Ionic Liquid-Coated Carbon Nanotubes as Efficient Metal-Free

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Ionic liquid-coated carbon nanotubes as efficient metalfree catalysts for the synthesis of chromene derivatives Mayank *, Beant Kaur Billing, Prabhat K Agnihotri, Navneet Kaur, Narinder Singh, and Doo Ok Jang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04048 • Publication Date (Web): 24 Jan 2018 Downloaded from http://pubs.acs.org on January 27, 2018

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ACS Sustainable Chemistry & Engineering

Ionic liquid-coated carbon nanotubes as efficient metal-free catalysts for the synthesis of chromene derivatives Mayank, Beant Kaur Billing, Prabhat K Agnihotri, Navneet Kaur, * Narinder Singh, * and Doo a

b

b

c,

a,

Ok Jang * d,

a

Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001,

India

b

School of Mechanical, Materials and Energy Engineering, Indian Institute of Technology Ropar,

Rupnagar, Punjab 140001, India

c

Department of Chemistry, Punjab University, Chandigarh 160014, India

d

Department of Chemistry, Yonsei University, Wonju 26493, Korea

*Corresponding authors; E-mail: [email protected]; [email protected]; [email protected]

ABSTRACT

ACS Paragon Plus Environment

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ACS Sustainable Chemistry & Engineering 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

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Efficient ionic liquid-coated carbon nanotubes (IL@CNTs) for the synthesis of chromene derivatives were developed. The characteristic features of IL@CNTs are that they are metal-free and have positively charged surfaces. The catalytic activity of IL@CNTs was evaluated for the synthesis of chromene derivatives in water under sonothermal conditions, affording high yields of the desired products. The present process is an eco-friendly method for the synthesis of chromene derivatives, authenticated with a high EcoScale score, low E-factor, and metal-free conditions.

KEYWORDS: ionic liquid, carbon nanotubes, catalyst, hybrid material, sonothermal, metal-free, chromene

INTRODUCTION Heterocyclic compounds play a major role in medicinal chemistry due to their diverse pharmacological properties. Most clinically used active pharmaceutical ingredients consist of 1

heterocyclic moieties. The pharmacological properties of heterocyclic compounds range from 2

the inhibition of simple voltage-gated receptors to the modulation of highly complex signaling cascades of cellular machinery. Among these, chromene derivatives have diverse 3-4

pharmacological properties, including anticancer, antimicrobial, antiviral, anticoagulant, and 5

6

7

8

anti-inflammatory activities. Therefore, developing synthetic methods for chromene derivatives 9

is important for the pharmaceutical industry. Among numerous methods developed, transitionmetal-catalyzed reactions are the most attractive methodologies for the synthesis of chromene derivatives.

10

A synthetic strategy capable of producing complex molecules with easily accessible building blocks can only be considered ideal when its hazard to the environment is minimal. However, 10


2

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the majority of available synthetic strategies (detailed in Table S1) involve extensive consumption of organic solvents, tedious work-up processes, and metal-based catalysts that prevent industrial scale-up.

11-12

Metal-based catalysts are especially problematic, as even traces of

toxic metals in pharmaceutical ingredients may cause severe health risks to the population.

13

Hence, synthetic strategies that utilize metal-free catalysts are in high demand for industrial applications. Along with a metal-free nature, the catalytic efficiency of a catalyst, which depends prominently on the surface area and morphological properties of the material, is also important.

14

Therefore, all these aspects should be considered carefully while designing a catalyst. In this context, carbon nanotubes (CNTs) are considered an ideal material showing remarkable properties, viz a non-toxic nature, exceptional physical strength, large surface area, excellent electron conductivity, high oxidation stability, and good chemical integrity.

15-16

CNTs have

surfaces containing carboxy groups that can be readily modified. Moreover, the catalytic activity of CNTs in the form of CNT-metal composites is well documented in literature.

17-19

The use of ionic liquids (ILs) as catalysts for the synthesis of heterocyclic compounds is well known; ILs have been used extensively for synthesizing heterocyclic compounds. Recently, Safaei-Ghomi and coworkers developed IL-supported Fe O nanoparticles, and used them for the 3

4

synthesis of chromene derivatives. Salunkhe and coworkers developed multi-cationic IL-based 20

catalysts, which were subsequently used for the microwave-assisted synthesis of chromene derivatives. Similarly, Rawat and coworkers reported the catalytic application of ILs, [TBA][Gly] 21

for the synthesis of indolyl-4H-chromenes derivatives. Other heterocyclic moieties, including 2, 22

3-disubstituted quinolones, 2,3-dihydroquinazolin, α-carbolines, pyrido/pyrazolopyrimide derivatives, 2-aminofurans, and triazolyl spirocyclic oxindoles, were also synthesized using the


3


catalytic properties of ILs.

23-25

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However, these methods required toxic metals, and had a narrow

scope of substrates. Considering these facts and with the objective of incorporating metal-free properties, we intend to decorate ILs on the surface of CNTs, producing IL@CNTs as a heterogeneous catalyst. In this work, the anionic part of the ILs was used to immobilize them over the CNTs, leaving behind a freely suspended cationic part for catalytic activity. The suspended cationic part produces high positive charge density on the surface of the CNTs, thus increasing their solubility in polar solvents, including green solvents such as water. The catalytic ability of IL@CNTs was explored for the synthesis of chromene derivatives using a sonothermal technique, which is an eco-friendly and economical energy source.

26-28

The developed protocol provided several

improvements in chromene synthesis compared to previously reported methods (Table S1).

29-30

The protocol exhibited a high EcoScale score, a low E-factor, and high catalyst reusability. RESULTS AND DISCUSSION Preparation of IL@CNTs Imidazolium and benzimidazolium-based ILs, IL-1 with two carboxyl groups and IL-2 with one carboxyl group, were chosen (Figure 1). IL-1 contains two distinctly situated carboxyl groups and can facilitate binding with discrete CNT entities, producing an expected networktype structure. On the other hand, IL-2 contains only a single carboxyl group and is expected to form a simpler morphology. These ILs were synthesized using methodologies published in the literature.

23–25


4

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Figure 1. Structures of IL-1 and IL-2. The fabrication of IL-CNTs is presented in Scheme 1. As per the previously reported procedure, the carboxyl groups on the surface of the CNTs were converted to hydrazides, – C(O)NHNH , by consecutive treatment with thionyl chloride and hydrazine. The modified 31

2

CNTs were finally attached to the ILs, affording IL-1@CNTs and IL-2@CNTs. Upon attaching the ILs to the CNT via the anionic parts, the freely hanging cationic part produced positive charges on the surface of the fabricated IL@CNTs, which are useful for catalytic activity.

Scheme 1. Fabrication of IL-CNTs. Characterization of CNTs and IL@CNTs


5


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The CNTs and IL@CNTs were characterized using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). The surface properties were also explored using Brunauer–Emmett–Teller (BET) studies. SEM was used to examine the surface morphology of the CNTs and IL@CNTs. The unpurified CNT cluster is shown at 5 µm scale in Figure 2A. The structural features were not uniform and amorphous impurities were observed. Upon purification, the surface morphology of CNTs was altered significantly and amorphous impurities were completely eliminated (Figure 2B). The structural features became clearly visible, and CNTs appeared to be organized in a well-defined clustered form. The diameter of the CNTs was found to be 0.2–0.3 µm. IL1@CNTs also showed well-organized structural features (Figure 2C). The clustering became much more organized, and the majority of CNTs aligned themselves parallel to each other. These observations are reasonable as cross bridging bonds by IL-1 tend to bring CNTs closer, producing organized cluster forms. The diameter was found to range from 0.2–0.35 µm. On the other hand, IL-2@CNTs showed the least organized clustering, and CNTs appeared to be randomly distributed throughout the sample (Figure 2D). This unorganized cluster formation was attributed to the lack of bridging bonds for IL-2. Herein, CNTs showed a diameter of about 0.2– 0.3 µm. To estimate the surface functionalities of IL-1@CNTs, FT-IR and TGA analysis were used. The FT-IR spectra of IL-1@CNTs, IL-2@CNTs, and bare CNTs are shown in Figure 2E. The FT-IR spectrum of CNTs shows a broad band at 3400 cm that was assigned to the stretching -1

vibration of the –OH of carboxylic acid. A band at ~1700 cm indicates the presence of C=O -1

groups. These observations are reasonable as the bare CNTs hold COOH functionalities on their


6

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surface, whereas in the FT-IR spectra of IL-1@CNTs and IL-2@CNTs, particularly 31

characteristic bands were also observed. The band at 3300 cm observed in the spectra of IL-1

1@CNTs and IL-2@CNTs was assigned to the stretching vibration of N-H functionalities. Another strong band observed at ~1700 cm is attributed to the presence of C=O functional -1

groups. Moreover, additional bands at ~3000-3100 cm corresponding to =C-H stretching are -1

also observed in both cases. The FT-IR spectra of IL@CNTs were also compared to those of pure IL-1 and IL-2 moieties (Figure S1). Moreover, EDX studies showed the presence of nitrogen along with carbon and oxygen on the surface of IL@CNTs (Figure 2F and G). These results confirmed the presence of ILs on the CNT surface. For further estimation, TGA analysis was performed, as shown in Figure 2H. In the bare CNTs, an 18% reduction in mass was observed over a wide temperature range (150–700 °C), while a 58% mass loss for IL-1@CNTs and a 38% mass loss for IL-2@CNTs were observed over the relatively narrow temperature range of 155– 510 °C. These prominent mass losses were attributed to the burning of the surface-associated ILs in IL@CNT materials. PXRD patterns were obtained to gather information about the different planes, crystal sizes, and impurities in CNTs, IL-1@CNTs, and IL-2@CNTs (Figure 2I). The XRD pattern of CNTs revealed a main peak at 25.97° corresponding to the 002 plane and a spacing of 0.34 nm. Additional planes at 100 and 004, corresponding to the 2θ values of 44° and 52°, respectively, were also observed.

26,27

In the case of IL-1@CNTs, in addition to the above-mentioned planes,

extra peaks at the 2θ values of 13°, 20°, and 22° were also observed. With IL-2@CNTs, an extra peak with a 2θ value of 13° appeared. The average crystallite size (L) was calculated using Scherrer’s equation (L = 0.9λ/βcosθ), where λ is the X-ray wavelength (1.5405 Å) and β is the


7


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full width at half maximum in radians. The crystallite sizes calculated for CNTs, IL-1@CNTs, and IL-2@CNTs were found to be 2.37, 1.20, and 1.75 nm, respectively.

Figure 2. SEM images of (A) unpurified CNTs, (B) purified CNTs, (C) IL-1@CNTs, and (D) IL-2@CNTs; (E) FT-IR spectra; (F) EDX spectrum of IL-1@CNTs; (G) EDX spectrum of IL2@CNTs; (H) TGA curves under nitrogen; (I) PXRD patterns of CNTs, IL-1@CNTs, and IL2@CNTs.


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In addition, to determine the surface properties of CNTs and IL@CNTs, BET studies were performed. The surface area, pore volume, and average pore diameter of CNTs, IL-1@CNTs, and IL-2@CNTs are listed in Table 1. These results revealed that upon IL coating, the surface properties of CNTs changed significantly. The surface area, pore volume, and average pore diameter were highest for IL-1@CNTs, followed by IL-2@CNTs, and minimal for bare CNTs. The nitrogen adsorption isotherms of CNTs, IL-1@CNTs, and IL-2@CNTs were investigated (Figure 3). The isotherms of IL@CNTs changed distinctively as compared to those of bare CNTs. The surface area, pore volume, and average pore diameter were increased for IL@CNTs compared to the bare CNTs. Heterogeneous catalysis depends significantly on the surface properties and these modifications in surface properties are typically important for facilitating the catalytic activity of the materials.

32

Table 1. Nitrogen adsorption BET measurements of CNTs, IL-1@CNTs, and IL-2@CNTs. Entry Catalyst

Surface area

Pore volume

Average pore diameter

(m g )

(cm g )

(nm)

37.40

0.055

3.5

2

−1

3

−1

1

CNTs

2

IL-1@CNTs

331.10

0.95

3.8

3

IL-2@CNTs

187.54

0.48

3.6


9


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Figure 3. Nitrogen adsorption isotherms of CNT, IL-1@CNTs, and IL-2@CNTs.

Synthesis of chromene derivatives The reaction of 4-hydroxycoumarin with 3-bromobenzaldehyde and malononitrile was chosen as a model reaction for examining catalytic activity (Scheme 2). An aqueous solution of 4-hydroxycoumarin, 3-bromobenzaldehyde, and malononitrile along with the catalyst was sonicated for 20 min at room temperature and then analyzed by H NMR. The results are 1

summarized in Table 2. Without catalyst, the yield of product 1 was poor (Table 2, entry 1), while the efficiency of the reaction improved somewhat by employing CNTs, IL-1, or IL-2 as a catalyst (entries 2-4). When IL-1@CNTs and IL-2@CNTs were employed as catalysts, the efficiency of the reaction was further increased, affording 94% and 91% yields of product 1, respectively (entries 5 and 6). This indicates that IL-1@CNTs were comparable to IL-2@CNTs as a catalyst for the reaction performed. Herein, IL-1@CNTs is a heterogeneous catalyst with


10

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enormous surface area, providing a huge surface for catalytic activities. During the course of the reaction, reactants get adsorbed onto the surface sites of CNTs and the attached ILs provide catalytic activity.

Scheme 2. Model reaction for evaluating catalytic activity. Table 2. Efficiency of the reaction depending on catalyst.

a

Entry 1 2 3 4 5 6 Measured by

Catalyst no catalyst CNTs IL-1 IL-2 IL-1@CNTs IL-2@CNTs H NMR.

Yield (%) 45 68 72 71 94 91

a

1

Having established the optimal reaction conditions, various chromene derivatives were then synthesized. The results are presented in Table 3. The yields of the chromene derivatives were independent of the aldehyde structures. With aldehydes containing either strong electrondonating or electron-withdrawing groups, the reaction proceeded smoothly, affording high yields of the corresponding products, irrespective of the IL@CNTs used. Heteroaromatic aldehydes were also employed, affording high yields of the expected products and illustrating the substrate generality of the reaction.


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Table 3. Synthesis of 4,5-dihydropyrano[3,2-c]chromene derivatives.

Entry Ar

Product

Yield (%)

a

IL-1@CNTs IL-2@CNTs

a

1

CH

2

94

91

2

3-MeO-C H

3

93

90

3

4-HO-3-MeO-C H

4

92

93

4

2,5-(MeO) -C H

5

90

89

5

3,4-(MeO) -C H

6

91

90

6

4-Cl-C H

7

93

90

7

2-NO -C H

8

94

91

8

1-naphthyl

9

90

88

9

3-pyridyl

10

90

89

10

4-pyridyl

11

91

87

6

5

6

4

6

2

2

6

2

6

6

4

6

4

3

3

3

Measured by H NMR. 1

The present protocol also produced 4H-benzo[h]chromene derivatives 12–18 using αnaphthol instead of 4-hydroxycoumarin (Table 4). The reactions performed without malononitrile gave bis-coumarin derivatives 19–25 (Table 5). These reaction conditions highlight the substrate generality, producing excellent yields regardless of the substrate structure.


12

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Thus, benzaldehydes with electron-donating or electron-withdrawing groups produced the corresponding products in excellent isolated yields, irrespective of the IL@CNTs.

Table 4. Synthesis of 4H-benzo[h]chromene derivatives.

Entry

a

Ar

Product

Yield (%)

a

IL-1@CNTs

IL-2@CNTs

12

93

90

1

CH

2

2-HO-C H

13

90

91

3

4-F-C H

14

91

90

4

4-Cl-C H

15

90

91

5

4-MeO-C H

16

93

91

6

2-Cl-C H

17

94

91

8

3-HO-C H

18

91

88

6

5

6

6

4

4

6

4

6

6

4

4

6

4


Table 5. Synthesis of bis(4-hydroxy-2H-chromen-2-one) derivatives.


13


Entry

a

Ar

Product

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Yield (%)

a

IL-1@CNTs

IL-2@CNTs

19

91

89

1

CH

2

2-HO-C H

20

90

90

3

4-Cl-C H

21

89

92

4

2-NO -C H

22

92

90

5

4-HO-C H

23

90

93

6

3-pyridyl

24

93

90

7

4-pyridyl

25

90

89

6

5

6

4

6

4

2

6

6

4

4


Next, we examined the recyclability of the catalysts. After filtration of the reaction mixture, the residue was washed three times with water and once with methanol. The reaction of 4-hydroxycoumarin with 3-bromobenzaldehyde and malononitrile was carried out five times using the recovered catalyst. Herein, the margin of catalyst that was lost during the recovery procedure was carefully compensated by adding the same amount from another similar reaction batch. The results are presented in Figure 4. The yield of product 1 was found to be 89% with IL-1@CNTs and 85% with IL-2@CNTs at the end of the fifth catalytic cycle. This showed that the catalytic activity of IL@CNTs was retained without detrimental effects on the efficiency of the reaction over five runs.


14

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Figure 4. Catalytic efficiency of recovered IL@CNTs.

The catalysts recovered after the fifth cycle were investigated using various techniques. The SEM images of recovered IL-1@CNTs and IL-2@CNTs are shown in Figure 5A and B. The recovered IL-1@CNTs showed structural features similar to the fresh one, whereas some trivial changes were observed in recovered IL-2@CNTs. The recovered IL-1@CNTs and IL2@CNTs showed the presence of desired nitrogen along with oxygen and carbon elements on its surfaces (Figure 5C and D). TGA analysis was performed to investigate IL loss from the IL@CNT surface after the fifth cycle. The TGA showed significant mass loss at the temperature range 300 – 350 °C (Figure 5E). PXRD patterns of IL-1@CNTs and IL-2@CNTs were comparable to that of freshly prepared IL@CNTs (Figure 5F). The commutative results of SEM, EDX, TGA, and PXRD of the recovered catalysts revealed the intactness of the catalysts even after the end of the fifth cycle. In the case of IL-2@CNTs, the structural changes that were


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observed in the recovered catalysts seem to be responsible for the minor reduction in the yield of the product after the fifth reaction cycle.

Figure 5. SEM images of recovered (A) IL-1@CNTs and (B) IL-2@CNTs; EDX spectrum of recovered (C) IL-1@CNTs and (D) IL-2@CNTs; (E) TGA curves of recovered IL@CNTs; (F) PXRD patterns of CNTs and IL@CNTs.

Finally, to explore the green chemistry aspect of the reaction, the Eco-Scale score and Efactor for the reaction were calculated. An Eco-Scale score of 64 was assigned (Table S2), along with a low E-factor of 0.13 (Table S3), indicating an environmentally friendly process. Moreover, the present process has several advantages over previously reported methods (Table S1), including a high yield of desired products, a short reaction time, a simple work-up process, substrate generality, use of water as a solvent, and catalyst recyclability. Mechanism


16

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The reaction of 4-hydroxycoumarin with 3-bromobenzaldehyde and malononitrile in the presence of IL-1@CNTs was monitored with H NMR at different time intervals (Figure 6). 1

After 1 min, characteristic peaks of the starting materials at 4.39, 8.04, and 8.47 ppm were observed along with a peak at 4.45 ppm that corresponds to the aliphatic protons of product 1. Upon further sonication, steady augmentation of the peak at 4.45 ppm, along with the reduction of the peaks at 4.39, 8.04, and 8.47 ppm indicated the gradual formation of product 1. After 20 min, the reactant peaks had completely disappeared, indicating the completion of the reaction. To compare the catalytic activities of IL-1@CNTs and IL-2@CNTs, we performed the same reaction in the presence of IL-2@CNTs instead of IL-1@CNTs, following the reaction with H 1

NMR (Figure S3). Although the reaction was complete in 20 min, the reaction rate was relatively slow in the initial phase. The difference in reaction rates is attributed to the varied surface and structural features of the catalysts, such as the network-type structure for IL-1@CNTs and the straight structure for IL-2@CNTs.


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Figure 6. Time-dependent H NMR spectra of a reaction mixture of 4-hydroxycoumarin, 31

bromobenzaldehyde, and malononitrile in the presence of IL-1@CNTs.

A plausible catalytic mechanism of IL@CNTs for the synthesis of chromene derivatives is proposed (Scheme 3). IL@CNTs have a high surface area and positive charge density on the surface. They also have hydrogen bond-forming ability with the electron-rich centers of the reactants. The intensely positively charged surface of IL@CNTs and/or hydrogen bonding activate functional groups such as carbonyl and nitrile. The condensation of an aldehyde with malononitrile is promoted by IL@CNTs, which coordinates to the oxygen of the carbonyl group, producing a benzylidenemalononitrile intermediate. A sequence of addition and cyclization of 4hydroxycoumarin to the resulting benzylidenemalononitrile is also promoted by IL@CNTs, to give the final product and regenerate the IL@CNTs. To validate the proposed mechanism, FT-IR spectra of 3-bromobenzaldehyde and malononitrile were recorded in the presence of IL@CNTs


18

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(Figure S2). Shifts in the carbonyl (C=O) stretch peak of 3-bromobenzaldehyde and nitrile (CN) stretch peak of malononitrile were observed. These results indicate that IL@CNTs interact with carbonyl and nitrile functionalities, supporting the proposed mechanism.

Scheme 3. Plausible mechanism for the IL@CNTs-catalyzed synthesis of chromene derivatives. CONCLUSIONS We have prepared nanotubes coated with ionic liquids, IL@CNTs, and evaluated them as catalysts for the synthesis of chromene derivatives in water at room temperature with a sonothermal method. IL@CNTs are highly efficient for the reaction at only trace amounts (0.5 mol%) and recyclable without significant loss of catalytic activity. There was no difference in terms of the catalytic activity between IL-1@CNTs and IL-2@CNTs. The present method was found to have a high EcoScale score and a low E-factor, showing that it is environmentally benign. Characteristics of the present process include a short reaction time, a high yield, easy


19


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work-up, use of a green solvent (water), and the use of an inexpensive, non-toxic, metal-free, and reusable catalyst.

EXPERIMENTAL Preparation of IL@CNTs CNTs were prepared by the method reported in the literature. Likewise, imidazolium and 31,32

benzimidazolium-based ILs, IL-1 and IL-2, were synthesized using literature methods.

23–25

A mixture of CNTs (1 g) and an excess of SO Cl and NH NH 2H O was stirred at room 2

2

2

2

.

2

temperature for 3 h. A mixture of IL-1 (1 g) or IL-2 (1 g) and an excess of SO Cl in CH Cl was 2

2

2

2

stirred at room temperature for 4 h. The modified CNTs were added to the above solution, and the resulting mixture was stirred for 4 h. The precipitate was then filtered.

Typical procedure for the synthesis of chromene derivatives A mixture of 4-hydroxycoumarin (10 mmol), malononitrile (10 mmol), a benzaldehyde derivative (10 mmol), and 0.5 mol% of IL@CNTs in deionized water (10 mL) was sonicated using the PlsM mode for 20 min at room temperature. The precipitate was filtered and washed with water and minimal quantity of methanol to precipitate the purified product. H and CHN 1

analysis techniques were used for characterization of the product.


20

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2-Amino-4-(3-bromophenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (1):

33

1

H NMR (400 MHz, DMSO-d ) δ 7.85 (dd, J = 7.9, 1.8 Hz, 1H), 7.68 (td, J = 8.2, 1.8 Hz, 1H), 6

7.50–7.37 (m, 6H), 7.29–7.19 (m, 2H), 4.46 (s, 1H). Elem. Anal. Calcd. for C H BrN O : C, 19

11

2

3

57.74; H, 2.81; N, 7.09. Found: C, 57.76; H, 2.79; N, 7.10. 2-Amino-5-oxo-4-phenyl-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (2): mp = 241– 34

242 °C; H NMR (400 MHz, DMSO-d ) δ 7.87 (d, J = 8.0 Hz, 1H), 7.67–7.65 (m, 1H), 7.47–7.41 1

6

(m, 2H), 7.35 (s, 2H), 7.29–7.26 (m, 2H), 7.22–7.18 (m, 3H), 4.41 (s, 1H). Elem. Anal. Calcd. for C H N O : C, 72.15; H, 3.82; N, 8.86. Found: C, 75.17; H, 3.80; N, 8.88. 19

12

2

3

2-Amino-4-(3-methoxyphenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (3): mp = 239–240 °C; H NMR (400 MHz, DMSO-d ) δ 7.85 (dd, J = 7.9, 1.8 Hz, 1H), 7.67 (td, 35

1

6

J = 8.2, 2.1 Hz, 1H), 7.49–7.39 (m, 2H), 7.37 (s, 2H), 7.19 (t, J = 7.9 Hz, 1H), 6.82–6.70 (m, 3H), 4.38 (s, 1H), 3.68 (s, 3H). Elem. Anal. Calcd. for C H N O : C, 69.36; H, 4.07; N, 8.09. 20

14

2

4

Found: C, 69.33; H, 4.11; N, 8.19. 2-Amino-4-(4-hydroxy-3-methoxyphenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3carbonitrile (4): mp = 252–253 °C; H NMR (400 MHz, DMSO-d ) δ 8.88 (s, 1H), 7.84 (dd, J = 35

1

6

7.9, 1.7 Hz, 1H), 7.71–7.61 (m, 1H), 7.52–7.38 (m, 2H), 7.30 (s, 2H), 6.77 (d, J = 1.9 Hz, 1H), 6.65 (d, J = 8.0 Hz, 1H), 6.56 (dd, J = 8.2, 2.1 Hz, 1H), 4.31 (s, 1H), 3.68 (s, 3H). Elem. Anal. Calcd. for C H N O : C, 66.30; H, 3.89; N, 7.73. Found: C, 66.31; H, 3.90; N, 7.71. 20

14

2

5

2-Amino-4-(2,5-dimethoxyphenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (5): mp = 232–233 °C; H NMR (400 MHz, DMSO-d ) δ 7.86 (dd, J = 7.9, 1.5 Hz, 1H), 7.66 (t, 36

1

6

J = 7.9 Hz, 1H), 7.44 (dd, J = 16.9, 8.1 Hz, 2H), 7.23 (s, 2H), 6.88 (d, J = 8.8 Hz, 1H), 6.78–6.70


21


Page 22 of 30

(m, 1H), 6.61 (d, J = 3.0 Hz, 1H), 4.60 (s, 1H), 3.61 (s, 3H), 3.60 (s, 3H). Elem. Anal. Calcd. for C H N O : C, 67.02; H, 4.28; N, 7.44. Found: C, 67.05; H, 4.26; N, 7.45. 21

16

2

5

2-Amino-4-(3,4-dimethoxyphenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (6): mp = 233–234 °C; H NMR (400 MHz, DMSO-d ) δ 7.85 (d, J = 6.8 Hz, 1H), 7.67 (t, J = 36

1

6

7.2 Hz, 1H), 7.50–7.37 (m, 3H), 7.31 (s, 2H), 6.88–6.77 (m, 2H), 6.75–6.65 (m, J = 10 Hz, 1H), 4.36 (s, 1H), 3.67 (s, 6H). Elem. Anal. Calcd. for C H N O : C, 66.02; H, 4.28; N, 7.44. Found: 21

16

2

5

C, 66.03; H, 4.29; N, 7.46. 2-Amino-4-(4-chlorophenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (7):

36

mp = 262–263 °C; H NMR (400 MHz, DMSO-d ) δ 8.27 (s, 1H), 7.85 (d, J = 7.9 Hz, 1H), 7.71– 1

6

7.64 (m, 1H), 7.50–7.40 (m, 4H), 7.33–7.26 (m, 4H), 4.44 (s, 1H). Elem. Anal. Calcd. for C H ClN O : C, 65.06; H, 3.16; N, 7.99. Found: C, 65.09; H, 3.14; N, 7.95. 19

11

2

3

2-Amino-4-(2-nitrophenyl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (8):

37

mp = 239–240 °C; H NMR (400 MHz, DMSO-d ) δ 7.67 (d, J = 8.0 Hz, 2H), 7.63–7.61 (m, 2H), 1

6

7.61–7.59 (m, 2H), 7.59 (s, 2H), 7.51–7.40 (m, 2H), 5.20 (s, 1H). Elem. Anal. Calcd. for C H N O : C, 63.16; H, 3.07; N, 11.63. Found: C, 63.14; H, 3.10; N, 1.66. 19

11

3

5

2-Amino-4-(naphthalen-1-yl)-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (9):

38

1

H NMR (400 MHz, DMSO-d ) δ 8.39 (d, J = 8.2 Hz, 1H), 7.95–7.85 (m, 2H), 7.78 (d, J = 8.0 6

Hz, 1H), 7.73–7.65 (m, 1H), 7.60–7.45 (m, 3H), 7.45–7.35 (m, 2H), 7.35–7.25 (m, 3H), 5.43 (s, 1H). 2-Amino-5-oxo-4-(pyridin-3-yl)-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (10): mp 39

= 239–240 °C; H NMR (400 MHz, DMSO-d ) δ 8.49 (s, 1H), 8.41 (d, J = 4.0 Hz, 1H), 7.87 (d, J 1

6


22

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= 8.0 Hz, 1H), 7.67–7.65 (m, 2H), 7.47–7.41 (m, 4H), 7.29–7.26 (m, 1H), 4.51 (s, 1H). Elem. Anal. Calcd. for C H N O : C, 68.14; H, 3.49; N, 13.24. Found: C, 68.14; H, 3.49; N, 13.25. 18

11

3

3

2-Amino-5-oxo-4-(pyridin-4-yl)-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile (11): mp 29

= 239–240 °C; H NMR (400 MHz, DMSO-d ) δ 8.47 (d, J = 8.0 Hz, 2H), 7.85 (d, J = 7.9 Hz, 1

6

1H), 7.71–7.69 (m, 1H), 7.49 (s, 2H), 7.49–7.43 (m, 2H), 7.28 (d, J = 8.5 Hz, 2H), 4.47 (s, 1H). Elem. Anal. Calcd. for C H N O : C, 68.14; H, 3.49; N, 13.24. Found: C, 68.16; H, 3.51; N, 18

11

3

3

13.28. 2-Amino-4-phenyl-4H-benzo[h]chromene-3-carbonitrile (12): mp = 210–212 °C; H NMR 40

1

(400 MHz, CDCl ) δ 8.17 (d, J = 8.2 Hz, 1H), 7.79–7.77 (d, J = 8.0 Hz, 1H), 7.56–7.49 (m, 3H), 3

7.26–7.22 (m, 5H), 7.00 (d, J = 8.5 Hz, 1H), 4.86 (s, 1H), 4.72 (s, 2H). Elem. Anal. Calcd. for C H N O: C, 80.52; H, 4.73; N, 9.39. Found C, 80.48; H, 4.68; N 9.41. 20

14

2

2-Amino-4-(2-hydroxyphenyl)-4H-benzo[h]chromene-3-carbonitrile (13): mp = 265–268 40

°C; H NMR (400 MHz, DMSO-d ) δ 8.54 (d, J = 11.7 Hz, 1H), 8.19 (d, J = 8.3 Hz, 1H), 7.96 1

6

(dd, J = 12.2, 2.7 Hz, 2H), 7.84 (d, J = 8.0 Hz, 1H), 7.76 (d, J = 9.2 Hz, 1H), 7.63–7.45 (m, 3H), 7.23–7.08 (m, 3H), 6.93 (d, J = 8.8 Hz, 1H), 5.25 (s, 1H). Elem. Anal. Calcd. for C H N O : C, 20

14

2

2

76.42; H, 4.49; N, 8.91. Found C, 76.39; H, 4.46; N 8.88. 2-Amino-4-(4-fluorophenyl)-4H-benzo[h]chromene-3-carbonitrile (14): mp = 236–238 °C; 40

1

H NMR (400 MHz, CDCl ) δ 8.14 (d, J = 8.1 Hz, 1H), 7.76 (d, J = 7.8 Hz, 1H), 7.59–7.43 (m, 3

3H), 7.16 (dd, J = 8.4, 5.4 Hz, 3H), 6.96 (t, J = 9.4 Hz, 3H), 5.12 (s, 2H), 4.82 (s, 1H). Elem. Anal. Calcd. for C H FN O: C, 75.94; H, 4.14; N, 8.86. Found C, 75.88; H, 4.19; N, 8.89. 20

13

2


23


Page 24 of 30

2-Amino-4-(4-chlorophenyl)-4H-benzo[h]chromene-3-carbonitrile (15): mp = 240–243 °C; 40

1


3H), 7.30–7.25 (m, 2H), 7.16 (d, J = 8.4 Hz, 2H), 6.97 (d, J = 8.5 Hz, 1H), 4.86 (s, 1H), 4.76 (s, 2H). Elem. Anal. Calcd. for C H ClN O: C, 72.18; H, 3.94; N, 8.42. Found C, 72.25; H, 3.90; N, 20

13

2

8.49. 2-Amino-4-(4-methoxyphenyl)-4H-benzo[h]chromene-3-carbonitrile (16): mp = 194-195 40

o

C; H NMR (400 MHz, CDCl ) δ 8.15 (d, J = 8.1 Hz, 1H), 7.77 (d, J = 7.9 Hz, 1H), 7.59–7.45 1

3

(m, 3H), 7.13 (d, J = 8.6 Hz, 2H), 7.00 (d, J = 8.5 Hz, 1H), 6.83 (d, J = 8.7 Hz, 2H), 4.82 (s, 1H), 4.75 (s, 2H), 3.76 (s, 3H). Elem. Anal. Calcd. for C H N O : C, 76.81; H, 4.91; N, 8.53. Found C, 21

16

2

2

76.85; H, 4.87; N, 8.58. 2-Amino-4-(2-chlorophenyl)-4H-benzo[h]chromene-3-carbonitrile (17): mp = 237-238 C; 40

1

o


3H), 7.41–7.34 (m, 1H), 7.16 (s, 3H), 7.05 (d, J = 8.5 Hz, 1H), 5.55 (s, 1H), 4.80 (s, 2H). Elem. Anal. Calcd. for C H ClN O: C, 72.18; H, 3.94; N, 8.42. Found C, 72.15; H, 3.99; N, 8.39. 20

13

2

2-Amino-4-(3-hydroxyphenyl)-4H-benzo[h]chromene-3-carbonitrile (18): mp = 246– 40

249 °C; H NMR (400 MHz, DMSO-d ) δ 8.22 (s 1H), 8.20 (d, J = 8 Hz, 1H), 7.86 (d, J = 8 Hz, 1

6

1H), 7.59-7.54 (m, 5H), 6.57 (d, J = 8 Hz, 2H), 6.56 (d, J = 8 Hz, 2H), 4.76 (s, 1H). Anal. Calcd. for C H N O : C, 76.42; H, 4.49; N, 8.91. Found C, 76.0; H, 4.51; N, 8.89 20

14

2

2

3,3'-(Phenylmethylene)bis(4-hydroxy-2H-chromen-2-one) (19): mp = 228-229 C; H NMR 41

o

1

(400 MHz, DMSO-d ) δ 17.55 (s, 2H), 7.76 (d, J = 7.9 Hz, 2H), 7.45 (t, J = 7.9 Hz, 2H), 7.23– 6

7.15 (m, 4H), 7.11 (t, J = 7.3 Hz, 2H), 7.06–6.98 (m, 3H), 6.22 (s, 1H). Elem. Anal. Calcd for C H O : C, 72.81; H, 3.91. Found: C, 72.84; H, 3.95. 25

16

6


24

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3,3'-((2-Hydroxyphenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (20): mp = 165-167 41

o

C; H NMR (400 MHz, DMSO-d ) δ 17.11 (s, 1H), 8.28 (d, J = 4.9 Hz, 1H), 8.12 (s, 2H), 7.74 1

6

(dd, J = 7.6, 2.1 Hz, 2H), 7.51 (dd, J = 7.9, 2.1 Hz, 1H), 7.48–7.42 (m, 2H), 7.23–7.14 (m, 4H), 7.11 (d, J = 7.9 Hz, 1H), 7.06–6.99 (m, 1H), 6.21 (s, 1H). Elem. Anal. Calcd for C H O : C, 25

16

7

70.09; H, 3.76. Found: C, 69.91; H, 3.79. 3,3'-((4-Chlorophenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (21): mp = 261-263 C; 42

1

o

H NMR (400 MHz, CDCl ) δ 17.17 (s, 1H), 8.04 (d, J = 7.3 Hz, 2H), 7.44 (td, J = 7.6, 1.8 Hz, 3

2H), 7.34–7.03 (m, 8H), 6.27 (s, 1H). Elem. Anal. Calcd for C H ClO : C, 67.20; H, 3.38. Found: 25

15

6

C, 67.25; H, 3.34. 3,3'-((2-Nitrophenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (22): mp = 220-222 C; 43

1

o

H NMR (400 MHz, DMSO-d ) δ 16.72 (s, 1H), 8.79 (s, 1H), 7.71 (d, J = 7.3 Hz, 2H), 7.51–7.41 6

(m, 4H), 7.30 (q, J = 7.3, 3.7 Hz, 2H), 7.18 (d, 4H), 6.43 (s, 1H). Elem. Anal. Calcd for C H NO : C, 65.65; H, 3.31; N, 3.06. Found: C, 65.61; H, 3.24; N, 3.02. 25

15

8

3,3'-((4-Hydroxyphenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (23): mp = 212-213 32

o

C; H NMR (400 MHz, DMSO-d ) δ 8.93 (s, 1H), 7.77 (d, J = 7.8 Hz, 2H), 7.45 (t, J = 7.8 Hz, 1

6

2H), 7.28–7.07 (m, 4H), 6.83 (d, J = 8.2 Hz, 2H), 6.52 (d, J = 8.7 Hz, 2H), 6.12 (s, 1H). Elem. Anal. Calcd for C H O : C, 70.09; H, 3.76. Found: C, 70.20; H, 3.68. 25

16

7

3,3'-(Pyridin-3-ylmethylene)bis(4-hydroxy-2H-chromen-2-one) (24): mp = 273-274 C; H 32

o

1

NMR (400 MHz, DMSO-d ) δ 17.45 (s, 1H), 8.79 (s, 1H), 8.24 (dd, J = 6.7, 3.7 Hz, 2H), 7.77 (d, 6

J = 7.9, 2H), 7.58–7.33 (m, 3H), 7.27–7.00 (m, 5H), 6.25 (s, 1H). Elem. Anal. Calcd for C H NO : C, 69.73; H, 3.66; N,3.39. Found: C, 69.75; H, 3.67; N, 3.40. 24

15

6


25


Page 26 of 30

3,3'-(Pyridin-4-ylmethylene)bis(4-hydroxy-2H-chromen-2-one) (25): mp = 274-275 C; H 32

o

1

NMR (400 MHz, DMSO-d ) δ 17.40 (s, 1H), 8.28 (d, J = 6.7 Hz, 2H), 8.13 (s, 1H), 7.76 (dd, J = 6

7.9, 2.4 Hz, 2H), 7.54 –7.41 (m, 2H), 7.27 –7.12 (m, 4H), 7.02 (d, J = 4.9 Hz, 2H), 6.20 (s, 1H). Elem. Anal. Calcd for C H NO : C, 69.73; H, 3.66; N,3.39. Found: C, 69.70; H, 3.56; N, 3.44. 24

15

6

ASSOCIATED CONTENT Supporting Information. The following files are available free of charge. Calculation of E-factor and EcoScale FT-IR spectra of IL-1, IL-2, IL-1@CNTs, and IL-2@CNTs. 1

H and 13C NMR data for products

AUTHOR INFORMATION Corresponding Author *Corresponding authors; E-mail: [email protected]; [email protected]; [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT Mayank and BK Billing are thankful to IIT Ropar for the fellowship. REFERENCES


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Synopsis Carbon nanotubes coated with ionic liquids (IL@CNTs) were prepared. IL@CNTs were evaluated for the synthesis of chromene derivatives in water.


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Ionic Liquid-Coated Carbon Nanotubes as Efficient Metal-Free

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