Lifshitz Assa, Tamburu Carmen, Suslensky Aya, Dubnikova Faina
Department of Physical Chemistry, The Hebrew University, Jerusalem 91904, Israel.
J Phys Chem A. 2006 Jul 13;110(27):8248-58. doi: 10.1021/jp056339v.
The thermal decomposition of anthranil diluted in argon was studied behind reflected shock waves in a 2 in. i.d. pressurized driver single-pulse shock tube over the temperature range 825-1000 K and overall densities of approximately 3 x 10(-5) mol/cm(3). Two major products: aniline and cyclopentadiene carbonitrile (accompanied by carbon monoxide) and four minor products resulting from the decomposition were found in the postshock samples. They were, in order of decreasing abundance, pyridine, CH(2)=CHCN, HCN and CHC-CN, and comprised only a few percents of the overall product distribution. Quantum chemical calculations were carried out to determine the sequence of the unimolecular reactions that lead to the formation of cyclopentadiene carbonitrile and of phenylnitrene/phenylimine that are the precursors of aniline. They form aniline by reactions with traces of water impurities. To produce cyclopentadiene carbonitrile, two main processes must take place: CO elimination and ring contraction from a six- to a five-membered ring. It was shown that this can occur via two parallel pathways where CO elimination takes place prior to or following ring contraction. Singlet potential energy surfaces for all the elementary reactions that lead to the formation of cyclopentadiene carbonitrile and phenylnitrene/phenylimine were obtained. Their rate constants were calculated on the basis of the results of the quantum chemical calculations using transition-state theory. A kinetic scheme containing these reactions was constructed and multiwell calculations were performed to evaluate the mole percent of the products as a function of temperature. A very serious disagreement between the experimental results and the results of calculations showed that the singlet PESs could not account for the observed experimental rates. No other singlet PESs that lead to the formation of these products could be found. In view of this observation, attempts to find pathways that lead to the formation of cyclopentadiene carbonitrile and phenylnitrene/phenylimine on triplet surfaces were made. Such surfaces were found, and singlet <--> triplet intersystem crossing probabilities and crossing rate constants were calculated as well as the rate constants of all the elementary steps on the triplet surfaces. A reaction scheme was constructed and multiwell calculations were performed, including also the pathways on the singlet surfaces, to evaluate the mole percent of the products as a function of temperature. The agreement between the experimental results and these calculations was quite satisfactory.
在内径为2英寸的加压驱动单脉冲激波管中，于825 - 1000 K的温度范围以及约3×10⁻⁵ mol/cm³的总密度条件下，研究了氩气稀释的邻氨基苯甲酸在反射激波后的热分解。在激波后样品中发现了两种主要产物：苯胺和环戊二烯腈（伴有一氧化碳），以及分解产生的四种次要产物。按丰度递减顺序，它们依次为吡啶、CH₂=CHCN、HCN和CHC - CN，且仅占总产物分布的百分之几。进行了量子化学计算，以确定导致环戊二烯腈以及苯胺前体苯氮烯/苯亚胺形成的单分子反应顺序。它们通过与痕量水杂质的反应形成苯胺。为了生成环戊二烯腈，必须发生两个主要过程：CO消除以及从六元环到五元环的环收缩。结果表明，这可以通过两条平行途径发生，其中CO消除在环收缩之前或之后进行。获得了所有导致环戊二烯腈和苯氮烯/苯亚胺形成的基元反应的单重态势能面。基于量子化学计算结果，使用过渡态理论计算了它们的速率常数。构建了包含这些反应的动力学方案，并进行了多阱计算，以评估产物的摩尔百分比随温度的变化。实验结果与计算结果之间存在非常严重的分歧，表明单重态势能面无法解释观察到的实验速率。未发现导致这些产物形成的其他单重态势能面。鉴于此观察结果，尝试在三重态表面上寻找导致环戊二烯腈和苯氮烯/苯亚胺形成的途径。找到了这样的表面，并计算了单重态⇄三重态系间窜越概率和窜越速率常数以及三重态表面上所有基元步骤的速率常数。构建了一个反应方案并进行了多阱计算，其中也包括单重态表面上的途径，以评估产物的摩尔百分比随温度的变化。实验结果与这些计算之间的一致性相当令人满意。
