黃 強(qiáng),周麗梅,蔣曉慧,周婭芬,郎文成

(四川省化學(xué)合成與污染控制重點(diǎn)實(shí)驗(yàn)室,西華師范大學(xué)化學(xué)化工學(xué)院,四川 南充 637009)

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Cu-rGO催化的咪唑N-芳基化反應(yīng)性能研究

黃 強(qiáng),周麗梅,蔣曉慧,周婭芬,郎文成

(四川省化學(xué)合成與污染控制重點(diǎn)實(shí)驗(yàn)室,西華師范大學(xué)化學(xué)化工學(xué)院,四川 南充 637009)

研究了氧化還原石墨烯負(fù)載銅(Cu-rGO)催化的咪唑N-芳基化反應(yīng).催化劑進(jìn)行了紅外光譜(IR),X-射線(xiàn)單晶衍射(XRD),X-射線(xiàn)光電子能譜(XPS)等表征.研究結(jié)果表明,該催化劑具有高的催化活性,僅使用0.5mol%量的催化劑對(duì)反應(yīng)就具有高的催化效率.催化劑可以循環(huán)使用3次沒(méi)有大的活性下降,且通用性好.

銅;石墨烯;N-芳基化反應(yīng);芳基鹵;機(jī)理

石墨烯,是一種獨(dú)特的單原子層狀碳結(jié)構(gòu)材料,近幾年來(lái)受到了廣泛研究[1-3].石墨烯材料具有優(yōu)越的導(dǎo)電性能和高的比表面積,在電化學(xué)、傳感器和生物化學(xué)中存在廣泛應(yīng)用[4-6].隨著石墨烯材料的興起,開(kāi)發(fā)石墨烯基質(zhì)的高性能多相催化劑用于有機(jī)反應(yīng)也引起了人們的關(guān)注.尤其是,石墨烯材料作為催化劑對(duì)C-C/N/O/S類(lèi)型的偶聯(lián)反應(yīng)進(jìn)行了大量研究[7,8].例如,石墨烯負(fù)載Pd納米粒子(GO-NH2-Pd0)用于Suzuki-Miyaura偶聯(lián)反應(yīng)[9],石墨烯二氧化釕催化劑(G-RuO2)用于有氧條件下的交叉脫氫偶聯(lián)反應(yīng)[10],這些石墨烯基質(zhì)的催化劑都具有高的催化性能.

2013年,Paramita課題組首次使用銅石墨烯基質(zhì)催化劑(Cu-G)研究了C-N/O的偶聯(lián)反應(yīng)[11].該催化劑具有高的活性和穩(wěn)定性.此后,人們又報(bào)道了銅納米粒子負(fù)載的氧化還原石墨烯(rGO/Cu NPs)的制備[12],它可以作為高活性和可循環(huán)的多相催化劑用于甲酰胺和初級(jí)胺的合成.這些研究在有機(jī)合成反應(yīng)中具有重要意義.

盡管C-N類(lèi)型的偶聯(lián)反應(yīng)已有報(bào)道,但這些研究中,高催化劑用量增加了反應(yīng)成本,同時(shí),制備這種高效的石墨烯基質(zhì)催化劑也需要極大的成本和時(shí)間.因此,進(jìn)一步提高催化劑的催化效率具有極其重要的研究?jī)r(jià)值.基于此,本文通過(guò)簡(jiǎn)單的方法制備了銅石墨烯復(fù)合材料(Cu-rGO),進(jìn)一步研究了其催化N-芳基化反應(yīng)的活性及通用性.

1 實(shí)驗(yàn)部分

1.1 氧化石墨烯的合成

實(shí)驗(yàn)中,采用改進(jìn)的Hummer方法合成氧化石墨烯(GO)[13].2g石墨烯粉置于燒杯中,冰浴攪拌下加入100mL 98%的H2SO4.接著加入2g NaNO3和12g KMnO4,移除冰浴加熱到38℃攪拌過(guò)夜.向反應(yīng)液中加入120mL H2O,并劇烈攪拌,顏色由棕色變?yōu)榻瘘S色.繼續(xù)攪拌30min,加入25mL 30% H2O2除去固體雜質(zhì)MnO2.混合液抽濾,獲得的固體用稀鹽酸洗滌,水洗至中性.

1.2 rGO和Cu-rGO材料的合成

200mg GO和75mg CuCl2·2H2O混合超聲分散到200mL的水中形成均勻的懸浮液.然后室溫下滴加20mL 5%的NaBH4水溶液至混合液中,持續(xù)攪拌反應(yīng)24h.抽濾,固體用水洗3次,無(wú)水乙醇洗2次,60℃真空干燥.rGO的合成方法與Cu-rGO合成方法類(lèi)似.

1.3 Cu-rGO催化的N-芳基化反應(yīng)

1mmol芳基鹵,1.2mmol咪唑,3mmol堿,0.5mol%催化劑加入到反應(yīng)試管中,充入氮?dú)獗Ｗo(hù).再加入2mL DMSO作為溶劑110℃攪拌反應(yīng)24h.待反應(yīng)液冷卻后加入20mL水洗滌,然后用15mL乙酸乙酯萃取3次,有機(jī)相用無(wú)水Na2SO4干燥.粗產(chǎn)品通過(guò)硅膠柱分離提純,計(jì)算收率.

2 結(jié)果與討論

2.1 載體及其催化劑的表征

圖1a為GO,rGO,Cu-rGO的紅外光譜.3433.0cm-1,1748.5cm-1,1635.5cm-1,和1070.1cm-1分別符合GO中OH,C=O,C=C,和C-O-C官能團(tuán)的伸縮振動(dòng)特征峰[4].1389.1cm-1為GO中OH的彎曲振動(dòng)特征峰.對(duì)于rGO材料,C=O的伸縮振動(dòng)特征峰消失,說(shuō)明GO已經(jīng)被還原.還原銅鹽和GO混合液時(shí),rGO特征峰進(jìn)一步削弱.這說(shuō)明銅鹽能夠促進(jìn)GO的進(jìn)一步還原[14].

圖1b顯示了催化劑Cu-rGO的XRD圖譜.由圖可知,2θ=10.5°為GO的特征衍射峰.GO還原以后,2θ=9.3°具有弱的衍射峰,表明室溫下只能部分還原GO.然而,對(duì)于Cu-rGO催化劑,GO的特征衍射峰完全消失,表明GO被進(jìn)一步還原.說(shuō)明CuCl2有利于GO的還原.此外,在25.4°和42.6°附近出現(xiàn)了新的衍射峰,這可能是由于層狀石墨烯的堆疊所致[15].材料中,沒(méi)有發(fā)現(xiàn)銅的特征衍射峰.

圖2a和b分別為GO,Cu-rGO的掃描電子顯微鏡(SEM)圖,可以看出,GO和rGO都具有扭曲的層結(jié)構(gòu).c和d分別為GO,Cu-rGO的透射電子顯微鏡(TEM)圖.觀察發(fā)現(xiàn),在rGO層表面并沒(méi)有銅納米粒子(Cu NPs).說(shuō)明室溫還原過(guò)程中,銅可能沒(méi)有被還原形成Cu NPs.

基于以上分析,XPS表征進(jìn)一步確認(rèn)了銅的價(jià)態(tài).從圖3c中可以看到,在935 eV處有很強(qiáng)的峰,為Cu2+特征峰.932.2 eV具有弱的峰,符合低價(jià)銅的特征峰[16].結(jié)果表明,材料中銅主要以二價(jià)形成存在,制備過(guò)程中金屬未能徹底還原.此外,本文也對(duì)石墨烯材料的C1s能譜進(jìn)行了分析,結(jié)果如圖3a和b.可以看出,石墨烯具有四個(gè)不同的特征峰,分別位于284.6,285.4,286.6和288.6 eV處,符合C=C,C-C,C-O和O=C-O官能團(tuán)的骨架結(jié)構(gòu)[17].然而,當(dāng)該催化劑循環(huán)使用5次以后,O=C-O官能團(tuán)的峰消失,這可能是因?yàn)樵诟邷胤磻?yīng)過(guò)程中,石墨烯邊緣脫羧所致[18].

2.2 催化N-芳基化反應(yīng)

以碘苯和咪唑反應(yīng)作為模板,系統(tǒng)研究了Cu-GO催化劑對(duì)于N-芳基化反應(yīng)的催化性能.首先使用0.5mol%催化劑量篩選了反應(yīng)條件,結(jié)果列于表1中.結(jié)果表明,使用3mmol NaOH作為堿在110℃下反應(yīng)24h能夠獲得最高的收率.

表1 催化劑反應(yīng)條件的選擇.

EntryBaseTemperature(℃)Isolatedyield(%)a1 KOH11068.72 NaOH11072.0,88.1b,94.7c,98.9d3 LiOH11079.24 K2CO311023.35 Na2CO311014.26 Cs2CO311045.17 NaOH10075.8d8 NaOH9042.2d9 NaOH12099.0d10 -11012.1

Reaction conditions：1 mmol iodobenzene,1.2 mmol imidazole,0.5 mol% Cu-rGO;2mL DMSO;t=24 h.a:1.2 mmol base,b:2 mmol base,c:2.5 mmol base,d:3 mmol base.

催化劑的通用性是考察催化劑性能的重要指標(biāo).基于此,本實(shí)驗(yàn)對(duì)反應(yīng)的底物進(jìn)行了一系列的研究,結(jié)果列于表2中.從表中可以看出,該催化劑除對(duì)于活潑性極差的氯苯具有很低的催化活性外,對(duì)其它多種底物都具有較好的催化性能.同時(shí),帶有吸電子基團(tuán)的芳基鹵活性普遍高于供電子基團(tuán)的活性.

2.3 催化劑的循環(huán)和活性比較

通過(guò)碘苯和咪唑的反應(yīng)研究了Cu-rGO催化劑的循環(huán)性能.如圖4a所示,催化劑至少可以循環(huán)3次沒(méi)有大的活性下降.然而,循環(huán)5次以后,催化劑活性出現(xiàn)明顯下滑.通過(guò)能量色散光譜(EDS)對(duì)反應(yīng)前后催化劑中銅含量進(jìn)行分析,如圖4b.結(jié)果發(fā)現(xiàn),催化劑中銅的含量有明顯的減少.因此,催化劑中銅的流失可能是引起催化活性下降的主要因素.

此外,催化劑的活性比較列于表3中.結(jié)果發(fā)現(xiàn),與其它報(bào)道相比,本研究中使用的催化劑具有更高的催化效率,僅使用0.5mol%催化劑量就可以實(shí)現(xiàn)高達(dá)98.9%的收率.這在實(shí)際應(yīng)用中具有更高的經(jīng)濟(jì)價(jià)值.

表3 不同催化劑在N-芳基化反應(yīng)中的活性比較.

CatalystsAmountofcatalystYield(%)ReferenceCu-G(13%Cu)Cu10mol%94.011PANI-CuCu2.5mol%92.019CuI/INDION-770Cu10%94.020Cu-rGOCu0.5mol%98.9Thisstudy

3 結(jié) 論

總之,本文成功制備了Cu-rGO催化劑,通過(guò)IR,XRD和XPS等方法對(duì)催化劑進(jìn)行了表征.用于C-N偶聯(lián)反應(yīng),該催化劑具有高的催化活性和通用性.與其它多相催化劑相比,催化效率更高,僅0.5mol%的催化劑用量就能實(shí)現(xiàn)高的催化效率.催化劑循環(huán)使用3次沒(méi)有大的活性損失.進(jìn)一步研究石墨烯基質(zhì)催化劑在有機(jī)催化中的應(yīng)用將是我們下一步研究的工作.

[1] JI J,ZHANG G,CHEN H,et al.Sulfonated Graphene as Water-Tolerant Solid Acid Catalyst[J].Chemical Science,2011,2(3),484-487.

[2] YAN J,WANG Z,WANG H,et al.Rapid and Energy-Efficient Synthesis of a Graphene-CuCo Hybrid as High Performance Catalyst[J].Journal of Materials Chemistry,2012,22(22),10990-10993.

[3] FERNANDEZ-MERINO M,VILLAR-RODIL S,PAREDES J,et al.Identifying Efficient Natural Bioreductants for the Preparation of Graphene and Graphene-Metal Nanoparticle Hybrids with Enhanced Catalytic Activity from Graphite Oxide[J].Carbon,2013,63,30-44.

[4] ZHAO Y,SONG X,SONG Q,et al.a Facile Route to the Synthesis Copper Oxide/Reduced Graphene Oxide Nanocomposites and Electrochemical Detection of Catechol Organic Pollutant[J].CrystEngComm,2012,14(20),6710-6719.

[5] SHIN H,KIM K,BENAYAD A,et al.Efficient Reduction of Graphite Oxide by Sodium Borohydride and Its Effect on Electrical Conductance[J].Advanced Functional Materials,2009,19(12),1987-1992.

[6] OUYANG Y,CAI X,SHI Q,et al.Poly-L-Lysine-Modified Reduced Graphene Oxide Stabilizes the Copper Nanoparticles with Higher Water-Solubility and Long-Term Additively Antibacterial Activity[J].Colloids and surfaces B:Biointerfaces,2013,107,107-114.

[7] METIN ?,HO S F,ALP C,et al.Ni/Pd Core/Shell Nanoparticles Supported on Graphene as a Highly Active and Reusable Catalyst for Suzuki-Miyaura Cross-Coupling Reaction[J].Nano Research,2012,6(1),10-18.

[8] HUANG Q,ZHOU L,JIANG X,et al.Synthesis of Copper Graphene Materials Functionalized by Amino Acids and Their Catalytic Applications[J].ACS Applied Materials & Interfaces,2014,6(16),13502-13509.

[9] SHANG N,FENG C,ZHANG H,et al.Suzuki-Miyaura Reaction Catalyzed by Graphene Oxide Supported Palladium Nanoparticles[J].Catalysis Communications,2013,40,111-115.

[10] MENG Q,LIU Q,ZHONG J,et al.Graphene-Supported RuO2Nanoparticles for Efficient Aerobic Cross-Dehydrogenative Coupling Reaction in Water[J].Organic Letters,2012,14(23),5992-5995.

[11] MONDAL P,SINHA A,SALAM N,et al.Enhanced Catalytic Performance by Copper Nanoparticle-Graphene Based Composite[J].RSC Advances,2013,3(16),5615-5623.

[12] Fakhri P,Jaleh B,NASROLLAHZADEH M.Synthesis and Characterization of Copper Nanoparticles Supported on Reduced Graphene Oxide as a Highly Active and Recyclable Catalyst for the Synthesis of Formamides and Primary Amines[J].Journal of Molecular Catalysis A:Chemical,2014,383-384,17-22.

[13] HUMMERS J,OFFEMAN R.Preparation of Graphitic Oxide[J].Journal of the American Chemical Society,1958,80(6),1339-1339.

[14] ZHOU Q,GAO J,PENG M,et al.Large-scale Synthesis of Graphene by the Reduction of Graphene Oxide at Room Temperature Using Metal Nanoparticles as Catalyst[J].Carbon,2013,52,559-564.

[15] WANG G,YANG J,PARK J,et al.Facile Synthesis and Characterization of Graphene Nanosheets[J].Journal of Physical Chemistry C,2008,112(22),8192-8195.

[16] 綦小龍,周麗梅,蔣曉慧,等.蒙脫土負(fù)載Cu+催化氮雜環(huán)化合物的N-芳基化反應(yīng)[J].催化學(xué)報(bào),2012,33(12),1877-1882.

[17] CHEN W,YAN L,BANGAL P R.Chemical Reduction of Graphene Oxide to Graphene by Sulfur-Containing Compounds[J].Journal of Physical Chemistry C,2010,114(47),19885-19890.

[18] QUALLICH J,MORRISSEY P M.A General Oxindole Synthesis[J].Synthesis,1993,1993,51-53.

[19] KANTAM M L,ROY M,ROY S,et al.Polyaniline Supported CuI:an Efficient Catalyst for C-N Bond Formation by N-Arylation of N(H)-Heterocycles and Benzyl Amines with Aryl Halides and Arylboronic Acids,and Aza-Michael Reactions of Amines with Activated Alkenes[J].Catalysis Communications,2008,9,2226-2230.

[20] JOSEPH P J, PRIYADARSHINI S, KANTAM M L, et al. Sulfonic Acid Containing Cation-Exchanger Resin “INDION-770” and Copper(i) Salts: a Novel Reusable Catalyst for N-Arylation of NH-Heterocycles with Haloarenes[J]. Catalysis Science & Technology, 2011, 1 (2) 234-238.

N-Arylation of Imidazole Catalyzed by Cu-rGO Composite

HUANG Qiang, ZHOU Li-mei, JIANG Xiao-hui, ZHOU Ya-fen, LANG Wen-cheng

(Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, Sichuan, Nanchong 637009, China)

An efficient catalytic system for N-arylation reactions on heterogeneous copper reduced Graphene based catalyst (Cu-rGO) was described. The as-prepared catalyst was characterized by a variety of techniques， including Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), etc. The results showed that the high activity was obtained by low dosage of catalyst, and 0.5 mol% of the catalyst was sufficient. The catalyst could be reused for 3 times without significant loss in activity, and also showed high catalytic activity with a wide variety of substituents.

Copper; Graphene; N-arylation; Aryl halide; Mechanism

1673-5072(2015)01-0030-06

2014-09-01

國(guó)家自然科學(xué)基金(批準(zhǔn)號(hào)21303139);四川省教育廳項(xiàng)目(批準(zhǔn)號(hào)11ZA035).

黃 強(qiáng)(1988-),男,四川南充人,西華師范大學(xué)化學(xué)化工學(xué)院碩士研究生,主要從事有機(jī)催化研究.

周麗梅(1977-),女,四川德陽(yáng)人,西華師范大學(xué)化學(xué)化工學(xué)院副教授,主要從事有機(jī)催化研究.

O643.3

A