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卤代苯与酚类化合物反应制取二芳基醚是现代有机合成中的一个重要反应.传统的二苯醚合成方法是铜催化卤代苯与酚类化合物的Ullmann型C-O偶联反应,但是这种方法需要苛刻的反应条件.后来,人们发现了Pd(0)和Cu(Ⅰ)基催化剂,但是前者成本较高,且需要使用昂贵的配体,因此其应用受到了限制,而铜作为一种成本较低的催化剂受到了越来越多的关注.铜催化剂可以分为均相和非均相两大类.均相铜催化剂使用的是铜盐,并且需要加入配体,成本较高,且不易分离和循环利用.非均相铜催化剂研究较多的是CuO,Cu_2O及Cu纳米颗粒,其中Cu_2O纳米颗粒催化剂对Ullmami型C-O偶联反应具有很高的催化活性,但是它在潮湿的空气中容易被氧化,因此需要寻找一种合适的载体防止Cu_2O纳米颗粒被氧化.SiC具有优良的化学稳定性及导电导热性能,并且作为载体已经成功应用到很多热催化及光催化反应中.本文以高比表面积的SiC为载体,以二乙二醇作为溶剂和还原剂,采用传统的两步液相还原法制备了Cu_2O/SiC催化剂,并通过X射线衍射、X射线光电子能谱、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和H_2程序升温还原等方法对Cu_2O/SiC催化剂进行了表征.SEM和TEM结果表明,Cu_2O纳米颗粒均匀分散在SiC表面,同时上述表征结果都表明Cu在SiC上主要以Cu_2O的形式存在.将制备的Cu_2O/SiC催化剂用于催化卤代芳烃与酚类的Ullmami C-O偶联反应中.以碘苯和苯酚的Ullmami C-O偶联反应为模型实验,考察了反应温度、反应时间、溶剂、碱的种类及用量和催化剂用量等条件的影响,得到了碘苯与苯酚Ullmami C-O偶联反应的最优反应条件为:卤代芳烃14 mmol,酚类14 mmol,1.0当量的Cs_2CO_3,Cu_2O/SiC(5 wt%)10 mg,四氢呋喃10 mL,在Ar气氛下150℃反应3h.在该条件下,二苯醚收率达到97%,转化频率(TOF)高达1136 h~(-1).Cu_2O/SiC催化剂对Ullmann C-O偶联反应具有很好的普适性,并且对Ullmann C-S偶联反应也表现出很高的活性,TOF高达1186 h~(-1).以碘苯和苯酚的Ullmami C-O偶联反应为基准实验,对催化剂的循环稳定性进行了考察.Cu_2O/SiC催化剂五次循环后二苯醚的收率从97%降低至64%,这主要是由于活性组分Cu_2O的流失所致.
The reaction of halogenated benzene with phenolic compounds to produce diaryl ethers is an important reaction in modern organic synthesis. The conventional synthesis of diphenyl ethers is copper-catalyzed Ullmann-type CO coupling reaction of halogenated benzene with phenolic compounds, but This method requires harsh reaction conditions.Next, Pd (0) and Cu (I) -based catalysts were discovered, but the former is costly and requires the use of expensive ligands, so its use is limited and copper as a A less costly catalyst is receiving more and more attention.Copper catalysts can be divided into two kinds: homogeneous and heterogeneous.Homogeneous copper catalysts use copper salts, and the ligands need to beadded with high cost , And difficult to separate and recycle.The heterogeneous copper catalysts are mostly CuO, Cu_2O and Cu nanoparticles, of which Cu_2O nanoparticle catalyst has a high catalytic activity for Ullmami CO coupling reaction, The air is easy to be oxidized, so we need to find a suitable carrier to prevent the oxidation of Cu 2 O nanoparticles.SiC has excellent chemical stability and electrical conductivity, and as a carrier has been successfully applied to a lot of thermal catalytic and photocatalytic Reaction.In this paper, the high specific surface area of SiC as a carrier, with diethylene glycol as a solvent and reductant, prepared by conventional two-step liquid phase reduction Cu_2O / SiC catalyst, and by X-ray diffraction, X-ray photoelectron energy The results of SEM and TEM show that the Cu 2 O nanoparticles are uniformly dispersed on the surface of SiC and the above characterization results Both showed that Cu existed mainly in the form of Cu_2O on SiC. The prepared Cu_2O / SiC catalyst was used to catalyze Ullmami CO coupling reaction of halogenated aromatics and phenols. Ullmami CO coupling reaction of iodobenzene and phenol was used as a model The optimum reaction conditions for the coupling reaction of iodobenzene with phenol Ullmami CO were obtained as follows: halogenated aromatic hydrocarbon 14 mmol, phenol (14 mmol), 1.0 equivalent of Cs 2 CO 3, 10 mg of Cu 2 O / SiC (5 wt%) and 10 mL of tetrahydrofuran were reacted at 150 ℃ for 3 h under Ar atmosphere. Under these conditions, the yield of diphenyl ether reached 97% TOF) up to 1136 h ~ (-1). Cu_2O / SiC catalyst has good universality to Ullmann CO coupling reaction and also shows high activity to Ullmann CS coupling reaction with TOF up to 1186 h ~ (-1) .Ulmami with iodobenzene and phenol CO coupling reaction as a benchmark experiment, the cyclic stability of the catalyst was investigated.Cu 2 O / SiC catalyst after five cycles of diphenyl ether yield decreased from 97% to 64%, mainly due to the loss of Cu 2 O Due.