Ionic Liquid-Mediated Urea Pyrolysis to Cyanuric Acid: Experimental Protocol and Mechanistic Insights
Ionic Liquid-Mediated Urea Pyrolysis to Cyanuric Acid: Experimental Protocol and Mechanistic Insights
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DOI：
10.1021/acs.iecr.2c02791
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发表时间：
2022-10
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通讯作者：
Yusif Abdullayev;Valentina Javadova;I. Valiyev;A. Talybov;Cavanshir Salmanov;J. Autschbach
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作者：
Yusif Abdullayev;Valentina Javadova;I. Valiyev;A. Talybov;Cavanshir Salmanov;J. Autschbach
三聚尿酸（CA）是阻止水中氯光降解的关键前体。因此，CAis在工业上主要用作氯稳定剂。与尿素相比，尿素的成本较高，需要一个经济的生产方案。作为现有方法的替代方案，我们首次提出了氢硫酸二甲基铵[dmaH][HSO4]离子液体（IL）介导的尿素热解方法。根据时间、催化剂负载、溶剂和温度等参数对反应进行优化。优化后的方法不需要使用溶剂；IL作为溶剂/催化剂体系，在220°C条件下，在30分钟内产生ecain，产率为70%。IL催化剂的循环使用试验表明，该催化剂可重复使用4次而不损失催化活性。利用密度泛函理论研究了IL对尿素热解反应的催化活性。计算了尿素转化toca3的反应谱，按照二缩脲、三缩脲和三缩脲环化步骤进行，每个步骤都有氨的挤压。还包括无IL反应谱，以观察IL在反应中的作用。考虑到异氰酸（ICA）作为尿素热解产物之一的实验观察，我们还测试了异氰酸（ICA）通过三聚化的构象可能性。计算表明，aticaformation （TS-ICA， ΔG‡= 27.1 kcal/mol）比biuret formation （TS1-IL， ΔG‡= 41.2 kcal/mol）低14.1 kcal。进一步的机理研究表明，尿素热解遵循直接的三聚化路线。
Cyanuric acid (CA) is a critical precursor preventing the photodegradation of chlorine in water. So mainly,CAis utilized in the industry as a chlorine stabilizer. Compared to urea, the higher cost ofCAnecessitates an economic protocol to produce. As an alternative to current methods, we proposed dimethyl ammonium hydrosulfate [dmaH][HSO4] ionic liquid (IL)-mediated urea pyrolysis toCAfor the first time. The reaction was optimized based on changing parameters: time, catalyst loading, solvent, and temperature. The optimized method does not require solvent utilization; IL acts as a solvent/catalyst system to produceCAin an ∼70% yield at 220 °C in 30 min. The recycle test of the IL catalyst shows that it can be reused four times without the loss of catalytic activity. The IL catalytic activities on the urea pyrolysis reaction are studied using density functional theory (DFT). The reaction profile of urea conversion toCAis calculated to follow biuret, triuret, and triuret cyclization steps, with extrusion of ammonia in each step. The IL-free reaction profile is also included to observe the IL role in the reaction. Considering experimental observation of isocyanic acid (ICA) as one of the urea pyrolysis products, we also testedCAformation possibilities viaICAtrimerization. The calculations show thatICAformation (TS-ICA, ΔG‡= 27.1 kcal/mol) is 14.1 kcal lower than biuret formation (TS1-IL, ΔG‡= 41.2 kcal/mol). Further mechanistic studies imply that urea pyrolysis toCAfollows a straightforwardICAtrimerization route.