- Email: [email protected]
Solid base catalysts obtained from hydrotalcite precursors, for Knoevenagel synthesis of cinamic acid and coumarin derivatives
Applied Catalysis A: General 308 (2006) 13–18 www.elsevier.com/locate/apcata
Solid base catalysts obtained from hydrotalcite precursors, for Knoevenagel synthesis of cinamic acid and coumarin derivatives E. Angelescu a,*, O.D. Pavel a, R. Bıˆrjega b, R. Za˘voianu a, G. Costentin c, M. Che c a
Department of Chemical Technology and Catalysis, Faculty of Chemistry, University of Bucharest, 4-12 Regina Elisabeta Bd., S3, 030018 Bucharest, Romania b S.C. ZECASIN S.A., Splaiul Independentei 202, S6, Bucharest, Romania c Lab. de Re´activite´ de Surface, UMR 7609, University Pierre et Marie Curie, 4 Place Jussieu, Case 178, 75252 Paris Cedex 05, France Received 24 November 2005; received in revised form 3 April 2006; accepted 3 April 2006 Available online 18 May 2006
Abstract The goal of this paper was to study the synthesis of the cinamic acid, coumarin-3-carboxilic acid and their ethylesters by Knoevenagel condensation using the solid base catalysts obtained from calcined Mg–Al, Mg–Al + Ln (Ln = Dy, Gd) and Li–Al hydrotalcites, under solvent free conditions. Correlations between the basicity of the catalysts and the advancement degree in the pathway of the condensation reaction have also been investigated. # 2006 Elsevier B.V. All rights reserved. Keywords: Calcined hydrotalcites; Solid base catalysts for cinamic acid and coumarin derivatives synthesis
1. Introduction Many organic syntheses of fine chemicals and drugs often use mineral or organic acids and bases as homogeneous catalysts. The recovery of these conventional catalysts is difficult and their utilization is associated with environmental pollution because large quantities of waste are produced. The application of solid acidic and basic catalysts in clean technologies and sustainable chemistry is a ‘‘green’’ alternative for benign processes with high yield and selectivity along with waste reduction, easier catalysts recovery procedures, and safer and easier operation modes. These solid catalysts do not need a polar solvent and the reaction can be conducted at higher temperature or in vapor phase under heterogeneous conditions [1]. For many reactions, the search for more easily available solids able to act as basic solids catalysts is of great interest [2–4]. Hydrotalcites (HTs)orlayered doublehydroxides (LDHs)with general formula [M1x2+Mx3+(OH)2]x+Ax/nnmH2O consist of brucite-like layers which have a positive charge compensated by anionic species in the interlayer space along with water molecules
* Corresponding author. Tel.: +40 21 4103178/138; fax: +40 21 3159249. E-mail address: [email protected] (E. Angelescu). 0926-860X/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2006.04.011
[1–3]. The M2+ and M3+ ions occupy octahedral sites and there is no evidence for ordering of the cations. The compounds with general formula [M+Al2(OH)6]XmH2O (X = OH, Cl, Br, NO3, etc.) with LDH structure are limited only to Li+ which has ˚ for Li+ an ionic radius comparable to that of Mg2+ (0.76 A 2+ ˚ for Mg ) [5]. Their structure is constituted of compared to 0.72 A cation-containing layers with octahedral aluminum arranged in a gibbsite-like structure where the octahedral vacancies are occupied by Li+ ions [6–10]. The hydrotalcites and the corresponding mixed oxides obtained by thermal treatment could be used as basic solid catalysts in Knoevenagel condensation reactions to obtain for example, derivatives of cinamic acid, coumarin acid or coumarin. Cinamic esters as well as coumarin (2H-1-benzopyran-2-one) or its derivatives are important products in cosmetics, perfumery and pharmaceutical industry [11,12]. They are synthesized via Knoevenagel [13], Perkin [14], Pechman [15], Reformatsky [16] and Witing [17] reactions using different acidic and basic catalysts [12,18]. Particularly, for the Knoevenagel condensation, amines, carboxylic or Lewis acids under homogeneous conditions [19] and aluminum oxide [20], cationic exchanged zeolites [21], alkali-containing MCM-41 [22], tert-butoxide on xonotlite [23], montmorillonite [18] or bentonite clays [24,25] under solid phase synthesis have been used.
14
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
To our knowledge, the activity of LDH-derived catalysts containing lanthanides or lithium in this type of reaction has not yet been investigated. Moreover, the data published until now stipulate that coumarin is obtained directly and do not take in consideration the advancement degree of the condensation process along with the by-products formed during the consecutive steps. Therefore, in this paper we have chosen to investigate the synthesis of cinamic acid, coumarin-3carboxylic acid and their esters by Knoevenagel condensation of benzoic aldehyde and diethylmalonate and salycilaldehyde with diethylmalonate, respectively, assisted by Mg–Al, Mg– Al + Ln (Ln = Dy, Gd) and Li–Al mixed oxides catalysts obtained from the corresponding LDH precursors. In order to get more valuable informations on the advancement degree of the condensation process, the products and the by-products have been analyzed by gas-chromatography coupled with MS spectrometry. Correlations with the basic character of the catalysts and the advancement degree of the condensation reaction have also been investigated. 2. Experimental 2.1. Catalysts preparation The Mg–Al and Mg–Al + Ln layered double hydroxides (Ln = Dy, Gd) and the corresponding mixed oxides were prepared according to procedures already described [26]. The LDH with chemical composition [LiAl2(OH)7]2H2O was prepared by a wet chemical route involving the reaction under refluxing condition of a hydrated alumina gel Al2O3yH2O (80 < y < 120) with LiOH (Li2O/Al2O3 > 0.5) in presence of hydrophilic solvents such as ethanol. The hydrated alumina gel was obtained by hydrolysis of Al(O–iC3H7)3. The resulting gel was filtered and washed with hot demineralized water, then dried at 90 8C for 24 h. In order to obtain Li–Al LDH the alumina gel was suspended in a conical flask containing an ethanolic solution of LiOH (Li/Al = 4 in 50% ethanol and 50% water) and refluxed for 8 h under continuous magnetic stirring. The reaction vessel was fitted with a water-cooled condenser and an alkali-guard tube to prevent CO2 contamination. The as-obtained solid product was washed until free of unreacted LiOH (pH 8–8.5) then it was filtered and dried at 90 8C for 24 h. The mixed oxides derived from the dried Mg–Al, Mg– Al + Ln and Li–Al LDHs were obtained upon thermal treatment at 460 8C for 18 h under nitrogen flow. 2.2. Catalysts characterization The X-ray diffraction (XRD) data were collected on a computer assisted DRON-3 diffractometer equipped with a graphite monochromator using the Cu Ka radiation (l = 1.5418) in an angular range from 7 to 808, a step width of 0.058 and an acquisition time of 2 s for each step. Surface areas were determined from N2 adsorption– desorption isotherms using the BET equation using a Carlo Erba equipment.
FT-IR spectra were recorded on a BioRad FTS 135 spectrometer using the KBr pellet technique. The spectra wavenumber domain was between 400 and 4000 cm1. While preparing the KBr pellets the same concentration of hydrotalcite in KBr was used (e.g. 0.01%). The spectra have been recorded using the same energy of the IR beam and the background due to KBr spectrum was substracted. Basicity measurements were carried out by CO2–TPD using a micro-reactor device. The sample was pretreated in nitrogen at 460 8C for 3 h, then cooled to 80 8C prior to the adsorption of CO2 at this temperature. After adsorption of CO2 (30 mL/min) for 1 h, the sample was flushed with N2 for 1 h at 120 8C in order to remove the physisorbed CO2. The desorption curve upon temperature was recorded at a heating rate of 10 8C/min from 120 to 500 8C using a recorder connected to a GC equipped with a TCD detector. Catalytic tests were performed in a glass batch reactor equipped with a condenser system. 10 mmole aldehyde, 15 mmole diethylmalonate and 1 g catalyst were stirred and heated at 160 8C in a silicon oil bath. After 24 h of reaction under reflux, the reactor was cooled to room temperature and 50 ml methanol was added in order to render soluble all the organic compounds (heated again under reflux for 10 min). The catalyst was removed by filtration and the organic phase was concentrated under vacuum, then analyzed by GC using a K072320 Termo-Quest chromatograph equipped with a FID detector and a capillary column of 30 m length and 0.324 mm diameter and DB-5 stationary phase. Highly pure N2 (99.999%) was used as carrier gas. The reaction products were identified also by mass spectrometer-coupled chromatography, using a GC/MS/MS VARIAN SATURN 2100 T equipped with a CPSIL 8 CB Low Bleed/MS column of 30 m length and 0.25 mm diameter. 3. Results and discussion The structural data of LDH precursors of the catalysts are presented in Table 1. Table 1 Structural data of the LDH precursors of the catalysts Catalysts
Lattice meters
para-
Intensities ratio
˚) a (A
˚) c (A
I0 0 3/I1 1 0
I0 0 3/I0 0 6
3.069 3.069 3.070
23.643 23.864 23.810
7.35 4.94 4.16
2.54 2.37 2.29
D (%)a
b
Mg–Al LDHs Mg–Al Mg–Al + Dy Mg–Al + Gd Catalysts
Li–Al LDH Li–Al a
Lattice meters
para-
4.67 14.41 17.52 D (%)a
Intensities ratio
˚) a (A
˚) c (A
I0 0 3/I3 0 0
I0 0 3/I0 0 6
5.101
22.695
4.39
1.72
3.03
D (%) disorder degree along c-axis calculated as the ratio between the FWHM and the area of the basal reflection (0 0 3). b From reference [26].
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
Fig. 1. The XRD patterns of the Li–Al LDH sample (a) and their mixed oxide obtained upon calcinations, (b) with (*) are denoted peaks belonging to LiAlO20.25H2O phase.
The XRD patterns of Mg–Al and Mg–Al + Ln (Ln = Dy, Gd) LDH samples have already been presented in our previous paper [26]. It has been shown that the LDH structure was not altered due to the addition of rare-earth elements (REEs). There was apparently no modification of the lattice parameter a, ascertaining the non-substitution in the brucite layer of the REEs, while the lattice parameter c increased slightly suggesting the intercalation of REEs in the interlayer region. In the calcined samples, denoted Mg(Al)O, Mg(Al/Ln)O, the formation of a Mg(Al3+ Ln3+)O solid solution of MgOpericlase type has been identified. This is a defective structure with a certain degree of cation vacancies generated by the introduction of Al3+ and Ln3+ in the octahedral sites [27,28]. The XRD pattern of as-prepared Li–Al catalyst corresponds to the structure of LDH of the LiAl2(OH)72H2O type (JCPDS file 40-0710). The diffractogram could be indexed as a primitive hexagonal cell using the space group P32 (1 4 5) (JCPDS file 31-0704) or P63/mcm (1 9 3) [7]. The XRD pattern was indexed in space group P32 (1 4 5) as in JCPDS file 310704 and 40-0710 (Fig. 1) in order to get comparable basal reflections with those of Mg–Al LDHs. The Li–Al LDH structure is still under debate [6,7] due to different locations proposed for Li+ ions either in tetrahedral sites below the aluminum layer or in octahedral sites in gibbsite layers similar to those observed in Mg–Al LDHs structures. However, one
15
should bear in mind that the lattice parameter a reflects different structures for the two types of LDHs: the ‘‘Mg(OH)2-brucite’’ type layer structure of common Mg–Al LDHs and the ‘‘Al(OH)3-gibbsite’’ type layer structure of Li–Al LDH, respectively. The calcined sample is denoted (Li/Al)O. The calcined form of Li–Al LDH presents a main phase corresponding to LiAlO2 (JCPDS file 44-0224) mixed with fine particles of a hydrated form LiAlO20.25H2O (JCPDS file 210487). The textural data and basicity measurements of the calcined samples are gathered in Table 2. It shows the predominance of mesoporosity, reflected by the values of the mean pore diameters. The overall basicities of mixed oxides samples originating from the Mg–Al type LDHs are comparable. The Mg(Al/Gd)O sample exhibits a higher overall basicity but similar percentages of weak, medium-strength and strong basic sites. The weak basic sites are associated with surface OH groups; the medium-strength basic sites are related to oxygen bridging Mg2+–O2 and Al3+/Ln3+–O2 pairs [29,30]. The strong basic sites are O2– anions of the lattice in the vicinity of the brucitetype layer defects [26,31]. The mixed oxides obtained via the calcination of Li–Al LDH exhibit the lowest overall basicity but, the highest population of weak and medium-strength basic sites representing 38% of the overall basicity in comparison with 18–20% for Mg(Al)O and Mg(Al/Ln)O samples. The FT-IR spectra of Mg–Al and Li–Al LDHs are shown in Fig. 2. Both spectra display a broad absorption band at 3400– 3500 cm1 attributed to the stretching vibration of hydrogenbonded in the OH groups located between the brucite/gibbsite layers. This maximum is displaced depending the different compositions of LDH (Li–Al or Mg–Al), in agreement with the literature data [2,8] published until now. The deformation vibration of water molecules appears at 1630–1650 cm1 and its magnitude depends on the hydration degree and the nature of interlayer anions. The interlayer carbonate ion may exist either as mono or bidentate and presents characteristic bands at around 1485, 1420 and 1375 cm1 [2]. The Li–Al LDH spectrum exhibits sharp peaks around 1000, 740 and 540 cm1 characteristic of AlO6 octahedras and a strong and sharp peak at 1300 cm1 due to the intercalation of Li(OH)2 in the intermediate layer [8]. The calcined LDH samples were tested in Knoevenagel condensation of diethylmalonate with benzaldehyde (Fig. 3, A
Table 2 Textural data and basicity of mixed oxides obtained via LDH samples calcinations Surface area (m2 g1)
Catalyst
a
Mg(Al)O Mg(Al/Dy)O a Mg(Al/Gd)O a (Li–Al)O a
188 164 228 151
From reference [26].
Vol. ads. (cm3 g1)
0.258 0.223 0.367 0.423
˚) Mean pore size (A
55 54 64 56
Basicity (mmole CO2 g1 103) (%) Overall basicity (%)
Weak (%)
Medium (%)
Strong (%)
310.2 309.9 490.2 259.7
18.8 18.0 25.1 21.1
33.8 41.0 63.8 78.5
257.6 250.9 401.3 160.1
(100) (100) (100) (100)
(6) (6) (5) (8)
(11) (13) (13) (30)
(83) (81) (82) (62)
16
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18 Table 3 The activity and selectivity of mixed oxides derived from LDHs in Knoevenagel reaction—A route (Fig. 3) Catalyst
Mg(Al)O Mg(Al/Dy)O Mg(Al/Gd)O (Li–Al)O
Conversion of aldehyde (%) 43 32 59 37
Selectivity (%) IA
IIA
IIIA
By-products
43 30 25 20
21 24 22 31.5
4 21 26 32
32 25 27 16.5
Molar ratio malonic ester/benzaldehyde = 1.5/1.
Fig. 2. The FT-IR spectra of Li–Al and Mg–Al LDH samples.
route) and salicylaldehyde (Fig. 3, B route), respectively. The reactions proceed by successive steps as presented in Fig. 3. Some previous experimental tests of condensation on Mg(Al)O using malonic acid and salicylaldehyde lead to low conversion levels (12–20%). These results may be attributed to the poisoning of active basic sites of the catalysts by malonic acid. The results of experiments carried out along the A or B route are presented in Tables 3 and 4. They evidence that the progression of the chemical transformation is different depending upon catalyst. For route A, the conversion of aldehyde varies between 32 and 59%, as a function of catalyst, the most active being the Mg(Al/Gd)O catalyst. High selectivity in cinamic acid and ethylester (63%) was obtained on (Li/Al)O; also, only a small amount of by-products was formed. The mixed oxide Mg(Al)O promotes the condensation reaction particularly to yield the first product of condensation (IA). The modified Mg(Al/Dy)O and Mg(Al/Gd)O
Fig. 3. The reaction pathway for the synthesis of cinamic acid and coumarin derivatives by Knoevenagel condensation.
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
17
Table 4 The activity and selectivity of mixed oxides obtained from hydrotalcite precursors in Knoevenagel condensation—B route (Fig. 3) Catalyst
Mg(Al)O Mg(Al/Dy)O Mg(Al/Gd)O (Li–Al)O
Conversion of aldehyde (%)
88 80 94 83
Selectivity (%) IB (C14)
IIB (C11)
IIIB (C12)
IVB (C10)
VB (C9)
VIB (C9)
By-products
Compounds with a-pyrone ring IIIB + IVB + VIB
9.1 3.9 1.8 2.2
19.2 29.4 20.9 8.0
12.6 8.5 6.3 56.0
3.2 6.8 5.1 1.5
3.8 2.7 3.0 6.3
29.3 24.7 39.6 21.3
22.8 24.0 23.3 4.7
45.1 40.0 51.0 78.8
Molar ratio malonic ester/salicylaldehyde = 1.5/1.
catalysts favour in almost the same measure the formation of IA, IIA and IIIA compounds leading to an unselective transformation. The catalysts that contain Mg lead also to almost double amounts of by-products compared to the (Li/Al)O. For B route, high conversions of salicylaldehyde have been obtained for all the catalysts tested. The main result is that (Li/ Al)O catalyst is the most selective among the series, leading to the lowest amount of by-products and the highest selectivity in coumarin derivatives with benzo-a-pyrone ring. All tested catalysts promoted the advanced condensation to form transcinamic acid and ester, which are the precursors of coumarin compounds. One reaction pathway converts the ortho-hydroxibenzylidendiethylmalonate (IB) to coumaric acid ethyl ester (IIB) and coumarinic acid ethyl ester (IIB0 ). The product IIB0 is very unstable and undergoes cyclisation to coumarin (VIB). Meanwhile, according to a parallel reaction route the elimination of an esteric group from IB leads to the closure of the coumarinic ring yielding the coumarin-3-carboxylic acid ethyl ester (IIIB) and coumarin-3-carboxylic acid (IVB), which are also precursors of coumarin (VIB). The (Li/Al)O catalyst which has the highest amount of weak and medium basic sites is the more efficient for advancing the reaction towards the formation of coumarin derivatives. As already suggested, hydrotalcites and mixed oxides behave as ditopic catalysts, which contain both basic and acidic sites [18,32]. The basic sites associated to the negative charges dispersed over the entire sheets of surface oxygen atoms activate the Knoevenagel condensation. Furthermore, acidic properties of these compounds may influence the stabilization of the anionic intermediate and yield of the reaction [33]. The results correlated with the basicity of the catalysts lead to the conclusion that the advancement degrees of both condensation reactions are promoted by weak and mediumstrength basic sites. The formation of the by-products may be related to the presence of the strong basic sites, which may promote the aldolic and crotonic condensations of the carbonylic reactant. From the data presented in Tables 2 and 3 it may be seen that the amount of by-products varies in the same order as the percentage of strong basic sites in the catalysts: MgðAlÞO > MgðAl=GdÞO > MgðAl=DyÞO > ðLiAlÞO The different activities of Mg–Al and Li–Al mixed oxides may be also a consequence of the structural differences between the catalysts precursors (‘‘Mg(OH)2-brucite’’ type layer for
Mg–Al and ‘‘Al(OH)3-gibbsite’’ type layer for Li–Al, respectively). It might be assumed that particularly for Knoevenagel condensation of salicyaldehyde with diethylmalonate to secure good yields in coumarin compounds both acidic and basic sites are required. This assumption is supported by the reported results of low yield in coumarin synthesis via condensation of phenols with ethylacetoacetate on basic MgO [12] and good results in Knoevenagel condensation on complex acid and basic oxides containing montmorillonite clay [18]. 4. Conclusions These results shown that the synthesis of cinamic acid and coumarin derivatives via Knoevenagel condensation were catalysed by mixed oxides obtained from Mg/Al, Mg–Al + Ln (Ln = Dy, Gd) and Li/Al LDH precursors. The above-described method is a simple, efficient and environmentally benign. A dependence of the activity and selectivity on the chemical composition and the catalyst basicity was evidenced. It was additionally observed that a higher advancement degree of the reaction requires a higher concentration of weak and medium basic sites. Acknowledgement The financial support of this research through Grant 4-44/2004 in the framework of the National Plan of Research, Development and Innovation—CERES Programme of the Romanian Minister of Education and Research is gratefully acknowledged. References [1] B.F. Sels, D.E. de Vos, P. Jacobs, Catal. Rev. 43 (2001) 443. [2] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173. [3] S. Albertazzi, F. Basile, A. Vaccari, in: F. Wypych, K.G. Satyanarayana (Eds.), Clay Surfaces. Fundamentals and Applications, Interface Science and Technology, vol. 1, Elsevier, 2004, p. 497. [4] Y. Ono, J. Catal. 216 (2003) 216. [5] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751. [6] A.V. Besserguenev, A.M. Fogg, R.J. Francis, S.J. Price, D. O’Hare, Chem. Mater. 9 (1997) 241. [7] G.S. Thomas, P.V. Kannath, Mater. Res. Bull. 37 (2002) 705. [8] N. Nayak, T.R. Kutty, V. Jayaraman, G. Periaswamy, J. Mater. Chem. 7 (10) (1997) 2131. [9] I. Sissiko, E.T. Iyagba, R. Sahai, P. Biloen, J. Solid State Chem. 60 (1985) 283. [10] C.J. Serma, J.L. Rendom, J.E. Iglesias, Clays Clays Miner. 30 (1982) 180.
18
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
[11] H.D.R. Murray, J. Mendez, A.S. Brown, The Natural Coumarins: Occurrence, Chemistry and Biochemistry, Wiley, New York, 1982. [12] A. Ramani, B.M. Chanda, S. Velu, S. Sivansaker, Green Chem. 1 (3) (1999) 163. [13] G. Jones, Org. React. 15 (1967) 204. [14] J.R. Johnson, Org. React. 1 (1942) 210. [15] H.V. Pechman, C. Duisberg, Chem. Ber. 17 (1884) 929. [16] R.L. Shirner, Org. React. 1 (1942) 1. [17] N.S. Narashimahan, R.S. Mali, M.V. Barve, Synthesis (1979) 906. [18] F. Bigi, L. Chesini, R. Maggi, G. Sartori, J. Org. Chem. 64 (1999) 1033. [19] F.L. Tietze, U. Beifuss, in: B.M. Trust, L. Fleming, C.H. Heathcock (Eds.), Comprehensive Organic Synthesis, vol. 2, Pergamon Press, Oxford, 1991, pp. 341–394. [20] J.A. Cabello, J.M. Campelo, E. Garcia, D. Luna, J.M. Marinas, J. Org. Chem. 49 (1948) 5195. [21] A. Corma, R.M. Martin-Aranda, J. Catal. 130 (1991) 130. [22] K.R. Kloestra, H. van Bekkum, J. Chem. Soc.: Chem. Commun. 10 (1995) 1005.
[23] S. Chalais, P. Laszlo, A. Mathy, Tetrahedron Lett. 26 (1985) 4453. [24] F. Delgano, J. Tamariz, G. Zepeda, M. Landa, R. Miranda, J. Garcia, Synth. Commun. 25 (1995) 753. [25] Y. Ono, T. Baba, Catalysis, vol. 15, Royal Soc. Chem, Cambridge, UK, 2000, p. 1. [26] R. Birjega, O.D. Pavel, G. Costentin, M. Che, E. Angelescu, Appl. Catal. A 288 (2005) 185. [27] V.K. Diez, C.R. Apesteguia, J.I. Di Cosimo, J. Catal. 215 (2003) 220. [28] A. Vaccari, Appl. Clay Sci. 14 (1999) 16. [29] M.R. Gelsthorpe, K.B. Mok, J.R.H. Ross, R.M. Sambrook, J. Mol. Catal. A 25 (1984) 253. [30] A. Corma, V. Fornes, M.R. Martin-Aranda, J.M. Krafft, H. Lauron-Pernot, M. Che, J. Catal. 235 (2005) 413. [31] A. Corma, V. Fornes, F. Rey, J. Catal. 148 (1994) 205. [32] G. Alberti, V. Constantino, in: L.J. Atwood, J.E.P. Davies, D.D. MacNicol, F. Vogtle (Eds.), Comprehensive Supramolecular Chemistry, vol. 7, Pergamon Press, Oxford, 1996, p. 1. [33] M.L. Bailly, C. Chizallet, G. Costentin, J.M. Krafft, H. Lauron-Pernot, M. Che, J. Catal. 235 (2005) 413.
Solid base catalysts obtained from hydrotalcite precursors, for Knoevenagel synthesis of cinamic acid and coumarin derivatives E. Angelescu a,*, O.D. Pavel a, R. Bıˆrjega b, R. Za˘voianu a, G. Costentin c, M. Che c a
Department of Chemical Technology and Catalysis, Faculty of Chemistry, University of Bucharest, 4-12 Regina Elisabeta Bd., S3, 030018 Bucharest, Romania b S.C. ZECASIN S.A., Splaiul Independentei 202, S6, Bucharest, Romania c Lab. de Re´activite´ de Surface, UMR 7609, University Pierre et Marie Curie, 4 Place Jussieu, Case 178, 75252 Paris Cedex 05, France Received 24 November 2005; received in revised form 3 April 2006; accepted 3 April 2006 Available online 18 May 2006
Abstract The goal of this paper was to study the synthesis of the cinamic acid, coumarin-3-carboxilic acid and their ethylesters by Knoevenagel condensation using the solid base catalysts obtained from calcined Mg–Al, Mg–Al + Ln (Ln = Dy, Gd) and Li–Al hydrotalcites, under solvent free conditions. Correlations between the basicity of the catalysts and the advancement degree in the pathway of the condensation reaction have also been investigated. # 2006 Elsevier B.V. All rights reserved. Keywords: Calcined hydrotalcites; Solid base catalysts for cinamic acid and coumarin derivatives synthesis
1. Introduction Many organic syntheses of fine chemicals and drugs often use mineral or organic acids and bases as homogeneous catalysts. The recovery of these conventional catalysts is difficult and their utilization is associated with environmental pollution because large quantities of waste are produced. The application of solid acidic and basic catalysts in clean technologies and sustainable chemistry is a ‘‘green’’ alternative for benign processes with high yield and selectivity along with waste reduction, easier catalysts recovery procedures, and safer and easier operation modes. These solid catalysts do not need a polar solvent and the reaction can be conducted at higher temperature or in vapor phase under heterogeneous conditions [1]. For many reactions, the search for more easily available solids able to act as basic solids catalysts is of great interest [2–4]. Hydrotalcites (HTs)orlayered doublehydroxides (LDHs)with general formula [M1x2+Mx3+(OH)2]x+Ax/nnmH2O consist of brucite-like layers which have a positive charge compensated by anionic species in the interlayer space along with water molecules
* Corresponding author. Tel.: +40 21 4103178/138; fax: +40 21 3159249. E-mail address: [email protected] (E. Angelescu). 0926-860X/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2006.04.011
[1–3]. The M2+ and M3+ ions occupy octahedral sites and there is no evidence for ordering of the cations. The compounds with general formula [M+Al2(OH)6]XmH2O (X = OH, Cl, Br, NO3, etc.) with LDH structure are limited only to Li+ which has ˚ for Li+ an ionic radius comparable to that of Mg2+ (0.76 A 2+ ˚ for Mg ) [5]. Their structure is constituted of compared to 0.72 A cation-containing layers with octahedral aluminum arranged in a gibbsite-like structure where the octahedral vacancies are occupied by Li+ ions [6–10]. The hydrotalcites and the corresponding mixed oxides obtained by thermal treatment could be used as basic solid catalysts in Knoevenagel condensation reactions to obtain for example, derivatives of cinamic acid, coumarin acid or coumarin. Cinamic esters as well as coumarin (2H-1-benzopyran-2-one) or its derivatives are important products in cosmetics, perfumery and pharmaceutical industry [11,12]. They are synthesized via Knoevenagel [13], Perkin [14], Pechman [15], Reformatsky [16] and Witing [17] reactions using different acidic and basic catalysts [12,18]. Particularly, for the Knoevenagel condensation, amines, carboxylic or Lewis acids under homogeneous conditions [19] and aluminum oxide [20], cationic exchanged zeolites [21], alkali-containing MCM-41 [22], tert-butoxide on xonotlite [23], montmorillonite [18] or bentonite clays [24,25] under solid phase synthesis have been used.
14
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
To our knowledge, the activity of LDH-derived catalysts containing lanthanides or lithium in this type of reaction has not yet been investigated. Moreover, the data published until now stipulate that coumarin is obtained directly and do not take in consideration the advancement degree of the condensation process along with the by-products formed during the consecutive steps. Therefore, in this paper we have chosen to investigate the synthesis of cinamic acid, coumarin-3carboxylic acid and their esters by Knoevenagel condensation of benzoic aldehyde and diethylmalonate and salycilaldehyde with diethylmalonate, respectively, assisted by Mg–Al, Mg– Al + Ln (Ln = Dy, Gd) and Li–Al mixed oxides catalysts obtained from the corresponding LDH precursors. In order to get more valuable informations on the advancement degree of the condensation process, the products and the by-products have been analyzed by gas-chromatography coupled with MS spectrometry. Correlations with the basic character of the catalysts and the advancement degree of the condensation reaction have also been investigated. 2. Experimental 2.1. Catalysts preparation The Mg–Al and Mg–Al + Ln layered double hydroxides (Ln = Dy, Gd) and the corresponding mixed oxides were prepared according to procedures already described [26]. The LDH with chemical composition [LiAl2(OH)7]2H2O was prepared by a wet chemical route involving the reaction under refluxing condition of a hydrated alumina gel Al2O3yH2O (80 < y < 120) with LiOH (Li2O/Al2O3 > 0.5) in presence of hydrophilic solvents such as ethanol. The hydrated alumina gel was obtained by hydrolysis of Al(O–iC3H7)3. The resulting gel was filtered and washed with hot demineralized water, then dried at 90 8C for 24 h. In order to obtain Li–Al LDH the alumina gel was suspended in a conical flask containing an ethanolic solution of LiOH (Li/Al = 4 in 50% ethanol and 50% water) and refluxed for 8 h under continuous magnetic stirring. The reaction vessel was fitted with a water-cooled condenser and an alkali-guard tube to prevent CO2 contamination. The as-obtained solid product was washed until free of unreacted LiOH (pH 8–8.5) then it was filtered and dried at 90 8C for 24 h. The mixed oxides derived from the dried Mg–Al, Mg– Al + Ln and Li–Al LDHs were obtained upon thermal treatment at 460 8C for 18 h under nitrogen flow. 2.2. Catalysts characterization The X-ray diffraction (XRD) data were collected on a computer assisted DRON-3 diffractometer equipped with a graphite monochromator using the Cu Ka radiation (l = 1.5418) in an angular range from 7 to 808, a step width of 0.058 and an acquisition time of 2 s for each step. Surface areas were determined from N2 adsorption– desorption isotherms using the BET equation using a Carlo Erba equipment.
FT-IR spectra were recorded on a BioRad FTS 135 spectrometer using the KBr pellet technique. The spectra wavenumber domain was between 400 and 4000 cm1. While preparing the KBr pellets the same concentration of hydrotalcite in KBr was used (e.g. 0.01%). The spectra have been recorded using the same energy of the IR beam and the background due to KBr spectrum was substracted. Basicity measurements were carried out by CO2–TPD using a micro-reactor device. The sample was pretreated in nitrogen at 460 8C for 3 h, then cooled to 80 8C prior to the adsorption of CO2 at this temperature. After adsorption of CO2 (30 mL/min) for 1 h, the sample was flushed with N2 for 1 h at 120 8C in order to remove the physisorbed CO2. The desorption curve upon temperature was recorded at a heating rate of 10 8C/min from 120 to 500 8C using a recorder connected to a GC equipped with a TCD detector. Catalytic tests were performed in a glass batch reactor equipped with a condenser system. 10 mmole aldehyde, 15 mmole diethylmalonate and 1 g catalyst were stirred and heated at 160 8C in a silicon oil bath. After 24 h of reaction under reflux, the reactor was cooled to room temperature and 50 ml methanol was added in order to render soluble all the organic compounds (heated again under reflux for 10 min). The catalyst was removed by filtration and the organic phase was concentrated under vacuum, then analyzed by GC using a K072320 Termo-Quest chromatograph equipped with a FID detector and a capillary column of 30 m length and 0.324 mm diameter and DB-5 stationary phase. Highly pure N2 (99.999%) was used as carrier gas. The reaction products were identified also by mass spectrometer-coupled chromatography, using a GC/MS/MS VARIAN SATURN 2100 T equipped with a CPSIL 8 CB Low Bleed/MS column of 30 m length and 0.25 mm diameter. 3. Results and discussion The structural data of LDH precursors of the catalysts are presented in Table 1. Table 1 Structural data of the LDH precursors of the catalysts Catalysts
Lattice meters
para-
Intensities ratio
˚) a (A
˚) c (A
I0 0 3/I1 1 0
I0 0 3/I0 0 6
3.069 3.069 3.070
23.643 23.864 23.810
7.35 4.94 4.16
2.54 2.37 2.29
D (%)a
b
Mg–Al LDHs Mg–Al Mg–Al + Dy Mg–Al + Gd Catalysts
Li–Al LDH Li–Al a
Lattice meters
para-
4.67 14.41 17.52 D (%)a
Intensities ratio
˚) a (A
˚) c (A
I0 0 3/I3 0 0
I0 0 3/I0 0 6
5.101
22.695
4.39
1.72
3.03
D (%) disorder degree along c-axis calculated as the ratio between the FWHM and the area of the basal reflection (0 0 3). b From reference [26].
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
Fig. 1. The XRD patterns of the Li–Al LDH sample (a) and their mixed oxide obtained upon calcinations, (b) with (*) are denoted peaks belonging to LiAlO20.25H2O phase.
The XRD patterns of Mg–Al and Mg–Al + Ln (Ln = Dy, Gd) LDH samples have already been presented in our previous paper [26]. It has been shown that the LDH structure was not altered due to the addition of rare-earth elements (REEs). There was apparently no modification of the lattice parameter a, ascertaining the non-substitution in the brucite layer of the REEs, while the lattice parameter c increased slightly suggesting the intercalation of REEs in the interlayer region. In the calcined samples, denoted Mg(Al)O, Mg(Al/Ln)O, the formation of a Mg(Al3+ Ln3+)O solid solution of MgOpericlase type has been identified. This is a defective structure with a certain degree of cation vacancies generated by the introduction of Al3+ and Ln3+ in the octahedral sites [27,28]. The XRD pattern of as-prepared Li–Al catalyst corresponds to the structure of LDH of the LiAl2(OH)72H2O type (JCPDS file 40-0710). The diffractogram could be indexed as a primitive hexagonal cell using the space group P32 (1 4 5) (JCPDS file 31-0704) or P63/mcm (1 9 3) [7]. The XRD pattern was indexed in space group P32 (1 4 5) as in JCPDS file 310704 and 40-0710 (Fig. 1) in order to get comparable basal reflections with those of Mg–Al LDHs. The Li–Al LDH structure is still under debate [6,7] due to different locations proposed for Li+ ions either in tetrahedral sites below the aluminum layer or in octahedral sites in gibbsite layers similar to those observed in Mg–Al LDHs structures. However, one
15
should bear in mind that the lattice parameter a reflects different structures for the two types of LDHs: the ‘‘Mg(OH)2-brucite’’ type layer structure of common Mg–Al LDHs and the ‘‘Al(OH)3-gibbsite’’ type layer structure of Li–Al LDH, respectively. The calcined sample is denoted (Li/Al)O. The calcined form of Li–Al LDH presents a main phase corresponding to LiAlO2 (JCPDS file 44-0224) mixed with fine particles of a hydrated form LiAlO20.25H2O (JCPDS file 210487). The textural data and basicity measurements of the calcined samples are gathered in Table 2. It shows the predominance of mesoporosity, reflected by the values of the mean pore diameters. The overall basicities of mixed oxides samples originating from the Mg–Al type LDHs are comparable. The Mg(Al/Gd)O sample exhibits a higher overall basicity but similar percentages of weak, medium-strength and strong basic sites. The weak basic sites are associated with surface OH groups; the medium-strength basic sites are related to oxygen bridging Mg2+–O2 and Al3+/Ln3+–O2 pairs [29,30]. The strong basic sites are O2– anions of the lattice in the vicinity of the brucitetype layer defects [26,31]. The mixed oxides obtained via the calcination of Li–Al LDH exhibit the lowest overall basicity but, the highest population of weak and medium-strength basic sites representing 38% of the overall basicity in comparison with 18–20% for Mg(Al)O and Mg(Al/Ln)O samples. The FT-IR spectra of Mg–Al and Li–Al LDHs are shown in Fig. 2. Both spectra display a broad absorption band at 3400– 3500 cm1 attributed to the stretching vibration of hydrogenbonded in the OH groups located between the brucite/gibbsite layers. This maximum is displaced depending the different compositions of LDH (Li–Al or Mg–Al), in agreement with the literature data [2,8] published until now. The deformation vibration of water molecules appears at 1630–1650 cm1 and its magnitude depends on the hydration degree and the nature of interlayer anions. The interlayer carbonate ion may exist either as mono or bidentate and presents characteristic bands at around 1485, 1420 and 1375 cm1 [2]. The Li–Al LDH spectrum exhibits sharp peaks around 1000, 740 and 540 cm1 characteristic of AlO6 octahedras and a strong and sharp peak at 1300 cm1 due to the intercalation of Li(OH)2 in the intermediate layer [8]. The calcined LDH samples were tested in Knoevenagel condensation of diethylmalonate with benzaldehyde (Fig. 3, A
Table 2 Textural data and basicity of mixed oxides obtained via LDH samples calcinations Surface area (m2 g1)
Catalyst
a
Mg(Al)O Mg(Al/Dy)O a Mg(Al/Gd)O a (Li–Al)O a
188 164 228 151
From reference [26].
Vol. ads. (cm3 g1)
0.258 0.223 0.367 0.423
˚) Mean pore size (A
55 54 64 56
Basicity (mmole CO2 g1 103) (%) Overall basicity (%)
Weak (%)
Medium (%)
Strong (%)
310.2 309.9 490.2 259.7
18.8 18.0 25.1 21.1
33.8 41.0 63.8 78.5
257.6 250.9 401.3 160.1
(100) (100) (100) (100)
(6) (6) (5) (8)
(11) (13) (13) (30)
(83) (81) (82) (62)
16
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18 Table 3 The activity and selectivity of mixed oxides derived from LDHs in Knoevenagel reaction—A route (Fig. 3) Catalyst
Mg(Al)O Mg(Al/Dy)O Mg(Al/Gd)O (Li–Al)O
Conversion of aldehyde (%) 43 32 59 37
Selectivity (%) IA
IIA
IIIA
By-products
43 30 25 20
21 24 22 31.5
4 21 26 32
32 25 27 16.5
Molar ratio malonic ester/benzaldehyde = 1.5/1.
Fig. 2. The FT-IR spectra of Li–Al and Mg–Al LDH samples.
route) and salicylaldehyde (Fig. 3, B route), respectively. The reactions proceed by successive steps as presented in Fig. 3. Some previous experimental tests of condensation on Mg(Al)O using malonic acid and salicylaldehyde lead to low conversion levels (12–20%). These results may be attributed to the poisoning of active basic sites of the catalysts by malonic acid. The results of experiments carried out along the A or B route are presented in Tables 3 and 4. They evidence that the progression of the chemical transformation is different depending upon catalyst. For route A, the conversion of aldehyde varies between 32 and 59%, as a function of catalyst, the most active being the Mg(Al/Gd)O catalyst. High selectivity in cinamic acid and ethylester (63%) was obtained on (Li/Al)O; also, only a small amount of by-products was formed. The mixed oxide Mg(Al)O promotes the condensation reaction particularly to yield the first product of condensation (IA). The modified Mg(Al/Dy)O and Mg(Al/Gd)O
Fig. 3. The reaction pathway for the synthesis of cinamic acid and coumarin derivatives by Knoevenagel condensation.
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
17
Table 4 The activity and selectivity of mixed oxides obtained from hydrotalcite precursors in Knoevenagel condensation—B route (Fig. 3) Catalyst
Mg(Al)O Mg(Al/Dy)O Mg(Al/Gd)O (Li–Al)O
Conversion of aldehyde (%)
88 80 94 83
Selectivity (%) IB (C14)
IIB (C11)
IIIB (C12)
IVB (C10)
VB (C9)
VIB (C9)
By-products
Compounds with a-pyrone ring IIIB + IVB + VIB
9.1 3.9 1.8 2.2
19.2 29.4 20.9 8.0
12.6 8.5 6.3 56.0
3.2 6.8 5.1 1.5
3.8 2.7 3.0 6.3
29.3 24.7 39.6 21.3
22.8 24.0 23.3 4.7
45.1 40.0 51.0 78.8
Molar ratio malonic ester/salicylaldehyde = 1.5/1.
catalysts favour in almost the same measure the formation of IA, IIA and IIIA compounds leading to an unselective transformation. The catalysts that contain Mg lead also to almost double amounts of by-products compared to the (Li/Al)O. For B route, high conversions of salicylaldehyde have been obtained for all the catalysts tested. The main result is that (Li/ Al)O catalyst is the most selective among the series, leading to the lowest amount of by-products and the highest selectivity in coumarin derivatives with benzo-a-pyrone ring. All tested catalysts promoted the advanced condensation to form transcinamic acid and ester, which are the precursors of coumarin compounds. One reaction pathway converts the ortho-hydroxibenzylidendiethylmalonate (IB) to coumaric acid ethyl ester (IIB) and coumarinic acid ethyl ester (IIB0 ). The product IIB0 is very unstable and undergoes cyclisation to coumarin (VIB). Meanwhile, according to a parallel reaction route the elimination of an esteric group from IB leads to the closure of the coumarinic ring yielding the coumarin-3-carboxylic acid ethyl ester (IIIB) and coumarin-3-carboxylic acid (IVB), which are also precursors of coumarin (VIB). The (Li/Al)O catalyst which has the highest amount of weak and medium basic sites is the more efficient for advancing the reaction towards the formation of coumarin derivatives. As already suggested, hydrotalcites and mixed oxides behave as ditopic catalysts, which contain both basic and acidic sites [18,32]. The basic sites associated to the negative charges dispersed over the entire sheets of surface oxygen atoms activate the Knoevenagel condensation. Furthermore, acidic properties of these compounds may influence the stabilization of the anionic intermediate and yield of the reaction [33]. The results correlated with the basicity of the catalysts lead to the conclusion that the advancement degrees of both condensation reactions are promoted by weak and mediumstrength basic sites. The formation of the by-products may be related to the presence of the strong basic sites, which may promote the aldolic and crotonic condensations of the carbonylic reactant. From the data presented in Tables 2 and 3 it may be seen that the amount of by-products varies in the same order as the percentage of strong basic sites in the catalysts: MgðAlÞO > MgðAl=GdÞO > MgðAl=DyÞO > ðLiAlÞO The different activities of Mg–Al and Li–Al mixed oxides may be also a consequence of the structural differences between the catalysts precursors (‘‘Mg(OH)2-brucite’’ type layer for
Mg–Al and ‘‘Al(OH)3-gibbsite’’ type layer for Li–Al, respectively). It might be assumed that particularly for Knoevenagel condensation of salicyaldehyde with diethylmalonate to secure good yields in coumarin compounds both acidic and basic sites are required. This assumption is supported by the reported results of low yield in coumarin synthesis via condensation of phenols with ethylacetoacetate on basic MgO [12] and good results in Knoevenagel condensation on complex acid and basic oxides containing montmorillonite clay [18]. 4. Conclusions These results shown that the synthesis of cinamic acid and coumarin derivatives via Knoevenagel condensation were catalysed by mixed oxides obtained from Mg/Al, Mg–Al + Ln (Ln = Dy, Gd) and Li/Al LDH precursors. The above-described method is a simple, efficient and environmentally benign. A dependence of the activity and selectivity on the chemical composition and the catalyst basicity was evidenced. It was additionally observed that a higher advancement degree of the reaction requires a higher concentration of weak and medium basic sites. Acknowledgement The financial support of this research through Grant 4-44/2004 in the framework of the National Plan of Research, Development and Innovation—CERES Programme of the Romanian Minister of Education and Research is gratefully acknowledged. References [1] B.F. Sels, D.E. de Vos, P. Jacobs, Catal. Rev. 43 (2001) 443. [2] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 11 (1991) 173. [3] S. Albertazzi, F. Basile, A. Vaccari, in: F. Wypych, K.G. Satyanarayana (Eds.), Clay Surfaces. Fundamentals and Applications, Interface Science and Technology, vol. 1, Elsevier, 2004, p. 497. [4] Y. Ono, J. Catal. 216 (2003) 216. [5] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751. [6] A.V. Besserguenev, A.M. Fogg, R.J. Francis, S.J. Price, D. O’Hare, Chem. Mater. 9 (1997) 241. [7] G.S. Thomas, P.V. Kannath, Mater. Res. Bull. 37 (2002) 705. [8] N. Nayak, T.R. Kutty, V. Jayaraman, G. Periaswamy, J. Mater. Chem. 7 (10) (1997) 2131. [9] I. Sissiko, E.T. Iyagba, R. Sahai, P. Biloen, J. Solid State Chem. 60 (1985) 283. [10] C.J. Serma, J.L. Rendom, J.E. Iglesias, Clays Clays Miner. 30 (1982) 180.
18
E. Angelescu et al. / Applied Catalysis A: General 308 (2006) 13–18
[11] H.D.R. Murray, J. Mendez, A.S. Brown, The Natural Coumarins: Occurrence, Chemistry and Biochemistry, Wiley, New York, 1982. [12] A. Ramani, B.M. Chanda, S. Velu, S. Sivansaker, Green Chem. 1 (3) (1999) 163. [13] G. Jones, Org. React. 15 (1967) 204. [14] J.R. Johnson, Org. React. 1 (1942) 210. [15] H.V. Pechman, C. Duisberg, Chem. Ber. 17 (1884) 929. [16] R.L. Shirner, Org. React. 1 (1942) 1. [17] N.S. Narashimahan, R.S. Mali, M.V. Barve, Synthesis (1979) 906. [18] F. Bigi, L. Chesini, R. Maggi, G. Sartori, J. Org. Chem. 64 (1999) 1033. [19] F.L. Tietze, U. Beifuss, in: B.M. Trust, L. Fleming, C.H. Heathcock (Eds.), Comprehensive Organic Synthesis, vol. 2, Pergamon Press, Oxford, 1991, pp. 341–394. [20] J.A. Cabello, J.M. Campelo, E. Garcia, D. Luna, J.M. Marinas, J. Org. Chem. 49 (1948) 5195. [21] A. Corma, R.M. Martin-Aranda, J. Catal. 130 (1991) 130. [22] K.R. Kloestra, H. van Bekkum, J. Chem. Soc.: Chem. Commun. 10 (1995) 1005.
[23] S. Chalais, P. Laszlo, A. Mathy, Tetrahedron Lett. 26 (1985) 4453. [24] F. Delgano, J. Tamariz, G. Zepeda, M. Landa, R. Miranda, J. Garcia, Synth. Commun. 25 (1995) 753. [25] Y. Ono, T. Baba, Catalysis, vol. 15, Royal Soc. Chem, Cambridge, UK, 2000, p. 1. [26] R. Birjega, O.D. Pavel, G. Costentin, M. Che, E. Angelescu, Appl. Catal. A 288 (2005) 185. [27] V.K. Diez, C.R. Apesteguia, J.I. Di Cosimo, J. Catal. 215 (2003) 220. [28] A. Vaccari, Appl. Clay Sci. 14 (1999) 16. [29] M.R. Gelsthorpe, K.B. Mok, J.R.H. Ross, R.M. Sambrook, J. Mol. Catal. A 25 (1984) 253. [30] A. Corma, V. Fornes, M.R. Martin-Aranda, J.M. Krafft, H. Lauron-Pernot, M. Che, J. Catal. 235 (2005) 413. [31] A. Corma, V. Fornes, F. Rey, J. Catal. 148 (1994) 205. [32] G. Alberti, V. Constantino, in: L.J. Atwood, J.E.P. Davies, D.D. MacNicol, F. Vogtle (Eds.), Comprehensive Supramolecular Chemistry, vol. 7, Pergamon Press, Oxford, 1996, p. 1. [33] M.L. Bailly, C. Chizallet, G. Costentin, J.M. Krafft, H. Lauron-Pernot, M. Che, J. Catal. 235 (2005) 413.