ARTICLE pubs.acs.org/IECR
Synthesis of Trimethylchlorosilane by [BMIM]Cl-nAlCl3 Ionic Liquids-Catalyzed Redistribution between Methyltrichlorosilane and Low-Boiling Products from the Direct Synthesis of Methylchlorosilanes Yiqian Jiang, Weiguang Chen, Yanjun Liu, Hengbo Yin,* Yutang Shen, Aili Wang, Longbao Yu, and Tingshun Jiang Faculty of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China ABSTRACT: Synthesis of trimethylchlorosilane by a catalytic redistribution reaction between methyltrichlorosilane and lowboiling products from the direct synthesis of methylchlorosilanes on 1-butyl-3-methylimidazolium chloroaluminate ionic liquids was investigated. The effects of experimental parameters, such as composition and loading of the ionic liquid catalysts, composition of reactants, and reaction temperature and time, on the redistribution reaction were studied in detail. Among the ionic liquid catalysts, [BMIM]Cl-3AlCl3 showed high catalytic activity in the redistribution reaction toward the formation of trimethylchlorosilane with a maximum yield of 72.5% at a lower reaction temperature of 60 °C. The conversions of the main reactants, such as methyltrichlorosilane and tetramethylsilane, were ca. 100%. The ionic liquid catalyst was easily separated from the reaction mixtures by the facile decantation method and exhibited good recycling performance in the redistribution reaction. In addition, the possible reaction route was also discussed.
1. INTRODUCTION Organochlorosilanes, especially trimethylchlorosilane and dimethyldichlorosilane, are the most important intermediates extensively used in the organosilicone industry. The direct synthesis of methylchlorosilanes via the reaction of silicon and methyl chloride in the presence of copper as a catalyst, discovered by Rochow and M€uller, is a dominant industrial process.1-4 However, in addition to the desired dimethyldichlorosilane and trimethylchlorosilane, a substantial amount of byproduct is unavoidably produced in the direct synthesis process. The weight percentage of byproduct comprising methyltrichlorosilane, low-boiling products, and high-boiling products is ca.15-20 wt % of the crude products. For the byproduct, methyltrichlorosilane is ca. 5-15 wt % of the crude products. Methyltrichlorosilane is rarely utilized for the preparation of silicones. At present, methyltrichlorosilane is mainly used to prepare pyrogenic silica. However, this process is an unsatisfactory solution because valuable methyl groups are turned into CO2 and water. The low-boiling products account for ca. 4-5 wt % of the crude products. The low-boiling products are mainly composed of tetramethylsilane (>50 wt %), methylhydrodichlorosilane, dimethylhydrochlorosilane, hydrotrichlorosilane, alkanes, and alkenes. Tetramethylsilane is useless in silicone industry because it has no functional groups on the silicon. The valuable methyl groups present in the low-boiling products have not been effectively used until now. Dimethyldichlorosilane is produced with a weight percentage more than 80% of the crude products by the direct synthesis process. However, trimethylchlorosilane is produced with a weight percentage of less than 1% of the crude products. Although it is possible to alter the ratios of trimethylchlorosilane and dimethyldichlorosilane in the direct process by changing the process r 2011 American Chemical Society
parameters, manufacturers are reluctant to risk upsetting a process on which considerable resource has been expended to optimize for production of dimethyldichlorosilane.5 It was reported that trimethylchlorosilane and dimethyldichlorosilane could be synthesized by the redistribution of the chloride and methyl groups among methyl- and chloro-enriched silanes by using AlCl3,3,6 Al2O3,5,7 and NaAlCl48 as catalysts. For example, dimethyldichlorosilane was synthesized by the catalytic redistribution reaction between methyltrichlorosilane and lowand high-boiling products enriched with alkyl groups on AlCl3 catalyst at a reaction temperature of ca. 250 °C and a pressure of 10 MPa.3 When the low-boiling products containing tetramethylsilane and dimethylhydrochlorosilane, etc., were saturated with HCl, AlCl3 catalyzed the formation of trimethylchlorosilane with a yield of 98% relative to tetramethylsilane and dimethyldichlorosilane with a yield of 96.5% relative to dimethylhydrochlorosilane at a reaction temperature of ca. 40 °C.9 Trimethylchlorosilane and dimethylhydrochlorosilane were also catalytically synthesized by the redistribution of low-boiling products on active alumina at a reaction temperature greater than 150 °C.5 When the redistribution reaction between dimethyldichlorosilane and low-boiling products was catalyzed by active alumina at 300-400 °C, trimethylchlorosilane concentration reached 67.2-70% .7 Among the mentioned catalysts, AlCl3 catalyst shows good catalytic activity in the redistribution reaction between alkyl- and chloride-enriched methylchlorosilanes. However, AlCl3 catalyst Received: November 2, 2010 Accepted: December 19, 2010 Revised: December 8, 2010 Published: January 6, 2011 1893
dx.doi.org/10.1021/ie1022207 | Ind. Eng. Chem. Res. 2011, 50, 1893–1898
Industrial & Engineering Chemistry Research
ARTICLE
Table 1. Composition of the Low-Boiling Products components
formula
wt %/%
tetramethylsilane
(CH3)4Si
50.06
hydrotrichlorosilane
HSiCl3
22.02
dimethylhydrochlorosilane
(CH3)2SiHCl
4.48
methylhydrodichlorosilane
CH3SiHCl2
13.53
others
alkane, alkene, etc.
9.91
suffers the recycling problem since it can be easily hydrolyzed in air, giving the formation of corrosive HCl. In addition to the recycling problem, AlCl3 catalyst also suffers the plugging problem in transport lines and distillation columns because it is easily sublimed at a high temperature. On the other hand, the use of AlCl3 catalyst involves a long reaction time problem.7 Therefore, in order to replace the AlCl3 catalyst in the redistribution reaction, it is necessary to search for an environmentally benign catalyst, which is active and recyclable under mild conditions. Recently, ionic liquids with melting points near ambient temperature or even lower have attracted increasing attention from researchers due to their outstanding properties, such as negligible vapor pressure, high thermal stability, and tunable composition.10-12 Lewis acidic ionic liquids have potential applications in catalytic reactions as possible replacement for AlCl3 catalyst and conventional molecular solvent.12-21 The catalytic activity of Lewis acidic ionic liquid catalysts can be tuned by changing their composition. In addition, Lewis acidic ionic liquid catalysts can be easily isolated from reaction mixtures and recycled. In our present paper, we report the synthesis of trimethylchlorosilane by catalytic redistribution reaction between methyltrichlorosilane and the low-boiling products from the direct synthesis of methylchlorosilanes on [BMIM]Cl-nAlCl3 ionic liquids. The effects of reaction parameters, such as reaction temperature, weight ratio of reactants, and composition and loading of the ionic liquids, on the redistribution reaction were investigated. The [BMIM]Cl-3AlCl3 ionic liquid catalysts showed high catalytic activity toward the formation of trimethylchlorosilane and good recycling performance.
Anhydrous AlCl3 was added slowly into a round-bottom flask containing the as-prepared [BMIM]Cl under stirring to prepare the ionic liquids. The reaction was carried out in a sealed glovebox under nitrogen atmosphere. The products were heated in a three-necked flask with a reflux condenser at 120 °C for 2 h under stirring and nitrogen atmosphere to ensure AlCl3 completely dissolved in the ionic liquids. The Lewis acidic ionic liquids [BMIM]Cl-nAlCl3 with different n values were prepared by changing the mole ratios of AlCl3 to [BMIM]Cl from 1.5:1, to 2:1, 2.5:1, and 3:1, respectively. 2.3. Redistribution Reaction between Methyltrichlorosilane and Low-Boiling Products. Given amounts of ionic liquids, methyltrichlorosilane, and low-boiling products were added into a 600 mL stainless steel autoclave reactor equipped with an electric stirrer, an inner temperature detector, and a coil heat exchanger. The total amount of methyltrichlorosilane and low-boiling products was 60 g. The reaction was carried out at different reaction temperatures ranging from 40 to 80 °C for different times under stirring at 500 rpm. After reaction, the reaction mixture was cooled to room temperature using cooling water and then to 15 °C in an ice-water bath. The reaction mixture was separated spontaneously into two layers. The under layer was the ionic liquid catalysts, and the upper layer was the reaction mixture of methylchlorosilanes. The ionic liquid catalyst and reaction mixture were separated by the decantation method. All collected reaction products were analyzed on a gas chromatograph, equipped with a flame ionization detector (FID) and an OV-1701 capillary column (0.25 mm 30 m). The conversions of methyltrichlorosilane, tetramethylsilane, dimethylhydrochlorosilane, and methylhydrodichlorosilane and yields of trimethylchlorosilane, dimethyldichlorosilane, and hydrotrichlorosilane were calculated according to the following equations
2. EXPERIMENTAL SECTION
½M1in - ½M1out 100% ½M1in
ð1Þ
conversionM4 ¼
½M4in - ½M4out 100% ½M4in
ð2Þ
½M2Hin - ½M2Hout 100% ½M2Hin
ð3Þ
½MHin - ½MHout 100% ½MHin
ð4Þ
conversionM2H ¼
2.1. Chemicals. Methyltrichlorosilane (99%) and the low-boiling
products produced in the direct synthesis of methylchlorosilanes were kindly supplied by Jiangsu Hongda New Materials Co. Ltd., Zhenjiang, China. The composition of the low-boiling products is listed in Table 1. N-Methylimidazolium (99%) was purchased from Yancheng Medical Chemical Factory, China. Anhydrous AlCl3 and n-chlorobutane were reagent grade and purchased from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. All chemicals were used as received without further purification. 2.2. Preparation of 1-Butyl-3-methylimidazolium Chloride ([BMIM]Cl) and [BMIM]Cl-nAlCl3 Ionic Liquids. [BMIM]Cl was prepared according to the method reported by Wilkes et al.22 A 1.5 mol amount of N-methylimidazolium and 1.7 mol of n-chlorobutane were added into a 500 mL three-necked flask equipped with a reflux condenser and a magnetic stirrer under stirring. A nitrogen stream was introduced into the reactor. The reaction was carried out under reflux at 80 °C for 48 h. The resultant mixture was cooled to 0 °C, and the product, [BMIM]Cl, turned to a solid. The unreacted n-chlorobutane was removed by decantation, and [BMIM]Cl was washed with ethyl acetate twice. The [BMIM]Cl was dried by a rotary evaporator at 80 °C and in a vacuum oven at 70 °C for 24 h.
conversionM1 ¼
conversionMH ¼
yieldM2 ¼
½M2out - ½M2in ½M1in þ ½M2in þ ½M3in þ ½M4in þ ½HSiCl3 in þ ½MHin þ ½M2Hin 100%
ð5Þ
yieldM3 ¼
½M3out - ½M3in ½M1in þ ½M2in þ ½M3in þ ½M4in þ ½HSiCl3 in þ ½MHin þ ½M2Hin 100%
ð6Þ
yieldHSiCl3 ¼
½HSiCl3 out - ½HSiCl3 in ½M1in þ ½M2in þ ½M3in þ ½M4in þ ½HSiCl3 in þ ½MHin þ ½M2Hin 100%
1894
ð7Þ
dx.doi.org/10.1021/ie1022207 |Ind. Eng. Chem. Res. 2011, 50, 1893–1898
Industrial & Engineering Chemistry Research
ARTICLE
Figure 1. Effect of the weight ratios of low-boiling products (LBP) to methyltrichlorosilane (M1) on the conversion and yield of methylchlorosilanes catalyzed by [BMIM]Cl-3AlCl3 ionic liquids at a reaction temperature of 60 °C for 240 min. The total amount of low-boiling products and methyltrichlorosilane was 60 g. [BMIM]Cl-3AlCl3 was 50 wt % of the reactants: (b) conversion of methyltrichlorosilane; (() conversion of tetramethylsilane; (0) conversion of dimethylhydrochlorosilane; (Δ) conversion of methylhydrodichlorosilane; (2) yield of trimethylchlorosilane; (9) yield of dimethyldichlorosilane; (O) yield of hydrotrichlorosilane.
where M1, M2, M3, M4, MH, M2H, and HSiCl3 represent methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, tetramethylsilane, methylhydrodichlorosilane, dimethylhydrochlorosilane, and hydrotrichlorosilane, respectively.
3. RESULTS AND DISCUSSION 3.1. Effect of Weight Ratios of Low-Boiling Products to Methyltrichlorosilane. The effect of the weight ratios of low-
boiling products to methyltrichlorosilane on the redistribution reaction catalyzed by [BMIM]Cl-3AlCl3 ionic liquids is illustrated in Figure 1. The experimental errors were less than 5% for all experiments, which were repeated at least two times. From Figure 1, it was found that conversion of methyltrichlorosilane was significantly increased from 48.0% to 100% when the weight ratio of low-boiling products to methyltrichlorosilane was increased from 1:1 to 2:1. The conversion was kept at 100% with further increasing the weight ratio to 4:1. The conversion of tetramethylsilane was ca. 100% when the weight ratios of low-boiling products to methyltrichlorosilane ranged from 1:1 to 4:1. The yield of trimethylchlorosilane was increased from 39.8% to 72.5% with increasing weight ratios of low-boiling products to methyltrichlorosilane from 1:1 to 4:1, indicating that formation of trimethylchlorosilane was through the redistribution reaction between tetramethylsilane present in the lowboiling products and methyltrichlorosilane. The yield of dimethyldichlorosilane was increased from 18.6% to 24.1% with increasing weight ratio of low-boiling products to methyltrichlorosilane from 1:1 to 2:1. Further increasing the weight ratio to 4:1 caused the yield of dimethyldichlorosilane to decrease to 2.2%. First, the redistribution reaction between tetramethylsilane and methyltrichlorosilane caused formation of both dimethyldichlorosilane and trimethylchlorosilane. Then the resultant dimethyldichlorosilane rapidly reacted with tetramethylsilane to produce trimethylchlorosilane. The conversions of methylhydrodichlorosilane and dimethylhydrochlorosilane were ca. 100%, and the yield of hydrotrichlorosilane was ca. 7% when the weight ratios of low-boiling products to methyltrichlrosilane varied from 1:1 to 2:1 and 4:1, respectively. The formation of hydrotrichlorosilane was probably due
Figure 2. Effect of the mole ratios of AlCl3 to [BMIM]Cl in the ionic liquid catalysts on the redistribution reaction between methyltrichlorosilane and low-boiling products at different reaction temperatures for 240 min. The total amount of low-boiling products and methyltrichlorosilane was 60 g with a weight ratio of 4:1. [BMIM]Cl-nAlCl3 was 50 wt % of the reactants: (b) conversion of methyltrichlorosilane; (() conversion of tetramethylsilane; (0) conversion of dimethylhydrochlorosilane; (Δ) conversion of methylhydrodichlorosilane; (2) yield of trimethylchlorosilane; (9) yield of dimethyldichlorosilane; (O) yield of hydrotrichlorosilane.
to the redistribution reactions between methyltrichlorosilane and methylhydrodichlorosilane or dimethylhydrochlorosilane because methylhydrodichlorosilane and dimethylhydrochlorosilane were very active compounds to supply methyl groups in the redistribution reactions catalyzed by AlCl3.9 3.2. Effects of Mole Ratios of AlCl3 to [BMIM]Cl and Reaction Temperature. Figure 2 shows the results of the redistribution reaction between methyltrichlorosilane and low-boiling products catalyzed by [BMIM]Cl-nAlCl3 ionic liquids with different mole ratios of AlCl3 to [BMIM]Cl at different reaction temperatures. When the reaction temperatures were 40, 60, and 80 °C, respectively, the conversions of methyltrichlorosilane were increased from 2.4% to 41.8%, 22.0% to 100%, and 21.3% to 100% with increasing the n values of [BMIM]Cl-nAlCl3 ionic liquids from 1.5 to 3. The conversions of tetramethylsilane were 1895
dx.doi.org/10.1021/ie1022207 |Ind. Eng. Chem. Res. 2011, 50, 1893–1898
Industrial & Engineering Chemistry Research
Figure 3. Effect of [BMIM]Cl-3AlCl3 loading on the redistribution reaction between methyltrichlorosilane and low-boiling products at a reaction temperature of 60 °C for 240 min. The total amount of lowboiling products and methyltricholorosilane was 60 g with a weight ratio of 4:1: (b) conversion of methyltrichlorosilane; (() conversion of tetramethylsilane; (0) conversion of dimethylhydrochlorosilane; (Δ) conversion of methylhydrodichlorosilane; (2) yield of trimethylchlorosilane; (9) yield of dimethyldichlorosilane; (O) yield of hydrotrichlorosilane.
increased from 30.1% to 62.8%, 54.0% to 97.6%, and 54.4% to 99.1%. The yields of trimethylchlorosilane were increased from 4.5% to 43.2%, 19.6% to 72.5%, and 20.7% to 71.5%. Raising the reaction temperature from 40 to 60 °C promoted the redistribution reaction between methyltrichlorosilane and tetramethylsilane, giving a high yield of trimethylchlorosilane. The yield of trimethylchlorosilane was not further increased when increasing the reaction temperature to 80 °C. The content of AlCl3 in the ionic liquid catalysts significantly affected the yield of trimethylchlorosilane. The increase in the yield of trimethylchlorosilane with increasing content of AlCl3 in the ionic liquid catalysts should be due to the increase in their Lewis acidity, which was certified by FTIR analysis.14 The yields of dimethyldichlorosilane were less than 10% under all the experimental conditions, meaning that dimethyldichlorosilane rapidly reacted with tetramethylsilane to form trimethylchlorosilane. At reaction temperatures of 40, 60, and 80 °C, the conversions of both dimethylhydrochlorosilane and methylhydrodichlorosilane were more than 86% when [BMIM]Cl-nAlCl3 ionic liquid catalysts had n values of 1.5-3. The yields of hydrotrichlorosilane were decreased from 10.7% to 0.5%, 8.0% to 4.1%, and 12.0% to 2.6%, respectively, with increasing AlCl3 content in the ionic liquid catalysts. The results revealed that the yield of hydrotrichlorosilane was decreased with an increase in the Lewis acidity of ionic liquid catalysts. 3.3. Effect of Ionic Liquid Loading. Figure 3 shows the effect of ionic liquid loading on the redistribution reaction between methyltrichlorosilane and low-boiling products. The conversion of methyltrichlorosilane increased from 8.9% to 100% with increasing ionic liquid loadings from 10% to 25% or more. The conversion of tetramethylsilane gradually increased from 76.5% to 97.6% with increasing ionic liquid loadings from 10% to 50%. The conversion of methylhydrodichlorosilane was more than 97% when the ionic liquid loadings were in a range of 10-50%. The conversion of dimethylhydrochlorosilane increased from 86.5% to 100% when the ionic liquid loadings were increased from 10% to 50%. The yield of trimethylchlorosilane increased from 34.0% to 72.5% with increasing the ionic liquid loadings from 10% to 50%. The yields of dimethyldichlorosilane and hydrotrichlorosilane were less than 4% and 8%, respectively. When increasing the ionic liquid loading, the redistribution reaction between methyltrichlorosilane and the low-boiling
ARTICLE
Figure 4. Effect of reaction time on the redistribution reaction between methyltrichlorosilane and low-boiling products catalyzed by [BMIM]Cl3AlCl3 at a reaction temperature of 60 °C. The total amount of lowboiling products and methyltricholorosilane was 60 g with a weight ratio of 4:1. [BMIM]Cl-3AlCl3 was 50 wt % of the reactants: (b) conversion of methyltrichlorosilane; (() conversion of tetramethylsilane; (0) conversion of dimethylhydrochlorosilane; (Δ) conversion of methylhydrodichlorosilane; (2) yield of trimethylchlorosilane; (9) yield of dimethyldichlorosilane; (O) yield of hydrotrichlorosilane.
Figure 5. Recycling perpormance of the [BMIM]Cl-3AlCl3 catalyst in the redistribution reaction between methyltrichlorosilane and the lowboiling products from the direct synthesis of methylchlorosilanes: (b) conversion of methyltrichlorosilane; (() conversion of tetramethylsilane; (0) conversion of dimethylhydrochlorosilane; (Δ) conversion of methylhydrodichlorosilane; (2) yield of trimethylchlorosilane; (9) yield of dimethyldichlorosilane; (O) yield of hydrotrichlorosilane.
products was improved, being beneficial to the formation of trimethylchlorosilane. Two patents disclosed the redistribution reaction of methylchlorosilanes by using active alumina as a catalyst.5,7 Trimethylchlorosilane and dimethylhydrochlorosilane were catalytically synthesized by the redistribution of low-boiling products on active alumina at a reaction temperature greater than 150 °C.5 The concentration of trimethylchlorosilane reached 67.2-70% when the redistribution reaction between dimethyldichlorosilane and low-boiling products was catalyzed by active alumina at 300-400 °C.7 As compared to those reported in the patents, when [BMIM]Cl-nAlCl3 ionic liquids were used as catalysts in the redistribution reaction between low-boiling products and methyltrichlorosilane, the reaction temperature was obviously decreased and methyltrichlorosilane was effectively converted to high-valued trimethylchlorosilane. 3.4. Effect of Reaction Time. Figure 4 shows the effect of the reaction time on the redistribution reaction between methyltrichlorosilane and low-boiling products. It was found that the conversions of methyltrichlorosilane, methylhydrodichlorosilane, and dimethylhydrochlorosilane were ca. 100% and the conversion of tetramethylsilane was more than 97% when the 1896
dx.doi.org/10.1021/ie1022207 |Ind. Eng. Chem. Res. 2011, 50, 1893–1898
Industrial & Engineering Chemistry Research
ARTICLE
Scheme 1. Possible Redistribution Reaction Routes Catalyzed by Ionic Liquids
reaction time was in a range of 120-480 min. The yield of trimethylchlorosilane was slightly increased from 72.0% to 72.5% and then decreased to 68.5% with prolonged the reaction time from 120 to 240 and 480 min. The yields of dimethyldichlorosilane and hydrotrichlorosilane were less than 6.0%. The experimental results showed that the optimum yield of trimethylchlorosilane was achieved when the redistribution reaction was carried out for 240 min. The equilibrium yield of trimethylchlorosilane was calculated by assuming that all the methyl groups were used to form trimethylchlorosilane. The equilibrium yield is 83.2%. The experimental result was lower than the calculated one. It can be explained that disilanes were probably formed because a trace amount of unidentified products with a longer residence time was also detected by GC analysis. 3.5. Recycling of the Ionic Liquid Catalyst. In order to investigate the recycling performance of the [BMIM]Cl-3AlCl3 ionic liquid catalyst, the recycle experiment was conducted. The total amount of methyltrichlorosilane and low-boiling products was 60 g with a weight ratio of low-boiling products to methyltrichlorosilane of 4:1. [BMIM]Cl-3AlCl3 ionic liquid was 50% of the reactants. The reaction was carried out at 60 °C for 240 min. After reaction, the reaction mixture and the ionic liquid catalyst were separated by the decantation method. The recovered ionic liquid catalyst was reused in the redistribution reaction. The recycling performance of the ionic liquid catalyst is shown in Figure 5. The conversions of methyltrichlorosilane and tetramethylsilane were slightly decreased from 100% to 94.0% and 97.6% to 85.2%, respectively, after the ionic liquid catalyst was reused four times. At the same time, the yield of trimethylchlorosilane was slightly decreased from 72.5% to 63.4%. We found that during the recovering process, the weight of the ionic liquid catalyst was reduced ca. 10% after being reused four times, probably due to the fact that ionic liquid was dissolved in the reaction mixture. When the catalyst was increased to the original amount by adding fresh ionic liquid and reused in the redistribution reaction, the catalytic performance was recovered. The results showed that [BMIM]Cl-3AlCl3 ionic liquid had good recycling performance in the redistribution reaction. 3.6. Possible Reaction Route. According to our present experimental results, the possible main reaction routes in the redistribution reaction catalyzed by ionic liquids were illustrated in Scheme 1. Methyltrichlorosilane molecules reacted with ionic liquids to form dechlorinated silane cations and chlorinated ionic liquid anions. The chlorine anion from methyltrichlorosilane was probably harbored by chloroaluminate anion, [Al2Cl7]-, because a chloroaluminate anion can coordinate with a chlorine anion to form two [AlCl4]- anions.19 The dechlorinated silane cations
reacted with tetramethylsilane molecules to form dimethyldichlorosilane molecules and trimethylsilane cations. Then the resultant trimethylsilane cations reacted with the chlorinated ionic liquid anions to form trimethylchlorosilane, and ionic liquids were recovered. Through similar processes as mentioned above, the resultant dimethyldichlorosilane reacted with tetramethylsilane to form trimethylchlorosilane. The methylhydrochlorosilanes supplied methyl groups in the redistribution reaction finally to form hydrotrichlorosilane.
4. CONCLUSIONS [BMIM]Cl-nAlCl3 ionic liquids showed good catalytic activity in the redistribution reaction between methyltrichlorosilane and the low-boiling products from the direct synthesis of methylchlorosilanes. The redistribution reaction was effectively catalyzed by [BMIM]Cl-nAlCl3 ionic liquids at lower reaction temperatures, giving a high yield of high-valued trimethylchlorosilane. The catalytic activity increased with the increase in the Lewis acidity of the ionic liquids. When [BMIM]Cl-3AlCl3 ionic liquid was used as the catalyst, the yield of trimethylchlorosilane reached 72.5% with conversions of methyltrichlorosilane and tetramethylsilane of ca. 100%, respectively, at a mild reaction temperature of 60 °C. The [BMIM]Cl-3AlCl3 ionic liquid catalyst could be easily separated from the reaction mixture by the facile decantation method and showed good recycling performance in the redistribution reaction. ’ AUTHOR INFORMATION Corresponding Author
*Tel.: þ86-511-88787591. Fax: þ86-511-88791800. E-mail: yin@ ujs.edu.cn.
’ ACKNOWLEDGMENT The work was financially supported by funds from Jiangsu Hongda New Materials Co. Ltd. and Zhenjiang Science and Technology Bureau (2006006). ’ REFERENCES (1) Rochow, E. G. The direct synthesis of organosilicon compounds. J. Am. Chem. Soc. 1945, 67, 963–965. (2) Acker, J.; Bohmhammel, K. Thermodynamic assessment of the copper catalyzed direct synthesis of methylchlorosilanes. J. Organomet. Chem. 2008, 693, 2483–2493. (3) Feldner, K.; Grape, W. Process for the preparation of dimethyldichlorosilane. U.S. Patent 4,552,973, 1985. (4) Lewis, L. N.; Ward, W. J. The use of a fixed-bed reactor to evaluate the interactions of catalysts and promoters in the methyl 1897
dx.doi.org/10.1021/ie1022207 |Ind. Eng. Chem. Res. 2011, 50, 1893–1898
Industrial & Engineering Chemistry Research
ARTICLE
chlorosilane reaction and to determine the effect of Cu in the form of the eta phase on this reaction. Ind. Eng. Chem. Res. 2002, 41, 397–402. (5) Marko, O. W. Method for redistribution and purification of methylsilanes. U.S. Patent 5,493,043, 1996. (6) McEntee, H. R. Preparation of organochlorosilanes. U.S. Patent 2,786,861, 1957. (7) Lewis, K. M.; Chang, C. F. Redistribution of organohalosilanes utilizing heat treated crystalline alumina catalysts. U.S. Patent 4,889,838, 1989. (8) Bluestein, B. A. Redistribution of organosilanes. U.S. Patent 2,717,257, 1955. (9) Finko, U.; Moretto, H. H. Conversion of low-boiling constituents from alkyl-chlorosilane synthesis. U.S. Patent 4,297,500, 1981. (10) Li, Z.; Jia, Z.; Luan, Y.; Mu, T. Ionic liquids for synthesis of inorganic nanomaterials. Curr. Opin. Solid State Mater. Sci. 2008, 12, 1–8. (11) Duan, Z.; Gu, Y.; Zhang, J.; Zhu, L.; Deng, Y. Protic pyridinium ionic liquids: Synthesis, acidity determination and their performances for acid catalysis. J. Mol. Catal. A: Chem. 2006, 250, 163–168. (12) Olivier-Bourbigou, H.; Magna, L. Ionic liquids: perspectives for organic and catalytic reactions. J. Mol. Catal. A: Chem. 2002, 182-183, 419–437. (13) Angueira, E. J.; White, M. G. Arene carbonylation in acidic, chloroaluminate ionic liquids. J. Mol. Catal. A: Chem. 2005, 227, 51–58. (14) Yang, Y. L.; Kou, Y. Determination of the Lewis acidity of ionic liquids by means of an IR spectroscopic probe. Chem. Commun. 2004, 40, 226–227. (15) Li, C.; Liu, W.; Zhao, Z. Efficient synthesis of benzophenone derivatives in Lewis acid ionic liquids. Catal. Commun. 2007, 8, 1834– 1837. (16) Yin, D.; Li, C.; Tao, L.; Yu, N.; Hua, S.; Yin, D. Synthesis of diphenylmethane derivatives in Lewis acidic ionic liquids. J. Mol. Catal. A: Chem. 2006, 245, 260–265. (17) Angueira, E. J.; White, M. G. Super acidic ionic liquids for arene carbonylation derived from dialkylimidazolium chlorides and MCl3 (M = Al, Ga, or In). J. Mol. Catal. A: Chem. 2007, 277, 164–170. (18) Liu, S.; Xie, C.; Yu, S.; Liu, F. Polymerization of R-pinene using Lewis acidic ionic liquid as catalyst. Catal. Commun. 2009, 10, 986–988. (19) Welton, T. Ionic liquids in catalysis. Coord. Chem. Rev. 2004, 248, 2459–2477. (20) Yuan, X.; Chen, M.; Dai, Q.; Cheng, X. Friedel-Crafts acylation of anthracene with oxalyl chloride catalyzed by ionic liquid of [bmim]Cl/AlCl3. Chem. Eng. J. 2009, 146, 266–269. (21) Chen, W.; Yin, H.; Zhang, Y.; Lu, Z.; Wang, A.; Shen, Y.; Jiang, T.; Yu, L. Acylation of salicylamide to 5-acetylsalicylamide using ionic liquids as dual catalyst and solvent. J. Ind. Eng. Chem. 2010, 16, 800–804. (22) Wilkes, J. S.; Levisky, J. A.; Wilson, R. A.; Hussey, C. L. Dialkylimidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy, and synthesis. Inorg. Chem. 1982, 21, 1263–1264.
1898
dx.doi.org/10.1021/ie1022207 |Ind. Eng. Chem. Res. 2011, 50, 1893–1898
