Scholarly article on topic 'Efficient one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles using SBA-Pr-SO3H as a green nano catalyst'

Efficient one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles using SBA-Pr-SO3H as a green nano catalyst Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Ghodsi Mohammadi Ziarani, Alireza Badiei, Negar Lashgari, Zahra Farahani

Abstract Sulfonic acid functionalized SBA-15 nanoporous material (SBA-Pr-SO3H) with a pore size of 6nm was found to be a green and effective solid acid catalyst in the one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions. SBA-Pr-SO3H was proved to be a recyclable, green, and highly efficient catalyst which could be easily handled, recovered, and reused several times without significant loss of reactivity.

Academic research paper on topic "Efficient one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles using SBA-Pr-SO3H as a green nano catalyst"

Journal of Saudi Chemical Society (2013) xxx, xxx-xxx

King Saud University Journal of Saudi Chemical Society

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Efficient one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles using SBA-Pr-SO3H as a green nano catalyst

Ghodsi Mohammadi Ziarani a,% Alireza Badiei b, Negar Lashgari a,b, Zahra Farahani a

a Department of Chemistry, Alzahra University, Vanak Square, P.O. Box 1993893973, Tehran, Iran b School of Chemistry, College of Science, University of Tehran, Tehran, Iran

Received 4 November 2012; accepted 18 January 2013

KEYWORDS

Nanoporous material; Substituted imidazoles; Solvent-free conditions; Functionalized SBA-15

Abstract Sulfonic acid functionalized SBA-15 nanoporous material (SBA-Pr-SO3H) with a pore size of 6 nm was found to be a green and effective solid acid catalyst in the one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions. SBA-Pr-SO3H was proved to be a recyclable, green, and highly efficient catalyst which could be easily handled, recovered, and reused several times without significant loss of reactivity.

© 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Imidazole and its derivatives are an important class of heterocyclic compounds that exhibit a wide range of biological and pharmacological activities. They show fungicidal (Sathe et al., 2011; Roongpisuthipong et al., 2010), analgesic (Sondhi et al., 2008), anti-inflammatory (Amir et al., 2011), antibacterial (Ganguly et al., 2011), and antitumor activities (Wittine et al., 2012). In addition, many members of this family act as selective inhibitors of p38 mitogenactivated protein (MAP)

kinase (Scior et al., 2011; Laufer et al., 2010), B-Raf kinase (Takle et al., 2006), and transforming growth factor P1 (TGF-P1) type 1 activin receptor-like kinase (ALK5) (Kim et al., 2010). Imidazole derivatives are also useful as potential corrosion inhibitors for transition metals such as iron, copper, zinc and their alloys (Bhargava et al., 2009).

In the literature, a number of methods have been reported for the synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted imidazoles. The synthetic strategy for the synthesis of 2,4,5-trisubstituted imidazoles is mainly based on the cyclocondensation of a 1,2-diketone with an aldehyde using ammonium acetate as the ammonia source while 1,2,4,5-tetra-substituted imidazoles are generally synthesized in a four-component condensation of aldehydes, 1,2-diketones, amines and ammonium acetate. Different conditions such as microwave irradiation on a solid support (Usyatinsky and Khmelnitsky, 2000; Oskooie et al., 2006; Xu et al., 2004), ultrasound irradiation (Shelke et al., 2009), ionic liquids (Siddiqui et al., 2005; Shaterian and Azizi, 2011), silica sulfuric acid (Shaabani and

* Corresponding author. Tel./fax: +98 2188041344. E-mail addresses: gmziarani@hotmail.com, gmohammadi@alzahra. ac.ir (G. Mohammadi Ziarani), abadiei@khayam.ut.ac.ir (A. Badiei). Peer review under responsibility of King Saud University.

1319-6103 © 2013 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/jjscs.2013.0L005

Rahmati, 2006), InCl3.3H2O (Sharma et al., 2008), sulfated tin oxide (Dake et al., 2012), and NiCl2.6H2O/Al2O3 (Heravi et al., 2007a) were tested for the synthesis of 2,4,5-trisubsti-tuted imidazoles. On the other hand, 1,2,4,5-tetrasubstituted imidazoles were synthesized using microwave (Balalaie and Arabanian, 2000; Kidwai et al., 2005), Keggin-type hetero-polyacids (Heravi et al., 2007b), Preyssler-type heteropoly acids (Javid et al., 2011), silica gel/NaHSO4 (Karimi et al., 2006), potassium dodeca tungstocobaltate trihydrate (K5CoW12O40.3H2O) (Nagarapu et al., 2007), Ytterbium tri-flate Yb(OTf)3 (Wang et al., 2006), molecular iodine (Kidwai and Mothsra, 2006; Kidwai et al., 2007), zinc oxide (Bahrami et al., 2011a), or HClO4-SiO2 (Kantevari et al., 2007).

Recently, different mesoporous ordered silicas (MOS) such as SBA-15 have received exceptional attention in the field of catalysis. SBA-15 is a well ordered hexagonal mesoporous sil-

ica structure with several unique characteristics such as large uniform pore size, high surface area, thick walls, and high thermal stability that has been functionalized and used in different reactions. The -SO3H Bransted acid groups on SBA-15 can be utilized for acid-catalyzed synthesis reactions. In other words, sulfonic acid functionalized SBA-15 behaves as an organic-inorganic hybrid catalyst wherein Bransted acid sites have been selectively created. There are a number of reports in which SBA-Pr-SO3H was tested as a catalyst in chemical transformations (Kureshy et al., 2009; Van Grieken et al., 2006; Bahrami et al., 2011b). Following our previous studies on the application of nanoporous heterogeneous solid catalysts to organic synthesis (Mohammadi Ziarani et al., 2009, 2010, 2011), we have discovered a green and highly efficient method for the synthesis of substituted imidazoles using SBA-Pr-SO3H as a nano-reactor under solvent-free conditions.

Table 1 SBA-Pr-SO3H catalyzed the synthesis of 2,4,5-trisubstituted imidazoles 4a-g under solvent-free conditions.

Entry X

Product

Time (min) Yielda (%) M.p. (°C)

Founded Reported

3 100 271-274 272-273 (Kidwai et al. (2007))

2 4-Cl

2 99 264-267 262-263 (Kidwai et al. (2007))

3 4-OMe ph'

226-229 226-228 (Heravi et al. (2007a))

4 4-OH

80 253-255 256-257 (Kidwai et al. (2005))

5 4-NMe-

93 257-259 257-258 (Wang et al. (2006))

6 3-NO2

9 87 263-265 265-267 (Kidwai et al. (2007))

7 2-OH

80 205-206 209-211 (Wang et al. (2006))

Isolated yields.

2. Experimental

All chemicals were obtained commercially and used without further purification. IR spectra were recorded from KBr disk using a FT-IR Bruker Tensor 27 instrument. Melting points were measured by using the capillary tube method with an electro thermal 9200 apparatus. The *H NMR and 13C NMR were run on a Bruker DPX, at 250 and 62.5 MHz using TMS as the internal standard. GC-Mass analysis was performed on a GC-Mass model: 5973 network mass selective detector, GC 6890 Agilent. SEM analysis was performed on a Philips XL-30 field-emission scanning electron microscope operated at 16 kV while TEM was carried out on a Tecnai G2 F30 at 300 kV.

2.1. SBA-15. Nanoporous silica synthesis and functionalization

The nanoporous compound SBA-15 was synthesized and func-tionalized according to our previous report (Mohammadi Zia-rani et al., 2010) and the modified SBA-15-Pr-SO3H was used as a nanoporous solid acid catalyst in the following reactions.

2.2. General procedure for the preparation of 2,4,5-trisubstituted imidazoles (4a-g)

The SBA-Pr-SO3H (0.02 g) was activated in vacuum at 100 0C and then after cooling to room temperature, benzil 1 (1 mmol, 0.21 g), benzaldehyde 2 (1 mmol), and ammonium acetate 3 (2 mmol, 0.23 g) were added to it. The mixture was heated under solvent-free conditions at 140 0C for an appropriate time. After completion of the reaction which was monitored by TLC using eluent (1:4 mL, petroleum ether: ethyl acetate), the mixture was washed with water completely and the solid product dissolved in hot ethyl acetate. Then, the mixture was filtered for removing the unsolvable catalyst and the filtrate was cooled to afford the pure product 4a-g.

2.3. General procedure for the synthesis of 1,2,4,5-tetrasubstituted imidazoles (6a-h)

The SBA-Pr-SO3H (0.02 g) was activated in vacuum at 100 0C and then after cooling to room temperature, benzil 1 (1 mmol, 0.21 g), benzaldehyde 2 (1 mmol), aniline or benzyl amine 5 (1 mmol) and ammonium acetate 3 (2 mmol, 0.23 g) were added to it. The mixture was heated under solvent-free conditions at 140 0C for an appropriate time (Table 1). After completion of the reaction which was monitored by TLC using eluent (1:4 mL, petroleum ether: ethyl acetate), the mixture was washed with water completely and the solid product dissolved in hot ethyl acetate. Then, the mixture was filtered for removing the unsolvable catalyst and the filtrate was cooled to afford the pure product 6a-h. The catalyst was washed subsequently with diluted acid solution, distilled water and then acetone, dried under vacuum and re-used for several times without significant loss of activity.

2.4. 2,4,5-Triphenylimidazole (4a)

*H NMR (250 MHz, CDCl3): d 7.21-8.09 (m, 15H, ArH), 12.68 (s, 1H. NH).

2.5. 2-(4-Chlorophenyl)-1,4,5-triphenylimidazole (6a)

IR (KBr) v max/cm"1: 1596, 1494, 1408. *H NMR (250 MHz, CDCl3): d 7.04-7.57 (m, 19H, ArH).

2.6. 1-Benzyl-2-(4-chlorophenyl)-4,5-diphenyl imidazole (6b)

IR (KBr) v max/cm"1: 1600, 1477, 1447, 1414. *H NMR (250 MHz, CDCl3): d 5.08 (s, 2H, CH2), 6.81-7.60 (m, 19H, ArH); 13C NMR (62.5 MHz, DMSO-d6): d 48.3, 125.9, 126.5, 126.8, 127.5, 128.1, 128.7, 128.75, 128.8, 128.85, 129.5, 130.2, 130.4, 130.8, 131.0, 134.3, 134.9, 137.3, 138.3, 146.8.

x - *erc

Ph^O /W-CH0 + - SBA-Pr-S03H ]r\

+ NH4OAc -►

Solvent-free H

140°C

3 4a-g

X = H, 4-CI, 4-OMe, 4-OH, 4-NMe2, 3-N02, 2-OH Scheme 1 Synthesis of 2,4,5-trisubstituted imidazoles 4a-g in the presence of SBA-Pr-SO3H.

X • CrCTO

NH4oac

Ph O 1

n NHj SBA-Pr-S03H

Solvent-free 140°C

X = 4-CI, 4-OMe, 4-Me, 4-NMe2, 3-N02, 3-OMe n = 0, 1

Scheme 2 Synthesis of 1,2,4,5-tetrasubstituted imidazoles 6a-h in the presence of SBA-Pr-SO3H.

Table 2 SBA-Pr-SO3H catalyzed the synthesis of 1,2,4,5-tetrasubstituted imidazoles 6a-h under solvent-free conditions.

Entry n X Product

Time (min) Yielda (%) Melting point (°C)

Founded Reported

0 4-Cl

4 100 156-158 158-160 (Kidwai et al. (2005))

1 4-Cl

0 4-OMe

0 4-Me

6 100 162-165 164-165 (Kidwai et al. (2005))

97 181-183 184-185 (Kidwai et al. (2007))

99 189-190 189-191 (Javid et al. (2011))

1 4-Me

95 163-165 165-168 (Kantevari et al. (2007))

0 3-NO2

1 4-NMe2

./^NMe26f 20 99 149-151 150-152 (Kantevari et al. (2007))

// N . .N03

95 248-250 244-246 (Kidwai et al. (2007))

1 3-OMe

// ^ _ ,OMe

84 125-127 128-130 (Kantevari et al. (2007))

Isolated yields.

2.7. 2-(4-Methoxylphenyl)-1,4,5-triphenylimidazole (6c)

IR (KBr) v max/cm"1: 1602, 1576, 1526, 1480. *H NMR (250 MHz, CDCl3): d 3.76 (s, 3H, OCH3), 6.74-7.60 (m, 19H, ArH). MS-EI: m/z 402 (M + , 100), 165, 77.

2.8. 1-Benzyl-2-(4-methylphenyl)-4,5-diphenyl imidazole (6e)

IR (KBr) v max/cm"1: 1600, 1484, 1448. *H NMR (250 MHz, CDCl3): d 2.36 (s, 3H, CH3), 5.09 (s, 2H, CH2), 6.80-7.59 (m, 19H, ArH).

2.9. 1-Benzyl-2-(4-dimethylaminophenyl)-4,5-diphenyl imidazole (6f)

IR (KBr) v max/cm"1: 1614, 1491, 1445. *H NMR (250 MHz, CDCl3): d 2.96 (s, 6H, 2 CH3), 5.09 (s, 2H, CH2), 6.68-7.56 (m, 19H, ArH).

3. Results and discussion

In this paper, we have described an efficient and green methodology for the simple synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles using SBA-Pr-SO3H as a

Figure 1 Reusability of SBA-Pr-SO3H in the synthesis of compound 4a.

catalyst under solvent-free conditions. The reactions between benzil 1, various aromatic aldehydes 2 and ammonium acetate 3 were carried out under optimum conditions (Scheme 1). The results are summarized in Table 1. From these results, we could see that all the reactions proceeded smoothly in very short reaction times to afford the corresponding imidazoles in excellent yields. It was reported that aliphatic aldehydes afforded the corresponding products in moderate yields (Shar-ma et al., 2008). We also found that a broad range of aromatic aldehydes carrying electron donating and electron withdrawing substituents reacted efficiently to furnish 2,4,5-trisubsti-tuted imidazoles in high yields. Moreover, the utility of this method was explored for the one-pot, four component synthesis of 1,2,4,5-tetrasubstituted imidazoles under the same reaction conditions (Scheme 2) and a variety of tetrasubstituted imidazoles were obtained in high yields using different aromatic aldehydes 2 and aniline or benzyl amine 5 (Table 2). After completion of the reaction, the acid catalyst was separated from the crude products and the recovered catalyst was washed consequently with diluted acid solution, water and then acetone, and dried under vacuum. The reusability of the catalyst was investigated under optimized conditions for the synthesis of the model compound 4a. As it is shown in Fig. 1, the process of recycling was completed four times and no significant decrease in activity was observed. The yields for the four runs were found to be 100%, 96%, 91%, and 82%, respectively.

The most probable mechanism for the synthesis of 2,4,5-tri-substitued imidazoles is shown in Scheme 3. Initially, the solid acid catalyst can activate the carbonyl groups of aldehyde 2 and benzil 1 to decrease the energy of transition state. Then nucleophilic attack of the nitrogen of ammonia, obtained from NH4OAc on the protonated carbonyl group 7, resulted in the formation of diamine intermediate 8. This intermediate in the presence of SBA-Pr-SO3H, condenses with benzil 9 to form intermediate 11 which in turn rearranges to the trisubstituted imidazoles 4a-g by a [1,5]-H shift.

Similarly, a plausible mechanism for the synthesis of 1,2,4,5-tetrasubstitued imidazoles was presented in Scheme 4. After the protonation of the carbonyl group of the aryl aldehyde 2 and the nucleophilic attack of the nitrogen atoms of

SBA-P1--SO3H

2 NH4oac

2nh3 -h2o

SBA-PI--S03H

h nh* 8

Ph^OH PhAoH+

Ph<i>N /=\

P^N^Vi 10

H2O p ^^Jl;

5]shift

Scheme 3 Proposed mechanism for the synthesis of 2,4,5-trisubstituted imidazoles.

NH4OHAc NH2 I NH3

SBA-Pr-SO3H

p^/,oh

^ pVn /=\

v x' In /)

H - H2O, Ph^N

Scheme 4 Proposed mechanism for the synthesis of 1,2,4,5-tetrasubstituted imidazoles.

Figure 2 Synthesis of substituted imidazoles using SBA-Pr-SO3H as a nano-reactor.

ammonia, obtained from NH4OAc, and aniline 5 to it, intermediate 12 is formed. In the presence of SBA-Pr-SO3H, intermediate 12 condenses with benzil 9 to form intermediate 14 which in turn forms tetrasubstituted imidazoles 6a-h by dehydration.

The high yields of reactions are attributed to the effect of nanopore size of about 6 nm of solid acid catalyst, which could act as nano-reactor (Fig. 2). The SBA-15 as a new nanoporous

silica can be prepared by using commercially available triblock copolymer Pluronic P126 as a structure directing agent (Zhao et al., 1998). The sulfonic acid functionalized SBA-15 was usually synthesized through a direct synthesis or post-grafting (Lim et al., 1998; Wight and Davis, 2002).

A schematic illustration for the preparation of SBA-Pr-SO3H was shown in Fig. 3. First, the calcined SBA-15 silica was functionalized with (3-mercaptopropyl) trimethoxysilane

SBA-Pr-SH SBA-Pr-S03H

Figure 3 Schematic illustration for the preparation of SBA-Pr-SO3H.

Table 3 Porosimetry values of SBA-15 and functionalized SBA-15.

Surface area (cm2 g ') Pore volume (cm3 g ') Pore diameter (nm)

SBA-15 649 0.806 6.2

SBA-Pr-SO3H 440 0.660 6.0

Figure 4 SEM image (left) and TEM image (right) of SBA-Pr-SO3H.

(MPTS) and then, the thiol groups were oxidized to sulfonic acid by hydrogen peroxide.

The surface area, average pore diameter calculated by the BET method and pore volume of SBA-Pr-SO3H are 440 m2 g"1, 6.0 nm and 0.660 cm3 g"1, respectively, which are smaller than those of SBA-15 due to the immobilization of sul-fonosilane groups into the pores (Table 3). Fig. 4 illustrates the SEM and TEM images of SBA-Pr-SO3H. SEM image (Fig. 4 left) shows uniform particles of about 1 im. The same morphology was observed for SBA-15. It can be concluded that morphology of solid was saved without change during the surface modifications. On the other hand, the TEM image (Fig. 4 right) reveals the parallel channels, which resemble the pores configuration of SBA-15. This indicates that the pore of SBA-Pr-SO3H was not collapsed during two step reactions.

4. Conclusions

In conclusion, we have developed an efficient and mild procedure for the synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetra-substituted imidazoles in the presence of SBA-Pr-SO3H under solvent-free conditions. The use of SBA-Pr-SO3H in this reaction has the advantages of being reusable and environmentally benign nano-reactor so that the reaction proceeds easily

in its nano-pores. Moreover, other advantages, such as excellent product yields, very short reaction times, mild reaction condition, and simple workup procedures, make this method an interesting alternative to other methodologies.

Acknowledgements

We gratefully acknowledge the financial support from the

Research Council of Alzahra University and University of

Tehran.

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