EP0000464A1 - Process for the purification of mercapto benzothiazole - Google Patents

Abstract

Process for the purification of mercaptobenzothiazole prepared according to known processes, characterized in that the crude product is treated with carbon tetrachloride or tetrachloro-1,1,2,2 ethylene.

Description

Mercaptobenzothiazole is known in the elastomer processing industry for its use as a vulcanization accelerator. It is also an important raw material in the synthesis of more sophisticated vulcanization accelerators adapted to the particular problems posed by the manufacture of articles as different as for example, tires, electric targets, shoe soles, seals. insulation. It is also used for a large part in the synthesis of phytosanitary compounds.

Most known manufacturing processes involve the reaction, in appropriate proportions, at high temperature and high pressure, of aniline, sulfur and carbon sulfide. Others use, either the reaction of thiocarbanilide, carbon sulfide and sulfur (US Patent No. 1,712,968 of May 5, 1929); either to the reaction of orthochlornitrobenzene, hydrogen sulfide or an alkali sulfide and carbon sulfide (US Patent 1,960,205 of 5/22/1934; Polish Patent No. 86988 of 12/15/1976); or again the reaction of benzothiazole and sulfur (German patent No. 2,551,060 of 5/26/1976). The reaction product obtained under such conditions is never directly usable as it is. It contains, in fact, unreacted raw materials, for example aniline, etc., by-products and intermediates such as benzothiazole, anilinobenzothiazole. Self purification The crude reaction product is necessary.

Many purification methods have been proposed to date. They basically use two techniques which differ mainly in concentrations, order of use, nature of the recommended reagents, treatment temperatures.

• - solubilisation du produit de réaction en milieu alcalin (hydroxyde d'ammonium, hydroxyde de sodium, chaux), précédé ou non d'un traitement en milieu acide minéral ;
• - séparation des impuretés insolubles par filtration ;
• - séparation des impuretés solubles après leur insolubili- sation par oxydation et/ou extraction à l'aide d'un solvant ;
• - précipitation du mercaptobenzothiazole par action d'un acide minéral.

The schematic diagram of the first technique is as follows:

• - solubilization of the reaction product in an alkaline medium (ammonium hydroxide, sodium hydroxide, lime), whether or not preceded by a treatment in mineral acid medium;
• - separation of insoluble impurities by filtration;
• - separation of soluble impurities after their insolubilization by oxidation and / or extraction using a solvent;
• - precipitation of mercaptobenzothiazole by the action of a mineral acid.

US patents 1,631,871, 2,658,864, 2,730,528 and 3,818,025 and French patent 2,135,807 illustrate the application in whole or in part of such a process.

In the other technique, the impurities are extracted by treatment of the reaction product with carbon sulfide or an emulsion of carbon sulfide and water.

US patents 2,090,233, 3,030,373 and 3,031,073 illustrate this embodiment.

• - récupération difficile des matières premières n'ayant pas réagi et que l'on a le plus grand inférât économique à recycler (aniline tout particulièrement),
• - nécessité d'opérer à des concentrations peu élevées pour favoriser la précipitation des impuretés, avec pour conséquence des appareillages de grandes dimensions,
• - pertes, par dégradation chimique, du mercaptobenzothiazole au cours des réactions d'oxydation destinées à insolubiliser les impuretés solubles en milieu alcalin,
• - pertes, par solubilisation dans le sulfure de carbone, du mercaptobenzothiazole ou recyclage inévitable d'une partie des impuretés si la quantité de sulfure de carbone est limitée,
• - enfin, et c'est peut-être l'inconvénient majeur de ces procédés, l'obligation d'avoir à traiter avant leur rejet de grands volumes d'effluents aqueux contenant de fortes charges polluantes. Ces traitements sont difficiles et co0teux. Les processus d'oxydation généralement appliqués ne conduisent pas aux molécules simples souhaitées d'azote, de gaz carbonique et d'anhydride sulfureux mais à un taux non acceptable de molécules solubles qui ne sont dégradées que par un traitement biologique complémentaire aggravant lourdement le coût des unités de production.

Although they are currently used industrially, these methods are not satisfactory and each have, in whole or in part, the following drawbacks

• - difficult recovery of raw materials which have not reacted and which have the greatest economic inferate to recycle (particularly aniline),
• - need to operate at low concentrations to promote the precipitation of impurities, resulting in large equipment,
• - losses, by chemical degradation, of mercaptobenzothiazole during oxidation reactions intended to insolubilize soluble impurities in an alkaline medium,
• - losses, by solubilization in carbon sulphide, of mercaptobenzothiazole or inevitable recycling of part of the impurities if the quantity of carbon sulphide is limited,
• - Finally, and this is perhaps the major drawback of these processes, the obligation to have to treat large volumes of aqueous effluents containing high pollutant loads before they are discharged. These treatments are difficult and expensive. The oxidation processes generally applied do not lead to the desired simple molecules of nitrogen, carbon dioxide and sulfur dioxide but to an unacceptable level of soluble molecules which are only degraded by a complementary biological treatment greatly aggravating the cost of production units.

However, it has been found, in the departments of the applicant, that it is possible, from the crude product resulting from known processes, to obtain mercaptobenzothiazole with a high yield and in a high state of purity, by means of a simplified technology. Thanks to this process, the unreacted intermediate products and raw materials are easily recyclable, the by-products can be separated without difficulty. On the other hand, due to the lack of use of water, the problems of effluent treatment are eliminated.

The process according to the invention for the purification of mercaptobenzothiazole is characterized in that the crude product obtained according to the known processes is treated with carbon tetrachloride or tetrachloro-1,1,2,2 ethylene (C1 ₂ C = C C1 ₂ ) with or without prior distillation of volatile products.

When the purification process is applied to the raw product separated from volatile products (such as aniline and benzothiazole, which can be recycled after recovery), in a first phase, the separation of volatile products can be carried out by distillation over a wide range of temperature (100 to 300 ° C).

Due to the risk of thermal decomposition of mercaptobenzothiazole, it is preferable that this temperature be less than 220 ° C, the interval of choice being 100 to 150 ^* C. preferably used a thin film evaporator scraper that allows to recover the solid product in powder form. The vacuum which it is necessary to maintain in the apparatus depends on the temperature chosen if it is generally between 10 and 200 millimeters of mercury.

In a second phase, the crude mercaptobenzothiazole to be purified, obtained after distillation, is suspended in carbon tetrachloride or tetrachloro-1,1,2,2 ethylene.

When the purification process is applied without prior separation of the volatile products, the crude reaction product is directly suspended in carbon tetrachloride or tetrachloro-1,1,2,2 ethylene. The recovery of recyclable products is carried out in this case by distillation of the solvent phase obtained after separation of the insoluble purified mercaptobenzothiazole.

In all cases, for reasons of economy, it is preferred to limit the concentration of the solid product in suspension in the solvent to a value of between 200 and 400 grams per liter. The dissolution of impurities is all the easier when the product to be purified is more finely divided. Any known means allows this condition to be easily achieved.

• - de 0°C à 77°C, température d'ébullition du tétrachlorure de carbone à la pression de 760 mm de mercure, préférentiellement dans l'intervalle de 10°C à 50°C,
• - de 0°C à 121°C, température d'ébullition du tétrachloro-1,1,2,2 éthylène à la pression de 760 mm de mercure, préférentiellement dans l'intervalle de 10°C à 80°C.

The treatment according to the invention can be carried out over a wide range of temperatures:

• - from 0 ° C to 77 ° C, boiling temperature of carbon tetrachloride at the pressure of 760 mm of mercury, preferably in the range of 10 ° C to 50 ° C,
• - from 0 ° C to 121 ° C, boiling temperature of 1,1,2,2 ethyl tetrachloro at the pressure of 760 mm of mercury, preferably in the range of 10 ° C to 80 ° C.

Carrying out the treatment at temperatures lower or higher than the above-mentioned preferential intervals does not harm the invention, but is of no particular interest and can unnecessarily complicate the apparatus.

The final recovery of the mercaptobenzothiazole is done by any known means of filtration and drying. The solu tion resulting from filtration is subjected to a distillation so as to recover the tetrachloride or tetrachloro-1,1,2,2 ethylene and to separate the products to be recycled in whole or in part.

The following examples illustrate the invention without limiting it.

EXAMPLE 1.

1000 grams of reaction product of aniline, sulfur and carbon sulfide are taken, at the temperature of 180 ° C., at the outlet of a mercaptobenzothiazole synthesis reactor and after degassing of the hydrogen sulfide. , whose composition is as follows:

This product is introduced into a scraper evaporator in which a temperature of 130 ° C. and a vacuum of 15 millimeters of mercury are established.

The volatile materials distill and by condensation, 54 grams of a light yellow oil are collected, assaying 57.3% in aniline and 35.2% in benzothiazole.

The solid product, extracted from the evaporator, ground, is suspended in 2300 ml of carbon tetrachloride, at a temperature of 25 ° C. After one hour of stirring, the suspension is filtered, washed with twice 300 ml of carbon tetrachloride, wrung and dried.

836.5 grams of a light yellow product are obtained, titrating 99% of mercaptobenzothiazole and of uncorrected melting point 177-180 _. C. The purification yield is 99.2%.

The fraction containing aniline and benzothiazole can be recycled in the synthesis reactor without further treatment. The carbon tetrachloride solution containing the by-products is distilled so as to recover the recyclable solvent. A non-distillable fraction weighing 109 grams is collected; it can be recycled in the manufacture of mercaptobenzothiazole.

The mercaptobenzothiazole subjected to purification is indifferently the crude product obtained according to any one of the known methods for its preparation; we can cite among others that of US Patent 1,631,871.

EXAMPLE 2.

The procedure is as in Example 1 but using tetrachloro-1,1,2,2 ethylene. The results are identical. The mercaptobenzothiazole subjected to purification is indifferently the crude product obtained according to any of the known methods for its preparation.

EXAMPLE 3.

1,000 grams of reaction product of aniline, sulfur and carbon sulfide, the composition of which is as follows, are taken at 200 ° C., at the outlet of a mercaptobenzothiazole synthesis reactor:

This product is introduced, with stirring, in approximately 30 minutes into 2,000 ml of 1,1,2,2,2-ethylene tetrachloro maintained by cooling to the temperature from 20 to 25 ° C.

After one hour of stirring, the suspension of mercaptobenzothiazole is filtered, washed with 2 to 3 times 300 ml of tetrachloro-1,1,2,2 ethylene, drained and dried. 827 grams of light yellow product are obtained, titrating 98.5% of mercaptobenzothiazole with an uncorrected melting point 177-180 ° C. The purification yield is 97.5%.

From the solvent phase recovered by filtration, 50 grams of a mixture of recyclable aniline and benzothiazole are obtained by distillation.

EXAMPLE 4.

The procedure is as in Example 3 but replacing the 1,1,2,2 ethyl tetraehloro by carbon tetrachloride. The results are identical.

Claims (7)

1) Process for the purification of the mercaptobenzothiazole prepared according to the known processes, characterized in that the crude product is treated with carbon tetrachloride or tetrachloro-1,1,2,2 ethylene. 2 °) Process as claimed in 1 °) in which the crude product is treated with carbon tetrachloride or tetrachloro-1,1,2,2 ethylene without prior separation of the volatile matter. 3 °) Process as claimed under 1 °) in which the crude product is treated with carbon tetrachloride or tetrachloro-1,1,2,2 ethylene after preliminary separation of the volatile matter by distillation under reduced pressure. 4 °) Process as claimed in 3 °) in which the distillation is carried out at a temperature below 220 ° C under 10 to 200 millimeters of mercury. 5 °) A process as claimed in each of claims 1, 2 and 3 characterized in that the crude product is suspended in carbon tetrachloride or 1,1,2,2 ethyl tetrachloride at an equal or lower temperature at the boiling point of the solvent. 6 °) Process as claimed under each of claims 1, 2, 3, 4 and 5 characterized in that the purified mercaptobenzothiazole, insolubilized in carbon tetrachloride or 1,1,2,2 ethyl tetrachloro is separated by all known physical means. 7 °) Process as claimed in each of claims 1, 2, 3, 4, 5 and 6 characterized in that the solvent phase obtained after separation of the purified mercaptobenzothiazole is distilled so as to be able to recover carbon tetrachloride or tetrachloro- 1,1,2,2 ethylene.