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Claisen–Schmidt condensation catalysis by natural phosphate
Applied Catalysis A: General 206 (2001) 217–220
Claisen–Schmidt condensation catalysis by natural phosphate Sa¨ıd Sebti∗ , Ahmed Saber, Abdallah Rhihil, Rachid Nazih, Rachid Tahir Laboratoire de Chimie Organique Appliquée, Université Hassan II, Faculté des Sciences Ben M’Sik B.P. 7955, Casablanca, Morocco Received 1 March 2000; received in revised form 25 April 2000; accepted 28 April 2000
Abstract The Claisen–Schmidt condensation is easily carried out with or without a solvent in the presence of natural phosphate (NP) alone, activated by water, benzyltriethylammonium chloride and both. The role of water and ammonium salt are clearly shown. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Natural phosphate; Heterogeneous catalysis; Claisen–Schmidt condensation; Activation; Water
1. Introduction Heterogeneous reactions that are facilitated reagents on various solid inorganic surfaces have received attention. The advantage of these methods over conventional homogeneous reactions is that they provide greater selectivity, enhanced reaction rates, cleaner product and manipulative simplicity. The heterogeneous catalysis of the Claisen–Schmidt condensation was carried out in the presence of alumina [1], barium hydroxide [2–6], barium hydroxide/ultrasonic [7] and recently hydrotalcite and zeolite [8–11]. In our laboratory, many reactions in heterogeneous media such as Knoevenagel reaction [12], hydration of nitriles [13], Friedel–Crafts condensation [14] and Michael reaction [15] have been devised earlier using natural phosphate and natural phosphate doped with mineral salt. Relatively inexpensive natural phosphate has been extensively used as a basic [12] and acid [14] catalyst. ∗ Corresponding author. Tel.: +212-1-464819; fax: +212-270-4675. E-mail address: [email protected] (S. Sebti).
In continuation of our ongoing program to develop a heterogeneous catalysis, we describe in this paper, the use of natural phosphate as an inorganic support of the Claisen–Schmidt condensation between acetophenone (1) and arylaldehyde (2) at room temperature with or without a solvent (Scheme 1).
2. Experimental 2.1. Preparation and characterization of catalyst Natural phosphate (NP) comes from an extracted ore in the region of Khouribga (Morocco). The fraction of 100–400 m is isolated, washed with water, calcined at 900◦ C for 2 h, sieved (63–160 m) and conserved at 150◦ C or in a desiccator. NP is identified by X-ray diffraction, IR spectroscopy and chemical analysis. Surface area of calcined NP was determined by the BET method from the adsorption–desorption isotherm of nitrogen at its liquid temperature, using a conventional volumetric apparatus (1 m2 g−1 ). The chemical composition of NP was determined as: P2 O5 (34.24%), CaO (54.12%), CO2 (1.13%),
0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 6 - 8 6 0 X ( 0 0 ) 0 0 6 0 4 - 9
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S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220 Table 1 Claisen–Schmidt condensation catalyzed by natural phosphate without solvent
Scheme 1.
MgO (0.68%), SiO2 (2.42%), Al2 O3 (0.46%), Fe2 O3 (0.36%), F− (3.37%), SO3 (2.21%), Na2 O (0.92%), K2 O (0.04%) and (Cd, Zn, Cu, U, Cr, V) (ppm). The basic properties of NP have been determined by the adsorption of phenol on phosphate at 25◦ C as: 616 mol g−1 (1 h); 898 mol g−1 (2 h) and 2066 mol g−1 (24 h). The acidic properties of NP have been demonstrated in the Friedel–Crafts reaction [14]. Indeed, the monoalkyl compounds of benzene and toluene have been obtained with yields (time) of 42% (24 h) and 91% (2 h), respectively, in the presence of NP alone. 2.2. General procedure 2.2.1. Without a solvent NP is used in the catalysis of the Claisen–Schmidt condensation without solvent under different conditions (Table 1). The general procedure is as follows: to a flask containing an equimolar mixture (2.5 mmol) of acetophenone (1) and arylaldehyde (2), NP (2.5 g) was added at room temperature. Workup included extraction with CH2 Cl2 , filtration and evaporation. Products were subsequently purified by distillation under vacuum or recrystallization and identified by 1 H NMR and IR spectroscopy. The same procedure was used for the reactions carried out with NP (2.5 g) activated with water (0.25 ml) and/or benzyltriethylammonium chloride (BTEAC) (0.06 g) water was always added in the last place. 2.2.2. With a solvent To improve the yields, we have worked with different solvents (Table 2). The procedure is as follows: acetophenone (5 mmol) and aldehyde (5 mmol) were dissolved in 5 ml of solvent or (5 ml solvent+2 ml
Product
Water (ml)
BTEAC (g)
Time (h)
Yield (%)
3a
0 0.25 0 0.25
0 0 0.06 0.06
24 24 24 24
10 12 60 77
3b
0 0.25 0 0 0.25
0 0 0.06 0.06 0.06
24 24 1 4 1
0 21 43 91 91
3c
0 0.25 0.25 0 0 0.25 0.25
0 0 0 0.06 0.06 0.06 0.06
24 1 24 1 24 0.25 0.5
28 20 75 37 79 85 92
water). NP (5 g) was added and the mixture was stirred at room temperature. After reaction time, NP was removed by filtration. The alkene (3) was purified by distillation under vacuum (3a and 3b) or recrystallized 3c and identified by 1 H NMR and IR spectroscopy.
3. Results and discussion 3.1. Without solvent The NP alone without solvent is slightly active in the Claisen–Schmidt condensation. The yields do not exceed 28% in 24 h of reaction, in the best case (Table 1). The rate is slow and the yields are poor in spite of the longer reaction times. The addition of water to NP improves the results obtained in the synthesis of alkenes (3a–3c). The addition of BTEAC remarkably increases the catalytic activity of NP in Claisen–Schmidt condensation. The yields are very high and the reaction times are clearly reduced. The simultaneous addition of water and BTEAC show a clear superiority in the activation of NP. Under these conditions all the alkenes (3a–3c) are obtained with good yields. So, the yields (times) are 77% (24 h), 91% (1 h) and 92% (0.5 h), respectively, for 3a, 3b
S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220
219
Table 2 Claisen–Schmidt condensation catalyzed by NP with different solvents Solvent
Methanol
Ethanol
Propan-1-ol
Propan-2-ol
Dioxane
DMF
Acetonitrile
THF
Yielda
75 79
2 96
0 84
0 86
0 84
2 69
0 56
0 42
(%) Yieldb (%) a b
Absence of water. Solvent/water (5 ml/2 ml).
and 3c. The addition of water to BTEAC improves the results obtained in the synthesis of alkenes. This results may be due to the fact that water dissolves the ammonium salt and facilitates its interaction with NP, what can provoke the activation of this last. It is worth noting that, in the same conditions and in absence of NP. Water, BTEAC or both do not promote this reaction. Secondary reaction e.g., Cannizzaro of aldehyde or condensation of ketone, were not observed. Only E isomer of alkenes (3a–3c) was formed. The use of solids catalysts is particularly interesting when they can be regenerated. In this case, NP was regenerated by calcination at 700◦ C during 15 min, and after eight successive recuperations, alkenes (3a–3c) are obtained with the same yields. The NP is a very good catalyst of Claisen–Schmidt condensation when it is used in the presence of small quantities of water and BTEAC without a solvent. The most important features of NP is his small and reactive surface area.
small molecule, can replace water while playing the role of solvent. It is worth noting that, NP is completely insoluble in water, not either in organic solvents. The best condition for synthesis of alkenes 3a are generalized to 3b and 3c (Table 3). We clearly show the activation of natural phosphate by water in all cases. Alkenes (3a–3c) are obtained with very high yields. Ethanol/water is an excellent solvent for Claisen–Schmidt condensation. The amount of solid catalyst influences the yield. Increasing the amount of NP from 50 to 500 mg increases the yield of alkenes 3a and 3b. For alkene 3c, 500 mg of NP lead to increase the reaction rate. Also, NP can be regenerated by calcination at 700◦ C for 15 min.
3.2. With a solvent We have carried out the synthesis of 3a in the presence of natural phosphate in different solvents. The obtained results are summed up in Table 2. The presence of water in medium seems not to be important because similar yields are obtained with methanol alone (75%) and methanol/water (79%). This behavior is different from that observed in other solvents. Water dramatically increases the yield from 2 to 96% with ethanol. In this case, 2 ml of water is the optimum condition for synthesis of alkene 3a (Fig. 1), addition of 1 or 3 ml of water lowered the yield. The activating role of water, very small and polar molecule, can be explained by its adsorption on NP facilitating the contact of the phosphate with substrates, soluble in the organic solvent. The methanol,
Fig. 1. Synthesis of alkene 3a by NP, EtOH and various quantity of water.
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S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220
Table 3 Claisen–Schmidt condensation catalyzed by NP with EtOH
References
Product
Weight NP (g)
Water (ml)
Time (h)
Yield (%)
3a
5 5 0.5 5
0 2 2 2
24 4 24 24
2 82 33 96
3b
5 5 0.5 5
0 2 2 2
24 1 8 4
18 69 48 91
3c
5 5 0.5 5
0 2 2 2
[1] R.S. Varma, G.W. Kabalka, L.T. Evans, R.M. Pagni, Synth. Commun. 15 (1985) 279. [2] J.V. Sinisterra, A.G-Raso, J.A. Cabello, J.M. Marinas, Synthesis (1984) 502. [3] A.R. Alcantara, J.M. Marinas, J.V. Sinisterra, Tetrahedron Lett. 28 (1987) 1515. [4] A. Aguilera, A.R. Alcantara, J.M. Marinas, J.V. Sinisterra, Can. J. Chem. 65 (1987) 1165. [5] S. Sathyanarayana, H.G. Krishnamurty, Curr. Sci. 57 (1988) 1114. [6] M.S. Climent, J.M. Marinas, Z. Mouloungui, Y. Le Bigot, M. Delmas, A. Gaset, J.V. Sinisterra, J. Org. Chem. 54 (1989) 3695. [7] A. Fuentes, J.M. Marinas, J.V. Sinisterra, Tetrahedron Lett. 28 (1987) 4541. [8] M.J. Climent, H. Garcia, J. Primo, A. Corma, Catal. Lett. 4 (1990) 85. [9] D. Tichit, M.H. Lhouty, A. Guida, B.H. Chiche, F. Figueras, A. Auroux, D. Bartalini, E. Garrone, J. Catal. 151 (1995) 50. [10] M.J. Climent, A. Corma, S. Iborra, J. Primo, J. Catal. 151 (1995) 60. [11] A. Guida, M.H. Lhouty, D. Tichit, F. Figueras, P. Geneste, Appl. Catal. 164 (1997) 251. [12] S. Sebti, A. Saber, A. Rhihil, Tetrahedron Lett. 35 (1994) 9399. [13] S. Sebti, A. Rhihil, A. Saber, N. Hanafi, Tetrahedron Lett. 37 (1996) 6555. [14] S. Sebti, A. Rhihil, A. Saber, Chem. Lett. 8 (1996) 721. [15] S. Sebti, H. Boukhal, N. Hanafi, S. Boulaajaj, Tetrahedron Lett. 40 (1999) 6207.
4 0.25 2 0.75
40 74 94 94
Natural phosphate, in absence or presence of solvent, is an interesting new catalyst for the Claisen– Schmidt reaction.
Acknowledgements We are grateful to the ‘Office Chérifien des Phosphates (OCP)’ and the ‘Centre d’Etude et de Recherches sur les Phosphates Minéraux (CERPHOS)’ for financial support. Thanks are expressed to Prof. J.A. Mayoral, University of Zaragoza, for co-operation in some of the work presented here.
Claisen–Schmidt condensation catalysis by natural phosphate Sa¨ıd Sebti∗ , Ahmed Saber, Abdallah Rhihil, Rachid Nazih, Rachid Tahir Laboratoire de Chimie Organique Appliquée, Université Hassan II, Faculté des Sciences Ben M’Sik B.P. 7955, Casablanca, Morocco Received 1 March 2000; received in revised form 25 April 2000; accepted 28 April 2000
Abstract The Claisen–Schmidt condensation is easily carried out with or without a solvent in the presence of natural phosphate (NP) alone, activated by water, benzyltriethylammonium chloride and both. The role of water and ammonium salt are clearly shown. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Natural phosphate; Heterogeneous catalysis; Claisen–Schmidt condensation; Activation; Water
1. Introduction Heterogeneous reactions that are facilitated reagents on various solid inorganic surfaces have received attention. The advantage of these methods over conventional homogeneous reactions is that they provide greater selectivity, enhanced reaction rates, cleaner product and manipulative simplicity. The heterogeneous catalysis of the Claisen–Schmidt condensation was carried out in the presence of alumina [1], barium hydroxide [2–6], barium hydroxide/ultrasonic [7] and recently hydrotalcite and zeolite [8–11]. In our laboratory, many reactions in heterogeneous media such as Knoevenagel reaction [12], hydration of nitriles [13], Friedel–Crafts condensation [14] and Michael reaction [15] have been devised earlier using natural phosphate and natural phosphate doped with mineral salt. Relatively inexpensive natural phosphate has been extensively used as a basic [12] and acid [14] catalyst. ∗ Corresponding author. Tel.: +212-1-464819; fax: +212-270-4675. E-mail address: [email protected] (S. Sebti).
In continuation of our ongoing program to develop a heterogeneous catalysis, we describe in this paper, the use of natural phosphate as an inorganic support of the Claisen–Schmidt condensation between acetophenone (1) and arylaldehyde (2) at room temperature with or without a solvent (Scheme 1).
2. Experimental 2.1. Preparation and characterization of catalyst Natural phosphate (NP) comes from an extracted ore in the region of Khouribga (Morocco). The fraction of 100–400 m is isolated, washed with water, calcined at 900◦ C for 2 h, sieved (63–160 m) and conserved at 150◦ C or in a desiccator. NP is identified by X-ray diffraction, IR spectroscopy and chemical analysis. Surface area of calcined NP was determined by the BET method from the adsorption–desorption isotherm of nitrogen at its liquid temperature, using a conventional volumetric apparatus (1 m2 g−1 ). The chemical composition of NP was determined as: P2 O5 (34.24%), CaO (54.12%), CO2 (1.13%),
0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 6 - 8 6 0 X ( 0 0 ) 0 0 6 0 4 - 9
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S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220 Table 1 Claisen–Schmidt condensation catalyzed by natural phosphate without solvent
Scheme 1.
MgO (0.68%), SiO2 (2.42%), Al2 O3 (0.46%), Fe2 O3 (0.36%), F− (3.37%), SO3 (2.21%), Na2 O (0.92%), K2 O (0.04%) and (Cd, Zn, Cu, U, Cr, V) (ppm). The basic properties of NP have been determined by the adsorption of phenol on phosphate at 25◦ C as: 616 mol g−1 (1 h); 898 mol g−1 (2 h) and 2066 mol g−1 (24 h). The acidic properties of NP have been demonstrated in the Friedel–Crafts reaction [14]. Indeed, the monoalkyl compounds of benzene and toluene have been obtained with yields (time) of 42% (24 h) and 91% (2 h), respectively, in the presence of NP alone. 2.2. General procedure 2.2.1. Without a solvent NP is used in the catalysis of the Claisen–Schmidt condensation without solvent under different conditions (Table 1). The general procedure is as follows: to a flask containing an equimolar mixture (2.5 mmol) of acetophenone (1) and arylaldehyde (2), NP (2.5 g) was added at room temperature. Workup included extraction with CH2 Cl2 , filtration and evaporation. Products were subsequently purified by distillation under vacuum or recrystallization and identified by 1 H NMR and IR spectroscopy. The same procedure was used for the reactions carried out with NP (2.5 g) activated with water (0.25 ml) and/or benzyltriethylammonium chloride (BTEAC) (0.06 g) water was always added in the last place. 2.2.2. With a solvent To improve the yields, we have worked with different solvents (Table 2). The procedure is as follows: acetophenone (5 mmol) and aldehyde (5 mmol) were dissolved in 5 ml of solvent or (5 ml solvent+2 ml
Product
Water (ml)
BTEAC (g)
Time (h)
Yield (%)
3a
0 0.25 0 0.25
0 0 0.06 0.06
24 24 24 24
10 12 60 77
3b
0 0.25 0 0 0.25
0 0 0.06 0.06 0.06
24 24 1 4 1
0 21 43 91 91
3c
0 0.25 0.25 0 0 0.25 0.25
0 0 0 0.06 0.06 0.06 0.06
24 1 24 1 24 0.25 0.5
28 20 75 37 79 85 92
water). NP (5 g) was added and the mixture was stirred at room temperature. After reaction time, NP was removed by filtration. The alkene (3) was purified by distillation under vacuum (3a and 3b) or recrystallized 3c and identified by 1 H NMR and IR spectroscopy.
3. Results and discussion 3.1. Without solvent The NP alone without solvent is slightly active in the Claisen–Schmidt condensation. The yields do not exceed 28% in 24 h of reaction, in the best case (Table 1). The rate is slow and the yields are poor in spite of the longer reaction times. The addition of water to NP improves the results obtained in the synthesis of alkenes (3a–3c). The addition of BTEAC remarkably increases the catalytic activity of NP in Claisen–Schmidt condensation. The yields are very high and the reaction times are clearly reduced. The simultaneous addition of water and BTEAC show a clear superiority in the activation of NP. Under these conditions all the alkenes (3a–3c) are obtained with good yields. So, the yields (times) are 77% (24 h), 91% (1 h) and 92% (0.5 h), respectively, for 3a, 3b
S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220
219
Table 2 Claisen–Schmidt condensation catalyzed by NP with different solvents Solvent
Methanol
Ethanol
Propan-1-ol
Propan-2-ol
Dioxane
DMF
Acetonitrile
THF
Yielda
75 79
2 96
0 84
0 86
0 84
2 69
0 56
0 42
(%) Yieldb (%) a b
Absence of water. Solvent/water (5 ml/2 ml).
and 3c. The addition of water to BTEAC improves the results obtained in the synthesis of alkenes. This results may be due to the fact that water dissolves the ammonium salt and facilitates its interaction with NP, what can provoke the activation of this last. It is worth noting that, in the same conditions and in absence of NP. Water, BTEAC or both do not promote this reaction. Secondary reaction e.g., Cannizzaro of aldehyde or condensation of ketone, were not observed. Only E isomer of alkenes (3a–3c) was formed. The use of solids catalysts is particularly interesting when they can be regenerated. In this case, NP was regenerated by calcination at 700◦ C during 15 min, and after eight successive recuperations, alkenes (3a–3c) are obtained with the same yields. The NP is a very good catalyst of Claisen–Schmidt condensation when it is used in the presence of small quantities of water and BTEAC without a solvent. The most important features of NP is his small and reactive surface area.
small molecule, can replace water while playing the role of solvent. It is worth noting that, NP is completely insoluble in water, not either in organic solvents. The best condition for synthesis of alkenes 3a are generalized to 3b and 3c (Table 3). We clearly show the activation of natural phosphate by water in all cases. Alkenes (3a–3c) are obtained with very high yields. Ethanol/water is an excellent solvent for Claisen–Schmidt condensation. The amount of solid catalyst influences the yield. Increasing the amount of NP from 50 to 500 mg increases the yield of alkenes 3a and 3b. For alkene 3c, 500 mg of NP lead to increase the reaction rate. Also, NP can be regenerated by calcination at 700◦ C for 15 min.
3.2. With a solvent We have carried out the synthesis of 3a in the presence of natural phosphate in different solvents. The obtained results are summed up in Table 2. The presence of water in medium seems not to be important because similar yields are obtained with methanol alone (75%) and methanol/water (79%). This behavior is different from that observed in other solvents. Water dramatically increases the yield from 2 to 96% with ethanol. In this case, 2 ml of water is the optimum condition for synthesis of alkene 3a (Fig. 1), addition of 1 or 3 ml of water lowered the yield. The activating role of water, very small and polar molecule, can be explained by its adsorption on NP facilitating the contact of the phosphate with substrates, soluble in the organic solvent. The methanol,
Fig. 1. Synthesis of alkene 3a by NP, EtOH and various quantity of water.
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S. Sebti et al. / Applied Catalysis A: General 206 (2001) 217–220
Table 3 Claisen–Schmidt condensation catalyzed by NP with EtOH
References
Product
Weight NP (g)
Water (ml)
Time (h)
Yield (%)
3a
5 5 0.5 5
0 2 2 2
24 4 24 24
2 82 33 96
3b
5 5 0.5 5
0 2 2 2
24 1 8 4
18 69 48 91
3c
5 5 0.5 5
0 2 2 2
[1] R.S. Varma, G.W. Kabalka, L.T. Evans, R.M. Pagni, Synth. Commun. 15 (1985) 279. [2] J.V. Sinisterra, A.G-Raso, J.A. Cabello, J.M. Marinas, Synthesis (1984) 502. [3] A.R. Alcantara, J.M. Marinas, J.V. Sinisterra, Tetrahedron Lett. 28 (1987) 1515. [4] A. Aguilera, A.R. Alcantara, J.M. Marinas, J.V. Sinisterra, Can. J. Chem. 65 (1987) 1165. [5] S. Sathyanarayana, H.G. Krishnamurty, Curr. Sci. 57 (1988) 1114. [6] M.S. Climent, J.M. Marinas, Z. Mouloungui, Y. Le Bigot, M. Delmas, A. Gaset, J.V. Sinisterra, J. Org. Chem. 54 (1989) 3695. [7] A. Fuentes, J.M. Marinas, J.V. Sinisterra, Tetrahedron Lett. 28 (1987) 4541. [8] M.J. Climent, H. Garcia, J. Primo, A. Corma, Catal. Lett. 4 (1990) 85. [9] D. Tichit, M.H. Lhouty, A. Guida, B.H. Chiche, F. Figueras, A. Auroux, D. Bartalini, E. Garrone, J. Catal. 151 (1995) 50. [10] M.J. Climent, A. Corma, S. Iborra, J. Primo, J. Catal. 151 (1995) 60. [11] A. Guida, M.H. Lhouty, D. Tichit, F. Figueras, P. Geneste, Appl. Catal. 164 (1997) 251. [12] S. Sebti, A. Saber, A. Rhihil, Tetrahedron Lett. 35 (1994) 9399. [13] S. Sebti, A. Rhihil, A. Saber, N. Hanafi, Tetrahedron Lett. 37 (1996) 6555. [14] S. Sebti, A. Rhihil, A. Saber, Chem. Lett. 8 (1996) 721. [15] S. Sebti, H. Boukhal, N. Hanafi, S. Boulaajaj, Tetrahedron Lett. 40 (1999) 6207.
4 0.25 2 0.75
40 74 94 94
Natural phosphate, in absence or presence of solvent, is an interesting new catalyst for the Claisen– Schmidt reaction.
Acknowledgements We are grateful to the ‘Office Chérifien des Phosphates (OCP)’ and the ‘Centre d’Etude et de Recherches sur les Phosphates Minéraux (CERPHOS)’ for financial support. Thanks are expressed to Prof. J.A. Mayoral, University of Zaragoza, for co-operation in some of the work presented here.