摘要
甲酰胺是重要的化工原料,广泛应用于农药和医药生产中,其合成方法备受关注.目前,主要通过胺与不同甲酰化试剂(甲酸、甲酸盐、甲酰胺和CO_(2)等)的N-甲酰化反应合成甲酰胺.但由于转酰化反应生成的副产物不可避免,原子经济性100%的直接甲酰化成为更理想的合成路径.典型的甲酰胺代表是N,N-二甲基甲酰胺(DMF),工业上通过CH3OH-NaOCH3催化剂催化二甲胺和CO直接甲酰化生成DMF.近年研究者发展了多种直接甲酰化的催化体系,例如N-杂环卡宾、KOH、K2CO3和Co@N掺杂碳催化剂和PdCo双金属催化剂等.本课题组也报道了Ru修饰的氧化铈(Ru/CeO_(2))和羟基磷灰石(Ru-HAP)催化的胺直接甲酰化(Green Chem.,2017,19,88-92和ChemCatChem,2021,13,41594163).然而,相较于伯胺,仲胺的直接甲酰化合成甲酰胺更加困难.因此,开发一种新的仲胺转化策略进而合成高附加值的甲酰胺非常必要.本文发展了一种基于羟基磷灰石负载的钌基催化剂(Ru-HAP)的接力催化策略,以实现仲胺转化为甲酰胺.并以二甲胺为例,研究了仲胺比伯胺难活化的原因.测试了甲胺和二甲胺的直接甲酰化活化能,结果表明,二甲胺与CO甲酰化反应的活化能(67.2 kJ·mol^(-1))高于甲胺与CO反应的活化能(47.6 kJ·mol^(-1)).而甲基甲酰胺与二甲胺转酰化合成DMF的活化能仅为29.9 kJ·mol^(-1)因此该反应更很容易进行.设计接力催化策略,首先甲胺与CO的进行甲酰化反应,生成的甲基甲酰胺可以作为甲酰化试剂再参与二甲胺的转酰化过程生成DMF.为实现上述接力策略,要求催化剂具有双重功能,即在第一步作为甲酰化活性位点,在第二步促进转酰化过程,进而获得DMF.利用过渡金属催化剂对甲酰化反应进行研究,结果表明,酸碱催化剂可有效催化转酰化反应.Ru-HAP由表面的RuOx和具有酸碱性质的载体HAP组成,是实现接力催化二甲胺高效转化的良好候选材料.红外光谱结果表明,Ru-HAP的RuOx物种可以同时激活胺和CO,是甲酰化反应的活性位点.结合实验结果,推测载体HAP是转酰化的活性位点.基于以上结果,提出了Ru-HAP接力催化促进二甲胺转化为DMF的机理.由于甲胺的甲酰化反应活化能较低,可以优先在RuOx物种上反应,随后,生成的甲基甲酰胺(MF)作为甲酰化试剂参与HAP催化的与二甲胺的转酰化合成DMF.在接力催化路径下,DMF的产率高达82%,远高于二甲胺直接甲酰化的产率(32%).此外,环境影响因子分析表明,新的合成DMF的接力策略比直接甲酰化过程对环境更友好,产生更少的废弃物.本文提出了一种以甲胺为促进剂,通过羟基磷灰石负载的Ru基催化剂(Ru-HAP)进而降低二甲胺生成DMF活化能的接力催化策略.利用该接力催化策略实现了二甲胺高效转化为甲酰胺.相比于直接甲酰化,接力催化策略减少了DMF进一步转化生成的副产物,并为仲胺转化为甲酰胺提供了新思路.
The direct formylation of amines with CO is an ideal way to produce formamides with 100%atom economy.However,the conversion of secondary amines via this process remains a great challenge owing to their low reactivity.In this study,a relay catalysis strategy was developed to lower the activation energy of dimethylamine to N,N′-dimethyl formaldehyde(DMF)over a Ru-hydroxyapatite(Ru-HAP)catalyst,with methylamine as a promoter.Through the relay catalysis of RuOx and HAP,the formylation of dimethylamine consists of two steps:(1)efficient direct formylation of methylamine with CO to produce the active intermediate methylformamide(MF)over RuOx species owing to its low activation energy,and(2)transformylation reaction of dimethylamine with the generated MF to produce DMF under the acid-base catalysis of HAP.Up to 82%yield of DMF was achieved,which is much higher than that with direct formylation of dimethylamine(32%).In addition,the lower environmental impact factor suggested that the relay catalysis strategy not only decreased the waste of DMF production,but also lowered the energy consumption for separation.This study presents a new path for the conversion of secondary amines to formamides.
作者
焦东霞
安静华
李会香
黄志鹏
王业红
王峰
Dongxia Jiao;Jinghua An;Huixiang Li;Zhipeng Huang;Yehong Wang;Feng Wang(State Key Laboratory of Catalysis,Dalian National Laboratory for Clean Energy,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning,China;University of Chinese Academy of Sciences,Beijing 100049,China;College of Chemistry,Chemical Engineering and Materials Science,Key Laboratory of Molecular and Nano Probes,Ministry of Education,Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in University of Shandong,Institute of Molecular and Nano Science,Shandong Normal University,Jinan 250014,Shandong,China)
基金
国家自然科学基金(22025206,21991090,21972139,22002076)
大连市高层人才创新支持计划(2020RT10)
辽宁振兴人才计划(XLYC2002012)
大连化学物理研究所基金(DICP I202234).
