The reversible reaction of OH radicals with 1,2,4,5-tetramethylbenzene (1245-TeMB, durene) leads to adducts at the substituted (ipso) and unsubstituted (ortho) positions of the ring. By the use of flash photolysis for production and resonance fluorescence for detection of OH, the gas-phase reactions of O₂ with these adducts were investigated over the temperature range of 300–340 K in He at 200 mbar. The decay of OH, generated by pulsed vacuum-UV photolysis of H₂O, was monitored under slow-flow conditions in the presence of 1245-TeMB and O₂ at concentrations of up to 19 × 10¹² cm^–3 and 2 × 10¹⁶ cm^–3, respectively. Triexponential OH decays resulted from the unimolecular decomposition of the two adducts, representing OH reservoirs with different stabilities. In the presence of O₂, additional adduct loss pathways exist, leading to faster OH consumption. Triexponential functions fitted to these decays were analyzed to obtain rate constants for the reactions of O₂ with both adducts. Rate constants in the range of (4–13) × 10^–15 and (0.3–3) × 10^–15 cm³ s^–1 were obtained for the ortho and the ipso adducts, respectively, depending on temperature and assumptions regarding details of the underlying mechanism of adduct isomer formation and isomerization. At O₂ concentrations exceeding about 1 × 10¹⁶ cm^–3, deviations from a linear dependence of the adduct loss rates on the O₂ concentration indicate an even more complex mechanism. The validity of the rate constants is therefore confined to O₂ concentrations below 1 × 10¹⁶ cm^–3. The adduct + O₂ rate constants for 1245-TeMB are greater than the corresponding previously obtained rate constants for benzene, toluene, and p- and m-xylene but smaller than those for hexamethylbenzene. The results are discussed in terms of the current knowledge about the mechanism of OH-induced degradation of aromatic compounds in the presence of O₂.

中文翻译：

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Ortho 和 Ipso 加合物 1,2,4,5-四甲基苯-OH 与 O2 的气相反应动力学

OH 自由基与 1,2,4,5-四甲基苯（1245-TeMB，durene）的可逆反应会在环的取代（同位）和未取代（邻位）位置产生加合物。通过使用闪光光解生产和共振荧光检测 OH，研究了O ₂与这些加合物的气相反应，在 200 毫巴的 He 中，在 300-340 K 的温度范围内。OH的衰减，通过H的脉冲真空紫外光解产生₂ O，用缓慢流动条件下在1245-天博和O的存在下监测₂在高达的浓度至19×10 ¹²厘米^-3和2×10 ¹⁶厘米^–3， 分别。三指数 OH 衰减是由两种加合物的单分子分解引起的，代表具有不同稳定性的 OH 储层。在 O ₂存在下，存在额外的加合物损失途径，导致更快的 OH 消耗。分析拟合这些衰变的三指数函数以获得O ₂与两种加合物反应的速率常数。分别获得了邻位加合物和 ipso 加合物在 (4–13) × 10 ^–15和 (0.3–3) × 10 ^–15 cm ³ s ^–1范围内的速率常数，这取决于温度和有关细节的假设加合物异构体形成和异构化的潜在机制。在 O ₂当浓度超过约 1 × 10 ¹⁶ cm ^{–3 时}，加合物损失率对 O ₂浓度的线性依赖性的偏差表明了一种更加复杂的机制。因此，速率常数的有效性仅限于低于 1 × 10 ¹⁶ cm ^{–3 的}O ₂浓度。1245-TeMB的加合物 + O ₂速率常数大于先前获得的苯、甲苯和p - 和m的相应速率常数-二甲苯但比六甲苯小。根据目前关于在 O ₂存在下 OH 诱导芳香族化合物降解机制的知识来讨论结果。