Weber Kevin H, Lemieux Jessy M, Zhang Jingsong
Department of Chemistry, University of California, Riverside, California 92521, USA.
J Phys Chem A. 2009 Jan 22;113(3):583-91. doi: 10.1021/jp808155a.
The thermal decomposition of ethyl and propyl iodides, along with select isotopomers, up to 1300 K was performed by flash pyrolysis with a 20-100 mus time scale. The pyrolysis was followed by supersonic expansion to isolate the reactive intermediates and initial products, and detection was accomplished by vacuum ultraviolet single photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The products monitored, such as CH(3), CH(3)I, C(2)H(5), C(2)H(4), HI, I, C(3)H(7), C(3)H(6), and I(2), provide for the simultaneous and direct observation of molecular elimination and bond fission pathways in ethyl and propyl iodides. In the pyrolysis of ethyl iodide, both C-I bond fission and HI molecular elimination pathways are competitive at the elevated temperatures, with C-I bond fission being preferred; at temperatures >or=1000 K, the ethyl radical products further dissociate to ethene + H atoms. In the pyrolysis of isopropyl iodide, both HI molecular elimination and C-I bond fission are observed and the molecular elimination channel is more important at all the elevated temperatures; the isopropyl radicals produced in the C-I fission channel undergo further decomposition to propene + H at temperatures >or=850 K. In contrast, bond fission is found to dominate the n-propyl iodide pyrolysis; at temperatures >or=950 K the n-propyl radicals produced decompose into methyl radical + ethene and propene + H atom. Isotopomer experiments characterize the extent of surface reactions and verify that the HI molecular eliminations in ethyl and propyl iodides proceed by a C1, C2 elimination mechanism (the 1,2 intramolecular elimination).
通过在20 - 100微秒时间尺度下的快速热解，对乙基碘和丙基碘以及选定的同位素异构体在高达1300 K的温度下进行热分解。热解后通过超声速膨胀来分离反应中间体和初始产物，并通过真空紫外单光子电离飞行时间质谱（VUV - SPI - TOFMS）进行检测。所监测的产物，如CH₃、CH₃I、C₂H₅、C₂H₄、HI、I、C₃H₇、C₃H₆和I₂，使得能够同时直接观察乙基碘和丙基碘中的分子消除和键断裂途径。在乙基碘的热解中，C - I键断裂和HI分子消除途径在高温下相互竞争，其中C - I键断裂更占优势；在温度≥1000 K时，乙基自由基产物进一步分解为乙烯 + H原子。在异丙基碘的热解中，观察到了HI分子消除和C - I键断裂，并且在所有升高的温度下分子消除通道更为重要；在C - I断裂通道中产生的异丙基自由基在温度≥850 K时进一步分解为丙烯 + H。相比之下，发现键断裂在正丙基碘热解中占主导；在温度≥950 K时，产生的正丙基自由基分解为甲基自由基 + 乙烯以及丙烯 + H原子。同位素异构体实验表征了表面反应的程度，并证实乙基碘和丙基碘中的HI分子消除是通过C1、C2消除机制（1,2分子内消除）进行的。
