Emeraldine Base Form of Polyaniline Nanofibers as New, Economical, Green, and Efficient Catalyst for Synthesis of <i>Z</i>-Aldoximes

Boddula, Rajender; Srinivasan, Palaniappan

doi:https://doi.org/10.1155/2014/515428

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Abstract Introduction Experimental Results and Discussion Conclusions Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2014 | Article ID 515428 | https://doi.org/10.1155/2014/515428

Emeraldine Base Form of Polyaniline Nanofibers as New, Economical, Green, and Efficient Catalyst for Synthesis of Z-Aldoximes

Rajender Boddula¹and Palaniappan Srinivasan¹

Academic Editor: Kun Qiao

Received13 Sept 2013

Revised06 Dec 2013

Accepted19 Dec 2013

Published06 Feb 2014

Abstract

A facile, clean, economical, efficient, and green process was developed for the preparation of Z-aldoximes at room temperature under solvent-free condition using emeraldine base form of polyaniline as novel catalyst. In this methodology, PANI base absorbed the by-product of HCl (polluting chemical) from hydroxylamine hydrochloride and converted to polyaniline-hydrochloride salt (PANI-HCl salt). This PANI-HCl salt could be easily recovered and used in new attempts without any purification in many areas such as catalyst, electrical and electronics applications meant for conducting polymers. As far as our knowledge is concerned, emeraldine base as catalyst in organic synthesis for the first time.

1. Introduction

Oximes and their derivatives are important intermediates in the synthesis of amides [1–4], nitro compounds, hydroximinoyl chlorides, nitrones [5], amines, azoles, nitrile oxides, chiral α-sulfinyl oximes, nitriles [6–8], and isoxazolines [9].

Both acids and general bases can act as catalysts for the preparation of oximes. A number of catalysts have been documented, such as [10], ZnO [11], CuSO₄ and K₂CO₃ [12], glycine [13], CaO [14], silica gel [15], or without any base, but coupled with microwave irradiation [16], MW [17], K₂CO₃/MW [18], wet basic Al₂O₃/MW and molecular sieve 4 Å [19], NaOH [20], Ionic Liquid/water Biphasic System [21], silicaphos (P₂O₅/SiO₂) [22], and HPA [23]. Many methods are not very satisfactory due to drawbacks such as low yields, problems of generation of polluting HCl, high reaction temperature, long reaction time, and use of organic solvents.

Chemical methods for the synthesis of oximes usually give a mixture of two geometrical isomers (Z and E). A few methods are available for the synthesis of E and Z either isomer of oximes [12, 24]. In many cases, E isomers were obtained from the Z forms by hydrochloride method or purified by column chromatography [25]. Consequently, there is a need for developing an efficient, cheaper, convenient, and nonpolluting method for the preparation of stereoselective oximes.

In this work, Z-aldoximes in excellent yield in short reaction time were prepared from aldehydes with hydroxylamine hydrochloride under solvent-free condition at room temperature using emeraldine form of polyaniline base as novel polymer base catalyst. In this method, PANI base absorbed the by-product of HCl from hydroxylamine hydrochloride and converted to PANI-HCl salt, which is very much useful in various applications and makes the methodology towards the area of “Green Chemistry.”

2. Experimental

2.1. Materials and Instrumentation

Aniline (reagent grade) from Merck was distilled before use; sodium persulfate, sodium hydroxide, hydroxylamine hydrochloride, and aromatic aldehydes are purchased from SD-Fine Chemicals, India, and were used without further purification unless otherwise noted. Powder of PANI samples was pressed into disk of 13 mm diameter and about 1.5 mm thickness under a pressure of 400 MPa. Resistance of the pellet was measured by two-probe method using digital multimeter 2010 (Keithley, Cleveland, Ohio, USA). FT-IR spectra of PANI samples were registered on a FT-IR spectrometer (Thermo Nicolet Nexus 670, USA) using the KBr pressed pellets technique. X-ray diffraction profiles for PANI powders were obtained on a Siemens/D-500 X-ray diffractometer, USA, using Cu Kα radiation, scan speed of 0.045°/min. Morphological studies of PANI powders were performed using Hitachi make (Japan) of field emission scanning electron microscope with field emission gun. The sample was mounted on a double-sided adhesive carbon disk and sputter-coated with a thin layer of gold to prevent sample from possible charging.

2.2. General Procedure for the Preparation of PANI Base

Polyaniline base was prepared by aqueous polymerization pathway by the reported procedure [26]. In a 250 mL round-bottomed flask, 60 mL of water was taken and 9.6 mL of HCl was added slowly with stirring. 1 mL of aniline was added to this mixture and the solution was kept under constant stirring at ambient temperature. 40 mL aqueous solution containing sodium persulfate (3.3 g) was added to this solution immediately. The reaction was allowed to continue for 4 h at ambient temperature (25–30°C). The precipitated polyaniline powder was filtered, washed with distilled water, and followed by acetone. Polyaniline salt synthesized above was stirred in 100 mL aqueous sodium hydroxide solution (1.0 M) for 4 h at ambient temperature. Polyaniline base powder was filtered, washed with excess water and finally with acetone, and dried at 50°C till a constant weight.

2.3. General Procedure for Preparation of Z-Aldoximes

In a typical reaction, a mixture of the aldehyde (1 mmol), hydroxylamine hydrochloride (1.2–1.5 mmol), and PANI base (100 mg) was grounded thoroughly in a mortar for 15–20 minutes. The mixture was washed with ethyl acetate and filtered to remove the catalyst. The filtrate was washed with water and brine solution and dried over anhydrous Na₂SO₄ followed by evaporation of solvent in vacuo to furnish the Z-aldoxime (Scheme 1). All the products were characterized by proton NMR and infrared spectra. The ¹H NMR and IR spectral results of the synthesized products are well matched with the same reported compound in the literature [12, 22, 23].

3. Results and Discussion

3.1. Polyaniline

Polyaniline (PANI) is the most important among all the conducting polymers due to its straight forward polymerization, chemical stability, relatively high conductivity, redox properties, and cheaper and potential applications in various fields [27–30]. Usually, polyaniline is being synthesized from monomer aniline either by chemical or electrochemical polymerization process. Chemical polymerization process is more feasible route to produce large-scale PANI for the industrial use as compared to electrochemical polymerization.

The structure of polyaniline is known as a para-linked phenylene amine imine. The base form of polyaniline can, in principle, be described by the following general formula (Figure 1).

In the generalized base form () measures the function of oxidized units. When , the polymer has no such oxidized groups and is commonly known as a leucoemeraldine base. The fully oxidized form, , is referred to as a pernigraniline base. The half-oxidized polymer, where the number of reduced units and oxidized units is equal, that is, , is of special importance and is termed as the emeraldine oxidation state or the emeraldine base form of polyaniline (PANI base). Partially oxidized emeraldine base is shown to be alternating copolymer of reduced and oxidized repeat units.

3.2. Catalyst Synthesis and Characterization

PANI base nanofibers were prepared directly by oxidizing aniline using sodium persulfate oxidant in the presence of hydrochloric acid, followed by dedoping the PANI-HCl salt to the polyaniline base (PANI). The infrared spectrum of PANI base (Figure 2(a)) showed major characteristic peaks at 3450, 2920, 2850, 1580, 1495, 1375, 1295, 1210, 1135, and 810 cm⁻¹, which are similar to the standard PANI [31, 32]. The infrared spectrum of polyaniline sample recovered after the reaction showed major characteristic peaks at 3440, 2920, 1565, 1490, 1380, 1295, 1215, 1135 and 810 cm⁻¹, which are similar to those of PANI base. In addition to these peaks, a peak appeared at 3225 cm⁻¹ (Figure 2(b)). This peak indicates that PANI base contains a dopant, that is, formation of PANI salt.

X-ray diffraction pattern of PANI base (Figure 3(a)) showed a broad peak around 2θ = 19°, which is characteristic peak of polyaniline base. XRD pattern of polyaniline sample recovered after the reaction (Figure 3(b)) showed peaks at 30, 27, and 14° indicating the formation of emeraldine salt form of polyaniline [33, 34].

Morphological structures of polyaniline samples were found out from scanning electron microscopy. PANI base showed nanofibers with more or less uniform size (Figure 4(a)), and polyaniline sample recovered after the reaction also showed nanofiber (Figure 4(b)).

(a)

(b)

Conductivity of the polyaniline sample recovered after the reaction showed 0.01 S/cm, which is 10 orders of magnitude higher than that of PANI base (insulator level, <10⁻¹² S/cm). Increase in conductivity result confirms that insulating PANI base is converted to doped PANI salt. EDAX showed the presence of 9.5% of chlorine element. The above results indicate the presence of HCl as dopant on polyaniline salt; that is, PANI base absorbed HCl from hydroxylamine hydrochloride during the reaction with aldehydes and converted to PANI-HCl salt.

3.3. Polyaniline Base as Catalyst in Stereoselective Synthesis of Aldoximes

In our group, polyaniline salts are being used as polymer based solid acid catalyst in organic transformations [35]. In this work, for the first time, PANI base is used as polymer base catalyst in the preparation of stereoselective synthesis of aldoximes. Product was not obtained when benzaldehyde was ground with hydroxylamine hydrochloride in the absence of catalyst for 1 h. However, with the use of polyaniline base gave Z-benzaldoxime product (92% yield) in 20 min. (Table 1, Entry-1).

In order to check the versatility of the polyaniline base catalyst, various types of aldehydes were reacted with hydroxylamine hydrochloride using PANI and the results are included in Table 1. As shown in Table 1, the reaction of hydroxylamine hydrochloride with different aromatic aldehydes, including those with electron withdrawing and donating substituents in the presence of PANI base catalyst, gave aldoximes in good to excellent yields with Z-stereoselectivity without any side products. The Z-stereochemistry of the products was determined from the ¹H-chemical shift of the C(H)=N group which appeared around 8–8.5 as a singlet (Table 1).

In a typical reaction, a mixture of benzaldehyde (5 mmol), hydroxylamine hydrochloride (6 mmol), and PANI base (500 mg) was ground thoroughly in a mortar for 20 minutes. The mixture was washed with ethyl acetate and filtered to remove the catalyst. Recovered catalyst after the reaction and polyaniline base were characterized by infrared, X-ray diffraction, EDAX, and conductivity measurements.

3.4. Use of Recovered Polyaniline-Hydrochloride Salt as Catalyst in Organic Reaction

In order to show the use of recovered PANI-HCl salt catalyst, the formed PANI-HCl salt was converted to PANI base by aqueous sodium hydroxide solution and again this PANI base was used as catalyst in the reaction of benzaldehyde with hydroxylamine hydrochloride to benzaldoxime (Scheme 2), which gave 91% yield. In addition, the formed PANI-HCl salt is tried out as polymer based solid acid catalyst in the synthesis of 2-phenyl benzimidazole (in 77% yield) from the reaction of o-phenylenediamine (1 mmol) and benzaldehyde (1 mmol) at room temperature in dichloroethane (5 mL) in 10 min. (Scheme 2). The PANI-HCl catalyst was reused for four more runs without significant decrease in activity.

4. Conclusions

In summary, good to excellent yields of stereoselective Z-aldoximes were prepared without any side products using only 1 : 1.2 ratio of reactants under solvent-free condition at room temperature with easily synthesizable, stable, easy, handlable, and usable catalyst by simple, clean, economical, and green process.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors thank Dr. Lakshmi Kantam, Director, and Dr. K.V.S.N. Raju, Head, PFM Division, IICT, for their support and encouragement. The authors thank CSIR in-house Project (MLP-0006) for funding. Rajender Boddula is indebted to UGC, India, for Senior Research Fellowship.

Supplementary Materials

Spectral data.

Supplementary Material

References

R. S. Ramón, J. Bosson, S. Díez-González, N. Marion, and S. P. Nolan, “Au/Ag-cocatalyzed aldoximes to amides rearrangement under solvent- and acid-free conditions,” Journal of Organic Chemistry, vol. 75, no. 4, pp. 1197–1202, 2010.
View at: Publisher Site | Google Scholar
M. A. Ali and T. Punniyamurthy, “Palladium-catalyzed one-pot conversion of aldehydes to amides,” Advanced Synthesis and Catalysis, vol. 352, no. 2-3, pp. 288–292, 2010.
View at: Publisher Site | Google Scholar
H. Fujiwara, Y. Ogasawara, K. Yamaguchi, and N. Mizuno, “A one-pot synthesis of primary amides from aldoximes or aldehydes in water in the presence of a supported rhodium catalyst,” Angewandte Chemie International Edition, vol. 46, no. 27, pp. 5202–5205, 2007.
View at: Publisher Site | Google Scholar
M. Kim, J. Lee, H.-Y. Lee, and S. Chang, “Significant self-acceleration effects of nitrile additives in the rhodium-catalyzed conversion of aldoximes to amides: a new mechanistic aspect,” Advanced Synthesis and Catalysis, vol. 351, no. 11-12, pp. 1807–1812, 2009.
View at: Publisher Site | Google Scholar
A. Koçak, S. Malkondu, and S. Kurbanli, “Synthesis of alkyl nitrones by reaction of aldehyde and ketone oximes with α,β-unstaturated esters in the presence of Lewis acid,” Russian Journal of Organic Chemistry, vol. 45, no. 4, pp. 591–595, 2009.
View at: Publisher Site | Google Scholar
M. K. Singh and M. K. Lakshman, “A simple synthesis of nitriles from aldoximes,” Journal of Organic Chemistry, vol. 74, no. 8, pp. 3079–3084, 2009.
View at: Publisher Site | Google Scholar
D. Saha, A. Saha, and B. C. Ranu, “Ionic liquid-promoted dehydration of aldoximes: a convenient access to aromatic, heteroaromatic and aliphatic nitriles,” Tetrahedron Letters, vol. 50, no. 44, pp. 6088–6091, 2009.
View at: Publisher Site | Google Scholar
H. S. Kim, S. H. Kim, and J. N. Kim, “Highly efficient Pd-catalyzed synthesis of nitriles from aldoximes,” Tetrahedron Letters, vol. 50, no. 15, pp. 1717–1719, 2009.
View at: Publisher Site | Google Scholar
S. Bhosale, S. Kurhade, U. V. Prasad, V. P. Palle, and D. Bhuniya, “Efficient synthesis of isoxazoles and isoxazolines from aldoximes using Magtrieve (CrO₂),” Tetrahedron Letters, vol. 50, no. 27, pp. 3948–3951, 2009.
View at: Publisher Site | Google Scholar
J.-J. Guo, T.-S. Jin, S.-L. Zhang, and T.-S. Li, “TiO₂/SO₄^2- : an efficient and convenient catalyst for preparation of aromatic oximes,” Green Chemistry, vol. 3, no. 4, pp. 193–195, 2001.
View at: Publisher Site | Google Scholar
H. Sharghi and M. Hosseini, “Solvent-free and one-step Beckmann rearrangement of ketones and aldehydes by zinc oxide,” Synthesis, no. 8, pp. 1057–1060, 2002.
View at: Google Scholar
H. Sharghi and M. H. Sarvari, “Selective synthesis of E and Z isomers of oximes,” Synlett, no. 1, pp. 99–101, 2001.
View at: Google Scholar
M. Maheswara, V. Siddaiah, K. Gopalaiah, V. M. Rao, and C. V. Rao, “A simple and effective glycine-catalysed procedure for the preparation of oximes,” Journal of Chemical Research, no. 6, pp. 362–363, 2006.
View at: Google Scholar
H. Sharghi and M. H. Sarvari, “A mild and versatile method for the preparation of oximes by use of calcium oxide 1,” Journal of Chemical Research, vol. 2000, no. 1, pp. 24–25, 2000.
View at: Google Scholar
A. R. Hajipour, I. Mohammadpoor-Baltork, K. Nikbaghat, and G. Imanzadeh, “Solid-phase synthesis of oximes,” Synthetic Communications, vol. 29, no. 10, pp. 1697–1701, 1999.
View at: Google Scholar
A. R. Hajipour, S. E. Mallakpour, and G. Imanzadeh, “A rapid and convenient synthesis of oximes in dry media under microwave irradiation,” Journal of Chemical Research Part S, no. 3, pp. 228–229, 1999.
View at: Google Scholar
B. P. Bandgar, V. S. Sadavarte, L. S. Uppalla, and R. Govande, “Chemoselective preparation of oximes, semicarbazones, and tosylhydrazones without catalyst and solvent,” Monatshefte für Chemie, vol. 132, no. 3, pp. 403–406, 2001.
View at: Publisher Site | Google Scholar
R. Kamakshi and B. S. R. Reddy, “Solventless rapid synthesis of oxime, semicarbazone, and phenylhydrazone derivatives from carbonyl compounds under microwave conditions,” Australian Journal of Chemistry, vol. 58, no. 8, pp. 603–606, 2005.
View at: Publisher Site | Google Scholar
G. L. Kad, M. Bhandari, J. Kaur, R. Rathee, and J. Singh, “Solventless preparation of oximes in the solid state and via microwave irradiation,” Green Chemistry, vol. 3, no. 6, pp. 275–277, 2001.
View at: Publisher Site | Google Scholar
I. Damljanovic, M. Vukicevic, and R. D. Vukicevic, “A simple synthesis of oximes,” Monatshefte für Chemie, vol. 137, pp. 301–305, 2006.
View at: Google Scholar
H. M. Luo, Y. Q. Li, and W. J. Zheng, “A novel ionic liquid/water biphasic system for the preparation of oximes,” Chinese Chemical Letters, vol. 16, no. 7, pp. 906–908, 2005.
View at: Google Scholar
H. Eshghi and Z. Gordi, “P₂O₅/SiO₂ as an efficient reagent for the preparation of Z-aldoximes under solvent-free conditions,” Phosphorus, Sulfur and Silicon and the Related Elements, vol. 180, no. 7, pp. 1553–1557, 2005.
View at: Publisher Site | Google Scholar
H. Eshghi, M. H. Alizadeh, and E. Davamdar, “Regioselective synthesis of Z-aldoximes catalyzed by H₃PMo₁₂O₄₀ under solvent-free conditions,” Journal of the Korean Chemical Society, vol. 52, no. 1, pp. 52–56, 2008.
View at: Google Scholar
T. Uno, B. Gong, and P. G. Schultz, “Stereoselective antibody-catalyzed oxime formation,” Journal of the American Chemical Society, vol. 116, no. 3, pp. 1145–1146, 1994.
View at: Google Scholar
A. I. Vogel, Text Book of Practical Organic Chemistry, Longman, London, UK, 4th edition, 1971.
S. Palaniappan and B. Rajender, “A novel polyaniline-silver nitrate-p-toluenesulfonic acid salt as recyclable catalyst in the stereoselective synthesis of β-amino ketones: “one-pot” synthesis in water medium,” Advanced Synthesis and Catalysis, vol. 352, no. 14-15, pp. 2507–2514, 2010.
View at: Publisher Site | Google Scholar
N. Gospodinova and L. Terlemezyan, “Conducting polymers prepared by oxidative polymerization: polyaniline,” Progress in Polymer Science, vol. 23, no. 8, pp. 1443–1484, 1998.
View at: Google Scholar
D. Zhang and Y. Wang, “Synthesis and applications of one-dimensional nano-structured polyaniline: an overview,” Materials Science and Engineering B, vol. 134, no. 1, pp. 9–19, 2006.
View at: Publisher Site | Google Scholar
S. Bhadra, D. Khastgir, N. K. Singha, and J. H. Lee, “Progress in preparation, processing and applications of polyaniline,” Progress in Polymer Science, vol. 34, no. 8, pp. 783–810, 2009.
View at: Publisher Site | Google Scholar
L. I. Dan, J. Huang, and R. B. Kaner, “Polyaniline nanofibers: a unique polymer nanostructure for versatile applications,” Accounts of Chemical Research, vol. 42, no. 1, pp. 135–145, 2009.
View at: Publisher Site | Google Scholar
E. T. Kang, K. G. Neoh, and K. L. Tan, “Polyaniline: a polymer with many interesting intrinsic redox states,” Progress in Polymer Science, vol. 23, no. 2, pp. 277–324, 1998.
View at: Google Scholar
Y. Furukawa, F. Ueda, Y. Hyodo, I. Harada, T. Nakajima, and T. Kawagoe, “Vibrational spectra and structure of polyaniline,” Macromolecules, vol. 21, no. 5, pp. 1297–1305, 1988.
View at: Google Scholar
J. P. Pouget, M. E. Józefowicz, A. J. Epstein, X. Tang, and A. G. MacDiarmid, “X-ray structure of polyaniline,” Macromolecules, vol. 24, no. 3, pp. 779–789, 1991.
View at: Google Scholar
D. Mahanta, G. Madras, S. Radhakrishnan, and S. Patil, “Adsorption of sulfonated dyes by polyaniline emeraldine salt and its kinetics,” Journal of Physical Chemistry B, vol. 112, no. 33, pp. 10153–10157, 2008.
View at: Publisher Site | Google Scholar
S. Palaniappan and A. John, “Conjugated polymers as heterogeneous catalyst in organic synthesis,” Current Organic Chemistry, vol. 12, no. 2, pp. 98–117, 2008.
View at: Publisher Site | Google Scholar

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Copyright © 2014 Rajender Boddula and Palaniappan Srinivasan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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