A process for the synthesis of allyl isothiocyanate

Abstract

The application relates to the technical field of organic synthesis, in particular to a synthesis process of allyl isothiocyanate, which comprises the following steps: adding a catalyst into a thiocyanate solution, stirring and dissolving to obtain a reaction bottom solution; adding allyl chloroformate into the reaction bottom solution drop by drop and carrying out heat preservation reaction; after the heat preservation is completed, the temperature is raised to 45-50 DEG C in a programmed heating mode, the reaction is completed, and heat preservation and standing are carried out for 1 h after the reaction is completed; after the standing is completed, lower salt water is separated, upper oily crude product is collected, and the oily crude product is washed and then transferred into a settling tank for settling; the settled crude product is subjected to negative pressure distillation to obtain allyl isothiocyanate finished product. The extremely flammable and explosive allyl chloride is abandoned, allyl chloroformate is used as a key reactant, the fire and explosion risks in the production, storage and transportation processes are greatly reduced from the source, the dependence on special explosion-proof facilities is reduced, and the safety investment is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a process for synthesizing allyl isothiocyanate. Background Technology

[0002] Allyl isothiocyanate, also known as synthetic mustard oil, is an important intermediate in organic synthesis. Allyl isothiocyanate is a colorless to pale yellow transparent oily liquid, which gradually darkens in color during storage. It is highly irritating, non-optically active, and widely used in pharmaceuticals, dyes, mineral processing, and food additives.

[0003] Chinese invention patent with publication number CN111533672A discloses a method for preparing allyl isothiocyanate, which uses allyl chloride as one of the starting materials to synthesize allyl isothiocyanate in the presence of a solvent.

[0004] While the aforementioned technologies reduce wastewater generation to some extent, they pose significant safety hazards. Specifically, allyl chloride is a highly flammable liquid with a flash point of only around -32°C. Its vapor can form an explosive mixture when mixed with air, which imposes extremely stringent safety requirements on the production, storage, and transportation processes. This leads to a substantial increase in investment in safety facilities during production, raising production costs and limiting the industrial-scale application of this technology. Summary of the Invention

[0005] In view of the deficiencies mentioned in the background art, the present invention provides a process for synthesizing allyl isothiocyanate, which aims to reduce the risk factor of raw materials and safely and efficiently prepare high-quality allyl isothiocyanate.

[0006] To achieve the above objectives, the synthesis process of the present invention includes the following steps: S1. Thiocyanate is prepared into a thiocyanate solution with a mass concentration of 40% to 50% using deionized water. 0.5% to 1% of the mass of the catalyst is added to the thiocyanate solution and stirred to dissolve, thus obtaining the reaction base solution. S2. Add allyl chloroformate dropwise to the reaction substrate, with a molar ratio of thiocyanate to allyl chloroformate of 1.05 to 1.15:1, and keep the reaction at a constant temperature. S3. After the heat preservation is completed, the temperature is raised to 45-50℃ using a programmed heating method. After the reaction is completed, the temperature is kept at that temperature and allowed to stand. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash it, and transfer it to a settling tank for settling. The settled crude product is then subjected to negative pressure distillation to obtain allyl isothiocyanate product.

[0007] As a further improvement of the present invention, in step S3, the step of heating to 45-50°C by programmed heating is as follows: first, the temperature is raised to 40-45°C and kept at that temperature for 2 hours; then the temperature is raised to 45-50°C and kept at that temperature for 3 hours.

[0008] As a further improvement of the present invention, the catalyst is a quaternary ammonium salt phase transfer catalyst.

[0009] As a further improvement of the present invention, the quaternary ammonium salt phase transfer catalyst is one or more of hexadecyltrimethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, and benzyltriethylammonium chloride.

[0010] As a further improvement of the present invention, the thiocyanate is one of sodium thiocyanate, ammonium thiocyanate, and potassium thiocyanate.

[0011] As a further improvement of the present invention, the dropping time of the allyl chloroformate is controlled at 3 to 5 hours.

[0012] As a further improvement of the present invention, in step S2, when adding allyl chloroformate, the temperature of the reaction base liquid is controlled at 25-30°C.

[0013] After adopting the above technical solution, the beneficial effects of the present invention are: This invention eliminates the use of highly flammable and explosive allyl chloride and instead uses allyl chloroformate as the key reactant, which greatly reduces the risk of fire and explosion during production, storage and transportation, reduces reliance on special explosion-proof facilities and significantly lowers safety investment. Attached Figure Description

[0014] To clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0015] Figure 1 The infrared spectrum is shown in Example 1. Detailed Implementation

[0016] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0017] I. Preparation of the reaction base liquid Select a suitable thiocyanate as the reaction raw material and use deionized water as the solvent to prepare a thiocyanate solution with a mass concentration of 40%–50%. The thiocyanate is sodium thiocyanate, but ammonium thiocyanate or potassium thiocyanate can also be used.

[0018] Add a quaternary ammonium salt phase transfer catalyst to the prepared thiocyanate solution, the amount of which is 0.5% to 1% of the thiocyanate mass. Stir continuously until the quaternary ammonium salt phase transfer catalyst is completely dissolved. Filter to remove insoluble matter to obtain the reaction base solution. The quaternary ammonium salt phase transfer catalyst is tetrabutylammonium bromide, but hexadecyltrimethylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, or benzyltriethylammonium chloride can also be used, or any two or more of the above catalysts can be combined.

[0019] II. Dropping Reaction The reaction substrate obtained in step S1 is placed in a reaction vessel, and the temperature of the reaction system is controlled at 25–30°C. At this temperature, allyl chloroformate is added dropwise to the reaction substrate through a constant pressure funnel over a period of 3–5 hours. The molar ratio of thiocyanate to allyl chloroformate is controlled at 1.05–1.15:1, with a slight excess of thiocyanate to ensure complete reaction of allyl chloroformate.

[0020] After the allyl chloroformate was added, the reaction was kept at this temperature for 2 hours. After the reaction was completed, the reaction system was first heated to 40-45°C and kept at this temperature for 2 hours; then the temperature was further increased to 45-50°C and kept at this temperature for 3 hours.

[0021] After the reaction is complete, stop heating and let it stand for 1 hour to allow the oil and water phases in the reaction system to fully separate, preparing for subsequent separation steps.

[0022] III. Separation and Finished Product Preparation After settling, the reaction system separated into two layers: a lower brine phase and an upper oily crude product. The lower brine phase was removed, and the collected oily crude product was washed with an equal volume of deionized water to remove trace amounts of brine and soluble impurities. The washed crude product was then transferred to a settling tank for 8–12 hours to remove any remaining water and solid impurities.

[0023] After sedimentation, the settled crude product is transferred to a distillation apparatus for negative pressure distillation. The vacuum degree is controlled at 0.08-0.09 MPa and the temperature is controlled at 40-60℃ to distill off low-boiling impurities and obtain crude product stock solution.

[0024] The distillation system was restored to atmospheric pressure, and the temperature was further increased to 60–90 °C under nitrogen inert protection to further distill the crude product. After refluxing the crude product for 0.5 h, the reflux ratio was controlled at 1–2:1 (i.e., 1–2 portions of the condensate were returned to the distillation system for further purification, and 1 portion was collected as the allyl isothiocyanate product). After distillation for 1.5–2 h, the distillate was collected as the allyl isothiocyanate product. During the distillation process, the byproduct allyl thiocyanate underwent complete thermal isomerization rearrangement to form allyl isothiocyanate.

[0025] Example 1 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0026] S1. Add 100g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 40%. Add 0.5g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.05:1, add 141.6g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time to 3h, maintain the reaction temperature at 25℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 40℃ and keep it at that temperature for 2h, then raise the temperature to 45℃ and keep it at that temperature for 3h, and then let it stand for 1h after the reaction is complete. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with 0.5 times the amount of water, and transfer to a settling tank for 12 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 1:1, and distilled for 2 h to obtain 96.7 g of allyl isothiocyanate product with a purity of 99.04%. The synthesis conversion rate in this experiment was 91.85%, and the distillation yield was 90.54%.

[0027] Figure 1 The infrared spectrum is that of allyl isothiocyanate.

[0028] Example 2 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0029] S1. Add 122.7g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 45%. Add 0.61g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.1:1, add 165.8g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time at 3.5h, maintain the reaction temperature at 25℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 40℃ and keep it at that temperature for 2h, then raise the temperature to 45℃ and keep it at that temperature for 3h, and then let it stand for 1h after the reaction is complete. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with 0.5 times the amount of water, and transfer to a settling tank for 12 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 1.25:1, and after distillation for 2 h, 115.2 g of allyl isothiocyanate was obtained with a purity of 99.34%. The synthesis conversion rate in this experiment was 94%, and the distillation yield was 90.92%.

[0030] Example 3 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0031] S1. Add 122.7g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 45%. Add 0.91g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.1:1, add 165.8g of allyl chloroformate dropwise to the reaction base solution. The dropwise addition time is controlled at 3h, the reaction temperature is maintained at about 28℃, and the reaction is kept at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 43℃ and keep it at that temperature for 2h, then raise the temperature to 48℃ and keep it at that temperature for 3h, and then let it stand for 1h after the reaction is complete. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with 0.5 times the amount of water, and transfer to a settling tank for 12 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 1.5:1, and after distillation for 2 h, 125.5 g of allyl isothiocyanate was obtained with a purity of 99.4%. The synthesis conversion rate in this experiment was 94.23%, and the distillation yield was 90.52%.

[0032] Example 4 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0033] S1. Add 150g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 50%. Add 1.5g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.15:1, add 193.9g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time to 3h, maintain the reaction temperature at 30℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 45℃ and keep it at that temperature for 2h, then raise the temperature to 50℃ and keep it at that temperature for 3h, and after the reaction is complete, keep it at that temperature and let it stand for 1h. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with 0.5 times the amount of water, and transfer to a settling tank for 12 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 1.75:1, and the distillation was continued for 2.5 h to obtain 135.6 g of allyl isothiocyanate product with a purity of 99.52%. The synthesis conversion rate in this experiment was 93.77%, and the distillation yield was 90.8%.

[0034] Example 5 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0035] S1. Add 150g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 50%. Add 1.0g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.15:1, add 193.9g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time at 4h, maintain the reaction temperature at 30℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 45℃ and keep it at that temperature for 2h, then raise the temperature to 50℃ and keep it at that temperature for 3h, and after the reaction is complete, keep it at that temperature and let it stand for 1h. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with an equal amount of water, and transfer to a settling tank for 12 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was subjected to distillation under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 2:1, and distillation was continued for 2.5 h to obtain 135.6 g of allyl isothiocyanate product with a purity of 99.55%. The synthesis conversion rate in this experiment was 93.59%, and the distillation yield was 91%.

[0036] Example 6 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0037] S1. Add 150g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 50%. Add 1.13g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.15:1, add 193.9g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time at 4h, maintain the reaction temperature at 30℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 45℃ and keep it at that temperature for 2h, then raise the temperature to 50℃ and keep it at that temperature for 3h, and after the reaction is complete, keep it at that temperature and let it stand for 1h. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with an equal amount of water, and transfer to a settling tank for 14 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 2:1, and distilled for 2 h to obtain 136.1 g of allyl isothiocyanate product with a purity of 99.58%. The synthesis conversion rate in this experiment was 94.07%, and the distillation yield was 90.84%.

[0038] Example 7 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0039] S1. Add 150g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 50%. Add 1.13g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.12:1, add 199.3g of allyl chloroformate dropwise to the reaction base solution. The dropwise addition time is controlled at 4h, the reaction temperature is maintained at 30℃, and the reaction is kept at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 45℃ and keep it at that temperature for 2h, then raise the temperature to 50℃ and keep it at that temperature for 3h, and after the reaction is complete, keep it at that temperature and let it stand for 1h. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with an equal amount of water, and transfer to a settling tank for 14 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 2:1, and distilled for 2.6 h to obtain 139.8 g of allyl isothiocyanate product with a purity of 99.57%. The synthesis conversion rate in this experiment was 94.26%, and the distillation yield was 90.6%.

[0040] Example 8 This embodiment provides a process for synthesizing allyl isothiocyanate. The specific preparation steps and technical details are as follows.

[0041] S1. Add 150g of sodium thiocyanate to 150g of deionized water, stir to dissolve, and prepare a sodium thiocyanate solution with a mass concentration of 50%. Add 1.13g of tetrabutylammonium bromide to the sodium thiocyanate solution, stir to dissolve, filter out the insoluble matter, and obtain the reaction base solution. S2. According to the molar ratio of sodium thiocyanate to allyl chloroformate of 1.12:1, add 199.3g of allyl chloroformate dropwise to the reaction base solution, control the dropwise addition time to 5h, maintain the reaction temperature at 30℃, and keep the reaction at the temperature for 2h after the dropwise addition is completed. After S3 and 2h of heat preservation, first raise the temperature to 45℃ and keep it at that temperature for 2h, then raise the temperature to 50℃ and keep it at that temperature for 3h, and then let it stand for 1h after the reaction is complete. S4. After settling, separate the lower brine layer, collect the upper oily crude product, wash with an equal amount of water, and transfer to a settling tank for 14 hours. The settled crude product is then subjected to negative pressure distillation to remove low-boiling impurities and obtain the crude product stock solution. S5. The crude product stock solution was distilled under normal pressure. After reflux for 0.5 h, the reflux ratio was controlled at 2:1, and distilled for 2.6 h to obtain 140.2 g of allyl isothiocyanate product with a purity of 99.61%. The synthesis conversion rate in this experiment was 90.4%, and the distillation yield was 90.65%.

[0042] The results from Examples 1-8 show that the synthesis process of the present invention can stably prepare allyl isothiocyanate with a conversion rate of around 90%, a distillation yield of over 90%, and a purity of ≥99.2%. Among these, Example 8, with a raw material ratio of 1.12:1, a catalyst addition of 0.75%, and a reflux ratio of 2:1, achieved the highest yield and purity, making it the optimal implementation method. Furthermore, the examples using ammonium (potassium) thiocyanate, when repeated under the same conditions, showed little difference in results and also met the requirements for industrial production.

[0043] The embodiments described above are not exhaustive and do not limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A process for synthesizing allyl isothiocyanate, characterized in that, Includes the following steps: S1. Thiocyanate is prepared into a thiocyanate solution with a mass concentration of 40% to 50% using deionized water. 0.5% to 1% of the mass of the catalyst is added to the thiocyanate solution and stirred to dissolve, thus obtaining the reaction base solution. S2. Add allyl chloroformate dropwise to the reaction substrate, with a molar ratio of thiocyanate to allyl chloroformate of 1.05 to 1.15:1, and maintain the temperature for reaction. S3. After the heat preservation is completed, the temperature is raised to 45-50℃ using a programmed heating method. After the reaction is completed, the temperature is kept at that temperature and allowed to stand. S4. After settling, separate the lower brine layer and collect the upper oily crude product. After washing, transfer it to a settling tank for settling. The settled crude product is then subjected to negative pressure distillation to obtain allyl isothiocyanate product.

2. The synthesis process of allyl isothiocyanate according to claim 1, characterized in that, In step S3, the process of heating to 45-50°C using a programmed temperature increase method is as follows: first, heat to 40-45°C and hold for 2 hours; then heat to 45-50°C and hold for 3 hours.

3. The synthesis process of allyl isothiocyanate according to claim 1, characterized in that: The catalyst is a quaternary ammonium salt phase transfer catalyst.

4. The synthesis process of allyl isothiocyanate according to claim 3, characterized in that: The quaternary ammonium salt phase transfer catalyst is one or more of hexadecyltrimethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, and benzyltriethylammonium chloride.

5. The synthesis process of allyl isothiocyanate according to claim 1, characterized in that: The thiocyanate is one of sodium thiocyanate, ammonium thiocyanate, and potassium thiocyanate.

6. The synthesis process of allyl isothiocyanate according to claim 1, characterized in that: The dripping time of the allyl chloroformate is controlled at 3 to 5 hours.

7. The synthesis process of allyl isothiocyanate according to claim 1, characterized in that, In step S2, when adding allyl chloroformate, the temperature of the reaction substrate is controlled at 25–30°C.

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