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Fe3O4@Boehmite-NH2-CoII NPs: An Environment Friendly Nanocatalyst for Solvent Free Synthesis of Coumarin Derivatives Through Pechmann Condensation Reaction

  • Somayeh Pakdel
  • Batool AkhlaghiniaEmail author
  • Arezou Mohammadinezhad
Original Article
  • 39 Downloads

Abstract

We report herein the synthesis of coumarin derivatives via the Pechmann condensation reaction in the presence of magnetic core–shell-like Fe3O4@Boehmite-NH2-CoII NPs. The aforesaid nanocatalyst which previously reported by our group, was found to be an efficient heterogeneous nanocatalyst in this reaction. Initially, the reaction conditions were optimized with different solvents, catalyst amounts and temperatures. Subsequently, the scope of the reaction was extended and the coumarin derivatives were obtained in reasonable yields. Interestingly, Fe3O4@Boehmite-NH2-CoII NPs was stable under reaction conditions and can be reused at least six times without a significant decrease in its catalytic activity. More importantly, using cobalt as a non-toxic, inexpensive, widely available and high-activity catalyst is great of interest than the most previously reported protocols.

Keywords

CoII immobilized on aminated Fe3O4@Boehmite nanoparticles (Fe3O4@Boehmite-NH2-CoII NPs) Pechmann condensation reaction Nanocatalyst Heterogeneous nanocatalyst Phenol β-Ketoesters 

1 Introduction

For many years coumarins (2H-chromen-2-ones) and their derivatives as one of the most important classes of oxygen heterocycles have been the focus of keen interest of many organic and medicinal chemists because of the broad spectrum of their biological and therapeutic properties. Many products along with a large number of natural products which contain the subunit of coumarin exhibit useful and variant biological activities, such as anthelmintic, hypnotic, insecticidal, antibacterial and anticancer properties [1, 2, 3] as well as inhibition of platelet aggregation [4], inhibition of steroid 5α-reductase [5] and of HIV-1 protease [6]. Despite of this wide range of biological applications, they are largely used as additives in food, cosmetics, fragrance, agrochemicals, optical brightening agents, dispersed fluorescent and tunable dye lasers [7]. Additionally, coumarins act as intermediates for the synthesis of fluoro coumarins, chromenes, coumarones, 2-acyl resorcinols and others [8, 9, 10]. Coumarins (2H-chromen-2-ones) have been synthesized by various routes such as Baylis–Hillman [11], Knoevenagel [12, 13, 14], Perkin [15], Reformatsky [16], Wittig [17], and Pechmann reactions [18]. The Pechmann method has been the most useful due to the good yields and using simple and inexpensive starting materials. The method based on a two-component (substituted phenols and β-ketoesters) coupling in the presence of acid catalysts. During recent years several acidic catalysts including different protic acid (such as H2SO4, HCl, H3PO4, F3CCO2H and Cl3CCOOH), Lewis acids [such as FeCl3, TiCl4, AlCl3, Y(NO3)3.6H2O, NbCl5, [KAl(SO4)2.12H2O], ZrCl4 and Sm(NO3)3.6H2O] and solid acids [such as Co/SBA-15, Fe3O4@SiO2@PrSO3H, MFRH, γ-Fe2O3@HAp-Ag, TiO2-Pr-SO3H, Fe3O4-DABCO, SnClx-SiO2, Fe3O4-SiO2-HMTA, ZrOCl2.8H2O/SiO2, C@TiO2-SO3-SbCl2, Fe3O4@SiO2@Et-PhSO3H and meglumine sulfate (MS)] have been employed for this reaction [19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]. However, most of these catalysts have to be used in stoichiometric amount or more to gain high yield. On the other hand, as they cannot be recovered or reused, the disposal of post reaction wastes creates severe environmental problems. Nowadays, owing to increasingly stringent environmental standards and economic pressures, cleaner and safer catalysts have been developed to prompt the Pechmann condensation. Using heterogeneous solid catalytic systems are the appropriate as they are easily recoverable, reusable and minimized the wastes [41, 42, 43, 44, 45]. Charming technique is the replacement of conventional separation methods (centrifugation and filtration) with magnetic separation approaches achieved by the immobilization of metal ions on functionalized incorporated magnetic nanoparticles (MNPs) into the solid supports such as Fe3O4@Boehmite-NH2-CoII NPs [46]. Notably, one of the interesting features of this technique is that it provides easy separation of catalysts from the reaction mixture by means of an external magnetic field as well as the prevention of MNP agglomeration. From our laboratory, use of Fe3O4@Boehmite-NH2-CoII NPs (Scheme 1) as magnetic nano structured catalyst has been explored for the Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions in a green solvent (H2O) and also selective oxidation of alcohols using household bleach [46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58]. In view of the great importance of coumarins (their biological and pharmacological activities) as well as the mentioned drawbacks of some previous reported methods, the search for the new readily available and green catalysts is still being actively pursued.
Scheme 1

The preparation of core–shell-like Fe3O4@Boehmite-NH2-CoII NPs

Based on our previous studies on the application of magnetic nano structured catalyst in organic synthesis [47], herein, we report a simple bench-top synthesis of coumarins (2H-chromen-2-ones) and their derivatives through Pechmann condensation reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs (Scheme 2).
Scheme 2

Synthesis of coumarin derivatives by the condensation reaction between substituted phenols and alkyl acetoacetates in the presence of Fe3O4@Boehmite-NH2-CoII NPs

2 Results and Discussion

Fe3O4@Boehmite-NH2-CoII NPs was prepared using a method previously reported in the literature and also was fully characterized [46]. The catalytic activity of the aforesaid nanocatalyst was evaluated in the synthesis of coumarin derivatives and the results were discussed in detail as follows.

2.1 Catalytic Preparation of Coumarin Derivatives Through Pechmann Condensation Reaction in the Presence of Fe3O4@Boehmite-NH2-CoII NPs (V)

The feasibility of Fe3O4@Boehmite-NH2-CoII NPs (V) catalyzed Pechmann condensation reaction was studied in the condensation reaction of resorcinol with ethyl acetoacetate as a model reaction. To find the best conditions for this reaction, our initial attempts focused to investigate the effect of experimental factors comprising the amount of catalyst, solvent and temperature. The results are listed in Table 1. To elucidate the catalytic activity of Fe3O4@Boehmite-NH2-CoII NPs (V) in this reaction, an experiment was conducted in the absence of catalyst. As shown in this Table, when equimolar quantities of resorcinol and ethyl acetoacetate were heated together in the absence of any catalyst at 80 °C, no change in the composition of reaction mixture was observed, even the experiment was driven for a long time (Table 1, entry 1). Treatment of resorcinol with ethyl acetoacetate in the presence of 5.5 mol % of Fe3O4@Boehmite-NH2-CoII NPs (V) at 80 °C under solvent-free conditions afforded the 7-hydroxy-4-methyl-2H-chromen-2-one in 80% yield after 30 min (Table 1, entry 2). The examination of different temperatures was demonstrated that 90 °C is the best temperature for the Pechmann condensation reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs (V) (Table 1, entries 3–5). Comparison of various catalyst loading reveals that 6.6 mol % of catalyst is the most efficient amount of Fe3O4@Boehmite-NH2-CoII NPs (V) for the preparation of 7-hydroxy-4-methyl-2H-chromen-2-one (Table 1, entries 6–8). To study the effect of reaction media on the yield and reaction time, a screening was performed with different refluxing solvents such as EtOH, MeOH, DMF, MeCN and H2O (Table 1, entries 9–13). It is evident that in solvent free condition the reaction moved faster with higher yield. To clarify more and more the vital role of Fe3O4@Boehmite-NH2-CoII NPs (V) in Pechmann condensation reaction, by applying the optimized reaction conditions (Table 1, entry 6) in a set of experiment the model reaction was conducted in the presence of Fe3O4 NPs, Boehmite NPs (I), Fe3O4@Boehmite NPs (II), Fe3O4@Boehmite-Pr–Cl(III), Fe3O4@Boehmite-Pr–Cl-NH2 (IV) and CoCl2.6H2O, respectively. It was found that any part of catalyst lonely cannot improve the results to an appreciable extent and the best yield was obtained in the presence of Fe3O4@Boehmite-NH2-CoII NPs (V) (It may be related to the formation of active CoII complex via the combination of an amino ligand (triethylenetetramine) with cobalt species and also, to the unique egg-like shape nanostructured catalyst which obtained from the amalgamation of Fe3O4 NPs with Boehmite NPs that has the properties of both components).
Table 1
Optimization of various reaction parameters for the synthesis of 7-hydroxy-4-methyl-2H-chromen-2-one
Open image in new window

Entry

Catalyst (mol %)

Solvent

Temperature (°C)

Time (min)

Isolated yield (%)

1

80

30/5 (h)

0/0

2

5.5

80

30

80

3

5.5

90

30

90

4

5.5

100

30

90

5

5.5

110

30

90

6

6.6

90

30

95

7

7.7

90

30

95

8

8.8

90

30

95

9

6.6

EtOH

Reflux

5 (h)

90

10

6.6

MeOH

Reflux

4 (h)

40

11

6.6

DMF

Reflux

5 (h)

30

12

6.6

CH3CN

Reflux

5 (h)

60

13

6.6

H2O

Reflux

7 (h)

Trace

14

6.6

Ultrasound

45

2 (h)

35

15

0.06 (g)a

90

4.5 (h)

80

16

0.06 (g)b

90

4 (h)

95

17

0.06 (g)c

90

4 (h)

95

18

0.06 (g)d

90

4 (h)

95

19

0.06 (g)e

90

4 (h)

95

20

6.6f

90

4.5 (h)

40

aReaction was performed in the presence of Fe3O4 NPs

bReaction was performed in the presence of Boehmite NPs (I)

cReaction was performed in the presence of Fe3O4@Boehmite NPs (II)

dReaction was performed in the presence of Fe3O4@Boehmite-Pr–Cl(III)

eReaction was performed in the presence of Fe3O4@Boehmite-Pr-NH2 (IV)

fReaction was performed in the presence of CoCl2.6H2O

Encouraged by the results obtained from the optimized reaction conditions, the generality and substrate scope of this catalytic system was evaluated for the reaction of various phenols with β-ketoesters (ethyl and methyl acetoacetate). The results are summarized in Table 2. According to the data, the conclusion could be derived that phenols containing electron-donating substituents (such as –OH and –NH2) gave the desired products in good to excellent yields (Table 2, entries 1–6 and 9–12) while no desired coumarin derivatives were observed in the case phenols bearing electron-withdrawing substituents (such as –Cl and –NO2) (Table 2, entries 7 and 8). Based on the proposed mechanism in Scheme 3, the nucleophilic addition of phenols to the carbonyl center of β-ketoester (intermediate II) was assisted by the presence of electron-releasing substituents which led to facile formation of intermediate III as an important step in the reaction rate. Interestingly, α-naphthol and β-naphthol were condensed with β-ketoester through Pechmann condensation reaction and produced the corresponding products smoothly (Table 2, entries 5–6 and 13–14). Comparatively, ethyl acetoacetate condensed more quickly than methyl acetoacetate in the presence of Fe3O4@Boehmite-NH2-CoII NPs (V) (Table 2, entries 1–6 vs. 9–14).
Table 2

Scope and functional group tolerance of Fe3O4@Boehmite-NH2-CoII NPs (V) catalyzed Pechmann condensation reaction

Scheme 3

Suggested mechanism for the preparation of coumarin derivatives through Pechmann condensation reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs (V)

All the synthesized compounds were identified in detailed using physical and spectroscopic data (melting point, mass spectrometry, FT-IR, 1H and 13C NMR spectroscopy), consistent in comparison with those reported previously or with authentic samples prepared by the conventional methods. The spectral data of all products are given in experimental section. Molecular ion peak in the MS spectra established the proposed structure of all products. FT-IR spectra exhibited a characteristic absorption band at 1714–1691 cm−1 due to carbonyl group of lactone ring. The formation of the products was also established by 1HNMR spectroscopy, wherein two sharp singlets at δ 2.45–2.30 and δ 6.26–5.79 ppm correspond to the C4–CH3 and =C–H confirm the formation of condensed products. Also, further evidence to prove the formation of the corresponding coumarin derivatives is the signals which appeared in the aromatic region. In 13C NMR spectra, resonating signals at δ 180–160, δ 163–153, δ 114–94 ppm correspond to C=O, =C4 and =C3, whereas –CH3 resonates at δ 23–18 ppm which approve the formation of desired products (see Supporting Information file).

A possible mechanistic pathway has been proposed for the preparation of coumarin derivatives through Pechmann condensation reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs (V) (Scheme 3). On the basis of this mechanism, activation of keto group of alkyl acetoacetate (I), followed by nucleophilic attack of substituted phenol (II), afforded the intermediate III. Re-aromatization of intermediate III produced IV. The transesterification (upon intramolecular attack of phenolic –OH) caused ring closure and subsequent elimination of R2OH leads to formation of V. The final step is dehydration that produced the corresponding coumarin derivatives (VI) and released the catalyst for the next cycle.

To investigate the stability of Fe3O4@Boehmite-NH2-CoII NPs (V) the leaching of catalyst was tested. This was performed by stopping the model reaction after 15 min and then separating the magnetic nanocatalyst from the reaction mixture using an external magnet. Thereafter, the reaction mixture was continued for another 15 min. No further substantial improvement in the yield of condensation reaction was observed which confirmed the absence of active cobalt species in reaction medium. ICP-analysis of the reaction mixture was also found to contain a negligible leaching of cobalt species (5.1 × 10−6 mol%).

The recyclability of Fe3O4@Boehmite-NH2-CoII NPs (V) was also investigated on model reaction under optimized reaction conditions. After each cycle, the separated nanocatalyst by a magnetic bar was washed with ethanol and acetone (3 × 5 mL) to remove residual organic compounds, dried at 50 °C overnight and reused in the next run. In each run, the catalytic performance of the recovered nanocatalyst was compared with that of the fresh Fe3O4@Boehmite-NH2-CoII NPs (V) (Fig. 1). It is evident from Fig. 1 that no significant change in catalytic activity was observed even after six recycle runs.
Fig. 1

Synthesis of 7-hydroxy-4-methyl-2H-chromen-2-one through the Pechmann condensation reaction in the presence of reused Fe3O4@Boehmite-NH2-CoII NPs (V)

The ICP-analysis of the 6th recycled nanocatalyst reveals that the cobalt content of the 6th reused nanocatalyst (1.06 mmol g−1) is less than that of fresh nanocatalyst (1.1 mmol g−1). The obtained results clearly certified that the nanocatalyst has good stability and reusability in the optimized reaction conditions.

Our attention next turned to compare the catalytic activity of Fe3O4@Boehmite-NH2-CoII NPs (V) with the previous reported catalysts in the Pechmann condensation reaction of resorcinol with ethyl acetoacetate (Table 3). It was observed that the catalytic activity of 6.6 mol % of Fe3O4@Boehmite-NH2-CoII NPs (V) is superior to the entries 1–4 and 10 with respect to the reaction temperature and entries 1, 3 and 8–10 in terms of the reaction time, presented in Table 3. Moreover, the outstanding magnetic recyclability and the simple separation procedure of present nanocatalyst add to the versatility of this method (compare with entries 1–9).
Table 3

Comparison of the catalytic activity of Fe3O4@Boehmite-NH2-CoII NPs (V) with some other catalysts reported for the synthesis of 7-hydroxy-4-methyl-2H-chromen-2-one

Entry

Catalyst

Solvent

Temperature (°C)

Time (min)

Reusability

Isolated yield %

Ref

1

Co/SBA15

100

5 (h)

12

95

[29]

2

C@TiO2-SO3-SbCl2

120

45

5

94

[38]

3

FeCl3·6H2O

Toluene

Reflux

16 (h)

92

[59]

4

SnClx–SiO2

120

35

90

[35]

5

ZrOCl2.8H2O/SiO2

90

40

8

94

[37]

6

Meglumine sulfate

100

40

92

[40]

7

Y(NO3)3.6H2O

90

45

92

[24]

8

Sc(OTf)3

80

5.5 (h)

75

[60]

9

ZrOCl2.H2O

80

24 (h)

91

[61]

10

Fe3O4@SiO2@Et-PhSO3H

120

4 (h)

7

93

[41]

11

Fe3O4@Boehmite-NH2-CoII NPs

90

30

6

95

Present study

3 Conclusion

In summary, Fe3O4@Boehmite-NH2-CoII NPs (V) was introduced as an efficient and magnetic heterogeneous nanocatalyst in the Pechmann condensation reaction for construction of coumarin derivatives by employing phenols and β-ketoesters under solvent free conditions. The obtained results clearly confirmed that the catalytic activity of the above-mentioned nanocatalyst is exactly dependent on the nature of the substituents on the phenyl rings of phenols (electron-donating substituents lead to formation of the desired products, while no products were observed in the presence of electron-withdrawing substituents). The notable features of the present study are as follows: (a) reasonable yields of the products, (b) short reaction times, (c) magnetic separation of the nanocatalyst by using an external magnetic field, (d) avoid of toxic catalyst and hazardous organic solvents, (e) low environmental impact, low cost and high recovery of the nanocatalyst up to six recycle runs without a significant decrease in its catalytic activity.

4 Experimental

4.1 General

The purity determinations of the products and the progress of the reactions were accomplished by TLC on silica gel polygram STL G/UV 254 plates (preparative TLC was carried out using a Merck GF 254 silica gel on a glass support). The melting points of products were determined with an Electrothermal Type 9100 melting point apparatus. The FT-IR spectra were recorded on an Avatar 370 FT-IR Thermo Nicolet spectrometer. The NMR spectra were recorded on 300 MHz Bruker Avance instruments in CDCl3 and DMSO-d6. Mass spectra were recorded with a CH7A Varianmat Bremem instrument at 70 eV electron impact ionization, in m/z (rel %). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was carried out on a 76004555 SPECTRO ARCOS ICP-OES analyzer. All yields refer to the isolated products after purification by thin layer chromatography.

4.2 Typical Procedure for the Preparation of 7-Hydroxy-4-Methyl-2H-Chromen-2-One

In a round bottom flask, Fe3O4@Boehmite-NH2-CoII NPs (V) (6.6 mol %, 0.06 g) was added to the mixture of resorcinol (1 mmol, 0.110 g) and ethyl acetoacetate (1 mmol, 0.130 g) at 90 °C. The reaction mixture stirred for 30 min. The progress of reaction was monitored by TLC (eluent, n-hexane/ethyl acetate, 3:1). After the completion of the reaction, the reaction mixture was diluted with ethanol and the nanocatalyst separated with an external magnet to obtain the crude product. Afterwards, the resulting crude product was purified by thin layer chromatography (eluent, n-hexane/ethyl acetate, 30:10) and the pure 7-hydroxy-4-methyl-2H-chromen-2-one was obtained as a pale yellow solid (% 95, 0.167 g).

Notes

Acknowledgements

The authors gratefully acknowledge the partial support of this study by Ferdowsi University of Mashhad Research Council (Grant No. p/3/47339).

Supplementary material

42250_2019_42_MOESM1_ESM.docx (6.7 mb)
Supplementary material 1 (DOCX 6812 kb)

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Copyright information

© The Tunisian Chemical Society and Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Chemistry, Faculty of ScienceFerdowsi University of MashhadMashhadIran

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