Method for generating alkyl cyclosiloxane by hydrolyzing alkyl chlorosilane

Abstract

The invention discloses a method for efficiently preparing alkyl cyclosiloxane through hydrolysis of alkyl chlorosilane, which comprises the following steps: stirring hydrochloric acid containing a catalyst, dropwise adding alkyl dichlorosilane into the hydrochloric acid containing the catalyst for hydrolysis reaction, standing for layering after the reaction is completed, separating out an organic phase, washing with water until the pH value is 7, collecting the organic phase, and drying to obtain the alkyl cyclosiloxane. And carrying out reduced pressure rectification to obtain the alkyl cyclosiloxane. According to the method disclosed by the invention, a high-temperature cracking process is not needed, and only a very small amount of imidazolium salt catalyst is used in the hydrolysis process of alkyl chlorosilane, so that the yield of cyclosiloxane can be greatly improved. The method is simple in steps, easy and convenient to operate, capable of being carried out at a low temperature, extremely small in catalyst adding amount, capable of being recycled and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cyclosiloxane preparation, and particularly relates to a method for hydrolyzing hydrocarbyl chlorosilane to generate alkyl cyclosiloxane. BACKGROUND

[0002] Siloxane polymers are widely used in the construction industry, automotive industry, aerospace, electronics, medical health, personal care, and many consumer products as insulating materials, spreading agents, defoamers, mold release agents, implants, drug delivery system matrices, adhesives, and sealants due to their excellent thermal stability, low temperature flexibility, low surface energy, high resistivity, and non-toxic properties. Cyclosiloxanes are important raw materials for producing siloxane polymers, and are widely used in deodorants, antiperspirants, and other daily chemicals due to their low viscosity, high volatility, and skin moisturizing properties. Therefore, cyclosiloxanes have important industrial applications.

[0003] Cyclosiloxanes can generally be prepared by high-temperature cracking of linear polysiloxane catalyzed by alkali. Chinese invention patent (CN104497035A) discloses a method for preparing cyclosiloxane by high-temperature cracking of Me2SiCl2 hydrolysate using KOH as a catalyst; but this method needs to first prepare linear polysiloxane, and has the disadvantages of high viscosity in the cracking process, uneven heat transfer, many side reactions, and high energy consumption.

[0004] Chinese invention application (CN115368401A) describes adding crown ether complex and K + to improve the yield of cyclosiloxane. The method for preparing cyclosiloxane in this application is to hydrolyze hydrocarbyl dichlorosilane to generate a mixture of cyclosiloxane and linear polysiloxane with various molecular weights. The main reaction equation for hydrolyzing hydrocarbyl dichlorosilane to prepare cyclosiloxane is as follows: To improve the yield of cyclosiloxane: Chinese invention patent (CN1203079C) describes that methyl hydrogen dichlorosilane is mixed with alkane and then dropped into a mixed solution of alkane, methanol and water to obtain a maximum cyclosiloxane yield of 88.96%; Chinese invention patent (CN102372736B) adopts a hydrolysis method in which hydrocarbyl hydrogen chlorosilane is dropped into a mixed solvent of water, an alkaline earth metal hydroxide or salt as a template agent and a low-boiling hydrocarbon as a solvent to obtain a maximum cyclosiloxane yield of 99.3%; Chinese invention patent (CN111072716A) adds a surfactant octylphenyl polyoxyethylene ether in the hydrolysis process to prevent the methyl vinyl silanol intermediate from polymerizing into linear siloxane, and high-purity methyl vinyl cyclosiloxane can be obtained after salting and rectification. However, the above processes all use a large amount of organic solvent or alkali, or cause emulsification problems, and the post-treatment needs to add a high-concentration salt solution for demulsification, which increases the separation process and cost, causes a large amount of waste liquid and residue, and brings safety hazards and environmental pollution risks.

[0005] Recently, phase transfer catalysts (Phase Transfer Catalysis) are important catalysts in chemical reactions, and their characteristics include mild reaction conditions, high safety, simple operation and good selectivity, and have been widely used in actual industrial processes. By adding a phase transfer catalyst in the hydrolysis process of hydrocarbyl dichlorosilane, the reaction of silane phase and water phase can be accelerated, and the concentration of hydroxyl silanol generated at the interface of the two phases can be controlled to prevent it from polymerizing into high-molecular-weight linear polysiloxane, thereby obtaining small-molecular-weight cyclosiloxane. SUMMARY

[0006] The present application provides a method for hydrolyzing hydrocarbyl chlorosilane to generate alkyl cyclosiloxane, which is simple to operate and low in cost.

[0007] To achieve the above-mentioned purpose, the present application provides a method for hydrolyzing hydrocarbyl chlorosilane to generate alkyl cyclosiloxane, which specifically comprises: stirring hydrochloric acid containing a catalyst, adding hydrocarbyl dichlorosilane into the hydrochloric acid containing the catalyst by dropping to carry out a hydrolysis reaction, and after the reaction is completed, standing and separating, separating out an organic phase and washing with water until pH=7, collecting the organic phase, and performing vacuum rectification to obtain alkyl cyclosiloxane.

[0008] Further, the catalyst is an imidazolium salt, and the structural formula is as follows: Among them, R1 and R2 in the cation are any one of straight-chain or branched alkyl with carbon chain length of C1-C10, and R1 and R2 are the same or different; the anion X – is Cl – , Br – , I –, tetrafluoroborate BF4 – , hexafluorophosphate PF6 – , acetate CH3COO – , trifluoroacetate CF3COO – , triflate CF3SO3 – , or sulfonate R-SO3 - .

[0009] Further, the R1 is any one of C1-C10 alkyl, and R2 is any one of C1-C4 alkyl; X – is Cl – or Br – .

[0010] Preferably, R1 is any one of methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl (more preferably any one of C3-C8 alkyl, which satisfies the dispersing ability of the organic phase and is not easy to cause emulsification); preferably R2 is any one of methyl, ethyl, propyl or butyl (more preferably methyl).

[0011] Further, the general formula of the hydrocarbyldichlorosilane is R3R4SiCl2; wherein R3 is a hydrogen atom, any one of C1-C10 alkyl, any one of C1-C10 halogenated alkyl, any one of C1-C10 alkenyl, or any one of C6-C10 alkylaryl; R4 is a hydrogen atom, any one of C1-C10 alkyl, any one of C1-C10 halogenated alkyl, any one of C1-C10 alkenyl, or any one of C6-C10 alkylaryl; and R3 and R4 are the same or different, but R3 and R4 are not simultaneously a hydrogen atom.

[0012] C1-C10 alkyl (such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, etc.); C1-C10 halogenated alkyl includes fluoroalkyl (such as trifluoromethyl, trifluoroethyl, etc.), chloroalkyl (such as chloropropyl, etc.); C1-C10 alkenyl such as vinyl, allyl, etc.; C6-C10 alkylaryl such as phenyl, chlorophenyl, benzyl, naphthyl, etc.).

[0013] Further, the general formula of the cyclic siloxane is (R3R4SiO) n , and n is 3-6.

[0014] Further, the concentration of the hydrochloric acid is 10-40%.

[0015] Further, the mass ratio of the hydrocarbyldichlorosilane to the hydrochloric acid is 0.1-5.0:1, preferably 0.6-2.0:1.

[0016] Further, the molar ratio of the imidazolium salt to the hydrocarbyldichlorosilane is 0.0001-0.01:1, preferably 0.0005-0.005:1.

[0017] Further, the temperature of the hydrocarbyldichlorosilane hydrolysis reaction is 0-50℃ (preferably 15-25℃), and the pressure is normal pressure-0.5 MPa; the hydrocarbyldichlorosilane dropwise addition rate is 0.1-5 g / min (preferably 0.5-1.0 g / min) to keep the system reaction temperature stable and avoid the generation of a large amount of high molecular weight linear polysiloxane; and the reaction time after dropwise addition is 5-30 min.

[0018] The added imidazolium salt catalyst in the present application is easily soluble in water, can be removed from the organic phase when extraction is layered, and is left in the aqueous phase for recycling.

[0019] Compared with the prior art, the present application has the following beneficial effects: 1) Compared with the existing method for preparing cyclic siloxanes, the present application does not need to carry out a high-temperature cracking process, the steps are simple and easy to operate, and the process can be carried out at a lower temperature, which is suitable for industrial production.

[0020] 2) The amount of the imidazolium salt catalyst used in the present application is extremely small, and the catalyst has the advantages of high activity and good selectivity of cyclic siloxanes. The structural characteristics of the catalyst can on the one hand control its water solubility and critical micelle concentration by precisely controlling the length of the N-alkyl carbon chain, so that it can dilute the concentration of the silanol intermediate at the organic phase / water phase interface, avoid its polycondensation into high molecular weight linear polysiloxane, and selectively dehydrate and condense into small molecular weight cyclic siloxanes; and on the other hand, it can avoid the defect of increasing the difficulty of separation due to emulsification. The imidazolium salt catalyst after the reaction is dissolved in the aqueous phase and is easy to separate, and can be reused in the hydrolysis system.

[0021] 3) Compared with the existing method for selectively generating cyclic siloxanes in the hydrolysis reaction of hydrocarbyldichlorosilane, the present application does not need to use additional organic solvents, which reduces the cost and is safe and environmentally friendly. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0023] Example 1 The hydrolysis reaction of alkyl dichlorosilane was carried out in a 500 mL three-necked round-bottom flask equipped with a constant-pressure dropping funnel, a thermometer with an adapter, and a reflux condenser connected to an HCl absorption device. 77 g of hydrochloric acid (containing 37% HCl) and 0.09 g of 1-hexyl-3-methylimidazolium bromide catalyst were added to the round-bottom flask, and the solution was magnetically stirred. Then, while stirring, 50 g of Me₂SiCl₂ (dimethyl dichlorosilane) was added through the constant-pressure dropping funnel at a rate of 1.0 g / min, while the temperature of the reaction mixture was controlled between 15-30 °C using a cold water bath. After the addition of Me₂SiCl₂ was complete, the reaction mixture was stirred for another 20 minutes. The reaction mixture was then allowed to stand for 20 minutes to achieve clear phase separation, and the siloxane product phase was subsequently separated from the aqueous phase. The siloxane product phase was then washed three times with water until pH=7. The siloxane phase was then dried with anhydrous Na2SO4, and a small sample was analyzed by gas chromatography to obtain the yield of each cyclic siloxane and the overall yield. The results are shown in Table 1. The crude siloxane product was subjected to vacuum distillation, and the collected fraction was the cyclic siloxane product, which included hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecylcyclohexasiloxane (D6).

[0024] Example 2 In this example, 0.08 g of 1-hexyl-3-methylimidazolium chloride catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0025] Example 3 In this example, 0.11 g of 1-hexyl-3-methylimidazolium iodide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0026] Example 4 In this example, 0.10 g of 1-decyl-3-methylimidazolium bromide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0027] Example 5 In this example, 0.10 g of 1-octyl-3-methylimidazolium bromide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0028] Example 6 In this example, 0.09 g of 1-butyl-3-methylimidazolium bromide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0029] Example 7 In this example, 0.12 g of 1-butyl-3-isopropylimidazolium bromide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0030] Example 8 In this example, 0.1 g of 1-propyl-3-butylimidazolium bromide catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0031] Example 9 In this embodiment, 77g of hydrochloric acid (containing 37% HCl) and 0.11g of 1-hexyl-3-methylimidazolium bromide catalyst were mixed and placed in a constant pressure dropping funnel, and added dropwise to 50g of Me2SiCl2 at a rate of 1.0g / min. The remaining steps were the same as in Example 1. The results are shown in Table 1.

[0032] Example 10 In this embodiment, hydrochloric acid containing 10% HCl was used, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0033] Example 11 In this embodiment, the dropping rate was changed to 0.5 g / min, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0034] Example 12 In this embodiment, no imidazolium salt catalyst was added. Instead, the aqueous phase remaining after the reaction in Example 1 was recovered and used as the aqueous phase in this embodiment. The remaining steps were the same as in Example 1. The results are shown in Table 1.

[0035] Comparative Example 1 In this embodiment, no imidazolium salt catalyst was added, and the remaining steps were the same as in Example 1. The results are shown in Table 1.

[0036] The results of hydrolysis of alkyl dichlorosilanes in each example and comparative example to obtain cyclic siloxanes are shown in Table 1: As shown in Table 1, different imidazolium salt catalysts can be used to prepare cyclic siloxanes with high selectivity via the hydrolysis of hydrocarbon dichlorosilanes.

[0037] Example 13 77 g of hydrochloric acid (containing 37% HCl) and 0.09 g of 1-hexyl-3-methylimidazolium bromide catalyst were added to a round-bottom flask, and the solution was magnetically stirred. Then, while stirring, 50 g of methylphenyl dichlorosilane (MePhSiCl2) was added at a rate of 1.0 g / min through a constant-pressure dropping funnel, while simultaneously controlling the temperature of the reaction mixture between 15-30 °C using a cold water bath. After the addition of MePhSiCl2 was complete, the reaction mixture was stirred for another 20 minutes. The reaction mixture was then allowed to stand for 20 minutes to allow for clear phase separation, and the siloxane product phase was subsequently separated from the aqueous phase. The siloxane product phase was then washed three times with water until pH 7. The siloxane phase was then dried with anhydrous Na2SO4, and a small sample was taken for gas chromatography analysis to obtain the yield of each cyclic siloxane and the total yield, which yielded 14.7% (MePhSiO)3, 52.1% (MePhSiO)4 and 7.1% (MePhSiO)5.

[0038] Example 14 77 g of hydrochloric acid (containing 37% HCl) and 0.06 g of 1-hexyl-3-methylimidazolium bromide catalyst were added to a round-bottom flask, and the solution was magnetically stirred. Then, while stirring, 50 g of methylnaphthyldichlorosilane (MeNaphSiCl2) was added at a rate of 1.0 g / min through a constant-pressure dropping funnel, while simultaneously controlling the temperature of the reaction mixture between 15-30 °C using a cold water bath. After the addition of MeNaphSiCl2 was complete, the reaction mixture was stirred for another 20 minutes. The reaction mixture was then allowed to stand for 20 minutes to allow for clear phase separation, and the siloxane product phase was subsequently separated from the aqueous phase. The siloxane product phase was then washed three times with water until pH=7. The siloxane phase was then dried with anhydrous Na2SO4, and a small sample was taken for gas chromatography analysis to obtain the yield of each cyclic siloxane and the total yield, which yielded 21.7% (MeNaphSiO)3, 40.1% (MeNaphSiO)4 and 4.1% (MeNaphSiO)5.

Claims

1. A method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes, characterized in that: The method specifically involves: stirring hydrochloric acid containing a catalyst, adding alkyl dichlorosilane to the hydrochloric acid containing the catalyst by dropwise for hydrolysis reaction, allowing the mixture to stand and separate into layers after the reaction is complete, separating the organic phase and washing it with water until pH=7, collecting the organic phase and performing vacuum distillation to obtain alkyl cyclic siloxane.

2. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The catalyst is an imidazolium salt, with the following structural formula: In the cation, R1 and R2 are either straight-chain or branched alkyl groups with a carbon chain length of C1-C10, and R1 and R2 may be the same or different; the anion X – For Cl – ,Br – I – Tetrafluoroborate (BF4) – PF6 hexafluorophosphate – Acetate CH3COO – Trifluoroacetate CF3COO – Trifluoromethanesulfonate CF3SO3 – or sulfonate R-SO3 - Any one of them.

3. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 2, characterized in that: R1 is any one of C1-C10 alkyl groups, and R2 is any one of C1-C4 alkyl groups; X – For Cl – or Br – .

4. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The general formula of the hydrocarbon-based dichlorosilane is R3R4SiCl2; Wherein, R3 is a hydrogen atom, any one of the C1-C10 alkyl groups, any one of the C1-C10 haloalkyl groups, any one of the C1-C10 alkenyl groups, or any one of the C6-C10 alkylaryl groups; R4 is a hydrogen atom, any one of the C1-C10 alkyl groups, any one of the C1-C10 haloalkyl groups, any one of the C1-C10 alkenyl groups, or any one of the C6-C10 alkylaryl groups; and R3 and R4 may be the same or different, but R3 and R4 may not both be hydrogen atoms.

5. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The general formula of the cyclic siloxane is (R3R4SiO). n n is 3-6.

6. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The concentration of the hydrochloric acid is 10-40%.

7. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The mass ratio of the hydrocarbon-based dichlorosilane to hydrochloric acid is 0.1-5.0:

1.

8. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The molar ratio of the imidazolium salt to the hydrocarbon dichlorosilane is 0.0001-0.01:

1.

9. The method for hydrolyzing hydrocarbon chlorosilanes to generate alkyl cyclic siloxanes according to claim 1, characterized in that: The hydrolysis reaction of the hydrocarbon dichlorosilane is carried out at a temperature of 0-50℃ and a pressure of atmospheric pressure to 0.5MPa; the dropping rate of the hydrocarbon dichlorosilane is 0.1-5g / min, and the reaction time is 5-30min after the dropping is completed.

10. The method for hydrolyzing alkylchlorosilanes to generate alkylcyclic siloxanes according to claim 1, characterized in that: The hydrolysis reaction of the hydrocarbon-based dichlorosilane is carried out at a temperature of 15-25℃.

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