- Email: [email protected]
Alkylation of toluene with aliphatic alcohols and 1-octene catalyzed by cation-exchange resins
Reactive & Functional Polymers 44 (2000) 1–7 www.elsevier.com / locate / react
Alkylation of toluene with aliphatic alcohols and 1-octene catalyzed by cation-exchange resins a,
b,c
a
Elizabeth Roditi Lachter *, Rosane Aguiar da Silva San Gil, , David Tabak , ´ Gonc¸alves Costa a , Cristiane P.S. Chaves b , Jaqueline Araujo ´ dos Santos a Valeria a
˜ ´ ´ ´ , Departamento de Quımica ´ ´ Organica , Instituto de Quımica da Universidade Federal do Rio de Laboratorio de Polımeros e Catalise ˜ , CT-Bloco-A, Sala-605, CEP-21949 -900, Rio de Janeiro, RJ, Brazil Janeiro, Ilha do Fundao b ˜ ´ ˆ ´ ´ ´ ´ Laboratorio de Ressonancia Magnetica Nuclear, Departamento de Quımica Organica , Instituto de Quımica , UFRJ, Quımica , Brazil c ˆ Departamento de Ciencias Naturais, CCBS, UNI-RIO, Rio de Janeiro, Brazil Received 13 July 1998; received in revised form 8 June 1999; accepted 17 June 1999
Abstract The catalytic activity of macroreticular cation-exchange resin (Amberlyst-15) was evaluated for the reaction of toluene with isopropanol, 1-octanol, 2-octanol and 1-octene at 808C, in the liquid phase. The best results were achieved with octene. The reaction yielded only monoalkylation products. The conversion of octene was 75% after 4 h of reaction. In the reaction with isopropanol the main product was propene. In the reaction with 1-octanol and 2-octanol the conversion was very low and the main products were the octyl ethers. 2000 Elsevier Science B.V. All rights reserved. Keywords: Cation-exchange resin; Amberlyst-15; Alkylation; Friedel-Crafts reaction; Octene; Octanol; Isopropanol
1. Introduction The Friedel-Crafts alkylation reaction is a very useful tool for the synthesis of alkylaromatic compounds both in the laboratory and on an industrial scale [1,2]. The reaction is generally carried out with alkylating reagents such as alkenes, alkyl chlorides and alcohols by using a stoichiometric amount of Lewis and ¨ Bronsted acids [1]. The alkylation of benzene with ethylene and propylene to produce ethylbenzene and cumene respectively is widely used in the petrochemical *Corresponding author. Fax: 155-21-290-4746. E-mail address: [email protected] (E.R. Lachter)
industry. Cumene is an important intermediate mainly used for the production of phenol and acetone while ethylbenzene is the intermediate for styrene production [3]. The production of long chain alkylbenzenes, as intermediates for detergents is another important industrial process. In the petrochemical industry these benzene alkylations are usually catalyzed by AlCl 3 (for ethylbenzene), HF (for long chain alkylbenzenes) and by ‘‘solid phosphoric acids’’ (for cumene) in spite of their low selectivity and high corrosiveness [3,4]. In recent years, the use of heterogeneous catalysts in liquid phase reactions has greatly increased due to their advantages such as high activity and selectivity, reusability, ease of
1381-5148 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S1381-5148( 99 )00071-1
2
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
separation, no corrosion or disposal of effluent problems, etc. [3]. Various catalysts for the alkylation reaction of aromatic compounds with alkenes, alcohols or alkyl chlorides such as zeolite [5], nafion-H [6] and clays [7,8] have been used as a catalyst. Recently, we have focused our attention on the utilization of solid acid catalysts as the ion-exchange resins in the alkylation of aromatic compounds with alcohols [9–11]. The lower reactivity / stability of acid resins prevents their use in the alkylation of benzene [12]. However, some fundamental studies on acid resin catalyst in non-polar media have been carried out on the alkylation reaction using olefins [13–18]. The present work was undertaken to study the alkylation of toluene with isopropanol, 1-octanol, 2-octanol and 1-octene in the presence of acid cation-exchange resins as catalysts.
2. Previous studies Friedel-Crafts alkylation reactions in solution generally give complex reaction mixtures. The formation of reactant (and product) catalyst complexes, the increased tendency of alkylated products toward further alkylation and isomerization, coupled with long contact of reactant with the catalyst, result in a complex mixture of products. Polyalkylation, isomerization, transalkylation, dealkylation and polymerization all occur under the normal reaction conditions. There is, therefore, substantial interest to carry out alkylation reactions with solid acid catalysts, which decrease these side reactions. Condon [19] obtained 38% o-, 27% m- and 35% p-cymene by isopropylating toluene under conditions which dealkylation and isomerization were believed to be unimportant. This distribution was obtained when the reaction was catalyzed with aluminum chloride-nitromethane in benzene as solvent or with boron fluoride etherate at 658C. Simons and Hart [20] reported that a hydrogen chloride catalyzed iso-
propylation yielded a distribution of 31% o-, 25% m- and 44% p-cymene. Schlater and Clark [21] obtained 41% o-, 26% m- and 33% pcymene with HF and phosphoric acid catalysts. Alkylation of toluene with isopropyl alcohol and H 2 SO 4 (80%) at 708C furnished 35% of p-cymene and diisopropyltoluene [22]. Mesoporous silica and acid-treated montmorillonite supported aluminium chloride (prepared by reaction of the support with either AlCl 3 or RAlCl 2 in an aromatic solvent) is particularly effective in catalyzing the reactions of alkenes with aromatics such as that of 1octene with benzene. The activity of the solid acid is comparable to that of homogeneous AlCl 3 but its selectivity towards monoalkylation is significantly superior. Complete conversion of the alkene is achieved after 2 h, at room temperature and up to 80% selectivity for monoalkylate [23]. The alkylation of benzene with C 12 olefinparaffin and HF has been used until now. A number of zeolites, pillared clays and Brazilian clays have been patented and commercial versions have been published [23,24]. However, information about the use of resin catalysts is almost non-existent in the available literature. The alkylation of toluene with ethylene to give p-ethyl toluene has been very successful using a zeolite catalyst. However, to date, efficient resin catalysts have not been developed [25]. No systematic study has been carried out on the alkylation of aromatic compounds with alcohols and olefins catalyzed by ion-exchange resins. To explore the potential of solid acid catalysts for this type of reaction we have carried out a study on the alkylation of toluene by isopropanol, octanol and octene over Amberlyst-15. 3. Experimental
3.1. Materials The toluene, isopropanol, 2-octanol and 1octene used were commercial products (Spec-
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
trograde) and were dried as described in the literature [26]. The beads of sulfonated styrene / divinylbenzene (DVB) copolymers were ob˜ tained in the H form from Rohm and Haas, Sao Paulo, Brazil (Amberlyst-15) and they are macroporous resins. Before use, the resins were treated, as described in the literature, for removal of water [27]. The properties of the treated sulfonated poly(styrene / divinylbenzene) resins are listed in Table 1.
3.2. General reaction procedure The reaction was carried out in a roundbottom 100 ml 3-necked flask provided with a reflux condenser, a nitrogen gas inlet and a septum for sample removal. The reaction mixture was magnetically stirred at atmospheric pressure and temperature was kept at 808C by means of a constant-temperature bath. In all experiments, the order of addition to the reactor was catalyst, substrate and alcohol or 1-octene. The amounts of substrate, alkylating agent and catalyst are listed in Table 2. Table 1 Physical properties of Amberlyst-15 Physical property
Amberlyst-15
Shape Internal surface area (m 2 / g) Weight capacity (meq / g) Crosslink density (%DVB) Porosity (vol.%) Temperature stability (K)
beads 55 4.75 20–25 36.0 293
3
Samples of the reaction mixture were periodically withdrawn and analyzed by high resolution gas chromatography and proton nuclear magnetic resonance.
3.3. Analytical procedure The variation of the substrates, alkylating agents and product contents was followed by using a GC model 500 gas chromatograph equipped with an hydrogen flame ionization detector system and capillary column SE-54, 25 m, 0.5 mm. The temperature was programmed from 80 to 2908C (108C / min) with H 2 (2 ml / min) as carrier gas. The identification of some of the products as described above was carried out by using computerized gas chromatography–mass spectrometry analysis (C–GC–MS) on a HP-5987 instrument employing a SE-54 glass capillary column (25 m30.25 mm) programmed from 60 to 2808C (68C / min) with H 2 (2 ml / min) as carrier gas. The variation of 1-octene concentration during the course of the reaction was followed by 1 H NMR spectroscopy (Bruker, DRX-300, 300 MHz for 1 H).
4. Results and discussion The acid–catalyzed alkylation of toluene with isopropanol, 1-octanol, and 2-octanol gave
Table 2 Alkylation of toluene with alcohols and 1-octene catalyzed by Amberlyst-15 a Alkylating agent
Conversion (%)
Product distribution (%)
Isopropanol
100
1-Octanol 2-Octanol
,2 ,5
1-Octene
75
propene b and o-, m- and p-cymene (42:17:41)c,d octyl ether c octyl-toluene (28.2) and octyl ether (71.2)d mono-octyltoluene 2.0:11.4:17.3:13.3:56.0 e
Reaction time, 4 h; temp., 808C; toluene / alcohol or olefin510:1; dry resin / alkylating agent50.1 mEq H 1 / 1 mmol. Not determined. c Traces. d Determined by GLC. e Isomers of o-, m-, p- of octyl-toluene; 4-octyl-toluene (2.11%), 3-octyl-toluene (17.3%) and 2-octyl-toluene (56%). a
b
4
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
olefin, ether and alkylation products in different proportions depending on the alkylating agent. The reaction with 1-octene furnished only the alkylated product.
o-42%, m-17%, p-41%. The formation of propene was confirmed by bubbling the gas effluent into a solution of Br 2 / CCl 4 .
4.2. Alkylation with octanol 4.1. Alkylation with isopropanol The standard conditions for the Friedel-Crafts alkylation employ an alkyl halide and a Lewis acid catalyst such as aluminium chloride. The conditions, however, coproduce a hydrogen halide which often induces side reactions and the production of many by-products. In addition, disposal of the aluminium hydroxide residue excreted by usual workup causes additional environmental problems. Therefore, a reaction process which does not generate the hydrogen halide byproducts has been the target of extensive research. Alcohols are preferable alkylating agents rather than alkyl halides and olefins because hydrogen halides are not coproduced and no ready polymerization takes place. The reaction of toluene with isopropanol over Amberlyst-15 (Scheme 1) gave cymene in low yield, although the isopropyl alcohol conversion was 100% (Table 2).This result would be due to formation of propene which escapes from the reaction medium. The analysis by GLC showed that the reaction gave predominantly ortho-para substitution in accordance with a typical electrophilic aromatic substitution pathway. The isomer distribution observed for cymene was:
Low conversion (,5%) was achieved in the alkylation of toluene with 1-octanol and 2-octanol in the conditions employed. The main products were octyl ethers isomers (Scheme 2 and Fig. 2). The low conversion when alcohols were used as alkylating agent is related to the low Hammet acidity of the resins. The formation of ether was studied from various primary and secondary alcohols and Nafion-H, a superacid catalyst, with good yields [28].
4.3. Alkylation with octene The alkylation of toluene with 1-octene (Scheme 3) was used as a model reaction for the synthesis of long chain linear alkylbenzenes which are precursors of biodegradable surfactants. The conversion of 1-octene was plotted as a function of time for the alkylation of toluene (Fig. 1). The results about isomer composition of the alkylation products showed that the reaction gave predominantly 2-octyltoluene (Table 2) and the selectivity for the monoalkyltoluene was 100% (Fig. 2). The cation exchange resins are capable of
Scheme 1.
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
5
Scheme 2.
Scheme 3.
generating a carbenium ion intermediate from most of the alkyl substrates tested at the conditions employed which could readily undergo electrophilic substitution (before or after skelet-
al rearrangement) with the readily available aromatic solvent. The initial carbenium ion intermediate could possibly be generated by electrophilic addition of a proton to the double
6
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
Fig. 1. Conversion of 1-octene in the alkylation of toluene catalyzed by Amberlyst-15.
Fig. 2. Products distribution in the alkylation of toluene with 2-octanol and 1-octene.
bond under appropriate reaction conditions. In the reaction of benzene with 4-octene, catalyzed by p-toluenesulfonic acid, the observed high percentage of 2-phenyloctane (65%) in comparison to 3- and 4-phenyloctane (21%) and
(15%), respectively could be due to the steric preference of the arylation step [29]. The toluene alkylation with 1-heptene, in liquid phase, at 908C over K10 montmorillonites and Y zeolites was studied by Magnoux et al. [30]. The main products were monoheptyltoluenes, diheptyltoluenes and heptene dimers with both catalysts. In our work, alkylation with 1-octene over cation exchange resins furnished better results. The selectivity in 2phenylalkane, which is the most biodegradable isomers was high (56%). Octene dimers and dioctyltoluenes were not observed. The present study has clearly shown that cation exchange resins can be used as an efficient catalyst in the alkylation of aromatic hydrocarbons with long chain olefins under relatively mild conditions. The model reaction which was carried out using toluene as the aryl substrate resulted in excellent yields of alkyl aromatic compounds. In contrast to other solid acids such as zeolite and clay catalyzed FriedelCrafts reactions, the extent of the formation of undesired products from side reactions such as dimerization, polyalkylation, etc. was minimal with the resin-catalyzed reaction. The ability to recover and reuse the catalyst from the reaction mixtures, the minimal generation of environmentally unfriendly waste and the high specificity of the reaction, are important advantages of the Amberlyst-15 catalyst over the other conventional Friedel-Crafts catalysts and solid acids. Studies of the effect of particle size, catalyst loading, mole ratio and temperature are in progress in our laboratory. 5. Conclusions The alkylation of toluene with octene can be successfully carried out in the presence of Amberlyst-15 as catalyst. The present method for the synthesis of monooctyltoluene gives 75% yield. The Amberlyst-15 showed the possibility of alkyl ether synthesis from long chain alcohols.
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
Acknowledgements We thank the Conselho Nacional de Desen´ ´ volvimento Cientıfico e Tecnologico (CNPq) ˜ ´ ´ ´ and Fundac¸ao Universitaria Jose Bonifacio (FUJB) for financial support. References [1] G.A. Olah (Ed.), Friedel Crafts and Related Reactions, John Wiley, New York, 1964. [2] Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edn. 2 (1978) 50. [3] G. Bellussi, G. Pazzuconi, C. Prego, G. Girotti, G. Terzoni, J. Catal. 157 (1995) 227. [4] A.P. Bolton, in: J.A. Rabo (Ed.), Zeolite Chemistry and Catalysis, Am. Chem. Soc., Washington DC, 1976, p. 762 (ACS Monogr. Ser., 171). [5] I.I. Ivanova, D. Brunel, J.B. Nagy, E.G. Derouane, J. Mol. Catal. 95 (1995) 243. [6] G.A. Olah, G.K.S. Prakash, J. Sommer, in: Superacids, Wiley, New York, 1985, p. 243, Ch. 5. [7] P. Laszlo, A. Mathy, Helv. Chim. Acta 70 (1987) 577. [8] S.R. Chitinis, M.M. Sharma, React. and Functional Polym. 32 (1997) 93. [9] M.S.M. Silva, C.L. Costa, M.M. Pinto, E.R. Lachter, React. Polym. 25 (1995) 55. [10] M. Morais, E.F. Torres, L.M.P.M. Carmo, N.M.R. Pastura, W.A. Gonzalez, A.C.B. Santos, E.R. Lachter, Catalysis Today 28 (1996) 17. [11] M. Morais, W.S.F. Pinto, W.A. Gonzalez, L.M.P.M. Carmo, N.M.R. Pastura, E.R. Lachter, Appl. Catal. 138 (1996) L7.
7
[12] H. Widdecke, in: D.C. Sherrington, P. Hodge (Eds.), Synthesis and Separation using Functional Polymers, Wiley, New York, 1988, p. 149, Ch. 4. [13] J. Klein, H. Widdecke, Chem. Ing. Tech. 51 (1979) 560. [14] C. Buttersack, H. Widdecke, J. Klein, J. Mol. Catal. 35 (1986) 77. [15] C. Buttersack, H. Widdecke, J. Klein, J. Mol. Catal. 38 (1986) 365. [16] C. Buttersack, J. Klein, H. Widdecke, React. Polym. 5 (1987) 181. [17] A. Chakrabarti, M.M. Sharma, React. Polym. 20 (1993) 1. [18] A.B. Dixit, G.D. Yadav, React. and Funct. Polym. 31 (1996) 237. [19] F.E. Condon, J. Am. Chem. Soc. 71 (1949) 3544. [20] J.H. Simons, H. Hart, J. Am. Chem. Soc. 69 (1947) 679. [21] M.J. Schlatter, R.D. Clark, J. Am. Chem. Soc. 75 (1953) 361. [22] A. Kirrmann, M. Graves, Bull. Soc. Chim. France 5 (1934) 494. [23] J.H. Clark, D.J. Macquarrie, Chem. Soc. Reviews 25 (1996) 303. [24] R.A. San Gil, A.W.S. Guarino, M.R.M.P. Aguiar, L.C. Dieguez, Third European Congress on Catalysis (EUROPACAT III) Abstracts (1997) 125. [25] M.M. Sharma, React. Funct. Polymer 26 (1995) 3. [26] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals, 2nd ed, Pergamon, Oxford, 1980. ´ J. Tejero, F. Cunil, J.F. Isquierdo, React. [27] M. Iborra, C. Fite, Polym. 21 (1993) 65. [28] G. Olah, T. Shammat, G. Prakash, Catal. Letters 46 (1997) 1. [29] M.P.D. Mahindaratne, K. Wimalasena, J. Org. Chem. 63 (1998) 2858. [30] P. Magnoux, A. Mourran, S. Bernard, M. Guisnet, Stud. Surf. Sci. Catal. 108 (1997) 107.
Alkylation of toluene with aliphatic alcohols and 1-octene catalyzed by cation-exchange resins a,
b,c
a
Elizabeth Roditi Lachter *, Rosane Aguiar da Silva San Gil, , David Tabak , ´ Gonc¸alves Costa a , Cristiane P.S. Chaves b , Jaqueline Araujo ´ dos Santos a Valeria a
˜ ´ ´ ´ , Departamento de Quımica ´ ´ Organica , Instituto de Quımica da Universidade Federal do Rio de Laboratorio de Polımeros e Catalise ˜ , CT-Bloco-A, Sala-605, CEP-21949 -900, Rio de Janeiro, RJ, Brazil Janeiro, Ilha do Fundao b ˜ ´ ˆ ´ ´ ´ ´ Laboratorio de Ressonancia Magnetica Nuclear, Departamento de Quımica Organica , Instituto de Quımica , UFRJ, Quımica , Brazil c ˆ Departamento de Ciencias Naturais, CCBS, UNI-RIO, Rio de Janeiro, Brazil Received 13 July 1998; received in revised form 8 June 1999; accepted 17 June 1999
Abstract The catalytic activity of macroreticular cation-exchange resin (Amberlyst-15) was evaluated for the reaction of toluene with isopropanol, 1-octanol, 2-octanol and 1-octene at 808C, in the liquid phase. The best results were achieved with octene. The reaction yielded only monoalkylation products. The conversion of octene was 75% after 4 h of reaction. In the reaction with isopropanol the main product was propene. In the reaction with 1-octanol and 2-octanol the conversion was very low and the main products were the octyl ethers. 2000 Elsevier Science B.V. All rights reserved. Keywords: Cation-exchange resin; Amberlyst-15; Alkylation; Friedel-Crafts reaction; Octene; Octanol; Isopropanol
1. Introduction The Friedel-Crafts alkylation reaction is a very useful tool for the synthesis of alkylaromatic compounds both in the laboratory and on an industrial scale [1,2]. The reaction is generally carried out with alkylating reagents such as alkenes, alkyl chlorides and alcohols by using a stoichiometric amount of Lewis and ¨ Bronsted acids [1]. The alkylation of benzene with ethylene and propylene to produce ethylbenzene and cumene respectively is widely used in the petrochemical *Corresponding author. Fax: 155-21-290-4746. E-mail address: [email protected] (E.R. Lachter)
industry. Cumene is an important intermediate mainly used for the production of phenol and acetone while ethylbenzene is the intermediate for styrene production [3]. The production of long chain alkylbenzenes, as intermediates for detergents is another important industrial process. In the petrochemical industry these benzene alkylations are usually catalyzed by AlCl 3 (for ethylbenzene), HF (for long chain alkylbenzenes) and by ‘‘solid phosphoric acids’’ (for cumene) in spite of their low selectivity and high corrosiveness [3,4]. In recent years, the use of heterogeneous catalysts in liquid phase reactions has greatly increased due to their advantages such as high activity and selectivity, reusability, ease of
1381-5148 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S1381-5148( 99 )00071-1
2
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
separation, no corrosion or disposal of effluent problems, etc. [3]. Various catalysts for the alkylation reaction of aromatic compounds with alkenes, alcohols or alkyl chlorides such as zeolite [5], nafion-H [6] and clays [7,8] have been used as a catalyst. Recently, we have focused our attention on the utilization of solid acid catalysts as the ion-exchange resins in the alkylation of aromatic compounds with alcohols [9–11]. The lower reactivity / stability of acid resins prevents their use in the alkylation of benzene [12]. However, some fundamental studies on acid resin catalyst in non-polar media have been carried out on the alkylation reaction using olefins [13–18]. The present work was undertaken to study the alkylation of toluene with isopropanol, 1-octanol, 2-octanol and 1-octene in the presence of acid cation-exchange resins as catalysts.
2. Previous studies Friedel-Crafts alkylation reactions in solution generally give complex reaction mixtures. The formation of reactant (and product) catalyst complexes, the increased tendency of alkylated products toward further alkylation and isomerization, coupled with long contact of reactant with the catalyst, result in a complex mixture of products. Polyalkylation, isomerization, transalkylation, dealkylation and polymerization all occur under the normal reaction conditions. There is, therefore, substantial interest to carry out alkylation reactions with solid acid catalysts, which decrease these side reactions. Condon [19] obtained 38% o-, 27% m- and 35% p-cymene by isopropylating toluene under conditions which dealkylation and isomerization were believed to be unimportant. This distribution was obtained when the reaction was catalyzed with aluminum chloride-nitromethane in benzene as solvent or with boron fluoride etherate at 658C. Simons and Hart [20] reported that a hydrogen chloride catalyzed iso-
propylation yielded a distribution of 31% o-, 25% m- and 44% p-cymene. Schlater and Clark [21] obtained 41% o-, 26% m- and 33% pcymene with HF and phosphoric acid catalysts. Alkylation of toluene with isopropyl alcohol and H 2 SO 4 (80%) at 708C furnished 35% of p-cymene and diisopropyltoluene [22]. Mesoporous silica and acid-treated montmorillonite supported aluminium chloride (prepared by reaction of the support with either AlCl 3 or RAlCl 2 in an aromatic solvent) is particularly effective in catalyzing the reactions of alkenes with aromatics such as that of 1octene with benzene. The activity of the solid acid is comparable to that of homogeneous AlCl 3 but its selectivity towards monoalkylation is significantly superior. Complete conversion of the alkene is achieved after 2 h, at room temperature and up to 80% selectivity for monoalkylate [23]. The alkylation of benzene with C 12 olefinparaffin and HF has been used until now. A number of zeolites, pillared clays and Brazilian clays have been patented and commercial versions have been published [23,24]. However, information about the use of resin catalysts is almost non-existent in the available literature. The alkylation of toluene with ethylene to give p-ethyl toluene has been very successful using a zeolite catalyst. However, to date, efficient resin catalysts have not been developed [25]. No systematic study has been carried out on the alkylation of aromatic compounds with alcohols and olefins catalyzed by ion-exchange resins. To explore the potential of solid acid catalysts for this type of reaction we have carried out a study on the alkylation of toluene by isopropanol, octanol and octene over Amberlyst-15. 3. Experimental
3.1. Materials The toluene, isopropanol, 2-octanol and 1octene used were commercial products (Spec-
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
trograde) and were dried as described in the literature [26]. The beads of sulfonated styrene / divinylbenzene (DVB) copolymers were ob˜ tained in the H form from Rohm and Haas, Sao Paulo, Brazil (Amberlyst-15) and they are macroporous resins. Before use, the resins were treated, as described in the literature, for removal of water [27]. The properties of the treated sulfonated poly(styrene / divinylbenzene) resins are listed in Table 1.
3.2. General reaction procedure The reaction was carried out in a roundbottom 100 ml 3-necked flask provided with a reflux condenser, a nitrogen gas inlet and a septum for sample removal. The reaction mixture was magnetically stirred at atmospheric pressure and temperature was kept at 808C by means of a constant-temperature bath. In all experiments, the order of addition to the reactor was catalyst, substrate and alcohol or 1-octene. The amounts of substrate, alkylating agent and catalyst are listed in Table 2. Table 1 Physical properties of Amberlyst-15 Physical property
Amberlyst-15
Shape Internal surface area (m 2 / g) Weight capacity (meq / g) Crosslink density (%DVB) Porosity (vol.%) Temperature stability (K)
beads 55 4.75 20–25 36.0 293
3
Samples of the reaction mixture were periodically withdrawn and analyzed by high resolution gas chromatography and proton nuclear magnetic resonance.
3.3. Analytical procedure The variation of the substrates, alkylating agents and product contents was followed by using a GC model 500 gas chromatograph equipped with an hydrogen flame ionization detector system and capillary column SE-54, 25 m, 0.5 mm. The temperature was programmed from 80 to 2908C (108C / min) with H 2 (2 ml / min) as carrier gas. The identification of some of the products as described above was carried out by using computerized gas chromatography–mass spectrometry analysis (C–GC–MS) on a HP-5987 instrument employing a SE-54 glass capillary column (25 m30.25 mm) programmed from 60 to 2808C (68C / min) with H 2 (2 ml / min) as carrier gas. The variation of 1-octene concentration during the course of the reaction was followed by 1 H NMR spectroscopy (Bruker, DRX-300, 300 MHz for 1 H).
4. Results and discussion The acid–catalyzed alkylation of toluene with isopropanol, 1-octanol, and 2-octanol gave
Table 2 Alkylation of toluene with alcohols and 1-octene catalyzed by Amberlyst-15 a Alkylating agent
Conversion (%)
Product distribution (%)
Isopropanol
100
1-Octanol 2-Octanol
,2 ,5
1-Octene
75
propene b and o-, m- and p-cymene (42:17:41)c,d octyl ether c octyl-toluene (28.2) and octyl ether (71.2)d mono-octyltoluene 2.0:11.4:17.3:13.3:56.0 e
Reaction time, 4 h; temp., 808C; toluene / alcohol or olefin510:1; dry resin / alkylating agent50.1 mEq H 1 / 1 mmol. Not determined. c Traces. d Determined by GLC. e Isomers of o-, m-, p- of octyl-toluene; 4-octyl-toluene (2.11%), 3-octyl-toluene (17.3%) and 2-octyl-toluene (56%). a
b
4
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
olefin, ether and alkylation products in different proportions depending on the alkylating agent. The reaction with 1-octene furnished only the alkylated product.
o-42%, m-17%, p-41%. The formation of propene was confirmed by bubbling the gas effluent into a solution of Br 2 / CCl 4 .
4.2. Alkylation with octanol 4.1. Alkylation with isopropanol The standard conditions for the Friedel-Crafts alkylation employ an alkyl halide and a Lewis acid catalyst such as aluminium chloride. The conditions, however, coproduce a hydrogen halide which often induces side reactions and the production of many by-products. In addition, disposal of the aluminium hydroxide residue excreted by usual workup causes additional environmental problems. Therefore, a reaction process which does not generate the hydrogen halide byproducts has been the target of extensive research. Alcohols are preferable alkylating agents rather than alkyl halides and olefins because hydrogen halides are not coproduced and no ready polymerization takes place. The reaction of toluene with isopropanol over Amberlyst-15 (Scheme 1) gave cymene in low yield, although the isopropyl alcohol conversion was 100% (Table 2).This result would be due to formation of propene which escapes from the reaction medium. The analysis by GLC showed that the reaction gave predominantly ortho-para substitution in accordance with a typical electrophilic aromatic substitution pathway. The isomer distribution observed for cymene was:
Low conversion (,5%) was achieved in the alkylation of toluene with 1-octanol and 2-octanol in the conditions employed. The main products were octyl ethers isomers (Scheme 2 and Fig. 2). The low conversion when alcohols were used as alkylating agent is related to the low Hammet acidity of the resins. The formation of ether was studied from various primary and secondary alcohols and Nafion-H, a superacid catalyst, with good yields [28].
4.3. Alkylation with octene The alkylation of toluene with 1-octene (Scheme 3) was used as a model reaction for the synthesis of long chain linear alkylbenzenes which are precursors of biodegradable surfactants. The conversion of 1-octene was plotted as a function of time for the alkylation of toluene (Fig. 1). The results about isomer composition of the alkylation products showed that the reaction gave predominantly 2-octyltoluene (Table 2) and the selectivity for the monoalkyltoluene was 100% (Fig. 2). The cation exchange resins are capable of
Scheme 1.
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
5
Scheme 2.
Scheme 3.
generating a carbenium ion intermediate from most of the alkyl substrates tested at the conditions employed which could readily undergo electrophilic substitution (before or after skelet-
al rearrangement) with the readily available aromatic solvent. The initial carbenium ion intermediate could possibly be generated by electrophilic addition of a proton to the double
6
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
Fig. 1. Conversion of 1-octene in the alkylation of toluene catalyzed by Amberlyst-15.
Fig. 2. Products distribution in the alkylation of toluene with 2-octanol and 1-octene.
bond under appropriate reaction conditions. In the reaction of benzene with 4-octene, catalyzed by p-toluenesulfonic acid, the observed high percentage of 2-phenyloctane (65%) in comparison to 3- and 4-phenyloctane (21%) and
(15%), respectively could be due to the steric preference of the arylation step [29]. The toluene alkylation with 1-heptene, in liquid phase, at 908C over K10 montmorillonites and Y zeolites was studied by Magnoux et al. [30]. The main products were monoheptyltoluenes, diheptyltoluenes and heptene dimers with both catalysts. In our work, alkylation with 1-octene over cation exchange resins furnished better results. The selectivity in 2phenylalkane, which is the most biodegradable isomers was high (56%). Octene dimers and dioctyltoluenes were not observed. The present study has clearly shown that cation exchange resins can be used as an efficient catalyst in the alkylation of aromatic hydrocarbons with long chain olefins under relatively mild conditions. The model reaction which was carried out using toluene as the aryl substrate resulted in excellent yields of alkyl aromatic compounds. In contrast to other solid acids such as zeolite and clay catalyzed FriedelCrafts reactions, the extent of the formation of undesired products from side reactions such as dimerization, polyalkylation, etc. was minimal with the resin-catalyzed reaction. The ability to recover and reuse the catalyst from the reaction mixtures, the minimal generation of environmentally unfriendly waste and the high specificity of the reaction, are important advantages of the Amberlyst-15 catalyst over the other conventional Friedel-Crafts catalysts and solid acids. Studies of the effect of particle size, catalyst loading, mole ratio and temperature are in progress in our laboratory. 5. Conclusions The alkylation of toluene with octene can be successfully carried out in the presence of Amberlyst-15 as catalyst. The present method for the synthesis of monooctyltoluene gives 75% yield. The Amberlyst-15 showed the possibility of alkyl ether synthesis from long chain alcohols.
E.R. Lachter et al. / Reactive & Functional Polymers 44 (2000) 1 – 7
Acknowledgements We thank the Conselho Nacional de Desen´ ´ volvimento Cientıfico e Tecnologico (CNPq) ˜ ´ ´ ´ and Fundac¸ao Universitaria Jose Bonifacio (FUJB) for financial support. References [1] G.A. Olah (Ed.), Friedel Crafts and Related Reactions, John Wiley, New York, 1964. [2] Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edn. 2 (1978) 50. [3] G. Bellussi, G. Pazzuconi, C. Prego, G. Girotti, G. Terzoni, J. Catal. 157 (1995) 227. [4] A.P. Bolton, in: J.A. Rabo (Ed.), Zeolite Chemistry and Catalysis, Am. Chem. Soc., Washington DC, 1976, p. 762 (ACS Monogr. Ser., 171). [5] I.I. Ivanova, D. Brunel, J.B. Nagy, E.G. Derouane, J. Mol. Catal. 95 (1995) 243. [6] G.A. Olah, G.K.S. Prakash, J. Sommer, in: Superacids, Wiley, New York, 1985, p. 243, Ch. 5. [7] P. Laszlo, A. Mathy, Helv. Chim. Acta 70 (1987) 577. [8] S.R. Chitinis, M.M. Sharma, React. and Functional Polym. 32 (1997) 93. [9] M.S.M. Silva, C.L. Costa, M.M. Pinto, E.R. Lachter, React. Polym. 25 (1995) 55. [10] M. Morais, E.F. Torres, L.M.P.M. Carmo, N.M.R. Pastura, W.A. Gonzalez, A.C.B. Santos, E.R. Lachter, Catalysis Today 28 (1996) 17. [11] M. Morais, W.S.F. Pinto, W.A. Gonzalez, L.M.P.M. Carmo, N.M.R. Pastura, E.R. Lachter, Appl. Catal. 138 (1996) L7.
7
[12] H. Widdecke, in: D.C. Sherrington, P. Hodge (Eds.), Synthesis and Separation using Functional Polymers, Wiley, New York, 1988, p. 149, Ch. 4. [13] J. Klein, H. Widdecke, Chem. Ing. Tech. 51 (1979) 560. [14] C. Buttersack, H. Widdecke, J. Klein, J. Mol. Catal. 35 (1986) 77. [15] C. Buttersack, H. Widdecke, J. Klein, J. Mol. Catal. 38 (1986) 365. [16] C. Buttersack, J. Klein, H. Widdecke, React. Polym. 5 (1987) 181. [17] A. Chakrabarti, M.M. Sharma, React. Polym. 20 (1993) 1. [18] A.B. Dixit, G.D. Yadav, React. and Funct. Polym. 31 (1996) 237. [19] F.E. Condon, J. Am. Chem. Soc. 71 (1949) 3544. [20] J.H. Simons, H. Hart, J. Am. Chem. Soc. 69 (1947) 679. [21] M.J. Schlatter, R.D. Clark, J. Am. Chem. Soc. 75 (1953) 361. [22] A. Kirrmann, M. Graves, Bull. Soc. Chim. France 5 (1934) 494. [23] J.H. Clark, D.J. Macquarrie, Chem. Soc. Reviews 25 (1996) 303. [24] R.A. San Gil, A.W.S. Guarino, M.R.M.P. Aguiar, L.C. Dieguez, Third European Congress on Catalysis (EUROPACAT III) Abstracts (1997) 125. [25] M.M. Sharma, React. Funct. Polymer 26 (1995) 3. [26] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals, 2nd ed, Pergamon, Oxford, 1980. ´ J. Tejero, F. Cunil, J.F. Isquierdo, React. [27] M. Iborra, C. Fite, Polym. 21 (1993) 65. [28] G. Olah, T. Shammat, G. Prakash, Catal. Letters 46 (1997) 1. [29] M.P.D. Mahindaratne, K. Wimalasena, J. Org. Chem. 63 (1998) 2858. [30] P. Magnoux, A. Mourran, S. Bernard, M. Guisnet, Stud. Surf. Sci. Catal. 108 (1997) 107.