Hexamethyldisiloxane and preparation method thereof

Abstract

The present invention discloses hexamethyldisiloxane and a preparation method thereof. The preparation method comprises the following steps: mixing octamethylcyclotetrasiloxane, a gallium catalyst, and methyllithium to obtain a mixed reaction system; reacting the mixed reaction system, quenching, and separating to obtain the hexamethyldisiloxane. The preparation method of hexamethyldisiloxane according to an embodiment of the present invention produces hexamethyldisiloxane by reacting the mixed reaction system of octamethylcyclotetrasiloxane, the gallium catalyst, and methyllithium. No additional chloride ions are introduced during the preparation process. The entire preparation process is mild and controllable, the raw materials are readily available, the gallium catalyst is reusable, a low-temperature reactor is not required, and subsequent purification is simplified. The resulting hexamethyldisiloxane is of high purity.

Description

Technical Field

[0001] The present invention relates to the field of fine chemical synthesis, in particular to hexamethyldisiloxane and a preparation method thereof. Background Art

[0002] Traditionally, hexamethyldisiloxane is synthesized using trimethylchlorosilane, water, and sodium hydroxide via alkaline hydrolysis. This process inevitably involves the presence of chloride ions, which places high demands on hexamethyldisiloxane for high-end applications. Chloride ions can enhance corrosion, significantly shortening the lifespan of equipment. This effect is most pronounced in acidic cleaning agents. For example, in pressure vessels made of austenitic stainless steel, the presence of chloride solutions can cause stress corrosion, even in trace amounts. Both downstream silicone processing and high-end cleaning industries require hexamethyldisiloxane products with low silanol and chloride content.

[0003] Another major use for hexamethyldisiloxane is as a raw material for the synthesis of hexamethyldisilazane, an important pharmaceutical intermediate. Currently, hexamethyldisiloxane sold domestically has a purity of >99% and contains numerous impurities, including organic solvents such as toluene and tetrahydrofuran. This results in significant variation in hexamethyldisiloxane quality, making it difficult to use in demanding applications.

[0004] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0005] The present invention aims to provide a method for preparing hexamethyldisiloxane, which has the advantages of no additional chloride ion introduction during the preparation process, mild and controllable reaction conditions, readily available raw materials, and reusable gallium catalyst.

[0006] Another object of the present invention is to provide hexamethyldisiloxane.

[0007] To achieve the above object, an embodiment of the present invention provides a method for preparing hexamethyldisiloxane, comprising the following steps:

[0008] mixing octamethylcyclotetrasiloxane, a gallium catalyst, and methyllithium to obtain a mixed reaction system;

[0009] The mixed reaction system is reacted, quenched, and separated to obtain hexamethyldisiloxane.

[0010] In one or more embodiments of the present invention, the gallium catalyst is selected from gallium, gallium salts and gallium-containing complexes; and / or,

[0011] The gallium catalyst accounts for 0.1 to 4 mol% of the total reaction system; and / or,

[0012] The molar ratio of the methyllithium to octamethylcyclotetrasiloxane is greater than or equal to 4:1.

[0013] In one or more embodiments of the present invention, the step of mixing octamethylcyclotetrasiloxane, gallium catalyst and methyllithium comprises:

[0014] Octamethylcyclotetrasiloxane and gallium catalyst were mixed under stirring, and methyllithium solution was added.

[0015] In one or more embodiments of the present invention, the step of adding the methyllithium solution comprises:

[0016] Under cooling conditions, the methyllithium solution was added dropwise to the mixed system of octamethylcyclotetrasiloxane and gallium catalyst.

[0017] In one or more embodiments of the present invention, the methyllithium solution is any one of a methyllithium diethyl ether solution and a methyllithium diethoxymethane solution.

[0018] In one or more embodiments of the present invention, the reaction conditions of the mixed reaction system are: reaction at a temperature of 100 to 180° C. and stirring for 4 to 12 hours.

[0019] In one or more embodiments of the present invention, the quenching step comprises:

[0020] After the mixed reaction system reacts, a quencher is added to perform quenching.

[0021] In one or more embodiments of the present invention, the quencher comprises one of an ethanol aqueous solution and an ice-water mixture.

[0022] In one or more embodiments of the present invention, the step of separating comprises:

[0023] The mixed reaction system after quenching is filtered and purified to obtain hexamethyldisiloxane.

[0024] An embodiment of the present invention provides hexamethyldisiloxane, which is prepared by reacting a mixed reaction system of octamethylcyclotetrasiloxane, a gallium catalyst, and methyllithium.

[0025] Compared with the prior art, the method for preparing hexamethyldisiloxane according to an embodiment of the present invention produces hexamethyldisiloxane through a mixed reaction system of octamethylcyclotetrasiloxane, a gallium catalyst, and methyllithium. No additional chloride ions are introduced during the preparation process, and the entire preparation process is mild and controllable. Raw materials are readily available, the gallium catalyst is reusable, a low-temperature reactor is not required, and subsequent purification is easy. The produced hexamethyldisiloxane has high purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of a method for preparing hexamethyldisiloxane according to one embodiment of the present invention; DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0028] Unless expressly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising", etc., will be understood to include the stated elements or components but not to exclude other elements or other components.

[0029] like Figure 1 As shown, a method for preparing hexamethyldisiloxane according to a preferred embodiment of the present invention comprises the following steps:

[0030] S1. Mixing octamethylcyclotetrasiloxane, a gallium catalyst and methyllithium to obtain a mixed reaction system.

[0031] The process of mixing octamethylcyclotetrasiloxane, gallium catalyst and methyllithium in step S1 may specifically be as follows: octamethylcyclotetrasiloxane and gallium catalyst are mixed under stirring, and methyllithium solution is added.

[0032] It is understandable that due to the relatively active properties of methyllithium itself, a methyllithium solution is generally added to the mixed system of octamethylcyclotetrasiloxane and gallium catalyst to act as a buffer. The methyllithium solution can specifically be any one of a methyllithium ether solution and a methyllithium diethoxymethane solution. Specifically, the methyllithium solution is commercially available methyllithium ether solution or methyllithium diethoxymethane solution. The concentration of methyllithium in the methyllithium ether solution is 1.0 to 2.0 mol / L, with methyllithium ether solutions of 1.0 mol / L and 1.6 mol / L being more common. The concentration of methyllithium in the methyllithium diethoxymethane solution is 2 to 3.1 mol / L.

[0033] Furthermore, in order to avoid a violent reaction in the subsequent mixed reaction system, the step of adding the methyllithium solution may specifically include:

[0034] Under a cooling environment, the methyllithium solution is added dropwise to the mixed system of octamethylcyclotetrasiloxane and gallium catalyst. The cooling environment can be understood as placing the mixed system of octamethylcyclotetrasiloxane and gallium catalyst under a circulating water cooling system. Specifically, during the process of adding the methyllithium solution dropwise to the mixed system of octamethylcyclotetrasiloxane and gallium catalyst, a circulating water cooling system is used to ensure that the temperature during the addition process is as close to room temperature as possible to avoid a violent reaction.

[0035] It is understood that during the dropwise addition of the methyllithium solution, the mixed reaction system is already in the reaction process, and the cooling environment is only required to remove the exothermic heat of reaction in a timely manner. After the dropwise addition of the methyllithium solution is complete, the subsequent step S2 can be entered. The stirring and cooling environment conditions are intended to reduce the possibility of a violent reaction during the mixing process, and the actual reaction needs to be heated before it is started.

[0036] Specifically, the gallium catalyst can be selected from gallium, gallium salts and gallium-containing complexes, wherein the gallium salt can be any one of gallium nitrate and freshly prepared gallium hydroxide.

[0037] The gallium catalyst accounts for 0.1 to 4 mol% of the total reaction system.

[0038] S2. The mixed reaction system is reacted, quenched, separated, and hexamethyldisiloxane is obtained, and quenched.

[0039] The reaction conditions of the mixed reaction system in step S2 are: reacting at a temperature of 100 to 180° C. with stirring for 4 to 12 hours.

[0040] Specifically, the separation step includes filtering and purifying the quenched mixed reaction system to obtain hexamethyldisiloxane.

[0041] Specifically, the quenching step includes: adding a quencher after the mixed reaction system has reacted to quench the reaction, thereby terminating the reaction. The quencher can be added slowly until the mixed reaction system no longer heats up, indicating the quenching reaction is complete. Upon completion of the reaction (or after the reaction time reaches a predetermined time), unreacted methyllithium in the mixed reaction system may pose a risk. Therefore, the quencher is added to quench the reaction, converting the methyllithium into lithium oxide / lithium hydroxide, thereby reducing the risk.

[0042] Furthermore, the quencher includes one of an ice-water mixture (0° C.) and an ethanol aqueous solution. For example, a 20% ethanol aqueous solution can be used as the quencher.

[0043] Furthermore, the filtration step can separate solid byproducts, the gallium catalyst, and other impurities. Solid byproducts may include lithium oxide, lithium hydroxide, and the like. This process not only separates the solid byproducts, but also allows the gallium catalyst to be recycled and reused, thereby reducing the production cost.

[0044] Furthermore, the purification can be a simple distillation or a more complex rectification process, depending on the required purity of the final hexamethyldisiloxane.

[0045] The following is the reaction equation for the preparation of hexamethyldisiloxane in one embodiment of the present invention:

[0046]

[0047] Here, RT stands for room temperature, and Ga stands for gallium catalyst.

[0048] The preparation method of hexamethyldisiloxane of the present invention comprises subjecting octamethylcyclotetrasiloxane to a ring-opening reaction in the presence of a gallium catalyst and methyllithium to obtain hexamethyldisiloxane. Based on the aforementioned principle and reaction equation, it can be seen that to improve product purity and yield, the molar ratio of octamethylcyclotetrasiloxane to methyllithium is preferably 1:4, meaning that both octamethylcyclotetrasiloxane and methyllithium react completely, resulting in fewer byproducts and side reactions. However, achieving an absolute 1:4 ratio is difficult in actual production. Therefore, in actual production, the amount of methyllithium may be slightly higher, for example, a molar ratio of methyllithium to octamethylcyclotetrasiloxane of approximately 4.1:1, thereby reducing the amount of byproducts during the ring-opening process of octamethylcyclotetrasiloxane.

[0049] An embodiment of the present invention provides hexamethyldisiloxane, which can be prepared by reacting the above-mentioned mixed reaction system of octamethylcyclotetrasiloxane, a gallium catalyst and methyllithium.

[0050] The hexamethyldisiloxane and its preparation method of the present invention will be described in detail below with reference to specific examples.

[0051] Example 1

[0052] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium into a 2000mL reactor and stir for 30min. Prepare 1L of 1.6mol / L methyllithium solution, keep it at room temperature under condensed water cooling, and slowly add it dropwise into the octamethylcyclotetrasiloxane solution. The temperature needs to be controlled not to be too high during the process, and the reaction needs to be stirred throughout. After the addition is completed, raise the temperature to 180℃ and stir the reaction for 12h, then add 200mL of quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide, and recover the silver metallic gallium. The remaining liquid is distilled to obtain 92.4g of the component at 100-103℃, with a yield of 62.9% and a purity of 93.2% as determined by GC-MS.

[0053] Example 2

[0054] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.56g (0.008mol, 2mol%) of metallic gallium into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium ether solution and slowly add it dropwise into the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining at room temperature. The temperature must be controlled not to be too high during the process and the reaction must be stirred throughout. After the addition is complete, raise the temperature to 180℃ and stir the reaction for 12 hours. Then, add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide and recover the silver metallic gallium. The remaining liquid is distilled to obtain 104.1g of a component at 100-103℃, with a yield of 72.2% and a purity of 96.1% as determined by GC-MS.

[0055] Example 3

[0056] 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 1.12g (0.016mol, 4mol%) of metallic gallium were added to a 2000mL reactor and stirred for 30 minutes. One liter of a 1.6mol / L methyllithium ether solution was prepared and slowly added dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining it at room temperature. The temperature must be controlled to prevent it from rising too high, and the reaction must be stirred throughout. After the addition is complete, the temperature is raised to 180°C and stirred for 12 hours. Then, 200mL of a quencher, ice-water mixture (0°C), is added. After the system temperature stabilizes, the generated lithium oxide and lithium hydroxide are filtered out, and the silver metallic gallium is recovered. The remaining liquid is distilled to yield 107.3g of a component at 100-103°C, with a yield of 74.7% and a purity of 95.3% as determined by GC-MS.

[0057] Example 4

[0058] 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.028g (0.0004mol, 0.1mol%) of metallic gallium were added to a 2000mL reactor and stirred for 30 minutes. One liter of a 1.6mol / L methyllithium ether solution was prepared and slowly added dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining it at room temperature. The temperature must be controlled to prevent it from rising too high, and the reaction must be stirred throughout. After the addition is complete, the temperature is raised to 180°C and stirred for 12 hours. Then, 200mL of a quencher, ice-water mixture (0°C), is added. After the system temperature stabilizes, the generated lithium oxide and lithium hydroxide are filtered out, and the silver metallic gallium is recovered. The remaining liquid is distilled to yield 59.7g of a component at 100-103°C, with a yield of 39.2%. The purity determined by GC-MS analysis is 91.7%.

[0059] Example 5

[0060] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium ether solution, maintain room temperature under condensed water cooling, and slowly add it dropwise into the octamethylcyclotetrasiloxane solution. The temperature needs to be controlled not to be too high during the process, and the reaction needs to be stirred throughout. After the addition is completed, raise the temperature to 140℃ and stir the reaction for 12 hours, then add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide, and recover the silver metallic gallium. The remaining liquid is distilled to obtain 8.1g of a component at 100-103℃, with a yield of 5.6%. The purity tested by GC-MS is 90.5%.

[0061] Example 6

[0062] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium ether solution, maintain room temperature under condensed water cooling, and slowly add it dropwise into the octamethylcyclotetrasiloxane solution. The temperature needs to be controlled not to be too high during the process, and the reaction needs to be stirred throughout. After the addition is completed, raise the temperature to 100℃ and stir the reaction for 12 hours, then add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide, and recover the silver metallic gallium. The remaining liquid is distilled to obtain 3.6g of a component at 100-103℃, with a yield of 2.5%. The purity tested by GC-MS is 88.9%.

[0063] Example 7

[0064] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium ether solution, keep it at room temperature under condensed water cooling, and slowly add it dropwise into the octamethylcyclotetrasiloxane solution. The temperature needs to be controlled not to be too high during the process, and the reaction needs to be stirred throughout. After the addition is completed, raise the temperature to 180℃ and stir the reaction for 4h, then add 200mL of quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide, and recover the silver metallic gallium. Distillation gives 50.4g of a component at 100-103℃, with a yield of 39.8% and a purity of 95.8% as determined by GC-MS.

[0065] Example 8

[0066] 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium were added to a 2000mL reactor and stirred for 30 minutes. One liter of a 1.6mol / L methyllithium ether solution was prepared and slowly added dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining at room temperature. The temperature must be controlled to prevent it from being too high, and the reaction must be stirred throughout. After the addition is complete, the temperature is raised to 180°C and stirred for 8 hours. Then, 200mL of a quencher, ice-water mixture (0°C), is added. After the system temperature stabilizes, the generated lithium oxide and lithium hydroxide are filtered out, and the silver metallic gallium is recovered. Distillation yields 85.6g of a component at 100-103°C, with a yield of 59.4% and a purity of 92.6% as determined by GC-MS.

[0067] Example 9

[0068] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium ether solution and slowly add it dropwise into the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining at room temperature. The temperature must be controlled not to be too high during the process and the reaction must be stirred throughout. After the addition is complete, raise the temperature to 180℃ and stir the reaction for 24 hours. Then, add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide and recover the silver metallic gallium. Distillation yields 102.6g of a component at 100-103℃, with a yield of 71.3% and a purity of 93.7% as determined by GC-MS.

[0069] Example 10

[0070] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of metallic gallium in a 1500mL reactor and stir for 30 minutes. Prepare 600mL of a 2.7mol / L diethoxymethane solution of methyllithium and slowly add it dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining at room temperature. The temperature must be controlled not to be too high during the process and the reaction must be stirred throughout. After the addition is complete, raise the temperature to 180℃ and stir the reaction for 12 hours. Then, add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter out the generated lithium oxide and lithium hydroxide and recover the silver metallic gallium. Distillation yields 94.6g of a component at 100-103℃, with a yield of 74.7% and a purity of 89.7% as determined by GC-MS.

[0071] Example 11

[0072] 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of gallium metal were added to a 2000mL reactor and stirred for 30 minutes. One liter of a 1.6mol / L methyllithium ether solution was prepared and slowly added dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining at room temperature. The temperature must be controlled to be below zero, and the reaction must be stirred throughout. After the addition is complete, the reaction mixture is heated to 180°C and stirred for 24 hours. Then, 250mL of a 20% aqueous ethanol quencher was added. After the system temperature stabilized, the generated lithium oxide and lithium hydroxide were filtered out, and the silvery gallium metal was recovered. The reaction was stopped. The generated lithium oxide and lithium hydroxide were filtered out, and the silvery gallium metal was recovered. Distillation yielded 99.9g of a component at 100-103°C, with a yield of 69.4% and a purity of 92.2% as determined by GC-MS.

[0073] Comparative Example 1

[0074] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and add it to a 2000mL reactor, stirring and mixing for 30min. Prepare 1L of 1.6mol / L methyl lithium ether solution, cool it with condensed water, keep it at room temperature, and slowly add it dropwise into the octamethylcyclotetrasiloxane solution. The temperature needs to be controlled not to be too high during the process, and the reaction needs to be stirred throughout. After the addition is completed, raise the temperature to 180℃ and stir the reaction for 24h, then add 200mL of a quencher 0℃ ice-water mixture (0℃) solution. After the system temperature stabilizes, filter and collect the reaction residue. After the reaction residue is separated and the organic phase is collected and distilled, no component at 100-103℃ is obtained. The product (hexamethyldisiloxane) is almost absent by separation and filtration, because it can be assumed that octamethylcyclotetrasiloxane and methyl lithium ether solution have hardly reacted.

[0075] Comparative Example 2

[0076] Take 115.7g (0.39mol) of octamethylcyclotetrasiloxane and 0.28g (0.004mol, 1mol%) of gallium metal into a 2000mL reactor and stir for 30 minutes. Prepare 1L of 1.6mol / L methyl lithium etherate solution and slowly add it dropwise to the octamethylcyclotetrasiloxane solution while cooling with condensed water and maintaining it at room temperature. The temperature must be controlled not to be too high during the process, and the reaction must be stirred throughout. After the addition is complete, raise the temperature to 90℃ and stir the reaction for 12 hours. Then, add 200mL of a quencher ice-water mixture (0℃). After the system temperature stabilizes, filter and collect the reaction residue. The reaction residue is separated and the organic phase is collected and distilled. No component meeting the test conditions of 100-103℃ was collected. The product (hexamethyldisiloxane) was almost absent through separation and filtration, as it can be assumed that the octamethylcyclotetrasiloxane and methyl lithium etherate solution have hardly reacted.

[0077] In summary, the beneficial effects of the preparation method of hexamethyldisiloxane according to the embodiment of the present invention are as follows: no additional chloride ions are introduced during the preparation process, the conditions of the entire preparation process are mild and controllable, the raw materials are readily available, the gallium catalyst is reusable, no low-temperature reactor is required, and the subsequent purification difficulty is low, and the hexamethyldisiloxane obtained is of high purity.

[0078] In addition, since no additional chloride ions are introduced into the raw materials and reaction system when preparing hexamethyldisiloxane using the above preparation method, the chloride ion content in the prepared hexamethyldisiloxane is low, and other impurities are easy to separate, which can facilitate the subsequent purification process.

[0079] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing hexamethyldisiloxane, characterized in that: The following steps are involved: mixing octamethylcyclotetrasiloxane, a gallium catalyst, and methyllithium to obtain a mixed reaction system; The mixed reaction system is reacted, quenched, and separated to obtain hexamethyldisiloxane; The reaction conditions of the mixed reaction system are: reaction at a temperature of 100 to 180° C. for 4 to 12 hours; and the gallium catalyst is metallic gallium.

2. The method for preparing hexamethyldisiloxane according to claim 1, wherein The gallium catalyst accounts for 0.1 to 4 mol% of the total reaction system; and / or, The molar ratio of the methyllithium to octamethylcyclotetrasiloxane is greater than or equal to 4:

1.

3. The method for preparing hexamethyldisiloxane according to claim 1, wherein The step of mixing the octamethylcyclotetrasiloxane, the gallium catalyst and the methyllithium comprises: The octamethylcyclotetrasiloxane and the gallium catalyst were mixed under stirring, and the methyllithium solution was added.

4. The method for preparing hexamethyldisiloxane as claimed in claim 3, wherein The step of adding methyllithium solution comprises: Under cooling conditions, a methyllithium solution was added dropwise to the mixed system of octamethylcyclotetrasiloxane and gallium catalyst.

5. The method for preparing hexamethyldisiloxane as claimed in claim 4, wherein The methyllithium solution is any one of a methyllithium ether solution and a methyllithium diethoxymethane solution.

6. The method for preparing hexamethyldisiloxane according to claim 1, wherein The quenching step comprises: After the mixed reaction system reacts, a quencher is added to perform quenching.

7. The method for preparing hexamethyldisiloxane according to claim 6, wherein The quencher comprises one of an ethanol aqueous solution and an ice-water mixture.

8. The method for preparing hexamethyldisiloxane according to claim 1, wherein The separation step comprises: The mixed reaction system after quenching is filtered and purified to obtain the hexamethyldisiloxane.

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