Highly efficient and rapid synthesis of imines in the presence of nano-ordered MCM-41- SO3H heterogeneous catalyst

Scientia Iranica C (2013) 20 (3), 592–597

Sharif University of Technology Scientia Iranica Transactions C: Chemistry and Chemical Engineering www.sciencedirect.com

Highly efficient and rapid synthesis of imines in the presence of nano-ordered MCM-41-SO3 H heterogeneous catalyst E. Ali, M.R. Naimi-Jamal ∗ , M.G. Dekamin Research Laboratory of Green Organic Synthesis & Polymers, Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, Iran Received 9 August 2012; revised 29 November 2012; accepted 8 January 2013

KEYWORDS Imines; Carbonyl compounds; MCM-41-SO3 H; Mesoporous materials; Green chemistry.

Abstract Nano-ordered MCM-41 anchored sulfonic acid (MCM-41-SO3 H) was used as an efficient heterogeneous catalyst for the synthesis of Schiff bases by the reaction of different aryl/alkyl aldehydes or ketones with primary amines at room temperature with high to excellent yields. This mesoporous catalyst can be reused at least four times without significant loss to its catalytic potential. © 2013 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction The condensation of carbonyl compounds with primary amines to produce the corresponding imines was first discovered in 1864 by Hugo Schiff. Hence, imines are often referred to as Schiff bases or azomethines [1]. The imine formation is one of the most important reactions in organic and medicinal chemistry [2]. For instance, imines are used as versatile components in the asymmetric synthesis of α -aminonitriles [3], preparation of secondary amines by hydrogenation [4], and in cycloaddition reactions [5]. In addition, imines have been discovered to have a wide range of biological activities such as lipoxygenase inhibition, anti-inflammatory, anti-cancer [6], antibacterial, and antifungal behavior [7]. Many procedures have been introduced for the preparation of imines in the literature since the pioneering work of Hugo Schiff. Among recent methods or techniques for the preparation of imines, the use of ionic liquids [8], infrared [9], microwave [6], and ultrasound [10] irradiation can be mentioned. However, the main problem which affects the

∗

Corresponding author. Tel.: +98 21 77240289. E-mail address: [email protected] (M.R. Naimi-Jamal). Peer review under responsibility of Sharif University of Technology.

yield of the products originates in the existence of equilibrium conditions between the reactants and the corresponding imines, along with water, as a byproduct of the reaction. To overcome this problem, various dehydrating agents such as P2 O5 /SiO2 [11], MgSO4 -Mg(ClO4 )2 [12], fuming TiCl4 [13] or aromatic solvents forming azeotropic mixtures with water at high temperatures have been used. Such methodologies often suffer from complicated procedures, moisture sensitive catalysts or reagents, large quantities of toxic aromatic solvents, huge amounts of costly dehydrating agents or catalysts, high reaction temperatures, and long reaction times. In addition, some of these methods are limited only to the synthesis of aldimines and are not suitable for preparation of ketimines. Therefore, the development of more efficient and rapid protocols to produce imines remains in high demand. On the other hand, ordered mesoporous materials are used for fine chemical synthesis as heterogeneous solid catalysts. Nano-ordered mesoporous materials offer high surface areas with high concentrations of active sites [14]. In 1992, researchers at the Mobil Corporation made a major discovery of the M41S family of silicate/aluminosilicate mesoporous molecular sieves with exceptionally large uniform pore structures. It should be taken into account that a decisive choice of surfactant, adding auxiliary organic chemicals and changing reaction parameters (e.g. temperature or composition of the reactants and templates) can play significant roles in controlling mesoporous structure [15]. Furthermore, it is likely to improve mesoporous materials by the functionalization of their surfaces by

1026-3098 © 2013 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved. doi:10.1016/j.scient.2013.02.007

E. Ali et al. / Scientia Iranica, Transactions C: Chemistry and Chemical Engineering 20 (2013) 592–597

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Scheme 1: General method for the preparation of imines.

covalent anchoring of active groups such as sulfonic acid. For instance, MCM-41, a member of the M41S family, does not show acidic properties, but its acidic functionality can be enriched by means of grafting sulfonic acid onto its surface through silanol groups [16]. Along this line, a variety of mesoporous sulfonic acids have been introduced and their applications as catalysts in chemical transformations have been investigated in recent years [17]. Herein, we wish to report our results on an efficient, rapid and simple method for the synthesis of imines in the presence of nano-ordered MCM-41 anchored sulfonic acid (MCM-41-SO3 H) in EtOH (Scheme 1). Figure 1: FT-IR spectrum of MCM-41-SO3 H.

2. Experimental 2.1. Materials N-Cetyl-N , N , N-trimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS, >98%), diethylamine (synthetic grade) and absolute EtOH were purchased from Merck and used without further purification. All other chemicals were provided by Merck or Aldrich and used as received, except liquid aldehydes and aniline which were distilled prior to use. MCM-41 [17], M-MCM-41s (M = B, Al, Fe, Zn) [18a] and MCM-41-SO3 H [18b] were prepared on the basis of previously reported methods. General procedure for preparation of MCM-41 To 42 mL deionized water in a 500 mL beaker, 2.7 g diethylamine was added at ambient temperature and stirred. Then, 1.47 g cetyltributylammonium bromide (CTAB) was gradually added to the above mixture until a clear solution was obtained. Tetraethyl orthosilicate (2.1 g) was added drop-wise to the solution and the pH was fixed at 8.5 by addition of 1 M HCl solution. After 2 h, the resulting solid product was filtered and washed several times with deionized water, and dried at 45 °C for 12 h. The obtained MCM-41 was calcined at 550 °C for 5 h to remove all the surfactant [17]. General procedure for preparation of M-MCM-41s The procedure is the same as for the preparation of MCM41, but before adjusting the pH with 1 M HCl, one should add 0.032 g boric acid, 0.06 g Al(OH)3 , 0.13 g FeCl3 · 6H2 O, or 0.11 g ZnCl2 , as the source for B, Al, Fe or Zn, respectively [18a]. General procedure for preparation of MCM-41-SO3 H MCM-41 (1 g) was suspended in CH2 Cl2 (5 mL) in a 100 mL round bottom flask equipped with a gas outlet tube and a dropping funnel containing a solution of chlorosulfonic acid (2 mL) in dichloromethane (15 mL). The chlorosulfonic acid solution was added drop-wise to the obtained suspension over a period of 30 min at room temperature. The HCl gas evolved from the reaction mixture was conducted via the gas outlet tube into a NaOH solution. After the completion of the reaction, the solvent was evaporated under reduced pressure and the MCM-41-SO3 H was collected as a white solid [18b]. 2.2. Instruments FT-IR spectra were recorded as KBr pellets on a Shimadzu FT IR-8400 spectrometer. GC chromatograms were recorded on a Perkin Elmer 8400 instrument. Melting points were determined

using an Electrothermal 9100 apparatus and are uncorrected. All reactions were protected from air moisture using a CaCl2 guard tube. Analytical TLC was carried out using Merck 0.2 mm silica gel 60 F-254 on Al-plates. Nitrogen adsorption isotherms at 76 K were measured using a Micromeritics ASAP 2020 volumetric adsorption analyzer. SEM micrographs were obtained using a VEGA II TESCAN microscope. 2.3. Typical experimental procedure for the preparation of imines In a round bottom flask, MCM-41-SO3 H (0.01 g) was slowly added to a mixture of an aldehyde or ketone (1.0 mmol) and amine (1.0 mmol) in 2 mL EtOH. The resulting mixture was stirred at room temperature. The progress of the reaction was monitored by TLC. Then, the heterogeneous catalyst was separated from the reaction mixture by filtration and washed with hot EtOH or EtOAc. The filtrate was then evaporated under reduced pressure to obtain essentially pure products in most cases. The pure product was obtained upon recrystallization from EtOH, when necessary. All the products are known imines and their structures were secured on the basis of their analytical and/or spectral data, compared with literature data. 3. Results and discussion 3.1. Characterization of nanocatalyst MCM-41-SO3 H The nanocatalyst MCM-41 was modified by the SO3 H acidic group to create acidic sites on its surface. The MCM-41-SO3 H was characterized by SEM, BET and FT-IR spectroscopy. In FTIR spectroscopy (Figure 1), the broad band in the region of 3200–3400 cm−1 is assigned to the O–H stretching vibration of hydroxyl groups. The bands at 1286 cm−1 and 1321 cm−1 are due to the symmetric and asymmetric stretching vibrations of S=O of the sulfonic acid group. Moreover, a strong band at 1174 cm−1 is assigned to the Si–O–Si asymmetric stretching vibrations and a band at 850 cm−1 related to its symmetric stretching vibrations. The SEM micrographs are shown in Figure 2. As can be seen, the powder is aggregated, maybe due to strong hydrogen bonding between the SO3 H groups. However, some non-aggregated particles are shown with width less than 100 nm. The BET Adsorption average pore width (4 V/A) was measured as 3.4 nm and BJH adsorption average pore width (4 V/A) was measured as 2.6 nm. These confirm that the pores are in the nanoscale.

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Figure 2: The SEM micrographs of MCM-41-SO3 H. Table 1: Comparison of the influence of different catalysts of the nano-ordered MCM-41 family on the yield of the model reaction.a

Entry 1 2 3 4 5 6 7 8

Catalyst Al-MCM-41 B-MCM-41 Zn-MCM-41 Fe-MCM-41 MCM-41-SO3 H MCM-41-SO3 H MCM-41-SO3 H MCM-41-SO3 H

a b c

Amount of catalyst (g)

Yieldb (%)

Time (min)

0.01 0.01 0.01 0.01 0.005 0.01 0.02 0.1

20 60 120 30 1 1 1 1

59 61 52 64 70 86c 77 53

Reaction conditions: p-nitrobenzaldehyde (1a, 1.0 mmol), p-toluidine (2a, 1.0 mmol), EtOH (2 mL), room temperature. Isolated yield. Crude yield was quantitative.

3.2. Optimization of the reaction conditions The reaction of p-nitrobenzaldehyde (1a) and p-toluidine (2a) in absolute EtOH at room temperature was selected as the model reaction. In order to find the optimized reaction conditions, the effect of the type and amount of the catalyst, solvent, temperature, and reaction time on the yield of the model reaction was studied. 3.2.1. Effect of the different catalysts and amount of catalyst To compare the catalytic activity of some of the members of the MCM-41 family such as Al-MCM-41, B-MCM-41, Zn-MCM41, Fe-MCM-41 and MCM-41-SO3 H, their catalytic activities were studied in the model reaction. As can be concluded from Table 1, MCM-41-SO3 H was the most effective catalyst for this reaction, presumably due to its higher Bronsted acidic activity. Interestingly, it was found that the corresponding imine (3a) has been quantitatively prepared in the presence of MCM-41-SO3 H, after only one minute. The other mesoporous catalysts required much longer reaction times compared to MCM-41-SO3 H. Furthermore, the optimized amount of the MCM-41-SO3 H was also found to be 0.01 g per 1.0 mmol of the aldehyde 1 according to Table 1, Entry 6.

Table 2: The effect of various solvents and temperature on the yield of the model reaction.a Entry 1 2 3 4 5 6

Solvent n-Hexane CH2 Cl2 Et2 O EtOAc EtOH EtOH

Temperature (°C)

Time (min)

Yield (%)b

r.t. r.t. r.t. r.t. r.t. Reflux

15 30 20 30 1 1

66 78 75 65 86 87

a Reaction conditions: p-nitrobenzaldehyde (1a, 1.0 mmol), p-toluidine (2a, 1.0 mmol), MCM-41-SO3 H (0.01 g), solvent (2 mL). b Isolated yield.

3.2.2. Effect of different solvents and temperature The effect of various polar and non-polar solvents such as n-hexane, CH2 Cl2 , Et2 O, EtOAc and EtOH was studied on the reaction of 1a with 2a in the presence of MCM-41-SO3 H. As shown in Table 2, EtOH was found to be the best choice, considering its more environmentally friendly nature and higher yield of product (Entry 5). The influence of the temperature on the yield of the desired product was also investigated. However, it was found that

E. Ali et al. / Scientia Iranica, Transactions C: Chemistry and Chemical Engineering 20 (2013) 592–597

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Table 3: Rapid and efficient preparation of imines catalyzed by nano-ordered MCM-41-SO3 H under optimized conditions.a Entry

Carbonyl compound (1)

Amine (2)

1

Yield (%)b

m.p. (°C)

Product (3)

Time (min)

3a

1

94 (86)

126–128

2

2a

3b

1

89 (80)

89–91

3

2a

3c

1

96 (72)

140–142

4

2a

3d

1

91 (77)

126–128

5

2a

3e

1

89 (75)

91–93

3f

2

85 (61)

38–40

2b

3g

5

82 (46)

194–196

6

7 8

1a

2b

3h

1

95 (73)

90–92

9

1b

2b

3i

1

96 (75)

65–66

10

1d

2b

3j

1

91 (65)

62–64

11

1e

2b

3k

1

93 (87)

63–65

12

2b

3l

1

95 (82)

106–108

13

2b

3m

1

95 (70)c

55–57

3n

1

93 (77)

55–57

14

1a

15

1b

2c

3o

1

91 (78)

61–63

16

1e

2c

3p

1

87 (70)

40–42

17

1g

2c

3q

5

93 (60)

204–206

18

2b

3r

30

90 (61)

49–51

19

2b

3s

30

88 (59)

122–124

20

2b

3t

30

89 (55)

122–124

a b c

Reaction condition: carbonyl compound (1.0 mmol), amine (1.0 mmol), MCM-41-SO3 H (0.01 g), absolute EtOH (2 mL), room temperature. Crude yield, determined by GC. Numbers in parenthesis refer to isolated yields. Only 10% yield of the desired product was detected at room temperature without catalyst after 4 h.

temperature does not play a considerable role in improving the reaction yield (Table 2, Entries 5 and 6). The optimized conditions (0.01 g MCM-41-SO3 H, EtOH, r.t.) were then developed for different carbonyl compounds. The results have been summarized in Table 3. Aromatic aldehydes afforded excellent yields with short reaction times, whereas the

reaction of ketones required a longer time for completion. The lower reactivity of ketones compared to aldehydes is related to the steric hindrance around the carbonyl group of ketones. Since furfural (1i) is susceptible to polymerization under strong acidic conditions [19], its reaction with aniline (2b) was investigated in the absence of MCM-41-SO3 H in a separate

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Scheme 2: Reaction of p-chlorobenzaldehyde (1d) and p-hydroxyacetophenone (1j) with aniline (2b) under the optimized reaction conditions.

reaction. Interestingly, only 10% yield of the desired product 3m was detected at room temperature without any catalyst after 4 h. However, it reacted well with 2b and produced the corresponding imine 3m in the presence of MCM-41-SO3 H in quantitative yield without formation of any polymerization side reaction (Table 3, Entry 13). As shown in Table 3, the crude yield of the products was quantitative in most cases. However, as is well known for imines, the isolated yield of the desired product, 3 was somewhat less than the crude yield. This may be due to the hydrolysis of imines to their corresponding carbonyl compounds and amines during the work up procedure. Some of the hydrolysis can be prevented using anhydrous solvents or by fast work up and keeping the crude reaction mixture away from moisture. However, this protocol is promising for performing one-pot reactions with the in situ prepared imines as intermediate; hence it would not be necessary to purify the produced imines prior to further use. To study the chemoselectivity of the method, the reaction of a mixture of p-chlorobenzaldehyde (1d, 1.0 mmol) and p-hydroxyacetophenone (1j, 1.0 mmol) with aniline (2b, 1.0 mmol) in EtOH was investigated in the presence of 0.01 g of the catalyst. It was observed that imine formation started immediately after adding the catalyst. The only product was the corresponding aldimine 3j, whereas the ketone remained practically intact (Scheme 2). 3.3. Catalyst reusability and stability The reusability of the catalyst was studied in four consecutive runs for the model reaction. After each run, the catalyst was filtered and exhaustively washed with EtOH, EtOAc, and acetone, respectively and then dried. The recycled catalyst was examined in the next run for the model reaction. As seen in Figure 3, the MCM-41-SO3 H catalyst promotes the reaction with remarkable retaining catalytic activity each time. Examination of the FT-IR spectra of MCM-41-SO3 H, before and after the regeneration, indicated that the structure of MCM-41-SO3 H is sufficiently stable during the recycling process. 4. Conclusion In summary, different kinds of imines have been prepared using nano-ordered MCM-41-SO3 H as a strong and effective heterogeneous catalyst. Among the advantages of the method, the following can be mentioned: (i) the process is very simple and no laborious azeotropic separation of water is needed; (ii) by means of this heterogeneous catalyst, aldimines and

Figure 3: Recyclability of nano-ordered MCM-41-SO3 H catalyst in four consecutive runs.

especially ketimines have been produced at room temperature without using any toxic aromatic solvents with high to quantitative yields; (iii) the reaction time is very short (just one minute in most cases); and (iv) the catalyst can be reused several times without remarkable loss of its catalytic potential. Acknowledgment We acknowledge the Research Council of Iran University of Science and Technology (IUST) for partial financial support of this work. References [1] Layer, R.W. ‘‘The chemistry of imines’’, Chem. Rev., 63(5), pp. 489–510 (1963). [2] Sithambaram, S., Kumar, R., Son, Y. and Suib, S. ‘‘Tandem catalysis: direct catalytic synthesis of imines from alcohols using manganese octahedral molecular sieves’’, J. Catal., 253(2), pp. 269–277 (2008). [3] Jiao, Z., Feng, X., Liu, B., Chen, F., Zhang, G. and Jiang, Y. ‘‘Enantioselective Strecker reactions between aldimines and trimethylsilyl cyanide promoted by chiral N , N ′ -dioxides’’, Eur. J. Org. Chem., 2003(19), pp. 3818–3826 (2003). [4] Cao, Y.Q., Dai, Z., Chen, B.H. and Liu, R. ‘‘Sodium borohydride reduction of ketones, aldehydes and imines using PEG400 as catalyst without solvent’’, J. Chem. Technol. Biotechnol., 80(7), pp. 834–836 (2005). [5] Moustafa, M.M.A.R. and Pagenkopf, B.L. ‘‘Ytterbium triflate catalyzed synthesis of alkoxy-substituted donor–acceptor cyclobutanes and their formal [4 + 2] cycloaddition with imines: stereoselective synthesis of piperidines’’, Org. Lett., 12(21), pp. 4732–4735 (2010). [6] Gopalakrishnan, M., Sureshkumar, P., Kanagarajan, V. and Thanusu, J. ‘‘New environmentally-friendly solvent-free synthesis of imines using calcium oxide under microwave irradiation’’, Res. Chem. Intermediat., 33(6), pp. 541–548 (2007). [7] Hania, M.M. ‘‘Synthesis of some imines and investigation of their biological activity’’, E. J. Chem., 6(3), pp. 629–632 (2009).

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Elham Ali was born in 1985 in Tehran, Iran. She completed her B.S. degree in Chemistry at Shahid Beheshti University, Tehran, in 2008, and her M.S. degree in Organic Chemistry at Iran University of Science & Technology, Tehran, in 2010. Her research interests include: organocatalysis, nanocatalysts, and organic synthesis.

Mohammad Reza Naimi-Jamal was born in Mashhad, Iran, in 1968. He received his B.S., M.S. and Ph.D. degrees in Organic Chemistry from Sharif University of Science and Technology, Tehran, Iran in 1990, 1993 and 1999, respectively. In 1998, he was recipient of a one-year scholarship for further study in Justus-Liebig Universität Giessen, Germany, and visited Universität Oldenburg, Germany, as a Post-doctoral from 2000 to 2005. Since 2005, he has been Associate Professor of Organic Chemistry in Iran University of Science and Technology, Tehran, Iran. He is a member of some scientific societies such as the Iranian Chemical Society (ICS), American Chemical Society (ACS), Verein Deutscher Ingenieure (VDI), and Iranian Polymer Society (IPS). His research interests include: green (environmentally benign) chemistry, solid-state and solvent-free synthesis of organic substances, and catalytic and asymmetric organic reactions.

Mohammad G. Dekamin was born in Nahavand, Iran, in 1972. He received a B.S. degree in Chemistry from Shahid Chamran University, Ahwaz, in 1995, a M.S. Degree in Organic Chemistry from Shahid Beheshti University, Iran, in 1997, and a Ph.D. degree in the same subject from Sharif University of Technology (SUT), Tehran, in 2002. He is currently Associate Professor of Organic Chemistry at Iran University of Science and Technology (IUST), Tehran, Iran. His research interests involve green and environmentally-benign chemistry, heterogeneous catalysis and organocatalysis, nanotechnology and pharmaceuticals. He has published over 34 research papers in reputable international journals.