Method for continuously producing 2, 5-dihydroxy-1, 4-dithiane

Abstract

The invention relates to a method for continuously producing 2, 5-dihydroxy-1, 4-dithiane, which comprises the following steps: pre-cooling a chloroacetaldehyde solution and a sodium hydrosulfide solution, mixing in a pipeline mixer, reacting in a reaction kettle, continuously producing, and post-treating to obtain a finished product, the molar yield is more than 95%, the content is more than 98%, the melting point is 140-145 DEG C, and the appearance is white granular crystal. And the requirements of downstream products can be better met. The method has the characteristics of high efficiency, continuous production, stable process, high product quality, high yield, low cost, environmental friendliness and convenience in industrial popularization.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a method for continuously producing 2,5-dihydroxy-1,4-dithiane. Background Art

[0002] 2,5-Dihydroxy-1,4-dithiane is a chemical substance with the appearance of white to light yellow crystalline powder. CAS registration number 40018-26-6, molecular formula C4H8O2S2, molecular weight 152.24, mainly used as pharmaceutical intermediates such as lamivudine and emtricitabine, as a synthetic raw material for biological scaffold thiazolidinone compounds, and can also be used as a fragrance regulator.

[0003] The preparation of 2,5-dihydroxy-1,4-dithiane usually adopts cyclization reaction of chloroacetaldehyde and sodium hydrosulfide in water system (Formula I). ​​Because industrial chloroacetaldehyde usually contains 10% aqueous solution of hydrogen chloride, which is strongly acidic, and sodium hydrosulfide is a strong alkaline substance, the contact reaction process between the two releases heat strongly, which is easy to cause overheating, resulting in aggravation of reverse reaction, increase of reaction impurities, and reduced yield. In production, the reaction is controlled by dripping. The yield in industrial production is about 90%. The reaction takes more than 6 hours to complete. After the reaction is completed, it needs to be kept warm for about 2 hours, and the material needs to be centrifuged for about 2 hours, that is, the single batch production time is long, which takes more than 12 hours, and there are long equipment occupancy time and low production capacity.

[0004]

[0005] German patent DE 3149653 C2 discloses a method for preparing 2,5-dihydroxy-1,4-dithiane, using a monochloroacetaldehyde aqueous solution at a pH of 0.5-1.5 to react with sodium hydrosulfide while maintaining the pH of the translation mixture at 7-9, but the yield is only 80%.

[0006] Chinese patent 201811455127.7 describes a method for synthesizing 2,5-dihydroxy-1,4-dithiane, which involves adjusting the pH of chloroacetaldehyde, preparing a sodium hydrosulfide solution, dripping a portion of the sodium hydrosulfide solution, dripping reaction, and a aging step. The operation is cumbersome, the stability is poor, the error between batch operations is large, the yield is only about 90%, and the content of 2,5-dihydroxy-1,4-dithiane in the finished product is only about 97%.

[0007] Chinese patent application 202110650172.3 describes a method for preparing 2,5-dihydroxy-1,4-dithiane, which involves adding chloroacetaldehyde prepared in the application to an aqueous sodium hydrosulfide solution and then reacting. The method requires the use of chloroacetaldehyde prepared in the application to obtain a higher yield. In the preparation process of chloroacetaldehyde, dichloromethane, vinyl acetate, tetrabutylammonium bromide, and chlorine are first added to obtain 1,2-dichloroethanol acetate, and then even fuming sulfuric acid is used for thermal decomposition to obtain chloroacetaldehyde. Therefore, the preparation method has a high risk factor, cumbersome operation, and high instability.

[0008] Therefore, there is a need in the art for a method for preparing 2,5-dihydroxy-1,4-dithiane with high yield, high purity of reaction products, simple operation and short production cycle. Summary of the invention

[0009] The purpose of the present invention is to provide a method for continuously producing 2,5-dihydroxy-1,4-dithiane with high yield, short reaction time, high production efficiency and simple operation.

[0010] In a first aspect of the present invention, the present invention provides a method for continuously producing 2,5-dihydroxy-1,4-dithiane, comprising the following steps:

[0011] s1, providing a second chloroacetaldehyde solution and a sodium hydrosulfide solution;

[0012] s2, precooling the second chloroacetaldehyde solution and the sodium hydrosulfide solution respectively;

[0013] s3, pumping the second chloroacetaldehyde aqueous solution and sodium hydrosulfide solution precooled in step s2 into a pipeline mixer for mixing and preliminary reaction, wherein the molar ratio of the raw material sodium hydrosulfide to chloroacetaldehyde is controlled to be 1-2:1 during the pumping process, and the temperature of the pipeline mixer is controlled to be 0-20°C;

[0014] s4. The mixed materials in the pipeline enter into an insulated reactor for continuous reaction, while controlling the pH value between 8 and 11 and the reactor temperature between 5 and 30° C. to obtain the 2,5-dihydroxy-1,4-dithiane.

[0015] In another preferred embodiment, in step s1, the mass content of chloroacetaldehyde in the second chloroacetaldehyde aqueous solution is 6-8.5%, preferably 7.5-8.5%, for example 8%.

[0016] In another preferred example, in step s1, the pH of the second aqueous chloroacetaldehyde solution is between 2 and 5, preferably between 3 and 5, for example, 3, 3.5, 4, 4.5, 5.

[0017] In another preferred embodiment, in step s1, the second chloroacetaldehyde aqueous solution is prepared by the following method, comprising the steps of providing a first chloroacetaldehyde aqueous solution, and adjusting the pH to 2 to 5 using a first alkaline reagent to obtain a second chloroacetaldehyde aqueous solution.

[0018] In another preferred embodiment, the first chloroacetaldehyde aqueous solution is prepared from chlorine gas and vinyl chloride.

[0019] In another preferred embodiment, the first chloroacetaldehyde aqueous solution is synthesized from a production line.

[0020] In another preferred embodiment, the mass content of chloroacetaldehyde in the first chloroacetaldehyde aqueous solution is 7% to 11%, preferably 9% to 10%.

[0021] In another preferred embodiment, the first alkaline agent is selected from the following group: sodium carbonate or its solution, sodium bicarbonate or its solution, potassium carbonate or its solution, potassium bicarbonate or its solution, sodium hydroxide or its solution, potassium hydroxide or its solution, or a combination thereof.

[0022] In another preferred embodiment, the weight concentration of sodium bicarbonate in the sodium bicarbonate solution is 10 wt %.

[0023] In another preferred embodiment, in the step s1, the sodium hydrosulfide solution is a commercially available industrial liquid.

[0024] In another preferred embodiment, in step s1, the mass concentration of sodium hydrosulfide in the sodium hydrosulfide solution is 25-50%, preferably 30%-45%, preferably 32%, 38% or 43%, and more preferably 32%.

[0025] In another preferred embodiment, in step s2, the second chloroacetaldehyde aqueous solution and the sodium hydrosulfide solution are precooled to the same or different precooling temperatures, respectively.

[0026] In another preferred embodiment, in step s2, the second chloroacetaldehyde aqueous solution is precooled to -5 to 10°C, preferably 0 to 5°C.

[0027] In another preferred embodiment, in step s2, the sodium hydrosulfide solution is precooled to -20 to 5°C, preferably -10 to 0°C.

[0028] In another preferred embodiment, in step s3, the second chloroacetaldehyde aqueous solution and sodium hydrosulfide solution precooled in step s2 are pumped into the pipeline mixer through a metering pump.

[0029] In another preferred embodiment, in step s3, during the process of pumping into the pipeline mixer, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1 to 1.8:1, more preferably 1.2 to 1.5:1, for example 1.3:1.

[0030] In another preferred embodiment, in step s3, the pipeline mixer is cooled in advance by a jacket.

[0031] In another preferred embodiment, in step s3, the pipeline mixer is pre-cooled to 0-15°C, more preferably 5-15°C, such as 10-15°C.

[0032] In another preferred embodiment, the step s3 is performed at a temperature below 20°C, preferably 0-15°C, more preferably 5-15°C, for example 10-15°C.

[0033] In another preferred embodiment, in step s3, the time for the mixing and preliminary reaction is 0.5 to 10 minutes, preferably 1 to 5 minutes, and more preferably 1 to 2 minutes.

[0034] In another preferred embodiment, in step s3, the precooled second chloroacetaldehyde aqueous solution and sodium hydrosulfide solution stay in the pipeline mixer for 0.5 to 10 minutes, preferably 1 to 5 minutes, and more preferably 1 to 2 minutes.

[0035] In another preferred embodiment, the step s3 comprises: after precooling is completed, the second chloroacetaldehyde aqueous solution and the sodium hydrosulfide solution precooled in step s2 are respectively continuously pumped into a pipeline mixer by a metering pump for mixing and preliminary reaction, and the pipeline mixer is preliminarily cooled to 0-15° C. by a jacket; when the metering pump continuously pumps the material, the molar ratio of the raw material sodium hydrosulfide to chloroacetaldehyde is controlled to be 1.2-1.5:1.

[0036] In another preferred embodiment, in step s4, the reactor is an insulated reactor, and the temperature is controlled by a jacket.

[0037] In another preferred embodiment, in step s4, the temperature of the reactor is controlled at 10-25°C.

[0038] In another preferred embodiment, in step s4, the pH is controlled between 8.5 and 10.5, for example, 9, 9.5, 10, or 10.5.

[0039] In another preferred embodiment, in step s4, the reactor continuously adds the second alkaline reagent by interlocking the pH meter in the reactor with the second alkaline reagent, thereby controlling the pH value.

[0040] In another preferred embodiment, the second alkaline agent is selected from the following group: sodium carbonate or its solution, sodium bicarbonate or its solution, potassium carbonate or its solution, potassium bicarbonate or its solution, sodium hydroxide or its solution, potassium hydroxide or its solution, or a combination thereof.

[0041] In another preferred embodiment, in the sodium bicarbonate solution, the weight concentration of sodium bicarbonate is 10wt%.

[0042] In another preferred embodiment, in step s4, the residence time of the material in the reactor is 2-4 hours, for example, 3 hours.

[0043] In another preferred embodiment, the step s4 comprises: the materials after pipeline mixing enter into an insulated reactor, the temperature of the materials is controlled to 10-25°C by means of jacket temperature control, and the second alkaline reagent is continuously added by means of an interlocking method of a pH meter in the reactor and a second alkaline reagent to maintain the pH value at 8-10, and the residence time of the materials in the reactor is controlled at 2-4 hours, followed by separation, washing and drying post-treatment steps to obtain 2,5-dihydroxy-1,4-dithiane.

[0044] In another preferred embodiment, the step s4 also includes a post-processing step.

[0045] In another preferred embodiment, the step s4 further comprises: continuously extracting the reaction mixture in the reactor into a centrifuge for solid-liquid separation to obtain a wet product of 2,5-dihydroxy-1,4-dithiane; and then acid washing, water washing and drying to obtain a finished product.

[0046] In another preferred embodiment, the method comprises the following steps:

[0047] (a) neutralizing the first chloroacetaldehyde solution in a neutralization reactor to obtain a second chloroacetaldehyde solution;

[0048] (b) adding the second chloroacetaldehyde solution into the first precooler, and adding the sodium hydrosulfide solution into the second precooler, and precooling them respectively;

[0049] (c) pumping the second chloroacetaldehyde aqueous solution in the first precooler into a pipeline mixer through a metering pump, and pumping the sodium hydrosulfide solution in the second precooler into the pipeline mixer through a metering pump, mixing and preliminarily reacting in the pipeline mixer, wherein the molar ratio of the raw material sodium hydrosulfide to chloroacetaldehyde is controlled to be 1 to 2:1 during the pumping process;

[0050] (d) The mixture in the pipeline mixer is put into a reactor for reaction, while controlling the pH value between 8 and 11. After staying for 2 to 4 hours, the mixture is continuously taken out into a centrifuge for solid-liquid separation, and then post-processed to obtain 2,5-dihydroxy-1,4-dithiane.

[0051] In another preferred embodiment, the method comprises the following steps:

[0052] S1. Adjust the pH of chloroacetaldehyde

[0053] A chloroacetaldehyde aqueous solution is prepared by using chlorine and vinyl chloride, and the pH is adjusted to 2-5 by using sodium bicarbonate to obtain a neutralized solution of chloroacetaldehyde; the mass content of the obtained chloroacetaldehyde is 6-8%;

[0054] S2. Material precooling

[0055] Precool the industrial 32% sodium hydrosulfide solution and the neutralized solution of chloroacetaldehyde obtained in step S1, respectively, wherein the sodium hydrosulfide solution is precooled to -10°C to 0°C, and the chloroacetaldehyde aqueous solution is precooled to 0 to 5°C;

[0056] S3, pipeline pre-reaction

[0057] After precooling, the two materials are continuously pumped into the pipeline mixer by metering pumps for mixing and preliminary reaction. The pipeline mixer is cooled to 0-15°C by a jacket in advance. When the metering pump continuously pumps the materials, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1.2-1.5:1;

[0058] S4. Material reaction and extraction

[0059] The materials after pipeline mixing enter the heat preservation reactor, and the temperature of the materials is controlled to 10-25°C by means of jacket temperature control. At the same time, sodium bicarbonate solution is continuously added by means of a pH meter in the reactor and 10% sodium bicarbonate interlocking method to maintain the pH value at 8-10. The residence time of the materials in the reactor is controlled to be 2-4 hours, and then they are continuously extracted to the centrifuge for solid-liquid separation to obtain 2,5-dihydroxy-1,4-dithiane wet product;

[0060] S5. Post-processing and product drying output

[0061] The wet product is washed with acid and water to obtain 2,5-dihydroxy-1,4-dithiane, and then dried in a double cone vacuum dryer below 60°C to obtain a finished product. The yield is above 95%, the content is above 98%, and the melting point is between 140 and 145°C, which can better meet the use of downstream products.

[0062] In a second aspect of the present invention, a device is provided, the device comprising: a first precooler, a second precooler, a first metering pump, a second metering pump, a pipeline mixer, and a reaction kettle;

[0063] The first precooler is connected to the pipeline mixer, the second precooler is connected to the pipeline mixer, the pipeline mixer is connected to the reactor, the first metering pump pumps the material in the first precooler into the pipeline mixer, and the second metering pump pumps the material in the second precooler into the pipeline mixer.

[0064] Furthermore, the device is configured to carry out the method for continuously producing 2,5-dihydroxy-1,4-dithiane as described in the first aspect of the present invention.

[0065] In another preferred example, the device further comprises a neutralization reactor, wherein the neutralization reactor is connected to the first precooler.

[0066] In another preferred embodiment, the device further comprises a centrifuge, wherein the reactor is connected to the centrifuge.

[0067] In another preferred embodiment, the first precooler, the first precooler, the pipeline mixer, and the reactor each independently further include a jacket and a temperature control device.

[0068] It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, they will not be described one by one here. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 A process flow diagram for the production of 2,5-dihydroxy-1,4-dithiane is shown. DETAILED DESCRIPTION

[0070] After extensive and in-depth research, the inventors have discovered for the first time a method for preparing 2,5-dihydroxy-1,4-dithiane by connecting a pipeline mixer and a reactor in series.

[0071] Through the strong heat exchange effect of the pipeline mixer and the control of the temperature of the pre-reaction and secondary reaction kettles, and continuous extraction, the existing crystals in the kettle can increase the crystal size and fluidity of the material, eliminating the reaction and aging crystal growing time in the traditional process, so that the material residence time is controlled to be less than 5 hours, greatly improving the equipment capacity and reducing the operating workload. The obtained 2,5-dihydroxy-1,4-dithiane has a high yield (over 95%), high purity, short melting range, and better product quality.

[0072] The present invention has been completed on this basis.

[0073] the term

[0074] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0075] As used herein, the terms "comprise", "include", and "contain" are used interchangeably and include not only closed definitions, but also semi-closed and open definitions. In other words, the terms include "consisting of", "consisting essentially of".

[0076] As used herein, when used in reference to a specific recited numerical value, the term "about" means that the value may vary by no more than 1% from the recited value. For example, as used herein, the expression "about 100" includes all values ​​between 99 and 101 (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

[0077] Preparation method of the present invention

[0078] The present invention provides a method for continuously producing 2,5-dihydroxy-1,4-dithiane, which comprises the following steps:

[0079] S1. Adjust the pH of chloroacetaldehyde

[0080] A chloroacetaldehyde aqueous solution is prepared by using chlorine and vinyl chloride, and the pH is adjusted to 2-5 by using sodium bicarbonate to obtain a neutralized solution of chloroacetaldehyde; the mass content of the obtained chloroacetaldehyde is 6-8%;

[0081] S2. Material precooling

[0082] Precool the industrial 32% sodium hydrosulfide solution and the neutralized solution of chloroacetaldehyde obtained in step S1, respectively, wherein the sodium hydrosulfide solution is precooled to -10°C to 0°C, and the chloroacetaldehyde aqueous solution is precooled to 0 to 5°C;

[0083] S3, pipeline pre-reaction

[0084] After precooling, the two materials are continuously pumped into the pipeline mixer by metering pumps for mixing and preliminary reaction. The pipeline mixer is cooled to 0-15°C by a jacket in advance. When the metering pump continuously pumps the materials, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1.2-1.5:1;

[0085] S4. Material reaction and extraction

[0086] The materials after pipeline mixing enter the heat preservation reactor, and the temperature of the materials is controlled to 10-25°C by means of jacket temperature control. At the same time, sodium bicarbonate solution is continuously added by means of a pH meter in the reactor and 10% sodium bicarbonate interlocking method to maintain the pH value at 8-10. The residence time of the materials in the reactor is controlled to be 2-4 hours, and then they are continuously extracted to the centrifuge for solid-liquid separation to obtain 2,5-dihydroxy-1,4-dithiane wet product;

[0087] S5. Post-processing and product drying output

[0088] The wet product is washed with acid and water to obtain 2,5-dihydroxy-1,4-dithiane, and then dried in a double cone vacuum dryer below 60°C to obtain a finished product. The yield is above 95%, the content is above 98%, and the melting point is between 140 and 145°C, which can better meet the use of downstream products.

[0089] The technical difficulties of the present invention are as follows:

[0090] 1. The overall operation mode is different. The intermittent reaction in the traditional process is replaced by continuous reaction, which improves intelligence and reduces the operating workload;

[0091] 2. Key control parameters:

[0092] ① A continuous reaction is carried out by connecting a pipeline reactor and a tank reactor in series. The temperature of the pipeline reactor is controlled at 0-10°C, and the temperature of the tank reactor is controlled at 10-25°C.

[0093] ② The residence time is 2 to 4 hours;

[0094] ③ In the reaction ratio, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1.2-1.5:1.

[0095] The present invention precools the material and then pumps it into a pipeline mixer for mixing and preliminary reaction, and then directly enters the reactor for reaction, thereby achieving continuous production, improving production efficiency, effectively controlling the heat release of the reaction, shortening the processing time of dropping raw materials and aging crystals, and improving production capacity.

[0096] Preferably, the sodium hydrosulfide solution is a commercially available industrial liquid with a mass concentration of 32%, 38% or 43%, preferably a 32% index solution.

[0097] Preferably, chloroacetaldehyde is synthesized on a production line with a mass concentration of 7% to 11%, preferably 9% to 10%.

[0098] Preferably, when the raw material is continuously metered and pumped, the molar ratio of sodium hydrosulfide to chloroacetaldehyde is 1.2 to 1.5:1, preferably 1.3:1.

[0099] Preferably, the residence time of the material in the pipeline mixer is 1 to 5 minutes, preferably 1 to 2 minutes.

[0100] Preferably, the temperature of the pipeline mixer is controlled at 0-15°C, preferably 10-15°C.

[0101] Preferably, the material after the reaction in the pipeline mixer enters the heat preservation reactor, and the material temperature is controlled to 10-25°C by means of jacket temperature control. At the same time, sodium bicarbonate solution is continuously added by means of the pH meter in the reactor and the 10% sodium bicarbonate interlocking method to maintain the pH value at 8-10. After the residence time of the reactor material is controlled at 2-4 hours, it is continuously taken out to the centrifuge for solid-liquid separation. The temperature is preferably 15-20°C, the pH value is preferably 9, and the material residence time is preferably 3 hours.

[0102] The 2,5-dihydroxy-1,4-dithiane obtained at last is white granular crystals. The melting range of the obtained 2,5-dihydroxy-1,4-dithiane is short, between 135°C and 147°C, preferably between 136°C and 146°C, more preferably between 140°C and 146°C, more preferably between 140°C and 145°C, more preferably between 142°C and 145°C. The product yield is above 92%, for example, above 93%, above 94%, above 95%, above 95.5%. The content of 2,5-dihydroxy-1,4-dithiane in the product is above 97%, for example, above 97.5%, above 98%, above 98.5%.

[0103] The beneficial effects of the present invention are:

[0104] 1. The present invention prepares 2,5-dihydroxy-1,4-dithiane by connecting a pipeline mixer and a reactor in series. The temperature of the pre-reaction is controlled by the strong heat exchange effect of the pipeline mixer. The temperature of the secondary reactor is controllable and continuously extracted. The crystals in the reactor can increase the crystal size and fluidity of the material, eliminating the reaction and aging crystal growing time in the traditional process. Therefore, the process of the present invention can greatly shorten the reaction time and improve the equipment capacity.

[0105] 2. By adopting the continuous production process provided by the present invention, taking the pipeline mixer and a reactor connected in series as an example, the material residence time is controlled to be 3 hours, which can achieve the effect of 12 hours of intermittent reaction in traditional production, and the production capacity is increased by 4 times.

[0106] 3. The product yield of the method of the present invention is high (can exceed 95%), high purity and short melting range.

[0107] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods for the unrecorded specific conditions in the following examples are usually based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are weight percentages and weight parts.

[0108] Example 1

[0109] A method for continuously producing 2,5-dihydroxy-1,4-dithiane, comprising: a pipeline mixer and a reactor connected in series, such as Figure 1 As shown, the method comprises the following steps:

[0110] ① Adjust the pH of chloroacetaldehyde

[0111] A chloroacetaldehyde aqueous solution prepared by chlorine and vinyl chloride, wherein the chloroacetaldehyde content is 9.5%, is adjusted to pH 3.5 by sodium bicarbonate to obtain a chloroacetaldehyde neutralized solution having a chloroacetaldehyde content of 6-8%.

[0112] ②Material precooling

[0113] The industrial 32% sodium hydrosulfide solution and the neutralized solution of chloroacetaldehyde obtained in the above step ① are precooled separately, wherein the sodium hydrosulfide solution is precooled to -10°C to 0°C, and the chloroacetaldehyde aqueous solution is precooled to 0 to 5°C.

[0114] ③Pipeline pre-reaction

[0115] After precooling, the two materials are continuously pumped into the pipeline mixer by metering pumps for mixing and preliminary reaction. The pipeline mixer is pre-cooled to 0-15°C by a jacket. When the metering pump continuously pumps the materials, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1.2-1.5:1.

[0116] ④ The materials after pipeline mixing enter the insulation reactor, and the temperature of the materials is controlled at 20°C by means of jacket temperature control. At the same time, sodium bicarbonate solution is continuously added through the interlocking method of the pH meter in the reactor and 10% sodium bicarbonate, while maintaining the pH value at 9.0. The residence time of the materials in the reactor is controlled at 3 hours, and then they are continuously extracted to the centrifuge for solid-liquid separation to obtain 2,5-dihydroxy-1,4-dithiane wet product.

[0117] ⑤ The wet product is washed with acid and water to obtain 2,5-dihydroxy-1,4-dithiane, and then dried in a double cone vacuum dryer below 65°C to obtain a finished product with a yield of 95.67%, a content of 98.5%, a melting range of 141.0-143.5°C, and an appearance of white granular crystals.

[0118] Embodiment 2:

[0119] A method for continuously producing 2,5-dihydroxy-1,4-dithiane is prepared by connecting a pipeline mixer and a reactor in series, and the method comprises the following steps:

[0120] ① Adjust the pH of chloroacetaldehyde

[0121] A neutralized solution of chloroacetaldehyde prepared by chlorine and vinyl chloride, wherein the chloroacetaldehyde content is 10%, is adjusted to pH 3.5 by sodium bicarbonate to obtain a chloroacetaldehyde aqueous solution having a mass content of 8.5%.

[0122] ②Material precooling

[0123] The industrial 32% sodium hydrosulfide solution and the neutralized solution of chloroacetaldehyde obtained in the above step ① are precooled separately, wherein the sodium hydrosulfide solution is precooled to -10°C to 0°C, and the chloroacetaldehyde aqueous solution is precooled to 0 to 5°C.

[0124] ③Pipeline pre-reaction

[0125] After precooling, the two materials are continuously pumped into the pipeline mixer by metering pumps for mixing and preliminary reaction. The pipeline mixer is pre-cooled to 0-15°C by a jacket. When the metering pump continuously pumps the materials, the molar ratio of the raw materials sodium hydrosulfide and chloroacetaldehyde is controlled to be 1.2-1.5:1.

[0126] ④ The materials after pipeline mixing enter the insulation reactor, and the temperature of the materials is controlled at 18°C ​​by means of jacket temperature control. At the same time, sodium bicarbonate solution is continuously added through the interlocking method of the pH meter in the reactor and 10% sodium bicarbonate, while maintaining the pH value at 9.5. The residence time of the materials in the reactor is controlled at 3 hours, and then they are continuously extracted to the centrifuge for solid-liquid separation to obtain 2,5-dihydroxy-1,4-dithiane wet product.

[0127] ⑤ The wet product is washed with acid and water to obtain 2,5-dihydroxy-1,4-dithiane, and then dried in a double cone vacuum dryer below 65°C to obtain a finished product with a yield of 96.67%, a content of 98.2%, a melting range of 142.0-143.5°C, and an appearance of white granular crystals.

[0128] Comparative Example 1

[0129] The same as Example 1, except that: Comparative Example 1 is a traditional intermittent reaction mode.

[0130] 1) Add 330 kg of 9.50% chloroacetaldehyde solution to the preparation kettle, cool to below 10°C, slowly add 68.1 kg of sodium bicarbonate solid, adjust pH to 2-5, and keep the neutralized solution at 0-10°C for standby use.

[0131] 2) Add 30 kg of water to the reactor, start stirring, and maintain the temperature in the system at 15-20°C. At the same time, add 105 kg of 32% sodium hydrosulfide solution through the control of the high-level tank and the flowmeter. After the sodium hydrosulfide solution is added for 5 minutes, the chloroacetaldehyde neutralization solution obtained in step 1) is added at the same time, and the temperature in the system is maintained at 15-20°C. Due to the intense exothermic reaction, the sodium hydrosulfide solution is added for about 10 hours, and the chloroacetaldehyde neutralization solution is added for about 8 hours.

[0132] 3) After the dropwise addition is completed, the reaction solution is aged at 15-20°C for 2 hours. The reaction solution is filtered, the filter cake is rinsed with water until the filter cake pH test paper is neutral, then soaked and washed with 0.3% hydrochloric acid, and finally washed with water until the filtrate pH test paper is neutral, the wet filter cake is dried at 65°C, and the dryness loss is detected to be ≤0.5%, then the drying can be stopped to obtain 270kg of white powdery 2,5-dihydroxy-1,4-dithiane, with a yield of 88.82%, a content of 97%, and a melting range of 136.2-145.3°C.

[0133] According to the applicant's experience in intermittent reactions, it is not possible to achieve complete dripping within 2 hours while stably controlling the temperature under this batch. If the temperature is guaranteed to be controlled, the dripping cannot be completed within 2 hours. If the dripping is forced to be completed within 2 hours, the temperature cannot be controlled.

[0134] The results of the 2,5-dihydroxy-1,4-dithiane products obtained in different embodiments are compared and shown in Table 1 below.

[0135] Table 1: Comparison of the results of the present invention and the conventional batch reaction to produce 2,5-dihydroxy-1,4-dithiane

[0136] Serial number Comparison item content Traditional intermittent Example 1 1 Processing time 12 hours 3 hours 2 Yield 88.82％ 95.67％ 3 Appearance of dithiane Off-white powder White granular crystals 4 Dithiane content 97％ 98.5％ 5 Melting Range 136.2～145.3℃ 141.0～143.5℃

[0137] In summary, the present invention can solve the problems of low yield of existing 2,5-dihydroxy-1,4-dithiane, long equipment occupancy time and small production capacity. Compared with the prior art, the present invention can increase the product yield from 90% to more than 95%, and at the same time reduce the intermittent processing time from 12 hours to about 3 hours, shorten the product melting range from 135-150°C to 140-145°C, shorten the melting range, increase the product content, improve the product quality, and greatly improve the rate of equipment output of materials, which is conducive to reducing product costs and improving product competitiveness.

[0138] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as reference individually. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for continuously producing 2,5-dihydroxy-1,4-dithiane, comprising the following steps: s1, providing a second chloroacetaldehyde solution and a sodium hydrosulfide solution; s2, precooling the second chloroacetaldehyde solution and the sodium hydrosulfide solution respectively; s3, pumping the second chloroacetaldehyde aqueous solution and sodium hydrosulfide solution precooled in step s2 into a pipeline mixer for mixing and preliminary reaction, wherein the molar ratio of the raw material sodium hydrosulfide to chloroacetaldehyde is controlled to be 1-2:1 during the pumping process, and the temperature of the pipeline mixer is controlled to be 0-20°C; s4. The mixed materials in the pipeline enter into an insulated reactor for continuous reaction, while the pH is controlled between 8 and 11 and the temperature of the reactor is controlled between 5 and 30° C. to obtain the 2,5-dihydroxy-1,4-dithiane.

2. The method according to claim 1, characterized in that In the step s1, the mass content of chloroacetaldehyde in the second chloroacetaldehyde aqueous solution is 6 to 8.5%, preferably 7.5 to 8.5%; the pH of the second chloroacetaldehyde aqueous solution is between 2 and 5, preferably between 3 and 5; In the step s1, the mass concentration of sodium hydrosulfide in the sodium hydrosulfide solution is 25% to 50%, preferably 30% to 45%.

3. The method according to claim 1, characterized in that In the step s2, the second chloroacetaldehyde aqueous solution is precooled to -5 to 10°C, preferably 0 to 5°C; the sodium hydrosulfide solution is precooled to -20 to 5°C, preferably -10 to 0°C.

4. The method according to claim 1, characterized in that In the step s3, during the process of pumping into the pipeline mixer, the molar ratio of the raw materials sodium hydrosulfide to chloroacetaldehyde is controlled to be 1 to 1.8:1, more preferably 1.2 to 1.5:

1.

5. The method according to claim 1, characterized in that In step s3, the precooled second chloroacetaldehyde aqueous solution and sodium hydrosulfide solution stay in the pipeline mixer for 0.5 to 10 minutes, preferably 1 to 5 minutes, and more preferably 1 to 2 minutes.

6. The method according to claim 1, characterized in that In step s4, the temperature of the reactor is controlled at 10-25° C.; and the pH is controlled between 8.5 and 10.

5.

7. The method according to claim 1, characterized in that The residence time of the materials in the reactor is 2-4 hours.

8. The method according to claim 1, characterized in that The step s4 comprises: the materials after pipeline mixing enter into an insulated reactor, the temperature of the materials is controlled to 10-25°C by means of jacket temperature control, and the second alkaline reagent is continuously added by means of a pH meter in the reactor and an interlocking method with the second alkaline reagent to maintain the pH value at 8-10, the residence time of the materials in the reactor is controlled to be 2-4 hours, and then the post-processing steps of separation, washing and drying are performed to obtain 2,5-dihydroxy-1,4-dithiane.

9. The method according to claim 1, characterized in that The method comprises the following steps: (a) neutralizing the first chloroacetaldehyde solution in a neutralization reactor to obtain a second chloroacetaldehyde solution; (b) adding the second chloroacetaldehyde solution into the first precooler, and adding the sodium hydrosulfide solution into the second precooler, and precooling them respectively; (c) pumping the second chloroacetaldehyde aqueous solution in the first precooler into a pipeline mixer through a metering pump, and pumping the sodium hydrosulfide solution in the second precooler into the pipeline mixer through a metering pump, mixing and preliminarily reacting in the pipeline mixer, wherein the molar ratio of the raw material sodium hydrosulfide to chloroacetaldehyde is controlled to be 1 to 2:1 during the pumping process; (d) The mixture in the pipeline mixer enters the reactor for reaction while controlling the pH value between 8 and 11. After staying for 2 to 4 hours, the mixture is continuously taken out to the centrifuge for solid-liquid separation, and then 2,5-dihydroxy-1,4-dithiane is obtained through post-treatment.

10. A device, characterized in that: The device comprises: a first precooler, a second precooler, a first metering pump, a second metering pump, a pipeline mixer, and a reaction kettle; The first precooler is connected to the pipeline mixer, the second precooler is connected to the pipeline mixer, the pipeline mixer is connected to the reactor, the first metering pump pumps the material in the first precooler into the pipeline mixer, and the second metering pump pumps the material in the second precooler into the pipeline mixer. Furthermore, the device is configured to carry out the method for continuously producing 2,5-dihydroxy-1,4-dithiane as claimed in claim 1.

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