Electrochemical Synthesis of Dichlorodiphenylsilane

Abstract

This invention belongs to the field of electrochemical synthesis technology, specifically relating to a method for the electrochemical synthesis of dichlorodiphenylsilane using benzene and silicon tetrachloride as raw materials. The method involves using a diaphragm-free electrolytic cell, adding an electrolyte, benzene, and silicon tetrachloride to the cell to form a reaction system. Under inert gas protection and electrolytic conditions, dichlorodiphenylsilane is generated. The electrolyte consists of acetonitrile as a solvent, a supporting electrolyte, and a buffer solution. This invention eliminates the need for transition metal catalysts, high temperature and high pressure conditions, oxidants, or reductants; it directly uses electrons as the oxidant, making it environmentally friendly. The reaction apparatus is simple and easy to operate, and the yield can be consistently maintained at approximately 70%.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical synthesis technology, specifically relating to a method for electrochemically synthesizing dichlorodiphenylsilane using benzene and silicon tetrachloride as raw materials. Background Technology

[0002] Electrochemical organic synthesis, as a green and efficient synthetic strategy, has received increasing attention in the field of green chemistry. In recent years, electrochemical dehydrogenation cross-coupling reactions and free radical cascade reactions have been developed, enabling the formation of various chemical bonds such as C-C, C-S, C-Cl, and C-Si bonds through electrochemical synthesis. Dichlorodiphenylsilane is a widely used intermediate in silicon-based fine chemical products, an important precursor for the preparation of silane coupling agents, and a monomer for silicon-containing organic polymers. Its applications cover multiple fields, including polymers, catalysts, lubricants, surfactants, and resins.

[0003] The common methods for synthesizing dichlorodiphenylsilane are as follows:

[0004] ① Metal-catalyzed direct synthesis method: Chlorobenzene is reacted with a silicon-copper catalyst. The reaction temperature is generally between 400 and 600°C. The amount of copper catalyst is generally 30% to 50%. Alternatively, silicon-silver catalyst can be used (silicon powder:silver powder = 9:1). The reaction can proceed well at 400°C. However, the reaction products contain 10% phenyltrichlorosilane and 24% diphenyldichlorosilane, and toxic dichlorobiphenyl and biphenyl will be generated.

[0005] ② Grignard reagent method: Chlorobenzene is used as a raw material to generate phenyl Grignard reagent (phenyl magnesium chloride) under the catalysis of lithium salt (lithium chloride or lithium fluoride) or aluminum trichloride. Two equivalents of phenyl magnesium chloride are added to a 0.9 equivalent of silicon tetrachloride solution. Diphenyl dichlorosilane is the main reaction product with a yield as high as 77%. The yield of dichlorodiphenylsilane decreases to 17% when the ratio of phenyl magnesium chloride to silicon tetrachloride reaches 2:2.2, and the yield of the byproduct phenyl trichlorosilane is 47%. The yield can fluctuate greatly.

[0006] ③ A method involves reacting bromobenzene with n-butyllithium in diethyl ether at -78°C to produce n-butylbenzene, which is then reacted sequentially with 0.5 equivalents of tetrachlorosilane and 2 equivalents of trichlorophenylsilane to produce dichlorodiphenylsilane. This method requires the use of the more hazardous n-butyllithium and is carried out at extremely low temperatures.

[0007] The above-mentioned existing technologies have the following problems: (1) the reaction yield is low or unstable; (2) harsh conditions such as high temperature or low temperature cause huge safety hazards and economic costs; (3) the use of heavy metal catalysts causes environmental pollution; (4) toxic polychlorinated biphenyls are generated, causing difficulties in post-processing; (5) the reaction uses extremely flammable and dangerous reagents.

[0008] Therefore, it is of great significance to develop an efficient synthesis method for dichlorodiphenylsilane that has mild reaction conditions, simple process, and is environmentally friendly. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for the electrocatalytic synthesis of dichlorodiphenylsilane using benzene and silicon tetrachloride. The method has mild reaction conditions, is environmentally friendly, has a high yield, and meets the requirements of green chemistry for organic synthesis.

[0010] To address the aforementioned technical problems, this invention provides a method for the electrochemical synthesis of dichlorodiphenylsilane (i.e., a method for the electrochemical synthesis of dichlorodiphenylsilane from silicon tetrachloride). The method utilizes a diaphragm-free electrolytic cell, adding an electrolyte, benzene, and silicon tetrachloride to the cell to form a reaction system. Under the protection of an inert gas (e.g., nitrogen), dichlorodiphenylsilane is generated under electrolytic conditions. The electrolyte consists of acetonitrile as a solvent, a supporting electrolyte, and a buffer solution.

[0011] The supporting electrolyte is any of the following: tetrabutylammonium bromide, tetrabutylammonium tetrafluorophosphate, or tetrabutylammonium tetrafluoroborate;

[0012] The added buffer solution was acetic acid;

[0013] Benzene serves as both a substrate and a solvent, and the total amount of solvent is defined as the sum of the amounts of benzene and acetonitrile used; benzene accounts for 30-50% of the total solvent volume.

[0014] The ratio of silicon tetrachloride to total solvent is 0.1–0.2 mol silicon tetrachloride / L total solvent;

[0015] The ratio of buffer solution to total solvent is 0.1–0.2 mol buffer solution / L total solvent;

[0016] The ratio of supporting electrolyte to total solvent is 0.1–0.2 mol / L supporting electrolyte;

[0017] The electrolysis temperature is room temperature (15℃~30℃), the reaction time is 4~12 hours, and the resulting reaction solution contains dichlorodiphenylsilane.

[0018] Note: The product can be obtained by performing routine post-treatment on the reaction solution. Specifically:

[0019] The solvent was removed from the obtained reaction solution by rotary evaporation, and the residue was separated by column chromatography using hexane / ethyl acetate (8-10:1, v / v) as the eluent. The collected eluent was then removed by rotary evaporation to obtain the product dichlorodiphenylsilane.

[0020] An improvement to the electrochemical synthesis method of dichlorodiphenylsilane of the present invention:

[0021] Current density is 100-200 A / m 2 .

[0022] As a further improvement to the electrochemical synthesis method of dichlorodiphenylsilane of the present invention:

[0023] The anode of the diaphragmless electrolytic cell is a graphite electrode, and the cathode is a copper sheet electrode.

[0024] As a further improvement to the electrochemical synthesis method of dichlorodiphenylsilane of the present invention:

[0025] Benzene accounts for 50% of the total solvent volume;

[0026] The ratio of silicon tetrachloride to total solvent is 0.2 mol silicon tetrachloride / L total solvent;

[0027] The ratio of buffer solution to total solvent is 0.1 mol buffer solution / L total solvent;

[0028] The ratio of supporting electrolyte to total solvent is 0.1 mol of supporting electrolyte / L of total solvent;

[0029] Current density is 100A / m 2 The electrolysis time is 8 hours.

[0030] As a further improvement to the electrochemical synthesis method of dichlorodiphenylsilane of the present invention:

[0031] Benzene accounts for 50% of the total solvent volume;

[0032] The ratio of silicon tetrachloride to total solvent is 0.2 mol silicon tetrachloride / L total solvent;

[0033] The ratio of buffer solution to total solvent is 0.15 mol buffer solution / L total solvent;

[0034] The ratio of supporting electrolyte to total solvent is 0.1 mol of supporting electrolyte / L of total solvent;

[0035] Current density is 150 A / m 2 The electrolysis time is 4 hours.

[0036] The electrode selected in this invention has good electrochemical stability and activity in the system described in this invention, and can be used repeatedly.

[0037] In this invention, the reaction substrates are benzene and silicon tetrachloride, with benzene also serving as a solvent.

[0038] The reaction described in this invention is carried out under a nitrogen protective atmosphere, which can prevent side reactions between oxygen and water vapor and the substrate, and is more conducive to improving the reaction yield.

[0039] The electrode reaction equation of this invention is as follows: Figure 1 As shown. The electrode reaction mechanism is as follows. Figure 2 As shown.

[0040] The reaction of this invention does not require a catalyst.

[0041] The present invention has the following benefits:

[0042] The reaction of this invention does not require a transition metal catalyst, high temperature and high pressure conditions, oxidant or reducing agent. It directly uses electrons as the oxidant, which is green and environmentally friendly. The reaction device is simple and easy to operate, and the yield can be stabilized at about 70% (67% to 74%). Attached Figure Description

[0043] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] Figure 1 This is the electrode reaction equation of the present invention;

[0045] Figure 2 This is the electrode reaction mechanism of the present invention.

[0046] according to Figure 2 It can be seen that silicon tetrachloride undergoes heterolytic cleavage near the anode to form chloride anions and silicon trichloride cations; the chloride anions lose electrons at the anode to generate chlorine free radicals, which then generate chlorine gas; the silicon trichloride cations electrophilically attack the benzene ring to generate trichlorophenylsilane and protons; the trichlorophenylsilane repeats the above steps to form chloride anions and dichlorophenyl cations, which then attack the benzene ring to generate dichlorodiphenylsilane. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0048] The product of this invention was confirmed to be dichlorodiphenylsilane by conventional proton and carbon NMR spectroscopy.

[0049] The diaphragmless electrolytic cell used in this invention is a conventional sealed electrolytic cell with four holes on the cell cover: an air inlet, an air outlet, and two electrode insertion holes. A graphite electrode is used as the anode, and a copper sheet electrode is used as the cathode.

[0050] Example 1:

[0051] Before the reaction begins, open the electrolytic cell cover and add the electrolyte and substrate (benzene and silicon tetrachloride) into the electrolytic cell chamber. Close the cover and insert two electrodes into the electrolytic cell through the electrode insertion holes (and install the corresponding sealing rings). Connect the inlet pipe to the inlet hole on the electrolytic cell cover, and connect one end of the outlet pipe to the outlet hole on the electrolytic cell cover and the other end to the exhaust gas treatment device. Before the reaction begins, purge the electrolytic cell chamber with nitrogen through the inlet pipe for 20 minutes (to ensure that there is no air inside the electrolytic cell chamber). Then begin the reaction by introducing nitrogen and controlling the pressure inside the electrolytic cell chamber to atmospheric pressure. Electrolyze for 8 hours at a constant current of 10 mA at room temperature, with a current density of 100 A / m³. 2 The electrolyte composition and substrate are shown in Table 1 below:

[0052] Table 1

[0053] Components Dosage molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutyltetrafluoroborate ammonium 0.001 mol (0.329 g) 0.1 mol / L Acetic acid 0.001 mol (0.06 g) 0.1 mol / L silicon tetrachloride 0.002 mol (0.34 g) 0.2 mol / L

[0054] During the reaction, the generated gas is discharged through the gas outlet to the tail gas treatment device.

[0055] After electrolysis for 8 hours, the resulting reaction solution (containing acetonitrile, benzene, dichlorodimethylsilane, acetic acid, tetrabutylammonium tetrafluoroborate, etc.) was placed on a rotary evaporator to remove the solvent. Specifically, the solvent (benzene and acetonitrile) was removed in a vacuum rotary evaporator (0.1 MPa, 40°C). The residue was separated by column chromatography on 200-mesh silica gel using hexane / ethyl acetate (10:1 volume ratio) as the eluent at a flow rate of 3 ml / min. The product from the 2nd to the 7th minute was collected, and the eluent was removed by rotary evaporation (0.1 MPa, 45°C) to obtain the product dichlorodiphenylsilane. The current efficiency was 67%, and the yield was 74%.

[0056]

[0057] Example 2: Compared with Example 1, the electrolyte composition and substrate were changed as shown in Table 2; the rest were the same as in Example 1.

[0058] Table 2:

[0059]

[0060]

[0061] The product dichlorodiphenylsilane was obtained with a current efficiency of 61% and a yield of 69%.

[0062] Example 3: Compared with Example 1, the electrolyte composition and substrate were changed as shown in Table 3 below; the rest were the same as in Example 1.

[0063] Table 3:

[0064] Components Dosage molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutyltetrafluoroborate ammonium 0.002mol 0.2 mol / L Acetic acid 0.001mol 0.1 mol / L silicon tetrachloride 0.001mol 0.1 mol / L

[0065] The product dichlorodiphenylsilane was obtained with a current efficiency of 63% and a yield of 71%.

[0066] Example 4: Compared with Example 1, the electrolyte composition and substrate were changed as shown in Table 4; the rest were the same as in Example 1.

[0067] Table 4:

[0068] Components Dosage molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutyltetrafluoroborate ammonium 0.001mol 0.1 mol / L Acetic acid 0.002mol 0.2 mol / L silicon tetrachloride 0.001mol 0.2 mol / L

[0069] The product dichlorodiphenylsilane was obtained with a current efficiency of 65% and a yield of 72%.

[0070] Example 5: Compared with Example 1, the electrolysis time at room temperature was changed from 8h to 12h; the rest is the same as Example 1.

[0071] The product dichlorodiphenylsilane was obtained with a current efficiency of 58% and a yield of 67%.

[0072] Example 6: Compared to Example 1, the constant current is changed from 10mA to 20mA; that is, the current density is 200A / m. 2 The rest is the same as in Example 1.

[0073] The product dichlorodiphenylsilane was obtained in a yield of 70%.

[0074] Example 7: Compared to Example 1, the electrolyte composition and substrate were changed as shown in Table 5 below; the electrolysis time was changed from 8 hours to 4 hours; and the constant current was changed from 10 mA to 15 mA; that is, the current density was 150 A / m 2 The rest is the same as in Example 1.

[0075] The product dichlorodiphenylsilane was obtained with a current efficiency of 66% and a yield of 74%.

[0076] Table 5

[0077] Components mass / volume molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutyltetrafluoroborate ammonium 0.329g 0.1 mol / L Acetic acid 0.09g 0.15 mol / L silicon tetrachloride 0.34g 0.2 mol / L

[0078] Example 8: Compared with Example 1, “tetrabutyltetrafluoroborate” in Table 1 is replaced with “tetrabutyltetrafluorophosphate”, and the molar amount remains unchanged, that is, the molar concentration is still 0.1 mol / L; the rest is the same as Example 1.

[0079] The product dichlorodiphenylsilane was obtained with a current efficiency of 65% and a yield of 73%.

[0080] Example 9: Compared with Example 1, "tetrabutylammonium tetrafluoroborate" in Table 1 is replaced with "tetrabutylammonium bromide", and the molar amount remains unchanged, that is, the molar concentration is still 0.1 mol / L; the rest is the same as Example 1.

[0081] The product dichlorodiphenylsilane was obtained with a current efficiency of 59% and a yield of 68%.

[0082] Comparative Example 1, relative to Example 1: The amount of "tetrabutyltetrafluoroborate ammonium" in Table 1 was changed from 0.329g to 1.645g, that is, the corresponding molar concentration was changed from 0.1mol / L to 0.5mol / L. The rest is the same as in Example 1.

[0083] The product dichlorodiphenylsilane was obtained with a current efficiency of 42% and a yield of 46%.

[0084] In Comparative Example 1, the excessive concentration of the added supporting electrolyte reduced the ion mobility in the solution, thus decreasing the current efficiency and yield.

[0085] Comparative Example 2, relative to Example 1: The use of the supporting electrolyte "tetrabutyltetrafluoroborate" in Table 1 was omitted, that is, the amount of "tetrabutyltetrafluoroborate" was 0. Everything else was the same as in Example 1.

[0086] In Comparative Example 2, due to the lack of a supporting electrolyte, the weak acid acetic acid cannot conduct electricity in the organic solvent, therefore no current flows. The product dichlorodiphenylsilane cannot be obtained.

[0087] Comparative Example 3, relative to Example 1: The amount of "tetrabutyltetrafluoroborate ammonium" in Table 1 was changed from 0.329g to 0.1645g, that is, the corresponding molar concentration was changed from 0.1mol / L to 0.05mol / L. The rest is the same as in Example 1.

[0088] The product dichlorodiphenylsilane was obtained with a current efficiency of 47% and a yield of 52%.

[0089] In Comparative Example 3, the concentration of the added supporting electrolyte was too low, which reduced the conductivity of the solution and the electrochemical reaction activity, thus reducing the current efficiency and yield.

[0090] Comparative Example 4, relative to Example 1: The use of acetic acid in Table 1 was omitted, that is, the amount of acetic acid used was 0; the rest was the same as in Example 1.

[0091] The product dichlorodiphenylsilane was obtained in a yield of 15%.

[0092] In Comparative Example 4, due to the lack of hydrogen ions, there is no coupling between the hydrogen evolution reaction and the anodic reaction.

[0093] Comparative Example 5, compared to Example 1: the concentration of acetic acid in the electrolyte was increased, that is, the concentration of acetic acid was changed from 0.1 mol / L to 0.5 mol / L; the rest was the same as in Example 1.

[0094] The product dichlorodiphenylsilane was obtained in a yield of 29%.

[0095] In Comparative Example 5, the excessively high concentration of acetic acid reduced the mobility of electrolyte ions and increased side reactions, leading to a decrease in electrochemical reactivity.

[0096] Comparative Example 6, compared to Example 1: The constant current was changed from 10mA to 50mA; that is, the current density was 500A / m. 2 The rest is the same as in Example 1.

[0097] The product dichlorodiphenylsilane was obtained with a current efficiency of 35% and a yield of 21%.

[0098] In Comparative Example 6, the excessively high electrical current led to an excessively high overpotential, causing the reaction to become too vigorous, resulting in various side reactions and a decrease in yield.

[0099] Comparative Example 7, compared to Example 1: The reaction was not carried out under a nitrogen atmosphere; the reaction inlet and outlet were connected to the atmosphere, and the reaction was conducted in air. Everything else was the same as in Example 1.

[0100] The product dichlorodiphenylsilane was obtained with a current efficiency of 48% and a yield of 41%.

[0101] In Comparative Example 7, water vapor in the air reacts with silicon tetrachloride to produce silicic acid and hydrogen chloride, resulting in a decrease in yield.

[0102] Comparative Example 8, relative to Example 1: the acetonitrile in the electrolyte was replaced with 5 ml of ethanol; the rest was the same as in Example 1.

[0103] The product dichlorodiphenylsilane was obtained with a current efficiency of 53% and a yield of 50%.

[0104] In Comparative Example 8, the electrochemical window of ethanol is not as wide as that of acetonitrile in this system, which can lead to side reactions in the electrolyte itself, thus reducing the yield.

[0105] Comparative Example 9: Compared to Example 1, the anode material was replaced with copper instead of graphite; otherwise, it was the same as Example 1.

[0106] The product dichlorodiphenylsilane was obtained with a current efficiency of 10% and a yield of 3%.

[0107] Only when graphite is used as the anode material can the required reaction at the anode be better promoted. In Comparative Example 9, if copper is used as the anode material, copper will lose its charge and become copper ions that dissolve into the electrolyte. Furthermore, the catalytic activity of copper at the anode is much lower than that of graphite, which will lead to a decrease in the reaction yield.

[0108] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for the electrochemical synthesis of dichlorodiphenylsilane, characterized in that: A diaphragmless electrolytic cell is used, with a graphite electrode as the anode and a copper sheet electrode as the cathode. An electrolyte, benzene, and silicon tetrachloride are added to the electrolytic cell to form a reaction system. Under inert gas protection and electrolysis conditions, dichlorodiphenylsilane is generated. The electrolyte consists of acetonitrile as a solvent, a supporting electrolyte, and a buffer solution; the added buffer solution is acetic acid.

2. The method for electrochemical synthesis of dichlorodiphenylsilane according to claim 1, characterized in that: The supporting electrolyte is any of the following: tetrabutylammonium bromide, tetrabutylammonium tetrafluorophosphate, or tetrabutylammonium tetrafluoroborate; Benzene serves as both a substrate and a solvent; the total solvent volume is defined as the sum of the amounts of benzene and acetonitrile used; benzene accounts for 30-50% of the total solvent volume. The ratio of silicon tetrachloride to total solvent is 0.1~0.2 mol silicon tetrachloride / L total solvent; The ratio of buffer solution to total solvent is 0.1~0.2 mol buffer solution / L total solvent; The recommended electrolyte-to-total-solvent ratio is 0.1-0.2 mol / L total solvent. The electrolysis temperature is room temperature, the reaction time is 4 to 12 hours, and the resulting reaction solution contains dichlorodiphenylsilane.

3. The method for electrochemical synthesis of dichlorodiphenylsilane according to claim 2, characterized in that: Current density is 100~200A / m 2 .

4. The method for electrochemical synthesis of dichlorodiphenylsilane according to claim 3, characterized in that: Benzene accounts for 50% of the total solvent volume; The ratio of silicon tetrachloride to total solvent is 0.2 mol silicon tetrachloride / L total solvent; The ratio of buffer solution to total solvent is 0.1 mol buffer solution / L total solvent; The ratio of supporting electrolyte to total solvent is 0.1 mol of supporting electrolyte / L of total solvent; Current density is 100A / m 2 The electrolysis time is 8 hours.

5. The method for electrochemical synthesis of dichlorodiphenylsilane according to claim 3, characterized in that: Benzene accounts for 50% of the total solvent volume; The ratio of silicon tetrachloride to total solvent is 0.2 mol silicon tetrachloride / L total solvent; The ratio of buffer solution to total solvent is 0.15 mol buffer solution / L total solvent; The ratio of supporting electrolyte to total solvent is 0.1 mol of supporting electrolyte / L of total solvent; Current density is 150A / m 2 The electrolysis time is 4 hours.

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