Ru-Ferrite-Decorated Graphene (RuFG): A Sustainable and Efficient

Research Article pubs.acs.org/journal/ascecg

Ru-Ferrite-Decorated Graphene (RuFG): A Sustainable and Efficient Catalyst for Conversion of Aromatic Aldehydes and Nitriles to Primary Amides in Aqueous Medium Ramen Jamatia,† Ajay Gupta,† and Amarta Kumar Pal*,† †

Department of Chemistry, Centre for Advanced Studies, North-Eastern Hill University, Shillong 793022, India S Supporting Information *

ABSTRACT: Graphite oxide was synthesized and subsequently decorated with Ruferrite NPs which was characterized properly. The graphite oxide was reduced upon embedding of Ru-ferrite NPs, which is reflected in powder XRD, TGA, FT-IR, and Raman analyses. The paramagnetic nature of RuFG was confirmed from VSM analysis which particularly makes it a recyclable candidate in catalysis. The prepared RuFG was successively utilized for the conversion of aromatic aldehyde or nitrile to the corresponding primary amides in aqueous medium. The RuFG catalyst proved to be highly efficient providing excellent yields within a short period of time. The catalyst could be recycled and reused for eight consecutive runs without significant loss in catalytic activity. ICP-AES analysis of the reused catalyst confirmed insignificant leaching. TON (270) and TOF (270 h−1) calculations of the present RuFG catalyst show superiority from that of the reported metal-supported heterogeneous catalyst. KEYWORDS: Ru-ferrite-decorated graphene, Magnetically separable, Recyclable catalyst, Primary amides, Higher TON and TOF

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INTRODUCTION Development of sustainable protocol for chemical transformations is a great challenge for the synthetic community. A catalyst is an essential ingredient of any sustainable development.1 Therefore, development of a robust, efficient, reusable, and eco-friendly catalyst addresses the issues of sustainability. Nanocatalysts act as bridges between homogeneous and heterogeneous catalysts.2 On one hand, they eliminate the nonreusability issue, and on the other hand, they offer a huge surface area for catalysis. So, development of nanocatalysts plays a crucial role in sustainable development. In this regard, graphene-based nanomaterials, the latest concept in the field of chemistry, have emerged as an advanced tool to most synthetic as well as material chemists. Over the years, graphene as a catalyst support had considerable interest due to its outstanding chemical and thermal stability, easy preparation, low cost, rich surface chemistry, and high surface area.3−5 Magnetic nanoparticles are of substantial interest to the research community because of their potential applications in biomedicine/biotechnology, magnetic resonance imaging, data storage, and catalysis.6,7 Several groups have reported the use of graphene- or graphene oxide-supported metal/metal oxide as a catalyst for application in various organic reactions such as Fischer−Tropsch synthesis,8−10 electrocatalysis,11 Suzuki− Miyaura coupling reactions,12,13 hydrogenation,14,15 oxidation,16 and reduction.17 Various graphene-supported metal catalysts are reported in the literature.8−20 Among various graphene-supported catalysts, the incorporation of various monometallic and bimetallic magnetic nanoparticles holds a prime position in catalysis in terms of both economics and © 2017 American Chemical Society

sustainability due to the significance of being separated via a simple external magnetic field.1,2 Therefore, the development of a magnetic nanoparticle-decorated GO-based catalyst is increasing important. Among millions of organic reactions, amide bond formation is very important because it is present in proteins and peptides, a huge number of drugs, natural products, fine chemicals, and lubricants.21−25 Due to its relative significance, a number of protocols have been reported for the amidation process.23−33 Several heterogeneous catalysts have also been developed for amidation, such as nano[Fe3O4]-[Ru(OH)]x,34 nano-Fe@ SiO2Ru,35 Fe3O4-RAPTA,36 Nafion-Ru,37 and ChRu.38 Each catalyst has their own advantages, but at the same time, they suffer some drawbacks. Recently, the SBA-15/En-Cu catalyst successfully demonstrated the conversion of aldehyde to amide.39 Though, copper metal is cheap, its reaction time is too long (2−3 days). Therefore, its TOF value should be extremely low. This is, in turn, a major drawback of this protocol. From the above literature survey, it is clear that there is enough room for the development of a new catalyst for amide bond synthesis that would address several issues relating to sustainability and environment. It is also known that a Rubased catalyst like Grubb’s catalyst, Wilkinson’s catalyst, and many more acquires a supreme position in catalysis. Likewise, we design RuFG as a heterogeneous catalyst for the said reaction. This is the first report of a magnetically separable Received: March 24, 2017 Revised: June 10, 2017 Published: July 20, 2017 7604

DOI: 10.1021/acssuschemeng.7b00897 ACS Sustainable Chem. Eng. 2017, 5, 7604−7612

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ACS Sustainable Chemistry & Engineering Scheme 1. Schemetic Representation for Synthesis of RuFG

Figure 1. PXRD pattern of graphite oxide (A) and RuFG (B).

ruthenium-based graphene catalyst. To the best of our knowledge, only a few reports are available for the synthesis of Ru graphene.40−42 Our catalyst is more economical than Ru graphene due to its magnetical recoverability. In view of the above considerations, we synthesized RuFG and applied it to amide bond preparation. The catalyst efficiently drove the reaction to completion in 1−4 h providing the desired amide derivatives. Both aldehyde and nitriles were tested, and they afforded good to excellent yields (80−95%) of the desired products. The catalyst RuFG was paramagnetic, allowing for its easy separation and recyclability for up to eight consecutive runs.

The TEM images of Ru-ferrite NPs and RuFG at various magnifications are specified in Figure 2. Figure 2A and B shows the TEM images of Ru-ferrite NPs with the particle size ranging from 5 to 30 nm, which were prepared according to a previously reported synthetic strategy.45 In the TEM images of RuFG (Figure 2C−E), the incorporation of nanometer-sized Ru-ferrite NPs on the surface of the graphene sheet is evident. Figure 2G shows the distribution of nanoparticles for Figure 2C. A higher magnification TEM image of RuFG (Figure 2E) shows the distribution of Ru NPs, and it is observed that some of the Ru NPs remained free in the graphene sheet while the others are dispersed on ferrite NPs. Figure 2F shows the SAED image of the prepared catalyst. The SEM images of GO (Figure S.I. 1A) and EDX spectra (Figure S.I. 1B) of GO clearly confirm the grafting of Ru-ferrite NPs on to the graphene sheet (Figure S.I. 1D). From ICP-AES analysis, it was confirmed that a low loading of 1.347% of Ru was present in the prepared catalyst. The comparative FT-IR spectra revels that the reduction of GO occurred during the embedding process of Ru-ferrite NPs on GO (Figure S.I. 2). X-ray photoelectron spectroscopy (XPS) was used to depict the composition of RuFG and the oxidation state of ruthenium species. An XPS survey and C 1s spectrum of prepared GO (Figure 3A and B) show the presence of various functionalities corresponding to GO.46 In the XPS survey spectrum of RuFG (Figure 3C), Ru, Fe, C, and O species are all observed pointing toward the successful preparation of the graphitic material. Figure 3D represents the C 1s and Ru 3d XPS spectrum of RuFG. In the XPS spectrum of RuFG, the peaks due to ruthenium can be typically deconvoluted into two types. The peak at 281 eV is ascribed

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RESULT AND DISCUSSION The synthetic strategy for RuFG involves in situ reduction of RuCl3 and dopping of Fe3O4 and Ru on the GO surface (Scheme 1). After successfully synthesizing RuFG, the catalyst was then characterized by various characterization techniques. The powder X-ray diffraction (PXRD) analysis serves as a powerful means of characterizing metal-incorporated GO material. Figure 1, displays the PXRD pattern of GO (Figure 1A) and RuFG (Figure 1B). The disappearance of the (001) peak in PXRD of RuFG (Figure 1B) is due to the crystal growth of Ru-ferrite NPs in between the interlayer of GO which effectively exfoliated GO.13,43,44 The prominent peaks in the PXRD pattern of RuFG at 2θ = 30.22, 35.63, 43.34, 53.78, 57.27, and 62.85 are attributed to (220), (311), (400), (422), (511), and (440) reflections of ferrite nanoparticles, respectively. The diffraction peak of Ru was similarly not observed in Figure 1B due to the loading of Ru.24,25,36 7605


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ACS Sustainable Chemistry & Engineering

Figure 2. TEM images of Ru-ferrite NPs at 100 nm (A) and 20 nm (B). TEM images of RuFG at 100 nm (C), 20 nm (D), and 5 nm (E). SAED image of RuFG (F). Histogram of nanoparticles from panel 2C (G).

to RuO2 species in a +4 oxidation state, and the peaks at 284.4 and 280.3 eV are assigned to Ru species in a zero (0) oxidation state.40,47 The remaining peaks from 283 to 290 eV are assigned to various functionalities of graphene. To analyze the prepared graphitic material, advantage of Raman spectroscopy was taken. Raman spectrum of the prepared GO, Ru-ferrite NPs, and RuFG are given in Figure 4. After embedding of Ru-ferrite NPs on GO, a slight shift of the D-band toward lower frequency (∼1357.0 cm−1) and Gband toward higher frequency (∼1599.6 cm−1) was observed (Figure 4A). An increment in the value of ID/IG (1.56 from 1.06) was as well detected. These observations further support the reduction of GO during the incorporation process of Ruferrite NPs in graphene sheets.48 Further, the presence of RuO2 species in the prepared RuFG can be confirmed from the small peaks present at ∼508, 657, and 713 cm−1, which are close to those reported.40 Figure 5 shows the magnetization curves for ferrite NPs, Ruferrite NPs, and RuFG. The saturation magnetization (Ms) value of both ferrite NPs and Ru-ferrite Nps (49.9 and 49.4 emu/g, respectively) indicates a strong ferromagnetic nature. As is evident from a VSM graph (Figure 5), the Ms value of prepared RuFG was found to be 15.83 emu/g, which is much lower than that of ferrite or Ru-ferrite Nps. The lower Ms value of RuFG may be because of the carbon atoms π-shell of graphene, as is reported in the literature.49,50

TGA analysis (Figure 6) was used to study the structural difference of graphite, GO, ferrite NPs, Ru-Fe3O4NPs, and RuFG. From Figure 6, it was observed that less than a 10% weight loss was observed in the case of pristine graphite, ferrite, and Ru-ferrite NPs. The TGA thermogram of RuFG shows three prominent weight losses. The first weight loss below 130 °C corresponds to the loss of water molecules. The second weight loss is observed at around 230 °C with a weight loss of approximately ∼5% unlike that of GO. The third weight loss (∼10%) is again attributed to degradation of the carbon skeleton of a graphene sheet.51 The prepared RuFG was subsequently utilized for the catalytic conversion of aldehydes or nitriles to the corresponding amides. We instigated the investigation by taking pchlorobenzaldehyde (1a) as the model substrate (Scheme 2). At the outset, a mixture of p-chlorobenzaldehyde (1a, 1 mmol) and hydroxylamine hydrochloride (1 mmol) in water (5 mL), devoid of any catalyst, was put to the test under room temperature. The reaction failed to convert the substrates to the corresponding amide (2a). Increasing the temperature (40, 60, 80, and 100 °C) of the model reaction did not result in any conversion of the starting substrate to product (Table 1). Therefore, it was concluded that in deprivation of any catalyst the model reaction was unable to produce the amide. Then, the model reaction was set up with a catalyst (RuFG, 25 mg) at room temperature. It was also a disappointment whereby no desired product was obtained. However, when the same 7606


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Figure 3. XPS survey spectrum of GO (A), C 1s XPS spectrum of GO (B), XPS survey spectrum of RuFG (C), and Ru 3d deconvoluted RuFG (D).

Figure 4. Comparative Raman spectrum of Ru-ferrite NPs and RuFG (A) and of GO and RuFG (B).

Figure 5. Magnetization curves for ferrite NPs, Ru-ferrite NPs, and RuFG.

Figure 6. TGA analysis of graphite, GO, ferrite NPs, Ru-ferrite NPs, and RuFG.

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ACS Sustainable Chemistry & Engineering Scheme 2. Model reaction for the conversion of aldehyde to amide

Scheme 3. General Scheme for RuFG-Catalyzed Conversion of Aldehyde to Amide

Table 1. Stardardization of Various Reaction Parametersa

outcomes are given in Table 2. It was observed that all the reactions progressed to completion within 2 h providing the

Entry

Catalyst

Temperature (°C)

Time (h)

Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13

No catalyst No catalyst No catalyst No catalyst No catalyst Ru-ferrite NPs Ru-ferrite NPs GO RuFG RuFG RuFG RuFG RuFG

r.t. 40 60 80 100 80 100 80 r.t 40 60 80 100

1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5

0 0 0 0 0 69 76 0 0 24 73 94 94

b

Table 2. RuFG-Catalyzed Conversion of Aldehyde to Amidea

a

Reaction conditions: p-chlorobenzaldehyde (1a, 1 mmol), hydroxylamine hydrochloride (1 mmol), catalyst (25 mg), and water (5 mL) without use of any base. bIsolated yield calculated after purifying pchlorobenzamide by column chromatography (silica 60−120 mesh).

reaction was heated at 40 °C a poor conversion (24%) of substrates to amide (2a) was observed. To increase the efficiency of the reaction, various temperatures were employed, and the results are listed in Table 1. At 80 °C, the model reaction efficiently converted the substrates to the corresponding product in 94% yield in 1.5 h. As evident from Table 1, a decrease in temperature principally leads to a lower yield of the product. Above 80 °C, no escalation in the efficiency of the reaction was observed. The model reaction was also performed with GO as well as Ru-ferrite NPs (Table 1). However, it was observed that only moderate yield (69%) of the amide product was obtained in the case of Ru-ferrite NPs in 1.5 h. GO as the catalyst was ineffective for the present catalytic conversion of aldehyde to amide. After fixating the optimum temperature and the catalyst, next, the catalyst loading was scrutinized. Initially, the model reaction was inspected without catalyst at 80 °C. No conversion of reactant to product was observed. Therefore, the model reaction was explored under various loadings (5−30 mg) of catalyst (Figure S.I. 3). The best result for the present catalytic process was witnessed when the reaction was carried out with 25 mg of catalyst loading to provide an isolated yield of 94%. Further, an increase in catalyst loading (30 mg) did not lead to any paramount enhancement of the reaction. Likewise, scrutiny of various solvents for the present catalytic process was performed (Figure S.I. 4). It was of note that the catalyst was ineffective in solvents such as EtOH and toluene, achieving very low yield (39% and 37%, respectively) of product. A relatively better yield (56%) was observed in the case of DMSO. Dioxane and water produced brilliant results, converting the model substrate to product in excellent isolated yield (93% and 94%, respectively) in 1.5 h. Next, we sought to inspect the efficacy of the present catalytic process. The optimized condition was then applied on a range of aldehydes (Scheme 3). Various p-, m-, and osubstituted aromatic aldehydes were put to the test, and the

a

Reaction conditions: Aldehydes (1 mmol), hydroxylamine hydrochloride (1 mmol), RuFG (25 mg), and water (5 mL) were heated at 80 °C without use of any base for the time mentioned in Table 2 unless otherwise mentioned. Isolated yield calculated after purifying by column chromatography (silica 60−120 mesh). bReaction carried out with hydroxylamine hydrochloride (2 mmol).

desired amide (2a−n) in excellent yields (83−95%). Dialdehyde such as terepthaldehyde was also put to the test. It was observed that irrespective of the loading of hydroxylamine hydrochloride the reaction furnished a diamide (2o). However, lower yield (44%) was observed when hydroxylamine hydrochloride was used in 1 mmol scale. Hence, to increase the yield of the corresponding diamide product (2o), 2 mmol of hydroxylamine hydrochloride was used. Allylic aldehyde such as cinnamaldehyde was also investigated. Cinnamaldehyde produced the desired amide product (2p) in good yield (88%). Further, disubstituted aromatic aldehydes such as 2-chloro-5nitrobenzaldehyde and 3-chloro-5-nitrobenzaldehyde were scanned. The reactions furnished the respective products 2q and 2r in good isolated yields of 83% and 81%, respectively, at a comparatively extended time of 4 h. Next, inspection of fused aromatic aldehydes such as 9-anthraldehyde and 1-naphthaldehyde were carried out under the present catalytic process. Both the substrates proceeded to provide the corresponding amide (2s and 2t) derivatives in excellent yields of 88% and 86%, respectively. Heterocyclic aldehydes were also investigated, and it was found that the present catalyst efficiently produced the desired products (2u and 2x) in good yield as given in Table 2. 7608


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ACS Sustainable Chemistry & Engineering Under optimized conditions, all desired amides precipitated upon cooling after reaction completion. But for maximum purity, column chromatography was employed, after which the desired product was characterized by various spectroscopic techniques. After successful demonstration of the present catalytic process in the conversion of the Csp2-H bond conversion of aldehydes to the Csp2-N bond of amide. We next shifted our focus toward the conversion of aromatic nitriles to amides under the same standardized conditions (Scheme 4). Initially, Scheme 4. Scheme for RuFG-Catalyzed Amidation of Nitriles

the amidation reaction was carried out with 2-pyridinecarbonitrile (1 mmol), RuFG (25 mg), and water (5 mL) at 80 °C. It was astonishing to observe that the reaction produced the desired product (2u) in excellent yield (87%) in 1 h. Encouraged by the present success, we next scanned various aromatic nitriles. All the reactions proceeded to completion providing the desired amides (2b, 2c, 2e−g, 2j, 2l, 2m, 2u−w) in good to excellent yields, which are reflected in Table 3. From

Figure 7. Hot filtration test for leaching of catalyst.

between p-chlorobenzaldehyde and hydroxylamine hydrochloride, the catalyst was separated, and the reaction was continued for another 1.5 h. No enhancement of the product yield was observed after separating the catalyst. This result in turn proves that either no leaching or very negligible leaching occurred. To further substantiate our present claim, an ICPAES analysis was done. From the ICP-AES analysis, it was observed that negligible leaching (0.565 ppm) of the catalyst occurred. This indicates that the Ru-ferrite NPs are firmly embedded on the surface of graphene. We designed our catalyst in such a way that for recovery there was no need of centrifugation and filtration. After completion of the model reaction between p-chlorobenzaldehyde and hydroxylamine hydrochloride, the catalyst was recuperated via an external magnet washed carefully with water, EtOH, and diethyl ether. It was then used in another set of reactions under the same experimental condition. The recuperated catalyst showed almost equal efficiency as the fresh catalyst providing the desired product in excellent yield of 94%. This paramagnetic catalyst could be reused up to eight consecutive runs without any significant loss in efficiency of the catalyst (Figure 8). The morphology and composition of the recuperated catalyst were analyzed using TEM, SEM, and EDX (Figure S.I. 5 and S.I. 6). Finally, a comparative study of turn over number (TON) and turn over frequency (TOF) of the present catalyst with that of some previously reported methodologies employing ruthenium metal-supported heterogeneous catalyst were calculated based on the amount of active metal used.34−38 The results are given in Table 4. In the present study, RuFG provided the highest TON and TOF values in comparison to these reported catalysts as given in Table 4, entry 6. The calculated TON and TOF values of RuFG are 270 and 270 h−1.

Table 3. RuFG-Catalyzed Amidation of Nitrilesa

a

Reaction conditions: Aromatic nitriles (1 mmol), RuFG (25 mg), and water (5 mL) were heated at 80 °C for the time mentioned in Table 3. Isolated yield calculated after isolation of pure amide product from column chromatography (silica 60−120 mesh).

Table 3, it is clear that various o-, m-, and p-substituted benzonitriles formed the desired products (2b, 2c, 2e−g, 2j, 2l, 2m) in good to excellent yields (84−92%) within 2 h. It is known that indole shows a broad spectrum of biological activities, and it is also present in numerous natural product and medicines.52−54 So, we were very interested to synthesize indole amides. Therefore, 4-cyanoindole was put to the test, and the reaction proceeded to afford the desired amide (2v) in 80% isolated yield. Further, 2-(4-bromophenyl)-2-phenylacetonitrile was investigated under the present catalytic process. Good isolated yield (85%) of the corresponding product (2w) was observed as given in Table 3. The plausible mechanistic pathway for the conversion of aldehyde or nitrile to amide is outlined in Scheme S.I. 1. A hot filtration test was carried out to check the leaching of the catalyst (Figure 7). After 0.5 h of the model reaction

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CONCLUSION In conclusion, we have successfully synthesized Ru-ferritedecorated graphene sheets. The prepared RuFG catalyst was completely characterized by various characterization techniques. We also examined the catalytic efficiency of RuFG as a heterogeneous catalyst in conversion of aldehyde or nitriles to amide. RuFG furnished brilliant results in the said conversion. Further, the paramagnetic nature of the catalyst makes it easily 7609


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mL of concentrated sulfuric acid (H2SO4, 98%). The resulting solution was kept in an ice bath, and 4 g of potassium permanganate (KMnO4) was added slowly in portions over an hour under stirring to avoid any explosion. After the completion of the addition, the reaction mixture was allowed to stir for another hour. The mixture was then heated slowly to 45 °C, and stirring was continued for another hour (observation: a thick brown paste is obtained at this stage). After the completion of the time mentioned, 20 mL of deionized (DI) water was added and heated at 45 °C for another 30 min. Then, 180 mL of DI water was mixed followed by dropwise addition of hydrogen peroxide (H2O2, 30%) until the color of the solution changed from drak brown to yellowish brown. The prepared graphite oxide was then recovered by centrifugation and filtration. After that, it was washed with DI water (3 mL × 10 mL), EtOH (3 mL × 10 mL) and diethyl ether (3 mL × 10 mL). Finally, graphite oxide was dried under vacuumn. Preparation of RuFG. Prepared GO (500 mg) and 360 mL deionized water were sonicated for a period of 1 h. Ferrite NPs (1 g) and ruthenium trichloride (0.25 mmol, 52 mg) were added to it, and the sonication was continued for 1 h. Then, 1 M NaOH solution was added to the resulting suspension until pH 13 was attained. The resulting colloidal suspension was then allowed to stir under room temperature for a period of 24 h. After the time mentioned, the paramagnetic catalyst was separated by application of an external magnet, washed with water (5 mL × 10 mL), EtOH (3 mL × 5 mL), diethyl ether (2 mL × 5 mL) and dried at 50 °C for 24 h. Procedure for Conversion of Aldehyde to Amide. A mixture of aldehydes (1 mmol), hydroxylamine hydrochloride (without base, 1 mmol; 2 mmol in case of terepthaldehyde), catalyst (RuFG, 25 mg), and water (5 mL) was heated at 80 °C for the time mentioned in Table 2. After completion of the reaction (TLC), the catalyst was separated by an external magnet and washed with water (3 mL × 5 mL), EtOH (2 mL × 5 mL), diethyl ether (2 mL × 5 mL) and dried. It was then employed for another cycle under the same experimental conditions. Then, the reaction mixture was extracted with ethyl acetate (3 mL × 5 mL), and the organic layer was washed with brine (1 × 5 mL) and dried over anhydrous Na2SO4. The reaction mixture was reduced under vacuum, and the crude reaction mass was purified by column chromatography to afford pure products (2a−t, 2u, 2x). Procedure for Conversion of Nitrile to Amide. A mixture of nitriles (1 mmol), catalyst (RuFG, 25 mg), and water (5 mL) was heated at 80 °C for the mentioned time frame as indicated in Table 3. After that, the catalyst was recuperated by application of an external magnetic field. The recuperated catalyst was washed with water (3 mL × 5 mL), EtOH (2 mL × 5 mL), diethyl ether (2 mL × 5 mL) and dried. The catalyst was then used for another cycle under the same reaction condition. The reaction mixture was extracted with ethyl acetate (3 mL × 5 mL), washed with water (3 mL × 5 mL), brine (1 mL × 5 mL) and dried (Na2SO4). The reaction mass was reduced under vacuum and then purified by column chromatography using ethyl acetate and hexane as the eluent to afford pure products (2b, 2c, 2e−g, 2j, 2l, 2m, 2u−w).

Figure 8. Recyclability chart of RuFG catalyst.

separable by application of an external magnet. The catalyst was successfully recycled and reused for eight successful runs without any significant loss in its catalytic efficiency or much depreciation of product yield. Further, the calculated TON and TOF values of our present RuFG catalyst show superiority over that of the previously reported metal-supported heterogeneous catalysts.

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EXPERIMENTAL SECTION

Melting points were determined in open capillaries and are uncorrected. Infrared (FT-IR) spectra were recorded on a Spectrum BX (FT-IR) instrument (PerkinElmer) (υmax in cm−1) on KBr disks. 1 H and 13C NMR (400 and 100 MHz, respectively) spectra were recorded on a Bruker Avance II-400 spectrometer in CDCl3 (chemical shifts in δ with TMS as internal standard). Mass spectra were recorded on a Waters ZQ-4000. Transmission electron microscopy (TEM) images were recorded on a JEOL JSM 100CX. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectra were recorded on a JSM-6360 (JEOL). Vibrating sample magnetometry (VSM) was carried out on a Lakeshore, Model:7410 series. Thermogravimetric analysis (TGA) was recorded on a PerkinElmer Precisely STA 6000 simultaneous thermal analyzer. CHN was recorded on a CHN-OS analyzer (PerkinElmer 2400, Series II). Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis was carried out on an Arcos simultaneous ICP spectrometer. Powder XRD analysis was recorded on a Bruker D8 XRD instrument SWAX. Raman analysis was carried out on a Horiba Jobin Vyon, Model LabRam HR. X-ray photoelectron spectroscopy (XPS) was recorded on a PHI 5000 Versa Prob II, FEI, Inc. Preparation of Graphite Oxide (GO). Graphite Oxide (GO) was prepared according to the modified Hummer’s method from graphite powder.11 Graphite (1 g) and sodium nitrate (0.5 g) was added in 20

Table 4. Comparative Study of TON and TOF Values of RuFG with Other Reported Metal-Supported Heterogeneous Catalystsa Entry

Catalyst

Catalyst loading (mg) [active metal in mg]

Time (h)

Yield (%)

TON

TOF (h−1)

1 2 3 4 5 6

nano[Fe3O4]-[Ru(OH)]x nano-Fe@SiO2Ru Fe3O4-RAPTA Nafion-Ru ChRu RuFG

100 [3.220] 100 [3.96] 100 [1.6] 30 [4.2] 25 [1.603] 25 [0.337]

0.5 1.0 1.5 12 1.0 1.0

85 88 88 97 89 90

27 22 56 23 56 270

54 22 37 2 56 270

a

TON and TOF were calculated on the basis of isolated yield of benzamide obtained from benzonitrile (Table 3, 2b). TON was calculated using the formula molproductmolRu−1. TOF was calculated using the formula molproductmolRu−1 h−1. 7610


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00897. Experimental procedure, SEM and EDX images of GO and RuFG, comparative FT-IR spectrum of graphite, GO and RuFG, chart representing RuFG catalyst loading, solvent standardization chart, plausible mechanistic pathway, characterization of reused RuFG, analytical and spectral data of compounds 2a−x, and 1H and 13C spectra of all products (2a−x). (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel: +91 364 2307930, ext 2636. E-mails: amartya_pal22@ yahoo.com, [email protected]. Fax: +91 364 2550076. ORCID

Amarta Kumar Pal: 0000-0001-7838-3804 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Department of Chemistry of North-Eastern Hill University (NEHU) and University Grant Commission (UGC) for supporting this work under the Special Assistance Programme (SAP) and DST-Purse programme of NEHU, Shillong. We are thankful to the Sophisticated Analytical and Instrumentation Facility (SAIF) North-Eastern Hill University and Indian Institute of Technology (IIT)-Bombay. We are grateful to ACMS IIT-Kanpur and Central Instruments Facility (CIF) IIT-Guwahati. We also take this opportunity to thank the Institute of Advanced Study in Science and Technology (IASST), Guwahati.

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REFERENCES

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Ru-Ferrite-Decorated Graphene (RuFG): A Sustainable and Efficient

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