- Email: [email protected]
Reaction of o-phenylene diamine and carbon disulfide by potassium hydroxide at higher temperature
Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Short communication
Reaction of o-phenylene diamine and carbon disulfide by potassium hydroxide at higher temperature Maw-Ling Wang a,*, Yen-Chun Liu b a b
Department of Environmental Engineering, Hungkuang University, Shalu, Taichung County 43302, Taiwan Department of Chemical Engineering, Wu Feng Institute of Technology, Min-Hsiung, Chiayi County 62101, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 July 2008 Received in revised form 2 February 2009 Accepted 4 February 2009
A semi-continuous reactor was employed to study the reaction of o-phenylene diamine and carbon disulfide in a gas–liquid (KOH solution/organic solvent) two-phase medium to produce potassium salt of 2-mercaptobenzimidazole (C6H4(N)(NH)CSK+, ArSK+). Gas-phase carbon disulfide of higher temperature is continuously introduced to the reactor for reaction. The main advantage of the present system is that the reaction can be carried out at a relatively higher temperature in the semi-continuous reactor. No quaternary ammonium salt is also required to obtain the desired reaction rate and the conversion. The conversion of o-phenylene diamine is low in the absence of potassium hydroxide. Potassium hydroxide does not directly participate in the reaction with o-phenylene diamine and carbon disulfide to synthesize 2-mercaptobenzimidazole (MBI). It merely reacts with the product 2mercaptobenzimidazole to form ArSK, and reacts with hydrogen sulfide which is a byproduct from the reaction of synthesizing 2-mercaptobenzimidazole. Nevertheless, the reaction is greatly enhanced in the presence of potassium hydroxide of an appropriate amount. Based on the experimental observation, a simple reaction mechanism is proposed, and a pseudo-first-order rate law is employed to describe the reaction. The effects of the reaction conditions, such as the amount of potassium hydroxide, the agitation speed, the initial concentration of carbon disulfide, the flow rate of gas-phase, the amount of ophenylene diamine and the temperature on the apparent rate constants (kapp) are investigated in detail. ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Synthesis of 2-mercaptobenzimidazole Gas–liquid reaction Semi-continuous reactor Potassium hydroxide
1. Introduction Phase-transfer catalysis (PTC) is an effective technique to synthesize products from two or more immiscible reactants which exist in different phases. Typically, quaternary ammonium salts were used as the phase-transfer catalyst to enhance this reaction (Sasson and Neumann, 1996; Starks et al., 1994). In the past, the procedure for synthesizing 2-mercaptobenzimidazole (MBI) has involved the reaction of o-phenylene diamine and reactants in a mixture of methanol–water catalyzed by active carbon (Van Allan and Deacon, 1963). However, this reaction needs to be carried out at a relatively high temperature in order to obtain the desired product over a long time period. In the later, quaternary ammonium salts (Blocher et al., 1966; Fournier, 1971; Goodman, 1975) were employed as a catalyst in the reaction of o-phenylene diamine and carbon disulfide to synthesize MBI. However, the kinetics and mechanism of the reaction have not been discussed. In addition, MBI has also been obtained by other techniques in using various reactants (Broada and Dehmlow, 1983; Yoshinori et al.,
* Corresponding author. Tel.: +886 4 2631 8652x4175; fax: +886 4 2652 9226. E-mail address: [email protected] (M.-L. Wang).
1990). Wang and Liu (1995, 1996a,b, 1997, 1998a,b, 2005) synthesized mercaptobenzimidazole from the catalyzed reaction of o-phenylene and carbon disulfide in a batch homogeneous solution or a two-phase solution by appropriate choice of the organic solvents. The primary advantage of these processes is that the catalyzed reaction is carried out at moderate reaction temperature. Nevertheless, the boiling point of carbon disulfide has limited the application of PTC to carry out the reaction at a higher temperature in the homogeneous solution or liquid–liquid two-phase solution. In this work, the reaction is promoted by adding potassium hydroxide. No quaternary ammonium salt is necessary to enhance the reaction. In order to increase the reaction rates, a higher temperature, from which a semi-continuous reactor was employed to carry out the reaction, is used in this study. The reaction of ophenylene diamine and carbon disulfide in the presence of KOH to synthesize MBI is carried out in a gas-phase/liquid solution twophase medium in this work. The main advantage of this new process is that a reaction temperature higher than boiling point of carbon disulfide is used to enhance the reaction. In order to fulfill this requirement in this study, a semi-continuous reactor (Wang and Liu, 2006) is employed to carry out the reaction in this work. Carbon disulfide (CS2) mixed with dichloromethane (CH2Cl2),
1876-1070/$ – see front matter ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2009.02.004
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Nomenclature ArSK kapp r1 X []
potassium salt of 2-mercaptobenzimidazole apparent rate constant reaction rate conversion of o-phenylene diamine concentration
Subscript 0 initial condition
which is used as the gas-phase, is introduced to the reactor for reaction with o-phenylene diamine in the presence of potassium hydroxide. Based on the experimental evidence, a simple reaction mechanism is proposed and the kinetics is developed. A pseudofirst-order rate law is sufficient to describe the kinetic behaviors. The effects of the reaction conditions, including the amount of potassium hydroxide, the concentration of carbon disulfide, the flow rate of gas-phase, the amount of o-phenylene diamine and temperature, on the conversion were investigated.
587
3. Reaction mechanism and kinetic model The gas–liquid reaction involves the mass transfer of gas-phase reactant from gas-phase to liquid-phase accompanied with the chemical reaction in gas–liquid system (Alper, 1983; Matsuo and Ishii, 1982; Perrys and Green, 1988). The key point of the reaction system is how to manipulate the equation of change of the multicomponents in applying to the physical system, i.e. the dissolving gas-phase reactant in the liquid-phase, the mass transfer of reactant and the chemical reaction resistance in the liquid-phase. For synthesizing 2-mercaptobenzimidazole from the two-phase reaction of o-phenylene diamine and carbon disulfide, the dissolved carbon disulfide in liquid-phase and the reaction of carbon disulfide and o-phenylene diamine in organic phase are important affecting the yield and the conversion. In a preliminary experiment, the reactivity of tetrabutylammonium bromide (TBAB or QBr) is low in this reaction. However, the reaction is greatly enhanced by adding potassium hydroxide of an appropriate amount even in the presence of quaternary ammonium halide. Thus, it is obvious that carbon disulfide is first dissolved in the organic phase. A reaction of synthesizing 2mercaptobenzimidazole is proposed, i.e.
2. Experimental 2.1. Materials Carbon disulfide (CS2), o-phenylene diamine (C6H4(NH2)2), potassium hydroxide (KOH), organic solvents including ethanol and dichloromethane, and other reagents used were all GR-grade chemicals for synthesis. 2.2. Procedures Kinetics of synthesizing 2-mercaptobenzimidazole: The reactor is a 125-mL four-necked Pyrex flask, capable of agitating the solution, inserting the thermometer, taking samples, and feeding the reactants. A reflux condenser is attached to the port of the reactor to recover the species from the gas-phase. The reactor is submerged into a constant temperature water batch in which the temperature can be controlled to 0.1 8C. To start an experimental run at one atmosphere pressure, known quantities of o-phenylene diamine, caffeine (internal standard), and potassium hydroxide (KOH) were dissolved in the organic-phase solution (ethanol and water mixture) and introduced into the reactor. The liquid solution was stirred mechanically by a two-bladed paddle (5.5 cm) at 700 rpm. Then, a mixture of carbon disulfide and dichloromethane in gas-phase is introduced to the liquid solution to initiate the reaction at one atmosphere pressure. During the reaction, an aliquot of 0.1 mL was withdrawn from the solution at a chosen time. The sample was immediately poured into methanol at 4 8C for dilution and retardation of the reaction and then analyzed by HPLC. The product MBI for identification was purified from the reaction by vacuum evaporation to strip off the organic solvent and carbon disulfide. Then, it was recrystallized from ethanol as white crystals. The product (MBI) and the reactants (carbon disulfide and ophenylene diamine) were identified by NMR and IR analyses. The results obtained from the instrumental analysis are consistent with those of the literature reports. An HPLC model (Shimadzu) with an absorbance detector (254 nm, SPD-6A) was employed to measure the amounts of reactants and product. The column used was Shim-Pack CLC-ODS RP-18 (5 mm). The eluent was CH3CN/ H2O = 20/80 (with 5 mM KH2PO4 + 0.1% H3PO4) (volume ratio) with a flow rate of 1.0 mL/min.
ðR1Þ H2 S þ 2KOH ! K2 S þ 2H2 O
(R2)
It is also obvious that potassium hydroxide does not directly participate from the reaction with o-phenylene diamine and carbon disulfide to synthesize MBI product. Then, MBI reacts with KOH to produce potassium salt of 2-mercaptobenzimidazole (ArSK) in the liquid solution. During the reaction, potassium hydroxide also reacts with hydrogen sulfide to enhance the reaction from the principle of Le Chatelier. In addition to the main reactions (R1), KOH will further react with CS2 to produce the inert inorganic substance including K2CO3 and K2CS3, i.e. 3CS2 þ 6KOH ! 2K2 CS3 þ K2 CO3 þ 3H2 O
(R3)
In this work, carbon disulfide was used in large excess relatively to its stoichiometric quantity. Based on the experimental observation, the reaction follows a pseudo-first-order rate law. Thus, we have r1 ¼
d½C6 H4 ðNH2 Þ2 ¼ kapp ½C6 H4 ðNH2 Þ2 dt
(1)
where kapp is the apparent rate constant. Integrating Eq. (1), we obtain lnð1 XÞ ¼ kapp t
(2)
where X is the conversion of o-phenylene diamine and is defined as X ¼1
½C6 H4 ðNH2 Þ2 ½C6 H4 ðNH2 Þ2 0
(3)
in which [C6H4(NH2)2]0 is the initial concentration of o-phenylene diamine. 4. Results and discussion In principle, it is difficult to carry out the liquid–liquid twophase reaction of carbon disulfide and o-phenylene diamine at temperature higher than 46.2 8C because the boiling point of
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
588
diamine are shown in Fig. 1. The conversion of o-phenylene diamine is low in the absence of alkali compounds. Ammonia (NH3), potassium hydroxide (KOH) and sodium hydroxide (NaOH) also enhance the reaction of o-phenylene diamine and carbon disulfide in the organic-phase solution. The order of the reactivity for these alkali compounds is: NaHCO3 Na2CO3 > NH3 KOH NaOH. Based on the experimental observation, the gas–liquid enhanced reaction of carbon disulfide and o-phenylene diamine by these alkali compounds follows a pseudo-first-order rate law. A rational reaction mechanism is proposed. The experimental data are expressed by the pseudo-first-order rate law. The dependence of the apparent rate constants (kapp) of the reaction on the alkali compounds is shown in Table 1. Sodium carbonate and sodium bicarbonate exhibit highest reactivity in enhancing the reaction. (b) Effects of the amount of potassium hydroxide Fig. 1. Effect of the alkali compounds on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 3.56 103 mole of alkali compound, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/ CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C, no KOH added for blank run.
carbon disulfide at atmosphere is 46.2 8C in a batch reactor. A larger amount of CS2 evaporates to the gas-phase in a batch reactor. In this work, the reaction, which is carried out under a semicontinuous reactor, can be operated at a temperature higher than the boiling point of carbon disulfide. The vapor-phase carbon disulfide can be recovered by using a condenser in a semicontinuous reactor. First, a mixture of carbon disulfide (b.p. 46.2 8C) and dichloromethane (b.p. 39.6 8C) in the gas-phase is prepared and then continuously fed to the reactor. The concentration of carbon disulfide is first set by mixing the appropriate amount ratio of CS2 and CH2Cl2 of the liquid phases. The liquid mixture is then heated to vapor-phase via a heater. The flow rate of feeding CS2/CH2Cl2 gas stream is controlled by a feed pump. Second, carbon disulfide is then dissolved in an EtOH/H2O solution which contains o-phenylene diamine and potassium hydroxide. Thus, carbon disulfide reacts with o-phenylene diamine to produce the desired product 2-mercaptobenzimidazole. Then, MBI further reacts with potassium hydroxide to produce the potassium salt of 2-mercaptobenzimidazole, which forwards the reaction toward to the right. The effects of the reaction conditions on the conversion of o-phenylene diamine and the rate are discussed below: (a) Effect of the alkali compounds The effects of the alkali compounds, including NaHCO3, Na2CO3, NH3, KOH and NaOH, on the conversion of o-phenylene
As stated, KOH does not participate directly in the reaction of o-phenylene diamine and carbon disulfide in synthesizing 2mercaptobenzimidazole. It merely acts as the compound in the reaction with MBI to form the potassium salt of MBI, and in the reaction with H2S to produce K2S. All these two reactions are both favorite toward the reaction (R1) of synthesizing MBI to the right. The role of potassium hydroxide in the mechanism of the reaction of o-phenylene diamine and carbon disulfide needed further study. The effects of the amount of potassium hydroxide on the conversion of o-phenylene diamine are shown in Fig. 2. The reaction follows pseudo-first-order rate law in using various amounts of KOH. As shown in Fig. 2, the conversion of o-phenylene diamine is increased with the increase in the amount of KOH. The dependence of the apparent rate constants (kapp) of the reaction on the concentrations of KOH and other alkali compounds are shown in Table 1. In the absence of alkali compounds, the reaction rate is low. However, the reaction is dramatically accelerated by adding a small amount of potassium hydroxide and other alkali compounds. (c) Effect of the agitation speed Fig. 3 shows the effect of the agitation speed on the conversion of o-phenylene diamine. The conversion is increased with the increase in the agitation speed. However, this change in conversion due to the variation of agitation speed is not significant. In general, this small deviation of conversion due to the change of the agitation speed can be attributed to the rapid dissolving rate of carbon disulfide and the rapid mass transfer of species in the liquid-phase solution. The liquid solution is homogeneous. Once the compound CS2 is
Table 1 Effects of the reaction conditions on the apparent rate constants kapp (min1); 0.20 g of KOH, 0.6747 g of C6H4(NH2)2, volume ratio of EtOH/H2O = 1/1 (100 mL), 1.43 mL/min of gas flow rate, 15 mL/100 mL of CS2/CH2Cl2, 700 rpm, 60 8C. Alkali compound kapp (103)
Blank 0.63
NH3 21.67
NaOH 23.20
KOH 23.17
Na2CO3 44.64
NaHCO3 46.43
EtOH/H2O kapp (103)
90/10 39.25
80/20 33.75
70/30 29.88
60/40 25.38
50/50 23.17
40/60 18.00
30/70 13.25
Stirring speed (rpm) kapp (103)
0 21.21
200 21.70
400 23.05
600 23.17
700 23.17
800 23.17
1000 23.17
[CS2] (mL) kapp (103)
3 10.48
6 13.21
9 15.24
12 17.26
15 23.17
20 23.18
Gas flow rate (mL/min) kapp (103)
0.98 26.43
1.43 23.17
2.27 15.95
2.91 12.98
3.43 10.12
[C6H4(NH2)2] (g) kapp (103)
0.200 42.20
0.400 29.15
0.675 23.17
0.800 17.68
1.000 14.02
Temperature (8C) kapp (103)
50 2.56
55 4.15
60 10.83
65 13.30
– – 1.200 10.12
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Fig. 2. Effect of the amount of KOH on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C, no KOH added for blank run.
589
Fig. 4. Effect of the amount of the concentration of CS2 on the conversion of ophenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/ CH2Cl2 = y mL/100 mL, 700 rpm, 60 8C.
dissolved in the organic solution, the mass transfer resistance of the species in the homogeneous solution is small. Therefore, the resistance of the dissolving rate of carbon disulfide in the organic solvent relatively to the resistance of the reaction rate is small. This confirms the argument for fast dissolving and mass transfer of CS2 in EtOH/H2O solution. The dependence of the apparent rate constant (kapp) on the agitation speed is also depicted in Table 1. As expected, the deviation in the kapp-value due to the variation of agitation speed from 0 to 1000 rpm is also small. (d) Effect of the concentration of carbon disulfide
reacts with o-phenylene diamine to produce 2-mercaptobenzimidazole in the homogeneous organic solution. Therefore, a high concentration of CS2 in the organic-aqueous solution is obtained when a higher concentration of CS2/CH2Cl2 in a gasphase is introduced to the reaction solution. This is why the conversion of o-phenylene diamine is increased using a larger concentration of CS2/CH2Cl2. The effect of the concentration of CS2 on the apparent rate constant kapp is also shown in Table 1. As expected, the conversion is increased with the increase in the concentration of carbon disulfide. (e) Effect of the gas flow rate
In this work, CH2Cl2 (inert) is used as the carrier to bring the gas-phase carbon disulfide to the liquid-phase reaction solution. It also acts as the diluter for carbon disulfide. In principle, CH2Cl2 and CS2 can be recovered from the semicontinuous reactor by using a condenser. The concentration of carbon disulfide is first set by mixing the appropriate amount ratio of CS2 and CH2Cl2 of liquid phases. Fig. 4 shows the effect of the concentration of CS2 on the conversion of o-phenylene diamine. As expected, the conversion is increased with the increase in the concentration of CS2. In general, carbon disulfide is first dissolved in EtOH/H2O solution and then
As stated, the gas flow rate is controlled by the feed pump. The effect of the gas flow rate on CS2/CH2Cl2 on the conversion of o-phenylene diamine is shown in Fig. 5 which indicates that the conversion is decreased with the increase in the flow rate. A larger flow rate promotes the amount of carbon disulfide escape to the vapor-phase from the liquid solution. Thus, the dissolved CS2 in the organic-aqueous solution is small at a larger flow rate of CS2/CH2Cl2. Hence the conversion of ophenylene diamine (or the reaction rate) is enhanced by a low flow rate of carbon disulfide. The dependence of the apparent rate constant (kapp) on the gas flow rate is shown in Table 1.
Fig. 3. Effect of the agitation speed on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 60 8C.
Fig. 5. Effect of the amount of the gas flow rate on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = y mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
590
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Fig. 6. Effect of the amount of the o-phenylene diamine on the conversion of ophenylene diamine; 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
Fig. 8. Effect of the volume ratio of EtOH/H2O on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/ 100 mL, 700 rpm, 60 8C.
Naturally, the apparent rate constant kapp is decreased with the increase in the flow rate. (f) Effect of the amount of o-phenylene diamine
diamine is shown in Fig. 7. The order of the reactivity of the reaction for using these organic solvents is: DMSO (46.5) > DMF (36.7)–MeCN (35.94) > EtOH (24.55). Using the organic solvent of a higher dielectric constant increases the conversion of o-phenylene diamine. (h) Effect of the volume ratio of EtOH/H2O
The effect of the amount of o-phenylene diamine on the conversion of o-phenylene diamine is shown in Fig. 6. The conversion is decreased with the increase in the concentration of o-phenylene diamine. This result is similar to that obtained from the liquid-phase reaction catalyzed by quaternary ammonium salts (Wang and Liu, 1995, 1996a,b, 1997, 1998a,b, 2005). The effect of the concentration of o-phenylene diamine on the apparent rate constant (kapp) is also shown in Table 1, which indicates that kapp-value is decreased with the increase in the concentration of o-phenylene diamine. (g) Effect of the organic solvent
The effect of the volume ratio of EtOH/H2O on the conversion of o-phenylene diamine is shown in Fig. 8. The conversion is increased with the increase in the volume ratio of EtOH/H2O. The reason is that CS2 is favorite to dissolve in a more hydrophobic organic substance, i.e. more amount of EtOH. (i) Effect of the temperature
The liquid-phase solution is formed by mixing organic solvent and water. In this work, water is added to dissolve potassium hydroxide. Therefore, both protic solvent and aprotic solvent can be served as the organic reagent. The effect of the organic solvent on the conversion of o-phenylene
As stated in the previous section, the boiling point of carbon disulfide is 46.2 8C. Thus, it is difficult to carry out the reaction higher than 46.2 8C in the liquid–liquid two-phase reaction. For synthesizing MBI from the reaction of carbon disulfide and ophenylene diamine. Furthermore, a semi-continuous reactor from which carbon disulfide in a gas-phase is introduced to the liquid-phase solution (o-phenylene diamine), is employed in order to promote the reaction in this work. By doing such an
Fig. 7. Effect of the organic solvents on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
Fig. 9. Effect of the temperature on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm.
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
591
arrangement, solution temperature higher than the boiling point of carbon disulfide is feasible.
Acknowledgement
The effect of the temperature on the conversion of ophenylene diamine is shown in Fig. 9. As expected, the conversion is increased with increased in the temperature. The reaction also follows a pseudo-first-order rate law. The activation energy for the reaction of o-phenylene diamine and carbon disulfide in the presence of potassium hydroxide in a gas–liquid two-phase medium is 29.2 kcal/mol according to an Arrhenius plot. The apparent rate constant (kapp), which is shown in Table 1, is increased with the increase in temperature.
The authors would like to thank the National Science Council of the ROC for the financial support for the study under contract no. NSC 92-0402-E-007-004.
5. Conclusion In this work, the reaction of o-phenylene diamine and carbon disulfide in the presence of KOH in the synthesis of 2mercaptobenzimidazole is successfully carried out in a semicontinuous reactor. Without using quaternary ammonium salt as the phase-transfer catalyst, the reaction is also greatly enhanced in the presence of alkali compounds, such as NaHCO3, Na2CO3, KOH, NaOH and NH3. A gas stream of CS2/CH2Cl2 mixture is continuously fed to the reactor for the reaction with o-phenylene diamine in the liquid-phase solution. By feeding the gas-phase carbon disulfide, the reaction can be carried out at a higher temperature to enhance the reaction. The present process provides the feasible conditions to carry out the reactions at higher temperature. The experimental results show that the reaction follows the pseudo-first-order rate law from which the apparent rate constants (kapp) at various reaction conditions were obtained. The dissolving rate of CS2 in the organic solvent and the mass transfer rate in the organic-phase solution are both larger. A high reaction rate (or conversion) is obtained using an organic solvent of higher dielectric constant. Therefore, the effect of the agitation speed on the conversion of o-phenylene diamine is insignificant. The conversion of ophenylene diamine is increased with the increase in the concentration of potassium hydroxide, temperature and the concentration of carbon disulfide. However, the conversion is decreased with the increase in the flow rate of CS2/CH2Cl2 and the concentration of o-phenylene diamine.
References Alper, E., Mass Transfer with Chemical Reaction in Multiphase, I & II, Martinus Nijhoff, New York, USA (1983). Blocher, S. H., A. Schultze, and H. W. Leverkusen, ‘‘Process for the Production of 2Mercaptobenzimidazole,’’ U.S. Patent, 3, 235, 559 (1966). Broada, W. and E. V. Dehmlow, ‘‘Thioharnstoffe Durch Drikom Ponentenreaktionen von Amien,’’ Liebigs Ann. Chem., 1837 (1983). Fournier, E., ‘‘Therapeutical Composition Containing 2-Mercaptobenzimidazole,’’ U.S. Patent, 3, 558, 775 (1971). Goodman, A., ‘‘2-Mercaptobenzimidazole Preparation,’’ U.S. Patent 3, 895, 025 (1975). Matsuo, H. and T. Ishii, ‘‘Mass Transfer with mth Order Chemical Reaction for MultiParticle Systems,’’ Chem. Eng. Sci., 37, 229 (1982). Perrys, R. H. and D. Green, Perry’s Chemical Engineers Handbook, 4th Ed., McGraw Hill, New York, USA (1988). Sasson, Y. and R. Neumann, Handbook of Phase Transfer Catalysis , Blackie Academic & Professional Chapman & Hall, Inc., New York, USA (1996). Starks, C. M., C. L. Liotta, and M. E. Halpern, Phase Transfer Catalysis, Fundamentals, Applications, and Industrial Perspectives , Chapman & Hall, Inc., New York, USA (1994). Van Allan, J. A. and B. D. Deacon, ‘‘2-Mercaptobenzimidazole,’’ Org. Synth., 569 (1963). Wang, M. L. and B. L. Liu, ‘‘Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Tertiary Amines in a Homogeneous Solution,’’ Ind. Eng. Chem. Res., 34 (11), 3688 (1995). Wang, M. L. and B. L. Liu, ‘‘Catalyzed Reaction of Carbon Disulfide and o-Phenylene Diamine by Tertiary Amine,’’ J. Mol. Catal. A: Chem., 105, 49 (1996a). Wang, M. L. and B. L. Liu, ‘‘Homogeneous Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Tertiary amines,’’ Int. J. Chem. Kinet., 28, 885 (1996b). Wang, M. L. and B. L. Liu, ‘‘Homogeneous Reaction of Carbon Disulfide and o-Phenylene Diamine in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Eng., 20 (4), 413 (1997). Wang, M. L. and B. L. Liu, ‘‘Catalyzed Reaction of Carbon Disulfide and o-Phenylene Diamine by Quaternary Ammonium Hydroxide,’’ Chem. Eng. Commun., 165, 177 (1998a). Wang, M. L. and B. L. Liu, ‘‘Reaction of Carbon Disulfide and o-Phenylene Diamine by Tertiary Amine in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Eng., 21 (3), 317 (1998b). Wang, M. L. and B. L. Liu, ‘‘Two-Phase Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Quaternary Ammonium Salts in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Chem. Engrs., 36 (5), 487 (2005). Wang, M. L. and B. L. Liu, ‘‘Semi-Continuous Gas–Liquid Phase-Transfer Catalyzed Reaction of o-Phenylene Diamine and Carbon Disulfide by Tetrabutylammonium Hydroxide,’’ J. Chin. Inst. Chem. Engrs., 37 (6), 557 (2006). Yoshinori, T., N. Hajime, K. Chizuko, M. Tshyuk, and A. Akira, ‘‘A New Route of 1,2Dithiole-3-thiones by the Reaction of Enaminones with Carbon Disulfide,’’ Heterocycles, 31, 1 (1990).
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Short communication
Reaction of o-phenylene diamine and carbon disulfide by potassium hydroxide at higher temperature Maw-Ling Wang a,*, Yen-Chun Liu b a b
Department of Environmental Engineering, Hungkuang University, Shalu, Taichung County 43302, Taiwan Department of Chemical Engineering, Wu Feng Institute of Technology, Min-Hsiung, Chiayi County 62101, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 July 2008 Received in revised form 2 February 2009 Accepted 4 February 2009
A semi-continuous reactor was employed to study the reaction of o-phenylene diamine and carbon disulfide in a gas–liquid (KOH solution/organic solvent) two-phase medium to produce potassium salt of 2-mercaptobenzimidazole (C6H4(N)(NH)CSK+, ArSK+). Gas-phase carbon disulfide of higher temperature is continuously introduced to the reactor for reaction. The main advantage of the present system is that the reaction can be carried out at a relatively higher temperature in the semi-continuous reactor. No quaternary ammonium salt is also required to obtain the desired reaction rate and the conversion. The conversion of o-phenylene diamine is low in the absence of potassium hydroxide. Potassium hydroxide does not directly participate in the reaction with o-phenylene diamine and carbon disulfide to synthesize 2-mercaptobenzimidazole (MBI). It merely reacts with the product 2mercaptobenzimidazole to form ArSK, and reacts with hydrogen sulfide which is a byproduct from the reaction of synthesizing 2-mercaptobenzimidazole. Nevertheless, the reaction is greatly enhanced in the presence of potassium hydroxide of an appropriate amount. Based on the experimental observation, a simple reaction mechanism is proposed, and a pseudo-first-order rate law is employed to describe the reaction. The effects of the reaction conditions, such as the amount of potassium hydroxide, the agitation speed, the initial concentration of carbon disulfide, the flow rate of gas-phase, the amount of ophenylene diamine and the temperature on the apparent rate constants (kapp) are investigated in detail. ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Synthesis of 2-mercaptobenzimidazole Gas–liquid reaction Semi-continuous reactor Potassium hydroxide
1. Introduction Phase-transfer catalysis (PTC) is an effective technique to synthesize products from two or more immiscible reactants which exist in different phases. Typically, quaternary ammonium salts were used as the phase-transfer catalyst to enhance this reaction (Sasson and Neumann, 1996; Starks et al., 1994). In the past, the procedure for synthesizing 2-mercaptobenzimidazole (MBI) has involved the reaction of o-phenylene diamine and reactants in a mixture of methanol–water catalyzed by active carbon (Van Allan and Deacon, 1963). However, this reaction needs to be carried out at a relatively high temperature in order to obtain the desired product over a long time period. In the later, quaternary ammonium salts (Blocher et al., 1966; Fournier, 1971; Goodman, 1975) were employed as a catalyst in the reaction of o-phenylene diamine and carbon disulfide to synthesize MBI. However, the kinetics and mechanism of the reaction have not been discussed. In addition, MBI has also been obtained by other techniques in using various reactants (Broada and Dehmlow, 1983; Yoshinori et al.,
* Corresponding author. Tel.: +886 4 2631 8652x4175; fax: +886 4 2652 9226. E-mail address: [email protected] (M.-L. Wang).
1990). Wang and Liu (1995, 1996a,b, 1997, 1998a,b, 2005) synthesized mercaptobenzimidazole from the catalyzed reaction of o-phenylene and carbon disulfide in a batch homogeneous solution or a two-phase solution by appropriate choice of the organic solvents. The primary advantage of these processes is that the catalyzed reaction is carried out at moderate reaction temperature. Nevertheless, the boiling point of carbon disulfide has limited the application of PTC to carry out the reaction at a higher temperature in the homogeneous solution or liquid–liquid two-phase solution. In this work, the reaction is promoted by adding potassium hydroxide. No quaternary ammonium salt is necessary to enhance the reaction. In order to increase the reaction rates, a higher temperature, from which a semi-continuous reactor was employed to carry out the reaction, is used in this study. The reaction of ophenylene diamine and carbon disulfide in the presence of KOH to synthesize MBI is carried out in a gas-phase/liquid solution twophase medium in this work. The main advantage of this new process is that a reaction temperature higher than boiling point of carbon disulfide is used to enhance the reaction. In order to fulfill this requirement in this study, a semi-continuous reactor (Wang and Liu, 2006) is employed to carry out the reaction in this work. Carbon disulfide (CS2) mixed with dichloromethane (CH2Cl2),
1876-1070/$ – see front matter ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2009.02.004
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Nomenclature ArSK kapp r1 X []
potassium salt of 2-mercaptobenzimidazole apparent rate constant reaction rate conversion of o-phenylene diamine concentration
Subscript 0 initial condition
which is used as the gas-phase, is introduced to the reactor for reaction with o-phenylene diamine in the presence of potassium hydroxide. Based on the experimental evidence, a simple reaction mechanism is proposed and the kinetics is developed. A pseudofirst-order rate law is sufficient to describe the kinetic behaviors. The effects of the reaction conditions, including the amount of potassium hydroxide, the concentration of carbon disulfide, the flow rate of gas-phase, the amount of o-phenylene diamine and temperature, on the conversion were investigated.
587
3. Reaction mechanism and kinetic model The gas–liquid reaction involves the mass transfer of gas-phase reactant from gas-phase to liquid-phase accompanied with the chemical reaction in gas–liquid system (Alper, 1983; Matsuo and Ishii, 1982; Perrys and Green, 1988). The key point of the reaction system is how to manipulate the equation of change of the multicomponents in applying to the physical system, i.e. the dissolving gas-phase reactant in the liquid-phase, the mass transfer of reactant and the chemical reaction resistance in the liquid-phase. For synthesizing 2-mercaptobenzimidazole from the two-phase reaction of o-phenylene diamine and carbon disulfide, the dissolved carbon disulfide in liquid-phase and the reaction of carbon disulfide and o-phenylene diamine in organic phase are important affecting the yield and the conversion. In a preliminary experiment, the reactivity of tetrabutylammonium bromide (TBAB or QBr) is low in this reaction. However, the reaction is greatly enhanced by adding potassium hydroxide of an appropriate amount even in the presence of quaternary ammonium halide. Thus, it is obvious that carbon disulfide is first dissolved in the organic phase. A reaction of synthesizing 2mercaptobenzimidazole is proposed, i.e.
2. Experimental 2.1. Materials Carbon disulfide (CS2), o-phenylene diamine (C6H4(NH2)2), potassium hydroxide (KOH), organic solvents including ethanol and dichloromethane, and other reagents used were all GR-grade chemicals for synthesis. 2.2. Procedures Kinetics of synthesizing 2-mercaptobenzimidazole: The reactor is a 125-mL four-necked Pyrex flask, capable of agitating the solution, inserting the thermometer, taking samples, and feeding the reactants. A reflux condenser is attached to the port of the reactor to recover the species from the gas-phase. The reactor is submerged into a constant temperature water batch in which the temperature can be controlled to 0.1 8C. To start an experimental run at one atmosphere pressure, known quantities of o-phenylene diamine, caffeine (internal standard), and potassium hydroxide (KOH) were dissolved in the organic-phase solution (ethanol and water mixture) and introduced into the reactor. The liquid solution was stirred mechanically by a two-bladed paddle (5.5 cm) at 700 rpm. Then, a mixture of carbon disulfide and dichloromethane in gas-phase is introduced to the liquid solution to initiate the reaction at one atmosphere pressure. During the reaction, an aliquot of 0.1 mL was withdrawn from the solution at a chosen time. The sample was immediately poured into methanol at 4 8C for dilution and retardation of the reaction and then analyzed by HPLC. The product MBI for identification was purified from the reaction by vacuum evaporation to strip off the organic solvent and carbon disulfide. Then, it was recrystallized from ethanol as white crystals. The product (MBI) and the reactants (carbon disulfide and ophenylene diamine) were identified by NMR and IR analyses. The results obtained from the instrumental analysis are consistent with those of the literature reports. An HPLC model (Shimadzu) with an absorbance detector (254 nm, SPD-6A) was employed to measure the amounts of reactants and product. The column used was Shim-Pack CLC-ODS RP-18 (5 mm). The eluent was CH3CN/ H2O = 20/80 (with 5 mM KH2PO4 + 0.1% H3PO4) (volume ratio) with a flow rate of 1.0 mL/min.
ðR1Þ H2 S þ 2KOH ! K2 S þ 2H2 O
(R2)
It is also obvious that potassium hydroxide does not directly participate from the reaction with o-phenylene diamine and carbon disulfide to synthesize MBI product. Then, MBI reacts with KOH to produce potassium salt of 2-mercaptobenzimidazole (ArSK) in the liquid solution. During the reaction, potassium hydroxide also reacts with hydrogen sulfide to enhance the reaction from the principle of Le Chatelier. In addition to the main reactions (R1), KOH will further react with CS2 to produce the inert inorganic substance including K2CO3 and K2CS3, i.e. 3CS2 þ 6KOH ! 2K2 CS3 þ K2 CO3 þ 3H2 O
(R3)
In this work, carbon disulfide was used in large excess relatively to its stoichiometric quantity. Based on the experimental observation, the reaction follows a pseudo-first-order rate law. Thus, we have r1 ¼
d½C6 H4 ðNH2 Þ2 ¼ kapp ½C6 H4 ðNH2 Þ2 dt
(1)
where kapp is the apparent rate constant. Integrating Eq. (1), we obtain lnð1 XÞ ¼ kapp t
(2)
where X is the conversion of o-phenylene diamine and is defined as X ¼1
½C6 H4 ðNH2 Þ2 ½C6 H4 ðNH2 Þ2 0
(3)
in which [C6H4(NH2)2]0 is the initial concentration of o-phenylene diamine. 4. Results and discussion In principle, it is difficult to carry out the liquid–liquid twophase reaction of carbon disulfide and o-phenylene diamine at temperature higher than 46.2 8C because the boiling point of
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
588
diamine are shown in Fig. 1. The conversion of o-phenylene diamine is low in the absence of alkali compounds. Ammonia (NH3), potassium hydroxide (KOH) and sodium hydroxide (NaOH) also enhance the reaction of o-phenylene diamine and carbon disulfide in the organic-phase solution. The order of the reactivity for these alkali compounds is: NaHCO3 Na2CO3 > NH3 KOH NaOH. Based on the experimental observation, the gas–liquid enhanced reaction of carbon disulfide and o-phenylene diamine by these alkali compounds follows a pseudo-first-order rate law. A rational reaction mechanism is proposed. The experimental data are expressed by the pseudo-first-order rate law. The dependence of the apparent rate constants (kapp) of the reaction on the alkali compounds is shown in Table 1. Sodium carbonate and sodium bicarbonate exhibit highest reactivity in enhancing the reaction. (b) Effects of the amount of potassium hydroxide Fig. 1. Effect of the alkali compounds on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 3.56 103 mole of alkali compound, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/ CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C, no KOH added for blank run.
carbon disulfide at atmosphere is 46.2 8C in a batch reactor. A larger amount of CS2 evaporates to the gas-phase in a batch reactor. In this work, the reaction, which is carried out under a semicontinuous reactor, can be operated at a temperature higher than the boiling point of carbon disulfide. The vapor-phase carbon disulfide can be recovered by using a condenser in a semicontinuous reactor. First, a mixture of carbon disulfide (b.p. 46.2 8C) and dichloromethane (b.p. 39.6 8C) in the gas-phase is prepared and then continuously fed to the reactor. The concentration of carbon disulfide is first set by mixing the appropriate amount ratio of CS2 and CH2Cl2 of the liquid phases. The liquid mixture is then heated to vapor-phase via a heater. The flow rate of feeding CS2/CH2Cl2 gas stream is controlled by a feed pump. Second, carbon disulfide is then dissolved in an EtOH/H2O solution which contains o-phenylene diamine and potassium hydroxide. Thus, carbon disulfide reacts with o-phenylene diamine to produce the desired product 2-mercaptobenzimidazole. Then, MBI further reacts with potassium hydroxide to produce the potassium salt of 2-mercaptobenzimidazole, which forwards the reaction toward to the right. The effects of the reaction conditions on the conversion of o-phenylene diamine and the rate are discussed below: (a) Effect of the alkali compounds The effects of the alkali compounds, including NaHCO3, Na2CO3, NH3, KOH and NaOH, on the conversion of o-phenylene
As stated, KOH does not participate directly in the reaction of o-phenylene diamine and carbon disulfide in synthesizing 2mercaptobenzimidazole. It merely acts as the compound in the reaction with MBI to form the potassium salt of MBI, and in the reaction with H2S to produce K2S. All these two reactions are both favorite toward the reaction (R1) of synthesizing MBI to the right. The role of potassium hydroxide in the mechanism of the reaction of o-phenylene diamine and carbon disulfide needed further study. The effects of the amount of potassium hydroxide on the conversion of o-phenylene diamine are shown in Fig. 2. The reaction follows pseudo-first-order rate law in using various amounts of KOH. As shown in Fig. 2, the conversion of o-phenylene diamine is increased with the increase in the amount of KOH. The dependence of the apparent rate constants (kapp) of the reaction on the concentrations of KOH and other alkali compounds are shown in Table 1. In the absence of alkali compounds, the reaction rate is low. However, the reaction is dramatically accelerated by adding a small amount of potassium hydroxide and other alkali compounds. (c) Effect of the agitation speed Fig. 3 shows the effect of the agitation speed on the conversion of o-phenylene diamine. The conversion is increased with the increase in the agitation speed. However, this change in conversion due to the variation of agitation speed is not significant. In general, this small deviation of conversion due to the change of the agitation speed can be attributed to the rapid dissolving rate of carbon disulfide and the rapid mass transfer of species in the liquid-phase solution. The liquid solution is homogeneous. Once the compound CS2 is
Table 1 Effects of the reaction conditions on the apparent rate constants kapp (min1); 0.20 g of KOH, 0.6747 g of C6H4(NH2)2, volume ratio of EtOH/H2O = 1/1 (100 mL), 1.43 mL/min of gas flow rate, 15 mL/100 mL of CS2/CH2Cl2, 700 rpm, 60 8C. Alkali compound kapp (103)
Blank 0.63
NH3 21.67
NaOH 23.20
KOH 23.17
Na2CO3 44.64
NaHCO3 46.43
EtOH/H2O kapp (103)
90/10 39.25
80/20 33.75
70/30 29.88
60/40 25.38
50/50 23.17
40/60 18.00
30/70 13.25
Stirring speed (rpm) kapp (103)
0 21.21
200 21.70
400 23.05
600 23.17
700 23.17
800 23.17
1000 23.17
[CS2] (mL) kapp (103)
3 10.48
6 13.21
9 15.24
12 17.26
15 23.17
20 23.18
Gas flow rate (mL/min) kapp (103)
0.98 26.43
1.43 23.17
2.27 15.95
2.91 12.98
3.43 10.12
[C6H4(NH2)2] (g) kapp (103)
0.200 42.20
0.400 29.15
0.675 23.17
0.800 17.68
1.000 14.02
Temperature (8C) kapp (103)
50 2.56
55 4.15
60 10.83
65 13.30
– – 1.200 10.12
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Fig. 2. Effect of the amount of KOH on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C, no KOH added for blank run.
589
Fig. 4. Effect of the amount of the concentration of CS2 on the conversion of ophenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/ CH2Cl2 = y mL/100 mL, 700 rpm, 60 8C.
dissolved in the organic solution, the mass transfer resistance of the species in the homogeneous solution is small. Therefore, the resistance of the dissolving rate of carbon disulfide in the organic solvent relatively to the resistance of the reaction rate is small. This confirms the argument for fast dissolving and mass transfer of CS2 in EtOH/H2O solution. The dependence of the apparent rate constant (kapp) on the agitation speed is also depicted in Table 1. As expected, the deviation in the kapp-value due to the variation of agitation speed from 0 to 1000 rpm is also small. (d) Effect of the concentration of carbon disulfide
reacts with o-phenylene diamine to produce 2-mercaptobenzimidazole in the homogeneous organic solution. Therefore, a high concentration of CS2 in the organic-aqueous solution is obtained when a higher concentration of CS2/CH2Cl2 in a gasphase is introduced to the reaction solution. This is why the conversion of o-phenylene diamine is increased using a larger concentration of CS2/CH2Cl2. The effect of the concentration of CS2 on the apparent rate constant kapp is also shown in Table 1. As expected, the conversion is increased with the increase in the concentration of carbon disulfide. (e) Effect of the gas flow rate
In this work, CH2Cl2 (inert) is used as the carrier to bring the gas-phase carbon disulfide to the liquid-phase reaction solution. It also acts as the diluter for carbon disulfide. In principle, CH2Cl2 and CS2 can be recovered from the semicontinuous reactor by using a condenser. The concentration of carbon disulfide is first set by mixing the appropriate amount ratio of CS2 and CH2Cl2 of liquid phases. Fig. 4 shows the effect of the concentration of CS2 on the conversion of o-phenylene diamine. As expected, the conversion is increased with the increase in the concentration of CS2. In general, carbon disulfide is first dissolved in EtOH/H2O solution and then
As stated, the gas flow rate is controlled by the feed pump. The effect of the gas flow rate on CS2/CH2Cl2 on the conversion of o-phenylene diamine is shown in Fig. 5 which indicates that the conversion is decreased with the increase in the flow rate. A larger flow rate promotes the amount of carbon disulfide escape to the vapor-phase from the liquid solution. Thus, the dissolved CS2 in the organic-aqueous solution is small at a larger flow rate of CS2/CH2Cl2. Hence the conversion of ophenylene diamine (or the reaction rate) is enhanced by a low flow rate of carbon disulfide. The dependence of the apparent rate constant (kapp) on the gas flow rate is shown in Table 1.
Fig. 3. Effect of the agitation speed on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 60 8C.
Fig. 5. Effect of the amount of the gas flow rate on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = y mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
590
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
Fig. 6. Effect of the amount of the o-phenylene diamine on the conversion of ophenylene diamine; 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
Fig. 8. Effect of the volume ratio of EtOH/H2O on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/ 100 mL, 700 rpm, 60 8C.
Naturally, the apparent rate constant kapp is decreased with the increase in the flow rate. (f) Effect of the amount of o-phenylene diamine
diamine is shown in Fig. 7. The order of the reactivity of the reaction for using these organic solvents is: DMSO (46.5) > DMF (36.7)–MeCN (35.94) > EtOH (24.55). Using the organic solvent of a higher dielectric constant increases the conversion of o-phenylene diamine. (h) Effect of the volume ratio of EtOH/H2O
The effect of the amount of o-phenylene diamine on the conversion of o-phenylene diamine is shown in Fig. 6. The conversion is decreased with the increase in the concentration of o-phenylene diamine. This result is similar to that obtained from the liquid-phase reaction catalyzed by quaternary ammonium salts (Wang and Liu, 1995, 1996a,b, 1997, 1998a,b, 2005). The effect of the concentration of o-phenylene diamine on the apparent rate constant (kapp) is also shown in Table 1, which indicates that kapp-value is decreased with the increase in the concentration of o-phenylene diamine. (g) Effect of the organic solvent
The effect of the volume ratio of EtOH/H2O on the conversion of o-phenylene diamine is shown in Fig. 8. The conversion is increased with the increase in the volume ratio of EtOH/H2O. The reason is that CS2 is favorite to dissolve in a more hydrophobic organic substance, i.e. more amount of EtOH. (i) Effect of the temperature
The liquid-phase solution is formed by mixing organic solvent and water. In this work, water is added to dissolve potassium hydroxide. Therefore, both protic solvent and aprotic solvent can be served as the organic reagent. The effect of the organic solvent on the conversion of o-phenylene
As stated in the previous section, the boiling point of carbon disulfide is 46.2 8C. Thus, it is difficult to carry out the reaction higher than 46.2 8C in the liquid–liquid two-phase reaction. For synthesizing MBI from the reaction of carbon disulfide and ophenylene diamine. Furthermore, a semi-continuous reactor from which carbon disulfide in a gas-phase is introduced to the liquid-phase solution (o-phenylene diamine), is employed in order to promote the reaction in this work. By doing such an
Fig. 7. Effect of the organic solvents on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm, 60 8C.
Fig. 9. Effect of the temperature on the conversion of o-phenylene diamine; 0.6747 g of C6H4(NH2)2, 0.20 g of KOH, 100 mL of solution (volume ratio = 1/1 of EtOH and water), flow rate = 1.43 mL/min, CS2/CH2Cl2 = 15 mL/100 mL, 700 rpm.
M.-L. Wang, Y.-C. Liu / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 586–591
591
arrangement, solution temperature higher than the boiling point of carbon disulfide is feasible.
Acknowledgement
The effect of the temperature on the conversion of ophenylene diamine is shown in Fig. 9. As expected, the conversion is increased with increased in the temperature. The reaction also follows a pseudo-first-order rate law. The activation energy for the reaction of o-phenylene diamine and carbon disulfide in the presence of potassium hydroxide in a gas–liquid two-phase medium is 29.2 kcal/mol according to an Arrhenius plot. The apparent rate constant (kapp), which is shown in Table 1, is increased with the increase in temperature.
The authors would like to thank the National Science Council of the ROC for the financial support for the study under contract no. NSC 92-0402-E-007-004.
5. Conclusion In this work, the reaction of o-phenylene diamine and carbon disulfide in the presence of KOH in the synthesis of 2mercaptobenzimidazole is successfully carried out in a semicontinuous reactor. Without using quaternary ammonium salt as the phase-transfer catalyst, the reaction is also greatly enhanced in the presence of alkali compounds, such as NaHCO3, Na2CO3, KOH, NaOH and NH3. A gas stream of CS2/CH2Cl2 mixture is continuously fed to the reactor for the reaction with o-phenylene diamine in the liquid-phase solution. By feeding the gas-phase carbon disulfide, the reaction can be carried out at a higher temperature to enhance the reaction. The present process provides the feasible conditions to carry out the reactions at higher temperature. The experimental results show that the reaction follows the pseudo-first-order rate law from which the apparent rate constants (kapp) at various reaction conditions were obtained. The dissolving rate of CS2 in the organic solvent and the mass transfer rate in the organic-phase solution are both larger. A high reaction rate (or conversion) is obtained using an organic solvent of higher dielectric constant. Therefore, the effect of the agitation speed on the conversion of o-phenylene diamine is insignificant. The conversion of ophenylene diamine is increased with the increase in the concentration of potassium hydroxide, temperature and the concentration of carbon disulfide. However, the conversion is decreased with the increase in the flow rate of CS2/CH2Cl2 and the concentration of o-phenylene diamine.
References Alper, E., Mass Transfer with Chemical Reaction in Multiphase, I & II, Martinus Nijhoff, New York, USA (1983). Blocher, S. H., A. Schultze, and H. W. Leverkusen, ‘‘Process for the Production of 2Mercaptobenzimidazole,’’ U.S. Patent, 3, 235, 559 (1966). Broada, W. and E. V. Dehmlow, ‘‘Thioharnstoffe Durch Drikom Ponentenreaktionen von Amien,’’ Liebigs Ann. Chem., 1837 (1983). Fournier, E., ‘‘Therapeutical Composition Containing 2-Mercaptobenzimidazole,’’ U.S. Patent, 3, 558, 775 (1971). Goodman, A., ‘‘2-Mercaptobenzimidazole Preparation,’’ U.S. Patent 3, 895, 025 (1975). Matsuo, H. and T. Ishii, ‘‘Mass Transfer with mth Order Chemical Reaction for MultiParticle Systems,’’ Chem. Eng. Sci., 37, 229 (1982). Perrys, R. H. and D. Green, Perry’s Chemical Engineers Handbook, 4th Ed., McGraw Hill, New York, USA (1988). Sasson, Y. and R. Neumann, Handbook of Phase Transfer Catalysis , Blackie Academic & Professional Chapman & Hall, Inc., New York, USA (1996). Starks, C. M., C. L. Liotta, and M. E. Halpern, Phase Transfer Catalysis, Fundamentals, Applications, and Industrial Perspectives , Chapman & Hall, Inc., New York, USA (1994). Van Allan, J. A. and B. D. Deacon, ‘‘2-Mercaptobenzimidazole,’’ Org. Synth., 569 (1963). Wang, M. L. and B. L. Liu, ‘‘Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Tertiary Amines in a Homogeneous Solution,’’ Ind. Eng. Chem. Res., 34 (11), 3688 (1995). Wang, M. L. and B. L. Liu, ‘‘Catalyzed Reaction of Carbon Disulfide and o-Phenylene Diamine by Tertiary Amine,’’ J. Mol. Catal. A: Chem., 105, 49 (1996a). Wang, M. L. and B. L. Liu, ‘‘Homogeneous Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Tertiary amines,’’ Int. J. Chem. Kinet., 28, 885 (1996b). Wang, M. L. and B. L. Liu, ‘‘Homogeneous Reaction of Carbon Disulfide and o-Phenylene Diamine in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Eng., 20 (4), 413 (1997). Wang, M. L. and B. L. Liu, ‘‘Catalyzed Reaction of Carbon Disulfide and o-Phenylene Diamine by Quaternary Ammonium Hydroxide,’’ Chem. Eng. Commun., 165, 177 (1998a). Wang, M. L. and B. L. Liu, ‘‘Reaction of Carbon Disulfide and o-Phenylene Diamine by Tertiary Amine in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Eng., 21 (3), 317 (1998b). Wang, M. L. and B. L. Liu, ‘‘Two-Phase Reaction of Carbon Disulfide and o-Phenylene Diamine Catalyzed by Quaternary Ammonium Salts in the Presence of Potassium Hydroxide,’’ J. Chin. Inst. Chem. Engrs., 36 (5), 487 (2005). Wang, M. L. and B. L. Liu, ‘‘Semi-Continuous Gas–Liquid Phase-Transfer Catalyzed Reaction of o-Phenylene Diamine and Carbon Disulfide by Tetrabutylammonium Hydroxide,’’ J. Chin. Inst. Chem. Engrs., 37 (6), 557 (2006). Yoshinori, T., N. Hajime, K. Chizuko, M. Tshyuk, and A. Akira, ‘‘A New Route of 1,2Dithiole-3-thiones by the Reaction of Enaminones with Carbon Disulfide,’’ Heterocycles, 31, 1 (1990).