]。将所获得的动力学信息与最近测得的逆反应的速率常数相结合，以计算所研究的自由基的熵和生成热值。在298 K下使用第二定律程序获得热力学值。熵值的结果如下（单位为J K-1 mol-1）：271 ± 7（CH_2Cl），280 ± 7（CHCl_2），279 ± 6（CH_3CHCl）和288 ± 5（CH_3CCl_2）。ΔfH°298的结果如下（单位为kJ mol-1）：117.3 ± 3.1（CH 2Cl）、89.0 ± 3.0（CHCl 2）、76.5 ± 1.6（CH 3CHCl）和42.5 ± 1.7（CH 3CCl 2）。由反应焓值求得的类似氯代烃的C-H键能（单位kJ mol-1）为：419.0 ± 2.3（CH_3Cl），402.5 ± 2.7（CH_2Cl），406.6 ± 1.5（CH_3CH_2Cl中的α-C-H键）和390.6 ± 1.5（CH_3CHCl中的α-C-H键）。根据R′+ O2 <$R′O2（R′= CH 2Cl或CHCl 2）平衡，计算了CH 2ClO 2自由基的生成热Δ fH ° 298（CH 2ClO 2）=-（4 ± 11）kJ mol-1和CHCl 2 O2自由基的生成热ΔfH°298（CHCl 2 O2）=-（17 ± 7）kJ mol-1。
The kinetics of the reactions of CH2Cl, CHCl2, CH3CHCl and CH3CCl2 with HBr have been investigated in a heatable tubular reactor coupled to a photoionization mass spectrometer. The radicals, R, were produced homogeneously in the reactor by pulsed 248 nm exciplex laser photolysis. The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature and pressure range. The reactions were studied separately over a wide temperature range and at these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ+ Student's t values, units in cm3 molecule–1 s–1): k(CH2Cl)=(6.6 ± 1.7)× 10–13 exp[–(4.1 ± 0.2) kJ mol–1/RT], k(CHCl2)=(4.1 ± 1.0)× 10–13 exp[–(9.8 ± 1.0) kJ mol–1/RT], k(CH3CHCl)=(3.0 ± 0.9)× 10–13 exp[+(3.0 ± 0.2) kJ mol–1/RT] and k(CH3CCl2)=(4.4 ± 0.9)× 10–13 exp[–(5.9 ± 0.7) kJ mol–1/RT]. The kinetic information obtained was combined with the what is known of the recently measured rate constants of the reverse reactions to calculate the entropy and the heat of formation values of the radicals studied. The thermodynamic values were obtained at 298 K using a second law procedure. The results for entropy values are as follows (units in J K–1 mol–1): 271 ± 7 (CH2Cl), 280 ± 7 (CHCl2), 279 ± 6 (CH3CHCl) and 288 ± 5 (CH3CCl2). The results for ΔfH°298 are as follows (units in kJ mol–1): 117.3 ± 3.1 (CH2Cl), 89.0 ± 3.0 (CHCl2), 76.5 ± 1.6 (CH3CHCl) and 42.5 ± 1.7 (CH3CCl2). The C—H bond energy of analogous chlorinated hydrocarbons derived from the enthalpy of reaction values are as follows (units in kJ mol–1): 419.0 ± 2.3 (CH3Cl), 402.5 ± 2.7 (CH2Cl2), 406.6 ± 1.5 (α-C—H bond in CH3CH2Cl) and 390.6 ± 1.5 (α-C—H bond in CH3CHCl2). Improved heats of formation for the CH2ClO2 radical, ΔfH°298(CH2ClO2)=–(4 ± 11) kJ mol–1, and for the CHCl2O2 radical, ΔfH°298(CHCl2O2)=–(17 ± 7) kJ mol–1 are also calculated from the previously measured R′+ O2⇌ R′O2(R′= CH2Cl or CHCl2) equilibriums.