CS260177B1 - Process for producing modified 2-mercaptobenzothiazole - Google Patents

Abstract

Modified 2-mercaptobenzothiazole is obtained from a solution of the calcium salt of 2-mercaptobenzothiazole by the action of excess sulfuric acid, with precipitation of 2-mercaptobenzothiazole and calcium sulfate, which are separated from the suspension by filtration. Excess sulfuric acid can be neutralized with excess calcium carbonate, the prepared mixture of 2-mercaptobenzothiazole, calcium sulfate, calcium carbonate is filtered from the reaction mixture, where the inorganic components serve as an inert carrier. The process can be used to produce a product that is used in the rubber industry.

Description

The invention relates to modified 2-mercaptobenzothiazole (captax) and a method for its isolation by precipitating the calcium salt of captax in excess sulfuric acid and neutralizing the excess sulfuric acid with hydroxide, oxide or calcium carbonate.

Kaptax is used to accelerate the sulfur vulcanization of unsaturated rubbers. It is produced by condensation of aniline, sulfur and carbon disulfide at a temperature of 240 to 300 ^° C and a pressure of 7 to 13 MPa. The obtained crude Kaptax is purified. Purification with aqueous solutions of alkali hydroxide or with a suspension of calcium hydroxide is known. Kaptax in the form of a soluble salt is separated from insoluble resinous substances. The salts of Kaptax are precipitated with hydrochloric acid to form a suspension of Kaptax.

In the AO No. 591 470, crude captax is dissolved in dilute alkaline solution, and by partial neutralization of the obtained captax salt with mineral acid and selective oxidation of the impurities present, pure captax is obtained.

In Japanese Patent No. 163*571 (1979), crude captax is dissolved in a sodium hydroxide solution and the benzthiazole is removed by distillation. The distillation residue is oxidized with hydrogen peroxide and atmospheric oxygen. After clarification, pure captax is obtained. The above methods obtain captax of high purity. The disadvantage is that mineral salts are discarded as waste during the purification of captax, thereby polluting the wastewater.

Additives to rubber and plastic mixtures, such as vulcanization accelerators, stabilizers, antioxidants, vulcanization inhibitors, etc. are mostly dosed in very small amounts of 0.05 to 2% by weight. In order to evenly disperse these small amounts of active substance throughout the entire volume of the polymer mass, as well as to reduce losses during weighing and handling, concentrates of these substances are often prepared before mixing the additive into the mixture. These concentrates are usually prepared by mechanical mixing of the appropriate inert (e.g. silicates, silicon dioxide, calcium carbonate, etc.) or polymer with the active substance, but this method may not achieve perfect homogeneity of the concentrate.

We have found that the above-mentioned shortcomings can be alleviated by a method of producing modified 2-mercaptobenzothiazole consisting of 40 to 80 wt. % 2-mercaptobenzothiazole, 20 to 40 wt. % calcium sulfate and up to 30 wt. % calcium carbonate. The inorganic components serve as a carrier for 2-mercaptobenzothiazole and all components are perfectly homogenized with each other. 2-Mercaptobenzothiazole is precipitated from its calcium salt with excess sulfuric acid to a pH value of the suspension of captax and calcium sulfate of 1 to 5. The mixture of captax and calcium sulfate is separated from the suspension. In the case of a requirement for a higher content of inert (calcium sulfate) than can be obtained by the reaction of the calcium salt of captax with sulfuric acid, calcium oxide, calcium hydroxide or calcium carbonate is added to the resulting suspension after precipitation of the calcium salt of captax with excess sulfuric acid, while at the same time the excess acid is neutralized to form the required amount of calcium sulfate. This method of isolation (precipitation) from the reaction mixture results in perfect homogenization of the active substance and the inert carrier.

The invention finds application in the vulcanization of rubber mixtures. The obtained product contains, in addition to captax, inorganic substances that serve as an inert carrier ensuring more precise dosing, better dispersion of the active ingredient and increased efficiency of the active ingredient — captax in the vulcanization mixture. Compared to the previous production method, the production of oveta produces significantly fewer soluble substances, especially inorganic salts, which have previously been waste. By reducing inorganic salts in wastewater, their quality will improve, which has an impact on improving the environment.

Example 1

Crude captax was prepared in a known manner by condensation of aniline, sulfur and carbon disulfide. The obtained melt was dissolved in a 10% by weight suspension of calcium hydroxide. The calcium salt of ¹ captax was filtered off from insoluble substances. From 1 l of an aqueous solution of calcium salt of captax with a concentration of 7.6% by weight, captax was precipitated with 113 ml of sulfuric acid with a concentration of 20% by weight. A mixture of captax and calcium sulfate was filtered off from the suspension, which was washed with 550 ml of water and dried. The obtained product (105.1 g) contained 69.6% by weight of captax and 28.9% by weight of calcium sulfate.

The obtained product was evaluated for application with Pneumax MBT (2-mercaptobenzothiazole) in a model vulcanization mixture based on natural rubber of the following composition:

Rubber (SMR-5L) Carbon black (Nlgros K) ZnO

Stearin

Sulfur

Vulcanization accelerator

100.0 parts by weight 35.0 parts by weight 3.0 parts by weight 2.0 parts by weight 2.25 parts by weight composition is given in table 1

The monitored basic vulcanization characteristics and physical-mechanical properties are summarized in Table 1.

Table 1 Accelerator Dosage Vulcanizing Physical-mechanical accelerator characteristics properties of vulcanizate volcano work. optimum Module Fortress Ductility (weight) safety ts, time of the vul- 300% in motion (%) works) Mooney, sewage (MPa) .(MPa) 120°C t9o, Rheo- * (minj meter 150 °C (min) Captax (Pneumax MBT) Modified 0.7 •15.0 13.3 12.8 18.0 374 ikaptax 0.7 15.1 13.8 12.5 17.8 382 Modified captax 1.0 14,-8 12.7 13.3 18.4 376

Note:

Pneumax MBT — content min. 95% wt. captax Modified captax — content 69.6% wt. captax

The obtained results point to the increased efficiency of the modified captax. Example 2

The procedure was as in Example 1, except that after precipitation of the calcium salt with sulfuric acid, 36 grams of micronized limestone was added to the suspension.

The obtained product contained 50.1% by mass. captax, 26.3% wt. calcium sulfate, 21.5% wt. calcium carbonate.

The invention finds application in the production of captax, which is used in the rubber industry.

Claims (2)

SUBJECT Process for producing a modified 2-mercaptobenzothiazole consisting of 40 to 80 wt. 2-mercaptobenzothiazole, 20 to 40 wt. % calcium sulfate and up to 30 wt. calcium carbonate, wherein the 2-mercaptobenzothiazole and the inorganic components which serve as carrier of the active substance are perfectly homogenized, by precipitating the 2-mercaptobenzothiazole from the aqueous solution of its calcium salt with a mineral acid, characterized by INVENTION that, after the precipitation of 2-mercaptobenzothiazole from its calcium salt with an excess of sulfuric acid to a pH of suspension 1 to 5, the mixture of 2-mercaptobenzothiazole and calcium sulfate is separated from the suspension or neutralized in excess the sulfuric acid with excess calcium carbonate and the mixture of 2-mercaptobenzothiazole, calcium sulfate and calcium carbonate is separated by filtration.