- Email: [email protected]
Kinetic study of dichlorocyclopropanation under phase-transfer catalysis and assisted by microwave irradiation
Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Kinetic study of dichlorocyclopropanation under phase-transfer catalysis and assisted by microwave irradiation Maw-Ling Wang a,*, Yu-Ming Hsieh b a b
Department of Safety, Health and Environmental Engineering, Hungkuang University, Shalu District, Taichung City 43302, Taiwan Department of Health Nutrition and Biotechnology, Asia-Pacific Institute Creativity, Toufen, Miaoli 35153, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 February 2014 Received in revised form 12 May 2014 Accepted 17 May 2014 Available online 21 June 2014
This work studies dichlorocyclopropanation which was performed by reacting olefins with chloroform in an alkaline solution of NaOH/organic solvent two-phase medium using phase-transfer catalysis (PTC) and microwave irradiation. The conventional quaternary ammonium salts were used as phase-transfer catalyst. A new compound 3-(N,N-dimethyloctylammonio)-propansulfonate (S-8) which was synthesized from the reaction of dimethyloctyl-amine and 1,3-propansultone, was also employed as the phasetransfer catalyst. We found that the catalyst (S-8) is more effective than those of the conventional quaternary ammonium salts in dichlorocyclopropanation. The addition was preceded via the production of dichlorocarbene from the reaction of chloroform and NaOH. The advantage of using microwave irradiation is that it increases the reaction rate and the conversion. Based on the experimental data, a rational mechanism of the interfacial reaction is proposed. The reactions follow a pseudo-first-order rate law. A rate expression was developed to describe the kinetic behavior from which the apparent rate constant (kapp) of the organic-phase reaction was obtained. The kinetics of the reaction in studying the effects of reaction conditions on the conversion of reactant and the apparent rate constant (kapp) were investigated in detail. Rational explanations of the resulting phenomena are provided. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Organic reaction kinetics Dichlorocyclopropanation Phase-transfer catalysis Microwave irradiation
1. Introduction The technique of phase-transfer catalysis (PTC) brings the reactants together, to react in two mutually insoluble phases, by adding a phase-transfer agent. The phase-transfer catalytic reactions may occur in the solution or at the interface of the two phases. It was developed for the synthesis of organic chemicals and is now widely applied in various industries [1–3]. Quaternary ammonium salts are the most extensively used catalysts. In comparison with the traditional methods, PTC has several advantages, such as no needs for expensive aprotic solvent; simpler work-up, shorted reaction time and lower reaction temperature [4]. However, this technique is still limited use for several reactions. To improve the reaction, the development of a new catalyst and/or the use of ultrasound and microwaves are the mostly popular techniques used by scientists and engineers. They allow easier cleaning and require no additional separation steps to obtain the product for using ultrasound and microwaves.
* Corresponding author. Tel.: +886 4 2631 8652x4175; fax: +886 4 2652 5245. E-mail address: [email protected] (M.-L. Wang).
Gedye et al. [5] and Giguerre et al. [6] are the first ones to use microwave heating to accelerate organic chemical transformations. Since then, numerous successful reactions which have dramatically improved the reaction rate have been disclosed. Microwave heating is a clean, selective and efficient method for organic synthesis [7–10]. The advantageous of using microwave irradiation is its instantaneous ‘‘in core’’ heating of materials, in a homogeneous and selective manner [11]. The combination of solid–liquid PTC [7,11] and liquid–liquid PTC [12] assisted by microwave irradiation yields satisfactory results. The products obtained from dichlorocyclopropanation are organic compounds, which have numerous applications in medical care, perfume production and the agricultural industry. The synthesis of dichlorocyclopropane was difficult before the development of phase-transfer catalysis. In 1954, Doering and Hoffmann [13] first synthesized dichlorocyclopropane from dihalocarbene (:CX2). Chloroform and potassium t-butoxide were employed to produce dihalocarbene. However, the conversion was low. Makosza and Wawrzyniewicz [14] discovered that dihalocarbene was greatly increased by the addition of a small amount of quaternary ammonium salt. Later, several papers [15–20] were published concerning the generation of dihalocarbene. In recent years, several papers have published in the literature for the
http://dx.doi.org/10.1016/j.jtice.2014.05.016 1876-1070/ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
2294
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
synthesis of organic compounds in liquid–liquid phase [21–25] and in solid–liquid phase. [26–29]. Therefore, phase-transfer catalysis is an effective method for increasing the amount of dihalocarbene. This study reports an efficient method for the synthesis of dichlorocyclopropane catalyzed by quaternary ammonium salts and 3-(N,N-dimethyloctylammonio)-propansulfonate (S-8) in the presence of sodium hydroxide under microwave irradiation [30,31]. The reaction is greatly enhanced by adding a small quantity of PTC and NaOH under microwave irradiation. Studies of the kinetics and the effects of various experimental parameters on the rate of the reaction were performed. Based on the experimental results, an appropriate interfacial reaction mechanism is proposed. 2. Experimental 2.1. Materials The reagents, 1-octene: Aldrich, USA, purity 98% Chloroform: Mallinckrodt, USA, HPLC grade. Benzyltriethylammonium chloride, BTEAC: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium chloride, TBAC: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium bromide, TBAB: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium iodide, TBAB: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium hydrogensulfate, TBAHS: RiedeldeHae¨n, Germany, G.R. grade. Tetrahexylammonium bromide, THAB: Riedel-deHae¨n, Germany, G.R. grade. Sodium hydroxide, NaOH: Riedel-deHae¨n, Germany, G.R. grade. Nonane: Fluka, Switzerland, purity 99%, dichloromethane: Mallinckrodt, USA, HPLC grade and 3-(N,N-dimethyloctylammonio)propansulfonate (S-8); sodium hydroxide (NaOH) and other reagents well all guaranteed grade (G.R.) chemicals for synthesis.
by the authors in the laboratory. It was prepared in the reaction of 1,3-propanesultane (1.2 g) and N,N-dimethyloctylamine (1.3 mL) in acetonitrile (20 mL) at 70 oC for 24 h. Then, 1,3-dinitrobenzene (0.001 g) was added to the reaction mixture. The solution was stirred under gentle reflux at 75 8C under nitrogen. To the cold reaction mixture, 20 mL diethyl ether was added and the precipitate was collected (90% yield), filtered and washed repeatedly with ether (3 times). After filtration, the S-8 product of high purity was obtained from the mixture of ethyl ether and acetone. The reactor was a 100 mL Pyrex round-bottomed flask, fitted with agitator, thermometer, sample port and feed port. Firstly, a 50% NaOH solution (6 g of NaOH + 6 g water) was prepared. Known quantities of chloroform (7.5 mL), S-8 catalyst (0.07 g or 0.25 mmol), 1-octene(5 mmol) and 0.5 g of nonane (internal standard) were put into the 100 mL reactor and stirred at 200 rpm for approximately 30 min in order to dissolve the S-8 catalyst in an organic-phase solution, which was controlled at the desired temperature. Sodium hydroxide solution was then added to the reactor to initiate the reaction Microwave irradiation was used to start the reaction simultaneously. The reaction mixture was stirred at 400 rpm and microwaves with a power 20 W (2455 MHz) were simultaneously passed through the reactor. An aliquot sample (0.05 mL) was withdrawn from the reaction solution and quenched in 3 mL of dichloromethane, at each time internal. The sample for analysis was withdrawn from the organic solution after the separation of liquid–liquid phase and then analyzed quantitatively using a GC using the internal standard. The conditions for analysis in the GC (Shimadzu GC-17A, Japan) were: capillary column (J & W Scientific Inc., db-1 column); stationary phase: 100% poly(dimethylsiloxane); column dimension: 15 m 0.525 mm; carrier gas: N2 (60 mL/min); detector: FID; and injection temperature: 250 8C. 3. Reaction mechanism and kinetic model In this work, the phase transfer catalyzed reaction of 1-octene with chloroform to produce 1,1-dichloro-2-hexyl-cyclopropane was successfully performed in an alkaline solution of NaOH/ chloroform two-phase medium using quaternary ammonium salts or S-8 catalyst (i.e., QSO3). The overall reaction can be expressed as: QSO3
C8 H16ðorgÞ þ CHCl3ðorgÞ þ NaOHðaqÞ ! C9 H16 Cl2ðorgÞ þ NaClðaqÞ 2.2. Instrumentation and equipment The CEM focused microwave synthesis system, model Discover1, was specially designed and constructed by CEM Corporation USA. The microwave enhances the ability to perform chemical reactions under controlled conditions in our laboratory scale. The temperature regulation of the reaction solution is specially designed by the Kohan Company for this CEM instrument (Discover-1 model) using liquid nitrogen gas circulating the environment of the reactor. The temperature regulation of the reaction solution is automated power control based on temperature feedback with infrared (IR) for volume-independent noninvasive temperature measurement and using liquid nitrogen gas circulating the environment of the reactor. Temperature is controlled within 1.0 8C. The frequency of microwave used in this experiment is 2455 MHz with output in the range of 0–60 W. The reactor was a 100 mL Pyrex round-bottom flask which was suspended at the center of the microwave chamber to get the maximum microwave energy. 2.3. Kinetics of the phase-transfer catalytic reaction The new catalyst S-8, i.e., [4-(dimethyloctylammonium) propansultan], a sulphopropylbetaine type compound, was synthesized
þ H2 O
(R1)
The detailed reaction mechanism is proposed as, The present reaction was performed in a high alkaline concentration of NaOH. Similarly, Hsieh [32] proposed that chloroform firstly reacts with NaOH to produce CCl3Na. This intermediate further reacts with the catalyst QSO3 to produce the active dichlorocarbene:CCl2 which is ready to react with olefin in the organic phase, i.e.,
CHCl3 þ NaOH ! CCl3 Na þ H2 O CCl3 Na þ QSO3 ! CCl3 Q þ SO3 Naþ
(R2)
C¼C þ : CCl2 ! CH2 ¼CH2 CCl2 Based on the experimental data, a pseudo-first-order rate law can also be used to describe the kinetic behavior of the reaction. For this, the rate expression for 1-octene is written as:
d½C8 H16 o ¼ kapp ½C8 H16 o dt
(1)
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
2295
where [C8H16]o denotes the concentration of 1-octene in the organic phase. The apparent rate constant kapp is defined as, kapp ¼ k1 ½: CCl2 o
(2)
where k1 is the intrinsic rate constant for organic-phase reaction. The concentration of dichlorocarbene in the organic phase [:CCl2]o, which is active, is considered to be a constant value. Integrating Eq. (1), we obtain, lnð1 XÞ ¼ kapp t
(3)
where X is the conversion of 1-octene and is defined as: X ¼ 1
½C8 H16 o ½C8 H16 o;i
(4)
The subscript ‘‘o’’ and ‘‘i’’ represent the species in organic phase and the initial condition of the species, respectively. The apparent rate constant kapp can be obtained from Eq. (3) in conjunction with the experimental data.
Fig. 2. A plot of the rate constants vs. various agitation speeds; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C microwave power 20 W.
4. Results and discussion Experimental data show that no byproducts were observed or detected during or after the reaction, which indicates that only 1,1dichloro-2-hexylcyclo- propane was produced from the reaction of 1-octene and chloroform using PTC (or catalyst S-8) in an alkaline solution of NaOH/chloroform under assisted microwave irradiation. Therefore, the consumption of the reactant equals the yield of the product. The effect of the reaction conditions on the conversion (X) of the limited reactant 1-octene and the apparent rate constant (kapp) are discussed below. 4.1. The effect of the agitation speed For a liquid–liquid two-phase reaction system, stirring agitation has an important effect on the reaction rate and conversion. Usually, increasing the kinetic energy of the system (i.e., stirring rate) tends to accelerate the reaction up to the limiting value for a Starks’ extraction reaction mechanism. After this, the reaction rate is not affected by further increase in the stirring rate. In this work, the effect of the agitation speed on the conversion and the reaction rate was studied for the range of 200 600 rpm and a microwave power of 20 W (2455 MHz), throughout the reaction. The results are shown in Fig. 1. In Fig. 1, the experimental data for the reaction
Fig. 1. A plot of ln(1 X) of 1-octene vs. time with various agitation speeds; 5 mmol of 1-octene, 7.5 mL of chloroform, 025 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C microwave power 20 W.
kinetics obeys the pseudo-first-order rate law and passes the point of origin a straight line for each experimental run. The apparent rate constants (kapp) were obtained from the slope of the straight lines. A plot of the rate constants (kapp) vs. various agitation speeds is shown in Fig. 2. The apparent rate constant increases linearly when the agitation speed is increased. There is a significant increase in the apparent rate constant (kapp) from 200 to 600 rpm. This phenomenon indicates that the reaction occurs at the interface of the two-phase solution, i.e., a Makosza interfacial reaction mechanism rather than a Starks extraction mechanism. Also, as indicated by Jayachandran and Wang [33], the interfacial area per unit volume of dispersion increased linearly with increasing stirring speed. Increasing the stirring speed changes the particle size of the dispersed phase, i.e., the reaction rate relates to the interfacial area. The activated energy obtained is 11.3 kcal mol1, in which the reaction is controlled by mass transfer and chemical reaction. The strong dependence of the reaction rate on the speed of stirring indicates that the dichlorocyclopropanation in two-phase solution is a type of interfacial mechanism. 4.2. The effect of the microwave power Microwaves have large and highly penetrating power with high frequency electromagnetic energy. They disseminate freely in air and reflect on metal surfaces and transform into energy as the microwave heat from the medium. In these experiments, the microwave reactor, model Discover-1 was used as described in Section 2. The effect of the microwave power on the apparent rate constant (kapp) was studied in the range 0 60 W, using with the same frequency of 2455 MHz. The data also obey the pseudo-firstorder rate law. Experimental data were also gathered from the reactions in the absence of microwave irradiation. As shown in Fig. 3, the apparent rate constant (kapp) increases linearly, when microwave power is increased. This phenomenon indicates that the microwave provides more energy for the reaction system. Thus, the reaction rate increases when microwave power is increased. The same trend is also observed in other studies [7,11,12]. In addition, certain literature shows that a very high yield and clean reactions have been obtained using only small amounts of energy in the literatures [28,30,31]. However, all of the experimental parameters were varied using a power of 20 W and the same frequency of 2455 MHz in all of the experimental runs.
2296
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
noted shows that the reaction occurs at the interface, as expected. The value of the apparent activation energy (Ea) shows that the reaction is controlled by the organic-aqueous interfacial reaction for an agitation speed of 400 rpm and microwave power of 20 W (2455 MHz). 4.4. Effect of the amount of NaOH
Fig. 3. A plot of the rate constants vs. various microwave power; 5 mmol of 1octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm,.
4.3. The effect of temperature In a general chemical reaction system, temperature has an important effect on the reaction rate. A phase-transfer catalytic reaction also has the same characteristic. In a phase-transfer catalytic reaction, high temperatures are not required. The reaction temperature is moderate. Therefore, no byproducts are generated from side reactions. In this study, the effect of temperature on the apparent rate constant (kapp) was determined in the range of 30 50 8C with the same microwave power used is 20 W (2455 MHz) for throughout the reaction. From the experimental data, it is clearly shows that the reaction rate and the conversion are both increased, as temperature and the effect of microwave are increased. This phenomenon indicates that the reactant molecules possess larger activated energy at a higher temperature, so the microwave easily pass through the reactor and the conversion is increased. It is worthy of note that the collisions between of the reactants at higher temperature are also increased, so the reaction rate is increased when temperature is increased. As shown in Fig. 4, the activation energy (Ea), which is obtained from the slope of the Arrhenius plot of ln(kapp) versus 1/T, is 11.3 kcal/mol. The Ea
Fig. 4. A plot of the rate constants vs. various reaction temperatures; 5 mmol of 1octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 400 rpm, microwave power 20 W.
In a phase-transfer catalytic reaction for the synthesis of dichlorocyclopropane, alkaline compounds also play an important role in promoting the reaction. The key point is that dichlorocarbene is produced from the reaction of chloroform and sodium hydroxide. In other words, no dichlorocarbene can be produced in the absence of sodium hydroxide. The most popular alkaline compounds are sodium hydroxide, potassium hydroxide and sodium bicarbonate. Based on the price of the reagents and their alkalinity, sodium hydroxide is the best choice among these three alkali compounds. The reaction rate is low when 1.5 g of NaOH is used in the reaction, but both the reaction rate and the conversion are increased as the amount of NaOH used is increased, up to 6 g. Within this range, the deprotonation of chloroform is directly increased by an increase in the amount of sodium hydroxide. In addition, the hydrolysis of dichlorocarbene is decreased by further increasing the amount of NaOH. However, water can not completely dissolve NaOH when the amount of NaOH exceeds 6 g. In this situation, the solution is saturated with NaOH which is unfavorable to the further generation of dichlorocarbene. For Fig. 5, the conversion of 1-octene is then decreased with an increase in the amount of NaOH of larger than 6 g. Under this situation, the solution is almost saturated with sodium hydroxide and becomes a slurry one. With a further increase in the amount of NaOH, solid particles of NaOH are suspended in the reaction solution in which the interfacial area was partly occupied by those NaOH particles. Therefore, the transfer of compounds through the interface and the reaction at the interface are decreased. Hence, the reaction is decreased at a higher amount of NaOH. Therefore, as shown in Fig. 5, the apparent rate constant is then decreased when the amount of NaOH used is increased to more than 6 g. 4.5. Effect of the amount of S-8 catalyst As stated, 3-(N,N-dimehtyloctylammonio)propansulfonate (S8) was employed as the phase-transfer catalyst in this work. The amount of S-8 catalyst used was 8.68–126 mg which gives a
Fig. 5. A plot of the rate constants vs. various amounts of NaOH; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
Fig. 6. A plot of ln(1 X) of 1-octene vs. time with various amounts of catalyst (S8); 5 mmol of 1-octene, 7.5 mL of chloroform, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
relative molar ratio for 1-octene of approximately 0.62–9 mol%. The experimental results which obey the pseudo-first-order rate law, are shown in Figs. 6 and 7, respectively. Fig. 6 shows the reaction is also increased when the amount of S-8 catalyst is increased. In the absence of S-8 catalyst, the conversion is low even after 20 min of reaction. However, the conversion is dramatically increased by the use of a small quantity of S-8 catalyst up to 0.25 mmol. The conversion or the reaction rates do not increase further when the amount of S-8 catalyst is further increased. Obviously, this experimental result is obtained from Fig. 7, even when the reaction is assisted by the microwave irradiation. In this situation, the catalyst S-8 is saturated in organic phase. From the proposed interfacial mechanism +QSO3 CCl2 @ QSO3(org) + CCCl2:(org), it is obvious that the reaction will proceed to the left side when the amount of QSO3(org) is oversaturated. Therefore, the content of:CCl2 decreases when the amount of catalyst S-8 is larger than 0.25 mmol. Hence, the reaction rate is decreased when the amount of QSO3 is further increased. This result is similar to that for the use of NaOH. In this situation, the solution is saturated with
Fig. 7. A plot of the rate constants vs. various amounts of catalyst (S-8); 5 mmol of 1octene, 7.5 mL of chloroform, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
2297
Fig. 8. A plot of the rate constants vs. various amounts of 1-octene; 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
S-8 catalyst, so the reaction rate is no longer increased when there is a further increase in the amount of S-8 catalyst. 4.6. The effect of the amount of 1-octene In this study, 1-octene was catalyzed using a phase-transfer catalyst assisted by microwave irradiation in a chloroform/alkaline aqueous solution of NaOH, which caused the dichlorocyclopropanation to produce a 1,1-dichloro-2-hexyl-cyclopropane product. It is obvious that the reaction also obeys a pseudo-first-order rate law. It is also found that the reaction rate, and the conversion decrease when the amount of 1-octene is increased. In principle, it is reasonable to predict that the reaction rate is increased when the amount of reactant is increased. For an interfacial reaction, the concentration of the 1-octene at the interphase is key to the promotion of the reaction. The corresponding apparent rate constant (kapp) was determined in the range 1.25–10 mmol of 1octene using microwave power of 20 W (2455 MHz) for throughout the reaction. The results are shown in Fig. 8.
Fig. 9. A plot of ln(1 X) of 1,7-octadiene vs. time with different kinds of catalysts; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of catalyst, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
2298
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
Table 1 Effect of quaternary ammonium salts and S-8 on the apparent rate constants (kapp). Kinds of phase-transfer catalyst
Apparent rate constant kapp (103 1/min)
TBAC TBAB THAI TBAHS BTEAC S-8
6.061 4.888 4.937 4.795 4.775 11.431
Reaction conditions: 5 mmol of 1-octene, 7.5 mL of chloroform, 6 g of NOH, 6 mL of water, 0.25 mmol of catalyst, 0.5 g of internal standard (nonane), 40 8C, 400 rpm, 20 W (2455 MHz).
4.7. The effect of the quaternary ammonium salts In this study, five quaternary ammonium salts and S-8 catalyst were used as the catalyst for dichlorocyclopropanation at 40 reaction temperature agitation speeds and a microwave power of 20 W (2455 MHz), throughout the reaction. The experimental data obey a pseudo-first-order rate law, for all of the quaternary ammonium salts and the S-8 catalyst. As shown in Fig. 9 and Table 1, the order of reactivity for these seven catalysts are: S8 > TBAC-TBAB-TBAI-TBAHS-BTEAC. A comparison of the experimental results for TBAC, TBAB, TBAI, TBAHS and BTEAC clearly shows that the reactivity of each of the quaternary salt is almost the same in spite of the different total numbers of carbons in the alkyl group of the cation in the quaternary ammonium salts and the corresponding anions. Nevertheless, S-8 catalyst exhibits high reactivity and enhances the reaction. In general, the most acceptable mechanisms of a phasetransfer catalytic reaction are the Starks extraction mechanism and the Makosza interfacial mechanism [2]. In this work, 1octene and chloroform, which are the two main reactants, are insoluble in water. Therefore, by viewing the generation of dichlorocarbene [34–36], the characteristics of such a phasetransfer catalytic reaction (PTC), which is quite different from that of Starks’s extraction mechanism. The occurrence of the reaction in this work can be attributed to the interfacial reaction proposed by Makosza and Wawrzyniewicz [14]. In 2003, Fedorynski [37] proposed the mechanism of dichlorocyclopropanation by using trialkylamines as a phase-transfer agent. Trialkylamines are active nucleophiles, reacting with carbene at the interfacial region to form ammonium ylides, which enter the organic phase to further produce carbene. In this work, the role of trialkylammonium propansultan is the same as that of trialkylamine. Thus, the main interfacial reactions of alkene with dichlorocarbene (:CCl2) so 3-(N,N-dimethyloctylammonio)-propansulfonate gave more better results.
5. Conclusion In this work, the synthesis of 1,1-dichloro-2-hexyl-cyclopropane, which is useful in industry, was successfully performed by the reaction of 1-octene in an alkaline solution of NaOH/ chloroform via dichlorocyclopropanation under phase-transfer catalytic and S-8 in combination with microwave irradiation. A rational reaction mechanism was proposed to explain the experimental results satisfactorily. We suggest that the reaction takes place at the interface between aqueous and organic phases. The overall reaction follows a pseudo-first-order rate law and the apparent rate constants were obtained from the experimental data. The reaction rate and the conversion both increase with the increase in the agitation speed, the microwave power, the amount of NaOH, S-8 catalyst and temperature. However, increasing the
amount of 1-octene decrease the reaction rate. Among the quaternary ammonium salts and the S-8 catalyst, S-8 exhibits high reactivity. Acknowledgment We thank the National Science Council Taiwan for financial support under Grant No. NSC-94-2214-E-241-001. References [1] Dehmlow EV, Dehmlow. SS phase transfer catalysis. Weinheim, Germany: Verlag Chemie; 1993. [2] Starks CM, Liotta CL, Helpern M. Phase transfer catalysis: fundamentals, applications and industrial perspective. New York, USA: Chapman & Hall; 1994. [3] Sasson Y, Neumann R, editors. Handbook of phase transfer catalysis. London, UK: Blackie Academic and Professional; 1997. [4] Entezari MH, Shameli AA. phase-transfer catalysis and ultrasonic waves I. Cannizzaro reaction. Ultrason Sonochem 2000;7:169–72. [5] Gedye R, Smith F, Westaway K, Ali H, Baldisera L, Laberge L, et al. J The use of microwave ovens for rapid organic synthesis. Tetrahedron Lett 1986;27:279– 82. [6] Giguere RJ, Bray TL, Duncan SM, Majetich G. Application of commercial microwave ovens to organic synthesis. Tetrahedron Lett 1986;27:4945–58. [7] Deshayes S, Liagre M, Loupy A, Luche J, Petit A. Microwave activation in phase transfer catalysis. Tetrahedron 1999;55:10851–70. [8] Bogdal D, Bednarz S, Lukasiewicz. M Microwave induced thermal gradients in solventless reaction synthesis. Tetrahedron 2006;62:9440–5. [9] Loupy A, Petit A, Bonnet. D Improvements in 1,3-dipolar cycloaddition of nitrones to fluorinated dipolarophiles under solvent-free microwave activation. J Fluorine Chem 1995;75:215–6. [10] Barush B, Prajapati D, Boruah A, Sandhu J. Microwave induced 1,3-dipolar cycloaddition reactions of nitrones. Synth Commun 1997;21:2563–7. [11] Yadav GD, Motirale BG. Microwave-irradiated synthesis of nitrophen using PEG 400 as phase transfer catalyst and solvent. Org Process Res Dev 2009;13:341–8. [12] Wang ML, Prasad SG. Microwave assisted phase-transfer catalytic ethoxylation of p-chloronitrobenzene-a kinetic study. J Taiwan Inst Chem Eng 2010;41:81–5. [13] Doering WE, Hoffmann AF. The addition of dichlorocarbene to oleins. J Am Chem Soc 1954;76:6162–5. [14] Makosza M, Wawrzynieicz M. Reaction of organic anions XXIV. catalytic method for preparation of dichlorocyclopropane derivatives in aqueous medium. Tetrahedron Lett 1969;53:4659–62. [15] Makosza M. Two-phase reactions in the chemistry of carbanions and halocarbenes—a useful tool in organic synthesis. Pure Appl Chem 1975;43:439–62. [16] Makosza M, Fedorynski M. Improved method of dibromocyclopropane derivatives synthesis in catalytic two-phase reaction. Synth Commun 1973;3:305–9. [17] Hiyama T, Sawada H, Tsukanaka M, Nozaki. b-Hydroxy-ethyltrialkylammonium ion as a selective phase-transfer catalyst for dichlorocyclopropanation. Tetrahedron Lett 1975;34:3013–6. [18] Julia S, Ginebreda A. A new method for generation of dichlorocarbene using solid–liquid phase transfer catalysis. Synthesis 1977;682–3. [19] Dehmlow EV, Wilkenloh J. Application of phase transfer catalysis, Part 29. dibromopropane addition hydrolysis competition in the presence of concentration sodium hydroxide. J Chem Res (S) 1984;396–7. [20] Nomura E, Taniguchi H, Otsuji Y. Calixarene-catalyzed generation of dichlorocarbene and its application to organic reactions. The catalytic action of octopus-type calix[6]arene. Bull Chem Soc Jpn 1994;67:792–9. [21] Walker MA. A high yield synthesis of N-alkylmaleimides using a novel modification of the Mitsunobu reaction. J Org Chem 1995;60:5352–5. [22] Saidi K, Darehkordi A. A conventients synthesis of N-aryltrifluoro-acetimidoyl phthalimide and succinimide. J Fluor Chem 2000;105:49–51. [23] Wilkes JS, Levisky JA, Wilson RA, Hussey CL. Dialkyl-imidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis. Inorg Chem 1982;21:1263–4. [24] Gesson JP, Jacquesy JC, Ramband D. A practical method for N-alkylation of succinimide and glutarimide. Bull Soc Chem Fr 1992;129:227–31. [25] Wang ML, Hsieh YM. Kinetic study of the synthesis of dichlorocyclopropane by trialkylammonium propansultans as new phase transfer catalysts. Chem Eng Commun 2007;194:477–94. [26] Dehmlow EV, Lipka BJ. A comparison of the effectiveness of various aqueous and solid bases and their mixtures in the N-alkylation of benzamide. J Chem Res (S) 1985;107(M):1418–22. [27] Wang ML, Chen WH, Wang FS. Kinetic study of synthesizing N-butylphthalimide under solid-liquid phase-transfer catalysis conditions. J Mol Catal A: Chem 2005;236:65–71. [28] Wang ML, Chen CJ. Kinetic study of synthesizing 1-(3-phenyl-propyl)-pyrrolilidine-2,5-dione under solid–liquid phase-transfer catalysis. Org Process Res Dev 2008;12:784–94.
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299 [29] Wang ML, Chen CJ. Kinetic study of synthesizing 1-(3-phenyl-propyl)-pyrrolilidine-2,5-dione under solid–liquid phase-transfer catalytic conditions assisted by ultrasonic irradiation. Org Process Res Dev 2010;14:737–45. [30] Lidstrom P, Tierney J, Wathey B, Westman J. Microwave assisted organic synthesis—a review. Tetrahedron 2001;57:9225–83. [31] Larhed M, Hallberg A. Microwave-assisted high-speed chemistry: a new technique in drug discovery. Drug Discov Today 2001;6:406–16. [32] Hsieh, YM. Study on the synthesis of dichlorocyclopropane by phase transfer catalysis. PhD thesis. Hsinchu, Taiwan: Department of Chemical Engineering, National Tsing Hua University; 2003. [33] Jayachandran JP, Wang ML. Regioselective dichlorocyclopropanation of 5vinyl cyclohexene using the new Dq-Br under controlled phase transfer catalysis conditions. React Kinet Catal Lett 2000;69(1):161–7.
2299
[34] Song QW, Yu B, Liu AH, He Y, Yang ZZ, Diao ZF, et al. PEG400-enhanced synthesis of gem-dichloroaziridines and gem-dichlorocyclopropanes via in situ generated dichlorocarbene. RCA Adv 2013;3:19009–14. [35] Sirovski F, Gorokhova M, Ruban S. Phase-transfer catalysis: kinetics and mechanism of dichlorocyclopropane formation in liquid/liquid and solid/ liquid systems. J Mol Catal A: Chem 2003;197:213–22. [36] Vivekanand PA, Balakrishnan T. Kinetics of dichlorocyclopropanation of vinylcyclohexane catalyzed by a new multi-site phase transfer catalyst. Catal Commun 2009;10:687–92. [37] Fedorynski M. Synthesis of gem-dihalocyclopropanes and their use in organic synthesis. Chem Rev 2003;103:1099–132.
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Kinetic study of dichlorocyclopropanation under phase-transfer catalysis and assisted by microwave irradiation Maw-Ling Wang a,*, Yu-Ming Hsieh b a b
Department of Safety, Health and Environmental Engineering, Hungkuang University, Shalu District, Taichung City 43302, Taiwan Department of Health Nutrition and Biotechnology, Asia-Pacific Institute Creativity, Toufen, Miaoli 35153, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 February 2014 Received in revised form 12 May 2014 Accepted 17 May 2014 Available online 21 June 2014
This work studies dichlorocyclopropanation which was performed by reacting olefins with chloroform in an alkaline solution of NaOH/organic solvent two-phase medium using phase-transfer catalysis (PTC) and microwave irradiation. The conventional quaternary ammonium salts were used as phase-transfer catalyst. A new compound 3-(N,N-dimethyloctylammonio)-propansulfonate (S-8) which was synthesized from the reaction of dimethyloctyl-amine and 1,3-propansultone, was also employed as the phasetransfer catalyst. We found that the catalyst (S-8) is more effective than those of the conventional quaternary ammonium salts in dichlorocyclopropanation. The addition was preceded via the production of dichlorocarbene from the reaction of chloroform and NaOH. The advantage of using microwave irradiation is that it increases the reaction rate and the conversion. Based on the experimental data, a rational mechanism of the interfacial reaction is proposed. The reactions follow a pseudo-first-order rate law. A rate expression was developed to describe the kinetic behavior from which the apparent rate constant (kapp) of the organic-phase reaction was obtained. The kinetics of the reaction in studying the effects of reaction conditions on the conversion of reactant and the apparent rate constant (kapp) were investigated in detail. Rational explanations of the resulting phenomena are provided. ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Organic reaction kinetics Dichlorocyclopropanation Phase-transfer catalysis Microwave irradiation
1. Introduction The technique of phase-transfer catalysis (PTC) brings the reactants together, to react in two mutually insoluble phases, by adding a phase-transfer agent. The phase-transfer catalytic reactions may occur in the solution or at the interface of the two phases. It was developed for the synthesis of organic chemicals and is now widely applied in various industries [1–3]. Quaternary ammonium salts are the most extensively used catalysts. In comparison with the traditional methods, PTC has several advantages, such as no needs for expensive aprotic solvent; simpler work-up, shorted reaction time and lower reaction temperature [4]. However, this technique is still limited use for several reactions. To improve the reaction, the development of a new catalyst and/or the use of ultrasound and microwaves are the mostly popular techniques used by scientists and engineers. They allow easier cleaning and require no additional separation steps to obtain the product for using ultrasound and microwaves.
* Corresponding author. Tel.: +886 4 2631 8652x4175; fax: +886 4 2652 5245. E-mail address: [email protected] (M.-L. Wang).
Gedye et al. [5] and Giguerre et al. [6] are the first ones to use microwave heating to accelerate organic chemical transformations. Since then, numerous successful reactions which have dramatically improved the reaction rate have been disclosed. Microwave heating is a clean, selective and efficient method for organic synthesis [7–10]. The advantageous of using microwave irradiation is its instantaneous ‘‘in core’’ heating of materials, in a homogeneous and selective manner [11]. The combination of solid–liquid PTC [7,11] and liquid–liquid PTC [12] assisted by microwave irradiation yields satisfactory results. The products obtained from dichlorocyclopropanation are organic compounds, which have numerous applications in medical care, perfume production and the agricultural industry. The synthesis of dichlorocyclopropane was difficult before the development of phase-transfer catalysis. In 1954, Doering and Hoffmann [13] first synthesized dichlorocyclopropane from dihalocarbene (:CX2). Chloroform and potassium t-butoxide were employed to produce dihalocarbene. However, the conversion was low. Makosza and Wawrzyniewicz [14] discovered that dihalocarbene was greatly increased by the addition of a small amount of quaternary ammonium salt. Later, several papers [15–20] were published concerning the generation of dihalocarbene. In recent years, several papers have published in the literature for the
http://dx.doi.org/10.1016/j.jtice.2014.05.016 1876-1070/ß 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
2294
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
synthesis of organic compounds in liquid–liquid phase [21–25] and in solid–liquid phase. [26–29]. Therefore, phase-transfer catalysis is an effective method for increasing the amount of dihalocarbene. This study reports an efficient method for the synthesis of dichlorocyclopropane catalyzed by quaternary ammonium salts and 3-(N,N-dimethyloctylammonio)-propansulfonate (S-8) in the presence of sodium hydroxide under microwave irradiation [30,31]. The reaction is greatly enhanced by adding a small quantity of PTC and NaOH under microwave irradiation. Studies of the kinetics and the effects of various experimental parameters on the rate of the reaction were performed. Based on the experimental results, an appropriate interfacial reaction mechanism is proposed. 2. Experimental 2.1. Materials The reagents, 1-octene: Aldrich, USA, purity 98% Chloroform: Mallinckrodt, USA, HPLC grade. Benzyltriethylammonium chloride, BTEAC: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium chloride, TBAC: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium bromide, TBAB: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium iodide, TBAB: Riedel-deHae¨n, Germany, G.R. grade. Tetrabutylammonium hydrogensulfate, TBAHS: RiedeldeHae¨n, Germany, G.R. grade. Tetrahexylammonium bromide, THAB: Riedel-deHae¨n, Germany, G.R. grade. Sodium hydroxide, NaOH: Riedel-deHae¨n, Germany, G.R. grade. Nonane: Fluka, Switzerland, purity 99%, dichloromethane: Mallinckrodt, USA, HPLC grade and 3-(N,N-dimethyloctylammonio)propansulfonate (S-8); sodium hydroxide (NaOH) and other reagents well all guaranteed grade (G.R.) chemicals for synthesis.
by the authors in the laboratory. It was prepared in the reaction of 1,3-propanesultane (1.2 g) and N,N-dimethyloctylamine (1.3 mL) in acetonitrile (20 mL) at 70 oC for 24 h. Then, 1,3-dinitrobenzene (0.001 g) was added to the reaction mixture. The solution was stirred under gentle reflux at 75 8C under nitrogen. To the cold reaction mixture, 20 mL diethyl ether was added and the precipitate was collected (90% yield), filtered and washed repeatedly with ether (3 times). After filtration, the S-8 product of high purity was obtained from the mixture of ethyl ether and acetone. The reactor was a 100 mL Pyrex round-bottomed flask, fitted with agitator, thermometer, sample port and feed port. Firstly, a 50% NaOH solution (6 g of NaOH + 6 g water) was prepared. Known quantities of chloroform (7.5 mL), S-8 catalyst (0.07 g or 0.25 mmol), 1-octene(5 mmol) and 0.5 g of nonane (internal standard) were put into the 100 mL reactor and stirred at 200 rpm for approximately 30 min in order to dissolve the S-8 catalyst in an organic-phase solution, which was controlled at the desired temperature. Sodium hydroxide solution was then added to the reactor to initiate the reaction Microwave irradiation was used to start the reaction simultaneously. The reaction mixture was stirred at 400 rpm and microwaves with a power 20 W (2455 MHz) were simultaneously passed through the reactor. An aliquot sample (0.05 mL) was withdrawn from the reaction solution and quenched in 3 mL of dichloromethane, at each time internal. The sample for analysis was withdrawn from the organic solution after the separation of liquid–liquid phase and then analyzed quantitatively using a GC using the internal standard. The conditions for analysis in the GC (Shimadzu GC-17A, Japan) were: capillary column (J & W Scientific Inc., db-1 column); stationary phase: 100% poly(dimethylsiloxane); column dimension: 15 m 0.525 mm; carrier gas: N2 (60 mL/min); detector: FID; and injection temperature: 250 8C. 3. Reaction mechanism and kinetic model In this work, the phase transfer catalyzed reaction of 1-octene with chloroform to produce 1,1-dichloro-2-hexyl-cyclopropane was successfully performed in an alkaline solution of NaOH/ chloroform two-phase medium using quaternary ammonium salts or S-8 catalyst (i.e., QSO3). The overall reaction can be expressed as: QSO3
C8 H16ðorgÞ þ CHCl3ðorgÞ þ NaOHðaqÞ ! C9 H16 Cl2ðorgÞ þ NaClðaqÞ 2.2. Instrumentation and equipment The CEM focused microwave synthesis system, model Discover1, was specially designed and constructed by CEM Corporation USA. The microwave enhances the ability to perform chemical reactions under controlled conditions in our laboratory scale. The temperature regulation of the reaction solution is specially designed by the Kohan Company for this CEM instrument (Discover-1 model) using liquid nitrogen gas circulating the environment of the reactor. The temperature regulation of the reaction solution is automated power control based on temperature feedback with infrared (IR) for volume-independent noninvasive temperature measurement and using liquid nitrogen gas circulating the environment of the reactor. Temperature is controlled within 1.0 8C. The frequency of microwave used in this experiment is 2455 MHz with output in the range of 0–60 W. The reactor was a 100 mL Pyrex round-bottom flask which was suspended at the center of the microwave chamber to get the maximum microwave energy. 2.3. Kinetics of the phase-transfer catalytic reaction The new catalyst S-8, i.e., [4-(dimethyloctylammonium) propansultan], a sulphopropylbetaine type compound, was synthesized
þ H2 O
(R1)
The detailed reaction mechanism is proposed as, The present reaction was performed in a high alkaline concentration of NaOH. Similarly, Hsieh [32] proposed that chloroform firstly reacts with NaOH to produce CCl3Na. This intermediate further reacts with the catalyst QSO3 to produce the active dichlorocarbene:CCl2 which is ready to react with olefin in the organic phase, i.e.,
CHCl3 þ NaOH ! CCl3 Na þ H2 O CCl3 Na þ QSO3 ! CCl3 Q þ SO3 Naþ
(R2)
C¼C þ : CCl2 ! CH2 ¼CH2 CCl2 Based on the experimental data, a pseudo-first-order rate law can also be used to describe the kinetic behavior of the reaction. For this, the rate expression for 1-octene is written as:
d½C8 H16 o ¼ kapp ½C8 H16 o dt
(1)
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
2295
where [C8H16]o denotes the concentration of 1-octene in the organic phase. The apparent rate constant kapp is defined as, kapp ¼ k1 ½: CCl2 o
(2)
where k1 is the intrinsic rate constant for organic-phase reaction. The concentration of dichlorocarbene in the organic phase [:CCl2]o, which is active, is considered to be a constant value. Integrating Eq. (1), we obtain, lnð1 XÞ ¼ kapp t
(3)
where X is the conversion of 1-octene and is defined as: X ¼ 1
½C8 H16 o ½C8 H16 o;i
(4)
The subscript ‘‘o’’ and ‘‘i’’ represent the species in organic phase and the initial condition of the species, respectively. The apparent rate constant kapp can be obtained from Eq. (3) in conjunction with the experimental data.
Fig. 2. A plot of the rate constants vs. various agitation speeds; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C microwave power 20 W.
4. Results and discussion Experimental data show that no byproducts were observed or detected during or after the reaction, which indicates that only 1,1dichloro-2-hexylcyclo- propane was produced from the reaction of 1-octene and chloroform using PTC (or catalyst S-8) in an alkaline solution of NaOH/chloroform under assisted microwave irradiation. Therefore, the consumption of the reactant equals the yield of the product. The effect of the reaction conditions on the conversion (X) of the limited reactant 1-octene and the apparent rate constant (kapp) are discussed below. 4.1. The effect of the agitation speed For a liquid–liquid two-phase reaction system, stirring agitation has an important effect on the reaction rate and conversion. Usually, increasing the kinetic energy of the system (i.e., stirring rate) tends to accelerate the reaction up to the limiting value for a Starks’ extraction reaction mechanism. After this, the reaction rate is not affected by further increase in the stirring rate. In this work, the effect of the agitation speed on the conversion and the reaction rate was studied for the range of 200 600 rpm and a microwave power of 20 W (2455 MHz), throughout the reaction. The results are shown in Fig. 1. In Fig. 1, the experimental data for the reaction
Fig. 1. A plot of ln(1 X) of 1-octene vs. time with various agitation speeds; 5 mmol of 1-octene, 7.5 mL of chloroform, 025 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C microwave power 20 W.
kinetics obeys the pseudo-first-order rate law and passes the point of origin a straight line for each experimental run. The apparent rate constants (kapp) were obtained from the slope of the straight lines. A plot of the rate constants (kapp) vs. various agitation speeds is shown in Fig. 2. The apparent rate constant increases linearly when the agitation speed is increased. There is a significant increase in the apparent rate constant (kapp) from 200 to 600 rpm. This phenomenon indicates that the reaction occurs at the interface of the two-phase solution, i.e., a Makosza interfacial reaction mechanism rather than a Starks extraction mechanism. Also, as indicated by Jayachandran and Wang [33], the interfacial area per unit volume of dispersion increased linearly with increasing stirring speed. Increasing the stirring speed changes the particle size of the dispersed phase, i.e., the reaction rate relates to the interfacial area. The activated energy obtained is 11.3 kcal mol1, in which the reaction is controlled by mass transfer and chemical reaction. The strong dependence of the reaction rate on the speed of stirring indicates that the dichlorocyclopropanation in two-phase solution is a type of interfacial mechanism. 4.2. The effect of the microwave power Microwaves have large and highly penetrating power with high frequency electromagnetic energy. They disseminate freely in air and reflect on metal surfaces and transform into energy as the microwave heat from the medium. In these experiments, the microwave reactor, model Discover-1 was used as described in Section 2. The effect of the microwave power on the apparent rate constant (kapp) was studied in the range 0 60 W, using with the same frequency of 2455 MHz. The data also obey the pseudo-firstorder rate law. Experimental data were also gathered from the reactions in the absence of microwave irradiation. As shown in Fig. 3, the apparent rate constant (kapp) increases linearly, when microwave power is increased. This phenomenon indicates that the microwave provides more energy for the reaction system. Thus, the reaction rate increases when microwave power is increased. The same trend is also observed in other studies [7,11,12]. In addition, certain literature shows that a very high yield and clean reactions have been obtained using only small amounts of energy in the literatures [28,30,31]. However, all of the experimental parameters were varied using a power of 20 W and the same frequency of 2455 MHz in all of the experimental runs.
2296
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
noted shows that the reaction occurs at the interface, as expected. The value of the apparent activation energy (Ea) shows that the reaction is controlled by the organic-aqueous interfacial reaction for an agitation speed of 400 rpm and microwave power of 20 W (2455 MHz). 4.4. Effect of the amount of NaOH
Fig. 3. A plot of the rate constants vs. various microwave power; 5 mmol of 1octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm,.
4.3. The effect of temperature In a general chemical reaction system, temperature has an important effect on the reaction rate. A phase-transfer catalytic reaction also has the same characteristic. In a phase-transfer catalytic reaction, high temperatures are not required. The reaction temperature is moderate. Therefore, no byproducts are generated from side reactions. In this study, the effect of temperature on the apparent rate constant (kapp) was determined in the range of 30 50 8C with the same microwave power used is 20 W (2455 MHz) for throughout the reaction. From the experimental data, it is clearly shows that the reaction rate and the conversion are both increased, as temperature and the effect of microwave are increased. This phenomenon indicates that the reactant molecules possess larger activated energy at a higher temperature, so the microwave easily pass through the reactor and the conversion is increased. It is worthy of note that the collisions between of the reactants at higher temperature are also increased, so the reaction rate is increased when temperature is increased. As shown in Fig. 4, the activation energy (Ea), which is obtained from the slope of the Arrhenius plot of ln(kapp) versus 1/T, is 11.3 kcal/mol. The Ea
Fig. 4. A plot of the rate constants vs. various reaction temperatures; 5 mmol of 1octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 400 rpm, microwave power 20 W.
In a phase-transfer catalytic reaction for the synthesis of dichlorocyclopropane, alkaline compounds also play an important role in promoting the reaction. The key point is that dichlorocarbene is produced from the reaction of chloroform and sodium hydroxide. In other words, no dichlorocarbene can be produced in the absence of sodium hydroxide. The most popular alkaline compounds are sodium hydroxide, potassium hydroxide and sodium bicarbonate. Based on the price of the reagents and their alkalinity, sodium hydroxide is the best choice among these three alkali compounds. The reaction rate is low when 1.5 g of NaOH is used in the reaction, but both the reaction rate and the conversion are increased as the amount of NaOH used is increased, up to 6 g. Within this range, the deprotonation of chloroform is directly increased by an increase in the amount of sodium hydroxide. In addition, the hydrolysis of dichlorocarbene is decreased by further increasing the amount of NaOH. However, water can not completely dissolve NaOH when the amount of NaOH exceeds 6 g. In this situation, the solution is saturated with NaOH which is unfavorable to the further generation of dichlorocarbene. For Fig. 5, the conversion of 1-octene is then decreased with an increase in the amount of NaOH of larger than 6 g. Under this situation, the solution is almost saturated with sodium hydroxide and becomes a slurry one. With a further increase in the amount of NaOH, solid particles of NaOH are suspended in the reaction solution in which the interfacial area was partly occupied by those NaOH particles. Therefore, the transfer of compounds through the interface and the reaction at the interface are decreased. Hence, the reaction is decreased at a higher amount of NaOH. Therefore, as shown in Fig. 5, the apparent rate constant is then decreased when the amount of NaOH used is increased to more than 6 g. 4.5. Effect of the amount of S-8 catalyst As stated, 3-(N,N-dimehtyloctylammonio)propansulfonate (S8) was employed as the phase-transfer catalyst in this work. The amount of S-8 catalyst used was 8.68–126 mg which gives a
Fig. 5. A plot of the rate constants vs. various amounts of NaOH; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of S-8, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
Fig. 6. A plot of ln(1 X) of 1-octene vs. time with various amounts of catalyst (S8); 5 mmol of 1-octene, 7.5 mL of chloroform, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
relative molar ratio for 1-octene of approximately 0.62–9 mol%. The experimental results which obey the pseudo-first-order rate law, are shown in Figs. 6 and 7, respectively. Fig. 6 shows the reaction is also increased when the amount of S-8 catalyst is increased. In the absence of S-8 catalyst, the conversion is low even after 20 min of reaction. However, the conversion is dramatically increased by the use of a small quantity of S-8 catalyst up to 0.25 mmol. The conversion or the reaction rates do not increase further when the amount of S-8 catalyst is further increased. Obviously, this experimental result is obtained from Fig. 7, even when the reaction is assisted by the microwave irradiation. In this situation, the catalyst S-8 is saturated in organic phase. From the proposed interfacial mechanism +QSO3 CCl2 @ QSO3(org) + CCCl2:(org), it is obvious that the reaction will proceed to the left side when the amount of QSO3(org) is oversaturated. Therefore, the content of:CCl2 decreases when the amount of catalyst S-8 is larger than 0.25 mmol. Hence, the reaction rate is decreased when the amount of QSO3 is further increased. This result is similar to that for the use of NaOH. In this situation, the solution is saturated with
Fig. 7. A plot of the rate constants vs. various amounts of catalyst (S-8); 5 mmol of 1octene, 7.5 mL of chloroform, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
2297
Fig. 8. A plot of the rate constants vs. various amounts of 1-octene; 7.5 mL of chloroform, 0.25 mmol of S-8, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
S-8 catalyst, so the reaction rate is no longer increased when there is a further increase in the amount of S-8 catalyst. 4.6. The effect of the amount of 1-octene In this study, 1-octene was catalyzed using a phase-transfer catalyst assisted by microwave irradiation in a chloroform/alkaline aqueous solution of NaOH, which caused the dichlorocyclopropanation to produce a 1,1-dichloro-2-hexyl-cyclopropane product. It is obvious that the reaction also obeys a pseudo-first-order rate law. It is also found that the reaction rate, and the conversion decrease when the amount of 1-octene is increased. In principle, it is reasonable to predict that the reaction rate is increased when the amount of reactant is increased. For an interfacial reaction, the concentration of the 1-octene at the interphase is key to the promotion of the reaction. The corresponding apparent rate constant (kapp) was determined in the range 1.25–10 mmol of 1octene using microwave power of 20 W (2455 MHz) for throughout the reaction. The results are shown in Fig. 8.
Fig. 9. A plot of ln(1 X) of 1,7-octadiene vs. time with different kinds of catalysts; 5 mmol of 1-octene, 7.5 mL of chloroform, 0.25 mmol of catalyst, 6 g of NaOH, 6 mL of water, 40 8C, 400 rpm, microwave power 20 W.
2298
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299
Table 1 Effect of quaternary ammonium salts and S-8 on the apparent rate constants (kapp). Kinds of phase-transfer catalyst
Apparent rate constant kapp (103 1/min)
TBAC TBAB THAI TBAHS BTEAC S-8
6.061 4.888 4.937 4.795 4.775 11.431
Reaction conditions: 5 mmol of 1-octene, 7.5 mL of chloroform, 6 g of NOH, 6 mL of water, 0.25 mmol of catalyst, 0.5 g of internal standard (nonane), 40 8C, 400 rpm, 20 W (2455 MHz).
4.7. The effect of the quaternary ammonium salts In this study, five quaternary ammonium salts and S-8 catalyst were used as the catalyst for dichlorocyclopropanation at 40 reaction temperature agitation speeds and a microwave power of 20 W (2455 MHz), throughout the reaction. The experimental data obey a pseudo-first-order rate law, for all of the quaternary ammonium salts and the S-8 catalyst. As shown in Fig. 9 and Table 1, the order of reactivity for these seven catalysts are: S8 > TBAC-TBAB-TBAI-TBAHS-BTEAC. A comparison of the experimental results for TBAC, TBAB, TBAI, TBAHS and BTEAC clearly shows that the reactivity of each of the quaternary salt is almost the same in spite of the different total numbers of carbons in the alkyl group of the cation in the quaternary ammonium salts and the corresponding anions. Nevertheless, S-8 catalyst exhibits high reactivity and enhances the reaction. In general, the most acceptable mechanisms of a phasetransfer catalytic reaction are the Starks extraction mechanism and the Makosza interfacial mechanism [2]. In this work, 1octene and chloroform, which are the two main reactants, are insoluble in water. Therefore, by viewing the generation of dichlorocarbene [34–36], the characteristics of such a phasetransfer catalytic reaction (PTC), which is quite different from that of Starks’s extraction mechanism. The occurrence of the reaction in this work can be attributed to the interfacial reaction proposed by Makosza and Wawrzyniewicz [14]. In 2003, Fedorynski [37] proposed the mechanism of dichlorocyclopropanation by using trialkylamines as a phase-transfer agent. Trialkylamines are active nucleophiles, reacting with carbene at the interfacial region to form ammonium ylides, which enter the organic phase to further produce carbene. In this work, the role of trialkylammonium propansultan is the same as that of trialkylamine. Thus, the main interfacial reactions of alkene with dichlorocarbene (:CCl2) so 3-(N,N-dimethyloctylammonio)-propansulfonate gave more better results.
5. Conclusion In this work, the synthesis of 1,1-dichloro-2-hexyl-cyclopropane, which is useful in industry, was successfully performed by the reaction of 1-octene in an alkaline solution of NaOH/ chloroform via dichlorocyclopropanation under phase-transfer catalytic and S-8 in combination with microwave irradiation. A rational reaction mechanism was proposed to explain the experimental results satisfactorily. We suggest that the reaction takes place at the interface between aqueous and organic phases. The overall reaction follows a pseudo-first-order rate law and the apparent rate constants were obtained from the experimental data. The reaction rate and the conversion both increase with the increase in the agitation speed, the microwave power, the amount of NaOH, S-8 catalyst and temperature. However, increasing the
amount of 1-octene decrease the reaction rate. Among the quaternary ammonium salts and the S-8 catalyst, S-8 exhibits high reactivity. Acknowledgment We thank the National Science Council Taiwan for financial support under Grant No. NSC-94-2214-E-241-001. References [1] Dehmlow EV, Dehmlow. SS phase transfer catalysis. Weinheim, Germany: Verlag Chemie; 1993. [2] Starks CM, Liotta CL, Helpern M. Phase transfer catalysis: fundamentals, applications and industrial perspective. New York, USA: Chapman & Hall; 1994. [3] Sasson Y, Neumann R, editors. Handbook of phase transfer catalysis. London, UK: Blackie Academic and Professional; 1997. [4] Entezari MH, Shameli AA. phase-transfer catalysis and ultrasonic waves I. Cannizzaro reaction. Ultrason Sonochem 2000;7:169–72. [5] Gedye R, Smith F, Westaway K, Ali H, Baldisera L, Laberge L, et al. J The use of microwave ovens for rapid organic synthesis. Tetrahedron Lett 1986;27:279– 82. [6] Giguere RJ, Bray TL, Duncan SM, Majetich G. Application of commercial microwave ovens to organic synthesis. Tetrahedron Lett 1986;27:4945–58. [7] Deshayes S, Liagre M, Loupy A, Luche J, Petit A. Microwave activation in phase transfer catalysis. Tetrahedron 1999;55:10851–70. [8] Bogdal D, Bednarz S, Lukasiewicz. M Microwave induced thermal gradients in solventless reaction synthesis. Tetrahedron 2006;62:9440–5. [9] Loupy A, Petit A, Bonnet. D Improvements in 1,3-dipolar cycloaddition of nitrones to fluorinated dipolarophiles under solvent-free microwave activation. J Fluorine Chem 1995;75:215–6. [10] Barush B, Prajapati D, Boruah A, Sandhu J. Microwave induced 1,3-dipolar cycloaddition reactions of nitrones. Synth Commun 1997;21:2563–7. [11] Yadav GD, Motirale BG. Microwave-irradiated synthesis of nitrophen using PEG 400 as phase transfer catalyst and solvent. Org Process Res Dev 2009;13:341–8. [12] Wang ML, Prasad SG. Microwave assisted phase-transfer catalytic ethoxylation of p-chloronitrobenzene-a kinetic study. J Taiwan Inst Chem Eng 2010;41:81–5. [13] Doering WE, Hoffmann AF. The addition of dichlorocarbene to oleins. J Am Chem Soc 1954;76:6162–5. [14] Makosza M, Wawrzynieicz M. Reaction of organic anions XXIV. catalytic method for preparation of dichlorocyclopropane derivatives in aqueous medium. Tetrahedron Lett 1969;53:4659–62. [15] Makosza M. Two-phase reactions in the chemistry of carbanions and halocarbenes—a useful tool in organic synthesis. Pure Appl Chem 1975;43:439–62. [16] Makosza M, Fedorynski M. Improved method of dibromocyclopropane derivatives synthesis in catalytic two-phase reaction. Synth Commun 1973;3:305–9. [17] Hiyama T, Sawada H, Tsukanaka M, Nozaki. b-Hydroxy-ethyltrialkylammonium ion as a selective phase-transfer catalyst for dichlorocyclopropanation. Tetrahedron Lett 1975;34:3013–6. [18] Julia S, Ginebreda A. A new method for generation of dichlorocarbene using solid–liquid phase transfer catalysis. Synthesis 1977;682–3. [19] Dehmlow EV, Wilkenloh J. Application of phase transfer catalysis, Part 29. dibromopropane addition hydrolysis competition in the presence of concentration sodium hydroxide. J Chem Res (S) 1984;396–7. [20] Nomura E, Taniguchi H, Otsuji Y. Calixarene-catalyzed generation of dichlorocarbene and its application to organic reactions. The catalytic action of octopus-type calix[6]arene. Bull Chem Soc Jpn 1994;67:792–9. [21] Walker MA. A high yield synthesis of N-alkylmaleimides using a novel modification of the Mitsunobu reaction. J Org Chem 1995;60:5352–5. [22] Saidi K, Darehkordi A. A conventients synthesis of N-aryltrifluoro-acetimidoyl phthalimide and succinimide. J Fluor Chem 2000;105:49–51. [23] Wilkes JS, Levisky JA, Wilson RA, Hussey CL. Dialkyl-imidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis. Inorg Chem 1982;21:1263–4. [24] Gesson JP, Jacquesy JC, Ramband D. A practical method for N-alkylation of succinimide and glutarimide. Bull Soc Chem Fr 1992;129:227–31. [25] Wang ML, Hsieh YM. Kinetic study of the synthesis of dichlorocyclopropane by trialkylammonium propansultans as new phase transfer catalysts. Chem Eng Commun 2007;194:477–94. [26] Dehmlow EV, Lipka BJ. A comparison of the effectiveness of various aqueous and solid bases and their mixtures in the N-alkylation of benzamide. J Chem Res (S) 1985;107(M):1418–22. [27] Wang ML, Chen WH, Wang FS. Kinetic study of synthesizing N-butylphthalimide under solid-liquid phase-transfer catalysis conditions. J Mol Catal A: Chem 2005;236:65–71. [28] Wang ML, Chen CJ. Kinetic study of synthesizing 1-(3-phenyl-propyl)-pyrrolilidine-2,5-dione under solid–liquid phase-transfer catalysis. Org Process Res Dev 2008;12:784–94.
M.-L. Wang, Y.-M. Hsieh / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 2293–2299 [29] Wang ML, Chen CJ. Kinetic study of synthesizing 1-(3-phenyl-propyl)-pyrrolilidine-2,5-dione under solid–liquid phase-transfer catalytic conditions assisted by ultrasonic irradiation. Org Process Res Dev 2010;14:737–45. [30] Lidstrom P, Tierney J, Wathey B, Westman J. Microwave assisted organic synthesis—a review. Tetrahedron 2001;57:9225–83. [31] Larhed M, Hallberg A. Microwave-assisted high-speed chemistry: a new technique in drug discovery. Drug Discov Today 2001;6:406–16. [32] Hsieh, YM. Study on the synthesis of dichlorocyclopropane by phase transfer catalysis. PhD thesis. Hsinchu, Taiwan: Department of Chemical Engineering, National Tsing Hua University; 2003. [33] Jayachandran JP, Wang ML. Regioselective dichlorocyclopropanation of 5vinyl cyclohexene using the new Dq-Br under controlled phase transfer catalysis conditions. React Kinet Catal Lett 2000;69(1):161–7.
2299
[34] Song QW, Yu B, Liu AH, He Y, Yang ZZ, Diao ZF, et al. PEG400-enhanced synthesis of gem-dichloroaziridines and gem-dichlorocyclopropanes via in situ generated dichlorocarbene. RCA Adv 2013;3:19009–14. [35] Sirovski F, Gorokhova M, Ruban S. Phase-transfer catalysis: kinetics and mechanism of dichlorocyclopropane formation in liquid/liquid and solid/ liquid systems. J Mol Catal A: Chem 2003;197:213–22. [36] Vivekanand PA, Balakrishnan T. Kinetics of dichlorocyclopropanation of vinylcyclohexane catalyzed by a new multi-site phase transfer catalyst. Catal Commun 2009;10:687–92. [37] Fedorynski M. Synthesis of gem-dihalocyclopropanes and their use in organic synthesis. Chem Rev 2003;103:1099–132.