Chemical Engineering Department, Al-Hussein Bin Talal University, Ma'an, Jordan.
J Phys Chem A. 2010 Jan 21;114(2):1060-7. doi: 10.1021/jp909025s.
This study develops the reaction pathway map for the unimolecular decomposition of catechol, a model compound for various structural entities present in biomass, coal, and wood. Reaction rate constants at the high-pressure limit are calculated for the various possible initiation channels. It is found that catechol decomposition is initiated dominantly via hydroxyl H migration to a neighboring ortho carbon bearing an H atom. We identify the direct formation of o-benzoquinone to be unimportant at all temperatures, consistent with the absence of this species from experimental measurements. At temperatures higher than 1000 K, water elimination through concerted expulsion of a hydroxyl OH together with an ortho H becomes the most significant channel. Rice-Ramsperger-Kassel-Marcus simulations are performed to establish the branching ratio between these two important channels as a function of temperature and pressure. All unimolecular routes to the reported major experimental products (CO, 1,3-C(4)H(6) and cyclo-C(5)H(6)) are shown to incur large activation barriers. The results presented herein should be instrumental in gaining a better understanding of the decomposition behavior of catechol-related compounds.
本研究提出了儿茶酚（一种存在于生物质、煤和木材中各种结构单元的模型化合物）的单分子分解反应途径图。针对各种可能的引发通道，计算了高压极限下的反应速率常数。研究发现，儿茶酚的分解主要通过羟基 H 迁移到邻位碳原子上，该碳原子上带有 H 原子。我们发现，邻苯醌的直接形成在所有温度下都不重要，这与实验测量中未检测到该物质的结果一致。在高于 1000 K 的温度下，通过协同逐出羟基 OH 和邻位 H 的方式脱水成为最重要的通道。进行 Rice-Ramsperger-Kassel-Marcus 模拟，以确定这两个重要通道的分支比作为温度和压力的函数。研究表明，报道的主要实验产物（CO、1,3-C(4)H(6)和环己 C(5)H(6)）的所有单分子途径都存在较大的活化能垒。本文的研究结果应该有助于更好地理解儿茶酚类化合物的分解行为。
