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Acylation over cation-exchanged montmorillonite
Journal of Molecular Catalysis, 42 (1987)
ACYLATION OVER CATION-EXCHANGED BICH CHICHE,
ANNIE
FINIELS,
229
229 - 235
CATHERINE
MONTMORILLONITE
GAUTHIER,
PATRICK
GENESTE
Laboratoire de Chimie Organique Physique et Cindtique Chimique Appliqukes, Ecole Nationale Sup&ieure de Chimie de Montpellier, 8, rue Ecole Normale, 34075 Montpellier Cedex (France) JEAN GRAILLE
and DANIEL
PIOCH
Division Chimie des Corps Gras, CIRAD-IRHO, (France) (Received November 24,1986;
UA 418
B. P. 5036, 34032 Montpellier Cedex
accepted February 2, 1987)
Summary The Friedel-Crafts acylation of aromatic compounds (benzene, toluene, xylene) with carboxylic acids (CH3(CH2),COOH, n = 0 - 14) was performed over cation-exchanged montmorillonites (H+, Al’+, Ni2+, Zr4+, Ce3+, Cu2+, La3+). Yields in ketones were found to be dependent upon the nature of the interlayer cation and on the acid chain length.
Introduction Montmorillonite clays have been extensively used in the past as acid catalysts [ 11. Recently cation-exchanged montmorillonites have been investigated as active and selective catalysts for the synthesis of organic compounds [ 21. These relatively abundant natural minerals are swelling layer-lattice silicates known as smectites. They possess mica-like structures in which the crystallites are made of negatively-charged silicate sheets with chargebalancing cations located between the sheets [3]. In contrast with micas, the interlayer cations (mainly Na+, Ca2+, K+) are readily exchangeable, and the interlamellar space occupied by the charge-neutralizing cation may swell upon sorption of water, alcohols and a variety of other organic molecules on the large internal surface area (-700 m2 g-l). Most of the chemical reactions occurring on montmorillonites are based on the acidic properties (Bronsted and Lewis acidity) of their surfaces [4]. The Brijnsted acidity is generated by the exchangeable cations, which, upon their polarizing action, enhance the dissociation of the interlayer water molecules. Partial dehydration increases the acidity. Natural montmorillonites have surface acidities, as measured by the Hammett Ho acidity 0304-5102/87/$3.50
0 Elsevier Sequoia Printed in The Netherlands
230
function, ranging from 1.5 to 3. Washing the clay with mineral acid, i.e. exchanging the interlamellar Na+, K+, etc. cations with protons, brings their surface acidity to He values between -5.6 to -8 [5]. The conjunction of a high-surface solid with a layered structure and a high acidity appeared promising for shape-selective acid-catalyzed reactions
[61.
A literature survey reports only a few examples of clay uses as catalysts in Friedel-Crafts reactions. A few patents relate alkylation of aromatic compounds with activated clays [ 71. We have chosen to investigate the Friedel-Crafts acylation reaction over zeolite and montmorillonite, which are crystalline aluminosilicates with’ usually well-defined structure and categorized as acid-type catalysts. Our aim was to study the activity and selectivity of these particular structures in the acylation reaction. In a previous study [8], we investigated the preparation and use of a Ce3+--Y zeolite in the acylation of aromatic compounds with carboxylic acids. The acylation reaction may be written as:
R,
l
CH,(CH, ) COOH
-
+ H20
n
R, = HorCH3 %= HorCH, n=o-14
Experimental Reagents All reagents were of analytical purity (from Fluka or Aldrich). The montmorillonite, originating from Sardinia, was crushed, separated from gross impurities and size-graded in a cyclone before delivery. Eighty-five percent of the particles were specified as being <75 pm. Cation exchange was carried out using a 0.5 M solution of the cation salt to be exchanged. After 24 h contact, the clay was centrifuged and washed repeatedly with deionized water until complete removal of excess salt. The clay was finally centrifuged, dried in an oven at 40 “C and finely ground. The <0.125 E.crn fraction was used as catalyst. The cation-exchange capacity (CEC) of the montmorillonite was ~130 meq per 100 g of dehydrated clay on the basis of chemical analysis data, and the level exchange of different clays was -15 - 20%.
231
General procedure The acylation reaction was performed in a 100 ml glass flask equipped with a Dean-Stark trap and a refrigerant if the reaction was performed at refluxing temperature of the aromatic compound. If the reaction temperature was higher than the boiling point, the reaction was carried out in a 100 ml batch reactor equipped with a magnetic-type stirrer. Before reaction, the clay was dehydrated either by azeotropic distillation with the aromatic compound or by drying at 150 “C under air flow for 6 h if the reaction was carried out in batch. 2 g of dehydrated clay, 40 ml of aromatic compound and 2 mmol of carboxylic acid were introduced in the batch and then heated to the required temperature. Otherwise, the carboxylic acid was added to the flask when no more water was observed in the trap. The mixture was heated during 24 h, then cooled and recovered by filtration and washing several times with the aromatic compound. The aromatic compound was evaporated and the products were purified by column chromatography. The yield was defined as the ratio of the sum of the aromatic ketones, expressed as molar equivalents, to the number of carboxylic acids initially introduced. Analytical methods Analyses were performed using a gas chromatograph equipped with a flame ionization detector, an on-column injector and a CP Wax 57 CB (Chrompack) capillary column (10 m X 0.22 mm). The ‘H NMR spectra were scanned in CDCls solution with a Briiker WP 80 CW spectrometer. GLC-mass spectral analyses were performed with a 5890 Hewlett-Packard using a OVl capillary column (10 m) coupled with a MS5970A mass spectrometer and a 2671G data system. X-ray diagrams were recorded on thin films of ion-exchanged clay using a CGR Teta 60 diffractometer (Cu-Ko radiation at a scanning speed of 2 0 mm-l).
Results As the clay acidity depends upon the nature of the exchanged cation, we have compared a series of cation-exchanged montmorillonites (Table 1). It appeared that A13+ and H+ were the most efficient cations, while Cu2+montmorillonite gave a negligible yield of product. According to Adams et al. [9] M3+-montmorillonites were expected to be more active. than divalent or monovalent ion-exchanged clays. Our results show that Zr4+montmorillonite is less active than H’montmorillonite in the acylation reaction, which can be explained by the four-fold lower amounts of Zr4+ than H+ in H+-montmorillonite or by Zr4+ hydrolysis to form polymerictype species.
232 TABLE 1 Acylation lonite?
of toluene
by dodecanoic
acid over different cation-exchanged
Exchanged cation in montmorillonite
% Yield (x2%) in acylated productsb (o + m + p)
non-exchanged Ala+ H+ Ni2+ Zr4+ Ce”+ cua+ La3+
:o 50 30 30 25 E E
montmoril-
*Cation-exchanged montmorillonite was regenerated by azeotropic reflux in aromatic compounds. bA secondary product (=2%), resulting from dismutation of the methyl group, was formed [ 7 ] :
A fraction of the carboxylic acid and acylated products was lost by sorption in the clay layers. 1 - 2% was recovered by desorption by refluxing in the aromatic compounds.
Noteworthy was that Ce 3+-faujasite was much more active than Ce’+montmorillonite in similar reaction conditions. This probably suggests that the cation effects on the acidity of a catalyst depend upon the framework in which it was exchanged, but it should also be considered that the CEC of zeolite is higher than in montmorillonite. Unexchanged montmorillonite gave a negligible yield and in a control experiment without clay, no reaction occured. The most interesting feature of acylation over zeolite and clay was the difference in selectivity of these two catalysts. With short and medium chain length acids (C, - C12) more meta-isomer was formed over the clay (Table 2). With longer chain (Cl6 - CZo) acids, exclusively para-isomer was formed over zeolite, while for the clay, the isomer distribution was apparently independent of the chain length of the acids (Table 3). The similar isomer distributions for clay and AlCls (Table 2) show that there is little or no shape selectivity over the clay for the acylation reaction with straight chain carboxylic acids. These results may suggest that the stereochemical hindrance to fit the organic molecules between the clay layers imposes less constraint than the cavities and channels in the zeolite structure. While in some cases, cation exchange could be more shape selective within one catalyst than another [lo], this influence did not predominate, as seen in
233 TABLE 2 Comparison of regioselectivity among clay, zeolite and AK& in the acylation of toluence Acyiating agent
Isomers over Cea+-Ya
Isomers over AP+-mont a (%I *
@) octanoic acid dodecanoic acid paimitic acid
Isomers over AlCla* (%I
0
m
P
0
m
P
0
m
P
3 3 0.5
3 3 1
94 94 98.5
5 5 5
9 11 10
86 84 85
4 4 4
16 15 12
80 81 84
aReaction temperature = 130 “C.
TABLE 3 Influence of chain length upon the percentage of isomer distribution in the acylation of toluene over A13+-montmoriilonite Acylating agent
acetic acid propanoic acid hexanoic acid octanoic acid dodecanoic acid palmitic acid
Isomers (%I 0
m
P
e 3 3 5 5 5
E 13 10 9 11 10
:4 87 86 86 85
TABLE 4 Influence of the exchanged toluene by lauric acid Exchanged cation
Ce3+
cation upon the isomer distribution
in the acylation of
Isomers @) 0
m
P
6 5 4
6 11 12
88 84 84
Table 4. Note that the metu/ortho ratio was unity for H’montmorillonite, while with other cations this ratio was -2. The influence of the chain length of the acid upon the yield of acylation appeared to be similar on clay and on zeolite [ 71 (Table 5). Adams et al. [ 111 observed the same behaviour in studying the yields of ether produced in relation to the carbon number of alk-1-enes.
234 TABLE 5 Acylation of toluene montmorillonite
by carboxylic
Acylating agent
Yield (%)
acetic acid propionic acid caproic acid octanoic acid lauric acid palmitic acid
f 12 28 45 60 80
acids CH3(CH&+?OOH
(n = 0 - 14)
over A13+-
TABLE 6 Acylation lonite
of benzene,
toluene and p-xylene
by octanoic
acid over A13+-montmoril-
Aromatic compounds
Reaction temperature (“C)
Yield (%)
benzene benzene toluene p-xylene
80 - 81* 160 110 - 111* 137 - 138*
E 26 45 50
*Reflux temperature.
The acylation was also performed with benzene and xylene. No reaction occurred below 100 “C (Table 6). The differences in activity below and above 100 “C were related directly to the incomplete loss of interlamellar water from the clay during azeotropic distillation [ 121. In conclusion, the synthesis of aromatic ketones may be achieved with an easy-to-handle and cheap catalyst. Investigations are being performed on pillared clays to improve the yield of acylation products in relation to the increase in surface acidity. References 1 B. K. G. Theng, The Chemistry of Clay-Organic Reactions, Hilger, London, 1974. 2 J. M. Thomas, in M. S. Whittingham and A. J. Jacobson (eds.), Intercalation Chemistry, Academic Press, New York, 1982, pp. 55 - 59. 3 R. E. Grim. Clay Mineralogy, 2nd edn., McGraw-Hill, New York, 1968, pp. 77, 188. 4 (a) M. M. Morland and K. V. Raman, Clays Clay Miner., 16 (1968) 393; (b) J. Helsen, J. Chem. Educ., 59 (1982) 1063. 5 H. A. Benesi and B. H. C. Winquist, Adu. Catal., 27 (1978) 170. 6 J. M. Adams, A. Bylina and S. H. Graham, Clays Clay Miner., 16 (1981) 325.
235 7 (a) U.S. Pat. 2945072 (1960) to G. G. Joris and N. J. Madison; (b) U.S. Pat. 2 930820 (1960) to R. S. Aries; (c) U.S. Pat. 3 965 043 (1976) to G. E. Stridde. 8 B. Chiche, A. Finiels, C. Gauthier, P. Geneste, J. Graille and D. Pioch, J. Org. Chem., 51 (1986) 2128. 9 J. M. Adams, T. V. Clapp and D. E. Clement, Clays Clay Miner., 18 (1983) 411. 10 R. B. Borade, A. B. HaIgeri and T. S. R. Rao Prasada, Proc. 7th Natl. Symp. Catal. (1985) 389. 11 J. M. Adams, T. V. Clapp, D. E. Clement and P. I. Reid, J. Mol. Catal., 27 (1984) 179. 12 J. M. Adams, D. E. Clement and S. H. Graham, Clays Clay Miner., 31 (1983) 129.
ACYLATION OVER CATION-EXCHANGED BICH CHICHE,
ANNIE
FINIELS,
229
229 - 235
CATHERINE
MONTMORILLONITE
GAUTHIER,
PATRICK
GENESTE
Laboratoire de Chimie Organique Physique et Cindtique Chimique Appliqukes, Ecole Nationale Sup&ieure de Chimie de Montpellier, 8, rue Ecole Normale, 34075 Montpellier Cedex (France) JEAN GRAILLE
and DANIEL
PIOCH
Division Chimie des Corps Gras, CIRAD-IRHO, (France) (Received November 24,1986;
UA 418
B. P. 5036, 34032 Montpellier Cedex
accepted February 2, 1987)
Summary The Friedel-Crafts acylation of aromatic compounds (benzene, toluene, xylene) with carboxylic acids (CH3(CH2),COOH, n = 0 - 14) was performed over cation-exchanged montmorillonites (H+, Al’+, Ni2+, Zr4+, Ce3+, Cu2+, La3+). Yields in ketones were found to be dependent upon the nature of the interlayer cation and on the acid chain length.
Introduction Montmorillonite clays have been extensively used in the past as acid catalysts [ 11. Recently cation-exchanged montmorillonites have been investigated as active and selective catalysts for the synthesis of organic compounds [ 21. These relatively abundant natural minerals are swelling layer-lattice silicates known as smectites. They possess mica-like structures in which the crystallites are made of negatively-charged silicate sheets with chargebalancing cations located between the sheets [3]. In contrast with micas, the interlayer cations (mainly Na+, Ca2+, K+) are readily exchangeable, and the interlamellar space occupied by the charge-neutralizing cation may swell upon sorption of water, alcohols and a variety of other organic molecules on the large internal surface area (-700 m2 g-l). Most of the chemical reactions occurring on montmorillonites are based on the acidic properties (Bronsted and Lewis acidity) of their surfaces [4]. The Brijnsted acidity is generated by the exchangeable cations, which, upon their polarizing action, enhance the dissociation of the interlayer water molecules. Partial dehydration increases the acidity. Natural montmorillonites have surface acidities, as measured by the Hammett Ho acidity 0304-5102/87/$3.50
0 Elsevier Sequoia Printed in The Netherlands
230
function, ranging from 1.5 to 3. Washing the clay with mineral acid, i.e. exchanging the interlamellar Na+, K+, etc. cations with protons, brings their surface acidity to He values between -5.6 to -8 [5]. The conjunction of a high-surface solid with a layered structure and a high acidity appeared promising for shape-selective acid-catalyzed reactions
[61.
A literature survey reports only a few examples of clay uses as catalysts in Friedel-Crafts reactions. A few patents relate alkylation of aromatic compounds with activated clays [ 71. We have chosen to investigate the Friedel-Crafts acylation reaction over zeolite and montmorillonite, which are crystalline aluminosilicates with’ usually well-defined structure and categorized as acid-type catalysts. Our aim was to study the activity and selectivity of these particular structures in the acylation reaction. In a previous study [8], we investigated the preparation and use of a Ce3+--Y zeolite in the acylation of aromatic compounds with carboxylic acids. The acylation reaction may be written as:
R,
l
CH,(CH, ) COOH
-
+ H20
n
R, = HorCH3 %= HorCH, n=o-14
Experimental Reagents All reagents were of analytical purity (from Fluka or Aldrich). The montmorillonite, originating from Sardinia, was crushed, separated from gross impurities and size-graded in a cyclone before delivery. Eighty-five percent of the particles were specified as being <75 pm. Cation exchange was carried out using a 0.5 M solution of the cation salt to be exchanged. After 24 h contact, the clay was centrifuged and washed repeatedly with deionized water until complete removal of excess salt. The clay was finally centrifuged, dried in an oven at 40 “C and finely ground. The <0.125 E.crn fraction was used as catalyst. The cation-exchange capacity (CEC) of the montmorillonite was ~130 meq per 100 g of dehydrated clay on the basis of chemical analysis data, and the level exchange of different clays was -15 - 20%.
231
General procedure The acylation reaction was performed in a 100 ml glass flask equipped with a Dean-Stark trap and a refrigerant if the reaction was performed at refluxing temperature of the aromatic compound. If the reaction temperature was higher than the boiling point, the reaction was carried out in a 100 ml batch reactor equipped with a magnetic-type stirrer. Before reaction, the clay was dehydrated either by azeotropic distillation with the aromatic compound or by drying at 150 “C under air flow for 6 h if the reaction was carried out in batch. 2 g of dehydrated clay, 40 ml of aromatic compound and 2 mmol of carboxylic acid were introduced in the batch and then heated to the required temperature. Otherwise, the carboxylic acid was added to the flask when no more water was observed in the trap. The mixture was heated during 24 h, then cooled and recovered by filtration and washing several times with the aromatic compound. The aromatic compound was evaporated and the products were purified by column chromatography. The yield was defined as the ratio of the sum of the aromatic ketones, expressed as molar equivalents, to the number of carboxylic acids initially introduced. Analytical methods Analyses were performed using a gas chromatograph equipped with a flame ionization detector, an on-column injector and a CP Wax 57 CB (Chrompack) capillary column (10 m X 0.22 mm). The ‘H NMR spectra were scanned in CDCls solution with a Briiker WP 80 CW spectrometer. GLC-mass spectral analyses were performed with a 5890 Hewlett-Packard using a OVl capillary column (10 m) coupled with a MS5970A mass spectrometer and a 2671G data system. X-ray diagrams were recorded on thin films of ion-exchanged clay using a CGR Teta 60 diffractometer (Cu-Ko radiation at a scanning speed of 2 0 mm-l).
Results As the clay acidity depends upon the nature of the exchanged cation, we have compared a series of cation-exchanged montmorillonites (Table 1). It appeared that A13+ and H+ were the most efficient cations, while Cu2+montmorillonite gave a negligible yield of product. According to Adams et al. [9] M3+-montmorillonites were expected to be more active. than divalent or monovalent ion-exchanged clays. Our results show that Zr4+montmorillonite is less active than H’montmorillonite in the acylation reaction, which can be explained by the four-fold lower amounts of Zr4+ than H+ in H+-montmorillonite or by Zr4+ hydrolysis to form polymerictype species.
232 TABLE 1 Acylation lonite?
of toluene
by dodecanoic
acid over different cation-exchanged
Exchanged cation in montmorillonite
% Yield (x2%) in acylated productsb (o + m + p)
non-exchanged Ala+ H+ Ni2+ Zr4+ Ce”+ cua+ La3+
:o 50 30 30 25 E E
montmoril-
*Cation-exchanged montmorillonite was regenerated by azeotropic reflux in aromatic compounds. bA secondary product (=2%), resulting from dismutation of the methyl group, was formed [ 7 ] :
A fraction of the carboxylic acid and acylated products was lost by sorption in the clay layers. 1 - 2% was recovered by desorption by refluxing in the aromatic compounds.
Noteworthy was that Ce 3+-faujasite was much more active than Ce’+montmorillonite in similar reaction conditions. This probably suggests that the cation effects on the acidity of a catalyst depend upon the framework in which it was exchanged, but it should also be considered that the CEC of zeolite is higher than in montmorillonite. Unexchanged montmorillonite gave a negligible yield and in a control experiment without clay, no reaction occured. The most interesting feature of acylation over zeolite and clay was the difference in selectivity of these two catalysts. With short and medium chain length acids (C, - C12) more meta-isomer was formed over the clay (Table 2). With longer chain (Cl6 - CZo) acids, exclusively para-isomer was formed over zeolite, while for the clay, the isomer distribution was apparently independent of the chain length of the acids (Table 3). The similar isomer distributions for clay and AlCls (Table 2) show that there is little or no shape selectivity over the clay for the acylation reaction with straight chain carboxylic acids. These results may suggest that the stereochemical hindrance to fit the organic molecules between the clay layers imposes less constraint than the cavities and channels in the zeolite structure. While in some cases, cation exchange could be more shape selective within one catalyst than another [lo], this influence did not predominate, as seen in
233 TABLE 2 Comparison of regioselectivity among clay, zeolite and AK& in the acylation of toluence Acyiating agent
Isomers over Cea+-Ya
Isomers over AP+-mont a (%I *
@) octanoic acid dodecanoic acid paimitic acid
Isomers over AlCla* (%I
0
m
P
0
m
P
0
m
P
3 3 0.5
3 3 1
94 94 98.5
5 5 5
9 11 10
86 84 85
4 4 4
16 15 12
80 81 84
aReaction temperature = 130 “C.
TABLE 3 Influence of chain length upon the percentage of isomer distribution in the acylation of toluene over A13+-montmoriilonite Acylating agent
acetic acid propanoic acid hexanoic acid octanoic acid dodecanoic acid palmitic acid
Isomers (%I 0
m
P
e 3 3 5 5 5
E 13 10 9 11 10
:4 87 86 86 85
TABLE 4 Influence of the exchanged toluene by lauric acid Exchanged cation
Ce3+
cation upon the isomer distribution
in the acylation of
Isomers @) 0
m
P
6 5 4
6 11 12
88 84 84
Table 4. Note that the metu/ortho ratio was unity for H’montmorillonite, while with other cations this ratio was -2. The influence of the chain length of the acid upon the yield of acylation appeared to be similar on clay and on zeolite [ 71 (Table 5). Adams et al. [ 111 observed the same behaviour in studying the yields of ether produced in relation to the carbon number of alk-1-enes.
234 TABLE 5 Acylation of toluene montmorillonite
by carboxylic
Acylating agent
Yield (%)
acetic acid propionic acid caproic acid octanoic acid lauric acid palmitic acid
f 12 28 45 60 80
acids CH3(CH&+?OOH
(n = 0 - 14)
over A13+-
TABLE 6 Acylation lonite
of benzene,
toluene and p-xylene
by octanoic
acid over A13+-montmoril-
Aromatic compounds
Reaction temperature (“C)
Yield (%)
benzene benzene toluene p-xylene
80 - 81* 160 110 - 111* 137 - 138*
E 26 45 50
*Reflux temperature.
The acylation was also performed with benzene and xylene. No reaction occurred below 100 “C (Table 6). The differences in activity below and above 100 “C were related directly to the incomplete loss of interlamellar water from the clay during azeotropic distillation [ 121. In conclusion, the synthesis of aromatic ketones may be achieved with an easy-to-handle and cheap catalyst. Investigations are being performed on pillared clays to improve the yield of acylation products in relation to the increase in surface acidity. References 1 B. K. G. Theng, The Chemistry of Clay-Organic Reactions, Hilger, London, 1974. 2 J. M. Thomas, in M. S. Whittingham and A. J. Jacobson (eds.), Intercalation Chemistry, Academic Press, New York, 1982, pp. 55 - 59. 3 R. E. Grim. Clay Mineralogy, 2nd edn., McGraw-Hill, New York, 1968, pp. 77, 188. 4 (a) M. M. Morland and K. V. Raman, Clays Clay Miner., 16 (1968) 393; (b) J. Helsen, J. Chem. Educ., 59 (1982) 1063. 5 H. A. Benesi and B. H. C. Winquist, Adu. Catal., 27 (1978) 170. 6 J. M. Adams, A. Bylina and S. H. Graham, Clays Clay Miner., 16 (1981) 325.
235 7 (a) U.S. Pat. 2945072 (1960) to G. G. Joris and N. J. Madison; (b) U.S. Pat. 2 930820 (1960) to R. S. Aries; (c) U.S. Pat. 3 965 043 (1976) to G. E. Stridde. 8 B. Chiche, A. Finiels, C. Gauthier, P. Geneste, J. Graille and D. Pioch, J. Org. Chem., 51 (1986) 2128. 9 J. M. Adams, T. V. Clapp and D. E. Clement, Clays Clay Miner., 18 (1983) 411. 10 R. B. Borade, A. B. HaIgeri and T. S. R. Rao Prasada, Proc. 7th Natl. Symp. Catal. (1985) 389. 11 J. M. Adams, T. V. Clapp, D. E. Clement and P. I. Reid, J. Mol. Catal., 27 (1984) 179. 12 J. M. Adams, D. E. Clement and S. H. Graham, Clays Clay Miner., 31 (1983) 129.