外文翻譯--石墨烯基催化劑在有機(jī)轉(zhuǎn)換中的多功能性（英文）

1、47ice | scienceGreen Materials Volume 1 Issue GMAT1Versatilities of graphene-based catalysts in organic transformations Garg and LingPages 47–61 http://dx.doi.org/10.1680/gmat.12.00008Review ArticleReceived 15/09/2012

2、 Accepted 15/10/2012Published online 26/10/2012Keywords: graphene/graphene oxide/graphite oxide/heterogeneous catalysis/organic synthesis/nanomaterialsICE Publishing: All rights reservedVersatilities of graphene-based c

3、atalysts in organic transformationsBhaskar Garg PhD Department of Chemistry, National Tsing Hua University, Hsinchu, TaiwanYong-Chien Ling PhD* Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan

4、The outstanding and unique physical, chemical and mechanical properties of graphene lead to the development of graphene-based catalysts for selective and efficient organic synthesis becoming an active research area in re

5、cent years. This critical review summarizes the versatile applications of graphene-based catalysts in organic synthesis. It provides a comprehensive overview of typical reactions including oxidation, carbon–carbon cross-

6、coupling, hydration, esterifica-tion, Pechmann condensation, aza-Michael addition, Knoevenagel condensation, Friedel-Crafts addition, ring-opening polymerization, ring opening of epoxides, decarboxylative cycloaddition,

7、amide formation, synthesis of dipyrrometh-ane, hydrogenation and/or reduction. The applications of graphene-based catalysts allow mild, selective and highly effective transformations and synthesis in a facile, regenerabl

8、e, recyclable and eco-friendly manner.1 2*Corresponding author e-mail address: ycling@mx.nthu.edu.tw1 21. IntroductionSince Geim and Novoselov’s milestone work in 2004,1 the chemistry of graphene has bloomed only recent

9、ly and has now become an indis-pensable part of material chemistry.2–4 This growing interest in graph-ene is mainly due to its exceptional properties5–8 combined with its environmentally benign character and ease of synt

10、hesis. Accordingly, the scaled up and unswerving fabrication of graphene derivatives, such as graphene oxide (GO) and reduced GO (RGO),9–12 offers a wide range of possibilities to synthesize graphene-based functional mat

11、erials that can be used either as supports for immobilizing active species or as metal-free catalysts.13,14 Given the colossal considera-tion motivated by the properties, graphene-based materials are now increasingly use

12、d in organic synthesis as alternative heterogeneous reusable catalysts for various selective transformations of simple and complex molecules. The purpose of the present review is to summa-rize the utility of graphene-bas

13、ed catalysts (Figure 1) with emphasis on the recent up-to-date synthetic applications.2. General information and structural features of graphene-based materialsGraphene, a two-dimensional single-layer carbon sheet with

14、 hexagonal packed lattice structure, serves as a potential building block for fullerenes, nanotubes and graphite having zero-, one- and three-dimensional structures, respectively.15 High-quality large-area graphene sheet

15、s can be obtained by epitaxial growth of sin-gle-crystal silicon carbide (SiC) via ultrahigh vacuum annealing.16 Nevertheless, the method has certain disadvantages and found unsuitable for large-scale production.In recen

16、t times, the most developed method to generate single-layered graphene in excellent yields consists of the initial oxida-tion of graphite to graphite oxide, followed by the subsequent exfoliation of graphite oxide to GO

17、sheets, and ultimately reduc-tion to graphene.17–19 The relatively harsh conditions used, either by following the Hummers (KMnO4 and NaNO3 in concentrated sulfuric acid)20,21 or the Staudenmaier method (NaClO3 in H2SO4 a

18、nd sulfuric acid),22–24 in chemical oxidation of graphite introduces a variety of oxygen-containing functionalities such as epoxides, alcohols and carboxylates into the material. In this context, the most accepted model

19、dealing with GO structure is the one by Lerf, Klinowski and coworkers21 (Figure 2), where it is proposed that the heavily oxygenated GO consists of hydroxyl and epoxide groups on the basal planes, while carboxyl at the e

20、dges. As a result, GO is moderately acidic (pH = 4·5 at 0·1 mg/mL)25 and powerful oxidant, Green Materials Volume 1 Issue GMAT1Versatilities of graphene-based catalysts in organic transformations Garg and Lin

21、g49Long et al., however, developed N-doped graphene nanosheets using high-temperature nitridation and explored their catalytic efficien-cies in aerobic oxidation. Thus, a variety of alcohols appended with electron-donati

22、ng and electron-withdrawing substituents afforded corresponding aldehydes selectively in >99% yields (Scheme 3).30 By using appropriate techniques, the authors demonstrated that the metal-free catalysis takes place on

23、 the graphitic SP2 nitrogen sites via the formation of a SP2 N-O2 adduct transition state that has a high chemical reactivity to alcohols.Very recently, Mirza-Aghayan et al. have investigated the oxidation of aromatic, h

24、eterocyclic and aliphatic alcohols to their respective aldehydes and ketones using graphite oxide under ultrasonic irra-diation.31 The obtained yields were low to high for heterocyclic and aliphatic alcohols, respectivel

25、y.3.2 Oxidation of unsaturated and saturated hydrocarbonsGiven the propensity of GO to oxidize various alcohols, Bielawski and coworkers examined the ability of graphite oxide to oxidize cis-stilbene 3 to benzyl 4,27 a

26、 transformation that is similar to Wacker oxidation. Under final optimized conditions, the 4 was isolated in 68% yield (Scheme 4).32 The protocol was further extended suc-cessfully to a broad range of reactions including

27、 the oxidation of olefins, methyl benzenes and diaryl methanes to their respective diones, aldehydes and ketones. In most cases, no by-products were observed, and the desired products were isolated in good to excel-lent

28、yields.Li et al. developed graphene sheet/polymeric carbon nitride nano-composites (GSCN) and used as a metal-free catalyst to activate O2 for the selective oxidation of saturated hydrocarbons. By fine tun-ing the weight

29、 ratio of precursor components, GSCN offered good conversion of cyclohexane 5 to cyclohexanone 6 with high selec-tivity over cyclohexanol 7 (Scheme 5).33 Besides its high stability, GSCN also exhibited high chemoselect

30、ivity for secondary C-H bonds in a range of saturated alkanes.3.3 Oxidation of thiols and sulfidesThe selective oxidation of thiols to disulfides and sulfides to sulfox-ides using graphite oxide has been reported by Bie

31、lawski and cow-orkers. Thus, when thiophenol 8 was treated with graphite oxide in CDCl3 in a sealed vessel, diphenyl disulfide 9 was formed quanti-tatively (Scheme 6).34 Similarly, the oxidation of diphenyl sulfide 10 to

32、 the corresponding diphenyl sulfoxide 11 was achieved in the presence of graphite oxide (Scheme 7).34The rapid proceeding (as short as 10 min in some cases) is an attractive feature of this oxidation protocol, which affo

33、rded desired products in moderate to excellent yields (51–100%) from 19 differ-ent substrates, examined under the experimental conditions.3.4 Oxidation of glutaraldehydeSelective oxidation of glutaraldehyde, 12 to gluta

34、ric acid, 13 using graphite oxide with aqueous H2O2 has been reported by Dai et al. (Scheme 8).35 A slight increase in catalytic activity of graphite oxide was detected after post-treatment with 50% aque-ous H2O2 solutio

35、n. Nevertheless, in the absence of H2O2, a high yield of 94·7% was also achievable, comparable with traditional Scheme 1. Oxidation of benzyl alcohol into benzaldehyde.HOGO (200 wt %)100°C, 24h, >98%O H1 2Sc

36、heme 2. Oxidation of hydroxyl derivatives into carbonyl derivatives.R ROHOHR ROHOOHOHR2R1 OR ROOOn nTBHP/CH3CN,65°CR /R1 /R2=H, CH3, PhGraphene immobilized oxo-vanadium Schiff base catalyst R2R1Scheme 3. Selective o

37、xidation of aromatic alcohols into aldehydes.R1OH ON-doped graphene1/2 O2R1=H, F, CH3, OCH3, NO2 R2=HR2R1R2 + H2OScheme 4. Oxidation of cis-stilbene into benzyl.O OGraphite oxide (200mg)CHCl3(0·5mL),100°C 24 h,