Ind. Eng. Chem. Res. 2001, 40, 4485-4490
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APPLIED CHEMISTRY Acylation and Related Reactions under Microwaves. 5. Development to Large Laboratory Scale with a Continuous-Flow Process1 Julien Marquie´ ,† Gean Salmoria,‡ Martine Poux,§ Andre´ Laporterie,*,† Jacques Dubac,*,† and Nicolas Roques| He´ te´ rochimie Fondamentale et Applique´ e (UMR 5069 CNRS), Universite´ Paul-Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France, Laboratoire d’Electronique, Ecole Nationale Supe´ rieure d’Electronique, Electrotechnique, Informatique et Hydraulique, 2 rue Camichel, 31071 Toulouse Cedex, France, Laboratoire de Ge´ nie Chimique, Ecole Nationale Supe´ rieure d'Inge´ nieurs de Ge´ nie Chimique, 18 Chemin de la Loge, 31078 Toulouse Cedex, France, and Rhodia Organique Fine, Centre de Recherche de Lyon, 85 rue des Fre` res Perret, 69192 Saint-Fons Cedex, France
Iron(III) chloride-catalyzed Friedel-Crafts acylation and sulfonylation of aromatics have been carried out using a continuous-flow microwave (MW) reactor. The MW applicator is a monomode waveguide fitted with power and temperature controls. The flow-through system operates at atmospheric pressure, and homogeneous conditions were ensured by using an excess of the aromatic. Factors that influence the reaction yield (MW power, ratio and flow rate of reactants) were optimized for two different types of substrate, two polar aromatic ethers, anisole (1) and phenetole (2), and a nonpolar arene, mesitylene (3). Although the energy yield was mainly influenced by the nature of the aromatic, the temperature necessary to achieve a high yield was reached in all cases. Methoxybenzophenone (7), 4-chloroethoxybenzophenone (8), and mesityl phenyl sulfone (9) were obtained from 1-3 and the corresponding acid chloride in 85-95% yield with a 1.2 L h-1 flow rate. 1. Introduction Friedel-Crafts (FC) type reactions such as acylation and sulfonylation suffer from the problem of the amount of catalyst required.2,3 Because of its complexation with the ketone or sulfone produced, the catalyst must be used in at least stoichiometric amounts in the presence of a solvent. Moreover, an “industrially friendly” chemical process must take account of the wastes generated after hydrolytic workup. A number of true catalysts are known,2e,g-y,3d-h but for the most part, they require high temperatures and long reaction times; furthermore, it is sometimes necessary to add large amounts of a metallic salt (such as the hazardous lithium perchlorate)2g,h,j and also to use a solvent. Recently, we have shown that, in FC reactions, microwave (MW) heating can advantageously replace classical heating4 by allowing (i) a close fit of the irradiation mode (continuous or sequential) with each reaction medium; (ii) efficient control of the given energetic power; and (iii) the development of strong temperature gradients, leading to a noticeable shortening of reaction times, in particular for the more reactive aromatic substrates (“expeditious conditions”). * Corresponding authors. E-mail: laporter@chimie. ups-tlse.fr. † Universite ´ Paul-Sabatier. ‡ Ecole Nationale Supe ´ rieure d’Electronique, Electrotechnique, Informatique et Hydraulique. § Ecole Nationale Supe ´ rieure d'Inge´nieurs de Ge´nie Chimique. | Centre de Recherche de Lyon.
For several years now, MWs have been popular in chemical engineering, for example, in the drying of pharmaceuticals and food products, the defrosting of frozen food, the processing of elastomers,5 or even the extraction of essential oils.6 Generating the energy necessary for chemical transformations directly inside the material rather than by an exterior to interior transfer (classical heating) is an idea that is gaining ground. As a matter of fact, in publications concerning MW technology, a growing number of patents for chemical syntheses are appearing.7 However, scale-up batch processes are hampered by problems such as the homogeneity of the electromagnetic field in the reactor, as well as the numerous difficulties in developing large, efficient, and safe cavities. For these reasons, the technology of using MW heating for chemical synthesis is not yet widely established in industry. Another way to treat larger reaction volumes, without increasing the volume of the reactor itself, is to use a continuous-flow system. Some laboratory-scale continuous microwave reactors (CMWR) have already been described.8-13 The two main systems use either a domestic multimode oven equipped with a Teflon coil,8,9 in which numerous organic syntheses have been conducted, some of them under high pressure (up to 1400 kPa) and at temperatures up to 200 °C, or a more advanced applicator (such as a monomode waveguide) that permits MW power control, coupled with a tubular reactor, for liquid10,13 or gaseous12 flow. The continuous-flow recycle reactor pro-
10.1021/ie0103299 CCC: $20.00 © 2001 American Chemical Society Published on Web 09/25/2001
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posed by one of us and co-workers, suitable for homogeneous and heterogeneous reactions, operates at atmospheric pressure in open- or closed-loop mode and is fitted with a temperature control system.10 The present paper reports our investigations on the scale-up of the syntheses, under MW irradiation, of aromatic ketones and sulfones, in solvent-free and homogeneous catalytic conditions, using a flow-through reactor. 2. Description and Advantages of the Continuous-Flow MW Apparatus Used The MW applicator used was the prototype previously fabricated in two of our laboratories14 and partially modified. It consists of a magnetron working at a frequency of 2.45 GHz (power range up to 800 W) and a waveguide of rectangular cross section, giving a TE10 mode propagation. The waveguide is fitted with a circulator, a water load (which absorbs the reflected power and protects the magnetron), and a directional coupler. Equipped with two probes connected to a wattmeter, this coupler measures the input and reflected power levels. To minimize the reflected power and to optimize the interaction between the electromagnetic field and the reaction medium, an adaptation of the system is achieved by means of regulating screws inserted into the waveguide. The tubular quartz reactor is dipped into the waveguide through a Teflon guide, which ensures its correct location, and is protected by brass tubing to avoid any leakage of waves (Figure 1). The reagent mixture was stirred beforehand in a three-neck flask until the entire quantity of catalyst (FeCl3) had been solubilized. Then, it was transferred by use of a variable-flow pump into the reactor through which the liquid progresses upward. The irradiated liquid flowed into a condenser and was collected at its exit. The temperature was measured on-line inside the reactor at the level of the irradiated zone (T1) and at the reactor exit (T2) using an optical fiber thermometer. The reaction resulted in the formation of a gaseous product (hydrogen chloride), which was exhausted by bubbling nitrogen into the reaction flow and also by use of suction at the top of reactor. This continuous-flow apparatus and the reactor are depicted in Figure 2. Batch experiments were carried out in a reactor of the same size but equipped with a Teflon stirrer paddle and a reflux condenser connected to a drying tube (CaCl2). The advantages of MW heating over conventional heating (insofar as the reaction mixture is able to absorb the MW energy) with respect to their use in a flowthrough process have been particularly well-described by Strauss et al.9 Because the reaction mixture is heated directly, its response to the MW irradiation is relatively rapid. Thus, the temperature gradient rises steeply, leading to a acceleration of the reaction, an essential condition in a flow-through system. Another important advantage of MW heating in a such system is the “on/ off condition”, i.e., the possibility to turning the MW source on or off instantaneously. This allows one to carry out MW irradiation in a sequential mode,4c-e an impossibility with conventional heating. It is also an important safety factor for both batch and flow-through reactions. These two main characteristics of MW heating, already advantageous in the case of batch reactions, are of major significance for the development of a continuous-flow system.
Figure 1. (a) Microwave apparatus and its applicator: 1, electric generator; 2, magnetron; 3, waveguide; 4, circulator; 5, water load; 6, wattmeter; 7, monomode cavity. (b) Detail of monomode cavity: 8, regulating screws; 9, short-circuit; 10, brass tubing.
Figure 2. Continuous-flow apparatus and reactor: 1, reaction mixture; 2, mechanical stirring; 3, dehydrating (CaCl2); 4, pump; 5, reactor (internal diameter 3 cm; useful volume 33 mL; irradiated volume 11 mL); 6, gas exit; 7, nitrogen bubbler; 8, optical fibers; 9, condenser; 10, collector.
3. Results and Discussion The operating conditions are derived from our previous work on the same reactions under MW heating using a batch system.4c-e Among the catalysts tested, iron(III) chloride exhibited very good activity and proved
Ind. Eng. Chem. Res., Vol. 40, No. 21, 2001 4487 Table 1. Benzoylation of Anisole (1) under Different MW Incident Powers Lasting 1 mina,b entry
Pi (W)
Pa (W)
F (%)
T (°C)
yield of ketone 7c (%)
1 2 3 4 5
79 73 57 42 35
74 69 52 41 34
94 95 91 98 97
140 137 135 120 110
95 95 95 75 60
a 1, 4.62 g (42.7 mmol); 4, 1.51 g (10.7 mmol); FeCl , 0.174 g 3 (1.07 mmol); overall volume ) 5.9 mL; no stirring. b Pi ) incident power; Pa ) absorbed power (Pa ) Pi - Pr); Pr ) reflected power; F (energy yield) ) Pa/Pi; T ) temperature at the end of the irradiation time. c Yield calculated by GC with respect to 4; ortho7/para-7 ) 6/94: T ) 60-300 °C (20 °C min-1), tR (ortho) ) 7.46 min, tR (para) ) 8.14 min.
Figure 3. Variation of the reflection factor (Γ) and of the temperature (T, °C) for the benzoylation of anisole (1) under MW irradiation (batch system; incident power (Pi) 79 W for 1 min; 1/4/ FeCl3 ) 4.62 g/1.51 g/0.174 g).
easily soluble in the hot reaction mixture. This catalyst, a common and inexpensive material, was chosen for this study. The use of an excess of the aromatic starting material removes the need for a solvent, a necessary condition for efficient and nonhazardous heating by MWs. Moreover, this excess of the aromatic (2-4 times the amount of the electrophilic reagent, the acid chloride) enables one to maintain the reaction mixture as a homogeneous liquid despite the fact that some of the products are solids, as in the case of diaryl sulfones. 3.1. Acylation of Aromatic Ethers. First, we examined the acylation of anisole (1) by benzoyl chloride (4). To know approximately the energy requirement for this reaction, a preliminary study was carried out in a batch reactor with a reagent ratio of 1/4/FeCl3 ) 4/1/ 0.1 (by mole). The reaction mixture was irradiated at different incident powers (Pi) for 1 min (Table 1). In a first experiment (entry 1), for Pi ) 79 W, almost quantitative conversion to ketone 7 was obtained (95%). Examining the reflected power (Pr) during this experiment, we observed that it decreases simultaneously with the progress of the reaction (Figure 3). The energy yield values (F ) Pa/Pi), which increase from 75% (t ) 0) to 96% (t ) 60 s), and the values of the reflection factor [Γ ) (Pr/Pi)1/2], which decrease from 0.50 (t ) 0) to 0.20 (t ) 60 s), show the anticipated variation with experimental conditions. In agreement with our previous observations, it is not surprising to see that, for a constant incident power, the absorbed power (Pa) increases during the reaction, as the ketone produced, 7, and especially its FeCl3 complex absorb the MWs more
Table 2. Benzoylation of Anisole (1) and Phenetole (2) Using the Continuous Microwave Reactora,b entry
experiment (fraction; mass)
Pi (W)
Pa (W)
F (%)
T1 (°C)
product, yieldc
1 2 3 4 5 6 7 8 9 10
Ad (1; 30 g) Ad (2; 200 g) Be (1; 30 g) Be (2; 43 g) Be (3; 155 g) Cf (1; 30 g) Cf (2; 300 g) Dg (1; 30 g) Dg (2; 100 g) Dg (3; 230 g)
365 365 250 330 380 266 256 200 206 250
160 160 115 156 176 221 235 184 188 235
44 44 46 47 47 83 92 92 91 94
20-120 120-140 20-80 80-110 110-140 20-140 140-145 20-150 150-160 160-175
7, 50% 7, 72% 7, 50% 7, 70% 7, 90% 7, 70% 7, 85% 8, 70% 8, 89% 8, 95%
a Experiments A-C, reaction between 1 and 4; experiment D, reaction between 2 and 5. b See Table 1; T1 ) temperature inside the irradiation chamber. c Yield calculated by GC with respect to 4 (ketone 7) or 2 (ketone 8); ortho-7/para-7 ) 6/94 (See Table 1); ortho-8/para-8 ) 9/91; T ) 125-300 °C (20 °C min-1), tR (ortho) ) 7.78 min, tR (para) ) 8.75 min. d 1, 2 mol; 4, 0.5 mol; FeCl3, 0.05 mol; flow rate, 48 mL min-1. e 1, 2 mol; 4, 0.5 mol; FeCl3, 0.05 mol; flow rate, 20 mL min-1. f 1, 2 mol; 4, 1 mol; FeCl3, 0.1 mol; flow rate, 22 mL min-1. g 2, 2 mol; 5, 1 mol; FeCl3, 0.1 mol; flow rate, 22 mL min-1.
strongly than do reactants 1 and 4.4c,d,f One can see (Figure 3) that Γ decreased more rapidly as soon as the reaction temperature was reached (∆Γ20-60s ) -0.25) relative to the beginning of the irradiation (∆Γ0-20s ) -0.05). Moreover, from results obtained for various Pi values (Table 1), it follows that an incident power of 57 W was sufficient to obtain a high yield of ketone 7, corresponding to an energy of about 530 J/mL of reaction mixture. Several experiments were carried out to determine the optimum concentration and flow rate of the reaction mixture into the CMWR. Three of them are reported in Table 2. For the first experiment (A), 2 mol of 1 and 0.5 mol of 4 were brought together with 0.05 mol of FeCl3, and the mixture was irradiated under 365 W power (Pi) with a 48 mL min-1 flow rate. After a head fraction (Table 2, entry 1), a regular flow was obtained for a middle fraction (entry 2), and the overall conversion into the aryl ketone 7 was 72%. The absorbed power did not exceed 160 W, and the energy yield was 44%. For the second experiment (B), the flow rate was reduced to 20 mL min-1, and two middle fractions were obtained (Table 2, entries 4,5). With an incident power of 330 W, the yield did not increase with respect to that of the preceding experiment, but under 380 W, the temperature increased to 140 °C, and the yield rose to 90%. Unfortunately, the energy yield (47%) was similar to that previously observed; that is, more than one-half the incident energy was reflected. In this case (entry 5), knowing that -176 W of power was absorbed by a reaction flow of 11 mL (see Figure 2) during 33 s with a 20 mL min-1 flow rate, it is important to note that the absorbed energy, for almost the same yield of ketone 7 was identical (528 J mL-1) to that absorbed with the batch system. Previously, we have shown that the reaction species that absorb the most MW energy are the aryl ketone produced and its FeCl3 complex.4c To induce an acceleration of the reaction and then a steeper T gradient, the starting mixture was concentrated (Table 2, experiment C). Similarly, in the CMWR, we processed a mixture containing 2 mol of 1, 1 mol of 4, and 0.1 mol of FeCl3 with a 20 mL min-1 flow rate. For a weaker Pi than before, 256 W instead of 380 W, the energy yield became 92%, and the reaction yield was 85%. The
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Table 3. Sulfonylation of Mesitylene (3) Using the Continuous Microwave Reactora,b experiment Pi Pa F entry (fraction; mass) (W) (W) (%) 1 2 3
E (1; 30 g) E (2; 250 g) E (3; 100 g)
375 143 375 142 380 148
38 38 39
T1 (°C)
yield of sulfone 9c (%)
20-125 125-127 127-132
36 86 95
a 3, 2 mol; 6, 1 mol; FeCl , 0.05 mol; flow rate, 22 mL min-1. 3 See Table 1; T1 ) temperature inside the irradiation chamber. c Yield calculated by GC with respect to 6; T ) 125-300 °C (20 °C min-1), tR ) 8.58 min. b
temperature of the mixture in the irradiated part of the reactor oscillated between 140 and 145 °C. The same approach was used for the benzoylation of phenetole (2) by 4-chlorobenzoyl chloride (5) (experiment D). A 22 mL min-1 flow rate of a mixture 2/5/FeCl3 ) 2/1/0.1 (by mole) that absorbed a power of 206-250 W gave very high energy and reaction yields (Table 2, entries 9 and 10). These experimental conditions were close to those used for the experiment C, but because the boiling point of 2 is higher than that of 1, the reaction mixture was able to reach a somewhat higher temperature. This led to more rapid formation of the aryl ketone 8 and a better yield (95%) (entry 10). 3.2. Sulfonylation of Mesitylene. We now describe the use of the CMWR for the case of a nonpolar aromatic substrate, mesitylene (3), which, contrary to the aromatic ethers 1 and 2, is not heated by MW irradiation. The reaction studied was the sulfonylation of 3 by benzenesulfonyl chloride (6) in the presence of 5% (by mole) of FeCl3, this catalytic amount being sufficient for the corresponding batch reaction.4e The solution concentration (3/6 ) 2/1 by mole) and the flow rate (22 mL min-1) were the same as before. The results (Table 3) showed that, despite a high Pi (375-380 W), Pa remained weak because of a poor energy yield, below 40%; nevertheless, the reaction yield was high (95%). The energy yield could be increased in several different ways. However, it is not viable to improve the yield by increasing the concentration of reagent 6 because the reaction product (9) is a solid. Neither doubling the amount of catalyst nor halving the flow rate gave a noticeable increase in the energy yield. This fact seems related to the nonpolar nature of the aromatic substrate, as we shall demonstrate. Figure 4 reports the reflection factor values for the batch sulfonylation of 3 using 149 W of MW power for 1 min (yield of sulfone 9 ) 95%). With respect to the corresponding benzoylation of anisole (Figure 3), one can see that the Γ values were obviously higher, revealing a greater reflected power and, consequently, a lower energy yield and the variation of Γ during the MW heating was quite different: Γ increased at the beginning of the irradiation and then decreased as soon as the reaction started to occur (T ≈ 100 °C) to reach a value of 0.64, which corresponds to an energy yield of 58%. This is a result, on one hand, of the excess (with respect to 6) of the “MW-transparent” mesitylene at the beginning of the irradiation and, on the other hand, of the progressive formation above 100 °C of the sulfone 9, which, together with its FeCl3 complex, strongly absorbs the MWs.4e 4. Conclusion The MW applicator described in this work, and the appended measuring instruments (power, temperature),
Figure 4. Variation of the reflection factor (Γ) and of the temperature (T, °C) for the sulfonylation of mesitylene (3) under MW irradiation (batch system; incident power (Pi) 149 W for 1 min; 3/6/FeCl3 ) 3.60 g/2.65 g/0.120 g).
were used successfully to carry out Friedel-Crafts reactions on a large laboratory scale with a continuousflow process. The benzoylation of anisole and phenetole and the benzenesulfonylation of mesitylene were performed in the presence of a catalytic amount of iron(III) chloride. An excess of aromatic substrate allows one to operate in homogeneous medium and vitiates the need for solvent, a prerequisite condition for efficient and nonhazardous MW heating. Acylation and sulfonylation of aromatics are appropriate for these experiments, because the reaction product (ketone or sulfone) and its FeCl3 complex absorb the MWs more strongly than do the reactants. The factors influencing continuous-flow processes are of two types: those that can be modified and those beyond our control. Because the irradiation frequency is fixed (2.45 GHz), one cannot control the absorption power (i.e., the dielectric characteristics) of the chemical substances involved in the reaction. Factors over which one can have some control are the MW power given by the magnetron (Pi) and its reflected part (Pr), the ratio of reactants, and the flow rate in the reactor. An optimization of these factors allows the reaction to proceed efficiently in terms not only of product formation but also of energy yield, and with a very satisfactory flow rate for a laboratory-scale process. Finally, this study shows once more that the problem of MW heating in terms of the necessity to develop large irradiation cavities can be turned to advantage by the use of a CMWR. This methodology, which has been applied here to catalyzed reactions in homogeneous media and which can also be carried out heterogeneously,10 offers, when compared with conventional heating, the significant advantages of energy-savings and the rapid on/off capability of the electromagnetic source, a characteristic safety device of the process. 5. Experimental Section All reagents (1-6) and catalysts were purchased (high-grade purity) and used without purification.
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The products 7-9 were identified and their isomeric compositions were determined by comparison of their spectral data (NMR, GC-MS) with those of authentic samples.15-17
Conversion rates were determined by GC using tetradecane as the internal standard. The GC instrument was a Hewlett-Packard 6890 chromatograph equipped with a 30 m × 0.32 mm column (methyl silicone doped with 5% phenyl silicone, 0.25 µm). The GC-MS instrument was a Hewlett-Packard MS 5989 apparatus (EI 70 eV) equipped with a GC 5890 chromatograph. Typical Procedure. Synthesis of Methoxybenzophenone (7) (Table 2, experiment C). Anisole (1) (216.28 g; 2 mol), benzoyl chloride (4) (140.57 g; 1 mol), and iron(III) chloride (16.22 g; 0.1 mol) were introduced together in a 1-L feed tank and stirred under nitrogen atmosphere until the iron salt had been solubilized. The homogeneous mixture was circulated in the apparatus (Figure 2) at a flow rate of 20 mL min-1. The head fraction (1) required to initiate and stabilize the system, in particular the tuning of MW power conditions, was 30 g. Then, a middle fraction (2) of 300 g was collected. The residue fraction amounted to 26 g. In the collected fractions, the conversion rate to ketone 7 (with respect to 4) was determined by GC using tetradecane as the internal standard (Table 2, entries 6 and 7). The largest fraction (2) was treated with a saturated sodium carbonate aqueous solution. The layers were separated, and the aqueous layer was washed three times with dichloromethane. The combined organic phases were dried over sodium sulfate and concentrated under reduced pressure up to elimination of 1 in excess, which was recovered and recycled. The product 7 was obtained as an oil. The mass obtained was 151 g; 85% yield (fraction 2 only included). The isomeric ratio was ortho/para ) 6/94, as determined by GC (See Table 1). An analytical sample of 4-methoxybenzophenone (611-94-9) was isolated by chromatography (silicagel; pentane/ether, 9:1). Mp 60-62 °C (lit.15 mp 62-64 °C). 1H NMR (400 MHz; CDCl3): δ 3.85 (s, 3H, OMe); aromatic protons of p-methoxyphenyl group 6.93 and 7.80 (two divided doublets, 2H × 2, 3J ) 9.0 Hz); aromatic protons of phenyl group 7.44 (m, 2H), 7.53 (m, 1H), and 7.72 (m, 2H). Acknowledgment Support of this work by the Centre National de la Recherche Scientifique and Rhodia Organique Fine are gratefully acknowledged. We thank Professor Michael J. McGlinchey (McMaster University, Hamilton, Ontario, Canada) for his assistance in the preparation of the manuscript. Literature Cited (1) For part 4, see ref 4e. (2) For reviews concerning the FC acylation, see: (a) Olah, G. A. Friedel-Crafts and Related Reactions; Wiley-Interscience: New
York, 1964. (b) Olah, G. A. Friedel-Crafts Chemistry; WileyInterscience: New York, 1973. (c) Heaney, H. The Bimolecular Aromatic Friedel-Crafts Reaction. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, U.K., 1991; Vol. 2, Chapter 3.2, pp 733-752. (d) Taylor R. Electrophilic Aromatic Substitution; Wiley-Interscience: Chichester, U.K., 1990; pp 222-238. (e) Scheele, J. J. Electrophilic Aromatic Acylation. Ph.D. Thesis, Tech. Hogesh, Delft, The Netherlands, 1991; Chem. Abstr. 1992, 117, 130844y. (f) Mahato, S. B. Advances in the Chemistry of Friedel-Crafts Acylation. J. Indian Chem. Soc. 2000, 77, 175. For recent articles, see: (g) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Catalytic Friedel-Crafts Acylation Reactions Using Hafnium Triflate as a Catalyst in Lithium Perchlorate-Nitromethane. Tetrahedron Lett. 1995, 36, 409. (h) Hachiya, I.; Moriwaki, M.; Kobayashi, S. Hafnium(IV) Trifluoromethanesulfonate, An Efficient Catalyst for the Friedel-Crafts Acylation and Alkylation Reactions. Bull. Chem. Soc. Jpn. 1995, 68, 2053. (i) Kusama, H.; Narasaka, K. Friedel-Crafts Acylation of Arenes Catalyzed by Bromopentacarbonylrhenium(I). Bull. Chem. Soc. Jpn. 1995, 68, 2379. (j) Kawada, A.; Mitamura, S.; Kobayashi, S. Ln(OTf)3-LiClO4 as Reusable Catalyst System for Friedel-Crafts Acylation. J. Chem. Soc., Chem. Commun. 1996, 183. (k) Effenberger, F.; Eberhard, J. K.; Maier, A. H. The First Unequivocal Evidence of the Reacting Electrophile in Aromatic Acylation Reactions. J. Am. Chem. Soc. 1996, 118, 12572. (l) Izumi, J.; Mukaiyama, T. The Catalytic Friedel-Crafts Acylation Reaction of Aromatic Compounds with Carboxylic Anhydrides Using Combined Catalysts System of Titanium(IV) Chloride Tris(trifluoromethanesulfonate) and Trifluoromethanesulfonic Acid. Chem. Lett. 1996, 739. (m) Desmurs, J.-R.; Labrouille`re, M.; Dubac, J.; Laporterie, A.; Gaspard, H.; Metz, F. Bismuth(III) Salts in Friedel-Crafts Acylation. Ind. Chem. Libr. 1996, 8, 15-28. (n) Spagnol, M.; Gilbert, L.; Alby, D. Friedel-Crafts Acylation of Aromatics Using Zeolites. Ind. Chem. Libr. 1996, 8, 29-38. (o) Mikami, K.; Kotera, O.; Motoyama, Y.; Sakaguchi, H.; Maruta, M. Metal Bis(trifluoromethylsulfonyl)amides as Highly Efficient Lewis Acid Catalysts for Acylation Reactions. Synlett 1996, 171. (p) Desmurs, J.-R.; Labrouille`re, M.; Le Roux, C.; Laporterie, A.; Dubac J. Surprising Catalytic Activity of Bismuth(III) Triflate in the Friedel-Crafts Acylation Reaction. Tetrahedron Lett. 1997, 38, 8871. (q) Nishido, J.; Nakajima, H.; Saeki, T.; Ishii, A.; Mikami, K. Lanthanide Perfluoroalkylsulfonamide Catalysts for Fluorous Phase Organic Synthesis. Synlett 1998, 1347. (r) Re´pichet, S.; Le Roux, C.; Dubac, J.; Desmurs, J.-R. Bismuth(III) Trifluoromethanesulfonate: A Chameleon Catalyst for the Friedel-Crafts Acylation. Eur. J. Org. Chem. 1998, 2743, 3. (s) Kobayashi, S.; Iwamoto, S. Catalytic Friedel-Crafts Acylation of Benzene, Chlorobenzene, and Fluorobenzene Using a Novel Catalyst System, Hafnium Triflate and Trifluoromethanesulfonic Acid. Tetrahedron Lett. 1998, 39, 4697. (t) Nie, J.; Xu, J.; Zhou, G. Studies of the Lewis Acidity of Lanthanide Bis(trifluoromethyl)sulfonylamides and Lanthanide Bis(1,1,1,1,3,3,3-hexafluoro-2-propoxy)sulfonylamides. J. Chem. Res. (S) 1999, 446. (u) Freese, U.; Heinrich, F.; Roessner, F. Acylation of Aromatic Compounds on H-Beta Zeolites. Catal. Today 1999, 49, 237. (v) Baudry-Barbier, D.; Dormond, A.; Duriau-Montagne, F. Catalytic Activity of RareEarth-Supported Catalysts in Friedel-Crafts Acylations. J. Mol. Catal. A 1999, 149, 215. (w) Baudry-Barbier, D.; Dormond, A.; Richard, S.; Desmurs, J.-R. Catalytic Activity of Solvated and Unsolvated Lanthanide Halides in Friedel-Crafts Acylations. J. Mol. Catal. A 2000, 161, 23. (x) Matsuo, J.-i.; Odashima, K.; Kobayashi, S. Gallium Nonafluorobutanesulfonate as an Efficient Catalyst in Friedel-Crafts Acylation. Synlett 2000, 403. (y) Effenberger, F.; Buckel, F.; Maier, A. H.; Schmider, J. Perfluoroalkanesulfonic Acid-Catalyzed Acylations of Alkylbenzenes. Synthesis of Alkylanthraquinones. Synthesis 2000, 14327. (z) Hwang, J. P.; Prakash, G. K. S.; Olah, G. A. Trifluoromethanesulfonic AcidCatalyzed Novel Friedel-Crafts Acylation of Aromatics with Methyl Benzoate. Tetrahedron 2000, 56, 7199. (3) For reviews concerning FC sulfonylation, see: (a) Jensen, F. R.; Goldman, G. In Friedel-Crafts and Related Reactions; Olah, G. A., Ed.; Wiley-Interscience: New York, 1964; Vol. 3, pp 13191367. (b) Taylor, R. In Comprehensive Chemical Kinetics; Bamford, C.-H., Tipper, C. F. H., Eds.; Elsevier: New York, 1972; pp 7783. (c) ref 2d, pp 334-337. For recent articles, see: (d) Smith, K.; Ewart, G. M.; Randles, K. R. Regioselective Methanesulfonylation of Toluene Catalysed by Cation-Exchanged Zeolite β. J. Chem. Soc., Perkin Trans. 1 1997, 1085. (e) Olah, G. A.; Orlinkov, A.; Oxyglou, A. B.; Suria Prakash, G. K. Methanesulfonylation of
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Received for review April 12, 2001 Revised manuscript received July 15, 2001 Accepted July 23, 2001 IE0103299
