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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Thermochemical Property, Pathway and Kinetic Analysis on the Reactions of Allylic Isobutenyl Radical with O_2: an Elementary Reaction Mechanism for Isobutene Oxidation
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Thermochemical Property, Pathway and Kinetic Analysis on the Reactions of Allylic Isobutenyl Radical with O_2: an Elementary Reaction Mechanism for Isobutene Oxidation

机译：烯丙基异丁烯基自由基与O_2反应的热化学性质，途径和动力学分析：异丁烯氧化的基本反应机理

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摘要

Kinetics for the reactions of allylic isobutenyl radical (C-C(C)-C) with molecular oxygen are analyzed by using quantum Rice-Ramsperger-Kassel (QRRK) theory for k(E) and master equation analysis for falloff. Thermochemical properties and reaction path parameters are determined by ab initio-Moller-Plesset (MP2(full)/6-31g(d) and MP4(full)/6-31g(d,p)//MP2(full)/6-31g(d)), complete basis set model chemistry (CBS-4 and CBS-q with MP2(full)/6-31g(d) and B3LYP/6-31g(d) optimized geomertries), and density functional (B3LYP/6-31g(d) and B3LYP/6-311 + g(3df,2p)//B3LYP/6-31g(d)) calculations. An elementary reaction mechanism is constructed to model the experimental system, isobutene oxidation. The forward and reverse rate constants for initiation reaction C_2C=C + O_2 <-> C-C(C)-C +H_2O are determined to be 1.86 * 10~9 T~(1.301) exp(-40939 cal/RT) (cm~3 mol~(-1) s~(-1)) and 6.39 * 10~8 T~(0.944) exp(-123.14 cal/RT) (cm~3 mol~(-1) s~(-1)), respectively. Calculations on 2, 5-dimethylhexa-1,5-diene, methacrolein, isobutene oxides, and acetone product formation from reaction of isobutene oxidation mechanism are compared with experimental data. Reaction of allylic isobutenyl radical + O_2 forms an energized peroxy adduct [C=C(O)CCO·]~* with a shallow well (ca. 21 kcal/mol), which predominantly dissociates back to reactants. The reaction channels of the C=C(C)COO·~* adduct include reverse reaction to reactants, stabilization to C=C(C)COO· radical, O-O bond fission to C=C(C)CO·+ O, isomerization via hydrogen shift with subsequent β-scission or R·O-OH bond cleavage. The C=C(C)COO·~+ adduct can also cyclize to four- or five-member cyclic peroxide-alkyl radicals. All the product formation pathways of allylic isobutenyl radical with O_2 involve barriers that are above the energy of the initial reactants. This results in formation of isomers that exist in steady state concentration at early time in oxidation, at low to moderate temperatures. The primary reaction is reverse dissociation back to reactants, with slower reactions from the distributed isomers to new products. The concentration of allylic isobutenyl radical accumulates to relatively high levels and the radical is consumed mainly through radical-radical processes in moderate temperature isobutene oxidation. Reactions of C=C(C)COO·cyclization to four or five-member cyclic peroxides require relative high barriers due to the near complete loss of π bond energy for the terminal double bond's twist needed in the transition states. These barriers are calculated as 28.20 (24.95) and 29.72 (27.98) kcal/mol at CBS-q//MP2(full)/6-31g(d) level with A factors of 2.42 * 10~(10) (3.28 * 10~(10)) and 3.88 * 10~(10) (6.09 * 10~(10)) s~(-1) at 743 K, respectively, for four- and five-member ring cyclization. Data in parentheses are calculation at B3LYP/6-311 + g(3df,2p)//B3LYP/6-31g(d)). A new reaction path is proposed: C=C(C·)COOH <-> C=C(C·)CO·+ OH <-> C=Y(CCOC) + OH, which is responsible for methylene oxirane formation (Y = cyclic). The reaction barrier for the C=C(C·)COOH reaction to C=C(C·)CO·+ 0H is evaluated as 42.45 (41.90) kcal/mol with an A factor of 4 * 10~(15) s~(-1). The reaction barrier of C=C(C·)COOH → TS5 → C=Y(CCOC) + OH is calculated as 42.14 kcal/mol with an A factor of 6.95 * 10~(11) s~(-1) at 743 K.
机译：利用量子赖斯-拉姆斯珀格-卡塞尔（QRRK）理论对k（E）进行分析，并利用主方程分析法对烯丙基异丁烯基（C-C（C）-C）与分子氧的反应动力学进行了分析。热化学性质和反应路径参数由头算Moller-Plesset（MP2（满）/ 6-31g（d）和MP4（满）/ 6-31g（d，p）// MP2（满）/ 6- 31g（d）），完整的基集模型化学（具有MP2（full）/ 6-31g（d）和B3LYP / 6-31g（d）优化的土工力学的CBS-4和CBS-q）和密度泛函（B3LYP / 6-31g（d）和B3LYP / 6-311 + g（3df，2p）// B3LYP / 6-31g（d））计算。构建了基本的反应机理以对实验系统建模，即异丁烯氧化。引发反应C_2C = C + O_2 <-> CC（C）-C + H_2O的正向和反向速率常数确定为1.86 * 10〜9 T〜（1.301）exp（-40939 cal / RT）（cm〜 3 mol〜（-1）s〜（-1））和6.39 * 10〜8 T〜（0.944）exp（-123.14 cal / RT）（cm〜3 mol〜（-1）s〜（-1）） ， 分别。将由异丁烯氧化机理反应生成的2，5-二甲基六-1,5-二烯，甲基丙烯醛，异丁烯氧化物和丙酮产物形成的计算结果与实验数据进行了比较。烯丙基异丁烯基自由基+ O_2的反应与浅孔（约21 kcal / mol）形成激发的过氧加合物[C = C（O）CCO·]〜*，并主要解离为反应物。 C = C（C）COO·〜*加合物的反应通道包括对反应物的逆反应，对C = C（C）COO·自由基的稳定，OO键裂变为C = C（C）CO·+ O，异构化通过氢转移和随后的β断裂或R·O-OH键断裂。 C = C（C）COO·+加合物还可以环化成四元或五元环状过氧化物-烷基。具有O_2的烯丙基异丁烯基自由基的所有产物形成途径都涉及高于初始反应物能量的势垒。这导致形成异构体，该异构体在低温到中温下在氧化的早期以稳态浓度存在。主要反应是反向解离回到反应物，从分布的异构体到新产物的反应变慢。烯丙基异丁烯基自由基的浓度积累到相对较高的水平，并且该自由基主要通过中温异丁烯氧化中的自由基自由基过程被消耗。 C = C（C）COO·环化成四或五元环状过氧化物的反应需要相对较高的势垒，这是因为过渡态所需的末端双键的扭曲几乎完全丧失了π键能量。在CBS-q // MP2（full）/ 6-31g（d）浓度下，这些势垒计算为28.20（24.95）和29.72（27.98）kcal / mol，A因子为2.42 * 10〜（10）（3.28 * 10）对于四元和五元环环化，分别在743 K处（〜（10））和3.88 * 10〜（10）（6.09 * 10〜（10））s〜（-1）。括号中的数据是在B3LYP / 6-311 + g（3df，2p）// B3LYP / 6-31g（d）处计算得出的。提出了一种新的反应路径：C = C（C·）COOH <-> C = C（C·）CO·+ OH <-> C = Y（CCOC）+ OH，其负责亚甲基环氧乙烷的形成（Y =循环）。 C = C（C·）COOH反应生成C = C（C·）CO·+ 0H的反应势垒为42.45（41.90）kcal / mol，A因子为4 * 10〜（15）s〜 （-1）。计算C = C（C·）COOH→TS5→C = Y（CCOC）+ OH的反应势垒为42.14 kcal / mol，在743处的A因子为6.95 * 10〜（11）s〜（-1） K.

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