Benzimidazolium dicationic ionic liquid as an efficient and reusable catalyst for the synthesis of α-aminophosphonates and bis (α-aminophosphonates) under solvent-free condition

Article abstract of DOI:10.1080/10426507.2015.1012199

(Chemical Equation Presented) Benzimidazolium based on dicationic acidic ionic liquid (AIL) is designed, synthesized, and successfully used as a catalyst for the one-pot synthesis of α-aminophosphonates derivatives. The application of this AIL is studied in a new one-pot method for the synthesis of α-aminophosphonates derivatives under solvent-free conditions. The advantages of thismethod are the reusability of catalyst, high conversion, short reaction time, and simple experimental procedure.

Full text of DOI:10.1080/10426507.2015.1012199

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Phosphorus, Sulfur, and Silicon and the Related
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Benzimidazolium Dicationic Ionic Liquid as an
Efficient and Reusable Catalyst for the Synthesis of α-
aminophosphonates and Bis (α-aminophosphonates)
under Solvent-free Condition
Hossein Eshghia, Mahdi Mirzaeia, Maede Hasanpoura & Majid Mokaber-Esfahania
a Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, 91775-1436
Mashhad, Iran
Accepted author version posted online: 11 Feb 2015.
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To cite this article: Hossein Eshghi, Mahdi Mirzaei, Maede Hasanpour & Majid Mokaber-Esfahani (2015): Benzimidazolium
Dicationic Ionic Liquid as an Efficient and Reusable Catalyst for the Synthesis of α-aminophosphonates and Bis (α-
aminophosphonates) under Solvent-free Condition, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2015.1012199
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Benzimidazolium dicationic ionic liquid as an efficient and reusable catalyst for the
synthesis of α-aminophosphonates and bis (α-aminophosphonates) under solvent-free
condition
Hossein Eshghi,1*Mahdi Mirzaei, 1 Maede Hasanpour,1and Majid Mokaber-Esfahani1
aDepartment of Chemistry, School of Sciences, Ferdowsi University of Mashhad, 91775-1436
Mashhad, Iran
Abstract Benzimidazolium based on dicationic acidic ionic liquid (AIL)is designed,
synthesized, and successfully used as a catalyst for the one-pot synthesis of α-
aminophosphonates derivatives. The application of this acidic ionic liquid is studied in a new
one-pot method for the synthesis of α-aminophosphonates derivatives under solvent-free
conditions. The advantages of this method are the reusability of the catalyst, high conversion,
short reaction time, and simple experimental procedure.
NH2
O
OEt
OEt
H
P
R2
N
H
R1
R2
AIL( 10 mol %),
Solvent free, 500C
CHO
O
3a-3j
P OEt
OEt
+
H
EtO
EtO
O P EtO
R1
OEt P O
X
N
H
N
H
X
R1
R1
H2N
NH2
4a-4j
Keywords Acidic ionic liquid, Benzimidazolium cation, Reusable catalyst, α-
Aminophosphonates
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INTRODUCTION
In recent year ionic lidiuds(ILs) have received great attention due to their high thermal stability,
broad liquid range, biological activities such as antiviral, antifungal and anticancer activities,
catalyst in organic synthesis, analytical chemistry.1Dicationic ILs have also been used widely in
various fields of Science. Dicationic ionic liquids based organic cation contain moeties
imidazol,2 pyridine,3 6alkyl/aryl4 and chains contain alkyl, aryl, and alkoxy with different anion
were used as catalysis in organic synthesis.1a,1b,5
Benzimidazoles have received significant attention because of their biological activities such as
antihistaminic, antiphrastic, antiulcer, antihypertensive, antiviral, antifungal and anticancer
activities. 6 Many reports are available that benzimidazole has been used as organic cations ionic
lidiuds (ILs) in synthesis organic compound. 7
As a part of our green technology program we would also like to disclose here a more practical
green alternative for a new method to synthesize α-aminophosphonate by a three-component
condensation reaction. The application of ionic liquids in the synthesis of α-aminophosphonates
were reported.8
α-aminophosphonates are considered to be structural analogs of the corresponding esters of α-
aminoacids have been reported to exert several pharmacological activities such as their potential
usage as anticancer agents,9 antiviral activities,10 HIV protease,11 anti-thrombotic agents,12
inhibitors of protein tyrosine phosphatases,13 peptide mimics 14 and enzyme inhibitors.15
Recently, nucleophilic addition of phosphite to imines, catalyzed by an acid or a base, has
emerged as an important alternative for the synthesis of α-aminophosphonates. Typically, Lewis
acids such asSnCl2,16 Al(OTf)3,17 InCl3,18 Mg(ClO4)2,19 Mg(OTf)3,20 CeCl3•7H2O,21 FeCl3,22
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TiO2,23 NaHSO4-SiO2,24 nano Fe3O425 and ethyl ammonium nitrate 26 have been used as catalysts
for this process. However, these reactions could not be carried out efficiently in a single step
with carbonyl, amine and phosphite functionalities because amines and the water formed during
imine formation can decompose or deactivate these Lewis acids.
Herein, we report the synthesis of dicationic acidic ionic liquid (AIL) which contains
benzimidazolium cations, ethyleneoxy bridge and also a sulfonic acid group (That participates in
dissolving organic compounds in AIL with its ethyleneoxy bridge) and SO3H functional groups
act as a Brønsted AIL catalyst. we describe an efficient method for the synthesis of α-
aminophosphonates and bis-(α-aminophosphonates) through three-component reactions of
aldehydes, amines, and diethyl phosphite using catalytic amounts of AIL under solvent-free
conditions. (Scheme 1)
Scheme 1
RESULTS AND DISCUSSION
Preparation and characterization of dicationic acidic ionic liquid
We designed and synthesized AIL based on benzimidazolium cations with a triethylenoxy
spacer. In this protocol, we first synthesized 1,2-bis(2-(1H-benzimidazol-1-yl)ethoxy)ethane
through the reaction between benzimidazole and 1,2-bis(2- chloroethoxy)ethane in the presence
of potassium hydroxide in DMSO.27 Then, for acidic functionalization, we used chlorosulfonic
acid in dry dichloromethane and AIL (2) was obtained in 96 % yield as a viscous oil (Scheme 2).
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Scheme 2 Here
The IR spectrum of AIL showed a broad peak at 2700–3484 cm−1 related to the OH of the SO3H
groups. Moreover, two peaks observed in 1088 cm−1 and 1282 cm−1 correspond to the vibrational
modes of N-SO2 bond.
One of the key properties of Brønsted ILs is their Brønsted acidity which has a strong correlation
to the catalytic activity of this compound in the many organic synthesis reactions28. SO3H-
functionalized AIL have been employed as Brønsted IL catalysts for the synthesis of several
acid-catalyzed organic reactions. In recent years, there have been reports about Brønsted AIL
based on the sulfonic acid group which have good activity.7a,29 The purpose of the preparation of
this AIL is to increase the solubility7a of the organic compounds in the AIL through
triethyleneoxy spacer that increase its flexibility and hydrophobicity. Solubility of synthesized
AIL was determined in several selected solvents at ambient temperature. In general dicationic
ionic liquid showed good solubility in polar solvents, while insoluble in ethyl acetate, diethyl
ether, cyclohexane, and toluene, that may be attributed to the bridged oxygen atoms in cations
generating hydrogen bonding with polar solvent. In addition, longer oligo (ethylene glycol)
chains may improve the hydrophobicity of the overall AIL.30 In the synthesis of this AIL, the
sulfonic acid group is covalently tethered to the AIL benzimidazolium cation and this part of the
AIL can increase its hydrophilicity. So, features of both hydrophilicity and hydrophobicity are
responsible for increasing the dissolution of organic compounds in this AIL.
The pH value for the mentioned AIL was determined using a 0.1 mol L-1 solution of IL and was
titrated with 0.114 mol L-1 of NaOH (a solution of potassium hydrogen phetalate (KHP) was
prepared at concentration 0.100 M. 25.00 ml of KHP solution was further used to standardized a
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NaOH solution). The pH of the solution was measured using a calibrated glass electrode pH
meter. The pH value of the AIL is 2.2. This AIL can be used as a catalyst in many different
organic transformations.
The measurement of the acidic scale of this AIL was conducted on an UV-vis spectrophotometer
with a basic indicator according to the literature reported previously.7d,31,32 With the increase of
acidic scale of the AIL, the absorbance of the unprotonated form of the basic indicator decreased.
Whereas the protonated form of the indicator could not be observed because of its small molar
absorptivity and its location, so the [I]/[IH+] ( I represents indicator) ratio could be determined
from themeasured absorbance differences after addition of AIL, and then the Hammett function
H0, was calculated by using Eq (1). This value could be regarded as the relative acidity of the IL
H0=pK(I)aq + log [I]/[IH+]
Eq (1)
Under the same concentration of 4-nitroaniline (10 mg/L, pKa=0.99) and AIL (5 mmol/L) in
dichloromethane, we determined the H0value of the AIL. The maximum absorbance of the
unprotonated form of the indicator was observed at 350 nm in CH2Cl2. When AIL was added, the
absorbance of the unprotonated form of the indicator decreased (Figure S 1, Supplemental
Materials). The results obtained show the acidity strength of AIL (Table 1).
Table1 Here
Thermal gravimetric (TG) and derivative thermal gravimetric (DTA) analysis of AIL were
studied in a range of temperature between 25 and 600 ºC with a temperature increase rate of
10°C.min-1 in a Argon atmosphere (Figure S2 ) .The TG and DTA of the catalyst showed three
weight losses. The first observed in 80 ºC that related to loss H2O, the second weight loss
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observed after 320 ºC, and the three weight loss appears after 380 ºC. Therefore, AIL could be
applied as catalysts below 320 ºC, and decomposed after 320 ºC.
The reaction of diethyl phosphite, 4-cholorobenzaldehyde and 4-methoxy aniline was optimized
in different temperature and mol % of the catalyst. In the best conditions, the corresponding α-
aminophosphonate was obtained in high yield at 50 ºC in the presence of 10mol % of the
sulfonic acid functionalized dicationic ionic liquid (Table 2).
Table 2
In order to examine the scope of this process, several aromatic aldehydes and amines were
reacted under the optimized conditions and the results are shown in (Table 3). Both either
electron-donating or electron-withdrawing aldehydes and anilines reacted to form efficiently
giving excellent yields of the expected α-aminophosphonates.
The synthesized compounds (3a-3j) gave satisfactory elemental analyses, and their molecular
1
structure was confirmed by IR and H, 13C and 31P NMR spectroscopy that was reported
previously in literatures. The IR spectra showed the expected absorption bands at 2985–3305 and
1225–1236 cm-1, which are attributed to NH and P=O stretching vibrations, respectively.33 The
1H NMR spectra of compounds, recorded in CDCl3 solution, exhibit the signal of CHP proton as
a doublet of doublet at 4.64and 4.70 ppm (1a).34 The NH proton signal of (3a) appears as a
triplet. There is a correlation between NH,CHP and P that decouplage P indicate correlation
between NH, CHP and on addition of D2O the NH signal disappeared and the signal of CHP that
1
13
appeared as doublet, and the doublet at 55.4 ppm with JPC =155 Hz, observed in its C NMR
spectrum (Figure S3). The values are typical for the proton and carbon atom from a CHP
fragment.34 The methyl protons from the ethoxy groups give two triplets, owing to the
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nonequivalence of these groups. The POCH2 proton signals appear as three multiplets at about
3.60-4.20 ppm.
Bis(α-aminophosphonates) are interesting compounds, as they are multidentate ligands which
may be used for the extraction of metals from solutions and they can be employed as the
monomers for the preparation of macrocyclic or polymeric compounds carrying phosphonate and
amine moieties. In addition, and more importantly, investigation of their biological activity
would be of great interest.35 Through this study, it was also investigated the applicability of the
catalyst for the preparation of bis(α-aminophosphonates) via a one-pot three-component reaction
of structurally diverse diamines (1,4-phenylenediamine and 4,4'-diaminobiphenyl) (1.0 mmol),
electron-rich and electron-deficient aromatic aldehydes (2.0 mmol) and diethylphosphite(2.0
mmol) in the presence of AIL (10 mol%).
The reactions progressed well at 50 ºC and the desired bis(α-aminophosphonates) were produced
in excellent isolated yields (85–96%) (Scheme 1, Table 4). However, 1,2-phenylenediamine and
1,3-phenylenediamine failed to react under similar reaction conditions.
Table 3, Table 4
One of the advantages of this AIL is its ability to be recycled from the reaction medium. We
were able to readily separate the catalyst from the residue by washing with CH2Cl2. The catalyst
was recovered by evaporation of the water of the aqueous layer at 50 ºC in a vacuum oven which
gave 95 % yields and could be reused for the same experiment for four more times (Table 5).
The 1H NMR spectrum of the recycled AIL catalyst compared with the freshly prepared catalyst
and at significant purity was observed.
Table 5 Here
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This study compared with reported synthetic methods for the synthesis of α-aminophosphonate
(Table 6). As is shown in Table 6, AIL afforded the products in higher yields and in extremely
milder reaction conditions.
Table 6 Here
EXERIMENTAL
Materials and instrumentation
All reagents were purchased from Merck and used without further purification. The melting
points of the products were determined with an Electrothermal Type 9100 melting point
apparatus. The FT-IR spectra were recorded on an Avatar 370 FT-IR Thermal Nicolet
spectrometer. The mass spectra were recorded on a 5973 Network Mass Selective Detector. The
31
1H,13C and PNMR spectra were recorded on a Bruker AC 100 and Bruker DRX-400 Avance
spectrometers at 400 ,161.99 and 100.65 MHz, respectively, using DMSO-d6 or CDCl3 as the
deuterated solvents. Chemical shifts are reported in ppm downfield from TMS as internal
standard; coupling constants J are given in Hz.
Synthesis of 1,2-bis(2-(1H-benzimidazol-1-yl)ethoxy)ethane (1):
A mixture of benzimidazole (20 mmol, 2.36 g) and potassium hydroxide (20 mmol, 1.792 g) in
DMSO (25 ml) was stirred at 70 ºC for 0.5 h. After this time, 1,2-bis(2- chloroethoxy)ethane (10
mmol, 1.55 mL) was added to the reaction mixture and stirred for 24 h. The resulting mixture
was poured into of water (100 mL) and extracted with methylene chloride (3 × 20 mL). The
combined organic layer was washed with water (3 × 20 mL), dried with anhydrous MgSO4, and
concentrated to give 1,2-bis(2-(1H-benzimidazolimidazol-1-yl)ethoxy)ethane (1).
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1H NMR (CDCl3, 100 MHz) δ: 3.45 (s, 4H, CH2O), 3.76 (t, 4H, J = 4.6 Hz, CH2O), 4.64 (t, 4H,
J = 4.6 Hz, CH2O), 7.50-8.00 (m, 8H, Ar), 9.55 (s, 2H, NCHN).
Synthesis of 1,10-((ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))bis(3-sulfo-1H-benzimidazol-3-
ium) chloride (2):
A 100 mL round-bottomed flask was charged with 1,2-bis(2-(1H-benzimidazol-1-
yl)ethoxy)ethane (1) (10 mmol, 3.50 g) in dry CH2Cl2(50 mL), and then chlorosulfonic acid (20
mmol, 1.32 mL was added dropwise over a period of 30 min at room temperature. Afterward, the
reaction mixture was stirred for 1 h, and the CH2Cl2 was decanted. The residue was washed with
dry CH2Cl2 (3×20 mL) and dried under vacuum to give 1,10-((ethane-1,2-
diylbis(oxy))bis(ethane-2,1-diyl))bis(3-sulfo-1H-benzimidazol-3-ium) chloride (2) as a viscous
colorless oil.
1H NMR (DMSO, 400 MHz) δ: 3.40 (s, 4H, CH2O), 3.73 (t, 4H, J = 4.4 Hz. CH2O), 4.60 (t, 4H,
13
J = 4.4 Hz, CH2O), 7.48-7.90 (m, 8H, Ar), 9.47 (s, 2H, NCHN), 13.1 (b, 2H, SO3H). C NMR
(CDCl3, 100 MHz) 46.8(OCH2), 68.0 (-O-CH2CH2-O-), 69.9 (-N-CH2CH2O), 113.8(C7& C6),
114.8 (C5), 126.5 (C8), 130.6 (C4), 134.3(C9), 140.7(C2); m/z, calcd. for C20H24Cl2N4O8S2
[M]+: 582.04, found: 582.0
General procedure for preparation of α-aminophosphonate (3a-3j).
To a mixture of aldehydes (1.0 mmol), anilines (1.0 mmol), and diethyl phosphite (1.0 mmol),
AIL (2) (10 mol %) was added and stirred at 50ºC for appropriate time. After completion of the
reaction as monitored by TLC, the mixture was washed with CH2Cl2 (3 × 3 mL). The combined
extracts were filtered and the solvent was removed under reduced pressure to afford the crude
product, which was purified by recrystallization from ethylacetate/n-Hexane. The catalyst, which
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1
13
31
does not dissolve in CH2Cl2, remained in the residue. Selected H, C and P NMR spectra for
compound 3d are presented in the Supplemental Materials (Figures S 4 – S 6)
Selected spectroscopic data:
Diethyl (((4-chlorophenyl) amino) (4-methoxyphenyl) methyl) phosphonate (3a)36
1
Solid, Yield: 94%, m.p: 101-102 ºC.IR (νmax,cm−1): 3293 (NH), 1234 (P=O), 1055(P-OEt); H
NMR (CDCl3, TMS, 400 MHz): 1.15 (t, 3H, J=7.2 Hz, -P-OCH2-CH3), 1.30 ( t, 3H, J=7.2 Hz, -
P-OCH2-CH3), 3.60-3.75 (m, 1 H, -P-OCH2-CH3), 3.74 (s, 3 H, Ar-OCH3), 3.90-4.05 (m, 1 H, -
1
P-OCH2-CH3), 4.0-4.20 (m, 2H, -P-OCH2-CH3), 4.67 ( dd, 1H, JPH=23.2,2J=7.6 Hz, -CHP),
4.92 (m, 1H, NH), 6.53 (d, 2H, J=8.8 Hz, Ar), 6.88 (d, 2H, J=8.4 Hz, Ar), 7.05 (d, 2H, J=8.8 Hz,
3
Ar), 7.38 (d, 2H, J=8.4 Hz, Ar);13C NMR (CDCl3, TMS, 100 MHz): 16.2 (d, Jcp=6 Hz,-
OCH2CH3), 16.4 (d, 3Jcp= 6 Hz,- OCH2CH3), 55.2( Ar-OCH3), 55.4 (d, 1Jpc= 152 Hz, CHP), 63.1
2
2
(d, Jpc=6 Hz, -OCH2CH3), 63.3 (d, Jpc=6 Hz, - OCH2CH3), 114.1(Ar, C3), 115.0 ( Ar, C5),
3
122.9( Ar, C11), 127.2 ( Ar, C10, C12), 128.9 (d, Jpc=4.5, Ar, C9, C13), 144.9 (Ar, C4,C6),
2
31
145.0 (d, Jpc=13, Ar, C8), 159.0 (Ar, C2); P (162.5 MHz, CDCl3, TMS): 22.5 ppm. MS (EI)
m/z: 383.11(M+), 245; Elemental analysis for C18H23ClNO4P requires C, 56.32; H, 6.04; N, 3.65.
Found: C, 56.10; H, 5.90; N, 3.30%.
Diethyl (((4-chlorophenyl) amino) (p-tolyl) methyl) phosphonate(3b)37
1
Solid, Yield: 92%, m.p: 98-99ºC.IR (νmax, cm−1): 3305 (NH), 1225 (P=O), 1048(P-OEt); H
NMR (CDCl3, TMS, 100 MHz): 1.13 (t, 3H, J=7.0 Hz, -P-OCH2-CH3), 1.20 (t, 3H, J=7.0 Hz, -
P-OCH2-CH3) , 2.30 (s, 3H, Ar-CH3), 3.50-3.65 (m, 1H, -P-OCH2-CH3), 3.80-3.95 (m, 1H, -P-
OCH2-CH3) 4.05-4.15 (m, 2H, -P-OCH2-CH3), 4.67(d, 1H, J=22.5 Hz, -CHP), 4.70 (br, 1H,
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NH), 6.50 (d, 2H, J=8.4 Hz, Ar), 7.00-7.4 (m, 6H, Ar); 31P (162.5 MHz, CDCl3, TMS):23.2 ppm.
MS (EI) m/z: 367.81(M+), 229; Elemental analysis for C18H23ClNO3P requires C, 58.78; H, 6.30;
N, 3.81. Found: C, 58.45; H, 6.20; N, 3.61%.
Diethyl (((4-chlorophenyl)amino)(4-nitrophenyl)methyl)phosphonate (3d)38
1
Solid, Yield: 90%, m.p: 105-106ºC. IR (νmax, cm−1): 3300 (NH), 1230 (P=O), 1044 (P-OEt); H
NMR (CDCl3, TMS, 100 MHz): 1.03-1.40 (m, 6H, -P-OCH2-CH3), 3.80-4.20 (m, 4H, -P-OCH2-
CH3), 4.65 (d, 1H, J = 22.0 Hz, -CHP), 4.75 (br, 1H, NH), 6.60 (d, 2H, J = 8.0 Hz, Ar), 6.80-
3
7.50 (m, 6H, Ar); 13C NMR (CDCl3, TMS, 100 MHz): 16.3 (d, Jcp= 6 Hz,-OCH2CH3), 16.7 (d,
1
2
3Jcp= 7 Hz,- OCH2CH3), 55.7 (d, Jpc= 150 Hz, CHP), 63.2 (d, Jpc= 7 Hz, -OCH2CH3), 63.9 (d,
2Jpc= 7 Hz, - OCH2CH3), 117.0 (Ar, C3), 118.2 ( Ar, C5), 120.0 ( Ar, C11), 122.1 ( Ar, C10,
C12), 129.4 (Ar, C9, C13), 131.6 (Ar, C4,C6), 141.1 (, Ar, C8), 147.8 (Ar, C2); 31P (162.5 MHz,
CDCl3, TMS):20.8 ppm. MS (EI) m/z: 398.10 (M+), 262; Elemental analysis for C17H20ClN2O5P
requires C, 51.20; H, 5.06; N, 7.02. Found: C, 51.10; H, 5.01; N, 6.98%.
Diethyl ((4-nitrophenyl) (phenylamino) methyl) phosphonate(3g)37
Solid, Yield: 90%, m.p: 126-127ºC. IR (νmax, cm−1): 3287 (NH), 1232 (P=O), 1054(P-OEt);1H
NMR (CDCl3, TMS, 100 MHz): 1.1-1.4 (m, 6H, -P-OCH2-CH3), 3.50-4.14 (m, 4 H, -P-OCH2-
CH3), 4.50(br, 1H, NH), 4.60 (d, 1H, J=22.5 Hz, -CHP), 6.50-8.40 (m, 8H, Ar);31P (162.5 MHz,
CDCl3, TMS): 21.4 ppm MS (EI) m/z: 364.12 (M+), 226; Elemental analysis for C17H21N2O5P
requires C, 56.04; H, 5.81; N, 7.69. found: C, 55.80; H, 5.71; N, 7.34%.
Diethyl ((4-methoxyphenyl) (phenylamino) methyl) phosphonate (3j)36
Solid, Yield: 85%, m.p: 101-102ºC.IR (νmax, cm−1): 3293 (NH), 1232 (P=O), 1048(P-OEt);1H
NMR (CDCl3, TMS, 100 MHz): 1.20 (t, 3H, J=7.2 Hz, -P-OCH2-CH3), 1.25(t, 3H, J=7.2 Hz, -P-
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OCH2-CH3), 3.78(s, 3H, OCH3), 3.50-4.50 (m, 4 H, -P-OCH2-CH3), 4.50(d, 1H, J=23 Hz, CHP),
4.55(br, 1H, NH), 6.50-7.5(m, 8H, Ar);31P (162.5 MHz, CDCl3, TMS): 22.4 ppm; MS (EI) m/z:
349.14 (M+), 211; Elemental analysis for C18H24NO4P requires C, 61.88; H, 6.92; N, 4.016.
Found: C, 61.65; H, 6.87; N, 3.85%.
General procedure for preparation of bis α-aminophosphonate (4a-4j).
To a mixture of aldehydes (2.0 mmol), p-Phenylenediamine or benzidin (1 mmol), and diethyl
phosphite (2.0 mmol), AIL (10 mol %) was added and stirred at 50 ◦C for appropriate time. After
completion of the reaction as monitored by TLC, the mixture was washed with CH2Cl2 (3 × 30
mL). The combined extracts were filtered and the solvent was removed under reduced pressure
to afford the crude product, which was purified by recrystallization from ethylacetate/n-Hexane.
1
13
The catalyst, which does not dissolve in CH2Cl2, remained in the residue. Selected H, C and
31P NMR spectra for compound 4e are presented in the Supplemental Materials (Figures S 7 – S
9)
Spectroscopic data:
Tetraethyl- 1, 1’-biphenyl-4, 4’ bis [(4-(dimethylamino) phenyl) methylene]) diphosphonate
(4a)
Solid, Yield: 92%, m.p: 161-162ºC.IR (νmax, cm−1): 3292 (NH), 1230 (P=O), 1044(P-OEt); 1H NMR
(CDCl3, TMS, 400 MHz): 1.16 ( t, 6H, J=7.2 Hz,-P-OCH2-CH3), 1.30 ( t, 6H, J=7.2 Hz, -P-OCH2-
CH3), 3.67-3.73 (m, 2H, -P-OCH2-CH3), 2.93 (s, 12 H, -N(CH3)2), 3.93-3.99 (m, 2 H, -P-OCH2-
1
CH3), 4.07-4.18 (m, 4 H, -P-OCH2-CH3), 4.69 ( dd, 2H, JPH=23.6,2J=7.2 Hz, -CHP), 4.75 (br, 1H,
NH), 6.63 (d, 4H, J=8.4 Hz, Ar), 6.70 (d, 4H, J=8.8 Hz, Ar), 7.24 (d, 4H, J=8.8 Hz, Ar), 7.33 (dd,
1
3
4H, J=8.4,2J=2.2 Hz, Ar);13C NMR (CDCl3, TMS, 100 MHz): 16.3 ( d, Jcp=5.7 Hz,-P-OCH2CH3),
12
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16.4 ( d, 3Jcp= 5.7 Hz,-P-OCH2CH3), 40.5(-NCH3), 55.4 (d, 1Jpc= 152 Hz,CHP), 63.1(d, 2Jpc=9.9 Hz,-
2
P-OCH2CH3), 63.1 (d, Jpc=9.9 Hz,-P-OCH2CH3), 112.5 (C3´), 114.1 (C2), 123.0 (C2´), 127.0 (C3),
2
3
128.0(d, Jpc=5.5, C1´), 131.3 (C3), 145.1 (d, Jpc=14.8, C1), 150.2 (C4);31P (162.5 MHz, CDCl3,
TMS ): 23.3 ppm. MS (EI) m/z: 722.79 (M+), 584, 446; Elemental analysis for C38H52N4O6P2 requires
C, 63.50; H, 7.25; N, 7.75. Found: C, 63.40; H, 7.15; N, 7.70%.
Tetraethyl- 1, 1'-biphenyl-4, 4' bis [(4-(diethylamino) phenyl) methylene]) diphosphonate(4b)
Solid, Yield: 94%, m.p: 101-102ºC. IR (νmax, cm−1): 3299(NH), 1234 (P=O), 1054 (P-OEt);1H
NMR (CDCl3, TMS, 400 MHz): 1.12-1.26 ( m, 6H, -P-OCH2-CH3, 12H, -P-NCH2-CH3), 1.28 (
t, 6H, J=7.2Hz, -P-OCH2-CH3), 3.29 (q, 8 H, J=7.2Hz, -P-NCH2-CH3), 3.68-3.72 (m, 2 H, -P-
OCH2-CH3), 3.93-3.97 (m, 2 H, -P-OCH2-CH3), 4.08-4.14 (m, 4 H, -P-OCH2-CH3), 4.66 ( d, 2H,
J=23.2 Hz, -CHP), 4.70 (br, 2H,NH), 6.60-6.80 (m, 8H, Ar), 7.20-7.28(m, 8H, Ar);13C NMR
3
3
(CDCl3, TMS, 100 MHz):12.5 (-NCH2CH3), 16.2 (d, Jcp= 5 H, -P-OCH2CH3), 16.4 (d, Jcp= 5
1
2
Hz, -P-OCH2CH3), 44.3 (-NCH2CH3) , 55.4 (d, Jpc= 145 Hz, CHP), 63.0 (d, Jpc=8 Hz, -P-
OCH2CH3), 63.1(d, 2Jpc=8 Hz, -P-OCH2CH3), 111.9 (C3´), 114.1 (C2), 121.8 (C1´), 127.0 (C2´),
3
128.8 (C3), 131.2 (C4), 145.2 (d, Jcp= 15 Hz, C1), 147.5 (C4´);31P (162.5 MHz, CDCl3, TMS):
23.7 ppm. MS (EI) m/z: 778.90 (M+), 640, 502; Elemental analysis for C42H60N4O6P2 requires C,
64.76; H, 7.76; N, 7.19. Found: C, 64.60; H, 7.70; N, 7.04%.
Tetraethyl (1, 4-phenylene bis(azanediyl)) bis(p-methoxy methylene) diphosphonate(4c)
1
Solid, Yield: 96%, m.p: 156-157ºC. IR (νmax, cm−1): 3280 (NH), 1231 (P=O), 1051 (P-OEt); H
NMR (CDCl3, TMS, 400 MHz): 1.10-1.30 ( m, 12H, -P-OCH2-CH3), 3.69 (s, 6H, ArOCH3),
3.65-3.80 (m, 2H, -P-OCH2-CH3), 3.93-3.97 (m, 2 H, -P-OCH2-CH3), 4.08-4.14 (m, 4H, -P-
1
OCH2-CH3),4.36 (br, 2H, NH), 4.57 (2H, dd, JPH = 23 Hz,2JPH = 7.2 Hz, CHP), 6.57-6.70 (m,
13
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12H, Ar-H), 7.24-7.26 (m, 4H, Ar-H);13C NMR (CDCl3, TMS, 100 MHz): 16.29 (d, 3Jcp= 6 Hz, -
3
OCH2CH3), 16.4 (d, Jcp= 6Hz, -OCH2CH3), 44.3 (Ar-OCH3), 56.2 (d, Jpc= 152 Hz, CHP), 63.0
(-P-OCH2CH3), 63.0 (-P-OCH2CH3), 111.8 (C2), 114.6 (C3´), 115.2 (C2´), 121.8 (C3), 128.8 (d,
3
2Jpc= 5Hz, C1´), 140.7 (d, Jcp= 1.5 Hz, C1), 147.5 (C4), 152.4 (C4´); 31P (162.5 MHz, CDCl3,
TMS): 23.9 ppm. MS (EI) m/z: 696.71 (M+), 453, 415; Elemental analysis for C36H46N2O8P2
requires C, 62.06; H, 6.66; N, 4.02. Found: C, 61.90; H, 6.48; N, 3.90%.
Tetraethyl- 1, 1’-biphenyl-4, 4’ bis [(4-(isopropyl) phenyl) methylene])diphosphonate (4d)
Solid, Yield: 90%, m.p: 160-161ºC.IR (νmax, cm−1): 3296 (NH cm-1), 1236(P=O), 1065 (P-
OEt);1H NMR (CDCl3, TMS, 400 MHz): 1.07 (t, 6H, J=6.8 Hz, -P-OCH2-CH3), 1.17 ( d, 12H,
J=7 Hz, -CH(CH3)2), 1.27 ( t, 6H, J=6.8 Hz, -P-OCH2-CH3), 2.85-2.95 (m, 2H, -CH(CH3)2) 3.63-
3.71 (m, 2 H, -P-OCH2-CH3), 3.90-3.97 (m, 2 H, -P-OCH2-CH3), 4.08-4.16 (m, 4 H, -P-OCH2-
CH3), 4.60 ( d, 2H, J=24 Hz, -CHP), 4.68 (br, 2H, NH), 6.21 (d, 4H, J=8.4, Ar), 7.19 (d, 4H,
J=7.6, Ar), 7.18 (d, 4H, J=8.4, Ar), 7.38 (d, 4H, J=7.6, Ar);13C NMR (CDCl3, TMS, 100 MHz):
3
3
16.1 (d, Jcp= 6 Hz, -P-OCH2CH3), 16.4 (d, Jcp= 6 Hz, -P-OCH2CH3), 23.5 (CH(CH3)2), 33.7
(CH(CH3)2), 55.8 (d, 1Jpc= 150 Hz, CHP), 63.2 (d, 2Jpc=10 Hz), 63.3 (d, 2Jpc=10 Hz), 114.3 (C2),
2
3
126.5 (C3´), 127.0 (C2´), 127.7(d, Jpc=6Hz, C1´), 131.3 (C4), 133.0 (C3), 145.0 (d, Jpc=14Hz,
C1), 148.6 (C4´); 31P(162.5 MHz,CDCl3,TMS): 23.3 ppm. MS (EI) m/z: 720.35 (M+), 506, 368;
found: 720.30, Elemental analysis for C40H54N2O6P2 requires C, 66.65; H, 7.55; N, 3.89. Found:
C, 66.50; H, 7.50; N, 3.85%.
Tetraethyl- 1, 1’-biphenyl-4, 4’ bis [(p-tolylmethylene]) diphosphonate (4e)
Solid, Yield: 90%, m.p: 148-149ºC. IR (νmax, cm−1): 3296 (NH), 1232 (P=O), 1060 (P-OEt);1H
NMR (CDCl3, TMS, 400 MHz): 1.19 (t, 6H, J=7.2 Hz, -P-OCH2-CH3), 1.34 (t, 6H, J=7.2Hz, -P-
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OCH2-CH3), 2.36 (s, 6 H, Ar-CH3), 3.70-3.80 (m, 2H, -P-OCH2-CH3), 3.96-4.05 (m, 2H, -P-
OCH2-CH3), 4.13-4.23 (m, 4 H, -P-OCH2-CH3), 4.81( d, 2H, J=23.6 Hz,-CHP), 4.90 (br,
2H,NH), 6.67 (d, 4H, J=8.4, Ar), 7.20 (d, 4H, J=6.4, Ar), 7.33 (d, 4H, J=8.4, Ar), 7.43 (d, 4H,
3
J=6.4, Ar);13C NMR (CDCl3, TMS, 100 MHz): 16.2 (d, Jcp= 6 Hz, -P-OCH2-CH3), 16.5 (d,
3Jcp= 6 Hz, -P-OCH2-CH3), 21.1 (Ar-CH3), 55.9 (d, 1Jpc= 150 Hz, CHP), 63.2 (d, 2Jpc=10 Hz, -P-
2
OCH2-CH3), 63.3 (d, Jpc=10 Hz, -P-OCH2-CH3), 114.1( C2), 129.1(C2´), 131.4 (C3), 132.8
(C3´), 137.6 (C4), 145.9 (C1´), 146.4 (4´), 148.0 (C1);31P (162.5 MHz, CDCl3, TMS): 22.9 ppm.
MS (EI) m/z: 664.28 (M+), 506, 368; Elemental analysis for C36H46N2O6P2 requires C, 65.03; H,
6.98; N, 4.21. Found: C, 64.80; H, 6.88; N, 4.03%.
Tetraethyl (1, 4-phenylene bis(azanediyl)) bis(4-(dimethylamino)phenyl)methylene]))
diphosphonate (4f)
Solid, Yield: 94%, m.p: 155-156ºC. IR (νmax, cm−1): 3297 (NH),1233 (P=O), 1057 (P-OEt);1H
NMR (CDCl3, TMS, 400 MHz): 1.13 (t, 6 H, J=8.2, -P-OCH2-CH3), 1.27 (t, 6 H, J=7.2Hz, -P-
OCH2-CH3), 2.98(s, 12 H, -N(CH3)2), 3.65-3.71 (m, 2H, -P-OCH2-CH3), 3.89-3.95 (m, 2H, -P-
OCH2-CH3), 4.04-4.11 (m, 4 H, -P-OCH2-CH3), 4.53 (d, 2H, J=23.2 Hz, -CHP), 4.66 (br, 2H,
NH), 6.43(s, 4H, Ar), 6.69 (d, 4H, J=8.4 Hz, Ar), 7.27 (d, 4H, J=8.4 Hz, Ar); 13C NMR (CDCl3,
3
3
TMS, 100 MHz): 16.2( d, Jcp=6.1 Hz, -P-OCH2-CH3), 16.3( d, Jcp= 6.1Hz, -P-OCH2-
1
2
CH3),41.3(NCH3), 55.5 (d, Jpc= 151 Hz, CHP), 63.3 (d, Jpc=8.7 Hz, -P-OCH2-CH3), 63.4 (d,
2
2Jpc=8.7 Hz, -P-OCH2-CH3), 112.5 (C3´), 123.0 (C2), 128.3 (d, Jpc=7, C1´), 132.4 (C2´), 146.2
3
(d, Jcp= 13 Hz, C1), 148.0 ( C4´);31P (162.5 MHz, CDCl3, TMS ): 23.0 ppm. MS (EI) m/z:
646.30 (M+), 508, 370; Elemental analysis for C32H48N4O6P2 requires C, 59.43; H, 7.48; N, 8.66.
Found: C, 59.35; H, 7.41; N, 8.42%.
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Tetraethyl (1, 4-phenylene bis (azanediyl)) bis (4-(diethylamino) phenyl) methylene]))
diphosphonate (4g)
Solid, Yield: 92%, m.p: 150-151ºC.IR (νmax, cm−1): 3301 (NH), 1236 (P=O), 1064 (P-OEt);1H
NMR (CDCl3, TMS, 400 MHz): 1.13 (t, 12H, J=7.2Hz, -P-NCH2-CH3),1.31 (t, 6H, J= 7.0 Hz, -
P-OCH2-CH3), 1.16 (t, 6H, J= 8 Hz, -P-OCH2-CH3), 3.33 (q, 8H, J = 7.0 Hz, -P-NCH2-CH3),
3.66-4.73 (m, 2H, -P-OCH2-CH3), 3.91-3.98 (m, 2H, -P-OCH2-CH3), 4.07-4.17 (m, 4H, -P-
1
2
OCH2-CH3), 4.60 (2H, dd, JPH = 23 Hz, JPH = 7.2 Hz, CHP), 4.78 (br, 2H, NH), 6.52 (s, 4H,
Ar), 6.63 (d, 4H, J=8.2 Hz, Ar), 7.21 (d, 4H, J=8.2 Hz, Ar);13C NMR (CDCl3, TMS, 100
3
3
MHz):12.5(-NCH2CH3), 16.3 (d, Jcp= 5.6 Hz, -P-OCH2-CH3), 16.5 (d, Jcp= 5.6 Hz, -P-OCH2-
1
2
CH3), 44.3(-NCH2CH3), 55.3 (d, Jpc= 152.15 Hz, CHP), 63.0 (d, Jpc=7 Hz, -P-OCH2-CH3),
2
63.3(d, Jpc=7 Hz, -P-OCH2-CH3), 109.0 (C3´), 111.8 (C2), 115.5 ( C1´), 120.9 (C2´), 131.8
(C1), 147.5 (C4´);31P (162.5 MHz, CDCl3, TMS): 23.1 ppm. MS (EI) m/z: 702.80 (M+), 564,
426; Elemental analysis for C36H56N4O6P2 requires C, 61.52; H, 8.03; N, 7.97. Found: C, 61.20;
H, 7.95; N, 7.86%.
Tetraethyl (1,4-phenylene bis(azanediyl)) bis(p-methoxy methylene) diphosphonate (4h)
Solid, Yield: 96%, m.p: 158-159ºC. IR (νmax, cm−1): 3303 (NH), 1232(P=O), 1051 (P-OEt);1H
NMR (CDCl3, TMS, 400 MHz): 1.13 (t, 6H, J=7.20, -P-OCH2-CH3), 1.27 (t, 6H, J=7.20, -P-
OCH2-CH3), 3.68-3.74 (m, 2H, -P-OCH2-CH3), 3.78 (s, 6 H, Ar(CH3)2), 3.89-3.93 (m, 2 H, -P-
OCH2-CH3), 3.94-3.97 (m, 4H, -P-OCH2-CH3), 4.36 (br, 2H, NH), 4.59 ( d, 2H, J=23.6, -CHP),
1
6.43 (s, 4H, Ar), 6.85 (d, 4H, J=8.4, Ar), 7.34 (dd, 4H, JPH=8.4 Hz, 2JPH=2.4 Hz, Ar);13C NMR
3
3
(CDCl3, TMS, 100 MHz): 16.2 (d, Jcp= 6 Hz, -P-OCH2-CH3), 16.4 (d, Jcp= 6Hz, -P-OCH2-
CH3), 55.2 (Ar-OCH3), 56.4 (d, 1Jpc= 151 Hz, CHP), 63.0 (d, 2Jpc=7 Hz, -P-OCH2-CH3), 63.1 (d,
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3
2Jpc=7 Hz, -P-OCH2-CH3), 113.9 ( C3´), 115.5 (C2), 128.0 (C2´), 128.9 (C1´), 139.0 (d, Jpc= 3
Hz, C1), 159.2(C4´); 31P (162.5 MHz, CDCl3, TMS): 24.0 ppm. MS (EI) m/z: 620.24 (M+), 482,
368; Elemental analysis for C30H42N2O8P2 requires C, 58.06; H, 6.82; N, 4.51. Found: C, 57.96;
H, 6.78; N, 4.44%.
Tetraethyl (1,4-phenylene bis(azaneiyl)) bis(4-(isopropyl)phenyl)methylene]))
diphosphonate (4i)
1
Solid, Yield: 85%, m.p: 156-157ºC. IR (νmax, cm−1)3300 (NH), 1232 (P=O), 1033 (P-OEt); H
NMR (CDCl3, TMS, 400 MHz): 1.09-1.29 (m, 12H, POCH2CH3, 12H, CH(CH3)2), 2.86-2.88
(m, 2H, CH(CH3)2) 3.68-4.14 (m, 8 H, POCH2CH3), 4.78 (d, 2H, J=24 Hz, CHP), 4.55 (br, 2H,
3
NH), 6.63 (s, 4H, Ar), 7.19-7.85 (m, 8H, Ar);13C NMR (CDCl3, TMS, 100 MHz): 16.0 (d, Jcp=
3
5.5 Hz, -P-OCH2CH3), 16.3 (d, Jcp= 5.5 Hz, -P-OCH2CH3), 22.3 (-CH(CH3)2), 31.6 (-
CH(CH3)2), 55.3 (d, 1Jpc= 151 Hz, CHP), 63.2 (d, 2Jpc=8 Hz, -P-OCH2CH3), 63.3 (d, 2Jpc=8 Hz, -
3
P-OCH2CH3), 115.9 (C2), 117.4 (C3´), 126.19 (C2´), 129.2 (C1´), 142.0 (d, Jpc= 4 Hz, C1),
158.1 (C4´);31P (162.5 MHz, CDCl3, TMS): 23.3 ppm. MS (EI) m/z: 644.72 (M+), 506, 368;
Elemental analysis for C34H50N2O6P2 requires C, 63.34; H, 7.82; N, 4.35. Found: C, 63.20; H,
7.70; N, 4.10%.
Tetraethyl (1,4-phenylene bis(azanediyl)) bis(4-( p-tolylmethylene)methylene]))
diphosphonate (4j)
1
Solid, Yield: 86%, m.p: 162-163ºC. IR (νmax, cm−1): 3290 (NH), 1236 (P=O), 1068 (P-OEt); H
NMR (CDCl3, TMS, 400 MHz): 1.15( t, 6H, J=7.2 Hz, POCH2CH3), 1.31( t, 6H, J=7.2Hz,
POCH2CH3), 2.14 (s, 6 H, Ar-CH3), 3.65-3.71 (m, 2 H, POCH2CH3), 3.92-3.98(m, 2 H,
POCH2CH3), 4.01-4.18 (m, 4 H, POCH2CH3), 4.62( d, 2H, J=24.2 Hz, CHP), 4.80 (br, 2H, NH),
17
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6.50(s, 4H, Ar), 6.70 (d, 4H, J=7.6 Hz, Ar), 7.25 (d, 4H, J=7.6 Hz, Ar);13C NMR (CDCl3, TMS,
100 MHz): 16.2(d, 3Jcp= 6 Hz, -P-OCH2CH3), 16.5 (d, 3Jcp= 6 Hz, -P-OCH2CH3), 30.5 (Ar-CH3),
1
2
2
55.3(d, Jpc= 152 Hz, CHP), 63.0(d, Jpc=10 Hz, -P-OCH2CH3), 63.3(d, Jpc=10 Hz, -P-
2
3
OCH2CH3), 109.8 (C2), 112.5 (C2´), 115.56 (C3´), 128.0 (d, JPC = 5 Hz, C1´), 131.8 (d, JPC
=
15 Hz, C1), 145 (C4´);31P (162.5 MHz, CDCl3, TMS ): 23.0 ppm. MS (EI) m/z: 588.12 (M+),
450, 312; Elemental analysis for C30H42N2O6P2 requires C, 61.22; H, 7.19; N, 4.76. Found: C,
61.05; H, 7.10; N, 4.60%.
Conclusion
In conclusion, we have designed and synthesized an AIL based on benzimidazolium cations and
have successfully used it as a catalyst for the one-pot synthesis of α-aminophosphonate and
bis(α- aminophosphonate). The remarkable feature of this new catalyst is its ethyleneoxy bridge
which participates in dissolving organic compounds. The application of this AIL is studied in a
new one-pot method for the synthesis of α-aminophosphonate and bis(α- aminophosphonate)
derivatives under solvent-free conditions. The advantages offered by this protocol include
reusability of the catalyst, high conversion, short reaction time, and simple experimental
procedure
Acknowledgment:
We are grateful to Ferdowsi University of Mashhad Research Council for their financial support
of this work (GN: 3/25468).
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NH2
O
OEt
OEt
H
P
N
R2
H
R1
R2
AIL( 10 mol %),
Solvent free, 50°C
CHO
O
3a-3j
P OEt
OEt
+
H
EtO
EtO
R1
OEt P O O P EtO
X
N
H
N
H
X
R1
R1
H2N
NH2
4a-4j
compound
3a
4-OCH3
4-Cl
3b
3c
4-NO2
4-Cl
4c
3d
H
3e
4-Cl
H
3f
3-Cl
H
3g
3h
3i
H
H
4i
3j
4-OCH3
H
R1
4-CH3
4-Cl
4b
4-NO2
H
3-NO2
H
R2
compound
X
4-Cl
4d
4a
4e
4f
4g
4h
4j
R1
4-N(CH3)2 4-N(Et2)2
4-OCH3
4-CH(CH3)2
4-CH3
4-N(CH3)2 4-N(Et2)2
4-OCH3
4-CH(CH3)2
4-CH3
Scheme 1Three-component reaction of aromatic aldehydes with amines and diethylphosphite in
AIL.
24
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H
N
N
KOH
O
Cl
O
2
+
N
Cl
O
N
O
N
DMSO,
24 h,70°C
N
1
SO3H
Cl
N
dry CH2Cl2
1 h
N
O
N
O
N
N
+
2 ClSO3H
O
N
O
N
N
Cl
SO3H
2
Scheme 2 Synthesis of acidic ionic liquid
25
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Table 1 Calculation of the Hammett acidity function (H0) for AIL
Entry catalyst Amax [I]% [HI+]% H0
1
2
-------- 2.80 100
AIL 1.84 65
0
-----
1.25
35
Table 2. Optimization of reaction conditions for preparation of α-aminophosphonate (3a)
Entry
Catalyst (mol %) Temperature(ºC)
Time(h) Isolated Yield (%)
1
2
-
-
rt
24
24
20
30
50ºC
3
4
5
6
7
8
5
rt
1
1
1
1
1
1
55
60
50
75
96
80
10
20
5
rt
rt
50ºC
50ºC
50ºC
10
20
Reaction conditions: 4-methoxy benzaldhyde (1.0 mmol), 4- chloroaniline (1.0 mmol), diethyl
phosphite (1.0 mmol), and AIL as a catalyst.
26
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Table 3 Results of α-aminophosphonate derivatives synthesis using AIL (2)
Entry
3a
R1
R2
time
1
Yield %
94
Mp(ºC)
101-10236
98-9938
4-OCH3
4-CH3
4-Cl
4-Cl
1.5
92
3b
4-NO2
H
4-Cl
4-Cl
H
2
1.5
2
96
90
95
94-95
105-10639
77-8036
3c
3d
3e
4-Cl
3-Cl
4-NO2
3-NO2
4-OCH3
H
H
H
H
1
88
90
92
85
88-9023
126-12736
98-9936
3f
3g
3h
3j
1.5
2
2.5
100-10236
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Table 4 Results of bis α-aminophosphonate derivatives synthesis using AIL (2)
Entry
4a
4b
4c
R1
Time(h) Yiled % Mp(ºC)
1.5
2
92
88
96
90
90
94
92
96
85
86
161-162
158-159
156-157
160-161
148-149
155-156
150-151
158-15940
156-157
162-16340
4-N(CH3)2
4-N(Et)2
4-OCH3
1
4-CH(CH3)2
4-CH3
2
4d
4e
3
4-N(CH3)2
4-N(Et)2
4-OCH3
2.5
1.5
0.45
4f
4g
4h
4i
4-CH(CH3)2 3.5
4-CH3 1.5
4j
Table 5 Reported synthetic methods for the synthesis of α-aminophosphonate (3a)
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entry
catalyst
Solvent
Temperature( ºC)
Time(h)
24
Yield (%)
78
Ref.
41
1
2
3
organocatalyst
Fe/SWCNTs
ethanol
rt
36
42
Solvent free
50ºC
50ºC
2.5
93
Sodium Dodecyl H2O
Sulfate (SDS)
15 min 95
43
4
5
[psmim][HSO4]
AIL
H2O
rt
1
1
81
94
Solvent free
50ºC
This work
Table 6 Recyclability of AIL
Reusabilitya
Yield (%)b
AIL
94
Run 1
92
Run 2
90
Run 3
90
Run 4
86
aReusability of the recovered catalyst
1-4Reusability of the recovered catalyst in new runs from run 1 to run 4
b Isolated yields
29
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