Thiuram dicaprolactam disulfide and its preparation method and application

Abstract

The present invention discloses a dicaprolactam thiuram disulfide, a preparation method, and an application thereof. Caprolactam and carbon disulfide are reacted in a solvent to generate caprolactam dithiocarbamic acid, and a hydrogen peroxide solution is subsequently added dropwise to obtain dicaprolactam thiuram disulfide. The present invention has a simple production process, is easy to operate, has low cost, and is environmentally friendly. The obtained dicaprolactam thiuram disulfide has high purity, a high melting point, a white appearance, and exhibits good rapid vulcanization performance. It also does not suffer from the toxicity issues of common thiuram accelerators. Therefore, it is an environmentally friendly rubber vulcanization accelerator that supplements the variety of rubber vulcanization accelerators in the domestic market.

Description

Technical Field

[0001] The invention relates to dicaprolactam thiuram disulfide, and also relates to a preparation method and application of the same as a rubber additive, belonging to the technical field of chemical industry and rubber additives. Background Art

[0002] In recent years, with the rapid development of the rubber processing industry, the rapid development of the domestic automobile industry and the communications industry has driven the rapid growth of the rubber processing industry, providing unprecedented opportunities for the development of the rubber additive industry. Since joining the WTO, although the production of rubber accelerator products in my country has increased significantly, there is still a large gap in the intrinsic quality of products and "green" environmental protection technology. In particular, the international community is paying more and more attention to the toxicity of certain accelerator products that easily generate harmful substances such as nitrosamines during rubber processing. Research on the formation and effects of nitroso compounds has become a hot topic in the global rubber accelerator field. Therefore, new rubber accelerators are mostly designed to replace accelerator varieties that produce nitrosamines. Currently, vulcanization accelerators studied abroad that can produce carcinogenic nitrosamines include disulfide amino acid salts such as PZ, ZDC, ZDBDC, and NBC; sulfenamides such as NOBS and DEBS; thiurams such as TMTM (tetramethylthiuram monosulfide), TMTD (tetramethylthiuram disulfide), TETD (tetraethylthiuram disulfide), and TBTD (tetrabutylthiuram disulfide); and thioureas such as ETU and DETU. In response to this, numerous restrictive regulations have been introduced globally. For example, Germany enacted regulations to control nitrosamine levels as early as 1982. The United States, Japan, France, and the United Kingdom are also actively developing new vulcanization accelerators that do not produce nitrosamines and have successively ceased the use of nitrosamine-producing vulcanization accelerators. Therefore, the development of environmentally friendly vulcanization accelerators is essential. Summary of the Invention

[0003] The present invention aims to provide a thiuram dicaprolactam disulfide, which can be used as a rubber vulcanization accelerator. During use, the compound does not have the toxicity problem of current thiuram accelerators and is a new environmentally friendly rubber vulcanization accelerator.

[0004] The dicaprolactam thiuram disulfide provided by the present invention has the structural formula shown in the following formula I:

[0005]

[0006] The above-mentioned dicaprolactam thiuram disulfide has the appearance of white to light yellow powder and a melting point of 137-140°C.

[0007] The present invention also provides a method for preparing the above-mentioned dicaprolactam thiuram disulfide, which comprises the following steps:

[0008] (1) Caprolactam and carbon disulfide are reacted in a solvent to generate caprolactam dithiocarbamic acid as shown in Formula II; the reaction formula is as follows:

[0009]

[0010] (2) Add hydrogen peroxide solution dropwise to the reaction solution of step (1) to obtain dicaprolactam thiuram disulfide; the reaction formula is as follows:

[0011] .

[0012] Furthermore, in step (1), the amount of caprolactam and carbon disulfide is: 100-120 parts by weight of caprolactam, 74-96 parts by weight of carbon disulfide. Preferably, 100 parts by weight of caprolactam, 75 parts by weight of carbon disulfide.

[0013] Furthermore, in step (1), the solvent is water, a 5-80 wt% aqueous ethanol solution, or a combination thereof. The concentration of the aqueous ethanol solution can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, or 80 wt%. The purpose of the solvent is to serve as a reaction medium, and its amount can be adjusted according to actual needs. For example, the mass of the solvent can be 2-5 times the total mass of caprolactam and carbon disulfide.

[0014] Furthermore, in step (1), caprolactam and the solvent are first mixed evenly, and then carbon disulfide is added dropwise to the mixture.

[0015] Furthermore, in step (1), caprolactam and the solvent are mixed at room temperature.

[0016] Furthermore, in step (1), carbon disulfide is added dropwise to the mixed solution at low temperature. During the addition, the temperature of the mixed solution is controlled to be 5-15°C. The addition time is generally 15-30 minutes. After the addition is completed, the mixture is kept warm and reacted for 0.5-1 hour at this temperature.

[0017] Furthermore, in step (2), the hydrogen peroxide solution is added dropwise to the mixed solution of step (1). The temperature is controlled at 0-5°C during the addition of the hydrogen peroxide solution. The addition time is generally 30-60 minutes. After the addition is completed, the mixture is kept at 0-5°C for 2-3 hours.

[0018] Furthermore, in step (2), the concentration of hydrogen peroxide in the hydrogen peroxide solution added dropwise should not be too high. If it is too high, it will easily cause overoxidation, resulting in an increase in by-products and affecting the purity of the product. Experimental verification shows that the concentration of hydrogen peroxide in the hydrogen peroxide solution added dropwise is not higher than 15wt%. In actual operation, the hydrogen peroxide solution can be directly selected from commercially available hydrogen peroxide with a concentration of 15wt% or less, or a high-concentration commercially available hydrogen peroxide can be diluted to the desired concentration with the solvent in step (1) before being added dropwise.

[0019] Furthermore, when the amount of caprolactam is 100-120 parts by weight, the amount of hydrogen peroxide used is 65-92 parts by weight, where the amount of hydrogen peroxide used is based on a hydrogen peroxide concentration of 25-30 wt%. Preferably, when the amount of caprolactam is 100 parts by weight and the concentration of hydrogen peroxide is 27.5 wt%, the amount used is 65-77 parts by weight; more preferably, when the concentration of hydrogen peroxide is 27.5 wt%, the amount used is 70 parts by weight. When 25-30 wt% hydrogen peroxide is selected as the raw material, in step (2), in order to meet the requirement that the hydrogen peroxide concentration is not higher than 15%, the high-concentration hydrogen peroxide is first diluted to an appropriate concentration with the solvent in step (1) before being added dropwise.

[0020] Furthermore, in step (2), the reaction liquid after the hydrogen peroxide solution is added dropwise is post-treated to obtain the final product, and the post-treatment includes filtering the reaction liquid, washing the obtained solid, and drying the steps.

[0021] The dithiodicaprolactam thiuram obtained by the present invention has a white appearance, high purity, few impurities, a high melting point and a high yield. When used in a rubber additive, the vulcanization rate can be accelerated without generating harmful substances. The present invention is an environmentally friendly rubber additive with good prospects, especially an excellent rubber vulcanization accelerator.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The thiuram dicaprolactam disulfide of the present invention has high purity, a high melting point, and a white appearance, and can significantly accelerate the vulcanization rate. Regardless of whether the vulcanization temperature is increased, the sulfur dosage is changed, or white carbon black is added, the thiuram dicaprolactam disulfide can exhibit good rapid vulcanization performance and has universal applicability. In addition, the use of the thiuram dicaprolactam disulfide has no adverse effect on the physical properties of the vulcanized rubber.

[0024] 2. The use of the dithiodicaprolactam thiuram in the rubber processing process does not have the toxicity problem of common thiuram accelerators, and is an environmentally friendly rubber vulcanization accelerator, which supplements the number of rubber vulcanization accelerators in the domestic market.

[0025] 3. The present invention uses caprolactam as a raw material to first prepare caprolactam dithiocarbamic acid, and then obtains dithiodicaprolactam thiuram through hydrogen peroxide oxidation. The reaction raw materials have low toxicity and are more environmentally friendly.

[0026] 4. The production process of dithiodicaprolactam thiuram of the present invention is simple, easy to operate, low in cost, environmentally friendly, highly controllable, has high production efficiency, high product yield, low energy consumption, and has prospects for industrial application. DETAILED DESCRIPTION

[0027] The present invention is described in detail below through specific examples, but the use and purpose of these exemplary embodiments are only used to explain the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to them.

[0028] In the following examples, product yield = mass of product obtained / theoretical mass of product.

[0029] Example 1

[0030] A method for preparing thiuram disulfide dicaprolactam comprises the following steps:

[0031] 1. Weigh the following raw materials: 100 g caprolactam, 75 g carbon disulfide, 70 g 27.5 wt% hydrogen peroxide solution, and 450 g water.

[0032] 2. Add 100g of caprolactam to 380g of water according to the ratio, control the temperature to 5-10℃, then add 75g of carbon disulfide dropwise for 20 minutes. After the addition is complete, react at 5-10℃ for 1h to obtain the reaction solution.

[0033] 3. Dilute 70 g of 27.5 wt% hydrogen peroxide solution with 70 g of water, then control the temperature of the reaction solution in step 2 to 0-5 ° C, and add the diluted hydrogen peroxide solution dropwise thereto for 60 minutes. After the addition is complete, react at 0-5 ° C for 2.5 hours to obtain a reaction solution containing solids.

[0034] 4. The reaction liquid containing solids was filtered, washed, and dried under vacuum to obtain 163.7 g of dithiuram dicaprolactam. The resulting product was white in appearance, with a melting point of 139.2°C as measured by an automatic capillary melting point analyzer. The purity was 99.2% as measured by high-performance liquid chromatography, and the yield, calculated as caprolactam, was 98.4%.

[0035] Example 2

[0036] Thiuram dithiodicaprolactam was prepared according to the method of Example 1, except that 450 g of water in step 1 was replaced with 450 g of 50 wt% ethanol aqueous solution.

[0037] The obtained product was 158.4 g, with a white appearance and a melting point of 137.6° C. as measured by an automatic capillary melting point apparatus. The purity was 98.1% as measured by a high performance liquid chromatography analyzer. The yield based on caprolactam was 95.2%.

[0038] Example 3

[0039] Thiuram dithiodicaprolactam was prepared according to the method of Example 1, except that the amounts of the raw materials used in step 1 were: 110 g of caprolactam, 85 g of carbon disulfide, 78 g of 27.5 wt % hydrogen peroxide solution, and 450 g of water.

[0040] 180.6 g of the obtained product was white in appearance, with a melting point of 138.5° C. as measured by an automatic capillary melting point apparatus and a purity of 98.8% as measured by a high performance liquid chromatography analyzer. The yield based on caprolactam was 98.7%.

[0041] Example 4

[0042] A method for preparing thiuram disulfide dicaprolactam comprises the following steps:

[0043] 1. Weigh the following raw materials: 120 g of caprolactam, 96 g of carbon disulfide, 92 g of 27.5 wt% hydrogen peroxide solution, and 500 g of water.

[0044] 2. Add 120g of caprolactam to 408g of water according to the ratio, control the temperature to 5-10℃, then add 96g of carbon disulfide dropwise for 25 minutes. After the addition is complete, react at 5-10℃ for 1h to obtain the reaction solution.

[0045] 3. Dilute 92 g of 27.5 wt% hydrogen peroxide solution with 92 g of water, then control the temperature of the reaction solution in step 2 to 0-5°C, and add the diluted hydrogen peroxide solution dropwise thereto for 60 minutes. After completion of the addition, react at 0-5°C for 2.5 hours to obtain a reaction solution containing solids.

[0046] 4. The reaction liquid containing solids was filtered, washed, and dried under vacuum to obtain 195.8 g of dithiuram dicaprolactam. The resulting product was white in appearance, with a melting point of 137.9°C as measured by an automatic capillary melting point analyzer. The purity was 97.9% as measured by high-performance liquid chromatography, and the yield, calculated as caprolactam, was 98.1%.

[0047] Example 5

[0048] A method for preparing thiuram disulfide dicaprolactam comprises the following steps:

[0049] 1. Weigh the following raw materials: 100 g caprolactam, 75 g carbon disulfide, 70 g 27.5 wt% hydrogen peroxide solution, and 450 g water.

[0050] 2. Add 100g of caprolactam to 350g of water according to the ratio, control the temperature to 10-15℃, then add 75g of carbon disulfide dropwise for 20 minutes. After the addition is complete, react at 10-15℃ for 1h to obtain the reaction solution.

[0051] 3. Dilute 70 g of 27.5 wt% hydrogen peroxide solution with 100 g of water, then control the temperature of the reaction solution in step 2 to 0-5 ° C, add the diluted hydrogen peroxide solution dropwise thereto for 60 minutes, and react at 0-5 ° C for 3 hours after completion of the addition to obtain a reaction solution containing solids.

[0052] 4. The reaction liquid containing solids was filtered, washed, and dried under vacuum to obtain 164.0 g of thiuram disulfide caprolactam. The resulting product was white in appearance, with a melting point of 138.9°C as measured by an automatic capillary melting point apparatus and a purity of 99.0% as measured by high-performance liquid chromatography. The yield, calculated as caprolactam, was 98.6%.

[0053] Comparative Example 1

[0054] A method for preparing thiuram disulfide dicaprolactam comprises the following steps:

[0055] 1. Weigh the following raw materials: 100 g caprolactam, 75 g carbon disulfide, 70 g 27.5 wt% hydrogen peroxide solution, and 450 g water.

[0056] 2. Add 100g of caprolactam to 450g of water according to the ratio, control the temperature to 5-10℃, then add 75g of carbon disulfide dropwise for 20 minutes. After the addition is complete, react at 5-10℃ for 0.5-1h to obtain a reaction solution.

[0057] 3. Control the temperature of the reaction solution in step 2 to 0-5°C, add 70g of 27.5wt% hydrogen peroxide solution dropwise thereto for 60 minutes, and react at 0-5°C for 2-3 hours after completion of the addition to obtain a reaction solution containing solids.

[0058] 4. The reaction liquid containing solids was filtered, washed, and dried under vacuum to obtain 152.7 g of thiuram disulfide caprolactam. The resulting product was white in appearance, with a melting point of 128.4°C as measured by an automatic capillary melting point analyzer and a purity of 86.1% as measured by high-performance liquid chromatography. The yield, calculated as caprolactam, was 91.8%.

[0059] Performance Verification

[0060] 1. Experimental samples:

[0061] Thiuram disulfide caprolactam prepared in Example 1 and tetramethylthiuram disulfide (TMTD), a common commercial sample.

[0062] 2. Rubber sample formula (parts by weight):

[0063] 100 parts of natural rubber, 60 parts of carbon black N220, 2 parts of antioxidant 4020, 1 part of antioxidant RD, 2 parts of sulfur, 3.5 parts of zinc oxide, 2 parts of stearic acid, 1.25 parts of dithiodicaprolactam thiuram or 1.25 parts of TMTD of Example 1.

[0064] 3. The steps of rubber refining are as follows:

[0065] (1) Mixing in one stage of internal mixer:

[0066] Add natural rubber, carbon black N220, zinc oxide, stearic acid, antioxidant 4020 and antioxidant RD, mix for 300 seconds, drain at 140±5℃, and leave at room temperature for 8 hours to obtain a first-stage mixed rubber;

[0067] (2) Second stage mixing in open mill:

[0068] Preheat a section of mixed rubber on the roll mill for 1 minute, add sulfur, thiuram disulfide caprolactam or TMTD with a roll spacing of 2mm, cut 4 times on each side, make triangle packages 4 times with the minimum roll spacing, and roll 4 times with a roll spacing of 2.2mm, remove the sheet, and leave it for 6 hours for testing.

[0069] 4. Test results:

[0070] The rubber compound of Example 1 and conventional products on the market were refined, and relevant performance tests were performed according to GB / T 16584-1996 and GB / T 1233-2008. The relevant test data of the rubber compound are shown in Tables 1 and 2 below:

[0071]

[0072]

[0073] 5. Experimental conclusion:

[0074] From the above data, it can be seen that compared with tetramethylthiuram disulfide (TMTD), a conventional sample on the market, the dithiuram disulfide caprolactam of the present invention has a comparable vulcanization accelerating effect as TMTD, and has a longer scorch time than TMTD. It is a safe and environmentally friendly thiuram vulcanization accelerator and can replace TMTD in equal amounts for the production of rubber products, thus supplementing the variety of rubber vulcanization accelerators in the domestic market.

Claims

1. A dicaprolactam thiuram disulfide, characterized in that: It has the structural formula shown in the following formula I: 。 2. A method for preparing thiuram dicaprolactam disulfide according to claim 1, characterized in that: The following steps are involved: (1) reacting caprolactam and carbon disulfide in a solvent to generate caprolactam dithiocarbamic acid represented by formula II; (2) adding a hydrogen peroxide solution dropwise to the reaction solution of step (1) to react and obtain dicaprolactam thiuram disulfide; 。 3. The preparation method according to claim 2, wherein: The amount of caprolactam used is 100-120 parts by weight, the amount of carbon disulfide used is 74-96 parts by weight, and the amount of hydrogen peroxide solution used is 65-92 parts by weight, wherein the hydrogen peroxide solution has a hydrogen peroxide concentration of 25-30wt%.

4. The preparation method according to claim 2, wherein: In step (1), the solvent is selected from at least one of water and 5-80 wt% ethanol aqueous solution.

5. The preparation method according to claim 2, wherein: In step (1), caprolactam and solvent are first mixed evenly, and then carbon disulfide is added dropwise to the mixture.

6. The preparation method according to claim 5, wherein: In step (1), caprolactam and solvent are mixed at room temperature, and then carbon disulfide is added dropwise at a temperature of 5-15°C for 15-30 minutes. After the addition is complete, the mixture is kept warm for 0.5-1 hour.

7. The preparation method according to claim 2, wherein: In step (2), the concentration of the added hydrogen peroxide solution is not higher than 15 wt %.

8. The preparation method according to claim 7, characterized in that: In step (2), the hydrogen peroxide solution is obtained by mixing hydrogen peroxide having a concentration of 25-30 wt% with the solvent in step (1).

9. The preparation method according to claim 7, characterized in that: In step (2), the temperature of the reaction solution in step (1) is controlled at 0-5°C, and then the hydrogen peroxide solution is added dropwise for 30-60 minutes. After the addition is complete, the mixture is kept warm for 2-3 hours.

10. Use of the thiuram dicaprolactam disulfide according to claim 1 as a rubber additive.

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