Process for the preparation of a rubber vulcanizing agent, 1,1'-dithio-biscaprolactam

Abstract

This invention discloses a method for preparing the rubber vulcanizing agent 1,1'-dithiocaprolactam. Cyclohexane, caprolactam, and a polymerization inhibitor are mixed uniformly, and then disulfide dichloride and dipyridine are added alternately to the mixture. Finally, the reactants are filtered, and the cyclohexane mother liquor is recovered. The filtered solid is neutralized with sodium bicarbonate aqueous solution, and the final pH is controlled at 7.9–8.3. The 1,1'-dithiocaprolactam prepared by this method significantly reduces the polymerization of caprolactam and the generation of side reactions, resulting in a significantly improved product yield. The cyclohexane mother liquor can be directly reused. The product is a white powder with a heating loss ≤0.2%, melting point ≥135.0℃, yield ≥99.3%, and purity ≥99.5%. Furthermore, this method can be carried out on conventional equipment, uses room temperature reaction, is highly safe, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of rubber vulcanizing agent preparation, specifically relating to a method for preparing 1,1'-disulfide dicaprolactam. Background Technology

[0002] Traditional vulcanizing agent dimorpholine disulfide requires the use of secondary amine precursors in its synthesis, leading to the formation of nitrosamines in rubber products. This problem has remained unresolved for a long time and is now nearing obsolescence. 1,1'-Dicaprolactam disulfide, as a sulfur donor-type rubber vulcanizing agent, does not vulcanize at lower temperatures. The vulcanization reaction only begins when the temperature rises to the point where the sulfur donor decomposes to release active sulfur. Therefore, this vulcanizing agent is safe to operate, has no risk of scorching, and does not produce nitrosamines during vulcanization, completely avoiding carcinogenic risks. It complies with global environmental regulations such as REACH and FDA, making it the best alternative to dimorpholine disulfide. With the continuous expansion of market demand, the increasing demands for product quality, and the increasingly stringent environmental regulations, existing publicly available technologies are no longer sufficient to meet the actual needs of industrial production.

[0003] Currently, there are several main routes for the preparation of 1,1'-disulfide dicaprolactam: Route 1 (using excess caprolactam as an acid-binding agent) Patents CN 103044328 A, CN 116947760 A, CN 108117517 A, and the graduate thesis of Qingdao University of Science and Technology, "Research on the Synthesis Process of Rubber Vulcanizing Agents DTDM and DTDC" and "Synthesis and Performance Study of Lactam Disulfides," disclose a method for preparing 1,1'-disulfide dicaprolactam. This method involves dissolving caprolactam in an organic solvent, slowly adding disulfide dichloride under controlled temperature conditions to initiate the reaction; after the reaction, the pH is adjusted with an aqueous solution of sodium hydroxide or sodium carbonate, the solid and liquid are separated, and the solid is washed with water and dried to obtain the target product.

[0004] The drawbacks of this method are as follows: Because caprolactam itself has poor acid-binding ability, a caprolactam with a molar ratio of n(caprolactam):n(disulfur dichloride) ≥ 5:1 is required as the acid-binding agent. This results in a large amount of caprolactam existing in the acidic reaction system, which easily leads to partial polymerization, causing serious waste of raw materials and high unit consumption. After the reaction, sodium hydroxide or sodium carbonate aqueous solution is used for neutralization, further promoting the polymerization of unreacted caprolactam. Simultaneously, caprolactam has good water solubility, making recovery difficult, and 1,1'-disulfide dicaprolactam is easily decomposed in sodium hydroxide or sodium carbonate aqueous solution. These problems have not yet been effectively solved. The above-disclosed technology using caprolactam itself as the acid-binding agent yields a crude product yield of only 95%–96%, and further processing is required, making it unsuitable for large-scale, high-quality, and environmentally compliant industrial production requirements.

[0005] Route 2 (with added acid-binding agent) Patents US 3525737, CN 110256348 B, CN 108658864 B, and CN 105367496 A disclose a method for preparing 1,1'-dithiocaprolactam: caprolactam and an acid-binding agent (such as pyridine, triethylamine, or triethylenediamine) are dissolved in an organic solvent, and disulfide dichloride is slowly added under controlled temperature to carry out the reaction; after the reaction is completed, the pH is adjusted with an aqueous solution of sodium hydroxide or sodium carbonate, and the product is obtained by washing with solid water and drying. This method solves to some extent the problems of caprolactam's poor acid-binding ability, slow reaction rate, and difficulty in recovery due to its good water solubility. However, this process still has the following shortcomings: ① A large amount of caprolactam present in an alkaline reaction system is prone to partial polymerization, resulting in waste of raw materials; ② Pyridine has a strong odor, which seriously affects operation and post-processing; ③ The product 1,1'-dithiodicaprolactam is easily decomposed in aqueous solutions of sodium hydroxide or sodium carbonate; ④ As the basicity of acid-binding agents such as pyridine, triethylamine, and triethylenediamine increases, the following side reactions with disulfide dichloride increase:

[0006] Route 3 (Preparing sodium caprolactam first) Patent CN 110143922 B discloses a method for synthesizing 1,1'-disulfide dicaprolactam: caprolactam is heated to a molten state, and water is removed from the system under reduced pressure; solid sodium hydroxide is added, and the water generated during the reaction is further removed under reduced pressure to prepare sodium caprolactam salt; the obtained sodium salt then reacts with disulfide dichloride to generate 1,1'-disulfide dicaprolactam, with a yield of 90%–93%. However, with the increase of the feed amount, the water generated during the reaction cannot be removed in time, leading to the polymerization of caprolactam and a decrease in yield. Experiments with increased feed amount show that the yield of this process is only 83.15%, which does not have the prospect of industrial production.

[0007] To address the aforementioned problems, this invention proposes a method for preparing 1,1'-disulfide dicaprolactam. The 1,1'-disulfide dicaprolactam prepared according to this method can avoid the generation of waste gas, significantly reduce the polymerization of caprolactam and the side reaction between the acid-binding agent and disulfide dichloride, and increase the yield to over 99.0%, thus possessing promising prospects for industrial application. Summary of the Invention

[0008] The purpose of this invention is to address the technical deficiencies in the existing technology by providing a method for preparing the rubber vulcanizing agent 1,1'-dithiocaprolactam.

[0009] This invention is implemented through the following technical solutions: A method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide, characterized by comprising the following steps: (1) Add cyclohexane, caprolactam and polymerization inhibitor into the reactor in sequence, control the temperature at 20-25℃ and stir for 25-30 min; (2) At 20-25℃, slowly add a certain amount of disulfide dichloride and bipyridine, and after completion, control the temperature at 25-30℃ for 2-3 hours to react; (3) After the reaction is complete, the cyclohexane mother liquor is filtered and recovered for future use; (4) The filtered solids were neutralized with sodium bicarbonate aqueous solution, and the final pH was controlled at 7.9-8.3; (5) Secondary filtration, recovery of bipyridine from aqueous mother liquor, solid washing, drying and pulverizing to obtain the 1,1' dicaprolactam disulfide.

[0010] Preferably, the molar ratio of disulfide dichloride, caprolactam, and bipyridine is 1.0:2.0-2.01:1.0-1.03.

[0011] Preferably, the polymerization inhibitor is 2,2,6,6-tetramethylpiperidine oxide (TEMPO), and the amount used is 0.03% of the mass of caprolactam.

[0012] Preferably, the bipyridine is 2,2'-bipyridine.

[0013] Preferably, the mass of the cyclohexane is 3.5 times the mass of the caprolactam.

[0014] Preferably, the slow addition in step (2) refers to the alternating addition of disulfide dichloride in portions of 1 / 2, 1 / 4, and 1 / 4, and dipyridine in portions of 1 / 2 and 1 / 2, and adding them alternately. Preferably, the disulfide dichloride is added in the following alternating order: disulfide dichloride in portions of 1 / 2, dipyridine in portions of 1 / 2, disulfide dichloride in portions of 1 / 4, dipyridine in portions of 1 / 2, and disulfide dichloride in portions of 1 / 4.

[0015] Alternating addition can also involve alternating the following steps: dividing disulfide dichloride into 1 / 2, 1 / 2, dividing disulfide dichloride into 1 / 2, dipyridine, and dividing disulfide dichloride into 1 / 2.

[0016] Preferably, the sodium bicarbonate aqueous solution has a mass of 6% to 8%, more preferably 7.5%.

[0017] The 1,1'-dithiodicaprolactam prepared by this invention is a white powder with a loss on heating ≤0.2%, a melting point ≥135.0℃, a yield ≥99.3%, and a purity ≥99.5%.

[0018] The present invention has the following beneficial effects: The 1,1'-dithiocaprolactam product prepared by this method is a white powder with a heating loss of ≤0.2%, a melting point of ≥135.0℃, a yield of ≥99.3%, and a purity of ≥99.5%. Furthermore, this method can be carried out on conventional equipment, is simple to operate, and has high safety.

[0019] (1) The addition of a polymerization inhibitor was proposed for the first time, and the polymerization of caprolactam was effectively inhibited by alternating caprolactam and bipyridine binding acid.

[0020] (2) For the first time, bipyridine binding acid was used, which reduced the side reaction between traditional binding acid agents and disulfur dichloride and solved the problem of strong odor when using pyridine binding acid.

[0021] (3) Neutralization with sodium bicarbonate solution avoids the decomposition of 1,1'-dicaprolactam disulfide during the post-treatment process.

[0022] (4) Two solid-liquid separations are used to achieve direct use of the reaction solvent.

[0023] (5) Using the present invention to prepare 1,1'-dithiodicaprolactam, the product yield is increased to over 99.0% and no further purification is required. This method can be carried out on conventional equipment, adopts room temperature reaction, is highly safe, and is suitable for industrial production. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments provide a more detailed description of the invention. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Example

[0025] At room temperature, 800.00g cyclohexane, 228.60g (wt99.0%, 2.00mol) caprolactam, 0.07g Add 98.0% TEMPO (wt) polymerization inhibitor to a four-necked flask equipped with a condenser, and stir for 25-30 minutes while maintaining the temperature at 20-25°C. Then, while maintaining the temperature at 20-25°C, slowly add 69.60g (wt, 0.50mol) disulfide dichloride, 81.30g (wt, 0.51mol) dipyridine, and 34.80g (wt, 0.25mol) disulfide dichloride. Add 5 mol) of disulfur dichloride. After each addition of disulfur dichloride and dipyridine, stir for 1-2 hours at 20-25°C. After completion, separate the solid and liquid components, recover the liquid cyclohexane, and transfer the solid to a feeder. Add 2273.6 g (wt 7.5%, 2.03 ol) of sodium bicarbonate to the reactor, control the temperature at 20-25°C, and slowly add the above solid. After completion, stir at 20-25°C for 25-30 minutes, and control the pH at 7.9-8.3 until the reaction is complete. Perform a second solid-liquid separation, recover the liquid dipyridine, wash the solid twice, dry, and pulverize to obtain 286.9 g of 1,1'-disulfide dicaprolactam. The yield is 99.5%, the purity is 99.7% as determined by liquid chromatography, the loss on heating is 0.15%, the initial melting point is 135.3°C, and the appearance is a white powder. Example

[0026] At room temperature, 800.00 g of cyclohexane, 228.60 g (wt 99.0%, 2.00 mol) of caprolactam, and 0.07 g of other compounds were recovered. Add 98.0% TEMPO (wt) polymerization inhibitor to a four-necked flask equipped with a condenser, and stir for 25-30 minutes while maintaining the temperature at 20-25°C. Then, while maintaining the temperature at 20-25°C, slowly add 69.60g (wt, 0.50mol) disulfide dichloride, 81.30g (wt, 0.51mol) dipyridine, and 34.80g (wt, 0.25mol) disulfide dichloride. Add 5 mol) of disulfur dichloride. After each addition of disulfur dichloride and dipyridine, stir for 1-2 hours at 20-25°C. After completion, separate the solid and liquid phases, recover the liquid cyclohexane, and transfer the solid to a feeder. Add 2273.6 g (wt 7.5%, 2.03 ol) of sodium bicarbonate to the reactor, control the temperature at 20-25°C, and slowly add the above solid. After completion, stir at 20-25°C for 25-30 minutes, and control the pH at 7.9-8.3 until the reaction is complete. Perform a second solid-liquid separation, recover the liquid dipyridine, wash the solid twice, dry, and pulverize to obtain 287.3 g of 1,1'-disulfide dicaprolactam. The yield is 99.6%, the purity is 99.6% as determined by liquid chromatography, the loss on heating is 0.13%, the initial melting point is 135.5°C, and the appearance is a white powder. Example

[0027] At room temperature, 800.00 g of cyclohexane, 229.70 g (wt 99.0%, 2.01 mol), and 0.07 g of caprolactam were recovered. Add TEMPO (98.0% wt) polymerization inhibitor sequentially to a four-necked flask equipped with a condenser, maintain the temperature at 20–25°C, and stir for 25–30 minutes. Maintain the temperature at 20–25°C and slowly add 69.60 g (98.0% wt, 0.50 mol) disulfide dichloride, 82.10 g (98.0% wt, 0.515 mol) dipyridine, 34.80 g (98.0% wt, 0.25 mol) disulfide dichloride, 82.10 g (98.0% wt, 0.515 mol) dipyridine, and 34.80 g (98.0% wt, 0.515 mol) dipyridine. 25 mol) of disulfur dichloride was added, and after each addition of disulfur dichloride and dipyridine, the mixture was stirred at 20–25 °C for 1–2 h. After the reaction was complete, the solid and liquid phases were separated, and the liquid cyclohexane was recovered while the solid was transferred to a feeder. 2273.6 g (wt 7.5%, 2.03 ol) of sodium bicarbonate was added to the reactor, and the temperature was controlled at 20–25 °C. The solid was added slowly, and after the reaction was complete, the mixture was stirred at 20–25 °C for 25–30 min, with the pH controlled at 7.9–8.3 until the reaction was complete. A second solid-liquid separation was performed, and the liquid dipyridine was recovered. The solid was washed twice, dried, and pulverized to obtain 287.0 g of 1,1'-dicaprolactam disulfide. The yield was 99.5%, the purity was 99.7% as determined by liquid chromatography, the loss on heating was 0.15%, the initial melting point was 135.6 °C, and the appearance was a white powder.

[0028] Comparative Example 1 At room temperature, 1500.00 g of petroleum ether and 285.80 g (wt 99.0%, 2.50 mol) of caprolactam were sequentially added to a four-necked flask equipped with a condenser. The temperature was controlled at 45–50 °C, and the mixture was stirred for 30 min. At the same temperature, 69.60 g (wt 98.0%, 0.50 mol) of disulfide dichloride was added over 7–8 h. After this, the mixture was stirred at 45–50 °C for 1–2 h. Then, 750.00 g of sodium carbonate (wt 7.5%, 0.53 mol) was slowly added. After this, the mixture was stirred at room temperature for 25–30 min. The solid and liquid phases were separated. The caprolactam was recovered from the liquid phase. The solid was washed twice, dried, and pulverized to obtain 138.1 g of 1,1'-dicaprolactam disulfide. The yield was 96.7%, the purity was 95.3% as determined by liquid chromatography, the loss on heating was 0.12%, the initial melting point was 129.5 °C, and the product was a white powder.

[0029] This comparative example summarizes, optimizes, and repeatedly experiments the preparation methods disclosed in CN 103044328 A, CN 116947760 A, CN 108117517 A, and the graduate theses from Qingdao University of Science and Technology, "Research on the Synthesis Process of Rubber Vulcanizing Agents DTDM and DTDC" and "Synthesis and Performance Study of Caprolactam Disulfides." The optimal experimental results are: product yield of 96.7%, purity of 95.3% as determined by liquid chromatography, loss on heating of 0.12%, initial melting point of 129.5℃, appearance of white powder, and caprolactam recovery rate of 85%. The low yield, purity, initial melting point, and caprolactam recovery rate are mainly due to caprolactam polymerization.

[0030] Comparative Example 2 At room temperature, 720.00 g of n-heptane, 120.10 g (wt 99.0%, 1.05 mol) of caprolactam, 88.70 g (wt 98.0%, 1.1 mol) of pyridine, or 113.50 g (wt 98.0%, 1.1 mol) of triethylamine, or 61.70 g (wt 98.0%, 0.55 mol) of triethylenediamine were sequentially added to a four-necked flask equipped with a condenser. The temperature was controlled at 15–25 °C, and the mixture was stirred for 30 min. Add 69.60 g (wt 98.0%, 0.50 mol) of disulfide dichloride at 5–25℃ for 1–2 h. After completion, stir at 15–25℃ for 2.0–2.5 h. Slowly add 750.00 g of sodium carbonate (wt 7.5%, 0.53 mol). After completion, stir at room temperature for 25–30 min. Separate the solid and liquid. Recover pyridine, triethylamine, or triethylenediamine from the liquid. Wash the solid twice, dry, and pulverize to obtain 133.5 g of 1,1'-dicaprolactam disulfide. The yield is 92.6%, the purity is 99.2% as determined by liquid chromatography, the loss on heating is 0.13%, the initial melting point is 135.0℃, and the appearance is a white powder.

[0031] This comparative example was prepared according to the methods disclosed in US 3525737, CN 110256348 B, CN 108658864 B, and CN 105367496 A. The optimal experimental results were: yield 92.6%, purity 99.2% as determined by liquid chromatography, weight loss upon heating 0.13%, initial melting point 135.0℃, and appearance as a white powder. The low yield was mainly due to the increased basicity of the acid-binding agents pyridine, triethylamine, and triethylenediamine, leading to increased side reactions with disulfide dichloride and caprolactam polymerization.

[0032] Comparative Example 3 Add 1000g (wt 99.0%, 8.75mol) of caprolactam to a 5L reactor, and slowly heat to 130℃. At this point, the caprolactam is in a molten state. Start stirring and remove water from the system under reduced pressure at 0.1MPa for about 30 minutes. Slowly heat to 140℃, add 335.75g (wt 98.0%, 8.23mol) of sodium hydroxide solid, and continue to remove water generated during the reaction under reduced pressure at 0.1MPa for about 1.5 hours. Continue until no more water distills from the system, and the liquid surface is calm and free of bubbles. Slowly pour out the solution, cool to room temperature, pulverize, and store in a dry place for later use. If needed, repeat this process to prepare more sodium caprolactam salt.

[0033] 402.1g of the sodium caprolactam salt prepared above and 29.1g of caprolactam were added to a 5 L reactor. 2750g of 120# solvent oil was used, and the temperature was controlled at 35℃. Stirring was started, and 192.1g (wt 97.0%, 1.38mol) of disulfide dichloride was slowly added dropwise to the system. After approximately 2 hours, the addition of disulfide dichloride was complete. The temperature was maintained, and stirring continued for approximately 2.5 hours until the reaction was complete. 1000g of water was added for washing, and the mixture was stirred for 15 minutes. The mixture was then filtered, and the filter cake was dried to obtain 330.95g of solid. The yield was 83.15%, the purity was 99.01% as determined by liquid chromatography, the loss on heating was 0.15%, the initial melting point was 133.6℃, ​​and the appearance was a white powder.

[0034] This comparative example is based on the preparation method disclosed in CN 110143922 B, which was summarized, optimized, and repeatedly tested. The optimal experimental results were: product yield 83.15%, purity 99.01% as determined by liquid chromatography, loss on heating 0.15%, initial melting point 133.6℃, ​​and appearance as a white powder. The low yield was mainly due to the failure to remove the water generated during the reaction in time as the amount of feed increased, leading to the polymerization of caprolactam and a decrease in yield.

[0035] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a rubber vulcanizing agent, 1,1'-dicaprolactam disulfide, characterized in that... Includes the following steps: (1) Add cyclohexane, caprolactam and polymerization inhibitor into the reactor in sequence, control the temperature at 20-25℃ and stir for 25-30 min; (2) Add disulfur dichloride and bipyridine slowly at 20-25℃, and after completion, control the temperature at 25-30℃ for 2-3 hours to react; (3) After the reaction is complete, the cyclohexane mother liquor is filtered and recovered for future use; (4) The filtered solids were neutralized with sodium bicarbonate aqueous solution, and the final pH was controlled at 7.9-8.3; (5) The solid is washed, dried and pulverized to obtain the 1,1' dithiolactam.

2. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The molar ratio of disulfide dichloride, caprolactam, and bipyridine is 1.0:2.0-2.02:1.0-1.

05.

3. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The polymerization inhibitor is 2,2,6,6-tetramethylpiperidine oxide (TEMPO), and the amount used is 0.02% to 0.05% of the mass of caprolactam.

4. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The bipyridine is 2,2'-bipyridine.

5. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The mass of the cyclohexane is 3 to 5 times the mass of the caprolactam.

6. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The slow addition refers to the alternating addition of disulfide dichloride and dipyridine.

7. The method for preparing a rubber vulcanizing agent 1,1'-dicaprolactam disulfide according to claim 1, characterized in that, The sodium bicarbonate aqueous solution has a mass of 6% to 8%.

8. A method for preparing 1,1'-dithiocaprolactam according to any one of claims 1 to 7, characterized in that, The product is a white powder with a loss on heating ≤0.2%, melting point ≥135.0℃, yield ≥99.3%, and purity ≥99.5%.

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