Abstract Hydroxyl groups are one of the key factors for the development of coal spontaneous combustion. Although the reaction mechanism has been studied by many scholars, the effects of their positions in the molecule on the reaction characteristics have not been considered. In this paper, Ph-CH2-CH3 was selected as the basic unit to construct small coal molecule models with one hydroxyl at different positions. The microscopic parameters of each model were calculated by density functional theory (DFT), and the elementary reaction pathways and thermodynamic parameters of hydroxyl groups were explored. It was found that the hydrogen of -OH is the active site of nucleophilic reaction, the Cα-H bond of α-phenethyl alcohol and the O-H bonds of the other molecules are most vulnerable to oxygen. All the models can generate H2O in the process of oxidation, other products of alcoholic hydroxyl groups are highly active oxygen-containing free radicals, while that of phenolic hydroxyl groups are quinones or ketones. The results of intrinsic reaction coordinate (IRC) indicated that hydrogen captured by oxygen is endothermic, while the ·OH free radical capturing hydrogen is exothermic. The activation energy of oxygen capturing hydrogen is 98∼182 kJ/mol, which shows that the reaction can occur in the middle stage of coal spontaneous combustion (70∼120 ℃), and the reaction rate gradually accelerate with the increase of temperature. In the same conditions, the order of the oxidation reaction rates is 2-ethyl phenol > 3-ethyl phenol > 4-ethyl phenol > α-phenethyl alcohol > β-phenethyl alcohol, which is the same as the order of reaction activities but opposite to that of activation energies. The research is helpful to strengthen the judgment of coal spontaneous combustion risk and the development of flame retardant.

中文翻译：

---

煤自燃过程中不同位置羟基反应特性的量子化学计算

摘要 羟基是煤自燃发展的关键因素之一。虽然许多学者对反应机理进行了研究，但尚未考虑它们在分子中的位置对反应特性的影响。本文以Ph-CH2-CH3为基本单元构建不同位置具有一个羟基的煤小分子模型。采用密度泛函理论（DFT）计算各模型的微观参数，探索羟基的基元反应途径和热力学参数。发现-OH的氢是亲核反应的活性位点，α-苯乙醇的Cα-H键和其他分子的OH键对氧最敏感。所有模型在氧化过程中都会产生H2O，醇羟基的其他产物是高活性的含氧自由基，而酚羟基的产物是醌或酮。本征反应坐标(IRC)结果表明，氧捕获的氢是吸热的，而·OH自由基捕获的氢是放热的。氧捕氢活化能为98～182 kJ/mol，表明反应可发生在煤自燃中期（70～120℃），且反应速率随温度升高而逐渐加快。在相同条件下，氧化反应速率顺序为2-乙基苯酚>3-乙基苯酚>4-乙基苯酚>α-苯乙醇>β-苯乙醇，与反应活性顺序相同但相反到活化能。