Natural phosphate modified with lithium nitrate: A new efficient catalyst for the construction of carbon-carbon, carbon-sulfur, and carbon-nitrogen bonds

Article abstract of DOI:10.1080/10426500601160397

The addition of small amounts of lithium nitrate to natural phosphate followed by calcination gives a new catalyst Li/NP (weight ratio LiNO3/NP = 1/15). This material showed catalytic activity in the Michael addition of amines, mercaptans, and active methylene compounds to chalcone derivatives with high yields under mild reaction conditions. Li/NP is used as the catalyst for a facile synthesis of -amino acids, -sulfur acids, and 4 H-chromenes under heterogeneous conditions. The usual, undesirable byproducts from the Michael condensation such as 1,2-addition, bis-addition, and polymerization compounds are not observed with this method. The work-up procedure is simplified by simple filtration with the use of Li/NP.

Full text of DOI:10.1080/10426500601160397

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Phosphorus, Sulfur, and Silicon
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Natural Phosphate Modified
with Lithium Nitrate: A
New Efficient Catalyst
for the Construction of
Carbon–Carbon, Carbon–Sulfur,
and Carbon–Nitrogen Bonds
Mohamed Zahouily a , Bahija Mounir a , Hind Cherki
a b , Bouchaib Bahlaouan a , Ahmed Rayadh a & Saïd
Sebti b
a Laboratoire de Catalyse, Chimiométrie et
Environnement, UFR de Chimie Appliquée,
Université Hassan II, Faculté des Sciences et
Techniques, Mohammadia, Maroc
b Laboratoire de Chimie Organique, Catalyse et
Environnement, Université Hassan II, Faculté des
Sciences, Ben M'Sik Casablanca, Maroc
Published online: 29 Aug 2007.
To cite this article: Mohamed Zahouily , Bahija Mounir , Hind Cherki , Bouchaib
Bahlaouan , Ahmed Rayadh & Saïd Sebti (2007): Natural Phosphate Modified with
Lithium Nitrate: A New Efficient Catalyst for the Construction of Carbon–Carbon,
Carbon–Sulfur, and Carbon–Nitrogen Bonds, Phosphorus, Sulfur, and Silicon and the
Related Elements, 182:6, 1203-1217
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Phosphorus, Sulfur, and Silicon, 182:1203–1217, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601160397
Natural Phosphate Modified with Lithium Nitrate: A New
Efficient Catalyst for the Construction of Carbon–Carbon,
Carbon–Sulfur, and Carbon–Nitrogen Bonds
Mohamed Zahouily
Bahija Mounir
Laboratoire de Catalyse, Chimiome´trie et Environnement,
UFR de Chimie Applique´e, Universite´ Hassan II, Faculte´ des Sciences
et Techniques, Mohammadia, Maroc
Hind Cherki
Laboratoire de Catalyse, Chimiome´trie et Environnement,
UFR de Chimie Applique´e, Universite´ Hassan II, Faculte´ des Sciences
et Techniques, Mohammadia, Maroc; and Laboratoire de Chimie
Organique, Catalyse et Environnement, Universite´ Hassan II, Faculte´
des Sciences, Ben M’Sik Casablanca, Maroc
Bouchaib Bahlaouan
Ahmed Rayadh
Laboratoire de Catalyse, Chimiome´trie et Environnement, UFR de
Chimie Applique´e, Universite´ Hassan II, Faculte´ des Sciences et
Techniques, Mohammadia, Maroc
¨
Saıd Sebti
Laboratoire de Chimie Organique, Catalyse et Environnement,
Universite´ Hassan II, Faculte´ des Sciences, Ben M’Sik Casablanca,
Maroc
The addition of small amounts of lithium nitrate to natural phosphate followed by
calcination gives a new catalyst Li/NP (weight ratio LiNO3/NP = 1/15). This ma-
terial showed catalytic activity in the Michael addition of amines, mercaptans, and
active methylene compounds to chalcone derivatives with high yields under mild
reaction conditions. Li/NP is used as the catalyst for a facile synthesis of β-amino
acids, β-sulfur acids, and 4 H-chromenes under heterogeneous conditions. The
usual, undesirable byproducts from the Michael condensation such as 1,2-addition,
bis-addition, and polymerization compounds are not observed with this method. The
work-up procedure is simplified by simple filtration with the use of Li/NP.
Keywords 4H-chromene; β-amino acid; β-sulfur acid; heterogeneous catalysis; lithium
nitrate; Michael addition; natural phosphate
Received May 4, 2006; accepted June 6, 2006.
Address correspondence to Mohamed Zahouily, Laboratoire de Catalyse, Synthese
et Environnement, UFR de Chimie Applique´e, Universite´ Hassan II, Faculte´ des Sci-
ences et Techniques, Mohammadia B.P. 7955, Casablanca 20650 Morocco. E-mail:
mzahouily@yahoo.fr
1203

1204
M. Zahouily et al.
INTRODUCTION
The use of environmentally benign reaction media is very important in
the view of today’s environmentally conscious attitude. The generation
of wastes is dramatically important in the case of the synthesis of fine
chemicals and pharmaceuticals, and they consist primarily of inorganic
salts formed in the reaction or in subsequent neutralization steps. In
this sense, heterogeneous catalysts1 under solvent-free conditions at
r.t. play an important role.
Various solid catalysts have been found useful in heteroge-
neous media, including Mg-Al-hydrotalcite,2 zeolite,3 aluminium
oxide,4 montmorillonite/NiBr2,5 synthetic phosphate Na2CaP2O7,6
fluoroapatite,7 and hydroxyapatite,8 and other solid catalysts were used
with more or less success.9 We previously reported that Natural Phos-
phate (NP) alone is capable of catalyzing the Michael addition.10 We
have also shown that doping with potassium fluoride10a and sodium
nitrate10b increases the activity of natural phosphate.
The pharmaceutical industry requires the development of useful
carbon–nitrogen bond-forming reactions exhibiting high yield and se-
lectivity, low cost, safety, operational simplicity, mild reaction condi-
tions, and reduced environmental problems.
Recently, Shaikh and coworkers11 have shown that kaolinitic clay12
or commercially available montmorillonite K1013 are excellent cata-
lysts for the addition of amines to α,β-unsaturated carbonyl compounds.
However, these catalysts are only suitable for activating aliphatic
amines toward addition to α,β-unsaturated carbonyl compounds and
they failed for the less nucleophilic aromatic amines. This encouraged
us to investigate the reaction with natural phosphate doped by lithium
nitrate.
In this work, we present a practical and novel phosphate-catalyzed
Michael-type addition reaction of aliphatic and aromatic amines, thi-
ols and active methylene compounds, with α,β-unsaturated carbonyl
compounds at r.t. (Schemes 1, 2, and 3).
SCHEME 1

Natural Phosphate Modified with Lithium Nitrate
1205
SCHEME 2
SCHEME 3
EXPERIMENTAL
Preparation of the Catalyst and Structural Characteristics
NP used in this work was obtained in the Khouribga region (it is
available in raw form or treated form from CERPHOS Casablanca,
Morocco).14 Prior to use, this material requires initial treatments such
as crushing and washing. For use in organic synthesis, NP is treated
by techniques involving attrition, sifting, calcinations (900◦C), wash-
ing, and recalcination. These treatments lead to a fraction between
100 and 400 µm that is rich in phosphate and has the chemical com-
position P2O5 (34.24%), CaO (54.12%), F− (3.37%), SiO2 (2.42%), SO3
(2.21%), CO2 (1.13%), Na2O (0.92%), MgO (0.68%), Al2O3 (0.46%), Fe2O3
(0.36%), K2O (0.04%) and several metals (Zn, Cu, Cd, V, U, and Cr)
in the ppm range. The structure of the material is similar to that of
fluoroapatite (Ca10(PO4)6F2),15 as shown by X-ray diffraction pattern
and chemical analysis.15 In sedimentary rocks, phosphates are formed
from compounds derived from apa◦tite b◦y partia◦l isomorphic substitu-
tion: Ca2+ ions by Na+, Mg2+, Co2 , Fe3 , or Al3 , PO43− ions by VO34−
,
SO42−, CO23− or MnO4−; and F− by −OH or Cl−. These different sub-
stitutions cause distortions of the structure which depends on the na-
ture and the radii of the ions involved. This solid presented a very

1206
M. Zahouily et al.
FIGURE 1 SEM images of (a) NP and (b) Li/NP.
low surface area Brunauer, Emmett and Teller (BET) at ca. 1 m2 g−1
,
and the total pore volume was 0.005 cm3 g−1
.
Li/NP has been prepared by adding 10 g of NP to an aqueous solution
of 0.667 g (9.7 mmol) of lithium nitrate. The mixture was stirred for 1
h at r.t. evaporated to dryness, and dried at 100◦C for 2 h. The solid
obtained was calcined at 900◦C for 1 h to give the catalyst Li/NP (weight
ratio LiNO3/NP = 1/15). The X-ray diffraction pattern of this catalyst
is similar to that of NP. The mercury porosimetry data showed the pore
diameter range 0.0035–400 µm. The total surface area and the total
intruded volume are 0.24 m2 g−1, and 0.0831 cm3 g−1, and 0.14 m2 g−1
,
and 0.728 cm3 g−1 for LiNO3/NP non-calcined and LiNO3/NP calcined
at 900◦C, respectively.
The morphology of the solids surface was observed in Scanning
Electron Micrograph (SEM) images of Li/NP in comparison with NP
(Figure 1). It clearly appears that some modifications have taken place
at the surface of the catalyst.
Typical Experimental Procedure
To a flask containing an equimolar mixture (1.5 mmol) of nucleophile
2,12, or 14 (Schemes 1, 2 and 3) and chalcone derivative 1 in methanol
(1.5 mL), phosphate catalyst (Li/NP, 0.1 g) was added, and the mix-
ture was stirred at r.t. until completion of the reaction, as monitored by
TLC. The reaction mixture was filtered, and the catalyst was washed
with dichloromethane (15 mL). After concentration of the filtrate un-
der reduced pressure, the residue was subjected to chromatography or
recrystallization (hexane/ethyl acetate = 9/1) leading to the Michael
adduct product, whose structure was verified by 1H-,and 13C NMR, IR
spectroscopies, and melting points.

Natural Phosphate Modified with Lithium Nitrate
1207
RESULTS AND DISCUSSION
Construction of a Carbon–Nitrogen Bond in the Presence
of Li/NP
Aniline and chalcone (X = H, Scheme 1) were chosen as model sub-
strates to determine suitable reaction conditions. First, we proceeded
to study the solvent effect in the synthesis of product 3a using the Li/NP
(0.1 g) catalyst.
In the cases of hexane, tetrahydrofuran, and dioxane, no product
formation was observed. The use of 2-propanol, ethanol, and methanol
gave, after 3 h of the reaction, 37%, 58%, and 92% yield of 3a, respec-
tively. It can be concluded that methanol is the best solvent for this
reaction. A similar solvent effect has been observed in the use of the
natural phosphate catalyst.10a In the absence of the solvent, no prod-
uct was observed but only the starting material was recovered. This
behavior indicates that some solvent is needed to facilitate the contact
between the reagents and active sites.
The analysis of the amount of solvent utilized showed that with 0.5–
1.5 mL of methanol, the best yield was obtained. An increase in the
volume up to 2 mL slightly decreases the reaction yield (79%), and this
dropped further to 44% when a volume of 5 mL was used (Figure 2).
A large solvent volume reduced the concentration, which explains the
yield lowering.
Next, the role of calcination temperature was examined. We have
found that LiNO3/NP calcined at 900◦C gave the best yields of 3a, while
only a 48% yield of this product was obtained with LiNO3/NP calcined at
500◦C. The uncalcined catalyst or those calcined at 150◦C or 300◦C are
inactive in this reaction. The calcination procedure possibly produces
FIGURE 2 Influence of methanol as a solvent in the synthesis 3a.

1208
M. Zahouily et al.
the decomposition of supported LiNO3 into Li2O, generating the basic
sites of the new catalyst Li/NP.
The use of combinations of natural phosphate and lithium hydroxide
as a catalyst gave to product 3a with a moderate yield (70%, 3 h). with
the presence of NP alone the yield in 3a was 32% (3 h).
As it is reported that Li2O in the presence of moisture regenerates
lithium hydroxide as a strong basic compound and when in contacts
with methanol it yields a basic solution, we suspected that the activa-
tion of reagents could be promoted by basic methanolic solution. To this
end we carried out the same reaction in the basic solution obtained after
filtration of a stirred suspension of LiNO3/NP calcined at 900◦C, and
no formation of compound 3a was observed; only the starting material
was isolated, confirming the important role of the catalyst surface in the
activation of the reagents. In the presence of 0.0063 g of LiNO3 alone
(the present quantity in LiNO3/NP: 1/15 catalyst), no 1,4-addition prod-
uct was observed under the reaction conditions, and only the starting
material was isolated.
To determine the scope and limitation of this reaction, the opti-
mum conditions were applied to other substrates as shown in Table I
(Scheme 1). All products were isolated and identified by 1H-, 13C-NMR,
and IR spectroscopies, and melting points.
In all cases, the use of a low amount of Li/NP calcined remarkably
increased the catalytic activity and decreased the reaction time in the
construction of a carbon–nitrogen bond (Table I). The yields were good
to excellent (70% to 97%, Table I) except in the case of the reaction
of benzylamine with Michael acceptor bearing a methoxy group (X =
MeO) in the para position, which afforded a moderate yield (60%) of the
1,4-addition product. Products of undesirable side reactions resulting
from 1,2-addition, polymerization, and bis-addition were not observed.
Synthesis of β-Amino Acid and β-Sulfur Acid
Naturally occurring β-amino acids are compounds with an interesting
pharmacological profile.16 They are also found as components in a wide
variety of biologically active compounds17 including peptides such as
bestatin18 and pepstatin.19 The β-amino acids are also useful precursors
in the synthesis of β-lactams.20
The β-amino carbonyl compound 3a is a direct precursor to β-amino
acids. Schemes 4 and 5 illustrate our approach wherein the starting
materials is 1,4-adduct 3. β-amino carbonyl 3a is converted to oxime
4a, in the presence of Li/NP catalyst in an excellent yield (90%). The
oxime 4a was subjected to the reaction induced by thionyl chloride,
and the chemoselective Beckmann rearrangement gave anilide 5a.

Natural Phosphate Modified with Lithium Nitrate
1209
TABLE I Construction of a Carbon–Nitrogen Bond by Michael
Addition Using NP and Li/NP as Catalysts
Yield (%) (Time [h])a
R
X
Products
NPb
Li/NP
90 (3)
H 3a
86 (6)
Cl 3b
Me 3c
71 (14)
76 (24)
85 (20)
90 (14)
95 (8)
OMe 3d
97 (12)
H 3e
Cl 3f
64 (24)
75 (24)
82 (20)
76 (8)
Me 3g
18 (24)
23 (24)
70 (24)
60 (24)
OMe 3h
aYields of pure products isolated by chromatography and recrystallized from
n-hexane/ethyl acetate. The products were identified by 1H NMR, 13C- NMR, IR
spectroscopy, and melting points.
bReference 10b.

1210
M. Zahouily et al.
SCHEME 4
SCHEME 5
Finally, after two steps, β-amino acid 7a was obtained in a good yield
(Scheme 4).
On the other hand, the reaction of ethyl acrylate with an excess of
benzylamine in the presence of Li/NP furnished β-amino ester 10 as the
sole product due to a mono addition reaction (Scheme 5). The reaction
of benzylamine with an excess of ethyl acrylate in the presence of Li/NP
gave bis-addition product 8 in an excellent yield. β-amino diester 8 is a
direct precursor of β-amino diacid 9, which has been used as starting
material for the synthesis of heterocyclic compounds21 and derivatives
of nicopecotic acids.22

Natural Phosphate Modified with Lithium Nitrate
1211
Construction of Carbon–Sulfur Bond in the Presence of Li/NP
Recently, conjugate addition of mercaptans to enones has attracted con-
siderable interest6−9 as it leads to the synthesis of biologically active
compounds such as the calcium antagonist diltiazem.23 Thus, a num-
ber of procedures either based on the activation of thiol by a base or
activation of acceptor olefins with Lewis acids have been developed.9,24
The optimized conditions for construction of a carbon–nitrogen bond
are efficiently applied to the construction of a carbon–sulfur bond.
Several α,β-unsaturated carbonyl compounds such as chalcone, p-
methoxychalcone, p-chlorochalcone, and p-methylchalcone as acceptors
were subjected to this reaction with Li/NP as a catalyst and thiophe-
nol, m-aminothiophenol or ethyl thioglycolate as the nucleophile thiol
(Scheme 2, Table II). In all cases the use of natural phosphate modified
by lithium nitrate (Li/NP) as a heterogeneous catalyst in the construc-
tion of a carbon–sulfur bond allowed the isolation of products 13 rapidly
(1–8 min) and with excellent yields (90–96%; Table II).
Except in one case, all combinations led to the selectivity of the corre-
sponding expected 1,4-adducts. No byproducts resulting from the unde-
sirable 1,2-addition and/or bis-addition side reactions (observed under
classical conditions in some cases) were observed. However, a reaction of
2-aminothiophenol with Michael acceptor bearing in the para position
a nitro group (X = NO2, Table II, entry 10) gave an 85/15 mixture of 1,4-
and 1,3-addition products. The product 13a (X = H, R = Ph, Scheme 2)
was converted to β-sulfur acid (anilide of 3-phenyl-3-sulfinylpropanoic
acid) 7b by different steps (Scheme 4).
Construction of a Carbon–Carbon Bond in the Presence
of Li/NP
Under the best conditions for the previously discussed reactions, the
use of NP doped by lithium nitrate increases remarkably the catalytic
activity and decreases the reaction time in the formation of a carbon–
carbon bond (Scheme 3; Table III).
In all cases, the use of Li/NP as a heterogeneous catalyst in the
Michael addition allowed the isolation of products 15 rapidly and with
excellent yields (88–94%; Table III), except in the case where the nucle-
ophile is nitromethane. In the presence of 0.0063 g of LiNO3 alone (the
present quantity in the LiNO3/NP: 1/15 catalyst), no 1,4-addition prod-
uct was observed under the reaction conditions, and only the starting
material was isolated. No by-product resulting from the undesirable
1,2-addition and/or bis-addition side reactions (observed under classi-
cal conditions in some cases) were observed. However, a reaction of

1212
M. Zahouily et al.
TABLE II Construction of a Carbon–Sulfur Bond by Michael
Addition Using NP and Li/NP as a Catalyst
Yield (%) (Time [h])a
R
X
Products
NPb
Li/NP
90 (3)
H 13a
95 (15)
Cl 13b
Me 13c
OMe 13d
NO2 13e
H 13f
96 (15)
95 (20)
92 (35)
91 (07)
97 (10)
93 (3)
96 (6)
94 (8)
92 (1)
93 (1)
Cl 13g
96 (10)
95 (1)
(Continued on next page)

Natural Phosphate Modified with Lithium Nitrate
1213
TABLE II Construction of a Carbon–Sulfur Bond by Michael
Addition Using NP and Li/NP as a Catalyst (Continued)
Yield (%) (Time [h])a
R
X
Products
NPb
Li/NP
92 (2)
Me 13h
91 (10)
OMe 13i
NO2 13j
90 (10)
90 (2)
90 (04)c
90 (<1)c
aYields in pure products isolated by recrystallization with AcOEt/CH2Cl2 or
distillation under vacuum and identified by 1H, 13C-NMR, and IR spectroscopies.
bReference 10a.
cReaction found 85% of 1,4-addition product and 15% of 1,3-addition product.
nitromethane with various α,β-unsaturated carbonyl compounds 1 at
65◦C gives traces of polymerization products (not isolated).
The reaction of salicylaldehyde 16 with an excess of malononitrile
gave 4H-chromene 17 in an excellent yield (Scheme 6).
SCHEME 6

1214
M. Zahouily et al.
TABLE III Construction of a Carbon–Carbon Bond by Michael
Addition Using NP and Li/NP
Yield (%) (Time [min])a
R
X
Y
Products
NPb
NP/Li
H
CN
CN 15a
95 (30)
94 (15)
Cl
CN
CN
CN
CN 15b
CN 15c
CN 15d
56 (40)c
94 (150)
79 (120)
92 (25)c
95 (35)
90 (45)
Me
OMe
H
CN
CN
CO2Me 15e
CO2Me 15f
95 (60)
46 (60)
94 (20)
90 (55)
Cl
Me
CN
CN
CO2Me 15g
CO2Me 15h
75 (240)
83 (240)
93 (65)
91 (98)
OMe
H
NO2
NO2
H 15i
H 15j
90 (180)b
50 (180)b
90 (40)b
91 (50)b
Cl
(Continued on next page)

Natural Phosphate Modified with Lithium Nitrate
1215
TABLE III Construction of a Carbon–Carbon Bond by Michael
Addition Using NP and Li/NP (Continued)
Yield (%) (Time [min])a
R
X
Y
Products
NPb
NP/Li
Me
NO2
H 15k
90 (180)b
92 (55)b
OMe
NO2
H 15l
60 (180)b
88 (65)b
aYields of pure products isolated by recrystallization with AcOEt/CH2Cl2 or
distillation under vacuum and identified by 1H, 13C-NMR, and IR spectroscopies.
bThe reaction mixture was stirred at 65◦C; traces of polymerization products
were observed.
cReference 15a.
In all cases, the use of NP doped by lithium nitrate (Li/NP) remark-
ably increases the catalytic activity and decreases the reaction time in
the construction of carbon–nitrogen, carbon–sulfur, and carbon–carbon
bonds (Tables I–III). For the catalytic activity of Li/NP in this Michael
addition, we speculate that the reaction occurs at the surface rather
than inside tunnels of the catalyst. The acidic character of the NP
surface25 probably induces the polarization of the C O bond and the
basic sites enhance the thiol nucleophilicity. Consequently, the S C or
C C bond formation is accelerated, and the final product is obtained af-
ter protonation of the resulting enolate. In the case of the construction
of a carbon–nitrogen bond, the basic sites depronate RH2N+-C after
addition to the C C electron-poor bond.
TABLE IV Comparison of the Activity of Li/NP With Other
Phosphate Catalysts
Yield/% (Time)
Catalysts
13a
3a
Li/NP
NP
90 (3 min)
93 (3 h)
95 (15 min)10a
96 (5 min)10b
94 (20 min)
93 (20 min)
93 (5 min)
25 (2 h); 9 (8 h)10a
KF/NP
Na2CaP2O77
FAP8
95 (1 h)10b
—
—
—
HAP9

1216
M. Zahouily et al.
The results obtained in this reaction with Li/NP as a catalyst were
compared to those of other phosphates. Thus the activity of Li/NP
was higher than NP,10 synthetic phosphate Na2CaP2O7,6 fluoroapatite
(FAP),7 and hydroxyapatite (HAP),8 and slightly lower than potassium
fluoride–doped natural phosphate (KF/NP; Table IV).10
CONCLUSION
NP doped with lithium nitrate calcined at 900◦C is an efficient ba-
sic catalyst for the construction of carbon–nitrogen, carbon–sulfur, and
carbon–carbon bonds. The results depend on several factors, with the
nature and amount of solvent a playing decisive role. NP doped with
lithium nitrate is used as a catalyst for the facile synthesis of β-amino
acids, β-sulfur acids, and 4H-chromenes under heterogeneous condi-
tions. These results open the possibility for the use of this inexpensive
solid as a basic catalyst for other applications.
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Natural Phosphate Modified with Lithium Nitrate
1217
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