A cobalt-substituted Keggin-type polyoxometalate for catalysis of oxidative aromatic cracking reactions in water
A cobalt-substituted Keggin-type polyoxometalate for catalysis of oxidative aromatic cracking reactions in water
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DOI：
10.1039/d0cy01758b
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发表时间：
2020-12
影响因子：
5
通讯作者：
Yoshihiro Shimoyama;S. Tamura;Y. Kitagawa;Dachao Hong;Y. Kon
中科院分区：
文献类型：
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作者：
Yoshihiro Shimoyama;S. Tamura;Y. Kitagawa;Dachao Hong;Y. Kon
有效地将水中有害的苯环解毒为有用的羧酸是实现清洁水环境所不可或缺的。我们在本文中报道了在温和条件下使用具有钴取代的Keggin型聚氧乙烯酸盐（Co-POM）作为催化剂、Oxone®单过硫酸盐化合物作为牺牲氧化剂和碳酸氢钠作为添加剂的催化体系实现水中的氧化芳烃裂化（OAC）反应。碳酸氢钠在以乙基苯磺酸盐为模型底物的Co-POM选择性OAC反应中起着至关重要的作用。反应物种，其特征在于是钴（III）-氧基物种的基础上，31 P NMR，紫外-可见光谱，动力学，和理论分析。亲电性的钴（III）-氧基物种证明了一个负斜率的Hammett图中的初始速率从间二甲苯磺酸衍生物的OAC反应的线性关系。此外，我们还以苯为模型底物，验证了OAC在催化体系中的降解途径。根据1H NMR光谱分析，降解是通过钴（III）-氧自由基物质对苯的亲电攻击来引发的，产生苯酚，然后产生邻苯二酚、粘康酸、马来酸/富马酸、酒石酸衍生物和甲酸。
Efficient detoxification of harmful benzene rings into useful carboxylic acids in water is indispensable for achieving a clean water environment. We report herein that oxidative aromatic cracking (OAC) reactions in water were achieved using a catalytic system with a cobalt-substituted Keggin-type polyoxometalate (Co-POM) as a catalyst, an Oxone® monopersulfate compound as a sacrificial oxidant and sodium bicarbonate as an additive under mild conditions. Sodium bicarbonate plays a crucial role in the selective OAC reactions by Co-POM using ethylbenzenesulfonate as a model substrate. The reactive species was characterized to be a cobalt(III)-oxyl species based on 31P NMR, UV-vis spectroscopic, kinetic, and theoretical analyses. The electrophilicity of the cobalt(III)-oxyl species was demonstrated by a linear relationship with a negative slope in the Hammett plots of initial rates obtained from the OAC reactions of m-xylenesulfonate derivatives. Besides, we have verified the degradation pathway of the OAC reactions using benzene as a model substrate in the catalytic system. The degradation was initiated by an electrophilic attack of the cobalt(III)-oxyl species on benzene to yield phenol followed by producing catechol, muconic acid, maleic/fumaric acid, tartaric acid derivatives and formic acid on the basis of 1H NMR spectroscopic analysis.