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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Reactions of H_3O~+ (H_2O)_(0,1) with Alkylbenzenes from 298 to 1200 K
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Reactions of H_3O~+ (H_2O)_(0,1) with Alkylbenzenes from 298 to 1200 K

机译：H_3O〜+（H_2O）_（0,1）与298-1200 K烷基苯的反应

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摘要

Rate constants and branching fractions have been measured for the reactions of H_3O~+ and H_3O~+ (H_2O) with toluene (C_7H_8), ethylbenzene (C_8H_(10)), and n-propylbenzene (C_9H_(12)) as a function of temperature using a variable temperature-selected ion flow tube (VT-SIFT) and a high-temperature flowing afterglow (HTFA). The reactions have been studied up to 1200, 1000, and 900 K for toluene, ethylbenzene, and n-propylbenzene, respectively. The measurements are the first for H_3O~+ (H_2O) with these reactants. The H_3O~+ + alkylbenzene reaction rate constants are equal to the collision rate constants given by the Su-Chesnavich equation at all temperatures. Both nondissociative and dissociative proton-transfer products are observed. H_3O~+ reacts with toluene above 900 K to produce C_7H_9~+, C_7H_7~+, and C_6H_5~+ predominately, whereas only C_7H_9~+ is observed at lower temperatures. Proton transfer from H_3O~+ to ethylbenzene produces C_8H_(11)~+ exclusively at 300 K, and by 800 K, C_6H_7~+ is the major product with only minor amounts of C_8H_(11)~+ and C_7H_7~+ being formed. Both nondissociative and dissociative proton-transfer products are observed at all temperatures for H_3O~+ reacting with propylbenzene producing C_9H_(13)~+ as the major product at low temperatures and C_6H_7~+ and C_3H_7~+ as the major products at temperatures above 650 K, with minor amounts of C_7H_7~+ observed at all temperatures. For all three alkylbenzenes reacting with H_3O~+ (H_2O), nondissociative proton transfer dominates at low temperature; however, at 300 K, an association complex of all three alkylbenzenes with H_3O~+ (H_2O) is observed (14-18%). At higher temperatures, dissociative proton transfer is observed for H_3O~+ (H_2O) reacting with ethyl- and propylbenzene with similar product yields as observed in the H_3O~+ reactions. All of the H_3O~+ (H_2O) + alkylbenzene proton-transfer reactions are fast even though the proton affinity of H_3O~+ (H_2O) is 140 kJ mol~(-1) less than that of H_3O~+ making the H_3O~+ (H_2O) reactions endothermic. More specifically, the rate constant for the reaction of H_3O~+ (H_2O) with toluene is ca. half the collision rate constant at 300 K and equal to the collision rate constant at temperatures above 300 K even though the reaction is endothermic by 25 kJ mol~(-1). Similarly, the reaction rate constants for H_3O~+ (H_2O) reacting with ethyl- and propylbenzene are equal to the collision rate constant at all temperatures despite being endothermic by 21 and 19 kJ mol~(-1), respectively. Therefore, predictions based simply on reaction energetics would severely underestimate the reactivity of H_3O~+ (H_2O) with these alkylbenzenes. The possibilities of neutral water dimer production, ligand switching, uncertainties in the thermochemical data, and decomposition of the ionic products are considered to rationalize the observation of proton transfer where it is not thermodynamically feasible.
机译：测量了H_3O〜+和H_3O〜+（H_2O）与甲苯（C_7H_8），乙苯（C_8H_（10））和正丙基苯（C_9H_（12））反应的速率常数和支化分数使用可变温度选择离子流管（VT-SIFT）和高温流动余辉（HTFA）调节温度。对甲苯，乙苯和正丙基苯的反应分别进行了高达1200、1000和900 K的研究。对于这些反应物，H_3O〜+（H_2O）的测量是首次。在所有温度下，H_3O〜+ +烷基苯反应速率常数等于Su-Chesnavich方程给出的碰撞速率常数。观察到非解离和解离质子转移产物。 H_3O〜+与900 K以上的甲苯反应生成C_7H_9〜+，C_7H_7〜+和C_6H_5〜+，而在较低温度下仅观察到C_7H_9〜+。从H_3O〜+到乙苯的质子转移仅在300 K时产生C_8H_（11）〜+，而到800 K时，C_6H_7〜+是主要产物，仅形成少量C_8H_（11）〜+和C_7H_7〜+。在所有温度下均观察到非解离和解离质子转移产物，H_3O〜+与丙苯在低温下以C_9H_（13）〜+为主要产物，而C_6H_7〜+和C_3H_7〜+在650以上的温度为主要产物。 K，在所有温度下均观察到少量C_7H_7〜+。对于与H_3O〜+（H_2O）反应的所有三个烷基苯，在低温下非解离质子转移占主导。然而，在300 K时，观察到所有三个烷基苯与H_3O〜+（H_2O）的缔合络合物（14-18％）。在较高的温度下，观察到H_3O〜+（H_2O）与乙苯和丙基苯反应的解离质子转移，其产物收率与H_3O〜+反应中观察到的相似。尽管H_3O〜+（H_2O）的质子亲和力比H_3O〜+的质子亲和力低140 kJ mol〜（-1），但所有的H_3O〜+（H_2O）+烷基苯质子转移反应都很快。 （H_2O）反应吸热。更具体地，H_3O〜+（H_2O）与甲苯反应的速率常数为约。即使反应吸热25 kJ mol〜（-1），在300 K时碰撞速率常数的一半也等于在300 K以上温度时的碰撞速率常数。同样，H_3O〜+（H_2O）与乙苯和丙苯反应的反应速率常数在所有温度下均等于碰撞速率常数，尽管它们分别吸热21 kJ mol〜（-1）。因此，仅基于反应能学的预测将严重低估H_3O〜+（H_2O）与这些烷基苯的反应性。中性水二聚体的产生，配体转换，热化学数据的不确定性以及离子产物的分解的可能性被认为是合理化在热力学上不可行的质子转移的观察结果。

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