Solid catalysts for the production of fine chemicals: The use of natural phosphate alone and doped base catalysts for the synthesis of unsaturated arylsulfones

Article abstract of DOI:10.1016/j.tet.2003.11.086

The inexpensive natural phosphate, both alone and doped with potassium fluoride, is a new basic catalyst for the synthesis of α,β- unsaturated arylsulfones. Activation by water and benzyltriethylammonium chloride has also been investigated. When using an

Full text of DOI:10.1016/j.tet.2003.11.086

Tetrahedron 60 (2004) 1631–1635
Solid catalysts for the production of fine chemicals: the use of
natural phosphate alone and doped base catalysts for the synthesis
of unsaturated arylsulfones
a
a
a
Mohamed Zahouily,a Mohamed Salah, Bouchaib Bahlaouane, Ahmed Rayadh,
,
*
b
b
Abdelaziz Houmam, Emad A. Hamed and Saıd Sebti
c
¨
a
` ´ ´
Laboratoire de Catalyse, Synthese et Environnement, UFR de Chimie Appliquee, Faculte des Sciences et Techniques,
´
Universite Hassan II, Mohammadia B. P. 146, 20650 Maroc
bUniversity of Guelph, Departement of Chemistry and Biochemistry, Guelph, Ontario,Canada, N1G2W1
´ ´
Laboratoire de Chimie Organique Appliquee et Catalyse, Faculte des Sciences, Ben M’Sik B. P. 7955, Casablanca, Maroc
c
Received 15 August 2003; revised 30 October 2003; accepted 28 November 2003
Abstract—The inexpensive natural phosphate, both alone and doped with potassium fluoride, is a new basic catalyst for the synthesis of
a,b-unsaturated arylsulfones. Activation by water and benzyltriethylammonium chloride has also been investigated. When using an
ammonium salt, natural phosphate doped with potassium fluoride is an excellent solid support for the synthesis of a,b-unsaturated
arylsulfones, leading to excellent yields in a few minutes.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
useful temporary activating groups for alkylation,6 acyla-
tion7 and addition reactions.8
Heterogeneous catalysis is an important application of
porous solids possessing acid and Lewis basic sites. Studies
on solid acid catalysts are enormous. Though little attention
is devoted to basic catalysts in comparison with solid acid
catalysts, high activities and selectivities are often obtained
for many kinds of reaction.1 Numerous reactions including
isomerizations, additions, alkylations and cyclizations are
carried out industrially using liquid bases as catalysts.
Furthermore, many organic reactions require a stoichio-
metric amount of liquid bases. The advantages of hetero-
geneous catalysis over conventional homogeneous reactions
is that it provides greater selectivity, enhanced reaction
rates, cleaner product and manipulative simplicity. For these
reasons, heterogeneous catalysis can be considered as a new
attempt to develop the notion of ‘clean chemistry’.
The Knoevenagel condensation of arylsulfones and alde-
hydes is one of the most popular methods for synthesizing
unsaturated arylsulfones. The deprotonation of phenyl-
sulfonylalkanes generally involves strong bases such as
sodium hydride,9 butyl lithium10 or lithium di-isopropyl-
amide (LDA).11 However, the deprotonation energy
strongly depends on the presence of adjacent electron-
withdrawing groups such as an ester,3 nitrile or ketone.12
In recent years, the Knœvenagel condensation in hetero-
geneous media has been carried out in presence of
zeolites,13 organic resins,14 mixed magnesium–aluminium
oxides derived from hydrotalcites,15 sepiolites,16 alumino-
phosphonates oxynitrides (ALPON),17 and more recently,
synthetic phosphate Na2CaP2O7.18
Sulfones are important intermediates in organic synthesis.2
Their importance is due to the fact that arylsulfonyl groups
can stabilise adjacent carbanions3 and may easily be
removed by hydrolysis, reduction or elimination4 and,
when appropriate, may be eliminated to introduce carbon–
carbon double bonds into organic molecule.5 Thus they are
We have previously investigated the use of natural
phosphate to promote organic transformations19 and have
shown that its mildly basic proprieties can be exploited in
many synthetic applications.20 We have also shown that
doping with mineral salts increases the activity of natural
phosphate.20
In continuation of our ongoing program to develop clean
and economical processes for the production of fine
chemicals, we describe in this paper, the use of natural
phosphate (NP) alone and doped with KF as an inorganic
Keywords: Natural phosphate; Ammonium salt; Knœvenagel;
Heterogeneous catalysis; Arylsulfones; Recyclable catalyst.
*
Corresponding author. Tel.: þ212-61-62-80-76; fax: þ212-23-31-53-53;
e-mail address: m.zahouily@univh2m.ac.ma
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.11.086

1632
M. Zahouily et al. / Tetrahedron 60 (2004) 1631–1635
Table 1. Synthesis of products 3 by Knœvenagel condensation using NP
and KF/NP
Products
R
Solvent
Yield, % (time, h)a
NP (5 h) KF/NP (1 h)
Scheme 1.
3a
3a
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
H
H
H
H
NO2
NO2
Cl
Cl
Me
Me
OMe
OMe
MeOH
EtOH
56
58
60
68
72
87
66
80
50
64
46
60
64
60
68
77
82
95
75
88
60
76
58
70
support of the Knœvenagel condensation between phenyl-
sulfonylacetonitrile 2 and benzaldehyde or 4-substituted
benzaldehydes 1, at room temperature with a solvent
(Scheme 1).
MeOHb
EtOHb
EtOH
EtOHb
EtOH
EtOHb
EtOH
EtOHb
EtOH
2. Preparation of the catalyst and structural
characteristics
EtOHb
Natural phosphate (NP) used in this work was obtained in
the Khouribga region (Morocco).21 Prior to use this material
requires initial treatments such as crushing and washing. For
use in organic synthesis, the NP is treated by techniques
involving attrition, sifting, calcinations (900 8C), washing,
and recalcination. These treatments lead to a fraction
between 100 and 400 mm that is rich in phosphate and has
following chemical composition P2O5 (34.24%), CaO
(54.12%), F2 (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, Cr) in the range of ppm. The structure of the
material is similar to that of fluoroapatite (Ca10(PO4)6F2). In
sedimentary rocks, phosphates are formed from compounds
derived from apatite by partial isomorphic substitution:
Ca2þions by Naþ, Mg2þ, Co2þ, Fe3þ, or Al3þ, PO432 ions by
VO342, SO242, CO322 or MnO42, and F2 by 2OH or Cl2.
These different substitutions cause distortions of the
structure which depends on the nature and the radii of the
ions involved. This solid presented a very low surface area
a
Yields of pure products isolated by distillation under vacuum and
1
identified by H, 13C NMR, mass spectroscopy and IR spectroscopy.
The solvent/water ratio is 90:10.
b
prepared by Knœvenagel condensation catalyzed by NP
alone and doped with KF are summarized in Table 1.
In general, the use of NP as heterogeneous catalyst in the
Knœvenagel condensation has allowed the isolation of
a,b-unsaturated arylsulfones in moderates yields (Table 1).
The reactions are relatively slow. Only the isomer of
configuration E has been isolated.18
Solid catalysts become particularly interesting when they
can be regenerated. Indeed, in our case, NP was recovered
quantitatively by simple filtration and regenerated by
calcination for 15 min at 700 8C. The recovered catalyst
was reused several times without loss of activity, even
after the sixth, cycle product 3a was obtained in the same
yield.
(BET) at ca. 1 m2 g21
.
Under similar conditions, the use of NP doped with KF,
decreases remarkably the Knoevenagel reaction time
(Table 1).
KF/NP has been prepared by adding 8 g of NP to a 1 g KF
aqueous solution. The mixture was stirred, evaporated to
dryness and dried at 150 8C for 2 h. The catalyst KF/NP
(weight report KF/NP: 1:8)20c,d is a grey powder, the colour
of NP itself. The IR data shows the presence of some
additional H-bonded water at 3250 cm21 and 1636–
1675 cm21 for the supported solid. On the other hand, the
X-ray diffraction of KF/NP gives a diffraction pattern
almost identical to that of NP itself. Peak positions and
intensities are essentially unaltered. We showed pre-
viously20 that supporting KF on NP causes the formation
of a more open structure which incorporates KF in such a
way that crystalline KF is not formed in significant
quantities. However, it appears that the basic structure of
NP is not destroyed, indicating a less profound interaction
of KF with NP than is the case with alumina.22 The
morphology of the solid surface was observed in scanning
electron micrograph (SEM) images of KF/NP in comparison
with NP. It clearly appears that some modifications have
taken place at the surface of the catalyst.
The addition of water slightly increases the reaction yields
of the a,b-unsaturated arylsulfones 3 with either catalyst
(NP and KF doped NP). For example, the yield of alkene 3a
increases from 64 to 68% in methanol and from 64 to 77% in
ethanol when using KF/NP as a catalyst. Various quantities
of water have been used. Figure 1 shows that the best results
are obtained when 10% of water is added. This activation is
probably due to the interaction between water and the solid
surface. If a large amount of water is used a thin film of
water will be formed between the organic reagents and
catalyst which explain the decreasing of the yields (Fig. 1).
The best conditions for synthesizing the alkene 3a are
generalized to 3b, 3c, 3d and 3e (Table 1).
We clearly show that water increases the catalytic activity of
both NP alone and with KF/NP, in all cases. For example,
for the alkene 3b, the yield increases from 72 to 87% and
from 82 to 95% for the two catalysts NP alone and KF/NP,
respectively. However, under similar conditions, the best
catalytic activity was observed with the NP doped by KF
(Table 1).
3. Results and discussion
The results for a variety of a,b-unsaturated arylsulfones

M. Zahouily et al. / Tetrahedron 60 (2004) 1631–1635
1633
Figure 1. Influence of water in the synthesis of 3a.
Figure 2. Influence of BTEAC in the synthesis of 3b (KF/NP catalyst).
It has been shown previously that the addition of an
ammonium salt to natural phosphate,23 fluorapatite,24 or
hydroxyapatite25 increases the activity of these catalysts.
Therefore, we carried out the synthesis of the a,b-
unsaturated arylsulfone 3b with KF/NP in ethanol using
different amounts of benzyltriethylammonium chloride
(BTEAC). The results obtained after 40 min show that the
best yields are obtained with 0.050 g of BTEAC (Fig. 2).
Moreover, the kinetic curves for the synthesis of the alkene
3b in the absence and in the presence of BTEAC clearly
show the enhancement of the catalytic activity of KF/NP by
addition of the ammonium salt. The yields obtained after 10,
20, 30 and 40 min are 47, 75, 86, and 97% in the presence of
BTEAC and 20, 39, 52, and 68% without BTEAC.
acetonitrile 2 and substituted benzaldehyde derivatives
(1a–e) using NP and KF/NP as catalysts. Results from
Tables 1 and 2 show that the presence of electron acceptor
groups on the aromatic ring increases the reaction rate
proportionally to the value of the Hammet constant.
Meanwhile, the presence of electron donor groups decreases
the reaction rate, demonstrating the participation of the
aldehyde in the controlling step of the reaction.
Table 2. Synthesis of products 3 by Knœvenagel condensation using NP
and KF/NP, in the presence and in the absence of BTEAC
Entry Products
R
Solvent
Yield, % (time, h)a
NP KF/NP
Finally, this method was extended to the preparation of
several a,b-unsaturated arylsulfones (Table 2). In all cases,
the reaction afforded product 3 in high yields. The addition
of BTEAC caused a significant increase in the reaction rate
(Table 2). Similar effects were observed in the presence of
NP alone catalyst (Table 2). It is important to note that
BTEAC itself has no catalytic activity and seems to act only
as a phase transfer catalyst.
1
2
3
4
5
6
7
8
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
H
H
NO2
NO2
Cl
Cl
Me
Me
EtOH
EtOHb
EtOH
EtOHb
EtOH
EtOHb
EtOH
EtOHb
58 (5)
75 (5)
72 (5)
60 (1)
73 (0.8)/91 (1)
68 (0.6)/82 (1)
85 (3)/94 (4) 86 (0.5)/97 (0.6)
66 (5) 75 (1)
86 (4)/93 (5) 77 (0.6)/97 (1)
50 (5)
73 (5)
46 (5)
70 (5)
60 (1)
86 (1)
58 (1)
92 (1)
9
10
OMe EtOH
OMe EtOHb
The effect of electron acceptor or donor substituents on the
aromatic ring of benzaldehyde in the Knœvenagel conden-
sation was carried out in the reaction of phenylsulfonyl-
a
Yields of pure products isolated by distillation under vacuum and
identified by 1H, 13C NMR, mass spectroscopy and IR spectroscopy.
BTEAC 0.05 g.
b

1634
M. Zahouily et al. / Tetrahedron 60 (2004) 1631–1635
Thus, we estimate that the surface of the catalyst (NP or
KF/NP) presents multicatalytic active sites. The basic sites
polarize the C–H bond of the active methylene compound.
The acidic surface of NP26 probably coordinates with the
oxygen of the carbonyl carbon on which a partial positive
charge appears. Consequently, the C–C bond formation is
facilitated and the final alkene is obtained by the transfer of
a proton followed by dehydration.
Philips 1710 diffractometer using Cu Ka radiation and SEM
images were taken on a Hitac hi S-2400 microscope.
Melting points were determined with a ‘Thomas Hoover’
melting (capillary method) apparatus and are uncorrected.
Flash column chromatography was performed using Merck
silica gel 60 (230–400 mesh ASTM).
All reactions were carried out under atmosphere air.
Solvents and starting materials (Aldrich) were used without
further purification. The natural phosphate alone and doped
by potassium fluoride were prepared according to the
method we described previously.20
The activity of KF/NP/BTEAC seems to be higher than
other known catalysts (entry 2–11; Table 3) and slightly
lower than ALPON27 (atomic ratio Al:P:N¼1:0.95:0.42;
entry 12; Table 3).
5.2. General procedure for the syntheses of
a,b-unsaturated arylsulfones (3a–e)
Table 3. Comparison of KF/NP/BTEAC with several heterogeneous
catalysts in the synthesis of product 3a by Knœvenagel condensation
To a flask containing an equimolar mixture (1 mmol) of
aldehyde 1 and phenylsulfonylacetonitrile 2 in solvent
(methanol or ethanol: 1 ml), phosphate catalyst (NP or KF/
NP) 0.1 g was added and the mixture was stirred at room
temperature for a specified time (Tables 1 and 2). The
reaction mixture was filtered and the catalyst washed with
dichloromethane. After concentration of the filtrate under
reduced pressure the residue was subjected to chroma-
tography or distillation under vacuum leading to the
a,b-unsaturated sulfone as a solid. The product structure
Entry
Solid catalyst
Yields (time)
[(%) (time/h)] 3a
1
2
3
4
5
6
7
8
KF/NP/ BTEAC
KF/NP/Water
KF/NP
91 (1)
77 (1)
60 (1)
75 (5)
68 (5)
58 (5)
58 (1)
74 (1)
35 (2)
86 (2)
71 (2)
95 (2)a
NP/ BTEAC
NP/water
NP
18
Na2CaP2O7
Na2CaP2O7/water18
Zeolite–CsX25
MgO27
9
1
was analysed by H, 13C NMR, mass spectroscopy and IR
10
11
12
Mg–Al-hydrotalcite27
ALPON27
spectrometry.
a
The same procedure was used for the reactions carried out
with NP or KF/NP (0.1 g) activated with water (0.1 ml) or
BTEAC (0.050 g). Water or BTEAC were always added in
the last place. In the case of BTEAC, the products were
washed with water to eliminate the ammonium salt before
purification.
Atomic ratio Al:P:N¼1:0.95:0.42.
4. Conclusion
Natural phosphate doped with potassium fluoride is an
efficient basic catalyst for the Knoevenagel reaction.
Several a,b-unsaturated arylsulfones can be synthesis with
high yields using catalytic amounts of KF/NP. This catalyst
bring advantages such as high catalytic activity under very
mild liquid phase conditions, easy separation of the catalyst
by simple filtration, possible recycling of the catalyst, use of
non-toxic and inexpensive catalyst and especially, elimi-
nation of salts and by-product pollutants. This solid base
catalyst then becomes a practical alternative to soluble
bases. The addition of an ammonium salt increases the
reaction rate for all a,b-unsaturated arylsulfones syn-
thesized and the products were obtained in high yields.
5.3. Identifications of products
5.3.1. a-Phenylsulfonyl cinnamonitrile, 3a. White solid;
mp 130–132 8C; Rf (20% AcOEt/hexane) 0.46; nmax (KBr)
3031, 2218, 1578 cm21; dH (400 MHz CDCl3) 8.24 (1H, s,
vCH); 8.03 (2H, d, J¼8.4 Hz, HAr); 7.92 (2H, d, J¼
8.8 Hz, HAr); 7.74–7.70 (1H, m, HAr); 7.64–7.57 (3H, m,
HAr); 7.50 (2H, t, J¼8.0 Hz, HAr); dC (100 MHz CDCl3)
151.5, 137.8, 134.6, 134.1, 131.0, 130.1, 129.7, 129.5,
128.7, 114.8, 113.1; m/z (EI): 271 (M2þ, 5), 269 (63, Mþ),
128 (100), 101 (10), 77 (100), 51 (36%); HRMS (EI): Mþ,
found 269.0513. C15H11NO2S requires 269.0511.
5. Experimental
5.3.2. a-Phenylsulfonyl 4-nitrocinnamonitrile, 3b. White
solid; mp 140–142 8C; Rf (20% AcOEt/hexane) 0.37; nmax
(KBr) 3113, 2218, 1596 cm21; dH (400 MHz CDCl3) 8.34
(2H, d, J¼8.8 Hz, HAr); 8.30 (1H, s, vCHAr); 8.08 (2H, d,
J¼8.8 Hz, HAr); 8.04 (2H, d, J¼7.6 Hz, HAr); 7.77 (1H, t,
J¼7.6 Hz, HAr). dC (100 MHz CDCl3) 151.0, 148.0, 137.4,
136.0, 135.2, 131.5, 129.9, 129.0, 124.5, 115.5, 112.3; m/z
(EI): 314 (13, Mþ), 181 (5), 141 (53), 77 (100), 51 (22), 40
(36%); HRMS (EI): Mþ, found 314.0367. C15H10N2O4S
requires 314.0361.
5.1. General comments
1H and 13C NMR spectra were recorder at 400 and
100 MHZ, respectively, on a Bruker DRX-400 spectrometer
in CDCl3, using CDCl3 as internal standard. The chemical
shifts (d) are expressed in ppm relative to CDCl3 and
coupling constant (J) in Hertz. Mass spectra were obtained
on VG ZAB-HS mass spectrometer. IR spectra were
obtained on a FTIR (ATI Mattson-Genesis Series) and
reported in wave numbers (cm21). Surface area and pore
size analysis were carried out at 77 K on a Micromeritics
ASAP2010 instrument using nitrogen as adsorbent. X-ray
diffraction patterns of the catalysts were obtained on a
5.3.3. a-Phenylsulfonyl 4-chlorocinnamonitrile, 3c.
White solid; mp 152–1548C; Rf (20% AcOEt/hexane)
0.51; nmax (KBr) 3031, 2227, 1596 cm21; dH (400 MHz

M. Zahouily et al. / Tetrahedron 60 (2004) 1631–1635
1635
1976, 5895. (b) Giovannini, R.; Petrini, M. J. Chem. Soc.
Chem. Commun. 1997, 19, 12101.
CDCl3) 8.18 (1H, s, vCHAr); 8.02 (2H, d, J¼8.8 Hz, HAr);
7.87 (2H, d, J¼8.8 Hz, HAr); 7.75–7.71 (1H, m, HAr);
7.65–7.60 (2H, m, HAr); 7.51–7.46 (2H, m, HAr); dC
(100 MHz CDCl3) 149.9, 140.5, 137.6, 134.8, 132.1, 129.9,
129.5, 128.7, 128.5, 115.2, 112.9; m/z (EI): 305 (30, M2þ),
303 (57, Mþ), 162 (100), 126 (28), 77 (56), 51 (54), 40 (53);
HRMS (EI): Mþ, found 303.0128. C15H10ClNO2S requires
303.0121.
9. (a) Trost, B. M.; Verhœven, T. R. J. Am. Chem. Soc. 1977, 99,
8116. (b) Trost, B. M.; Verhœven, T. R. J. Am. Chem. Soc.
1978, 100, 3435.
10. Kondo, K.; Tunemoto, D. Tetrahedron Lett. 1975, 1007.
11. Olson, G. L.; Cheung, H.-O.; Morgan, K. D.; Neukon, C.;
Saucy, G. J. Org. Chem. 1976, 41, 3287.
12. Villemin, D.; Ben Alloum, A. Synth. Commun. 1991, 21, 63.
´ ´
13. Croma, A.; Formes, V.; Martin-Aranda, R. M.; Garcıa, H.;
5.3.4. a-Phenylsulfonyl 4-methylcinnamonitrile, 3d.
White solid; mp 144–146 8C; Rf (20% AcOEt/hexane)
0.47; nmax (KBr) 3031, 2227, 1596 cm21; dH (400 MHz
CDCl3) 8.20–7.20 (m, 9H, ArH and 1H, HCvC); 2.4 (s,
3H, CH3); dC (100 MHz CDCl3) 159.0, 139.9, 138.2, 135.2,
132.4, 131.3, 131.2, 129.3, 129.2, 114.9, 99.1, 21.5; m/z
(EI): 285 (20, M2þ), 283 (100, Mþ), 142 (29), 115 (27), 77
(100); HRMS (EI): Mþ, found 283.0669. C16H13NO2S
requires 283.0667.
Primo, J. Appl. Catal. 1990, 59, 237.
14. Tanabe, K. In Catalysis by acids and bases. Imelik, B.,
et al.Eds.; Elsevier: Amsterdam, 1985; p 1.
´
15. (a) Croma, A.; Formes, A. V.; Martin-Aranda, R. M.; Rey, F.
´
J. Catal. 1992, 134, 58. (b) Croma, A.; Formes, V.; Rey, F.
J. Catal. 1994, 148, 205.
16. Croma, A.; Martin-Aranda, R. M. J. Catal. 1991, 130, 130.
17. (a) Grange, P.; Bastians, Ph.; Conanec, R.; Marchand, R.;
Laurent, Y.; Gandia, L. M.; Montes, M.; Fernandes, J.;
Odriozola, J. A. Stud. Surf. Sci. Catal. 1994, 91, 389.
(b) Grange, P.; Bastians, Ph.; Conanec, R.; Marchand, R.;
Laurent, Y. Appl. Catal. A 1994, 114, L191. (c) Massinon, A.;
Odriozola, J. A.; Bastians, Ph.; Conanec, R.; Marchand, R.;
Laurent, Y.; Grange, P. Appl. Catal. 1996, 137, 9. (d) Climent,
5.3.5. a-Phenylsulfonyl 4-methoxycinnamonitrile, 3e.
White solid; mp 113–115 8C; Rf (20% AcOEt/hexane)
0.23; nmax (KBr) 3022, 2218, 1589 cm21; dH (400 MHz
CDCl3) 8.14 (1H, s, vCHAr); 8.01 (2H, d, J¼7.6 Hz, HAr);
7.92 (2H, d, J¼8.8 Hz, HAr); 7.69 (1H, t, J¼7.6 Hz, HAr);
7.60 (2H, t, J¼7.6 Hz, HAr); 6.98 (2H, d, J¼8.8 Hz, HAr);
3.89 (3H, s, OCH3); dC (100 MHz CDCl3) 164.5, 151.0,
138.5, 134.3, 133.7, 129.6, 128.4, 122.9, 115.0, 113.7,
110.9, 55.7; m/z (EI): 301 (10, M2þ), 299 (44, Mþ), 157
(100), 77 (33), 51 (10), 40 (16); HRMS (EI): Mþ, found
299.0621. C16H13NO3S requires 299.0616.
´ ´
M. J.; Croma, A.; Formes, V.; Fran, A.; Guil-Lopez, R.; Iborra,
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