Temperature‐dependent kinetics of the reactions of CH 2 OO with acetone, biacetyl, and acetylacetone
Temperature‐dependent kinetics of the reactions of CH 2 OO with acetone, biacetyl, and acetylacetone
复制标题
CH 2 OO 与丙酮、联乙酰和乙酰丙酮反应的温度依赖性动力学
DOI：
10.1002/kin.21625
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发表时间：
2023
影响因子：
1.5
通讯作者：
Murray, Craig
中科院分区：
文献类型：
--
作者：
Cornwell, Zachary A.;Enders, Jonas J.;Harrison, Aaron W.;Murray, Craig
利用闪光光解瞬态吸收光谱技术，在275-335 K范围内测量了丙酮（Ac）、丁二酮（BiAc）和乙酰丙酮（AcAc）与CH 2 OO反应的温度依赖性速率常数。测量在N2浴气体中在1080托的总压力下进行，其对应于这些反应的高压极限。所有三个反应都显示出具有负温度依赖性的线性Arrhenius图。在整个温度范围内，速率常数按Ac < AcAc <BiAc的顺序增加;在295 K时，速率常数为kAc =（4.8 ± 0.4）× 10- 13 cm 3s-1，kAcAc=（8.0 ± 0.7）× 10- 13 cm 3s-1，kBiAc =（1.10 ± 0.09）× 10- 11 cm 3s-1。对温度的敏感性以负活化能的大小为特征，其增加的顺序为AcAc < BiAc < Ac（Ea/R值分别为-1830 ± 170 K、-1260 ± 170 K和-460 ± 180 K）。CBS-QB 3计算表明，Ac和BiAc反应通过形成入口通道络合物，然后通过浸没过渡态进行1，3-偶极环加成以形成次级臭氧化物产物。对于BiAc反应，速率限制步骤似乎是将长程货车德瓦尔斯络合物重排为短程络合物，随后直接导致具有非常低的能垒的环加成过渡态。计算结果表明，AcAc的两条反应途径是竞争性的，在主要的烯醇酮互变异构体的C=O位和C=C位上的环加成过渡态自由能（ΔG° = +10.1 kcal mol-1，298 K）几乎相同.观察到的弱温度依赖性可能是由于这些途径之间的竞争。
Temperature‐dependent rate constants for the reactions of CH2OO with acetone (Ac), biacetyl (BiAc), and acetylacetone (AcAc) have been measured over the range 275–335 K using a flash photolysis, transient absorption spectroscopy technique. The measurements were performed at a total pressure of ∼80 Torr in N2bath gas, which corresponds to the high‐pressure limit for these reactions. All three reactions show linear Arrhenius plots with negative temperature dependences. Rate constants increase in the order Ac < AcAc « BiAc across the temperature range; at 295 K the rate constants arekAc= (4.8 ± 0.4) × 10–13cm3s–1,kAcAc= (8.0 ± 0.7) × 10–13cm3s–1, andkBiAc= (1.10 ± 0.09) × 10–11cm3s–1. Sensitivity to temperature, characterized by the magnitude of the negative activation energy, increases in the order AcAc < BiAc < Ac (Ea/Rvalues of –1830 ± 170 K, –1260 ± 170 K, and –460 ± 180 K, respectively). CBS‐QB3 calculations show that the Ac and BiAc reactions proceed via formation of an entrance channel complex followed by 1,3‐dipolar cycloaddition to form secondary ozonide products via a submerged transition state. For the BiAc reaction, the rate limiting step appears to be rearrangement of a long‐range van der Waals complex into the short‐range complex that subsequently leads directly to the cycloaddition transition state with a very low energy barrier. The calculations show that two reaction pathways are competitive for AcAc with nearly identical transition state free energies (ΔG° = +10.1 kcal mol–1at 298 K) found for cycloaddition at the C=O and at the C=C site of the dominant enolone tautomer. The weak temperature dependence observed is likely due to competition between these pathways.