Unprecedented EsterâAmide Exchange Reaction Using Highly

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Article

An unprecedented ester-amide exchange reaction using highly versatile two-dimensional graphene oxide supported base metal nanocatalyst Rakesh K Sharma, Aditi Sharma, Shivani Sharma, and Sriparna Dutta Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00498 • Publication Date (Web): 21 Feb 2018 Downloaded from http://pubs.acs.org on February 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

An unprecedented ester-amide exchange reaction using highly versatile two-dimensional graphene oxide supported base metal nanocatalyst Rakesh K. Sharma*, Aditi Sharma, Shivani Sharma and Sriparna Dutta Green Chemistry Network Centre, Department of Chemistry, University of Delhi, NewDelhi110007, India. Fax: +91-011-27666250; Tel: 011-276666250 Email: [email protected]

ABSTRACT: The present study is the first report of an atom economical and environmentally benign amidation of unactivated esters wherein a novel and highly versatile graphene oxide based cobalt nanocatalytic system has been effectively exploited for the synthesis of pharmaceutically significant amide derivatives under neutral reaction conditions. Experimental results revealed that the developed catalyst not only possesses immense potential to accelerate ester amide exchange reaction in absence of any additives but also exhibits several remarkable attributes like wide functional group tolerance, durability, high turnover numbers, improved yield, recycling and reusability for subsequent runs without any discernible loss in the catalytic activity. The enhanced catalytic performance may be attributed to the structure of 2-D graphene oxide based material which provides space between graphitic overlayers and metal surfaces making it work like a nanoreactor to expedite ester amide exchange reaction.

ACS Paragon Plus Environment

1

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 37

KEYWORDS: two-dimensional, graphene oxide, nanocomposite, cobalt, ester-amide exchange, economically viable

1.

INTRODUCTION

Amide motifs are one of most versatile functional groups in the repertoire of organic chemistry that not only underpin the connectivity of bioactive macromolecules but also widely occur in a vast array of synthetic auxiliaries and supramolecular assemblies owing to relative chemical inertness and remarkable bond strength.1-2 In fact, amide formation has been identified as the largest subset of frequently employed chemical transformations executed in many world renowned pharmaceutical companies like GSK, Astra Zeneca and Pfizer for the synthesis of highly potent drugs.3 Driven by this prevalence, a plethora of appealing approaches have been reported in the literature to synthesize amide derivatives which include direct amidation of carboxylic acid, dehydrogenative amidation of alcohols, amidation of aldehydes, amination of acid chlorides, transamidation of carbinols and nitration of arenes followed by reduction.4-12 Nevertheless, these conventional methodologies suffer from innate drawbacks such as intricate reaction procedures, harsh conditions, production of unwanted by-products and low yield that pose deleterious environmental threats.13 Hence, catalytic and waste-free generation of amides avoiding any hazardous as well as poor atom economy reagents has been highlighted as one of the formidable challenges for the scientific community by American Chemical Society Green Chemistry Institute Pharmaceutical Round Table (ACS GCIPR).14 In search of improved synthetic methodologies, amidation of esters that often employ transition metal catalysts such as lanthanum, nobelium, ruthenium and zirconium has emerged as viable gateway for obtaining amides since it provides notable benefits over traditional reaction chemistry including improved yield, better selectivity and higher turnover numbers.15-24 Despite such remarkable features, the


2

Page 3 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


large scale practical applicability of aforementioned protocols is still hampered as they fail to meet industrial requirements due to involvement of precious homogeneous catalytic systems. Therefore, rational design and development of versatile catalysts which can be effectively exploited to access such important compounds in a more economical way with higher efficiency has become a subject of continued research for organic chemists and researchers. Recently, heterogenization of active catalytic species has emerged as an elegant and ingenious methodology to generate organic-inorganic hybrid catalysts having immense potential to accelerate chemical transformations.24-31 Indeed, until now a great array of endeavors has been directed towards immobilization of existing metal complexes onto different solid support matrices such as organic polymers, dendrimers, mesoporous materials and so forth.32-37 In this perspective, advent of engineered nanomaterials has brought a major breakthrough in arena of catalysis as they can be effectively employed as support materials to generate novel quasihomogeneous catalysts exhibiting outstanding dispersion capability in reaction medium that address the diffusion problems associated with bulk catalytic systems. Among all the nanostructures enlisted in literature, graphene oxide offers excellent prospects to provide a scaffold for such third generation catalyst because of numerous impressive structural properties including thermal and chemical stability, good accessibility, high specific surface area and porosity. Besides, high thermal conductivity of graphene oxide allows the conduction and diffusion of heat released during catalytic reaction. Moreover, they offer tremendous opportunities of chemical modification or functionalization due to presence of abundant hydroxyl, epoxy, carboxyl and carbonyl groups on the surfaces which proliferates their use as an exceptional 2-D solid support material in different chemical reactions.38-44


3


Page 4 of 37

As a part of our ongoing research work focused on exploring the activities of organic-inorganic hybrid nanomaterials as a future material in sensors, metal scavengers and catalysts for various organic transformations, herein, we present a novel and versatile graphene oxide based cobalt nanocatalytic system (Co@BA@APTES@GO) that expedites ester amide exchange reaction to afford amide derivatives under neutral conditions.45-52 The newly developed nanostructured catalyst not only demonstrates benefits like the ease of product separation and recyclability upto eight cycles but also displays improved efficiency as a result of stable active site as well as better steric control of the reaction intermediate. To best of our knowledge this is the first example of an economical and environmentally benign aminolysis of esters wherein a cobalt based heterogeneous catalyst has been effectively exploited for the synthesis of pharmaceutically significant amides without any pre-activation steps and use of additives, thus rendering it an appealing alternative to the existing methodologies.

2.

EXPERIMENTAL SECTION Chemicals and Materials. Graphite powder (Sigma Aldrich), 3-aminopropyltriethoxysilane

(APTES) (Fluka), Benzoylacetone (BA) (Spectrochem Pvt. Ltd, India) were commercially procured. All other materials and reagents were acquired from Alfa Aesar and used as obtained without any further purification. Characterization. Fourier transform infrared (FTIR) was performed on a Perkin Elmer Spectrum 2000 FT-IR operated in the range of 4000- 400 cm-1 spectrometer using the KBr pellet method. Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku Miniflex 600 Diffractometer equipped with Cu/Ka radiation. The samples were scanned at 2θ range of 5–70° (λ = 0.154059 nm, 40 kV, 15 mA). Transmission electron microscopy (TEM) micrographs were acquired using TECNAI G2 T30 microscope by drying nanosheets droplet from ethanolic


4

Page 5 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


solution onto carbon coated copper grid. This technique was used to acquire information about the morphology of the nanosheets. Besides TEM, Field emission scanning electron microscopic (FESEM) images were recorded using on a Tescan Mira 3 microscope which gave information about morphological characteristics of synthesized nanomaterials and energy dispersive X-ray spectroscopy (EDS) equipped with the SEM instrument authenticated the detailed elemental composition of nanomaterials. Energy dispersive X-ray fluorescence (ED-XRF) spectroscopy was carried out using a Fischerscope X-Ray XAN-FAD BC. X-ray photoelectron spectroscopy (XPS) analysis was performed with multitechnique surface analysis system using monochromatized Al Kα radiation (1486.7 eV). The Nitrogen adsorption/desorption isotherms of the synthesized nanomaterials were measured at 77 K using MICROMERITICS ASAP2020 Surface Area Analyzer (Sample amount ≈ 500 mg). Before analysis, the samples were degassed at 130 °C for 12−14 h under 0.1333 Pascal pressure. Inductively coupled mass spectroscopy (ICP-MS) was also conducted in order to confirm the cobalt loading of the catalyst using ICPMS (Model no. 7700e). GC-MS hyphenated technique was used to analyze the derived products through Agilent gas chromatograph (6850 GC) with HP-5MS 5 % phenyl methyl siloxane capillary column (30.0 m x 250 µm x 0.25 µm) and a quadrupole mass filter-equipped 5975 mass selective detector (MSD) using helium as the carrier gas (rate 0.9 mL min-1). Isolated yield of amides were confirmed by 1H (400 MHz) using a JEOL JNM-EXCP 400. Synthesis of graphene oxide nanosheets (GO). Graphene oxide nanosheets were synthesized by the oxidation and exfoliation of graphite powder according to the modified hummers method.53 In a typical experiment, graphite powder (1 g), concentrated sulphuric acid (23 ml) and sodium nitrate (0.5 g) were mixed in a round bottom flask and the resulting mixture was continuously stirred for 30 min under ice-bath maintaining temperature 0-5 oC. KMnO4 (6 g) was


5


Page 6 of 37

then added to the suspension with gradual stirring and the flask was kept oxidizing at 0 oC for 2 h. Afterwards, the temperature of the mixture was raised to 35 oC for 30 min. Subsequently, 46 ml of deionized water was slowly added to the suspension with vigorous stirring and then the temperature was raised to 98 oC for 15 min using an oil bath. The reaction mixture was further diluted with 140 ml of deionized water followed by addition of 30% H2O2 solution which changed the colour of solution from brown to brilliant orange. The resulting suspension was centrifuged and washed with 5% HCl and deionized water. Finally, the obtained solid was dried at 70 oC to obtain graphene oxide nanosheets. Synthesis of amine functionalized graphene oxide nanosheets (APTES @GO). Initially, 1 g of as-prepared GO was dispersed in 50 ml of absolute ethanol by ultrasonication for 0.5 h to obtain exfoliated nanosheets. Subsequently, 2 mmol of APTES was added dropwise to the suspension with constant stirring and refluxed at 80 oC for 6 h.54 After cooling to room temperature, the obtained functionalized nanosheets were separated via centrifugation. The resulting black solid (APTES@GO) was washed several times with ethanol to remove residual APTES and dried under vacuum overnight. Synthesis of graphene oxide nanosheets based cobalt catalyst (Co@BA@APTES@GO). The as-prepared APTES@GO (0.5 g) was nicely dispersed in 30 ml of absolute ethanol again. Then, mixture of dispersed APTES@GO and 1-phenyl-1,3-butanedione (BA, 10 mmol) was refluxed at 80 oC for 5 h.55 After the stated time, the mixture was centrifuged, washed 2-3 times with ethanol to remove unreacted ligand and dried to afford black solid (BA@APTES@GO). In order to obtain, the final nanocatalyst, a solution of CoCl2.6H2O in acetone was prepared to which BA@APTES@GO was added and stirred continuously at room temperature for 9 h


6

Page 7 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(scheme 1). The obtained nanocomposites Co@BA@APTES@GO were isolated via centrifugation, washed and dried under vacuum at 70 oC.

Scheme 1. Schematic illustration for the synthesis of Co@BA@APTES@GO nanocatalyst. General method for the Co@BA@APTES@GO catalyzed amidation of esters. A mixture of 5 mmol of ethyl acetate, 6.5 mmol of benzyl amine, 1.2 ml of toluene and 25 mg of catalyst were refluxed at 110 oC for 20 h to achieve amidation of esters. After the stated time, the nanocatalyst was recovered by centrifugation at room temperature and washed thoroughly with ethyl acetate to reuse in sequential runs. Thereafter, the reaction product was extracted by using ethyl acetate and dried over anhydrous sodium sulphate. Finally, the product was quantified through Gas Chromatography Spectroscopic technique (GC-MS).


7


Page 8 of 37

3. RESULTS AND DISCUSSION FT-IR. FT-IR analysis was conducted in order to extract structural information of GO,

APTES@GO, BA@APT4ES@GO and Co@BA@APTES@GO by the identification of appropriate functional groups as shown in Figure. 1. FT-IR Spectrum of pure GO exhibits a broad vibrational peak at 3410 cm-1 depicting the presence of hydroxyl group and hydrogen bonded water molecules.56 Additionally, distinguishable absorption peaks at 1730, 1624, 1392, 1250 and 1064 cm-1 can be assigned to various stretching vibrations of C=O, C=C, =C-H, C-O and C-O-C bond respectively which provide a strong evidence for the presence of carboxylic acid and epoxy functional groups. After functionalization of GO with APTES, the appearance of two new peaks at 2941 and 1633 cm-1 verify the introduction of CH2 and NH2 groups of aminopropyl moiety respectively. Furthermore, vibrational assessments at 1117 and 1019 cm-1 correspond to stretching vibrations of Si-O and Si-O-C reveal the successful silylanization of GO nanosheets (APTES@GO).57 An enhanced sharp band appearing at 1630 cm-1 is associated with stretching vibrations of C=N (imine) group that corroborates the immobilization of ligand over amine functionalized graphene oxide (BA@APTES@GO).58 Notably, a red shift is observed in the spectrum of Co@BA@APTES@GO nanocatalyst compared to the imine vibrations of schiff base which can be attributed to electron delocalization of C=N and co-ordination interaction with cobalt metal. These results authenticate the successful anchoring of cobalt complex onto GO surface as Co@BA@APTES@GO.


8

Page 9 of 37

(d) 1322

3393

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1620

2930

1098 1028

(c) 3360

2941

1322 1630 1544 1108 1030

2941

1633

(b) 3402

1117 1019

(a)

1392 1730

3410

4000

3500

3000

2500

2000

1624

1250 1064

1500

1000

500

-1

Wavenumber (cm )

Figure 1. FT-IR spectra of (a) GO, (b) APTES@GO, (c) BA@APTES@GO and (d) Co@ BA@APTES@GO. SEM and TEM analysis. Scanning electron microscopy (SEM) and transmission electron

microscopy (TEM) are powerful magnification tools which provide considerable amount of information about the composition, morphology and texture of nanocomposites. The detailed morphology and internal structure of the synthesized nanostructured materials have been investigated using SEM and TEM techniques as shown in Figure. 2. The results obtained from SEM analysis reveal that GO is composed of twisted two-dimensional planar nanosheets having folded regions and wrinkled features where thickness is very small relative to the sheet area.59 The extent of protrusions and crumpling increases as we move from GO to APTES@GO to Co@BA@APTES@GO nanomaterials that provide enormous surface area and hence induces


9


Page 10 of 37

high degree of active catalytic sites for efficient chemical transformations.60 A representative TEM micrograph of GO further verifies the corrugated sheet like nature of material with a lateral dimension up to several micrometers.61 It is also noticed that the crumpled morphology is maintained even after functionalization of organic moieties which confirms that the microstructure of GO is not destroyed even after surface modification reactions. In addition, SEM image of the recovered nanocatalyst does not show any change in the shape and morphology of the nanosheets suggesting that the catalyst is robust enough to withstand the applied reaction conditions (Figure. S1, Supporting Information).

Figure 2. SEM micrographs of (a) GO, (b) APTES@GO, (c) Co@BA@APTES@GO, and TEM micrographs of (d) GO, (e) APTES@GO and (f) Co@BA@APTES@GO.


10

Page 11 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


XRD. XRD analysis was conducted in order to investigate the crystallographic structure,

chemical composition and physical properties of synthesized GO based nanomaterials. As shown in Figure. 3, XRD pattern of graphite exhibits an intense and narrow characteristic Bragg’s peak at 2θ = 26.6o having d-spacing 0.843 nm corresponding to (002) crystal plane.62 Further, comparative XRD analysis of graphite and GO reveals a shift with slightly broader reflection towards lower Bragg’s angle 2θ = 12.6o having d-spacing 0.846 nm corresponding to (001) plane which authenticates the formation of GO due to introduction of oxygenic functional groups and the water molecules trapped in interlayer spacing.63-64 On moving from GO to APTES@GO, the characteristic GO diffraction peak showed diminished intensity and a new peak around 2θ = 22o was observed which indicated the successful immobilization of aminopropyl moiety onto GO nanosheets.65 Further, after immobilization of the BA ligand on the amine functionalized GO surface and successive metallation it was found that both the diffraction peaks appeared but with reduced intensities. All these observations confirmed that nanostructure of GO is retained even after the surface modifications thereby indicating the stability of bare GO to withstand chemical modification reactions.66


11


(e)

(d)

(c)

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 37

(b)

(a)

10

20

30

40

50

60

70

Degrees (2θ) Figure 3. Powder XRD curves of (a) Graphite, (b) GO, (c) APTES@GO, (d) BA@APTES@GO and (e) Co@BA@APTES@GO. XPS. X-ray photoelectron spectroscopy was conducted in order to acquire information about

chemical and electronic states of elements present within the synthesized nanocomposites. The obtained spectra of GO, APTES@GO and Co@BA@APTES@GO have been presented in Figure 4. Compared to the XPS curve of GO, APTES@GO showed the appearance of two new bands at 101.2 eV and 399.1 eV corresponding to Si-O and C-N bonds. Apart from this, the curve also shows a noticeable decrease in the binding energy values of C−O−C and C−OH bonds. These observations clearly confirm the successful silylation of the GO support (silylation due to reaction between silanol group of APTES and surface hydroxyl groups of GO). On moving towards Co@BA@APTES@GO, we find that the N1s signal is shifted to a higher value


12

Page 13 of 37

indicating that a considerable amount of NH2 has been converted into N=C after condensation with 1-pheyl-1,3-butanedione.67 Besides, the emergence of distinct signals appearing at 781.4 and 801.1 eV correspond to the binding energy values of Co (II) which provides a concrete proof of the oxidation state of the metal present in the nanocatalyst.68 Considering the limitation of surface characterization by XPS, the cobalt content is determined by inductively coupled plasma mass spectrometry (ICP-MS) and the cobalt loading was detected to be 0.125 mmol g-1 (2.96 wt

(a)

800

600

Si 2s

Si 2p Si 2p

C 1s

O 1s

N 1s

(b)

C 1s

O 1s

N 1s

Co 2p 1/2 Co 2p 3/2

(c)

Si 2s

O 1s

C 1s

%) which means that 0.125 mmol of cobalt is present in 1 g of the catalyst.

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


400

200

0

Binding energy (eV) Figure 4. XPS spectra of (a) GO, (b) APTES@GO and (c) Co@BA@APTES@GO.


13


Page 14 of 37

Physicochemical characterizations. The elemental composition of the spectra of BA@APTES@GO

and Co@BA@APTES@GO are represented in Figure 5. The EDX spectrum of BA@APTES@GO samples was confirmed through EDX and ED-XRF. The EDX shows the presence of carbon, oxygen, nitrogen and silicon which firmly identify the incorporation of amine group and ligand on the surface of GO. Apart from these elements, appearance of an additional peak of cobalt metal authenticated the successful metallation of BA@APTES@GO. In addition to EDX technique, a well resolved peak of cobalt metal in ED-XRF spectrum of synthesized catalyst also verified the presence of cobalt in the final nanocatalyst (Figure 6).

Figure 5. EDX spectra of (a) APTES@GO and (b) Co@BA@APTES@GO catalyst.


14

Page 15 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. ED-XRF spectrum of Co@BA@APTES@GO catalyst. CATALYTIC EVALUATION The efficacy of the newly fabricated Co@BA@APTES@GO nanocatalyst was examined for the industrially significant aminolysis of esters in which ethyl acetate and benzyl amine were chosen as test substrates for model reaction. In order to obtain optimum reaction profile, the effect of various reaction parameters such as amount of catalyst, time, temperature and solvents were studied comprehensively for the amidation of esters. Catalyst screening and effect of catalyst loading. Initially, optimization of the reaction conditions was carried out by exploring the role of catalyst in the synthesis of amides. The test substrates were subjected to amidation of esters in the absence of catalyst. It was found that only 10% of the target amide product could be obtained which signified the need of a catalyst in this reaction. Thereafter, the efficacy of different metal based sources was investigated to achieve this transformation (Supporting Information, Table S1). A detailed analysis of the observed


15


results showed that the newly developed graphene oxide based cobalt nanocatalyst (Co@BA@APTES@GO) exhibited better catalytic activity in comparison to the other precious metal salts for the amidation of esters. It is also worth noting that nanostructured catalyst carried out the aminolysis of esters under mild reaction conditions without any waste generation and hence proved to be a better alternative in comparison to the homogeneous transition metal. Additionally, in order to investigate the effect of catalyst amount, the selected model reaction was carried out with different amounts of the synthesized heterogeneous cobalt catalyst. As the amount of catalyst was increased from 5 mg to 25 mg the conversion percentage changed from 55 to 100% (Figure 7). This constructive effect towards the reaction conversion can be attributed to the proportional increase in number of active sites with increase in catalytic amount. Finally, the amount of catalyst was fixed to 25 mg.

100

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 37

80 60 40 20 0 0 (0)

5 (0.015)

10 (0.03)

15 (0.045)

20 (0.06)

25 (0.075)

Amount of catalyst (mg/wt%)

Figure 7. Effect of amount of catalyst on amidation of esters [Reaction conditions: ethyl acetate (5 mmol), benzyl amine (6.5 mmol), toluene (1.2 mL), catalyst, 20 h, reflux (110 oC)]. Effect of various solvents. Solvents had a remarkable impact on conversion percentage of the

product formed in the amidation of esters. In order to achieve best catalytic conversion, the test


16

Page 17 of 37

substrates were subjected to different solvents of varying polarities like toluene, amyl alcohol, DMF, water as well as under solvent free conditions (Figure 8). It was observed that the conversion of reactants to products was poor in the presence of polar solvents (water, amyl alcohol, DMF) because of decreased reaction rate and deactivation of catalyst whereas in nonpolar solvents (n-heptane, toluene, benzene), not only the conversion percentage increased drastically but also the formation of amides was much quicker. The conversion percentage was found to be highest (100%) in the presence of toluene. So, rest of the studies were carried out by taking toluene as a solvent since the reaction didn’t proceed well in solvent free conditions and other commonly used solvents.

No Solvent DMF Amyl alcohol

Solvents

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Water n-Heptane Toluene 0

20

40

60

80

100

Conversion (%) Figure 8. Effect of solvents on the amidation of esters [Reaction conditions: ethyl acetate (5 mmol), benzyl amine (6.5 mmol), solvent (1.2 mL), catalyst (25mg), 20 h, reflux].


17


Effect of reaction time and temperature. Time and temperature are the two parameters which play a vital role in controlling the kinetic and thermodynamic activities of the reaction. In order to scrutinize the influence of time and temperature on amide formation, the test reaction was performed at different intervals of time period (5-20 h) for a diverse range of temperature (30-110 oC). A close comparison of results suggested that the conversion percentage increased from 10 to 100% as time was increased from 5 h to 20 h. These results have been presented in Figure 9 in which the conversion percentage is represented as a function of time and temperature. A careful examination of the results revealed that on increasing the temperature, a rise in conversion percentage occurred and best results were obtained at 110 oC when the reaction was continued for 20 h. Therefore, it was concluded that the optimum temperature and time for the amidation of esters were 110 oC and 20 h respectively.

100 80 60 40 20

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 37

0

20

110

C) ( e 70 ur t a 50 er p 30 m Te 90

5

Ti 1 m e( h)

10 5


o

18

Page 19 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9. Effect of time and temperature on amidation of esters [Reaction conditions: ethyl acetate (5 mmol), benzyl amine (6.5 mmol), toluene (1.2 mL), catalyst (25mg)]. Catalytic stability. In order to evaluate the intrinsic stability and heterogeneity of the newly synthesized Co@BA@APTES@GO nanocatalyst, a hot filtration test was carried out. For that, the model reaction was carried out under optimized reaction conditions using graphene oxide supported cobalt catalyst. After continuing stirring of the reaction mixture for about 10 h i.e. half of the reaction time, the catalyst was recovered via centrifugation. Subsequently, GC-MS of the supernatant was carried out in order to find out the conversion percentage and it was observed that the reaction had reached 79% completion at the end of 10 h. The resultant clear solution was subjected to further stirring until regular time. The GC-MS results suggested that the reaction was hard to occur even after prolonged time as the removal of catalyst had stopped the reactivity. Thus we conclude that there was no loss of catalytic components during the course of reaction. Recyclability test To evaluate the sustainability and large scale industrial applicability of the synthesized catalyst, a reusability test was performed. For doing so, the model reaction was carried out under optimized conditions. After the reaction completion, the catalyst was recovered from reaction mixture by centrifugation, washed with copious amount of ethyl acetate to remove the traces of previous reaction mixture and dried under vacuum. Subsequently, the recovered nanocatalyst was used again in further runs of the same reaction. It was found that in all the experiments, the conversion percentage of desired product remained almost the same. These results showed that the catalyst could be used for at least 8 cycles without any significant loss of catalytic activity which established the stability of the catalyst (Figure 10). This observation was further supported by FT-IR, TEM and SEM analysis of the recovered catalyst. FT-IR spectrum of recovered


19


catalyst reveals that the structure of recovered catalyst does not show any change in comparison with the fresh catalyst even after being subjected to 8 runs (Supporting Information, Figure S2).

100

80

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 37

60

40

20

0 1

2

3

4

5

6

7

8

No. of Runs Figure 10. Catalyst recycle runs for the amidation of esters [Reaction conditions: ethyl acetate (5 mmol), benzyl amine (6.5 mmol), toluene (1.2 mL), catalyst (25 mg), 20 h, reflux (110 oC)]. Co@BA@APTES@GO catalysed amidation of esters A series of amines were coupled with different esters to investigate the scope and generality of the ester-amide exchange protocol under the established reaction conditions (Table 1). Focussing on the ester substrates, it was observed that both small chains as well as long chain alkyl groups were well tolerated as they afforded the desired products with high conversion. However in case of amines, better results were observed in case of cyclic and unsubstituted aromatic amines whereas in the case of substituted benzylamines especially those containing electron


20

Page 21 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


withdrawing groups, the desired product could not be detected at all due to electronic effect. In general, this methodology offered a broad substrate scope and also showed good economic competitiveness in comparison to the literature precedents as a large number of amide derivatives could be synthesized using a much cheaper cobalt based graphene oxide supported nanocatalyst. Table 1. Amidation of esters using Co@BA@APTES@GO as catalysta

TONd

Uses

Time (h)

1

Anticonvulsant drug

20

100/99

320

2

Synthesis of SRX-251 for the treatment of pain associated with primary dysmenorrhoea

20

100/98

320

3

New carboxyalkyl inhibitors of brain enkephalinase

20

100/98

320

4

Used in antifungal drugs

20

70/65

224

5

Analgesic drugs to cure pain

20

30/23

90

6

Anticonvulsant drug

20

46/44

131

Entry

Ester

Amine


Conversion (%)b/Yieldc

21


Page 22 of 37

7

A highly potent antipsychotic and a major tranquilizer

20

47/40

150

8

Treatment or prevention of dengue infection

24

68/66

218

9

Herbicides

20

100/95

320

10

Preparation of psychotropic drug

24

13/10

42

Aripiprazole 11

New carboxyalkyl inhibitors of brain enkephalinase

20

60/55

192

12

Used as excipient (carrier ingredient) in human

24

Nil

-

13

Derivatives used as tyrosinase inhibitor

24

08/05

22

14

substituted benzamides are therapeutically used as neuroleptics and antipsychotics

24

46/39

70

-

20

10/5

32

Synthesis of antibiotics like ampicillin

24

Nil

-

24

Nil

-

15

16

17 -


22

Page 23 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

Reaction conditions: ester (5mmol), amine (6.5 mmol), toluene (1.2 ml), catalyst (25 mg), reflux at 110 °C. bConversion percentage was determined by GC-MS. Isolated yieldc. dTON is the no. of moles of product per mole of catalyst. Proposed reaction mechanism. A plausible reaction mechanism has been proposed for the

amidation of esters to afford amides (Scheme 2). The first step involves the oxidative addition of amine to graphene oxide supported cobalt nanocatalyst (A) to generate cobalt hydride complex B. In the next step, co-ordination of carbonyl group of ester leads to the formation of complex C. Thereafter, intramolecular nucleophilic attack of amino group at the carbonyl group of the ester results in formation of the amide and generation of the alkoxy intermediate D. Nucleophilic acyl substitution is followed by reductive elimination of alcohol which regenerates catalyst A.69-71


23


Scheme

2.

Plausible

mechanism

for

the

amidation

Page 24 of 37

of

esters

catalyzed

by

Co@BA@APTES@GO.

Comparison of the catalytic activity of Co@BA@APTES@GO with the previously reported catalytic systems. An extensive study of the previous literature reports on the esteramide exchange reaction reveals that although good catalytic results have been obtained in these cases, however no non-precious metal catalyst has been employed till date. This is for the very first time that cobalt which is a base metal catalyst has been utilized for concerned reaction. Besides, it is important to mention that all the earlier catalysts were homogeneous and had serious limitations associated. For instance, a homogeneous catalyzed reaction mixture could show probability of forming inactive dimers or aggregates that obstructed the catalytic active


24

Page 25 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


sites, thereby hampering its activity. On the contrary, the present protocol involves a supported heterogeneous cobalt catalyst that smartly overcomes this disadvantage by showing site isolation effect due to the immobilization of anchoring species as a result of which the active catalytic sites are separated out from each other, thus increasing the efficiency of the process. As a result of 2-D confinement effect, the synthesized catalyst exhibits superior reactivity in terms of high conversion percentage and reaction conditions because of the nanometer sized two dimensional structure of the nanocomposites that results in a net enhancement in the active catalytic sites. All these attributes collectively render this protocol a promising alternative to the literature precedents (Table S2).

4.CONCLUSION In summary, we have developed a novel, efficient and recyclable base metal nanocatalyst through covalent anchoring of 1-phenyl-1, 3-butandione cobalt complex onto amine functionalized graphene oxide nanosheets. Graphene oxide serves as an excellent platform for catalytic molecular engineering. In particular, the presence of abundant hydroxyl functionalities onto the surface of graphene oxide nanosheets allowed the successful loading of schiff base metal complex via successive surface modifications. 2-Dimensional Co@BA@APTES@GO nanocomposite exhibited remarkable efficacy for the synthesis of pharmaceutically important amides via oxidative ester-amide exchange reaction under mild condition. The exceptional activity of heterogeneous nanocatalyst could be accredited to presence of nanometer size of support material as well as 2-D confinement which provides large number of catalytically active sites. Besides, it could be conveniently recovered and reused several times without any significant degradation in its activity. Moreover, simple work up procedure, shorter reaction time, excellent durability, convenient recoverability and reusability are the unique advantages of


25


Page 26 of 37

this synthetic methodology which presented its potential for practical applications. We anticipate the developed graphene oxide based catalyst with added benefits of the flexibility in immobilization of chemical moieties onto graphene oxide nanosheets would promote several other industrially significant organic transformations in an environmentally benign manner. ASSOCIATED CONTENT Supporting Information. A brief statement as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.” AUTHOR INFORMATION Corresponding Author Green Chemistry Network Centre, Department of Chemistry, University of Delhi, NewDelhi110007,

India.

Fax:

+91-011-27666250;

Tel:

011-276666250

Email:

[email protected]. ACKNOWLEDGMENT One of the authors Aditi Sharma thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for the award of Junior Research fellowship. The author also thanks USIC-CIL, DU for FT-IR, SEM, TEM, XRD and DRDO for XPS analysis. REFERENCES (1)

Dunetz, J. R.; Magano, J.; Weisenburger, G. A. Large-Scale Applications of Amide Coupling Reagents for the Synthesis of Pharmaceuticals. Org. Process Res. Dev. 2016, 20, 140-177.


26

Page 27 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(2)

Valeur, E.; Bradley, M. Amide bond formation: beyond the myth of coupling reagents. Chem.Soc.Rev. 2009, 38, 606–631.

(3)

Lanigan, R. M.; Starkov, P.; Sheppard, T. D. Direct synthesis of amides from carboxylic acids and amines using B(OCH2CF3)3. J. Org. Chem. 2013, 78, 4512−4523.

(4)

Carey, J. S.; Laffan, D.; Thomsonc, C.; Williams, M. T. Analysis of the reactions used for the preparation of drug candidate molecules. Org. Biomol. Chem. 2006, 4, 2337– 2347.

(5)

Huang, Y.; Chen, T.; Li, Q.; Zhou, Y.; Yin, S.F. Copper catalyzed direct amidation of methyl groups with N–H bonds. Org. Biomol. Chem. 2015, 13, 7289–7293.

(6)

Saha, B.; Sengupta, G.; Sarbajna, A.; I Dutta, I.; Bera, J. K. Amide synthesis from alcohols and amines catalyzed by a Ru II–N-heterocyclic carbene (NHC)–carbonyl complex. J. Org. Chem. 2013, 12, 051.

(7)

Lundberg, H.; Tinnis, F.; Adolfsson, H. Direct Amide Coupling of Non‐activated Carboxylic Acids and Amines Catalysed by Zirconium (IV) Chloride. Chem. Eur. J. 2012, 18, 3822 – 3826.

(8)

Pattabiraman, V. R.; Bode, J. W. Rethinking amide bond synthesis. Nature 2011, 480, 471-479.

(9)

Xie, X.; Huynh, H. V. Tunable Dehydrogenative Amidation versus Amination Using a Single Ruthenium-NHC Catalyst. ACS Catal. 2015, 5 4143-4151.

(10)

Xie, P.; Xia, C.; Huang, H. Palladium-Catalyzed Oxidative Aminocarbonylation: A New Entry to Amides via C–H Activation. Org. Lett. 2013, 15, 3370-3373.


27


(11)

Page 28 of 37

Meng, G.; Shi, S.; Szostak M. Cross-Coupling of Amides by N–C Bond Activation. Synlett. 2016, 27, 2530-2540.

(12)

Der, J. E.; Garg, N. K. Breaking Amides using Nickel Catalysis. ACS Catal. 2017, 7, 1413-1423.

(13)

Gnanaprakasam, B.; Milstein, D. Synthesis of amides from esters and amines with liberation of H2 under neutral conditions. J. Am. Chem. Soc. 2011, 133, 1682–1685.

(14)

Krause, T.; Baader, S.; Erb, B.; Gooßen, L. J. Atom-economic catalytic amide synthesis from amines and carboxylic acids activated in situ with acetylenes. Nat. Commun. 2015, 7.

(15)

Bao, Y. S.; Baiyin, M.; Agula, B.; Jia, B. M.; Zhaorigetu, B. Energy-Efficient Green Catalysis: Supported Gold Nanoparticle-Catalyzed Aminolysis of Esters with Inert Tertiary Amines by C–O and C–N Bond Activations. J. Org. Chem. 2014, 79, 6715−6719.

(16)

Lenstra, D. C.; Nguyen, D. T.; Mecinovi, J. Zirconium-catalyzed direct amide bond formation between carboxylic esters and amines. Tetrahedron 2015, 7, 5547-5553.

(17)

Ali, M. A.; Siddiki, S. M. A. H.; Kon, K.; Shimizu, K.I. A Heterogeneous Niobium (V) Oxide Catalyst for the Direct Amidation of Esters. ChemCatChem. 2015, 7, 2705 – 2710.

(18)

Lee, J.; Muthaiah, S.; Honga, S. H. Tandem Synthesis of Amides and Secondary Amines from Esters with Primary Amines under Solvent‐Free Conditions. Adv. Synth. Catal. 2014, 356, 2653 – 2660.


28

Page 29 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19)

Fujiwara, R.; Shimizu, Y.; Morisaki, K.; Ohshima T.; Morimoto, H. Lanthanum (III) Triflate Catalyzed Direct Amidation of Esters. Org. Lett. 2014, 16, 2018−2021.

(20)

Han, Q.; Xiong, X.; Li, S. An efficient, green and scale-up synthesis of amides from esters and amines catalyzed by Ru-MACHO catalyst under mild conditions. Catal. Commun. 2015, 58, 85–88.

(21)

Han, C.; Lee, J. P.; Lobkovsky, E.; Porco, J. A. Catalytic ester-amide exchange using group (IV) metal alkoxide-activator complexes. J. Am. Chem. Soc. 2005, 127, 1003910044.

(22)

Lanigan, R. M.; Sheppard, T. D. Recent developments in amide synthesis: Direct amidation of carboxylic acids and transamidation reactions. Eur. J. Org. Chem. 2013, 7453–7465.

(23)

Kang, B.; Fu, Z.; Hong, S. H. Ruthenium-catalyzed redox-neutral and single-step amide synthesis from alcohol and nitrile with complete atom economy. J. Am. Chem. Soc. 2013, 135, 11704−11707.

(24)

Nguyen, D. T.; Lenstra, D. C.; Mecinović, J. Chemoselective calcium-catalysed direct amidation of carboxylic esters. RSC Advances, 2015, 5, 77658-77661.

(25)

Li, L.; Zhu, Y.; Lu, X.; Wei, M.; Zhuang, W.; Yang, Z.; Feng, X. Carbon heterogeneous surface modification on a mesoporous TiO2-supported catalyst and its enhanced hydrodesulfurization performance. Chem. Commun. 2012, 48, 11525–11527.


29


(26)

Page 30 of 37

Dang, T. T.; Zhu, Y.; Ngiam, J. S. Y.; Ghosh, S. C.; Chen, A.; Seayad A. M. Palladium nanoparticles supported on ZIF-8 as an efficient heterogeneous catalyst for aminocarbonylation. ACS Catal. 2013, 3, 1406−1410.

(27)

Julkapli, N. M.; Bagher, S. Graphene supported heterogeneous catalysts: an overview. Int. J. Hydrogen Energy. 2015, 40, 948-979.

(28)

Gawande M. B.; Brancoa, P. S.; Varma, R. S. Nano-magnetite (Fe3O4) as a support for recyclable catalysts in the development of sustainable methodologies. Chem. Soc. Rev. 2013, 42, 3371-3393.

(29)

Gan, W.; Dyson, P. J.; Laurenczy, G. Heterogeneous Silica‐Supported Ruthenium Phosphine Catalysts for Selective Formic Acid Decomposition. ChemCatChem. 2013, 5, 3124 – 3130.

(30)

Aghapoor, K.; Nia, L. E.; Mohsenzadeh, F.; Morad, M. M.; Balavar, Y.; Darab, H. R. Silica-supported bismuth (III) chloride as a new recyclable heterogeneous catalyst for the Paal–Knorr pyrrole synthesis. J. Organomet. Chem. 2012, 708, 25-30.

(31)

Soichiro, S.; Murakami, R.; Iwai, T.; Sawamura, M. Synthesis of primary and secondary alkylboronates through site-selective C(sp3)–H activation with silica-supported monophosphine–Ir catalysts. J. Am. Chem. Soc. 2013, 135, 2947−2950.

(32)

Basu, B.; Paul, S. An improved preparation of mesoporous silica-supported Pd as sustainable catalysts for phosphine-free Suzuki-Miyaura and Heck coupling reactions. Appl. Organometal. Chem. 2013, 27, 588–594.


30

Page 31 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33)

Bhanja, P.; Das, S. K.; Patraa, A. K.; Bhaumik, A. Functionalized graphene oxide as an efficient adsorbent for CO2 capture and support for heterogeneous catalysis. RSC. Adv. 2016, 6, 72055-72068.

(34)

Shao, L.; Huang, X.; Teschner, D.; Zhang, W. Gold supported on graphene oxide: an active and selective catalyst for phenylacetylene hydrogenations at low temperatures. ACS Catal. 2014, 4, 2369−2373.

(35)

Zhang, F.; Jiang, H.; Li, X.; Wu, X.; Li, H. Amine-functionalized GO as an active and reusable acid–base bifunctional catalyst for one-pot cascade reactions. ACS Catal. 2014, 4, 394−401.

(36)

Nie, R.; Wanga, J.; Wangb, L.; Qina, Y.; Chena, P.; Hou, Z. Platinum supported on reduced graphene oxide as a catalyst for hydrogenation of nitroarenes. Carbon 2012, 50, 586 – 596.

(37)

Shang, N.; Gao, S.; Feng, C.; Zhang, H.; Wang, C.; Wang, Z. Graphene oxide supported N-heterocyclic carbene-palladium as a novel catalyst for the Suzuki–Miyaura reaction. RSC Adv. 2013, 3, 21863-21868.

(38)

Fakhri, P.; Nasrollahzadeh, M.; Jaleh, B. Graphene oxide supported Au nanoparticles as an efficient catalyst for reduction of nitro compounds and Suzuki–Miyaura coupling in water. RSC Adv. 2014, 4, 48691-48697.

(39)

Compton, O.C.; Nguyen, S. T. Graphene Oxide, Highly Reduced Graphene Oxide, and Graphene: Versatile Building Blocks for Carbon‐Based Materials. Small 2010, 6, 711.


31


(40)

Page 32 of 37

Quintana, M.; Vazquez, E.; Prato, M. Organic functionalization of graphene in dispersions. Acc. Chem. Res. 2013, 46, 138–148.

(41)

Xia, Z.; Leonardi, F.; Gobbi, M.; Liu, Y.; Bellani, V.; Liscio, A.; Kovtun, A.; Li, R.; Feng X.; Orgiu, E.; Samorì, P.; Treossi, E.; Palermo V. Electrochemical Functionalization of Graphene at the Nanoscale with Self-Assembling Diazonium Salts. ACS Nano. 2016, 10, 7125−7134.

(42)

Layek, R. K.; Nandi, A. K. A review on synthesis and properties of polymer functionalized graphene. Polymer 2013, 54, 5087-5103.

(43)

Guo, Y.; Bao, C.; Song, L.; Yuan, B.; Hu, Y. In situ polymerization of graphene, graphite oxide, and functionalized graphite oxide into epoxy resin and comparison study of onthe-flame behavior. Ind. Eng. Chem. Res. 2011, 50, 7772-7783.

(44)

Deng, D.; Novoselov, K. S.; Fu, Q.; Zheng, N.; Tian, Z.; Bao, X. Catalysis with twodimensional materials and their heterostructures. Nature nanotechnology, 2016, 11, 218230.

(45)

Kim, I. Y.; Jo, Y. K.; Lee, J. M.; Wang, L.; Hwang, S. J. Unique advantages of exfoliated 2D nanosheets for tailoring the functionalities of nanocomposites. J. Phys. Chem. 2014, 5, 4149-4161.

(46)

Sharma, R. K.; Sharma. S.; Dutta. S.; Zboril, R.; Gawande, M. B. Silica-nanospherebased organic–inorganic hybrid nanomaterials: synthesis, functionalization and applications in catalysis. Green Chem. 2015, 17, 3207.


32

Page 33 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(47)

Sharma, R. K.; Monga, Y.; Puri, A.; Gaba, G. Magnetite (Fe3O4) silica based organic– inorganic hybrid copper (II) nanocatalyst: a platform for aerobic N-alkylation of amines. Green Chem. 2013, 15, 2800-2809.

(48)

Sharma, R. K.; Yadav, M.; Monga, Y.; Gaur, R.; Adholeya, A.; Zboril, R.; Varma, R. S.; Gawande, M. B. Silica-based Magnetic Manganese Nanocatalyst–Applications in the Oxidation of Organic Halides and Alcohols. ACS Sustainable Chem. Eng. 2016, 4 (3), 1123-1130.

(49)

Sharma, R. K.; Dutta. S.; Sharma. S. Nickel (ii) complex covalently anchored on core shell structured SiO2@Fe3O4 nanoparticles: a robust and magnetically retrievable catalyst for direct one-pot reductive amination of ketones. New J. Chem. 2016, 40, 2089-2101.

(50)

Gawande, M. B.; Monga, Y.; Zboril, R.; Sharma, R. K. Silica-decorated magnetic nanocomposites for catalytic applications. Coord. Chem. Rev. 2015, 288, 118-143.

(51)

Sharma, R. K.; Dutta. S.; Sharma. S.; Zboril, R.; Varma, R. S.; Gawande, M. B. Fe3O4 (iron oxide)-supported nanocatalysts: synthesis, characterization and applications in coupling reactions. Green Chem. 2016, 18, 3184-3209.

(52)

Sharma, R. K.; Dhingra, S. Designing and Synthesis of Functionalized Silica Gels and their Applications as Metal Scavengers, Sensors, and Catalysts: Green Chemistry Approach, LAP Lambert Academic Publishing, Germany. 2011.

(53)

Hummers, W. S.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339.


33


(54)

Page 34 of 37

Paul, S.; Clark, J. H. Structure-activity relationship between some novel silica supported palladium catalysts: a study of the Suzuki reaction. J. Mol. Catal. 2004, 215, 107–111.

(55)

Pereira, C.; Silva, J. F.; Pereira, A. M.; Araujo, J. P.; Blanco, G.; Pintadoc, Jose M.; Freire, C. [VO(acac)2] hybrid catalyst: from complex immobilization onto silica nanoparticles to catalytic application in the epoxidation of geraniol. Catal. Sci. Technol. 2011, 1, 784–793.

(56)

Etacheri, V.; Yourey, J. E.; Bartlett, B. M.

Chemically bonded TiO2–bronze

nanosheet/reduced graphene oxide hybrid for high-power lithium ion batteries. ACS Nano. 2014, 8, 1491–1499. (57)

Kim, D. S.; Dhand, V.; Rhee, K. Y.; Park, S. Study on the Effect of Silanization and Improvement in the Tensile Behavior of Graphene-Chitosan-Composite. J. Polym. 2015, 7, 527-551.

(58)

Khatri, P. K.; Choudhary, S.; Singh, R.; Jain, S. L.; Khatri, O. P. Grafting of a rheniumoxo complex on Schiff base functionalized graphene oxide: an efficient catalyst for the oxidation of amines. Dalton Trans. 2014, 43, 8054-8061.

(59)

Sun, Y.; Yang, S.; Chen, Y.; Ding, C.; Cheng, W.; Wang, X. Adsorption and desorption of U(VI) on functionalized graphene oxides: a combined experimental and theoretical study. Environ. Sci. Technol. 2015, 49, 4255−4262.

(60)

Zhao, Q.; Bai, C.; Zhang, W.; Li, Y.; Zhang, G.; Zhang, F.; Fan X. Catalytic Epoxidation of Olefins with Graphene Oxide Supported Copper (Salen) Complex. Ind. Eng. Chem. Res. 2014, 53, 4232-4238.


34

Page 35 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(61)

Kumar, P.; Kumar, A.; Sreedhar, B.; Sain, B.; Ray, S. S.; Jain, S. L. Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible‐Active Catalyst for the Photoreduction of Carbon Dioxide. Chem. Eur. J. 2014, 20, 6154 – 6161.

(62)

Luo, W.; Wan, J.; Ozdemir, B.; Bao, W.; Chen, Y.; Dai, J.; Hu, L.; Potassium ion batteries with graphitic materials. Nano Lett., 2015, 15, 7671-7677.

(63)

Reddy, T. N.; Manna, J.; Rana, R. K. Polyamine-mediated interfacial assembly of rGOZnO nanostructures: a bio-inspired approach and enhanced photocatalytic properties. ACS Appl. Mater. Interfaces, 2015, 7, 19684-19690.

(64)

Kovtyukhova, N. I.; Ollivier, P. J.; Martin, B. R.; Mallouk, T. E.; Chizhik, S. A.; Buzaneva, E. V.; Gorchinskiy, A. D.; Layer-by-layer assembly of ultrathin composite films from micron-sized graphite oxide sheets and polycations. Chem. Mater., 1999, 11, 771-778.

(65)

Allahresani, A. Mn (III) salen complex supported on graphene oxide nanosheets as a highly selective and recoverable catalyst for the oxidation of sulfides. J. Iran Chem Soc., 2017, 1-7

(66)

Li, Z.; Wu, S.; Zheng, D.; Liu, J.; Liu, H.; Lu, H.; Kan, Q. Dioxomolybdenum (VI) complex covalently attached to amino‐modified graphene oxide: heterogeneous catalyst for the epoxidation of alkenes. Appl. Organomet. Chem., 2014, 5, 317-323.

(67)

Zhang, W.; Zhao, Q.; Liu, T.; Gao, Y.; Li, Y.; Zhang, G.; Zhang, F.; Fan, X. Phosphotungstic acid immobilized on amine-grafted graphene oxide as acid/base


35


Page 36 of 37

bifunctional catalyst for one-pot tandem reaction. Ind. Eng. Chem. Res. 2014, 53, 14371441. (68)

Jafarpour, M.; Kargar, H.; Rezaeifard, A. A cobalt Schiff base complex on TiO2 nanoparticles as an effective synergistic nanocatalyst for aerobic C–H oxidation. RSC Advances, 2016 ,6, 25034-25046.

(69)

Tan, B. Y. H.; Teo, Y. C.; Efficient cobalt-catalyzed C–N cross-coupling reaction between benzamide and aryl iodide in water. Org. Biomol. Chem., 2014, 12, 7478-7481.

(70)

Yan, Q.; Xiao, T.; Liu, Z.; Zhang, Y. Cobalt‐Catalyzed Direct Amination of Arenes with Alkylamines via Bidentate‐Chelation Assistance. Adv. Synth. Catal., 2016 358, 27072711.

(71)

Du, C.; Li, P. X.; Zhu, X.; Han, J. N.; Niu, J. L.; Song, M. P. Cobalt-Catalyzed Oxidative C–H/N–H Cross-Coupling: Selective and Facile Access to Triarylamines. ACS Catal., 2017, 7, 2810-2814.


36

Page 37 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphical abstract (Pictogram):

The nanostructured catalyst has been fabricated through the covalent immobilization of 1-phenyl1, 3-butanedione (BA) onto amine functionalized graphene oxide nanosupport followed by its metallation with cobalt chloride. Highly versatile graphene oxide based cobalt nanocatalytic system has been effectively exploited for the synthesis of pharmaceutically significant amide derivatives under neutral reaction conditions.


1

Unprecedented EsterâAmide Exchange Reaction Using Highly

Recommend Documents

Unprecedented EsterâAmide Exchange Reaction Using Highly