EP0618911A1

EP0618911A1 - Process for producing benzothiazolyl-2-sulphenamides

Info

Publication number: EP0618911A1
Application number: EP93901029A
Authority: EP
Inventors: Ludwig Eisenhuth; Manfred Bergfeld
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 1991-12-21
Filing date: 1992-12-16
Publication date: 1994-10-12
Also published as: WO1993013084A1; CA2126336A1

Abstract

Procédé de fabrication de benzothiazolyl-2-sulfénamides, consistant à faire réagir un 2-mercaptobenzothiazol ou un disulfure de 2,2'-dibenzothiazolyle avec une amine aliphatique ou cycloaliphatique primaire ou secondiare, en présence de peroxyde d'hydrogène comme oxydant, en milieu aqueux, caractérisé en ce qu'on ajoute, en quantités dosées, dans un intervalle de temps de 60 minutes au minimum, et à une température comprise entre 30 et 70 °C, à une suspension aqueuse renfermant respectivement l'amine et le 2-mercaptobenzothiazol ou le disulfure de 2,2'-dibenzothiazolyle, dans un rapport compris entre 1,0 et 1,5 mole d'amine par mole de 2-mercaptobenzothiazol ou l'équivalent de disulfure de 2,2'-dibenzothiazolyle, une solution aqueuse de peroxyde d'hydrogène, de préférence en une quantité inférieure à 1,35 mole par mole de 2-mercaptobenzothiazol ou par équivalent de disulfure de 2,2'-dibenzothiazolyle. La quantité d'eau dans le mélange réactionnel ne doit pas dépasser 1500 g mar mole de 2-mercaptobenzothiazol. On dispose ainsi d'un procédé économique, et ne nuisant pas à l'environnement, de fabrication de benzothiazolyl-2-sulfénamides, avec des rendements et une sélectivité élevés.Process for the manufacture of benzothiazolyl-2-sulfenamides, consisting in reacting a 2-mercaptobenzothiazol or a 2,2'-dibenzothiazolyl disulphide with a primary or secondary aliphatic or cycloaliphatic amine, in the presence of hydrogen peroxide as oxidant, in medium aqueous solution, characterized in that one adds, in measured quantities, in a time interval of at least 60 minutes, and at a temperature of between 30 and 70°C, to an aqueous suspension containing respectively the amine and the 2- mercaptobenzothiazol or 2,2'-dibenzothiazolyl disulphide, in a ratio of between 1.0 and 1.5 mole of amine per mole of 2-mercaptobenzothiazol or the equivalent of 2,2'-dibenzothiazolyl disulphide, a solution aqueous hydrogen peroxide, preferably in an amount less than 1.35 mole per mole of 2-mercaptobenzothiazol or per equivalent of 2,2'-dibenzothiazolyl disulphide. The amount of water in the reaction mixture should not exceed 1500 g mar mole of 2-mercaptobenzothiazol. This provides an economical process, which does not harm the environment, for the manufacture of benzothiazolyl-2-sulfenamides, with high yields and high selectivity.

Description

Process for the preparation of benzothiazolyl-2-sulfenamides

* * *

Description:

The present invention relates to a process for the preparation of benzothiazolyl-2-sulfenamides from 2-mercapto-benzothiazoles and primary or secondary amines in the presence of an oxidizing agent.

Sulfenamides are used in large quantities as vulcanization accelerators.

The benzthiazolyl-2-sulfenamides are industrially prepared from the sodium salt of 2-mercaptobenzthiazole and the corresponding amine with sodium hypochlorite or chlorine. The reaction is carried out according to the following reaction scheme (example preparation N-cyclohexyl-benzothiazolyl-2-sulfenamide):

(NaOH) MBTNa + CgH ₁₁ NH ₂ + NaOCl + ^J äH ₂ S0 ₄ >

MBT-NHC ₆ H _{1; L} + NaCl + ^ Na ₂ S0 ₄ + H ₂ 0

(MBT = 2-mercaptobenzthiazolyl residue) The disadvantage here is above all the formation of large amounts of inorganic salts, which heavily pollute the wastewater and make recycling of the mother liquor and the wash water impossible. Numerous other processes for the preparation of benzothiazolyl-2-sulfenamides have been proposed which do not have these disadvantages.

For example, DE-PS 33 25 724 describes a method in which according to the general reaction scheme

(Cu cat.)

MBT + HNRR '+ h0 ₀ '-> MBT-NRR '+ H 0

² (NH ₃ ) ²

a 2-mercaptobenzothiazole or a dibenzthiazolyl-2,2'-disulfide with a primary or secondary amine in the presence of molecular oxygen, a copper catalyst and ammonia at temperatures from 0 to 100 ° C. in excess amine or its Mixture can be reacted with water as the reaction medium. With this process, a very pure product with economical process management (high space / time yields, reusability of the mother liquor and continuous operation) could be obtained with high yields and selectivities. This patent specification, to which express reference is hereby made, also gives a good overview of the relevant prior art.

Furthermore, numerous publications describe processes for the preparation of benzothiazolyl-2-sulfenamides from 2-mercaptobenzothiazole and corresponding amines with hydrogen peroxide as the oxidizing agent, for example DE-A-31 27 193 mentioned in DE-PS 33 25 724, and also EP-A2 -0 180 869, DE-A-30 21 429 and DE-A-27 26 901. These Processes with hydrogen peroxide can form an interesting alternative to the above-mentioned oxygen process in that - unlike in DE-PS 33 25 724 - they work without additional auxiliaries such as metal catalyst and ammonia and without pressure. However, the processes described are unsuitable for economical use because the yields are too low or the very high excesses of amine and hydrogen peroxide are required. These excesses in turn lead to a reduced selectivity through side reactions, for example to oxidation products of the amine, sulfites or sulfates.

According to DE-A-31 27 193, a process for the preparation of N-cyclohexyl-benzothiazolyl-2-sulfenamide with 1.5 to 5 moles of cyclohexylamine per mole of 2-mercaptobenzothiazole is described, sodium hypochlorite and hydrogen peroxide being mentioned as oxidizing agents (test examples) . In all experimental examples with hydrogen peroxide (Examples 9-11), 2-mercaptobenzothiazole is reacted with a triple stoichiometric amount of cyclohexylamine and a 1.35 times stoichiometric amount of hydrogen peroxide; the yields are given as 87.1%, 87.0% and 84.9%. A reworking of Example 9, however, only led to a yield of 76%.

According to EP-A2-0 180 869, a process for the preparation of benzothiazolyl-2-sulfenaιrιiden from 2-mercaptobenzthiazole or its salts and primary amines is described up to a conversion of only 95%, in which chlorine bleach, chlorine is preferred as the oxidizing agent and hydrogen peroxide come into consideration, the only test example relating to the use of hydrogen peroxide starting from the sodium salt of 2-mercaptobenzothiazole and the Prescription of addition of sulfuric acid and sodium hydroxide solution, so sodium sulfate is still formed as a by-product. However, as already mentioned, the prerequisite for an economical, environmentally friendly process is one without additional auxiliaries and without by-products polluting the wastewater with a sufficiently high yield. A specific reference to this cannot be found elsewhere in EP-A2-0 180 869.

The yield, which is still insufficient for a problem-free, economical process for the production of sulfenamides based on hydrogen peroxide, was only recently confirmed in a lecture by Ken M. Dear, "Cleaning Up Oxidations with H2O ₂ ", held at the "International Symposium" ORPEC ^r 91 ", 29./30. April 1991, TU Munich, can be read in the "Symposium Abstracts". Therein, the maximum achievable yields are given as 77% (compared to 95% when using chlorine-containing oxidizing agents), which is in line with the yield obtained in the above-mentioned post-processing of Example 9 of DE-A-31 27 193 only 76% N-cyclohexyl-benzothiazolyl-2-sulfenamide. This lecture also documents the current public interest in a process based on hydrogen peroxide with improved yields of sulfenamide.

It was therefore an object of the present invention to provide an environmentally friendly and economical process for the preparation of benzothiazolyl-2-sulfenamides in high yield and high selectivity, starting from 2-mercaptobenzothiazole or dibenzothiazolyl-2,2'-disulfide, corresponding amines and Hydrogen peroxide according to the general reaction scheme MBT + HNRR '+ H ₂ 0 ₂ >MBT-NRR' + 2H ₂ 0

to provide.

This object is achieved by a process for the preparation of benzothiazolyl-2-sulfenamides by reacting a 2-mercaptobenzothiazole or dibenzthiazolyl-2,2'-disulfide with a primary or secondary aliphatic or cycloaliphatic amine in the presence of hydrogen peroxide as the oxidizing agent in aqueous medium, characterized in that to an aqueous suspension of the respective amine and the 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide in a ratio in the range between 1.0 to 1.5 mol of amine per mol of 2-mercaptobenzthiazole or equivalent of dibenzthiazolyl An aqueous hydrogen peroxide solution is metered in at a temperature in the range from 30 to 70 ° C.

It was very surprising that high yields are obtained even and especially with a greatly reduced excess of the starting compound amine, which additionally has the advantage of saving raw materials compared to the high amounts required according to DE-A-31 27 193 and an increased selectivity .

According to the invention, 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide to be reacted as starting substance can be found, for example, in DE-PS 33 25 724 on page 3, lines 34 to 58, or page 3, line 64 to page 4, line 4 , mentioned connections. However, the unsubstituted 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide is preferably used. Of the amines to be reacted according to the invention, cyclohexylamine is preferably used.

According to the invention, both the amine and the hydrogen peroxide can be used in a very slight stoichiometric excess over the amount of 2-mercaptobenzothiazole or dibenzthiazolyl-2,2'-disulfide used. A larger excess is possible, but for general economic considerations, but also to guarantee the desired higher selectivities, the amine excess should be below 50 mol% and the hydrogen peroxide excess should preferably be below 35 mol% and particularly preferably below 20 mol%. , each based on the amount of 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide used.

It was also very surprising that the success according to the invention can be achieved with a suspension of the reaction mixture, because the prior art cited at the beginning for the preparation of cyclohexylbenzthiazolylsulfenamide all points to an application of the reactants in solution (see, for example, DE-A-31 27 193, Claim 1, section (b): "Oxidation of the resulting solution"). Since the production of such solutions is promoted by higher amine excesses, such as are used, for example, according to DE-A-31 27 193, the small amine excess according to the invention was not only a reduced product yield, but also one Reduced solubility of the reaction partners in water is to be expected and the amine content according to the invention has not been suggested either. In fact, only one suspension and no solution is obtained with the amine / 2-mercapto-benzothiazole ratio according to the invention with economically still acceptable amounts of water. In addition, it was surprisingly also found that, in the context of the invention, higher amounts of water even lead to losses in the product yield. A total amount of water in the reaction mixture of 2000 g per mol of 2-mercaptobenzothiazole should therefore not be exceeded. The process according to the invention is preferably carried out with a total amount of water of at most 1500 g and particularly preferably at most 1000 g per mol of 2-mercaptobenzothiazole. The total amount of water is to be understood here as the sum of the water used for the reaction batch and the water chemically formed by the reaction.

It is particularly advantageous, however, that the process according to the invention can be carried out with surprisingly small amounts of water and thus high space / time yields can be achieved. For the success according to the invention, it is obviously only essential with regard to the amount of water in the lower range that the solid particles suspended in water form a stirrable suspension.

The concentration of the aqueous hydrogen peroxide solution used in the process according to the invention can be varied within wide limits. It should not be too low so as not to reduce the yields by using relatively large amounts of water. Highly concentrated hydrogen peroxide solutions lead to losses in the product selectivity and should also be excluded for safety reasons. Concentrations to be used advantageously in the process according to the invention are therefore in the range from 5 to 30% by weight of hydrogen peroxide.

The time within which the aqueous hydrogen peroxide solution in the reaction approach is metered in: the longer these metering times are selected, the higher the product yields. Dosing is preferably carried out within a time of at least 60 minutes and particularly preferably of at least 150 minutes. In this way, yields above 90%, based on the 2-mercapto-benzothiazole or dibenzthiazolyl-2,2'-disulfide used, are essentially achieved.

As already mentioned, the reaction temperature in the process according to the invention influences the selectivity. It is advantageously in the range from 30 ° C to 70 ° C; According to the invention, the best results are achieved at reaction temperatures in the range from 40 ° C. to 60 ° C. Poor product yields are obtained above 70 ° C and below 30 ° C, in the latter case surprisingly associated with increased by-product formation (e.g. sulfite, sulfate and sulfinic and sulfonic acids of 2-mercaptobenzothiazole).

The method according to the invention can be carried out in a very simple manner. Auxiliaries such as catalysts or solvents are not required. Additions of water-miscible solvents, such as alcohols, may be advantageous, for example to improve the stirrability of the reaction mixture. However, preference is given to working without additional solvents and the amount of water being chosen such that a stirrable mixture of the starting compounds is formed in the form of a fine, homogeneous suspension, for example 2 parts by weight of water per 1 part by weight of 2-mercaptobenzothiazole / amine mixture.

In general, the 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide and the amine are mixed and mixed together with water in a reaction vessel Reaction temperature, for example 50 ° C, heated. However, the salt formed from 2-mercaptobenzothiazole and the respective amine, in particular cyclohexylamine, can also be introduced. In this latter case, only that amount of amine has to be added which is required for the stoichiometric excess desired in each case. The aqueous hydrogen peroxide solution is then evenly metered into the stirred mixture, the contents of the reaction vessel being kept at the reaction temperature. After the end of dosing there follows a relatively short post-reaction phase, for example of about 30 minutes, at the same temperature. The reaction mixture is then cooled to room temperature and the solid reaction product is filtered off and washed with water, optionally after washing with a mixture of the amine and water used in each case. The amine can be recovered from the mother liquor by distillation, and possibly also unreacted 2-mercapto-benzothiazole or dibenzthiazolyl-2,2'-disulfide.

The purity is determined by titration, HPLC and the melting point.

The product obtainable with the method according to the invention without additional cleaning measures is characterized by high purity with values above 98%.

The process according to the invention fulfills essential criteria for an environmentally friendly and economical process for the preparation of N-cyclohexylbenzthiazolyl-2-sulfenamides: A wastewater pollution is largely avoided, in particular due to the absence of by-products and Auxiliaries, such as catalysts and generally also solvents, an environmentally compatible oxidizing agent is used, simple chemical compounds in a small stoichiometric excess are used, and a simple, unpressurized reaction is a pure end product compared to the state of the art Technically superior high yield and high selectivity obtained.

The present invention is explained in more detail by the following experimental examples.

example 1

175 g of 95.5% strength 2-mercapto-benzothiazole (1 mol), 500 g of water and 118 g of cyclohexylamine (1.2 mol) were thoroughly mixed in a 1 l reactor with stirrer, reflux condenser and metering device. The fine suspension of the cyclohexylamine salt of 2-mercaptobenzothiazole obtained in this way was brought to 50 ° C. and reacted with vigorous stirring with a 12.6% strength aqueous hydrogen peroxide solution (1.1 mol), which was metered in over the course of 5 hours. The reaction temperature was always kept at 50 ° C. The mixture was then stirred at the same temperature for 30 min. The precipitate was filtered off after cooling to room temperature and washed with a 10% aqueous cyclohexylamine solution, then with water and dried.

This gave 250.2 g of a product which, in its analytical data (elemental analysis, IR, HNMR), is identical to cyclohexylbenzthiazolylsulfena id. The mother liquor still contained 4.3 g of unreacted 2-mercaptobenzothiazole. The 2-mercapto-benzothiazole conversion is 97.4% and the yield of cyclohexyl-benzothiazolylsulfenamide is 94.8% of theory.

The purity of the cyclohexylbenzthiazolylsulfenamide product is 99.1% (titration according to Lichty, J. Applied Chem., 2, 26, (1963)), the melting point 100-101 ° C.

Example 2

The procedure is as in Example 1, but the hydrogen peroxide solution is metered in over 3.5 h. Cyclohexylbenzthiazolylsulfenamide was thereby obtained in a yield of 92.6% of theory received (purity 98.5%).

Example 3

The procedure was as in Example 1, but the hydrogen peroxide solution was metered in over 1 h. Cyclohexylbenzthiazolylsulfenamide was obtained in a yield of 89.5% of theory receive.

Example 4

The procedure was as in Example 2, but the reaction temperature was raised to 60.degree. Cyclohexylbenzthiazolylsulfenamide was obtained in a yield of 93.4% of theory received (purity 98.2%).

Example 5

In this example, dibenzthiazolyl-2,2'-disulfide is used instead of 2-mercaptobenzthiazole.

In the reaction device described in Example 1, 332 g of dibenzthiazolyl-2,2'-disulfide (0.5 mol), 1.2 mol of cyclohexylamine and 640 g of water were reacted with vigorous stirring and warmed to 50.degree. 140 g of an aqueous hydrogen peroxide solution (0.55 mol) were metered in at this temperature within 3.5 h. The product was separated off as in Example 1 and in a yield of 96.7% of theory won (purity 98%).

Example 6

The procedure was as in Example 2, but the 2-mercaptobenzothiazole and cyclohexylamine were introduced in 630 g of water, and the hydrogen peroxide was metered in in a 24.6% solution (1.1 mol in 152 g of solution).

Cyclohexylbenzthiazolylsulfenamide was thereby obtained in a yield of 90.4% of theory obtained (mp. 100-101 ° C).

Example 7

The procedure was as in Example 1, but only 1.1 mol of cyclohexylamine were used.

Cyclohexylbenzthiazolylsulfenamide was obtained in a yield of 92.8% (mp. 100-101 ° C).

Example 8

The procedure was as in Example 1, but at a reaction temperature of 40 ° C. Cyclohexylbenzothiazolylsulfenamide was obtained in a yield of 92.1% of theory obtained (mp. 99-101 ° C). Example 9

The procedure was as in Example 1, but at a reaction temperature of 30 ° C. The yield of cyclohexylbenzthiazolylsulfenamide was 87.1% and the 2-mercapto-benzothiazole conversion was 93.8% of theory (Mp 99-101 ° C).

Example 10

This example shows the strong influence of the amount of water on the product yield.

The procedure was as in Example 1, but the amount of water for the preparation of the suspension from mercaptobenzothiazole and

Cyclohexylamine was increased from 500 g to 750 g. A product yield of only 83% was achieved

(Mp 99-101 ° C).

Example 11 (comparative example)

Example 1 from DE-A-31 27 193 was followed up: In a 250 ml glass reactor, 59.9 g of 50% aqueous cyclohexylamine and 0.1 mol of 2-mercaptobenzothiazole were heated to 85 ° C. with vigorous stirring, the temperature rising resulting 2-mercaptobenzothiazole cyclohexylamine salt largely dissolved. After cooling to 45 ° C., 92 g of 5% hydrogen peroxide (0.135 mol) were metered in over the course of 60 min with vigorous stirring. After stirring for 30 min at the same temperature, the mixture was cooled to room temperature and the precipitate was filtered off, washed with 10% cyclohexylamine solution and water and dried. Cyclohexylbenzthiazolylsulfenamide was thereby obtained in a yield of 75.6% of theory obtained (melting point 99-100 ° C; purity (titration according to Lichty) 97.6%).

Claims

* * * Claims:

1. Process for the preparation of benzothiazolyl-2-sulfenamides by reacting a 2-mercaptobenzothiazole or dibenzthiazolyl-2,2'-disulfide with a primary or secondary aliphatic or cycloaliphatic amine in the presence of hydrogen peroxide as an oxidizing agent in an aqueous medium , characterized in that to an aqueous suspension of the respective amine and the 2-mercaptobenzthiazole or dibenzthiazolyl-2,2'-disulfide in a ratio in the range between 1.0 to 1.5 mol of amine per mol of 2-mercaptobenzthiazole or equivalent dibenzthiazolyl An aqueous hydrogen peroxide solution is metered in at a temperature in the range from 30 to 70 ° C. to 2,2'-disulfide.

2. The method according to claim 1, characterized in that the total amount of water in the reaction mixture does not exceed 1500 g and preferably 1000 g per mol of 2-mercaptobenzothiazole.

3. The method according to claim 1 or Δ, "characterized gekenn¬ characterized in that the hydrogen peroxide in an amount below 1.35 mol and preferably below 1.2 mol per mol of 2-mercaptobenzothiazole or per equivalent of dibenzthiazolyl-2,2 ' -disulfide is used.

4. The method according to one or more of claims 1 to 3, characterized in that the aqueous hydrogen peroxide solution within a time of at least

60 minutes and preferably at least 150 minutes.

5. The method according to one or more of claims 1 to 4, characterized in that the reaction is carried out at a temperature in the range from 30 ° C to 70 ° C and preferably from 40 ° C to 60 ° C.

6. The method according to one or more of claims 1 to 5, characterized in that cyclohexylamine is used as the amine.