Dichlorodiphenyl silane electrochemical synthesis method

Abstract

The invention belongs to the technical field of electrochemical synthesis, and particularly relates to a method for electrochemical synthesis of dichlorodiphenyl silane by using benzene and silicon tetrachloride as raw materials, which comprises the following steps: using a diaphragm-free electrolytic bath, adding electrolyte, benzene and silicon tetrachloride into the electrolytic bath to form a reaction system, and generating dichlorodiphenyl silane under the protection of inert gas under the electrolysis condition, the electrolyte is composed of acetonitrile as a solvent, a supporting electrolyte and a buffer solution. The reaction does not need a transition metal catalyst, a high-temperature and high-pressure condition, an oxidizing agent or a reducing agent, electrons are directly used as the oxidizing agent, the method is green and environment-friendly, a reaction device is simple and convenient to operate, and the yield can be stabilized at about 70%.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical synthesis, and in particular relates to a method for electrochemically synthesizing dichlorodiphenylsilane using benzene and silicon tetrachloride as raw materials. Background Art

[0002] As a green and efficient synthesis strategy, electrochemical organic synthesis 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, and the formation of various chemical bonds such as CC, CS, C-Cl, and C-Si bonds can be achieved by electrochemical synthesis. Dichlorodiphenylsilane is a widely used silicon fine chemical intermediate. It is an important precursor for the preparation of silane coupling agents and a monomer for silicon-containing organic polymers. Its application areas cover polymers, catalyst additives, lubricants, surfactants, resins and many other fields.

[0003] The common synthesis method of dichlorodiphenylsilane is as follows:

[0004] ① Metal-catalyzed direct synthesis method: Chlorobenzene is reacted with silicon-copper contacts. The reaction temperature is generally between 400 and 600°C. The amount of copper catalyst is generally 30% to 50%. Alternatively, silicon-silver is used as contacts (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 the raw material to generate phenyl Grignard reagent (phenylmagnesium chloride) under the catalysis of lithium salt (lithium chloride or lithium fluoride) or aluminum chloride. 2 equivalents of phenylmagnesium chloride are added to 0.9 equivalents of silicon tetrachloride solution. Diphenyldichlorosilane is the main reaction product with a yield of up to 77%. The reaction varies with the ratio of phenylmagnesium chloride to silicon tetrachloride. When the ratio of phenylmagnesium chloride to silicon tetrachloride reaches 2:2.2, the yield of dichlorodiphenylsilane drops to 17%, and the yield of by-product phenyltrichlorosilane is 47%. The yield will fluctuate greatly.

[0006] ③ Use bromobenzene and n-butyl lithium to react under ether conditions at -78°C to generate n-butylbenzene, which is then reacted with 0.5 equivalents of tetrachlorosilane and 2 equivalents of trichlorophenylsilane to generate dichlorodiphenylsilane. This method requires the use of more dangerous n-butyl lithium and is carried out at extremely low temperatures.

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

[0008] Therefore, it is of great significance to develop an efficient synthesis method of dichlorodiphenylsilane with mild reaction conditions, simple process and green environmental protection. Summary of the invention

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

[0010] In order to solve the above technical problems, the present invention provides a method for electrochemical synthesis of dichlorodiphenylsilane (i.e., a method for electrochemically synthesizing dichlorodiphenylsilane from silicon tetrachloride), using a diaphragm-free electrolytic cell, adding an electrolyte, benzene and silicon tetrachloride into the electrolytic cell to form a reaction system, and generating dichlorodiphenylsilane under electrolytic conditions under the protection of an inert gas (e.g., nitrogen), wherein 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, tetrabutylammonium tetrafluoroborate;

[0012] The buffer added was acetic acid;

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

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

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

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

[0017] The electrolysis temperature is room temperature (15° C. to 30° C.), the reaction time is 4 to 12 hours, and the obtained reaction solution contains dichlorodiphenylsilane.

[0018] Note: The product can be obtained by performing conventional 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 eluent. The collected eluent was then rotary evaporated to remove the eluent to obtain the product dichlorodiphenylsilane.

[0020] As an improvement of the method for electrochemical synthesis of dichlorodiphenylsilane of the present invention:

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

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

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

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

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

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

[0029] The current density is 100A / m 2 , the electrolysis time is 8h.

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

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

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

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

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

[0035] The current density is 150A / m 2 , the electrolysis time is 4h.

[0036] The electrode selected in the present invention has good electrochemical stability and activity under the system described in the present invention and can be used in cycles for many times.

[0037] In the present invention, the reaction substrates are benzene and silicon tetrachloride, and benzene also serves as a solvent.

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

[0039] The electrode reaction equation of the present invention is as follows Figure 1 The electrode reaction mechanism is shown as Figure 2 shown.

[0040] The reaction of the present invention does not require a catalyst aid.

[0041] The present invention has the following benefits:

[0042] The reaction of the present invention does not require transition metal catalysts, high temperature and high pressure conditions, oxidants or reductants, and directly uses electrons as oxidants. It is green and environmentally friendly, has a simple reaction device, is easy to operate, and the yield can be stabilized at about 70% (67% to 74%). BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0044] Figure 1 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 known that silicon tetrachloride heterolytically splits into chloride anions and silicon trichloride cations near the anode; the chloride anions lose electrons at the anode to generate chloride free radicals and then generate chlorine gas, and the silicon trichloride cations electrophilically attack the benzene ring to generate trichloromonophenylsilane and protons; trichloromonophenylsilane repeats the above steps to heterolytically split into chloride anions and dichloromonophenyl cations, which then attack the benzene ring to generate dichlorodiphenylsilane. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0048] The product of the invention is confirmed to be dichlorodiphenylsilane through conventional nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance carbon spectrum.

[0049] The non-diaphragm electrolytic cell used in the present invention is a conventional sealed electrolytic cell, and the electrolytic cell cover has four holes: an air inlet, an air outlet, and two electrode insertion holes. A graphite electrode is used as an anode, and a copper sheet electrode is used as a cathode.

[0050] Embodiment 1:

[0051] Before the reaction starts, the electrolytic cell cover is opened, the electrolyte and substrate (benzene and silicon tetrachloride) are added into the electrolytic cell cavity, the electrolytic cell cover is closed, and two electrodes are inserted into the electrolytic cell through the electrode insertion hole (and corresponding sealing rings are installed), the air inlet pipe is connected to the air inlet hole on the electrolytic cell cover, one end of the air outlet pipe is connected to the air outlet hole on the electrolytic cell cover, and the other end is connected to the tail gas treatment device. Before the reaction starts, nitrogen is used to purge the electrolytic cell cavity for 20 minutes through the air inlet pipe (to ensure that there is no air in the electrolytic cell cavity); then the reaction is started, nitrogen is introduced, and the pressure in the electrolytic cell cavity is controlled to be normal pressure. Under a constant current of 10 mA, electrolysis is carried out at room temperature for 8 hours, and the current density is 100 A / m 2 , the electrolyte components and substrates are as shown in Table 1:

[0052] Table 1

[0053] Components Dosage Molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutylammonium tetrafluoroborate 0.001mol(0.329g) 0.1mol / L Acetic acid 0.001mol(0.06g) 0.1mol / L Silicon tetrachloride 0.002mol(0.34g) 0.2mol / L

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

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

[0056]

[0057] Example 2: Compared with Example 1: the electrolyte components and substrate are changed to those shown in Table 2; the rest are the same as 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 components and substrate are changed to those shown in Table 3; the rest are the same as Example 1.

[0063] Table 3:

[0064] Components Dosage Molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutylammonium tetrafluoroborate 0.002mol 0.2mol / L Acetic acid 0.001mol 0.1mol / L Silicon tetrachloride 0.001mol 0.1mol / 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 components and substrate are changed to those shown in Table 4; the rest are the same as Example 1.

[0067] Table 4:

[0068] Components Dosage Molar concentration benzene 5ml - Acetonitrile 5ml - Tetrabutylammonium tetrafluoroborate 0.001mol 0.1mol / L Acetic acid 0.002mol 0.2mol / L Silicon tetrachloride 0.001mol 0.2mol / L

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

[0070] Example 5: relative to Example 1: the electrolysis time at room temperature is 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 with Example 1: the constant current is changed from 10 mA to 20 mA; that is, the current density is 200 A / m 2 , the rest is the same as Example 1.

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

[0074] Example 7: Compared with Example 1, the electrolyte composition and substrate are changed to those shown in Table 5; and the electrolysis time is changed from 8 h to 4 h; the constant current is changed from 10 mA to 15 mA; that is, the current density is 150 A / m 2 , the rest is the same as 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 - Tetrabutylammonium tetrafluoroborate 0.329g 0.1mol / L Acetic acid 0.09g 0.15mol / L Silicon tetrachloride 0.34g 0.2mol / L

[0078] Example 8, relative to Example 1: "tetrabutylammonium tetrafluoroborate" in Table 1 is replaced by "tetrabutylammonium tetrafluorophosphate", the molar dosage 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, relative to Example 1: "tetrabutylammonium tetrafluoroborate" in Table 1 is replaced by "tetrabutylammonium bromide", the molar dosage 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: Compared with Example 1, the amount of "tetrabutylammonium tetrafluoroborate" in Table 1 was changed from 0.329 g to 1.645 g, that is, the corresponding molar concentration was changed from 0.1 mol / L to 0.5 mol / L. The rest was the same as Example 1.

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

[0084] In Comparative Example 1, since the concentration of the added supporting electrolyte is too high, the ion mobility in the solution is reduced, thereby reducing the current efficiency and yield.

[0085] Comparative Example 2, relative to Example 1: the use of the supporting electrolyte "tetrabutylammonium tetrafluoroborate" in Table 1 is eliminated, that is, the amount of "tetrabutylammonium tetrafluoroborate" is 0. The rest is the same as Example 1.

[0086] In this comparative example 2, since there is no supporting electrolyte, the weak acid acetic acid cannot conduct electricity in the organic solvent, so no current is conducted and the product dichlorodiphenylsilane cannot be obtained.

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

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

[0089] In Comparative Example 3, since the concentration of the added supporting electrolyte is too low, the conductivity of the solution decreases, the electrochemical reaction activity decreases, and thus the current efficiency and yield decrease.

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

[0091] The product dichlorodiphenylsilane was obtained with 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 anode reaction.

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

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

[0095] In Comparative Example 5, since the acetic acid concentration is too high, the mobility of electrolyte ions is reduced and the side reactions are increased, resulting in a decrease in electrochemical reaction activity.

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

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

[0098] In Comparative Example 6, due to the excessively high overpotential, the reaction was too intense, resulting in multiple side reactions and a decrease in yield.

[0099] Comparative Example 7, relative to Example 1: instead of reacting in a nitrogen atmosphere, the reaction inlet and outlet were connected to the atmosphere and placed in an air atmosphere, that is, the reaction was carried out in air. The rest was the same as Example 1.

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

[0101] In this comparative example 7, water vapor in the air reacts with silicon tetrachloride to generate 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 Example 1.

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

[0104] In this comparative example 8, the electrochemical window of ethanol in this system is not as wide as that of acetonitrile, which may cause side reactions in the electrolyte itself and thus reduce the yield.

[0105] Comparative Example 9, relative to Example 1: the anode material is replaced by copper from graphite; the rest is 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 of the anode be better promoted. In comparative example 9, when copper is used as the anode material, the copper element will lose electricity and become copper ions that dissolve into the electrolyte. In addition, the catalytic activity of copper at the anode is much lower than that of graphite, thus resulting in a decrease in the reaction yield.

[0108] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for electrochemical synthesis of dichlorodiphenylsilane, characterized in that: A non-diaphragm electrolytic cell is used, an electrolyte, benzene and silicon tetrachloride are added into the electrolytic cell to form a reaction system, and dichlorodiphenylsilane is generated under electrolysis conditions under the protection of an inert gas. The electrolyte consists of acetonitrile as a solvent, a supporting electrolyte and a buffer solution.

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, tetrabutylammonium tetrafluoroborate; The buffer added was acetic acid; Benzene is used as both substrate and solvent. The sum of the amounts of benzene and acetonitrile is defined as the total solvent. Benzene accounts for 30-50% of the total solvent volume. The dosage ratio of silicon tetrachloride to total solvent is 0.1-0.2 mol silicon tetrachloride / L total solvent; The ratio of the buffer to the total solvent is 0.1 to 0.2 mol buffer / L total solvent; The ratio of supporting electrolyte to total solvent is 0.1-0.2 mol supporting electrolyte / L total solvent; The electrolysis temperature is room temperature, the reaction time is 4 to 12 hours, and the obtained 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 2 or 3, characterized in that: The anode of the diaphragmless electrolytic cell is a graphite electrode and the cathode is a copper sheet electrode.

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

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

Images