WO2024142008A1

WO2024142008A1 - A process for the preparation of 2,2' dithiobisbenzanilide

Info

Publication number: WO2024142008A1
Application number: PCT/IB2023/063374
Authority: WO
Inventors: Lakshmanan JAYABALAN; Janardanan Kapyur NAMBOODIRI; Monojit CHAUDHURI
Original assignee: Nitrex Chemicals India Limited
Priority date: 2022-12-29
Filing date: 2023-12-29
Publication date: 2024-07-04

Abstract

The present disclosure relates to a process for the preparation of 2,2'- dithiobisbenzanilide The process involves the hydrolysis of benzothiazole, followed by subsequent oxidation, and the benzoylation of the resulting reaction products to yield 2,2'-dithiobisbenzanilide. The process of the present disclosure is a one-pot synthesis and uses a minimal amount of base for the synthesis of 2,2'-dithiobisbenzanilide. The process is simple, economical, eco-friendly, and commercially scalable.

Description

A PROCESS FOR THE PREPARATION OF 2,2’ DITHIOBISBENZANILIDE FIELD The present disclosure relates to a process for the preparation of 2,2’-dithiobisbenzanilide. DEFINITIONS As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise. Peptizers refer to a group of chemicals used in rubber industries as a processing aid to reduce the viscosity of rubber, and to enhance the uniform mixing of other additives such as vulcanizing agents, accelerators, fillers, activators, and the like during the rubber compounding. Rubber compounding refers to a process of blending different additives with raw rubber before the vulcanization, or curing. Initial melting point refers to a temperature at which the solid starts melting and the first drop of liquid is observed. BACKGROUND The background information herein below relates to the present disclosure but is not necessarily prior art. 2,2’-dithiobisbenzanilide (DBD) is used as a chemical peptizer in the rubber industry. DBD reduces the viscosity of a natural rubber and a synthetic rubber. It acts as a masticating agent and aids in promoting easy handling and uniform mixing during rubber compounding. The use of these agents provides a more productive and a less energy-intensive operation, by achieving the intended viscosity of the rubber. The structural representation of 2,2’- dithiobisbenzanilide (DBD) is given as a formula (I) below:

CA -57-9 The commercial peptizers containing 2,2’-dithiobisbenzanilide are available in various concentrations along with fillers, activating agents, metal boosters, processing oil, and the like. These peptizers are less toxic and environment friendly when compared to more toxic pentachlorothiophenol based chemical peptizers. Various methods for the preparation of 2,2’-dithiobisbenzanilide are known in the art. Conventionally known methods employ huge amounts of inorganic sulfides and inorganic bases, which leads to a higher amount of formation of inorganic salts in effluents. Additionally, the presence of higher salt levels in the effluent will lead to the inefficient secondary biological treatment of the effluents. Moreover, the conventional process steps use harmful and expensive reagents which make the process hazardous to the environment and costly. Further, the conventional processes provide the product with a comparatively low initial melting point. Therefore, there is felt a need to provide a process for the preparation of 2,2’- dithiobisbenzanilide that mitigates the aforestated drawbacks or at least provides a suitable alternative. OBJECTS Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows: It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative. Another object of the present disclosure is to provide a process for the preparation of 2,2’- dithiobisbenzanilide. Yet another object of the present disclosure is to provide a process for the preparation of 2,2’- dithiobisbenzanilide by avoiding acid and acid species during the step of oxidation. Still another object of the present disclosure is to provide a process for the preparation of 2, 2’-dithiobisbenzanilide, which is simple, efficient, and environment friendly. Yet another object of the present disclosure is to provide a process for the preparation of 2, 2’-dithiobisbenzanilide with a comparatively high purity and high yield. Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure. SUMMARY The present disclosure relates to a process for the preparation of 2, 2’-dithiobisbenzanilide. The process comprises heating a first base at a first predetermined temperature to obtain a heated base. The benzothiazole is hydrolyzed with the heated base under stirring at a second predetermined temperature for a first predetermined time period to obtain an alkali metal salt of ortho-aminothiophenol. The alkali metal salt of ortho-aminothiophenol is cooled to a third predetermined temperature to obtain a cooled alkali metal salt of ortho-aminothiophenol. The cooled alkali metal salt of ortho-aminothiophenol is oxidized with an oxidizing agent at a fourth predetermined temperature for a second predetermined time period to obtain 2,2’- dithiobisaniline. To the 2,2’-dithiobisaniline, predetermined amounts of a fluid medium, a second base, and an emulsifier are mixed to obtain a slurry. The slurry is cooled to a temperature in the range of 20°C to 30°C to obtain a cooled slurry comprising 2,2’- dithiobisaniline. The 2,2’-dithiobisaniline of the cooled slurry is benzoylated with a benzoyl halide at a temperature in the range of 20°C to 40°C for a third predetermined time period to obtain a product mass comprising 2,2’-dithiobisbenzanilide. The product mass is filtered to obtain a wet cake and a filtrate. The wet cake is washed with water followed by drying to obtain 2, 2’-dithiobisbenzanilide. In an embodiment of the present disclosure, the first base is at least one selected from the group consisting of sodium hydroxide, and potassium hydroxide. In an embodiment of the present disclosure, the first predetermined temperature is in the range of 110°C to 140°C. In an embodiment of the present disclosure, the second predetermined temperature is in the range of 120°C to 150°C. In an embodiment of the present disclosure, the first predetermined time period is in the range of 4 hours to 7 hours. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the first base is in the range of 1:2 to 1:5. In an embodiment of the present disclosure, the third predetermined temperature is in the range of 30°C to 40°C. In an embodiment of the present disclosure, the alkali metal salt of ortho-aminothiophenol is mixed with an agglomerating agent before cooling. In an embodiment of the present disclosure, the agglomerating agent is at least one selected from the group consisting of toluene, benzene, ortho-xylene, and mixed xylene. In an embodiment of the present disclosure, the oxidizing agent is hydrogen peroxide. In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 30°C to 40°C. In an embodiment of the present disclosure, the second predetermined time period is in the range of 3 hours to 5 hours. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the oxidizing agent is in the range of 1:0.1 to 1:0.8. In an embodiment of the present disclosure, the fluid medium is at least one selected from the group consisting of toluene, benzene, ortho-xylene, and mixed xylene. In an embodiment of the present disclosure, the fluid medium and the agglomerating agent are the same. In an embodiment of the present disclosure, the second base is at least one selected from the group consisting of sodium bicarbonate, and potassium bicarbonate. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the second base is in the range of 1:0.1 to 1:0.5. In an embodiment of the present disclosure, the emulsifier is at least one selected from the group consisting of nonylphenol ethoxylate, and cocoamine ethoxylate. In an embodiment of the present disclosure, the benzoyl halide is at least one selected from the group consisting of benzoyl chloride, benzoyl bromide, and benzoyl iodide. In an embodiment of the present disclosure, the third predetermined time period is in the range of 5 hours to 8 hours. DETAILED DESCRIPTION The present disclosure relates to a process for the preparation of 2,2’-dithiobisbenzanilide. Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail. The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements. The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure. Various methods for the preparation of 2, 2’-dithiobisbenzanilide are known in the art. Conventionally known methods employ huge amounts of inorganic base, which leads to a higher amount of formation of inorganic salts in effluents. Additionally, the presence of higher salt levels in the effluent will lead to the inefficient secondary biological treatment of the effluents. Moreover, the conventional process steps use harmful and expensive reagents which make the process hazardous to the environment and costly. Further, the conventional processes provide the product with a comparatively low initial melting point. The present disclosure provides an improved process for the preparation of 2, 2’- dithiobisbenzanilide. The process of the present disclosure is simple, environment friendly, economical, and results in improved yield and higher purity of 2, 2’-dithiobisbenzanilide, and is commercially scalable. In an aspect of the present disclosure, there is provided a process for the preparation of 2, 2’- dithiobisbenzanilide. The process is described in detail. In a first step, a first base is heated at a first predetermined temperature to obtain a heated base. Particularly, a predetermined amount of a first base is dissolved in water, followed by heating at a first predetermined temperature to obtain the heated base. In an embodiment of the present disclosure, the first base is at least one selected from the group consisting of sodium hydroxide, and potassium hydroxide. In an exemplary embodiment of the present disclosure, the first base is sodium hydroxide. In an embodiment of the present disclosure, the first predetermined temperature is in the range of 110°C to 140°C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 125°C. In a second step, benzothiazole is hydrolyzed with the heated base under stirring at a second predetermined temperature for a first predetermined time period to obtain an alkali metal salt of ortho-aminothiophenol. Benzothiazole is slowly added to the heated base under stirring at a second predetermined temperature for a first predetermined time period to obtain an alkali metal salt of ortho- aminothiophenol. In an exemplary embodiment, during the hydrolysis reaction of benzothiazole with the first base, particularly sodium hydroxide, sodium formate (HCOONa) is co-generated as a by- product along with the desired product i.e. sodium salt of ortho-aminothiophenol. Thus, the reaction mass comprising sodium salt of ortho-aminothiophenol along with HCOONa is taken as it is (without isolation and purification) for the subsequent step. In an embodiment of the present disclosure, similarly when the potassium hydroxide is used potassium formate is co-generated as a by-product. In an embodiment of the present disclosure, the second predetermined temperature is in the range of 120°C to 150°C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 130°C. In an embodiment of the present disclosure, the first predetermined time period is in the range of 4 hours to 7 hours. In an exemplary embodiment of the present disclosure, the first predetermined time period is 5 hours. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the first base is in the range of 1:2 to 1:5. In an exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the first base is 1:2.4. In another exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the first base is 1:2.2. In a third step, the alkali metal salt of ortho-aminothiophenol is cooled to a third predetermined temperature to obtain a cooled alkali metal salt of ortho-aminothiophenol. In an embodiment of the present disclosure, the third predetermined temperature is in the range of 30°C to 40°C. In an exemplary embodiment of the present disclosure, the third predetermined temperature is 34°C. In an embodiment of the present disclosure, the alkali metal salt of ortho-aminothiophenol is mixed with an agglomerating agent before cooling. In an embodiment of the present disclosure, the agglomerating agent is at least one selected from the group consisting of toluene, benzene, ortho-xylene, and mixed xylene. In an exemplary embodiment of the present disclosure, the agglomerating agent is toluene. In an embodiment of the present disclosure, the addition of an agglomerating agent makes the reaction less thicker and more efficient. In a fourth step, the cooled alkali metal salt of ortho-aminothiophenol is oxidized with an oxidizing agent at a fourth predetermined temperature for a second predetermined time period to obtain 2,2’-dithiobisaniline. Particularly, the oxidizing agent is dissolved in water and added to the cooled alkali metal salt of ortho-aminothiophenol at a fourth predetermined temperature followed by maturation to obtain 2,2’-dithiobisaniline. In an embodiment of the present disclosure, the oxidizing agent is hydrogen peroxide. In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 30°C to 40°C. In an exemplary embodiment of the present disclosure, the fourth predetermined temperature is 35°C. In an embodiment of the present disclosure, the second predetermined time period is in the range of 3 hours to 5 hours. In an exemplary embodiment of the present disclosure, the second predetermined time period is 3.5 hours. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the oxidizing agent is in the range of 1:0.1 to 1:0.8. In an exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the oxidizing agent is 1:0.52. In another exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the oxidizing agent is 1:0.55. In an exemplary embodiment of the present disclosure, the sodium hydroxide (NaOH) is generated as a by-product. The co-generated sodium formate (during the hydrolysis step) reacts with the generated sodium hydroxide (during the oxidation step) probably through an oxalic acid pathway to obtain sodium carbonate (represented as a reaction below). Thus, the formation of sodium carbonate indicates the neutralization of the by-product i.e. sodium hydroxide formed during the oxidation step.

In an embodiment of the present disclosure, potassium hydroxide functions similarly to sodium hydroxide when employed. Conventionally, the oxidation reaction needs to be performed in the presence of water- immiscible organic solvents to introduce a solvent barrier to prevent the deterioration of the product by contact with the sodium hydroxide being generated as the by-product or the oxidizing agent itself during the oxidation reaction. In contrast to the conventional methods, there is no requirement for introducing a solvent barrier or adding an acid such as H₂SO₄, an acid species, or salt of the strong base of a mild acid, namely bicarbonate in the oxidation step. Thus, the process of the present disclosure requires no alkali-neutralizing agent in the oxidation step, rather the co-generated by-product (sodium/potassium formate) can act as a strong alkali neutralizer. In a fifth step, predetermined amounts of a fluid medium, a second base, and an emulsifier are mixed with 2,2’-dithiobisaniline to obtain a slurry. The slurry is cooled to a temperature in the range of 20°C to 30°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline. In an exemplary embodiment of the present disclosure, the slurry is cooled to 25°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline. In an embodiment of the present disclosure, the fluid medium is at least one selected from the group consisting of toluene, benzene, ortho-xylene, and mixed xylene. In an exemplary embodiment of the present disclosure, the fluid medium is toluene. In an embodiment of the present disclosure, the mixed xylene is a combination of o-xylene, m-xylene, and p-xylene. In an embodiment of the present disclosure, the fluid medium and the agglomerating agent are the same. In an embodiment of the present disclosure, the second base is at least one selected from the group consisting of sodium bicarbonate and potassium bicarbonate. In an embodiment of the present disclosure, the second base is sodium bicarbonate. In an embodiment of the present disclosure, the mole ratio of benzothiazole to the second base is in the range of 1:0.1 to 1:0.5. In an exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the second base is 1:0.2. In another exemplary embodiment of the present disclosure, the mole ratio of benzothiazole to the second base is 1:0.4. In an embodiment of the present disclosure, the emulsifier is at least one selected from the group consisting of nonylphenol ethoxylate (nonyl phenoxypoly ethoxylethanol, CAS No. 9016-45-9), and cocoamine ethoxylate (ethanol, 2,2'-iminobis-, N-coco alkyl derivs., CAS No.61791-31-9). In an exemplary embodiment of the present disclosure, the emulsifier is nonylphenol ethoxylate. In an embodiment of the present disclosure, the slurry is cooled to a temperature in the range of 20°C to 30°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline. In an exemplary embodiment of the present disclosure, the cooling temperature is 25°C. In a sixth step, the 2,2’-dithiobisaniline in the cooled slurry is benzoylated with a benzoyl halide at a temperature in the range of 20°C to 40°C for a third predetermined time period to obtain a product mass comprising 2,2’-dithiobisbenzanilide. In an embodiment of the present disclosure, the benzoyl halide is at least one selected from the group consisting of benzoyl chloride, benzoyl bromide, and benzoyl iodide. In an embodiment of the present disclosure, the benzoyl halide is benzoyl chloride. In an embodiment of the present disclosure, the third predetermined time period is in the range of 5 hours to 8 hours. In an embodiment of the present disclosure, the third predetermined time period is 6 hours. In a final step, the product mass comprising 2,2’-dithiobisbenzanilide is filtered to obtain a wet cake and a filtrate. The wet cake is washed with water followed by drying to obtain 2,2’- dithiobisbenzanilide. In an embodiment of the present disclosure, the drying temperature is in the range of 80°C to 100°C. In an exemplary embodiment of the present disclosure, the drying temperature is 90°C. A schematic representation of the process for the preparation of 2,2’-dithiobisbenzanilide in accordance with an exemplary embodiment, is given below as Scheme I.

The present disclosure provides a simple process for the preparation of 2,2’- dithiobisbenzanilide from benzothiazole, which provides a higher yield of the product with greater purity. In an exemplary embodiment of the present disclosure, the overall yield of the final product i.e., 2,2’-dithiobisbenzanilide can be significantly increased if the final benzoylation step is performed after removing the excess sodium carbonate present in the mother liquor of the oxidation step. The excess sodium carbonate is formed by the addition of external sodium bicarbonate, which reacts with the excess sodium hydroxide (present after the oxidation step) to form sodium carbonate. In an exemplary embodiment of the present disclosure, the removal of excess sodium carbonate can be done by adding an inert solvent to the mother liquor of the oxidation step (before benzoylation). The inert solvent can also act as an agglomerating agent during the oxidation step, which is added in a small amount. The same inert solvent can be also added after the oxidation step for dissolving 2,2’-dithiobisaniline obtained in the oxidation step. Due to the addition of the inert solvent in the mother liquor of the oxidation step, a biphasic mixture is formed wherein the aqueous phase is removed thereby reducing the quantity of water. Due to the reduction of water quantity during the benzoylation step, overall yield and quality are improved. Hence, the use of the inert solvent and removal of excess sodium carbonate along with water provides a better yield of the final product i.e., 2, 2’- dithiobisbenzanilide. In an embodiment of the present disclosure, the sodium/potassium carbonate generated during the oxidation step is utilized in the benzoylation step. However, a mole excess of sodium/potassium carbonate during benzoylation in a biphasic medium (mother liquor) may cause a reduction in overall yield of the final product. In an embodiment of the present disclosure, the desired initial melting point is in the range of 138°C to 144°C. The present disclosure provides a cost-efficient and environment friendly process. In an embodiment, the preparation of 2,2’-dithiobisbenzanilide performed as a one-pot reaction and provided a comparatively better yield and purity. The process of the present disclosure is one pot synthesis wherein the process comprises three steps: the hydrolysis of benzothiazole to ortho-amino thiophenol-alkali metal salt, the subsequent oxidation of ortho-amino thiophenol-alkali metal salt to 2,2’-dithiobisaniline, and the final benzoylation to produce 2,2’-dithiobisbenzanilide. In the conventional process, the product of the second step is isolated as a solid before undergoing benzoylation. During this benzoylation step, an external base is added to neutralize the HCl generated. The process of the present disclosure is optimized, wherein the product from the first step, along with co- generated sodium/potassium formate, directly proceeds to the second step. The product of the second step, along with co-generated sodium/potassium carbonate, is then directly utilized in the third step of benzoylation. Further, the yield is improved by removing excess water and sodium/potassium carbonate formed during oxidation before benzoylation. In an industrial setting, this is achieved by draining a portion of the water layer from the bottom of the reaction vessel after oxidation, continuing the second step product in solution with a fluid medium to the upper layer, and allowing it to settle. The optimized process described in the present disclosure allows for the completion of all reaction steps within a single reaction vessel, transforming it into essentially a one-pot reaction in an industrial setting. These process steps enhance both the yield and purity (initial melting point) of the final product. The additional steps of adding a small amount of toluene in the oxidation step (prior to the addition of hydrogen peroxide) as an agglomerating agent, helps to reduce the viscosity of the reaction, making it more efficient. Toluene (other agglomerating agents) when added in small quantities, it serves as an agglomerating agent, carrying out the intended function. Additionally, the step of using the same as a fluid medium to dissolve the product of the second step, namely 2,2’-dithiobisaniline, creates a solution in the initial fluid medium and forms a distinct upper layer. This facilitates the separation of the bottom layer containing excess sodium carbonate and water before proceeding to the benzoylation step. Consequently, the elimination of excess water and sodium/potassium carbonate prevents the preferential alkali hydrolysis of the benzoyl halide, making it more readily available for the reaction. The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure. The present disclosure is further described in light of the following experiments which are set forth for illustration purposes only and not to be construed as limiting the scope of the disclosure. The following experiments are scalable to industrial/commercial process. EXPERIMENTAL DETAILS Example 1: Preparation of 2,2’-dithiobisbenzanilde in accordance with the present disclosure In a four-necked flask with a mechanical stirrer capable of stirring at 300-400 rpm and having provisions for a thermometer-pocket, a water-cooled reflux condenser, and a pressure- equalized addition funnel, 7.3 g of 97% sodium hydroxide (0.178 g mole) dissolved in 7.5 g water was charged and heated to 125°C to obtain a heated sodium hydroxide solution. To the heated sodium hydroxide solution, 10 g (0.074 g mole) of benzothiazole (97 % purity) was added slowly in a dropwise manner over a time period of 2 hours under stirring by maintaining the temperature at 130°C to obtain a first reaction mixture. The first reaction mixture was maintained at 130°C under stirring for 3 hours to obtain a first reaction mass comprising sodium salt of ortho-aminothiophenol. The so obtained sodium salt of ortho-aminothiophenol was mixed with 8 g of water and cooled to 34°C to obtain a cooled sodium salt of ortho-aminothiophenol. 2.62 g (0.0385 g mole) of 50% w/w hydrogen peroxide dissolved in 13.7 g water was added to cooled sodium salt of ortho-aminothiophenol, maintaining the reaction temperature at 35°C over 3 hours, followed by maturation at 35°C for 30 minutes to obtain a second reaction mass comprising 2,2’-dithiobisaniline. 18 ml of toluene was added to 2,2’-dithiobisaniline followed by adding 2.49 g of sodium bicarbonate and 0.10 g of nonylphenol ethoxylate emulsifier to obtain a slurry comprising 2,2’-dithiobisaniline. The slurry was cooled to 25°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline. To the cooled slurry comprising 2,2’-dithiobisaniline, 10.50 g (0.0747 g mole) of benzoyl chloride was added slowly under stirring for 2 hours maintaining the temperature at 30°C, followed by maturation at 30°C for 4 hours under stirring to obtain a product mass comprising 2,2’-dithiobisbenzanilide. The so obtained product mass comprising 2,2’-dithiobisbenzanilide was filtered by using a Buchner funnel to obtain a wet cake and a filtrate. The so obtained wet cake was washed with 100 g of hot water having a temperature of 45°C followed by drying in a hot-air oven at 90 °C until a constant weight was obtained. The yield of 2,2’-dithiobisbenzanilide was 13.45 g (82% yield on actual benzothiazole) and the initial melting point was 138°C. The filtrate containing about 16 ml of toluene was separated from the bottom aqueous layer and then preserved for recycling. The toluene layer contains a significant amount of dissolved 2,2’-dithiobisbenzanilide as estimated by qualitative Thin Layer Chromatographic technique along with another component (mono-benzoylated version of the product) to about 6-7 %, as estimated by comparison with known concentrations of standard DBD (2,2’-dithiobisbenzanilide). During the recycling/reuse of the toluene, the mono-benzoylated version of the product is converted to 2,2’-dithiobisbenzanilide during benzoylation. Example 2: Preparation of 2,2’-dithiobisaniline to detect the formation of sodium carbonate during the oxidation step In a four-necked flask with a mechanical stirrer capable of stirring at 300-400 rpm and having provisions for a thermometer-pocket, a water-cooled reflux condenser, and a pressure- equalized addition funnel, 20.15 g of 97% sodium hydroxide (0.488 g mole) dissolved in 21 g water was charged and heated to 125 °C to obtain a heated sodium hydroxide solution. To the heated sodium hydroxide solution, 30 g (0.222 g mole) of benzothiazole of 97 % purity was added slowly in a dropwise manner over a period of 2 hours under stirring by maintaining the temperature at 130° C to obtain a first reaction mixture. The first reaction mixture was maintained at 130°C under stirring for 3 hours to obtain a first reaction mass comprising sodium salt of ortho-aminothiophenol. The so obtained sodium salt of ortho-aminothiophenol was mixed with 24 g of water and cooled to about 34°C to obtain cooled sodium salt of ortho-aminothiophenol. 7.86 g (0.116 g mole) of 50% w/w hydrogen peroxide dissolved in 41.10 g water was added to cooled sodium salt of ortho-aminothiophenol maintaining the reaction temperature at 35°C over 3 hours, followed by maturation at 35°C for 30 minutes to obtain a second reaction mass comprising 2,2’-dithiobisaniline. 100 g of water was added to the second reaction mass comprising 2,2’-dithiobisaniline under stirring to obtain a slurry comprising 2,2’- dithiobisaniline. The so obtained slurry was filtered using a Buchner Funnel set up to obtain a wet cake and a filtrate. The wet cake was washed with water until the washings achieved the neutral pH to obtain a washed wet cake. The washed wet cake was dried in a hot air oven at 60 °C until a constant weight was obtained. The benzothiazole obtained was in pale yellow colour. The yield of 2,2’-dithiobisaniline was 24.25 g (90.72 % based on the actual benzothiazole) and the initial melting point was 92°C. The filtrate and the washings were combined and evaporated to dryness to obtain a solid residue. The solid residue was washed with dry acetone to remove moisture and organic residues followed by drying in a hot air oven at 105°C to obtain dried solid residue. The dried solid residue was mixed with a dilute 1N hydrochloric acid in a test tube. It was observed that the solid qualitatively gave out a brisk effervescence of carbon dioxide on mixing with dilute hydrochloric acid thus indicating the formation of sodium carbonate at an intermediate stage (oxidation step). Example 3: Preparation of 2, 2’-dithiobisbenzanilde in accordance with the present disclosure (removing the excess sodium carbonate and water before the benzoylation stage) In a four-necked flask with a mechanical stirrer capable of stirring at 300-400 rpm and having provisions for a thermometer-pocket, a water-cooled reflux condenser, and a pressure- equalized addition funnel, 32.59 g of 100% sodium hydroxide (0.815 g mole) dissolved in 35 g water was charged and heated to 125 °C to obtain a heated sodium hydroxide solution. To the heated sodium hydroxide solution, 50 g (0.370 g mole) of benzothiazole (97 % purity) was added slowly in a dropwise manner over a time period of 2 hours under stirring by maintaining the temperature at 130° C to obtain a first reaction mixture. The first reaction mixture was maintained at 130° C under stirring for 3 hours to obtain a first reaction mass comprising sodium salt of ortho-aminothiophenol. The so obtained sodium salt of ortho-aminothiophenol was mixed with 40 g of water and 3.5 ml of toluene and cooled to 34 °C to obtain a cooled sodium salt of ortho-aminothiophenol. 14 g (0.205 g mole) of 50% w/w hydrogen peroxide dissolved in 73.5 g water was added to cooled sodium salt of ortho-aminothiophenol maintaining the reaction temperature at 35°C over 3 hours, followed by maturation at 35°C for 30 minutes to obtain a second reaction mass comprising 2,2’-dithiobisaniline. 95 ml of toluene and 6.25 g of sodium bicarbonate were added to 2,2’-dithiobisaniline and heated to 60°C for 15 minutes under stirring and allowed to settle for 10 minutes at 60°C to obtain a biphasic layer comprising an organic layer and an aqueous layer. The organic layer and aqueous layer were separated to obtain the organic layer and aqueous layer (174 ml). 90 ml of aqueous layer was separated out to prevent the preferential alkali hydrolysis of the benzoyl halide, making it more readily available for the reaction. The remaining 84 ml of aqueous layer and organic layer was mixed followed by adding 0.50 g of nonylphenol Ethoxylate emulsifier to obtain a slurry comprising 2,2’-dithiobisaniline. The slurry comprising 2,2’-dithiobisaniline was cooled to 25°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline. To the cooled slurry comprising 2,2’-dithiobisaniline, 52.5 g of (0.0374 g mole) of benzoyl chloride was added slowly under stirring for 2 hours maintaining the temperature at 30°C followed by maturation at 30°C for 4 hours under stirring to obtain a product mass comprising 2,2’-dithiobisbenzanilide. The so obtained product mass comprising 2,2’-dithiobisbenzanilide was filtered by using a Buchner funnel to obtain a wet cake and a filtrate. The so obtained wet cake was washed with 500 g of hot water having a temperature of 45°C and dried in a hot-air oven at 90 °C until a constant weight was obtained. The yield of 2,2’-dithiobisbenzanilide was 74.50 g (91.0 % yield on actual benzothiazole) and the initial melting point was 142°C. The filtrate containing the organic layer (toluene) and aqueous layer was separated using a separating funnel and the bottom aqueous layer was discarded. The toluene layer contains a significant amount of dissolved 2,2’-dithiobisbenzanilide as estimated by qualitative Thin Layer Chromatographic technique along with another component (mono-benzoylated version of the product) to about 6-7 %, as estimated by comparison with known concentrations of standard DBD (2,2’-dithiobisbenzanilide). Further, the recovery of 2,2’-dithiobisbenzanilide led to an overall yield of 96% (on actual benzothiazole). During the recycling/reuse of the toluene, the mono-benzoylated version of the product is converted to 2,2’-dithiobisbenzanilide during benzoylation. Thus the organic toluene layer can be recycled for a certain number of batches until a significant build-up of other components are observed in the toluene filtrate. Example 4: Preparation of 2,2’-dithiobisbenzanilde in accordance with the present disclosure 2,2’-dithiobisbenzanilide was prepared similarly to the process steps and conditions as disclosed in Example 3 to establish the reproducibility of the process. The yield of 2,2’-dithiobisbenzanilide was 72.85 g (88.9% yield on actual benzothiazole) and the initial melting point was 142°C. Example 5: Preparation of 2,2’-dithiobisbenzanilde in accordance with the present disclosure 2,2’-dithiobisbenzanilide was prepared similarly to the process steps and conditions as disclosed in Example 3 to establish the reproducibility of the process, except the toluene filtrate (98ml) obtained was used as a fluid medium in the benzoylation step. The yield of the 2,2’-dithiobisbenzanilide was 78.2 g (95.5% yield on actual benzothiazole) and the initial melting point was 141°C. It was observed that the average isolated yield of 2, 2’-dithiobisbenzanilide by using the toluene filtrate after two reactions and one recycle is 93%. Additionally, the toluene filtrate obtained from example 5 contains approximately 6-7% of the product (2,2’- dithiobisbenzanilide), contributing to an overall conversion efficiency of 96% for the method on actual benzothiazole. TECHNICAL ADVANCEMENTS The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of 2,2’-dithiobisbenzanilide, that • is cost-efficient; • provides one-pot preparation for the preparation of 2,2’-dithiobisbenzanilide; • does not involve an alkali neutralizing agent in the oxidation step, rather the in-situ generated by-product itself can act as an alkali neutralizer; • does not require an externally added base in the final benzoylation step rather the base generated after the oxidation is utilized in the final benzoylation step; • uses a low amount of base after oxidation; • avoids the use of strong acids such as sulfuric acid during oxidation; • provides a comparatively higher yield of the product with better purity; • is an efficient process and gives minimum salt load in the effluent; • is simple, economical, results in higher yield and purity of the product; and • is commercially scalable and environment friendly. The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention. Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application. The numerical values given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary. While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

CLAIMS: 1. A process for the preparation of 2,2’-dithiobisbenzanilide, said process comprising the following steps: a. heating a first base at a first predetermined temperature to obtain a heated base; b. hydrolyzing benzothiazole with said heated base under stirring at a second predetermined temperature for a first predetermined time period to obtain an alkali metal salt of ortho-aminothiophenol; c. cooling said alkali metal salt of ortho-aminothiophenol to a third predetermined temperature to obtain a cooled alkali metal salt of ortho- aminothiophenol; d. oxidizing said cooled alkali metal salt of ortho-aminothiophenol with an oxidizing agent at a fourth predetermined temperature for a second predetermined time period to obtain 2,2’-dithiobisaniline; e. mixing predetermined amounts of a fluid medium, a second base, and an emulsifier with said 2,2’-dithiobisaniline to obtain a slurry, followed by cooling said slurry to a temperature in the range of 20°C to 30°C to obtain a cooled slurry comprising 2,2’-dithiobisaniline; f. benzoylating said 2,2’-dithiobisaniline from said cooled slurry with a benzoyl halide at a temperature in the range of 20°C to 40°C for a third predetermined time period to obtain a product mass comprising 2,2’-dithiobisbenzanilide; and g. filtering said product mass to obtain a wet cake and a filtrate; washing said wet cake with water followed by drying to obtain 2,2’-dithiobisbenzanilide.

2. The process as claimed in claim 1, wherein said first base is at least one selected from the group consisting of sodium hydroxide, and potassium hydroxide.

3. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 110°C to 140°C.

4. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 120°C to 150°C.

5. The process as claimed in claim 1, wherein said first predetermined time period is in the range of 4 hours to 7 hours.

6. The process as claimed in claim 1, wherein the mole ratio of benzothiazole to said first base is in the range of 1:2 to 1:5.

7. The process as claimed in claim 1, wherein said third predetermined temperature is in the range of 30°C to 40°C.

8. The process as claimed in claim 1, wherein said alkali metal salt of ortho- aminothiophenol is mixed with an agglomerating agent before cooling.

9. The process as claimed in claim 8, wherein said agglomerating agent is at least one selected from the group consisting of toluene, benzene, ortho-xylene, and mixed xylene.

10. The process as claimed in claim 1, wherein said oxidizing agent is hydrogen peroxide.

11. The process as claimed in claim 1, wherein said fourth predetermined temperature is in the range of 30°C to 40°C.

12. The process as claimed in claim 1, wherein said second predetermined time period is in the range of 3 hours to 5 hours.

13. The process as claimed in claim 1, wherein the mole ratio of benzothiazole to said oxidizing agent is in the range of 1:0.1 to 1:0.8.

14. The process as claimed in claim 1, wherein said fluid medium is at least one selected from the group consisting of toluene, benzene, ortho-xylene and mixed xylene.

15. The process as claimed in claims 1 and 8, wherein said fluid medium and said agglomerating agent are same.

16. The process as claimed in claim 1, wherein said second base is at least one selected from the group consisting of sodium bicarbonate, and potassium bicarbonate.

17. The process as claimed in claim 1, wherein the mole ratio of benzothiazole to said second base is in the range of 1:0.1 to 1:0.5.

18. The process as claimed in claim 1, wherein said emulsifier is at least one selected from the group consisting of nonylphenol ethoxylate, and cocoamine ethoxylate.

19. The process as claimed in claim 1, wherein said benzoyl halide is at least one selected from the group consisting of benzoyl chloride, benzoyl bromide, and benzoyl iodide.

20. The process as claimed in claim 1, wherein said third predetermined time period is in the range of 5 hours to 8 hours.