Synthesis of α-aminophosphonates using carbon nanotube supported imidazolium salt-based ionic liquid as a novel and environmentally benign catalyst

Article abstract of DOI:10.1080/10426507.2015.1072182

A supported acidic catalyst was easily prepared via anchoring imidazolium salt-based ionic liquid onto multiwalled carbon nanotube by covalent bonds. This novel immobilized acidic ionic liquid effectively catalyzed the one-pot synthesis of α-aminophosphonates from the reaction of amines and aldehydes with diethyl phosphite. The catalyst can be easily recovered and reused without appreciable change in its efficiency.

Full text of DOI:10.1080/10426507.2015.1072182

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Synthesis of α-Aminophosphonates using Carbon
Nanotube Supported Imidazolium Salt-Based Ionic
Liquid as a Novel and Environmentally benign
Catalyst
Kaveh Parvanak Boroujeni, Elham Rezazadeh Shirazi & Mohammad Mahdi
Doroodmand
To cite this article: Kaveh Parvanak Boroujeni, Elham Rezazadeh Shirazi & Mohammad
Mahdi Doroodmand (2015): Synthesis of α-Aminophosphonates using Carbon Nanotube
Supported Imidazolium Salt-Based Ionic Liquid as a Novel and Environmentally
benign Catalyst, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2015.1072182
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1072182
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Date: 23 November 2015, At: 11:34

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MULTIWALLED CARBON NANOTUBE-SUPPORTED IONIC LIQUID
SYNTHESIS OF α-AMINOPHOSPHONATES USING CARBON NANOTUBE
SUPPORTED IMIDAZOLIUM SALT-BASED IONIC LIQUID AS A NOVEL AND
ENVIRONMENTALLY BENIGN CATALYST
Kaveh Parvanak Boroujeni1,*, Elham Rezazadeh Shirazi1 and Mohammad Mahdi Doroodmand2
1Department of Chemistry, Shahrekord University, Shahrekord (115), Iran
2Department of Chemistry, Shiraz University, Shiraz, Iran
*E-mail: parvanak-ka@sci.sku.ac.ir; Fax: 0098-38-32324419
ABSTRACT
A supported acidic catalyst was easily prepared via anchoring imidazolium salt-based ionic
liquid onto multiwalled carbon nanotube by covalent bonds. This novel immobilized acidic ionic
liquid effectively catalyzed the one-pot synthesis of α-aminophosphonates from the reaction of
amines and aldehydes with diethyl phosphite. The catalyst can be easily recovered and reused
without appreciable change in its efficiency.
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Keywords
One-pot multi-component reactions; heterogeneous catalysis; carbon nanotubes; α-
aminophosphonates; aldehydes; ionic liquids
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INTRODUCTION
Carbon nanotubes (CNTs) have some unique properties, which make them attractive as
supports in the heterogenization of homogeneous catalysts.1,2 When compared to other
commonly used supports in heterogeneous catalysis, CNTs present the advantage of
extraordinary electrical, thermal and mechanical strength characteristics, resistance to chemical
attack in acidic and basic media, high surface areas, and low cost. They are cylindrically shaped
and their surface can be modified with various functional groups, which can be used as building
blocks for covalent and noncovalent attachment of catalytically active species.
Among different kinds of ionic liquids, Brønsted acidic ionic liquids have attracted
significant attention, as catalysts or dual catalyst-solvents, because they possess simultaneously
the proton acidity and the characteristic properties of ionic liquid.3 They are designed to replace
traditional mineral liquid acids such as sulfuric acid and hydrochloric acid in chemical
procedures. However, despite having the widespread application in organic synthesis, most of
them suffer from one or more of the following drawbacks such as laborious work-up procedures,
difficult to recover and recycle, disposal of spent catalyst, difficult to handle, and corrosion
problems. Thus, these shortcomings make them a prime target for heterogenization.4,5
The synthesis of α-aminophosphonates has attracted much attention recently due to their
structural analogy to α-amino acids and significant biological activities.6–8 Their potential as
plant growth regulators,9 herbicidals,10 antibiotics,11 enzyme inhibitors,12 HIV protease,13 anti-
thrombotic agents,14 and inhibitors of UDH-galactopyranose mutase15 is well documented. α-
Aminophosphonates are usually prepared by three component condensation of an aldehyde, an
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amine, and a phosphite. For this purpose several types of catalysts such as ZrCl4,16 AlCl3,17
LiClO4,18 SiO2-NH4HCO3,19 Al(OTf)3,20 ionic liquid [bmim]Cl-AlCl3,21 Mg(ClO4)2,22 Al2O3-
SbCl3,23 ZrOCl2.8H2O,24 TiO2,25 amberlyst-15,26 [Cu(3,4-tmtppa)](MeSO4)4,27 sulfamic acid,28
FeCl3,29 sodium dodecyl sulfate,30 mesoporous aluminosilicate nanocage,31 NbCl5,32
propylphosphonic anhydride,33 Yb(OTf)3,34 phosphomolybdic acid,35 and zirconocene
bis(perfluorobutanesulfonate)36 have been used. We have also reported recently the use of silica
gel-supported AlCl3 and polystyrene-supported Al(OTf)3 as heterogeneous catalysts for the
synthesis of α-aminophosphonates.37,38 Although these methods are suitable for certain synthetic
conditions, there exist some drawbacks such as the use of malodorous trialkyl phosphite as the
phosphorus nucleophile, low yields, high reaction temperature, long reaction times, tedious
work-up, and the use of unrecyclable, hazardous or difficult to handle catalysts. Sometimes,
some of the mentioned catalysts do not work well with electron-deficient amines and/or
secondary amines. On the other hand, the formation of α-hydroxyphosphonate or a product of its
rearrangement frequently accompanies the formation of α-aminophosphonates. In view of this,
utilizing eco-friendly and green catalysts for this useful reaction is in demand.
As part of our ongoing research on application of immobilized ionic liquids in organic
reactions37–40 we report the synthesis of 1-methyl-3-(ethoxysilylpropyl)imidazolium hydrogen
sulfate anchored on multiwalled carbon nanotube (MWCNT–[mpIm]HSO4) as an acidic ionic
liquid catalyst for the synthesis of α-aminophosphonates.
RESULTS AND DISCUSSION
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MWCNT was prepared by the catalytic decomposition of hydrocarbon in the gas phase by
chemical vapour deposition (CVD) procedure.2 In order to generate hydroxy groups on the
MWCNT surface, the carbon nanomaterials were subjected to a heat treatment in a synthetic air
flow (10 mL min-1) at 500 oC for 2 h.2 It is worth mentioning that although the distribution of the
hydroxy groups was not determined, they are presumed to exist primarily at the ends of
nanotubes and at sites along the sidewalls where increased curvature strain results in increased
reactivity.41
Scheme 1 shows the synthetic routes for MWCNT–[mpIm]HSO4. At first, (3-
chloropropyl)triethoxysilane was treated with 1-methylimidazole to yield 1-methyl-3-
(triethoxysilylpropyl)imidazolium cholride ([mpIm]Cl). Then, the hydroxy groups on the surface
of hydroxy functionalized multiwalled carbon nanotube (MWCNT–OH) reacted with [mpIm]Cl
to produce 1-methyl-3-(ethoxysilylpropyl)imidazolium chloride anchored on multiwalled carbon
nanotube (MWCNT–[mpIm]Cl). The resulting MWCNT–[mpIm]Cl was analyzed by elemental
analysis to quantify the percentage loading of the imidazolium moiety by measuring the nitrogen
content, giving 0.77 mmol Im per gram. Finally, the MWCNT–[mpIm]Cl was further treated
with H2SO4 to form MWCNT–[mpIm]HSO4 as a black solid. The loading amount of the acidic
sites in MWCNT–[mpIm]HSO4 obtained by means of acid base titration was found to be 0.82
mmol/g.42
Figure 1 shows the FT-IR spectra of MWCNT–OH and MWCNT–[mpIm]HSO4. After
converting MWCNT–OH into MWCNT–[mpIm]HSO4 it was observed that new peaks appeared
at 1030 and 1055 cm-1 due to C–O–Si stretching bands43 (Figure 1 (B)). Also the FT-IR spectrum
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of MWCNT–[mpIm]HSO4 exhibited two characteristic peaks at 1568 and 1658 cm-1, which are
due to the C=C and C=N stretching vibrations of the imidazole ring, respectively.4 The weak
absorption around 2957 cm-1 was assigned to C–H stretching vibration, which confirms the
presence of the propyl groups of the ionic liquid. The presence of the hydrogen sulfate
counteranions was confirmed by the absorbance peaks located at 1160, 1180, and 1225 cm-1,
resulting from the stretching vibrations of S=O.5
Immobilization of the ionic liquid on MWCNTs was further supported by
thermogravimetric analyses (TGA). Figure 2 shows TGA curves of MWCNT–OH and
o
MWCNT–[mpIm]HSO4. A slight weight loss was observed in each case around 100 C due to
the loss of moisture. In the case of MWCNT–[mpIm]HSO4 the second weight loss starting at
o
about 200 C is mainly assigned to the decomposition of the immobilized ionic liquid
([mpIm]HSO4) moieties. In the TGA curves of MWCNT–OH and MWCNT–[mpIm]HSO4 the
last weight losses at about 550–600 oC are likely due to the degradation of MWCNTs.
Scanning electron microscopy (SEM) photographs of MWCNT–OH and MWCNT–
[mpIm]HSO4 showed that the MWCNTs are well distributed and no amorphous carbon is
detected (Figure 3). In the TEM photograph of MWCNT–[mpIm]HSO4 (Figure 4 (B)) it can be
seen that the CNTs do not suffer damage after the functionalization and anion-exchange
processes and there are conglomerates of small particles on the surface of MWCNT due to
functionalization processes.
The catalytic activity of MWCNT–[mpIm]HSO4 was studied for the synthesis of α-
aminophosphonates by the three component condensation of aldehydes, amines, and diethyl
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phosphite. To optimize the reaction conditions, the reaction of benzaldehyde with aniline and
diethyl phosphite was used as a model reaction. Reactions at different conditions and various
molar ratios of substrates in the presence of MWCNT–[mpIm]HSO4 revealed that the best results
were obtained under solvent-free conditions at room temperature and aüülying a molar ratio of
benzaldehyde : aniline : diethyl phosphite : MWCNT–[mpIm]HSO4 of 1 : 1 : 1.2 : 0.07.
Therefore, we employed the above conditions for the conversion of various aldehydes to the
corresponding α-aminophosphonates. Both electron-deficient and electron-releasing
benzaldehydes reacted efficiently with aniline and diethyl phosphite to give the corresponding α-
aminophosphonates (Table 1, entries 1–8). Terephthaldehyde, 1-naphthaldehyde, and 2-
naphthaldehyde also gave the corresponding products in high yield (entries 9–11). This method
is even effective with aliphatic aldehydes, which normally produce low yields (entry 12). Acid
sensitive substrates such as cinnamaldehyde, furan-2-carbaldehyde, and thiophene-2-
carbaldehyde gave the corresponding α-aminophosphonates without any decomposition,
conjugate addition to the α,β-unsaturated carbonyl group or generation of polymeric by-products
under the present reaction conditions (entries 13–15). Also, substituted anilines and aliphatic
amines afforded the corresponding α-aminophosphonates in the presence of MWCNT–
[mpIm]HSO4 in high yields (entries 16–19). In addition, the coupling reaction of a secondary
amine like diethylamine with benzaldehyde and diethyl phosphite in the presence of MWCNT–
[mpIm]HSO4 at ambient temperatures resulted in the formation of tertiary α-aminophosphonate
in high yield (entry 20). Finally, ketones afforded the corresponding products in good yields
(entries 21–23). Noteworthy is that no competitive side reactions such as the formation of α-
hydroxyphosphonates were observed in these transformations.
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One notable achievement of MWCNT–[mpIm]HSO4 catalyst is the synthesis of bis(α-
aminophosphonates) by one-pot three-component condensation reaction between aldehydes,
diamines and diethyl phosphite. For example, benzaldehyde reacted with 4,4′-diamino-
benzophenone and diethyl phosphite at 40 °C in the presence of MWCNT–[mpIm]HSO4 to give
the desired product in 92 % yield (Scheme 2).
A possible mechanism for the formation of α-aminophosphonate is proposed in Scheme 3.
The aldehyde or ketone is first activated by MWCNT–[mpIm]HSO4. Nucleophilic addition of
the amine to the activated aldehyde or ketone followed by loss of H2O generates the imine
intermediate I, which is further activated by MWCNT–[mpIm]HSO4. Finally addition of diethyl
phosphite to the activated imine I affords the α-aminophosphonate.
Following these results, we further investigated the potential of MWCNT–[mpIm]HSO4
catalyst for the synthesis of 1-thioamidoalkyl-2-naphthols by one-pot multi-component
condensation of aromatic aldehydes with 2-naphthol and thioamides. For example, benzaldehyde
or p-methoxybenzaldehyde reacted with 2-naphthol and thioacetamide in the presence of
MWCNT–[mpIm]HSO4 in 1,2-dichloroethane at room temperature to give the corresponding 2-
naphthol derivatives in good yields (Scheme 4).
The reusability of the catalyst is a significant advantage particularly for commercial
applications. MWCNT–[mpIm]HSO4 recovered after a reaction can be washed with CH2Cl2 and
used again at least five times without any noticeable loss of its activity (Figure 5).
A comparison of the present procedure, using MWCNT–[mpIm]HSO4, with selected
previously known protocols is contained in Table 2. As can be seen in addition to having the
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general advantages attributed to the solid catalysts, MWCNT–[mpIm]HSO4 has a good
efficiency compared to many of the reported catalysts in the synthesis of α-aminophosphonates.
CONCLUSIONS
In conclusion, MWCNT–[mpIm]HSO4 is an efficient heterogeneous acid catalyst that
favorably combines the properties of ionic liquids and the advantages of solid supports. This
catalyst has an activity in the synthesis of α-aminophosphonate comparable to that of 1-butyl-3-
methyl-imidazolium hydrogen sulfate ionic liquid as far as we tested but offers its own
advantages originating from being supported on MWCNT: easier handling, reusability, and easy
workup. In addition, high yields, short reaction times, and mild reaction conditions are other
obvious advantages of the present method.
EXPERIMENTAL
Chemicals were either prepared in our laboratory or were purchased from Merck and
Fluka. Reaction monitoring and purity determination of the products were accomplished by GLC
or TLC on silica-gel polygram SILG/UV254 plates. Gas chromatography was performed with a
Shimadzu GC 14-A instrument. IR spectra were obtained with a Shimadzu model 8300 FT-IR
1
31
spectrophotometer. H, 13C and P NMR spectra were recorded in CDCl3 solutions at 400, 100,
and 162 MHz, respectively. Elemental analyses were performed with an Elementar Vario EL
instrument. TGA was carried out with a Stanton Redcraft STA-780 instrument applying a
heating rate of 20 °C / min. SEM and TEM images were obtained with a Hitachi S-3400N
scanning electron microscope and a Philips CM10 transmission electron microscope,
respectively. Mass spectra were carried out with a MICROMASS QUATTRO II triple
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quadrupole mass spectrometer. Melting points were determined with a Fisher-Jones melting-
point apparatus. The Supplemental Materials contains complete characterization data for the
known products.
Synthesis of [mpIm]Cl
A mixture of (3-chloropropyl)triethoxysilane (5 mmol) and 1-methylimidazole (5 mmol)
was stirred for 20 h at 80 °C under nitrogen atmosphere. The reaction mixture was concentrated
on a rotary evaporator under reduced pressure to afford the desired product44 (viscous oil; yield:
95 %).
Synthesis of multiwalled carbon nanotubes
MWCNT and MWCNT–OH were prepared as reported in our previously work.2
Synthesis of MWCNT–[mpIm]HSO4
To a stirried solution of [mpIm]Cl (5 mmol) in 1,2-dichloroethane (20 mL), MWCNT–OH
(1 g) was added and the mixture was refluxed for 20 h under nitrogen atmosphere. Then, the
solid was filtered off, washed with 1,2-dichloroethane (15 mL), and dried in a vacuum oven at
100 °C for 24 h. Afterwards, H2SO4 (10 mL, 8 M) was added dropwise to the resulting solid at
room temperature and the mixture was stirred at 40 °C for 48 h, filtered, washed with distilled
water (20 mL) and dried at 100 °C overnight to give MWCNT–[mpIm]HSO4.
Typical procedure for α-aminophosphonate synthesis
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A mixture of the aldehyde (1 mmol), the respective amine (1 mmol), diethyl phosphite (1.2
mmol) and MWCNT–[mpIm]HSO4 (0.07 mmol) was stirred for an appropriate time at room
temperature. After completion of the reaction (monitored by TLC), CH2Cl2 (10 mL) was added
to dilute the reaction mixture and the catalyst was filtered off and washed with CH2Cl2 (2 × 10
mL). Then, the filtrate was washed with H2O (2 × 10 mL) and the organic layer was separated,
dried (Na2SO4), and concentrated on a rotary evaporator under reduced pressure to give the crude
product. Whenever required, the products were purified by column chromatography on silica gel
(n-hexane / EtOAc). All products are known compounds and were identified by comparison of
their physical and spectral data with those of the authentic samples.
ACKNOWLEDGEMENTS
We gratefully acknowledge the partial support of this study by the Shahrekord University
and the Shiraz University Research Council, Iran.
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REFERENCES
1. Ajayan, P. M.; Zhou, O. Z. In Carbon Nanotubes: Synthesis, Structure, Properties, and
Application; eds.; Dresselhaus, M. S.; Dresselhaus, G.; Avouris, Ph.; Springer: Berlin, 2001.
2. Sharghi, H.; Beyzavi, M. H.; Safavi, A.; Doroodmand, M. M.; Khalifeh, R. Adv. Synth.
Catal. 2009, 351, 2391–2410.
3. Hallett, J. P.; Welton, T. Chem. Rev. 2011, 111, 3508–3576.
4. Parvanak Boroujeni, K.; Jafarinasab, M. Chin. Chem. Lett. 2012, 23, 1067–1070.
5. Parvanak Boroujeni, K.; Ghasemi, P. Catal. Commun. 2013, 37, 50–54.
6. Redmore, D. Topics in Phosphorus Chemistry; eds.; Griffith, E. J.; Grayson, M.; John Wiley
& Sons: New York, 1976.
7. Savignac, P.; Iorga, B. Modern Phosphonate Chemistry; CRC Press, 2003.
8. Zefirov, N. S.; Matveeva, E. D. Arkivoc 2008, 1–17.
9. Emsley, J.; Hall, D. Chemistry of Phosphorus; Harper and Row: London, 1976; pp. 494–498.
10. Hassal, C. H.; Hahn, E. F. Antibiotics; Springer: Berlin, 1983; Vol. 6, pp. 1–11.
11. Atherton, F. R.; Hassall, C. H.; Lambert, R. W. J. Med. Chem. 1986, 29, 29–40.
12. Allen, M. C.; Fuher, W.; Tuck, B.; Wade, R.; Wood, J. M. J. Med. Chem. 1989, 32, 1652–
1661.
12
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
13. Stowasser, B.; Budt, K. H.; Jian-Qi, L.; Peyman, A.; Ruppert, D. Tetrahedron Lett. 1992, 33,
6625–6628.
14. Meyer, J. H.; Barlett, P. A. J. Am. Chem. Soc. 1998, 120, 4600–4609.
15. Pan, W.; Ansiaux, C.; Vincent, S. P. Tetrahedron Lett. 2007, 48, 4353–4356.
16. Yadav, J. S.; Reddy B. V. S.; Sarita Raj K.; Reddy K. B.; Prasad A. R. Synthesis 2001, 2277–
2280.
17. Manjula, A.; Rao, B. V.; Neelakantan, P. Synth. Commun. 2003, 33, 2963–2969.
18. Azizi, N.; Saidi, M. R. Eur. J. Org. Chem. 2003, 4630–4633.
19. Kaboudin, B.; Rahmani, A. Synthesis 2003, 2705–2708.
20. Firouzabadi, H.; Iranpoor, N.; Sobhani, S. Synthesis 2004, 2692–2696.
21. Sun, P.; Yang, X.; Hu, Z. J. Chem. Res. 2006, 240–241.
22. Bhagat, S.; Chakraborti, A. K. J. Org. Chem. 2007, 72, 1263–1270.
23. Kumar, A. S.; Taneja, S. C.; Hundal, M. S.; Kapoor, K. K. Tetrahedron Lett. 2008, 49, 2208–
2212.
24. Bhagat, S.; Chakraborti, A. K. J. Org. Chem. 2008, 73, 6029–6032.
25. Hosseini Sarvari, M. Tetrahedron 2008, 64, 5459–5466.
13
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
26. Tajbakhsh, M.; Heydari, A.; Alinezhad, H.; Ghanei, M.; Khaksar, S. Synthesis 2008, 352–
354.
27. Sobhani, S.; Safaei, E.; Asadi, M.; Jelili, F. J. Organomet. Chem. 2008, 693, 3313–3317.
28. Mitragorti, S. D.; Pore, D. M.; Dasai, U. V.; Wadgaonkar, P. P. Catal. Commun. 2008, 9,
1822–1826.
29. Rezaei, Z.; Firouzabadi, H.; Iranpoor, N.; Ghaderi, A.; Jafari, M. R.; Jafari, A. A. Zare, H. R.
Eur. J. Med. Chem. 2009, 44, 4266–4275.
30. Sobhani, S.; Vafaee, A. Synthesis 2009, 1909–1915.
31. Vinu, A.; Kalita, P.; Balasubramanian, V. V.; Oveisi, H.; Selvan, T.; Mano, A.; Chari, M. A.;
Subba Reddy, B. V. Tetrahedron Lett. 2009, 50, 7132–7136.
32. Hou, J. T.; Gao, J. W.; Zhang, Z. H. Appl. Organometa. Chem. 2011, 25, 47–53.
33. Milen, M.; Ábrányi-Balogh, P.; Dancsó, A.; Frigyes, D.; Pongó, L.; Keglevich, G.
Tetrahedron Lett. 2013, 54, 5430–5433.
34. Shen, M. G.; Shang,S. B.; Song, Z. Q.; Wang, D.; Rao, X. P.; Gao, H.; Wang, J. Synth.
Commun. 2014, 44, 361–367.
35. Reddya, P. S.; Reddya, P. V. G.; Reddy, S. M. Tetrahedron Lett. 2014, 55, 3336–3339.
36. Li, N.; Wang, X.; Qiu, R.; Xu, X.; Chen, J.; Zhang, X.; Chen, S.; Yin, S. Catal. Commun.
2014, 43, 184–187.
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ACCEPTED MANUSCRIPT

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37. Parvanak Boroujeni, K.; Nasrolahi Shirazi, A. Heteroat. Chem. 2010, 21, 418–422.
38. Parvanak Boroujeni, K. Synth. React. Inorg. Met.-Org. Chem. 2011, 41, 173–176.
39. Parvanak Boroujeni, K.; Shojaei, P. Turk. J. Chem. 2013, 37, 756–764.
40. Parvanak Boroujeni, K.; Ghasemi, P.; Rafienia, Z. Monatsh. Chem. 2014, 145, 1023–1026.
41. Chen, Y.; Haddon, R. C.; Fang, S.; Rao, A. M.; Eklund, P. C.; Lee, W. H.; Dickey, E. C.;
Grulke, E. A.; Pendergrass, J. C.; Chavan, A.; Haley, B. E.; Smalley, R. E. J. Mater. Res.
1998, 13, 2423–2431.
42. Dry MWCNT–(mpIm)HSO4 (1 g) was added to 10 mL aqueous solution of NaCl (2 M), the
resulting mixture was stirred for 24 h and then the solution was titrated potentiometrically
with aqueous solution of NaOH (0.01 M) using phenolphthalein as a pH indicator.
43. Jing, S. Y. J. Korean Phys. Soc. 2002, 41, 769–773.
44. Chrobok, A.; Baj, S.; Pudlo, W.; Jarzebski, A. Appl. Catal. A Gen. 2009, 366, 22–28.
45. Singh, V.; Kaur, S.; Sapehiyia, V.; Singh, J.; Kad, G. L. Catal. Commun. 2005, 6, 57–60.
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Table 1 Synthesis of α-aminophosphonate derivatives
Time
(min)
Yield
(%)a
Entry
R1
R2
H
R3
Mp (°C) (Lit.)
1
Ph
Ph
40 (45)b 96 (95)b 90 (90–91)32
2
3
4
5
6
7
4-MeC6H4
4-MeOC6H4
4-HOC6H4
4-NO2C6H4
3-NO2C6H4
4-ClC6H4
H
H
H
H
H
H
Ph
Ph
Ph
Ph
Ph
Ph
36
95
62–65 (64–65)32
60 (63)b 93 (94)b 105–108 (102–103)32
65 93 oil
35 (33)b 95 (94)b 127–129 (120)25
33
50
96
92
95–97 (97–98)36
60–62 (58–59)32
8
4-BrC6H4
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
51
60
60
55
94
93c
91
94
94–97 (96–98)36
183–187 (185–186)32
126–128 (124–125)33
oil
9
Terephthaldehyde
1-Naphthaldehyde
2-Naphthaldehyde
CH3(CH2)2
C6H5CH=CH
Furan-2-
10
11
12
13
14
H
H
55 (60)b 93 (90)b oil
65
60
89
91
105–108 (105–106)32
54–56 (51–52)32
carbaldehyde
Thiophene-2-
carbaldehyde
Ph
15
Ph
58
93
72–74 (70)25
16
17
18
19
20
21
22
23
H
H
H
H
H
4-MeC6H4
4-NO2C6H4
C6H5CH2
CH3(CH2)2
(CH3CH2)2
Ph
38
70
50
96
90
95
114–117 (116–117)32
146–148 (146–147)32
oil
Ph
Ph
Ph
60 (65)b 94 (90)b oil
Ph
80
92
90
90
oil
Acetophenone
Cyclohexanone
2-Pentanone
114–116 (116–118)36
Ph
90 (95)b 90 (90)b 98–100 (109–110)32
Ph
93
90
oil
aIsolated yield.
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bValues in parenthesis: when the reaction was performed in the presence of 1-butyl-3-methyl-
imidazolium hydrogen sulfate ionic liquid ([bmIm]HSO4)45 at room temperature; molar ratio of
aldehyde : amine : diethyl phosphite : [bmIm]HSO4 is 1 : 1 : 1.2 : 0.1.
c2.4 equivalents of diethyl phosphite and 2 equivalents of aniline were used.
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Table 2 Comparison of the efficiencies of a number of different reported catalysts with that of
MWCNT–[mpIm]HSO4 for the condensation of aniline and 4-methoxybenzaldehyde with
diethyl phosphite
Entry
1
Cat./Solv./Temp.
ZrCl4/MeCN/r.t.
Time (min)
300
180
120
5
Yield (%)
9016
2
Al(OTf)3/neat/80 °C
9020
a
3
Ionic liquid [bmim]Cl–AlCl3 /neat/r.t.
Mg(ClO4)2/neat/r.t.
9521
4
9522
5
Al2O3-SbCl3/MeCN/r.t.
210
5
9223
6
ZrOCl2.8H2O/neat/r.t.a
9524
7
TiO2/neat/50 °C
150
180
120
45
9825
8
[Cu(3,4-tmtppa)](MeSO4)4/H2O/80 °C
Sulfamic acid/neat/r.t.
9027
9
8728
10
11
12
FeCl3/THF/60 °C
9229
Sodium dodecyl sulfate/H2O/50 °C
30
9830
240
9031
Mesoporous aluminosilicate nanocage
/MeCN/80 °C
13
14
Yb(OTf)3/H2O/PTSb/r.t.
60
8634
9036
180
Zirconocene
Bis(perfluorobutanesulfonate)/r.t.
15
16
17
SiO2-AlCl3/MeCN/reflux
Ps-Al(OTf)3/neat/r.t.
78
66
40
9237
9338
96
MWCNT–[mpIm]HSO4/neat/r.t.
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aWith benzaldehyde.
bPolyoxyethanyl α-tocopheryl sebacate.
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Figure 1 FT-IR spectra of MWCNT–OH (A) and MWCNT–[mpIm]HSO4 (B)
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Figure 2 TGA curves of MWCNT–OH (A) and MWCNT–[mpIm]HSO4 (B)
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Figure 3 SEM photographs of MWCNT–OH (A) and MWCNT–[mpIm]HSO4 (B)
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Figure 4 TEM photographs of MWCNT–OH (A) and MWCNT–[mpIm]HSO4 (B)
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Figure 5 Recyclability of MWCNT–[mpIm]HSO4 (0.07 mmol) in the reaction of benzaldehyde
(1 mmol), aniline (1 mmol), and diethyl phosphite (1.2 mmol) at room temperature. Reaction
time 40 min.
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Scheme 1 Synthesis of MWCNT–[mpIm]HSO4
25
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Scheme 2 Synthesis of bis(α-aminophosphonates) using MWCNT–[mpIm]HSO4
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Scheme 3 Proposed mechanism for the preparation of α-aminophosphonates
catalyzed by MWCNT–[mpIm]HSO4
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S
R
NHCMe
CHO
OH
S
MWCNT-[mpIm]HSO4
(0.1 mmol)
OH
C
R
+
+
Me
ClCH2CH2Cl / r.t.
NH2
(1 mmol)
(1 mmol)
(1.3 mmol)
R = H, 50 min, 91%
R = p-OMe, 55 min, 90%
Scheme 4 Synthesis of 1-thioamidoalkyl-2-naphthols using MWCNT–[mpIm]HSO4
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