CS230287B1 - Method of purifying 2-mercaptobenzthiazole - Google Patents

Description

The invention relates to a process for purifying 2-mercaptobenzothiazole prepared by a high pressure reaction of aniline, carbon disulphide and sulfur. The 2-mercaptobenzothiazole (2-MBT) melt prepared by this reaction is contaminated with feedstock residues, benzothiazole, 2-phenylaminobenzothiazole, thiocarbainilide, and high molecular weight polycondensation compounds based on 2-substituted arylthiazoles. On an industrial scale, the mixture from high pressure reactors expands against atmospheric pressure, thereby separating most of the volatile components mainly hydrogen sulfide, carbon disulphide and aniline. The crude 2-mercaptobenzothiazole melt is then refined by dissolving it in alkali containing sodium hydroxide, sodium carbonate, lime milk, or ammonia, using oxidizing agents in the presence of adsorbents. Oxidative degradation eliminates from the solution of the corresponding salt a portion of pitch which is filtered off on the adsorbent. In some cases, an organic water-immiscible solvent is added to the refining step to increase the degree of refining, in which the pitch substances are separated as a separate phase. The solvents are then recovered and the distillation residue is incinerated. In any case, however, by incomplete separation of the impurities in the expansion column, some of the toxic components get into the 2-mercaptobenzothiazole salt solutions and are further processed into final products, such as disulfides and disulfides, respectively. sulfeinamides, negatively affect the environment. When adsorbents or organic solvents are used, the losses of 2-mercaptobenzothiazole are greatly increased and the economy of combing is worsened.

For that reason. The crude 2-mercaptoben: thiazole from the expansion column is pretreated before refining in aqueous alkaline solutions according to new processes.

U.S. Pat. No. 2,090,233 utilizes carbon disulphide to remove residual volatile components and benzthiothiol, through which the melt of 2-mercaptobenzothiazole is washed and recovered from the solution of contaminants by distillation. The process is very demanding from a safety point of view and its further disadvantage is a reduction in the yield of 2-mercaptobenzothiazole due to losses in the distillation residue.

U.S. Patents 2,658,846, 2,730,528 and Japan. pat. No. 4886/1955 protects admixture separation processes in which the crude melt of 2-mercaptobenzothiazole passes from the expansion column to other refining columns in which j. is heated by superheated steam at 170 to 240 ° C. A disadvantage of these processes ' is the long residence time of the superheated melt at high temperatures, thereby decomposing the 2-mercaptobenzothiazole and sulfur, which conditions the crosslinking of the pure component and reduces the efficiency of the process. The processes of these patents require the use of large amounts of steam and cause problems with condensate disposal.

Jap. pat. No. 2,022,569 describes separating impurities from 2-mercaptobenzothiazole by distilling the crude melt at a pressure of 0.065 to 0.65 kPa and a temperature of 200 to 220 ° C. The distillate front fractions return to the pressure reaction of the aniline with carbon disulphide and sulfur, the bottoms of the distillation columns being burned. The disadvantage of the process is the considerable loss of 2-mercaptobenzothiazole in the distillation residues and the necessity to operate at low pressures with the possibility of the explosive mixtures being lifted by the non-insulation of the equipment.

AO 197 512 describes a highly efficient process for removing volatile constituents and benzothiazole from a crude melt of 2-mercaptobenzothiazole with a gaseous, intact carrier, which is hydrogen sulfide formed during the high pressure reaction of aniline, carbon disulphide and sulfur. The stream of recycled hydrogen sulphide, carbon disulphide, aniline, beinztiazole and thiocarbanide is removed from the crude 2-mercaptobenzothiazole melt directly in the expansion column downstream of the pressure reactor. A process that is highly efficient and has a positive environmental impact is that hydrogen sulfide gas is fed to the bottom of the expansion column where it comes into contact with the countercurrent flowing raw melt. For this purpose, a packed or trayed column may be used. The hydrogen sulphide saturated with the volatile constituents exits through the top of the column and the pre-purified melt falls into the boiling system, where it dissolves in the alkali and resp. in cyclohexylamine and the resulting inorganic, respectively. organic salts of 2-mercaptobemisthiazole are used to produce the final products of disulfide, resp. sulfenamide type. The volatiles were separated from the hydrogen sulphide by condensation and used to synthesize the 2-mercaptobinetic acid. To pre-purify the crude melt to the desired degree, 0.2 to 10 parts by weight of hydrogen sulphide transported to the column by a fan whose committee is determined by the pressure drop in the circuit is used per 1 part by weight of 2-mercaptobenzothiazole. The content of 2-mercaptobenzothiazole in the pre-purified melt ranges from 90 to 92, and the content of benzothiazole from 0.3% by weight.

It has now been found that the 2-mercaptobenzothiazole prepared by the high pressure reaction of aniline, carbon disulphide and sulfur can be purified according to the invention by treating the crude reaction mixture in one step with superheated steam at a temperature of 140-180 ° C, at 20 to 60 minutes in an amount of 0.8 to 1.1 parts by weight of steam per 1 part by weight of the crude mixture.

The 2-mercaptobenzothiazole can be purified by the apparatus according to the invention, which consists of a continuous tubular reactor, a pressure reducing valve, a separation column with an expansion zone and a refining zone, a condenser and a separator.

The major advantage of this method of purification is that the pre-purified crude melt of 2-mercaptobenzothiazole contains 90-92% by weight of the pure component and, after dissolution in sodium hydroxide, lime milk or in an excess of cyclohexylamine, respectively. morpholine is used for the economic and ecological preparation of pure products for the vulcanization of rubbers.

One possible modification according to the invention is shown in the attached drawing.

The device consists of a continuous tubular reactor 1, a pressure reducing valve

2, a separation column 3 with an expansion zone to remove the predominant purity of the volatile components 4 and a refining zone to remove the bulk of the volatile components 5, a condenser for steam condensate 6 and a separator for separating the aqueous layer 7.

Superheated water vapor can be used to remove volatile constituents and benzothiazole from the crude melt of 2-mercaptobenzothiazole if the treatment of the crude high pressure reaction mixture of aniline, carbon disulfide and sulfur takes place zoneally in a single separation column 3. In the expansion zone 4 of this expansion zone 4. the reaction mixture frees most of the volatile components, mainly hydrogen sulfide, carbon disulphide and aniline. It then falls into a refining zone 5 filled with Pall rings where the aniline and benzothiazole residues are removed by counter-current steam at 140-180 ° C. At a relatively short 30-minute residence time of the raw melt in the refining zone 5 of the separation column 3 and a steam feed rate of 0.8 to 1.1 parts by weight per 1 part by weight of the melt falling through from 0.8 to 1.1 parts by weight at 210 to 1.1 parts by weight 220 [deg.] C. there is no observable decomposition of 2-mercaptobenzothiazole and the pre-purification is carried out to a high degree, except for a toaster of one weight percent residual benzothiazole, which represents an average process efficiency of 85%.

Distillate leaving the separation column

3, it passes through a capacitor 6 and a phase separator in which the benzothiazole layer is separated from the water. The benzothiazole layer, after analysis, returns to the pressure synthesis of 2-mercaptobenzothiazole, or is used together with part of the aqueous layer to prepare 2-aminothiophenol-based derivatives.

The following examples illustrate but do not limit the invention.

Example 1

Product of continuous high pressure reaction of aniline, carbon disulphide and sulfur in hourly quantities:

2-mercaptobenzothiazole 2.80 kg hydrogen sulfide with carbon disulfide 0.79 kg aniline with benzothiazole 0.27 kg pitch 0.24 kg passes from the tubular reactor through an irrigation valve to the column separator expansion zone, from where at atmospheric pressure and temperature 210 up to 220 ° C expanded into a degassing system with 0.79 kg of hydrogen sulfide with carbon disulphide and 0.08 kg of aniline with benzothiazole. The residue falls into the refining zone of a Pall ring separator column, into which 3.2 kg of steam is fed at a temperature of 140-170 ° C, a pressure of 105 kPa, through a control circuit. In the exiting steam from the refining zone there are 0.010 kg of 2-mercaptobenzothiazole and 0.16 kg of aniline with benzothiazole. The separation zone of the separation column leaves 2.79 kg of 2-mercaptobenzothiazole 0.03 kg of benzothiazole and 0.24 kg of pitch-cointaminating components.

Example 2:

Pre-purified melt of composition [% by weight]

2-mercaptobenzothiazole 91.2 Benzothiazole 1.0 pitch component 7.8 is dissolved in an equivalent amount of sodium hydroxide diluted with water to a concentration of 3-5 wt% or at 10-100 mol% with stirring at 40-50 ° C. excess calcium hydroxide suspended in water. Conventional precipitation of 2-mercaptobenzothiazole from a solution of sodium or calcium salt with mineral acid, filtration of the suspension, washing with water and drying affords the final product containing 98% pure component in a yield of 98.4%.

By boiling the pre-purified melt of the above composition at 40 to 50 ° C in a 200 to 300% molar excess of cyclohexylamine and oxidizing the cyclohexylamine salt of 2-mercaptobenzothiazole with sodium hypochlorite, filtration of the suspension, washing with water and drying yields the final product containing 99.3 % N-cyclohexylbenzothiazole-2-sulfenamide in a yield of 90.2 percehta.

Oxidative treatment of the cyclohexylamine salt of 2-mercaptobenzothiazole prepared by boiling an unpurified melt containing 6% by weight of benzothiazole at a temperature of 40 to 50 ° C in a 200 to 300% molar excess of cyclohexylamine yields after filtration of the suspension, washing with water and drying. 1% N-cyclohexylhenzothiazole-2-sulfenamide in 87.1% yield.

Example 3

The distillate from the refining zone 5 of the separation column 3 passes through a condenser 6 to a separator 7 in which a benzothiazole layer of (by weight) benzothiazole aniline is separated.

2-mercaptobenzothiazole water hydrogen carbonate hydrogen sulfide

88.8 to 92.8 1.0 to 5.0 5.90 0.25 feet

This is diluted 1: 10 or more with fresh aniline and to a high pressure reaction! with carbon disulphide and sulfur is dosed in a molar ratio: (aniline + benzothiazole): carbon disulphide:

Sulfur = 1.0: 1.1 to 1.2: 1.0. By returning the benzothiazole fraction to the high pressure reaction of aniline with carbon disulphide and sulfur in a continuous rector at a terminal temperature of 280 to 290 ° C, yields of 2-mercaptohenzothiazole calculated on fresh aniline of 91% are achieved.

If desired, the benzothiazole layer together with the water separated in a continuous separator is used to produce 2-aminothiophenol derivatives. Hydrolysis of the mixture is carried out in a heated reactor at 100 ° C with an excess of concentrated sodium hydroxide solution. The hydrolytic decomposition product is the salt of 2-aminothiophenol and methanoic acid. From the reaction mixture, unreacted aniline is distilled off with water vapor and the residue is worked up to the final 2-aminothiophenol type products.

Claims (2)

SUBJECT 1. Spdsob purification of 2-mercaptobenzothiazole, prepared by high pressure reaction of aniline, sulfur and síirouhlíka characterized in that the crude reaction mixture was treated in one step by superheated steam having a temperature of 140 to 180 ^Q C and a pressure 101 to 120 kPa for 20 to 60 minutes, in an amount of 0.8 to 1.1 parts by weight of steam per 1 part by weight of the crude reaction mixture. 2. Apparatus according to claim 1, characterized in that it consists of a continuous tubular reactor (1), a pressure reducer (2), a separation column (3) with an expansion zone (4j) to remove most of the volatile components and a refining zone (1). 5J to remove the remaining volatile components, a condensate (6) for steam condensate and a separator (7) for separating the aqueous layer.