Xanthan sulfuric acid as an efficient biodegradable and recyclable catalyst for the one-pot synthesis of α-amino phosphonates

Article abstract of DOI:10.1002/jccs.201000194

A convenient and efficient procedure for the synthesis of α-amino phosphonates by a one-pot, three-component condensation of aldehydes, amine, and diethyl phosphite in the presence of xanthan sulfuric acid as a bio-supported catalyst under solvent-free conditions has been developed. A wide range of α-amino phosphonates have been obtained in high to excellent yields. Furthermore, the catalyst can be recovered simply and reused several times in subsequent reactions.

Full text of DOI:10.1002/jccs.201000194

Journal of the Chinese Chemical Society, 2010, 57, 1315-1320
1315
Xanthan Sulfuric Acid as an Efficient Biodegradable and Recyclable
Catalyst for the One-pot Synthesis of a-Amino Phosphonates
Guo-Ying Sun (
Jun Lu (
Tuo Xue (
), Jun-Tao Hou (
), Jing-Jie Dou (
),
),
), Yong-Jie Hou (
) and Zhan-Hui Zhang* (
)
The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050016, China
A convenient and efficient procedure for the synthesis of a-amino phosphonates by a one-pot,
three-component condensation of aldehydes, amine, and diethyl phosphite in the presence of xanthan sul-
furic acid as a bio-supported catalyst under solvent-free conditions has been developed. A wide range of
a-amino phosphonates have been obtained in high to excellent yields. Furthermore, the catalyst can be re-
covered simply and reused several times in subsequent reactions.
Keywords: Xanthan sulfuric acid; a-Aminophosphonates; One-pot synthesis; Aldehyde; Amine;
Diethylphosphite; Solvent-free.
INTRODUCTION
The great importance of a-amino phosphonates is
zine,34 b-cyclodextrin,35 mesoporous aluminosilicate nano-
cage,36 silica sulphuric acid37 Amberlite-IR 12038 as well as
heteropolyacids39 have been reported to promote this trans-
formation. However, these approaches have some disad-
vantages such as the use of expensive, moisture sensitive
and toxic catalysts, relatively long reaction times and the
use of harmful volatile organic solvent. Thus, there is still
the need to develop an efficient, mild and environmentally
benign protocol for the synthesis of a-amino phosphonates.
Recently, several biopolymers have been utilized as a
support for catalytic applications in organic synthesis as
they are biodegradable materials and renewable re-
sources.40-42 Among the various biopolymers, particularly,
xanthan has received much attention because it is the most
abundant bacterial exopolysaccharide in the world, which
is produced through fermentation. Unlike other gums, it is
very stable under a wide range of temperatures and pH val-
ues. Xanthan sulfuric acid can be easily prepared by the re-
action of xanthan with chlorosulfonic acid and it has been
reported as an efficient catalyst for the synthesis of a-ami-
no nitriles.43 In continuation of our work on the develop-
ment of new synthetic methods,44-47 we report for the first
time a facile and efficient synthetic strategy for the prepara-
tion of a-amino phosphonates using xanthan sulfuric acid
as a biodegradable and recyclable solid acid catalyst under
solvent-free conditions (Scheme I).
based on their structural analogues of the corresponding
a-amino acids and their presence in a number of biologi-
cally active compounds.1-3 Furthermore, it has been re-
ported that these compounds are used as enzyme inhibitors,
herbicids, insecticides, fungicides, antibiotics, pharmaco-
logical agents.4,5 Therefore it is not surprising that research
on their synthesis has received special attention.6-9 The
known method of their synthesis includes a two-step reac-
tion: the formation of imines from aldehydes and amines
(first step) and the nucleophilic addition of phosphites with
imines (second step), which obtains the desired a-amino
phosphonates.10,11
Currently, multicomponent reactions (MCRs) have
been rapidly developed because such reactions offer a wide
range of possibilities for the efficient construction of
highly complex molecules in a single procedural step, and
make the synthesis simpler and more environmentally
friendly.12-21 Recently, the synthesis of a-amino phospho-
nates by three-component coupling of aldehydes, amine,
and diethyl phosphite in the presence of an acid or a base
catalyst has been developed. A variety of catalysts that in-
clude In(OTf)3,22 InCl3,23 Al(H2PO4)3,24 LiClO4,25
Mg(ClO4)2,26 ZrOCl2·8H2O,27 SnCl2,28 BiCl3,29 TiO2,30
ZnO,31 NBS,32 PPh3,33 metallotetrapyridinoporphyra-
* Corresponding author. E-mail: zhanhui@126.com

1316 J. Chin. Chem. Soc., Vol. 57, No. 6, 2010
Sun et al.
Table 1. Optimization of reaction conditions for the synthesis of
Scheme I
4g
O
P
R1
R2
O
R1
H
H
xanthan sulfuric acid
solvent-free, 60 o
O
Amount of
catalyst (g)
Temperature
(oC)
Time
(min)
Yield (%)a
O
NH
P
+
R2NH2
+
Entry
O
O
C
O
2
4
1
3
1
2
3
4
5
6
7
8
9
no
60
60
60
60
60
60
25
40
50
60
80
60
60
60
50
120
60
60
30
45
95
95
95
95
5
0.02
0.04
0.06
0.08
0.10
0.04
0.04
0.04
RESULTS AND DISCUSSION
In the initial experiments, in order to evaluate the cat-
alytic efficiency of xanthan sulfuric acid in this three-com-
ponent reaction, reaction of 2-methoxybenzaldehyde, ani-
line and diethyl phosphate was selected as model. It
showed that only 30% of product could be obtained when a
mixture of 2-methoxybenzaldehyde, aniline and diethyl
phosphate was heated at 60 oC for 1 h in absence of catalyst,
which indicated that the catalyst should be necessary for
this transformation. The effect of amount of catalyst on the
yield and rate was also investigated. It was found that the
use of 0.04 g catalyst is sufficient to promote the reaction.
The fewer amounts gave a low yield even after long reac-
tion time, and the more amounts did not affect the effi-
ciency of this transformation. Meanwhile, we also tested
the effect of reaction temperature on this reaction. When
the reaction was carried out at room temperature, only trace
product was obtained (Table 1, entry 7). When the tempera-
ture was increased to 60 oC, the reaction proceeded smoothly
and maximum yield was obtained.
50
93
a Isolated yields.
pleted after 40-60 min affording corresponding a-amino-
phosphonates in good to excellent yields. No competitive
side reactions such as aromatic nucleophilic substitution of
halogen atom, nucleophilic cleavage of the O-Me group, or
decomposition of acid sensitive substrates were observed.
Encouraged by the above interesting results, we also
attempted to synthesis bis(a-aminophosphonate) to further
broaden the scope of this three-component reaction. To our
delight, the reactions of isophthalaldehyde with two equiv-
alents of 4-bromoaniline or benzene-1,4-diamine with two
equivalents of benzaldehyde resulted in formation of the
desired bis(a-aminophosphonates) (Scheme II) in high
yields under similar condition.
After optimization of the conditions, to delineate this
approach, we carried out this three-component coupling re-
action of a series of aldehydes, aromatic amines and diethyl
Finally, the recyclability of the catalyst was investi-
gated. After reaction, the catalyst can be easily separated by
simple filtration, washing with ethyl acetate, and drying in
a vacuum oven at 60 oC for 3 h. The recovered catalyst can
o
phosphate under solvent-free conditions at 60 C in the
presence of xanthan sulfuric acid. The reactions were com-
Scheme II
O
O
O
O
O
P
P
O
NH2
NH
HN
OHC
CHO
+ 2
O
H
xanthan sulfuric acid
solvent-free, 60 oC
P
+
2
O
O
4ad
Br
3
Br
Br
O
P
NH2
H
N
CHO
O
O
H
xanthan sulfuric acid
solvent-free, 60 oC
O
P
O
P
+
+ 2
O
2
O
O
N
H
O
NH2
4ae
3

Synthesis of a-Amino Phosphonates
J. Chin. Chem. Soc., Vol. 57, No. 6, 2010 1317
be reused for model reaction at least three additional times
in subsequent reaction without significant decrease in
product yields (95%, 94%, and 90%).
relatively short reaction times, high yields, mild reaction
conditions and the absence of organic solvent, which make
it a useful alternative to existing methods.
In conclusion, we have developed a new one-pot syn-
thesis of a-amino phosphonates by the reaction of alde-
hydes, amine, and diethyl phosphate using xanthan sulfuric
acid as an efficient, eco-friendly, reusable and biodegrad-
able catalyst. The advantages of the present procedure are
EXPERIMENTAL SECTION
Melting points were obtained with an X-4 apparatus.
IR spectra were recorded on a Shimadzu FTIR-8900 spec-
trometer. NMR spectra were taken with a Bruker DRX-500

1318 J. Chin. Chem. Soc., Vol. 57, No. 6, 2010
Sun et al.
spectrometer at 500 MHz (1H) and 125 MHz (13C) using
CDCl3 as the solvent. Elemental analysis was determined
on a Vario EL III CHNOS elemental analyzer.
(t, J = 7.0 Hz, 3H), 1.38 (t, J = 7.0 Hz, 3H), 3.96-4.19 (m,
6H), 6.32 (dd, J = 27.0 , 7.5 Hz, 1H), 6.77 (d, J = 9.0 Hz,
1H), 7.06 (dd, J = 9.0, 2.5 Hz, 1H), 7.47 (t, J = 8.0 Hz, 1H),
7.58 (t, J = 8.0 Hz, 1H), 7.65 (d, J = 8.0 Hz, 1H), 7.67 (d, J =
2.5 Hz, 1H), 8.05 (d, J = 8.0 Hz, 1H), 8.82 (dd, J = 10.5, 7.5
Hz, 1H); dC 14.6, 16.1 (d, 3JPC = 5.5 Hz), 16.3 (d, 3JPC = 5.5
Hz), 50.1 (d, 1JPC = 150.2 Hz), 63.6 (d, 2JPC = 7.0 Hz), 63.9
(d, 2JPC = 6.9 Hz), 64.2, 108.8, 115.8, 125.4, 127.0, 128.5
(d, JPC = 4.5 Hz), 128.9 (d, JPC = 4.0 Hz), 130.9 (d, JPC = 3.3
Hz), 133.0, 138.5 (d, JPC = 13.6 Hz), 149.1 (d, JPC = 5.2
Hz), 150.2; Anal. calcd. For C19H24N3O8P: C, 50.33; H,
5.34; N, 9.27. Found: C, 50.15; H, 5.60; N, 9.09.
Preparation of xanthan sulfuric acid
The preparation of xanthan sulfuric acid was carried
out following a reported procedure.43 To a magnetically
stirred suspension of xanthan (5.0 g) in CHCl3 (15 mL),
o
chlorosulfonic acid (1.00 g) was added dropwise at 0 C
during 2 h. HCl gas was removed from the reaction vessel
immediately. After completion of the addition, the mixture
was stirred for 3 h. Then, the mixture was filtered and
washed with methanol (25 mL) and dried at room tempera-
ture to obtain xanthan sulfuric acid as white powder (5.30
g).
[Anthracen-9-yl-(4-bromophenylamino)-methyl]-phos-
phonic acid diethyl ester (4aa)
General procedure for the preparation of a-amino-
phosphonates
Yellow crystals; IR (KBr): 3323, 1593, 1508, 1487,
1242, 1070, 954, 862, 779 cm-1; dH 0.62 (t, J = 7.0 Hz, 3H),
1.35 (t, J = 7.0 Hz, 3H), 3.21-3.29 (m, 1H), 3.67-3.74 (m,
1H), 4.20-4.26 (m, 2H), 5.21 (br s, 1H), 6.27 (d, J = 27.0
Hz, 1H), 6.33 (d, J = 9.0 Hz, 2H), 6.98 (d, J = 9.0 Hz, 2H),
7.41 (t, J = 7.5 Hz, 1H), 7.49 (t, J = 9.0 Hz, 1H), 7.52 (t, J =
8.0 Hz, 1H), 7.63 (t, J = 8.0 Hz, 1H), 7.94 (d, J = 8.0 Hz,
1H), 8.03 (d, J = 8.0 Hz, 1H), 8.41 (s, 1H), 8.42 (d, J = 8.0
Hz, 1H), 8.98 (d, J = 9.0 Hz, 1H); dC 15.8(d, 3JPC = 5.8 Hz),
16.6 (d, 3JPC = 5.6 Hz), 52.9 (d, 1JPC = 152.3 Hz), 63.1 (d,
2JPC = 7.0 Hz), 63.5 (d, 2JPC = 6.9 Hz), 109.8, 114.9, 122.5,
124.8, 125.2, 126.1, 126.2, 127.1, 129.2 (d, JPC = 4.5 Hz),
129.3, 129.9, 130.3 (d, JPC = 4.1 Hz), 130.6 (d, JPC = 8.5
To a mixture of aldehyde (1 mmol), amine (1 mmol),
and diethylphosphite (1 mmol), xanthan sulfuric acid (0.04
g) was added and the mixture was heated at 60 oC for an ap-
propriate time as indicated by TLC. The mixture was
cooled to room temperature and ethyl acetate (15 mL) was
added. The catalyst was filtered and washed with ethyl ace-
tate. The solvent was evaporated to give the crude product.
The crude product was purified by flash chromatography
(ethyl acetate/petroleum ether, 1:20) to afford the pure
product.
[(2-Nitrophenyl)-(4-nitrophenylamino)-methyl]-phos-
phonic acid diethyl ester (4v)
Hz), 131.2 (d, JPC = 1.8 Hz), 131.8, 131.9, 145.9 (d, JPC
=
Yellow crystals; IR (KBr): 3269, 1600, 1533, 1508,
1488, 1315, 1284, 1234, 1112, 1018, 950, 858 cm-1; dH 1.13
(t, J = 7.0 Hz, 3H), 1.33 (t, J = 7.0 Hz, 3H), 3.79-3.87 (m,
1H), 3.94-4.02 (m, 1H), 4.17-4.25 (m, 2H), 6.25 (dd, J =
26.0, 8.5 Hz, 1H), 6.41 (t, J = 8.5 Hz, 1H), 6.72 (d, J = 9.5
Hz, 2H), 7.49 (t, J = 7.5 Hz, 1H), 7.55 (t, J = 7.5 Hz, 1H),
7.23 (d, J = 7.5 Hz, 1H), 8.03 (d, J = 9.5 Hz, 2H), 8.05 (d, J
= 7.5 Hz, 1H); dC 15.9 (d, 3JPC = 5.5 Hz), 16.4 (d, 3JPC = 5.6
Hz), 49.7 (d, 1JPC = 151.1 Hz), 63.9 (d, 2JPC = 7.3 Hz), 64.1
13.4 Hz); Anal. calcd. For C25H25BrNO3P: C, 60.25; H,
5.06; N, 2.81. Found: C, 60.06; H, 4.92; N, 3.00.
[Anthracen-9-yl-(4-nitrophenylamino)-methyl]-phos-
phonic acid diethyl ester (4ab)
Yellow crystals; IR (KBr): 3313, 1596, 1508, 1477,
1311, 1286, 1228, 1112, 954, 864, 783 cm-1; dH 0.88 (t, J =
7.5 Hz, 3H), 1.25 (t, J = 7.5 Hz, 3H), 1.27 (t, J = 7.5 Hz,
3H), 3.51-3.59 (m, 1H), 3.78-3.94 (m, 3H), 4.07-4.18 (m,
2H), 6.38 (dd, J = 9.5 Hz, 1H), 6.45 (dd, J = 27.0, 6.0 Hz,
1H), 6.69 (dd, J = 9.0, 2.5 Hz, 1H), 7.42 (t, J = 7.5 Hz, 1H),
7.51-7.55 (m, 3H), 7.68 (t, J = 9.0 Hz, 1H), 7.95 (t, J = 8.0
Hz, 1H), 8.07 (d, J = 8.0 Hz, 2H), 8.46 (s, 1H), 8.47 (d, J =
8.0 Hz, 1H), 8.93 (d, J = 8.0 Hz, 1H), 9.41 (d, J = 9.0 Hz,
1H); dC 15.9 (d, 3JPC = 5.5 Hz), 16.4 (d, 3JPC = 5.4 Hz), 49.7
2
(d, JPC = 7.1 Hz), 112.5, 125.4 (d, JPC = 2.1 Hz), 126.2,
128.7 (d, JPC = 4.5 Hz), 129.1 (d, JPC = 3.1 Hz), 130.6,
133.6, 139.4, 149.3 (d, JPC = 5.3 Hz), 151.4 (d, JPC = 13.5
Hz); Anal. calcd. For C17H20N3O7P: C, 49.88; H, 4.92; N,
10.27. Found: C, 50.02; H, 5.15; N, 10.08.
[(4-Ethoxy-3-nitrophenylamino)-(2-nitrophenyl)-meth-
yl]-phosphonic acid diethyl ester (4w)
(d, 1JPC = 151.1 Hz), 63.9 (d, 2JPC = 7.2 Hz), 64.1 (d, 2JPC
=
7.1 Hz), 112.4, 125.4, 125.5, 126.2, 128.7 (d, JPC = 4.5 Hz),
129.2 (d, JPC = 3.1 Hz), 130.6, 130.7, 133.6, 139.4, 149.3
(d, JPC = 5.3 Hz), 151.4 (d, JPC = 13.5 Hz); For
C25H25N2O5P: C, 64.65; H, 5.43; N, 6.03. Found: C, 64.48;
Red-brown crystals; IR (KBr): 3355, 2977, 1616,
1569, 1525, 1475, 1425, 1357, 1263, 1217, 1184, 1112,
1045, 1020, 983, 873 cm-1; dH 1.28 (t, J = 7.0 Hz, 3H), 1.22

Synthesis of a-Amino Phosphonates
J. Chin. Chem. Soc., Vol. 57, No. 6, 2010 1319
H, 5.61; N, 5.86.
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1487, 1444, 1367, 1317, 1236, 1031, 962, 860, 796 cm-1;
dH 0.92 (t, J = 7.5 Hz, 6H), 1.27 (t, J = 7.5 Hz, 6H), 3.31-
3.39 (m, 2H), 3.69-3.77 (m, 2H), 4.12-4.14 (m, 4H), 4.67
(d, J = 24.0 Hz, 2H), 4.93 (s, 2H), 6.41 (d, J = 8.5 Hz, 4H),
7.12 (d, J = 8.5 Hz, 4H), 7.31 (t, J = 7.5 Hz, 1H), 7.37 (d, J =
7.5 Hz, 2H), 7.51 (s, 1H); dC 16.1(d, 3JPC = 5.5 Hz), 16.4(d,
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=
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ACKNOWLEDGMENT
We thank the National Natural Science Foundation of
China (20872025 and 21072042), the Nature Science
Foundation of Hebei Province (B2008000149), and the
Undergraduate Scientific and Technological Innovation
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