Optimized synthesis method of bis (pentamethylene) thiuram tetrasulfide

Abstract

The invention discloses an optimized synthesis method of bis (pentamethylene) thiuram tetrasulfide, which comprises the following steps: adding sulfur and piperidine into a reaction system in batches by utilizing the solubility difference of sulfur in carbon disulfide and water, so that condensation reaction is carried out step by step, the conversion rate of sulfur is increased, and the reaction system is controlled to keep constant temperature; and slowly dropwise adding hydrogen peroxide to carry out oxidation reaction to obtain the rubber vulcanization accelerator DPTT. According to the method, the condensation reaction process is split, so that the residual quantity of the intermediate product piperidine dithiocarbamate (PDC) and free sulfur is greatly reduced, and the content of bis (pentamethylene) thiuram tetrasulfide and the content of bis (pentamethylene) thiuram hexasulfide (DPTH) in the product are relatively stable. The total yield is stabilized at 96% or above, the initial melting point is stabilized at 112-114 DEG C, the PDC in the mother liquor is less than or equal to 6%, the free sulfur is less than or equal to 3%, the COD in the mother liquor is less than or equal to 3000 mg / L, the production operation is convenient and efficient, and the method has important industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of rubber additive synthesis technology, specifically relating to an optimized synthesis method for preparing tetrasulfide bispentamethylene thiuram by adding sulfur and piperidine in batches. Background Technology

[0002] DPTT tetrasulfide (dipentamethylene thiuram) is an important organic polysulfide compound widely used in the rubber industry, pesticide production, and pharmaceutical synthesis. It is particularly effective as a high-efficiency rubber additive in the production of natural rubber, diene synthetic rubber, and butyl rubber. DPTT decomposes upon heating to produce free sulfur, exhibiting high safety at operating temperatures during vulcanization. It also exhibits high crosslinking density, low reversion tendency, and the resulting vulcanized rubber demonstrates good heat resistance and aging resistance. Traditional DPTT synthesis methods typically involve a low-temperature condensation reaction of hexahydropyridine with carbon disulfide in water. Upon heating, a diluted oxidant is added to oxidize the condensation intermediate and crosslink sulfur. The dispersibility of sulfur powder in the reaction system significantly affects its conversion rate. However, sulfur powder is difficult to dissolve in water, which greatly reduces its dispersibility in water, resulting in the following problems with the target product: (1) High residual amount of intermediate product piperidine dithiocarbamate (salt), i.e. PDC intermediate, and low product yield: Due to the poor dispersibility of sulfur in the reaction solvent system, the conversion rate is low, the condensation reaction intermediate PDC is relatively excessive, and the sulfur cannot be completely crosslinked and oxidized into the target product, resulting in a high residual amount of PDC in the mother liquor and a reduced product yield; (2) Low proportion of DPTT in the finished product: The low conversion rate of sulfur powder leads to uncontrollable generation of hexasulfide product (DPTH), affecting the purity of the target product DPTT, and the product's initial melting point fluctuates greatly, reducing the stability of rubber vulcanization; (3) Increased wastewater treatment cost: The low conversion rate of sulfur leads to poor reaction selectivity, and the excessive side reactions result in excessively high COD in the mother liquor, increasing the subsequent wastewater treatment cost. Studies have shown that due to the uncontrollable length of polysulfide bonds and the competition of oxidation / vulcanization pathways, this synthesis reaction will inevitably generate a mixture of DPTT and DPTH. In the mixture, DPTT provides the primary vulcanization activity, while DPTH enhances the crosslinking density. However, to ensure basic vulcanization activity, the DPTT content still needs to be greater than 60%. Furthermore, when sulfur has poor dispersibility in the solvent system, a large amount of unreacted free sulfur will remain in the final product. Therefore, the current synthesis process needs to be optimized. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention discloses an optimized synthesis method for bis(pentamethylene)thiuram tetrasulfide. By adding sulfur and piperidine in batches, the dispersibility of sulfur in the solvent system is increased, and the condensation reaction is carried out stepwise, thereby improving the conversion rate of sulfur. This results in a significant reduction in PDC residue and free sulfur content, relative stability of DPTT and DPTH content, and a significant improvement in product yield and purity. The method is simple and efficient to operate.

[0004] The technical solution of the present invention is as follows: An optimized synthetic method for bis(pentamethylene)thiuram tetrasulfide includes the following steps: (1) Add the surfactant to deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add carbon disulfide to solution A to obtain mixed solvent system B; (3) Add a certain amount of sulfur powder to the mixture B and stir thoroughly until dissolved to obtain reaction system C; (4) Control the reaction system to maintain a certain temperature, slowly add a certain amount of piperidine to the reaction system C, and keep it at the temperature for a period of time to obtain condensate D; (5) Add the remaining amount of sulfur powder required for the reaction to the condensation solution D, and stir to make it evenly dispersed to obtain the reaction system E; (6) Control the reaction system to maintain a certain temperature, slowly add the remaining amount of piperidine required for the reaction to the reaction system E, and keep it at the temperature for a period of time to obtain the condensate F; (7) Heat the condensation solution F to a suitable temperature range, slowly add 27% hydrogen peroxide to the condensation solution F, continue heating and stirring to generate a light yellow precipitate, keep it warm for a period of time, and then wash and dry the precipitate to obtain rubber vulcanization accelerator DPTT.

[0005] Furthermore, in step (1), the surfactant is any one of sodium n-butylsulfonate, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate.

[0006] Furthermore, in step (1), the concentration of the surfactant in solution A is 0.55~0.85 g / L.

[0007] Furthermore, in step (2), the mass ratio of carbon disulfide to deionized water is 0.2~0.24:1.

[0008] Furthermore, in step (3), the mass ratio of sulfur powder to carbon disulfide is 0.45~0.6:1.

[0009] Furthermore, in step (4), the temperature is maintained at 20~30℃, the mass ratio of piperidine to carbon disulfide is 0.6~0.8:1, and the holding time is 0.5~1 h.

[0010] Furthermore, in step (5), the mass ratio of sulfur powder to carbon disulfide is 0.16~0.32:1.

[0011] Furthermore, in step (6), the temperature is maintained at 20~30℃, the mass ratio of piperidine to carbon disulfide is 0.2~0.4:1, and the holding time is 1~2 h.

[0012] Furthermore, in step (7), the temperature range is 40~50℃, the molar ratio of hydrogen peroxide to piperidine is 0.7~0.9 powder:1, and the heat preservation time is 1~2 h.

[0013] Beneficial effects: Compared with the prior art, the innovative points of this invention are: 1. Enhancing the dispersibility of sulfur in solvent systems: Sulfur powder is poorly soluble in water but readily soluble in carbon disulfide. However, at 25°C, 100 g of carbon disulfide can only dissolve 50.4 g of sulfur. Utilizing this physical property of carbon disulfide, a portion of sulfur is first added to a mixed solvent system of carbon disulfide and water. At this point, the sulfur dissolves directly in the carbon disulfide, greatly improving its dispersibility in the solvent system and facilitating the subsequent condensation reaction. Since the first batch of added sulfur has nearly saturated the carbon disulfide with dissolved sulfur, a small portion of the second batch of added sulfur continues to dissolve in the carbon disulfide, while most is dispersed in the water containing the added surfactant, allowing the condensation reaction to continue.

[0014] 2. Step-by-step condensation reaction: In traditional processes, the condensation reaction involves directly condensing all the sulfur (dispersed in water) and piperidine with carbon disulfide. This incomplete reaction results in a low sulfur conversion rate. This invention breaks down the condensation reaction into two steps. First, approximately half the amount of sulfur (dissolved in carbon disulfide) and piperidine react with all the carbon disulfide. This first step of condensation reaction is more thorough and significantly improves the conversion rate of sulfur and piperidine. Then, the remaining piperidine and the sulfur dispersed in water react with carbon disulfide. This second step of condensation reaction is comparable to the traditional process, but less complete than the first step.

[0015] Experimental results show that increasing the dispersibility and resolution-condensation reaction of sulfur is closely related to the yield and DPTH content of the final product. The DPTT vulcanization accelerator prepared by this method has a DPTT content of more than 85% in the final product and a total product yield of more than 96%. It effectively reduces the content of PDC (≤6%) and free sulfur (≤3%) in the mother liquor, reduces the occurrence of side reactions, and reduces the COD of the mother liquor (≤3000 mg / L). Detailed Implementation

[0016] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following specific embodiments are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention.

[0017] Example 1 (1) Add 1.3 g of sodium n-butylsulfonate to 2 L of deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add 400 g of carbon disulfide to solution A to obtain mixed solvent system B; (3) Add 180 g of sulfur powder to the mixture B and stir thoroughly until dissolved to obtain reaction system C; (4) Control the reaction system to be kept at 22℃, slowly add 240 g piperidine to the reaction system C, and keep it at the temperature for 0.5 h to obtain condensate D; (5) Add 126.8 g of sulfur powder to the condensation solution D and stir to disperse it evenly to obtain reaction system E; (6) Control the reaction system to be kept at 22℃, slowly add 168 g piperidine to the reaction system E, and keep it at the temperature for 1 h to obtain condensate F; (7) The condensation solution F is heated to 40°C. 422.6 g of 27% hydrogen peroxide is slowly added dropwise to the condensation solution F. The mixture is heated and stirred to generate a light yellow precipitate. After keeping it warm for 1 h, the precipitate is washed and dried to obtain rubber vulcanization accelerator DPTT.

[0018] Example 2 (1) Add 1.5 g of sodium dodecylbenzenesulfonate to 2 L of deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add 440 g of carbon disulfide to solution A to obtain mixed solvent system B; (3) Add 230 g of sulfur powder to the mixture B and stir thoroughly until dissolved to obtain reaction system C; (4) Control the reaction system to be kept at 25℃, slowly add 306 g piperidine to the reaction system C, and keep it at the temperature for 0.5 h to obtain condensate D; (5) Add 107.5 g of sulfur powder to the condensation solution D and stir to disperse it evenly to obtain reaction system E; (6) The reaction system was kept at 25°C. 134.3 g of piperidine was slowly added dropwise to the reaction system E and kept at this temperature for 1 h to obtain the condensate F. (7) The condensation solution F is heated to 45°C, and 521 g of 27% hydrogen peroxide is slowly added dropwise to the condensation solution F. The mixture is heated and stirred to generate a light yellow precipitate. After keeping it warm for 1.5 h, the precipitate is washed and dried to obtain rubber vulcanization accelerator DPTT.

[0019] Example 3 (1) Add 1.7 g of sodium dodecyl sulfate to 2 L of deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add 480 g of carbon disulfide to solution A to obtain mixed solvent system B; (3) Add 288 g of sulfur powder to the mixture B and stir thoroughly until dissolved to obtain reaction system C; (4) Control the reaction system to be kept at 28℃, slowly add 375.6 g piperidine to the reaction system C, and keep it at the temperature for 1 h to obtain condensate D; (5) Add 80 g of sulfur powder to the condensation solution D and stir to disperse it evenly to obtain reaction system E; (6) Control the reaction system to be kept at 28℃, slowly add 104.4 g piperidine to the reaction system E, and keep it at the temperature for 2 h to obtain condensate F; (7) The condensation solution F is heated to 48°C. 638.9 g of 27% hydrogen peroxide is slowly added dropwise to the condensation solution F. The mixture is heated and stirred to generate a light yellow precipitate. After keeping it warm for 2 h, the precipitate is washed and dried to obtain rubber vulcanization accelerator DPTT.

[0020] Comparative Example 1 (1) Add 1.5 g of sodium n-butylsulfonate to 2 L of deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add 455 g piperidine to solution A and mix it evenly with water to obtain solution B; (3) Add 342 g of sulfur powder to the mixture B according to the molar ratio of sulfur to piperidine of 2:1 and disperse it evenly to obtain reaction slurry C; (4) Control the reaction slurry to be kept at 25°C, slowly add 455 g of carbon disulfide to the reaction slurry C, and keep it at 25°C for 1 h to obtain condensate D; (5) Heat the condensation solution D to 45°C, slowly add 472 g of 27% hydrogen peroxide dropwise to the condensation solution D, continue heating and stirring for 1.5 h to generate a light yellow precipitate, and obtain the rubber vulcanization accelerator DPTT after washing and drying the precipitate.

[0021] The results of liquid chromatography, melting point determination, and COD detection of the samples prepared in each embodiment and comparative example are shown in the table below: project DPTT (%) DPTH (%) Total yield (%) PDC (%) Free sulfur (%) Initial melting point (°C) Mother liquor COD (mg / L) Example 1 90.5±0.5 6.2±0.5 97.5±1.0 3.1±0.1 0.8±0.1 113.6 1280±120 Example 2 87.7±0.5 7.5±0.5 97.2±1.0 3.8±0.1 1.6±0.1 113.1 1916±120 Example 3 85.4±0.5 10.1±0.5 96.8±1.0 5.2±0.1 2.4±0.1 112.8 2540±120 Comparative Example 1 81.2±0.5 3.5±0.5 91.1±1.0 16.5±0.1 6.2±0.1 111.9 10850±120 .

[0022] This invention utilizes the difference in solubility of sulfur in carbon disulfide and water. Sulfur and piperidine are added to the reaction system in batches to increase the dispersibility of sulfur in the mixed solvent system of water and carbon disulfide, allowing the condensation reaction to proceed in steps, thus improving the conversion rate of sulfur. The reaction system is kept at a constant temperature, and hydrogen peroxide is then slowly added dropwise for oxidation, yielding the rubber vulcanization accelerator DPTT. This method, by separating the condensation reaction process, significantly reduces the residual amount of the intermediate product piperidine dithiocarbamate (PDC) and free sulfur, and maintains relative stability in the content of tetrasulfide bis(pentamethylene thiuram) and hexasulfide bis(pentamethylene thiuram) (DPTH) in the product. The product obtained by this method has a DPTH content controlled below 11%, a free sulfur content ≤3%, an overall yield consistently above 96%, an initial melting point consistently between 112-114℃, and PDC ≤6% in the mother liquor. The production operation is convenient and efficient, possessing significant industrial application value.

[0023] It should be noted that the above embodiments are only used to illustrate the technical solutions and core innovations of the present invention, and are not intended to limit the present invention. For those skilled in the art, several improvements, substitutions, and optimizations can be made without departing from the principles and spirit of the present invention. Any reasonable changes based on the technical concept of the present invention fall within the protection scope of the present invention.

Claims

1. A method for synthesizing tetrasulfide bis(pentamethylenethiuram), characterized in that, The synthesis method includes the following steps: (1) Add the surfactant to deionized water and stir thoroughly until completely dissolved to obtain solution A; (2) Add carbon disulfide to solution A to obtain mixed solvent system B; (3) Add a certain amount of sulfur powder to the mixture B and stir thoroughly until dissolved to obtain reaction system C; (4) Control the reaction system to maintain a certain temperature, slowly add a certain amount of piperidine to the reaction system C, and keep it at the temperature for a period of time to obtain condensate D; (5) Add the remaining amount of sulfur powder required for the reaction to the condensation solution D, and stir to make it evenly dispersed to obtain the reaction system E; (6) Control the reaction system to maintain a certain temperature, slowly add the remaining amount of piperidine required for the reaction to the reaction system E, and keep it at the temperature for a period of time to obtain the condensate F; (7) Heat the condensation solution F to a suitable temperature range, slowly add hydrogen peroxide of a certain concentration to the condensation solution F, continue heating and stirring to generate a light yellow precipitate, keep it warm for a period of time, and then wash and dry the precipitate to obtain rubber vulcanization accelerator DPTT.

2. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (1), the surfactant is any one of sodium n-butylsulfonate, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate.

3. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (1), the concentration of the surfactant in solution A is 0.55~0.85 g / L.

4. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (2), the mass ratio of carbon disulfide to deionized water is 0.2~0.24:

1.

5. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (3), the mass ratio of sulfur powder to carbon disulfide is 0.45 to 0.6:

1.

6. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (4), the temperature is maintained at 20~30℃, the mass ratio of piperidine to carbon disulfide is 0.6~0.8:1, and the holding time is 0.5~1h.

7. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (5), the mass ratio of sulfur powder to carbon disulfide is 0.16 to 0.32:

1.

8. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (6), the temperature is maintained at 20~30℃, the mass ratio of piperidine to carbon disulfide is 0.2~0.4:1, and the holding time is 1~2h.

9. The method for synthesizing tetrasulfide bis(pentamethylenethiuram) according to claim 1, characterized in that, In step (7), the temperature range is 40~50℃, the molar ratio of hydrogen peroxide to piperidine is 0.7~0.9:1, and the heat preservation time is 1~2 h.