Preparation method of cresol trozole trisiloxane

Abstract

The invention provides a preparation method of cresol trozole trisiloxane, and belongs to the technical field of sun-screening agent preparation. The preparation method of cresol trozole trisiloxane comprises the following steps: carrying out Claisen rearrangement reaction on a concentrated solution of a compound as shown in a formula II to obtain a compound as shown in a formula III; and reacting the compound shown in the formula III with heptamethyltrisiloxane to obtain a compound shown in a formula IV. The concentrated solution of the compound shown in the formula II is subjected to the Claisen rearrangement reaction under the solvent-free condition to prepare the compound shown in the formula III, the reaction time for preparing the compound shown in the formula III is shortened, the reaction efficiency for preparing the compound shown in the formula III is improved, the yield for preparing the compound shown in the formula III is increased, the reaction time for preparing cresol trozole trisiloxane is shortened, and the yield of cresol trozole trisiloxane is increased. The reaction efficiency of cresol trozole trisiloxane preparation is improved, and the yield of cresol trozole trisiloxane preparation is improved.

Description

Technical Field

[0001] The invention relates to the technical field of sunscreen preparation, and in particular to a method for preparing drometrizole trisiloxane. Background Art

[0002] Sunscreens used in sunscreen cosmetics are divided into physical sunscreens and chemical sunscreens. Drometrizole trisiloxane is a commonly used new chemical sunscreen that is widely used in various mid-to-high-end brands of sunscreens, sunscreen lotions, hair care products and other products, with a maximum addition amount of 15%. Drometrizole trisiloxane is a new sunscreen containing a silicone structure, which has particularly good formula compatibility. Its maximum absorption wavelength is at 303 nanometers and 343 nanometers, basically covering the entire ultraviolet band of 280-400 nanometers, and can more comprehensively reduce ultraviolet damage to the skin. At the same time, due to the special conjugated structure and molecular hydrogen bonds in its molecular structure, it has long-term photostability, thereby better improving the SPF value of the compound system.

[0003] At present, about the synthesis of drometrizole trisiloxane, the literature reported is very few, in patent WO2012 / 055063, use 2-(2-hydroxy-5-methylphenyl) benzotriazole as raw material, use potassium carbonate as acidifying agent, water / benzyl alcohol (or diphenyl ether, tetralin and other high boiling point solvents) as mixed solvent, under phase transfer catalyst conditions, etherification reaction with methyl allyl chloride synthesizes intermediate I, then intermediate I undergoes Claisen rearrangement reaction under conditions higher than 200 ° C to synthesize key intermediate II, then intermediate II undergoes hydrosilylation with heptamethyl trisiloxane under Custer catalyst conditions to synthesize drometrizole trisiloxane. However, this synthetic route adopts a two-phase reaction system, needs to add a large amount of phase transfer catalyst, and the reaction time needs more than 17h, the reaction efficiency is low, and the post-treatment also needs liquid separation and washing, and the operation is cumbersome, and step three adopts traditional hydrosilylation addition, uses platinum catalyst, and the triazole structure in the molecule can reduce the activity of the catalyst, resulting in low reaction efficiency and reduced conversion rate. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing drometrizole trisiloxane, aiming to save the reaction time for preparing drometrizole trisiloxane, improve the reaction efficiency for preparing drometrizole trisiloxane, and improve the yield of drometrizole trisiloxane.

[0005] To achieve the above object, the present invention provides a method for preparing drometrizole trisiloxane, comprising the following steps:

[0006]

[0007] (1) The concentrated solution of the compound of formula II is subjected to Claisen rearrangement reaction to obtain the compound of formula III;

[0008] (2) The compound of formula III is reacted with heptamethyltrisiloxane to obtain the compound of formula IV.

[0009] Preferably, before step (1), the method further comprises:

[0010]

[0011] (3) The compound of formula I is reacted with 3-chloro-2-methylpropene to obtain the compound of formula II.

[0012] Preferably, the step (3) comprises:

[0013] Add the compound of formula I, 3-chloro-2-methylpropene, a basic compound and a catalyst into the first solvent, and react at 75-90° C. for 4-8 hours to obtain an organic phase;

[0014] The organic phase is washed with water, and the washed organic phase is concentrated to obtain a concentrated solution of the compound of formula II.

[0015] Preferably, the first organic solvent is selected from one or more of toluene, xylene, and anisole;

[0016] The alkaline compound is selected from one or more of potassium hydroxide, sodium hydroxide and potassium phosphate;

[0017] The molar ratio of the compound of formula I, 3-chloro-2-methylpropene and the basic compound is 1:1-1.5:1.5-2.0.

[0018] Preferably, the catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride and water.

[0019] Preferably, the step (1) comprises:

[0020] The concentrated solution of the compound of formula II is subjected to a Claisen rearrangement reaction at 175-190°C for 5-9h, and after the reaction is completed, the temperature is lowered to 10-35°C;

[0021] The first crystallization solvent is added and the crystalline solid is filtered to provide the compound of formula III.

[0022] Preferably, the first crystallization solvent is selected from one or more of isopropanol, ethanol and methanol.

[0023] Preferably, the step (2) comprises:

[0024] Add the compound of formula III and chloroplatinic acid catalyst to the second solvent, and dropwise add heptamethyltrisiloxane;

[0025] The solution was heated to 70-90°C and reacted for 2-4 hours to obtain a reaction solution;

[0026] Sampling and mid-control, after the sampling and mid-control are qualified, the reaction solution is desolventized and concentrated to obtain a concentrated solution of the compound of formula IV;

[0027] Adding a second crystallization solvent to the concentrated solution of the compound of formula IV to precipitate the compound IV;

[0028] The precipitated compound IV is filtered, and the filtered compound IV is dried under reduced pressure at 50-85° C. to a constant weight to obtain a dry compound IV.

[0029] Preferably, the second organic solvent is selected from one or more of toluene, xylene, and anisole;

[0030] The chloroplatinic acid catalyst is 0.0001 to 0.01 equivalents of chloroplatinic acid relative to the isopropanol solution;

[0031] The molar ratio of the heptamethyltrisiloxane to the compound of formula III is 1.0-1.2:1.

[0032] Preferably, the second crystallization solvent is a single solvent or a mixed binary system solvent; the single solvent is selected from methanol, ethanol, isopropanol or water, and the mixed binary system solvent is a solvent composed of acetone and a single solvent, or a solvent composed of tetrahydrofuran and a single solvent.

[0033] The present invention provides a method for preparing drometrizole trisiloxane, comprising the following steps: a concentrated solution of a compound of formula II is subjected to a Claisen rearrangement reaction to obtain a compound of formula III; and the compound of formula III is reacted with heptamethyl trisiloxane to obtain a compound of formula IV. Thus, the present invention prepares the compound of formula III by a Claisen rearrangement reaction of a concentrated solution of a compound of formula II in the absence of a solvent, thereby saving the reaction time for preparing the compound of formula III, improving the reaction efficiency for preparing the compound of formula III, and improving the yield of preparing the compound of formula III, thereby saving the reaction time for preparing drometrizole trisiloxane, improving the reaction efficiency for preparing drometrizole trisiloxane, and improving the yield of preparing drometrizole trisiloxane. The Claisen rearrangement reaction of the present invention utilizes the characteristics of generating high-boiling point and low-melting point intermediates in the step of synthesizing the compound of formula II, adopts a solvent-free reaction, reduces the use of high-boiling point solvents, reduces the pressure of solvent recovery, improves the yield of the Claisen rearrangement reaction, and thereby improves the yield of preparing drometrizole trisiloxane. The preparation method of drometrizole trisiloxane of the present invention uses 2-(2-hydroxy-5-benzyl)benzotriazole as a starting material and is mainly obtained through three-step synthesis, wherein the total yield is about 75%, thereby reducing the production cost. The intermediates in each step of the route of the present invention are easy to purify, the purity of the final product is above 99.0%, and the quality is easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1is the HPLC spectrum of 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole of the present invention;

[0035] Figure 2 The figure is the HPLC spectrum of drometrizole trisiloxane of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0037] The present invention provides a method for preparing drometrizole trisiloxane, comprising the following steps:

[0038]

[0039] (1) The concentrated solution of the compound of formula II is subjected to Claisen rearrangement reaction to obtain the compound of formula III;

[0040] (2) The compound of formula III is reacted with heptamethyltrisiloxane to obtain the compound of formula IV.

[0041] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used in the preparation, and commercially available products known to those skilled in the art can be used.

[0042] In the present invention, step (1) may include:

[0043] The concentrated solution of the compound of formula II is subjected to a Claisen rearrangement reaction at 175-190°C for 5-9h, and after the reaction is completed, the temperature is lowered to 10-35°C;

[0044] The first crystallization solvent is added and the crystalline solid is filtered to provide the compound of formula III.

[0045] In the present invention, the step (2) comprises:

[0046] Add the compound of formula III and chloroplatinic acid catalyst to the second solvent, and dropwise add heptamethyltrisiloxane;

[0047] The solution was heated to 70-90°C and reacted for 2-4 hours to obtain a reaction solution;

[0048] Sampling and mid-control, after the sampling and mid-control are qualified, the reaction solution is desolventized and concentrated to obtain a concentrated solution of the compound of formula IV;

[0049] Adding a second crystallization solvent to the concentrated solution of the compound of formula IV to precipitate the compound IV;

[0050] The precipitated compound IV is filtered, and the filtered compound IV is dried under reduced pressure at 50-85° C. to a constant weight to obtain a dry compound IV.

[0051] In the present invention, the first crystallization solvent is selected from one or more of isopropanol, ethanol and methanol.

[0052] In the present invention, the second organic solvent is selected from one or more of toluene, xylene and anisole.

[0053] In the present invention, the chloroplatinic acid catalyst is 0.0001 to 0.01 equivalents of chloroplatinic acid relative to the isopropanol solution.

[0054] In the present invention, the molar ratio of heptamethyltrisiloxane to the compound of formula III is 1.0-1.2:1.

[0055] In the present invention, the second crystallization solvent is a single solvent or a mixed binary system solvent; the single solvent is selected from methanol, ethanol, isopropanol or water, the mixed binary system solvent can be a solvent composed of acetone and a single solvent, and the mixed binary system solvent can be a solvent composed of tetrahydrofuran and a single solvent.

[0056] In the present invention, before step (1), the method further includes:

[0057]

[0058] (3) The compound of formula I is reacted with 3-chloro-2-methylpropene to obtain the compound of formula II.

[0059] In the present invention, step (3) may include:

[0060] Add the compound of formula I, 3-chloro-2-methylpropene, a basic compound and a catalyst into the first solvent, and react at 75-90° C. for 4-8 hours to obtain an organic phase;

[0061] The organic phase is washed with water, and the washed organic phase is concentrated to obtain a concentrated solution of the compound of formula II.

[0062] In the present invention, the first organic solvent is selected from one or more of toluene, xylene, and anisole;

[0063] In the present invention, the alkaline compound is selected from one or more of potassium hydroxide, sodium hydroxide, and potassium phosphate;

[0064] In the present invention, the molar ratio of the compound of formula I, 3-chloro-2-methylpropene and the basic compound is 1:1-1.5:1.5-2.0.

[0065] In the present invention, the catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride and water.

[0066] The technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention.

[0067] Example 1

[0068] 1) 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), anisole (200 g) and 3-chloro-2-methylpropene (41.8 g, 0.46 mol) were added to a 500 mL three-necked flask, and an alkali solution prepared by NaOH (29.9 g, 0.747 mol) and water (40 g) was added dropwise; the mixture was stirred at 80° C. for 4 hours; after the reaction was completed, the organic phase was separated, washed and concentrated for standby use, with a purity of 90.8%.

[0069] 2) Add the concentrated 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 175°C, react for 7 hours, and after the intermediate control is qualified, cool down, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.4% and a two-step yield of 95%.

[0070] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (100 g, 0.358 mol), heptamethyltrisiloxane (83.6 g, 0.376 mol), anisole (200 g), and chloroplatinic acid (0.01 g, 0.02 mmol) obtained in the previous step to a 500 mL three-necked flask; heat to 75 ° C, react for 2 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified, add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 143.7 g of the product, yield: 80%; HPLC purity 99.7%.

[0071] Example 2

[0072] 1) Add 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), xylene (200 g) and 3-chloro-2-methylpropene (41.8 g, 0.46 mol) into a 500 mL three-necked flask, and dropwise add an alkaline solution prepared by KOH (49.4 g, 0.88 mol) and water (40 g); stir at 75° C. for 6 hours; after the reaction is completed, separate the organic phase, wash the organic phase, and concentrate it for standby use, with a purity of 93.4%.

[0073] 2) Add the concentrated solution of 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 185° C., react for 5 h, cool after the intermediate control is qualified, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.7% and a two-step yield of 70%.

[0074] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (80 g, 0.286 mol), heptamethyltrisiloxane (101.7 g, 0.457 mol), toluene (160 g), and chloroplatinic acid (0.01 g, 0.02 mmol) obtained in the previous step into a 500 mL three-necked flask; heat to 70°C, react for 3 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified. Add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 114.9 g of the product, with a yield of 80%; HPLC purity of 99.43%.

[0075] Example 3

[0076] 1) Add 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), toluene (200 g), 3-chloro-2-methylpropene (41.8 g, 0.46 mol), tetrabutylammonium chloride (5 g), and potassium phosphate (140.1 g, 0.66 mol) into a 500 mL three-necked flask; stir at 90° C. for 8 hours; after the reaction is completed, wash the organic phase and concentrate it for standby use, with a purity of 98.2%.

[0077] 2) Add the concentrated solution of 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 185° C., react for 6 h, cool after the intermediate control is qualified, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.0% and a two-step yield of 85%.

[0078] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (80 g, 0.286 mol), heptamethyltrisiloxane (101.7 g, 0.457 mol), toluene (160 g), and chloroplatinic acid (0.01 g, 0.02 mmol) obtained in the previous step into a 500 mL three-necked flask; heat to 75°C, react for 2 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified. Add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 106.3 g of the product, with a yield of 74%; HPLC purity 99.25%.

[0079] Example 4

[0080] 1) Add 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), toluene (200 g), 3-chloro-2-methylpropene (41.8 g, 0.46 mol), tetrabutylammonium bromide (6 g), and potassium hydroxide (49.4 g, 0.88 mol) into a 500 mL three-necked flask; stir at 85° C. for 7 hours; after the reaction is completed, wash the organic phase and concentrate it for standby use, with a purity of 94.6%.

[0081] 2) Add the concentrated 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 190° C., react for 5 h, cool after the intermediate control is qualified, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.3% and a two-step yield of 83%.

[0082] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (80 g, 0.286 mol), heptamethyltrisiloxane (101.7 g, 0.457 mol), toluene (160 g), and chloroplatinic acid (0.01 g, 0.02 mmol) obtained in the previous step into a 500 mL three-necked flask; heat to 80°C, react for 4 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified. Add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 106.3 g of the product, with a yield of 76%; HPLC purity of 99.18%.

[0083] Example 5

[0084] 1) Add 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), xylene (200 g), 3-chloro-2-methylpropene (41.8 g, 0.46 mol), tetrabutylammonium chloride (5 g), and potassium phosphate (140.1 g, 0.66 mol) into a 500 mL three-necked flask; stir at 80° C. for 5 hours; after the reaction is completed, wash the organic phase and concentrate it for standby use, with a purity of 96.8%.

[0085] 2) Add the concentrated solution of 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 180°C, react for 5 hours, cool after the intermediate control is qualified, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.6% and a two-step yield of 84%.

[0086] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (80 g, 0.286 mol), heptamethyltrisiloxane (101.7 g, 0.457 mol), xylene (200 g), and chloroplatinic acid (0.01 g, 0.02 mmol) obtained in the previous step into a 500 mL three-necked flask; heat to 85°C, react for 2 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified. Add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 106.3 g of the product, with a yield of 77%; HPLC purity 99.36%.

[0087] Example 6

[0088] 1) Add 2-(2-hydroxy-5-benzyl)benzotriazole (100 g, 0.44 mol), toluene (200 g), 3-chloro-2-methylpropene (41.8 g, 0.46 mol) into a 500 mL three-necked flask, and dropwise add an alkaline solution prepared by KOH (49.4 g, 0.88 mol) and water (40 g); stir at 78° C. for 6 hours; after the reaction is completed, wash the organic phase and concentrate it for standby use, with a purity of 98.2%.

[0089] 2) Add the concentrated 2-{5-methyl-2-[(2-methyl-2-propene-1-yl)oxy]phenyl}-2H-benzotriazole prepared in the previous step into a 500 mL three-necked flask, heat to 188° C., react for 5 h, cool after the intermediate control is qualified, add isopropanol to crystallize and obtain 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole with a purity of 99.2% and a two-step yield of 85%.

[0090] 3) Add 2-(2'-hydroxy-3'-methallyl-5'-methylphenyl)benzotriazole (80 g, 0.286 mol), heptamethyltrisiloxane (101.7 g, 0.457 mol), toluene (160 g), and chloroplatinic acid (0.01 g, 0.02 mmol) prepared in the previous step into a 500 mL three-necked flask; heat to 90°C, react for 3 h, take a sample and concentrate to remove the solvent after the intermediate control is qualified. Add a mixed solution of isopropanol: methanol: water, crystallize and filter to obtain 106.3 g of the product, with a yield of 79%; HPLC purity 99.06%.

[0091] Therefore, the present invention prepares the compound of formula III by using the concentrated solution of the compound of formula II through a Claisen rearrangement reaction in the absence of a solvent, thereby saving the reaction time for preparing the compound of formula III, improving the reaction efficiency for preparing the compound of formula III, and improving the yield of preparing the compound of formula III, thereby saving the reaction time for preparing drometrizole trisiloxane, improving the reaction efficiency for preparing drometrizole trisiloxane, and improving the yield of preparing drometrizole trisiloxane.

[0092] The Claisen rearrangement reaction of the present invention utilizes the characteristics of the step of synthesizing the compound of formula II to generate high-boiling point and low-melting point intermediates, adopts a solvent-free reaction, reduces the use of high-boiling point solvents, reduces the pressure of solvent recovery, improves the yield of the Claisen rearrangement reaction, and further improves the yield of preparing drometrizole trisiloxane.

[0093] The preparation method of drometrizole trisiloxane of the present invention uses 2-(2-hydroxy-5-benzyl)benzotriazole as a starting material and is mainly obtained through three-step synthesis, wherein the total yield is about 75%, thereby reducing the production cost. The intermediates in each step of the route of the present invention are easy to purify, the purity of the final product is above 99.0%, and the quality is easy to control.

[0094] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing drometrizole trisiloxane, comprising the following steps: (1) The concentrated solution of the compound of formula II is subjected to Claisen rearrangement reaction to obtain the compound of formula III; (2) The compound of formula III is reacted with heptamethyltrisiloxane to obtain the compound of formula IV.

2. The method for preparing drometrizole trisiloxane according to claim 1, wherein: Before step (1), the method further includes: (3) The compound of formula I is reacted with 3-chloro-2-methylpropene to obtain the compound of formula II.

3. The method for preparing drometrizole trisiloxane according to claim 2, characterized in that: The step (3) comprises: Add the compound of formula I, 3-chloro-2-methylpropene, a basic compound and a catalyst into the first solvent, and react at 75-90° C. for 4-8 hours to obtain an organic phase; The organic phase is washed with water, and the washed organic phase is concentrated to obtain a concentrated solution of the compound of formula II.

4. The method for preparing drometrizole trisiloxane according to claim 3, characterized in that: The first organic solvent is selected from one or more of toluene, xylene, and anisole; The alkaline compound is selected from one or more of potassium hydroxide, sodium hydroxide and potassium phosphate; The molar ratio of the compound of formula I, 3-chloro-2-methylpropene and the basic compound is 1:1-1.5:1.5-2.

0.

5. The method for preparing drometrizole trisiloxane according to claim 3, characterized in that: The catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride and water.

6. The method for preparing drometrizole trisiloxane according to any one of claims 1 to 5, characterized in that: The step (1) comprises: The concentrated solution of the compound of formula II is subjected to a Claisen rearrangement reaction at 175-190°C for 5-9h, and after the reaction is completed, the temperature is lowered to 10-35°C; The first crystallization solvent is added and the crystalline solid is filtered to provide the compound of formula III.

7. The method for preparing drometrizole trisiloxane according to claim 6, characterized in that: The first crystallization solvent is selected from one or more of isopropanol, ethanol and methanol.

8. The method for preparing drometrizole trisiloxane according to claim 6, characterized in that: The step (2) comprises: Add the compound of formula III and chloroplatinic acid catalyst to the second solvent, and dropwise add heptamethyltrisiloxane; The solution was heated to 70-90°C and reacted for 2-4 hours to obtain a reaction solution; Sampling and mid-control, after the sampling and mid-control are qualified, the reaction solution is desolventized and concentrated to obtain a concentrated solution of the compound of formula IV; Adding a second crystallization solvent to the concentrated solution of the compound of formula IV to precipitate the compound IV; The precipitated compound IV is filtered, and the filtered compound IV is dried under reduced pressure at 50-85° C. to a constant weight to obtain a dry compound IV.

9. The method for preparing drometrizole trisiloxane according to claim 8, characterized in that: The second organic solvent is selected from one or more of toluene, xylene, and anisole; The chloroplatinic acid catalyst is 0.0001 to 0.01 equivalents of chloroplatinic acid relative to the isopropanol solution; The molar ratio of the heptamethyltrisiloxane to the compound of formula III is 1.0-1.2:

1.

10. The method for preparing drometrizole trisiloxane according to claim 8, characterized in that: The second crystallization solvent is a single solvent or a mixed binary system solvent; the single solvent is selected from methanol, ethanol, isopropanol or water, and the mixed binary system solvent is a solvent composed of acetone and a single solvent, or a solvent composed of tetrahydrofuran and a single solvent.

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