CS274352B1 - Method of cyclohexylamine regeneration from salts' aqueous solutions on base of 2-substituted benzothiazole from 2-substituted benzothiazole - Google Patents

Abstract

The solution concerns a method of regeneration of cyclohexylamine from water solutions of salts based on 2-substituted benzothiazole during production of N-cyclohexylbenzothiazolyl-2-sulfenamide from raw 2-mercaptobenzothiazole and sodium hypochlorite in surplus of cyclohexylamine. After separation of solid fraction and separation of the filtrate phases 1.4 to 5.0 weight parts of sodium hydroxide is added in the form of water solution per 100 weight parts of organic phase before entrance in atmospheric distillation. This results in releasing of cyclohexylamine from ionic bond on benzothiazolyl-2-sulfonic acid. The obtained distillate containing less then 1 percent by weight of benzothiazole is returned to the new synthesis of N-cyclohexylbenzothiazolyl-2-sulfenamide and the product from distillation columns is used as a secondary raw material.The solution can be used in chemical industry.

Description

The present invention relates to a process for the recovery of cyclohexylamine from aqueous solutions of 2-substituted benzothiazole-based salts in the production of N-cyclohexylbenzothiazolyl-2-sulfenamide used in the rubber industry for vulcanizing rubber mixtures.

Conventional processes for the preparation of N-cyclohexylbenzothiazolyl-2-sulfenamide are based on the oxidation of cyclohexylammoniumbenzothiazolyl-2-mercaptide, most commonly sodium hypochlorite or hydrogen peroxide. Cyclohexylammoniumbenzothiazolyl-2-mercaptide is obtained by reacting 2-mercaptobenzothiazole by liberating it from the alkaline, most often sodium, ammonium and ammonium salts thereof. calcium salt equivalent to a mineral acid in the presence of cyclohexylamine used in an excess of 0.04 to 0.20 moles per mole of 2-mercaptobenzothiazole. Said alkali salts of 2-mercaptobenzothiazole are obtained in the complex refining of crude 2-mercaptobenzothiazole in the form of aqueous solutions. Crude 2-mercaptobenzothiazole is produced by a primary booster reaction of aniline with carbon disulphide and sulfur in a tubular reactor at temperatures above 250 ° C; . .

The disadvantages of these processes for the preparation of N-cyclohexylbenzothiazolyl-2-sulfenamide are disclosed in CS 215 179 and CS 225 046. Both describe a principally new efficient process for producing the product based on direct oxidative condensation of crude 2-mercaptobenzothiazole in excess of 1.60 to 1.95 moles of cyclohexylamine per mole of 2-mercaptobenzothiazole with sodium hypochlorite. Thus, N-cyclohexylbenzothiazolyl-2-sulfenamide of high purity is obtained in a yield of over 91% calculated on the loaded 2-mercaptobenzothiazole. Expensive refining steps are avoided in the process, since the role of the refining agent is unnecessary cyclohexylamine, which after solid phase separation is recovered from the mother liquors by distillation according to the CS 221 005 principle.

The mother liquors form a system of 2 phases. Regeneration of cyclohexylamine from the aqueous phase, which contains only sodium chloride from the hypochlorite used, is not difficult and the recovery rate reaches 0.99.

The problems are concentrated in the field of cyclohexylamine recovery from the so-called. an organic phase containing all contaminants from the crude 2-mercaptobenzothiazole as well as by-products of the oxidation of the intermediate cyclohexylammonium-benzothiazolyl-2-mercaptide. The weight ratio of cyclohexylamine to water and the total amount of organic matter in this phase is 4: 6: 1 and varies depending on the purity of the crude 2-mercaptobenzothiazole input as well as the dilution of the oxidizing agent and cyclohexylamine. In addition to cyclohexylamine, part of the unreacted 2-mercaptobenzothiazole, which binds the amine in the form of a salt (cyclohexylammonium benzothiazolyl-2-mercaptide), is present in the organic phase. The presence of water for the hydrolytic cleavage of this salt and the release of cyclohexylamine in atmospheric distillation is not sufficient, therefore, to increase the efficiency of cyclohexylamine recovery even at the exact dosage of the N-cyclohexylbenzothiazolyl-2-sulfenamide synthesis reagents, 100 parts of organic phase 497 /. However, under the conditions of continuous production of N-cyclohexylbenzothiazolyl-2-sulfenamide, the dosing accuracy of the reactants during oxidation is a considerable problem and the 2-mercaptobenzothiazole is often pre-oxidized,

We have now found that, depending on the degree of pre-oxidation of 2-mercaptobenzothiazole with sodium hypochlorite in excess of cyclohexylamine in the synthesis of N-cyclohexylbenzothiazolyl-2-sulfenamide, its separation and separation of filtrates at 20 to 80 ° C reduction reactions, essentially on the side of the benzothiazole component, without apparent chemical conversion of cyclohexylamine. In the area of pre-oxidation of the mixture, the predominantly rganic phase filtrates, as the end product of the sequence of the said redox reactions of 2-mercaptobenzothiazole, remain strong benzothiazolyl-2-sulfonic acid via its sulfonic and sulfonic acid which binds the cyclohexylamine present. The process according to CS 249 497, based on adding the most equivalent amount of mineral alkali to the organic phase, which is not sufficient to cleave said ionic bond. As a result of such losses of cyclohexylamine, the process for producing N-cyclohexylbenzothiazole-2-sulfenamide is considerably more expensive and its ecology deteriorates.

CS 274 352 Bl

The above drawbacks overcome the process of cyclohexylamine regeneration from aqueous solutions of 2-substituted benzothiazole-based salts in the preparation of N-cyclohexylbenzothiazolyl-2-sulfenamide from crude 2-mercaptobenzothiazole and sodium hypochlorite in excess of cyclohexylamine after solids separation, sodium hydroxide phase separation, according to the invention. Summary of the invention consists in that, per 100 parts of the organic phase is added prior to entering the atmospheric distillation of 1.4 to 5.0 parts by weight ^of sodium hydroxide in aqueous Toztoku to give cyclohexylamine is released from the ionic bond to the benzothiazolyl-2-sulfonic acid the distillate obtained is returned to the re-synthesis of N-cyclohexylbenzothiazolyl-2-sulfenamide and the bottoms product of the distillation columns is used as a secondary raw material.

An essential advantage of the process for the regeneration of cyclohexylamine according to the invention over the known processes is the higher yield of the considerable expensive cyclohexylamine which is returned to the shredding process. Another advantage of alkalizing the organic phase with an excess of mineral alkali, in particular sodium hydroxide, after separating N-cyclohexylbenzothiazolyl-2-sulfenamide and separating the filtrates is the binding of sulfur dioxide from the breakdown of benzothiazolyl-2-sulfonic acid as well as hydrolysis of the benzothiazole formed to 2-aminothiophenol. The alkali salt of 2-aminothiophenol then remains in the fifth separator column product so that benzothiazole does not increase in the distillate above 1% by weight, resulting in a continuous process of N-cyclohexylbenzothiazolyl-2-sulfenamide production progressively deteriorating by reducing the synthesis synthesis yields . The bottom product of atmospheric distillation is subsequently divided into 2 phases, the upper phase consisting of an aqueous solution of 2-mercapto-benzothiazole sodium salt and sulfuric acid, and the lower pitch pitch consisting of high molecular weight polymer and polycondensation materials from the entire 2-mercaptobenzothiazole production process. N-cyclohexylbenzothiazolyl-2-sulfenamide. In the alkalization of the organic phase with an excess of sodium hydroxide according to the invention and the atmospheric distillation of cyclohexylamine in the form of an azeotropic mixture which, after replenishment with fresh cyclohexylamine, returns to the re-synthesis of N-cyclohexylbenzothiazolyl-2-sulfenamide. not only will the economy but also the ecology of the process significantly improve. The aqueous phase of the mixture of sodium salts of 2-mercaptobenzothiazole and sulfuric acids is refined with lime milk and the clear solution thus purified after separation of the solid lime sludge is used for the production of technical scale 2-mercaptobenzothiazole or for subsequent oxidation and oxidation condensation products based thereon. The lower pitch of pitch may advantageously be used for the 3ditivation of honest and building-insulating bitumens.

The invention is illustrated but not limited by the following examples.

Example 1

Comparative example within the meaning of CS 249 497.

To 100 g of the organic phase from the filtrates after separation of N-cyclohexylbenzothiazolyl-2-sulfenamide containing 39.8% by weight of cyclohexylamine is added 1.3 g of sodium hydroxide as a dilute defective solution. The solution in the boiling flask of the distillation apparatus is heated to 105 ° C and 118 g of azeotropic mixture containing 33.2% by weight of cyclohexylamine and 1.38% by weight of benzothiazole are distilled off at atmospheric pressure and 94-97 ° C. The yield of cyclohexylamine related to its feed in the organic phase was 98.45%. The distillation residue is divided into 2 phases, the technical utilization of which is difficult.

CS 274 352 Dl

IN

Example 2

For 100 g of the organic phase of the same composition as in Example 1, 1.4 g of sodium hydroxide in the form of a dilute aqueous solution is used for distillation. Under unchanged conditions, 118 g of an atotropic mixture are obtained containing 32.8% by weight of cyclohexylamine and 0.85% by weight of benzothiazole. The cyclohexylamine yield based on its organic phase feed is 99.0%.

The distillation residue contains in active phases active ingredients suitable for subsequent use only after acidification with mineral acid.

Example 3

For 100 g of the organic phase and composition shown in Example 1, 3.0 g of sodium hydroxide in the form of a dilute aqueous solution was used for distillation. Under unchanged conditions, 120 g of an azeotropic mixture are obtained containing 33.0% by weight of cyclohexylamine and 0.64% by weight of benzothiazole. The cyclohexylamine yield based on its organic phase feed is 99.5%.

The distillation residue was separated into 2 phases. The upper phase contains the sodium salt of 2-mercaptobenzothiazole and sulfuric acids. This is refined with lime milk and, after separation of the sludge, a clear solution containing 2 to 5% by weight of 2-mercaptobenzothiazole (according to the degree of dilution) is obtained which is suitable for the subsequent production of technical scale products as well as oxidation or oxidation-condensation products. its base. The bottom phase weighing 4 to 7 g contains a mixture of high molecular weight polymer and polycondensation materials from the high-pressure synthesis of 2-mercaptobenzothiazole as well as the subsequent production of N-cyclohexylbenzothiazolyl-2-sulfenamide. odorless. Due to its advantageous processing properties, it is used in the preparation of honest building insulation bitumens.

Example 4

For 100 g of the organic phase of the composition given in Example 1, 5.0 g of sodium hydroxide in the form of a dilute aqueous solution are used to distil cyclohexylamine. 120 g azeotropic are obtained under unchanged conditions. mixtures containing 33.1% by weight of cyclohexylamine and 0.53% by weight of benzothiazole. The yield of cyclohexylamine relative to the organic phase feed is 99.8%.

The nature of the distillation residue in both the aqueous and pitch phases corresponds to the data given in Example 2.

Claims (1)

OBJECT OF THE INVENTION Process for the recovery of cyclohexylamine from aqueous solutions of 2-substituted benzo-azole salts in the preparation of N-cyclohexylbenzothiazolyl-2-sulfenamide from crude 2-mercaptobenzothiazole and sodium hypochlorite in excess of cyclohexylamine after solids separation, phase separation of filtrates and alkalization of organic phase Sodium hydroxide, characterized in that 1.4 to 5.0 parts by weight of sodium hydroxide in the form of an aqueous solution are added per 100 parts by weight of the organic phase prior to entering the atmospheric distillation and the distillate obtained below 1% by weight of benzothiazole is returned to the careful synthesis N-cyklohexylbenzotiazolyl-2-sulfenamide.