DESC:FIELD
The present disclosure relates to a process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides.
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 indicate otherwise.
Rubber compounding refers to a process of blending different additives with raw rubber prior to vulcanization, or curing.
Initial melting point refers to a temperature at which the solid starts melting and the first drop of liquid is observed.
Aralkyl refers to alkyl that is substituted with an aryl group.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
N, N-disubstituted benzothiazole-2-sulfenamide compounds are used as ‘delayed action vulcanization accelerators’ in rubber compounding. These compounds have a longer delay in the onset of curing thus offering required scorch safety in the vulcanization process. The delayed action property is due to the steric nature of the substitution on the secondary nitrogen of these sulfenamide accelerators.
The sulfenamide accelerators find their use in the preparation of industrial rubber products that require higher stress-dynamic applications, metal-to-rubber bonding, steel-cord conveyor belts, thick cross-section rubber goods and the like. N, N-dibenzylbenzothiazole-2-sulfenamide is an important N, N-disubstituted benzothiazole-2-sulfenamide, as it is an eco-friendly accelerator.
Currently, the process for the preparation of N,N disubstituted benzothiazole-2-sulfenamides using 2,2’-dithiobisbenzothiazole or its thiol precursor i.e., 2-mercaptobenzothiazole as starting material is carried out either by oxidative coupling with the corresponding amines, or by the condensation of the corresponding N-chloroamines with the thiol precursors or further by in-situ chlorination techniques.
However, the conventional processes have some disadvantages such as N, N-dialkylbenzothiazole-2-sulfenamides obtained by such conventional process have a low yield or a low purity, use of higher amount of solvents like alcohols, tedious process conditions and difficulty in recovery and recycling of solvents and amines.
Therefore, there is felt a need to provide a process for the preparation of N, N- disubstituted benzothiazole-2-sulfenamides that mitigates the aforestated drawbacks or at least provide an alternative solution.
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 N, N-disubstituted benzothiazole-2-sulfenamides.
Yet another object of the present disclosure is to provide a process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides with a comparatively better purity and better yield.
Still another object of the present disclosure is to provide a simple and cost-effective process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides.
Another object of the present disclosure is to provide a process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides with industrially acceptable physical characteristics.
Still another object of the present disclosure is to provide an eco-friendly process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides that allows the recovery of reactants and solvents.
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 N, N-disubstituted benzothiazole-2-sulfenamides. The process comprises chlorinating a compound selected from a thiol substituted benzothiazole compound and a disulphide substituted benzothiazole compound by using a chlorinating agent in a first fluid medium at a first predetermined temperature, for a first predetermined time period to obtain benzothiazole-2-sulfenyl chloride. The benzothiazole-2-sulfenyl chloride is reacted with a secondary amine at a second predetermined temperature for a second predetermined time period to obtain a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines. The product mass is neutralized by using a base at a third predetermined temperature for a third predetermined time period to obtain a first biphasic mixture having a first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine and a first aqueous layer. The first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine is separated from the first biphasic mixture to obtain a separated first organic layer and a separated first aqueous layer. The free amine is removed from the separated first organic layer by using an acid at a fourth predetermined temperature for a fourth predetermined time period to obtain a second biphasic mixture having a second organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a second aqueous layer. The second organic layer is separated from the second biphasic mixture to obtain a separated second organic layer and distilling the separated second organic layer to obtain N, N-disubstituted benzothiazole-2-sulfenamide.
In an embodiment of the present disclosure, the thiol substituted benzothiazole compound is 2-mercaptobenzothiazole and the disulphide substituted benzothiazole compound is 2, 2’-dithiobisbenzothiazole.
In an embodiment of the present disclosure, the chlorinating agent is selected from the group consisting of chlorine gas and sulfuryl chloride.
In an embodiment of the present disclosure, the first fluid medium is selected from the group consisting of toluene, benzene and a chlorinated solvent.
In an embodiment of the present disclosure, the chlorinated solvent is selected from the group consisting of dichloromethane, dichloroethane, tetrachloroethylene and carbon tetrachloride
In an embodiment of the present disclosure, a volume to a mass ratio of the first fluid medium to the benzothiazole compound is in the range of 5:1 to 25:1.
In an embodiment of the present disclosure, the volume to the mass ratio of the first fluid medium to the benzothiazole compound is in the range of 8:1 to 15:1.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 30 oC to 70 oC.
In an embodiment of the present disclosure, the first predetermined time period is in the range of 20 minutes to 60 minutes.
In an embodiment of the present disclosure, the mole ratio of the benzothiazole compound to the chlorinating agent is in the range of 1:1 to 1:1.15.
In an embodiment of the present disclosure, the secondary amine is selected from the group consisting of N, N-dicyclohexylamine, N, N-dibenzylamine, N, N-diisopropylamine, N, N-diphenylamine, N-methyl-N-tert-butylamine, N-ethyl-N-tert-butylamine, N-methyl-N-cyclohexylamine, N-ethyl-N-cyclohexylamine, N-methyl-N-benzylamine, and N-ethyl-N-benzylamine.
In an embodiment of the present disclosure, the secondary amine is selected from the group consisting of N, N-dicyclohexylamine and N, N-dibenzylamine.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 5 oC to 20 oC.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 60 minutes to 120 minutes.
In an embodiment of the present disclosure, the mole ratio of the benzothiazole compound to the secondary amine is in the range of 1:2 to 1:6.
In an embodiment of the present disclosure, the base is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.
In an embodiment of the present disclosure, the mole ratio of the base to the benzothiazole compound is in the range of 1:1 to 3:1.
In an embodiment of the present disclosure, the third predetermined temperature is in the range of 50 °C to 80 °C.
In an embodiment of the present disclosure, the third predetermined time period is in the range of 60 minutes to 180 minutes.
In an embodiment of the present disclosure, the acid is at least one selected from the group consisting of sulphuric acid and acetic acid.
In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 60°C to 90°C.
In an embodiment of the present disclosure, the fourth predetermined time period is in the range of 30 minutes to 80 minutes.
In an embodiment of the present disclosure, the mole ratio of the acid to the benzothiazole compound is in the range of 0.5:1 to 4:1.
In an embodiment of the present disclosure, the distillation in step vi) is an azeotropic distillation and is carried out at a temperature in the range of 50 oC to 60 oC under a vacuum in the range of 400 mmHg to 600 mmHg.
In an embodiment of the present disclosure, water is added to the second organic layer to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer is separated from the third biphasic mixture followed by combining the third aqueous layer with the second aqueous layer to obtain a combined aqueous layer which is treated for amine recovery. The third organic layer is azeotropically distilled to separate the first fluid medium for reuse, to obtain a product mixture. The product mixture is cooled followed by filtration to obtain N, N disubstituted benzothiazole-2-sulfenamide.
In an embodiment of the present disclosure, N, N disubstituted benzothiazole-2-sulfenamide has a yield greater than 90% and a purity greater than 95%.
DETAILED DESCRIPTION
The present disclosure relates to a process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides.
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.
The sulfenamide accelerators find their use in the preparation of industrial rubber products that require higher stress-dynamic applications, metal-to-rubber bonding, steel-cord conveyor belts, thick cross-section rubber goods, and the like. Among these sulfenamide accelerators N, N-dibenzylbenzothiazole-2-sulfenamide is an important N, N-disubstituted benzothiazole-2-sulfenamide, as it is an eco-friendly accelerator.
Currently, the processes for the preparation of N, N disubstituted benzothiazole- 2-sulfenamides using 2,2’-dithiobisbenzothiazole or its thiol precursor i.e., 2-mercaptobenzothiazole as starting material is carried out, either by oxidative coupling with the corresponding amines, or by the condensation of the corresponding N-chloroamines with the thiol precursors or further by in-situ chlorination techniques.
However, the conventional processes have some disadvantages such as N, N disubstituted benzothiazole-2-sulfenamides obtained by such conventional process have a low yield or a low purity, use of higher amount of solvents like alcohols, tedious process conditions, and difficulty in recovery and recycling of solvents and amines.
The present disclosure provides an improved process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides.
The process of preparation of N, N-disubstituted benzothiazole-2-sulfenamides of the present disclosure is simple, environment friendly, economical and results in improved yield and higher purity of N, N-disubstituted benzothiazole-2- sulfenamides and is commercially scalable.
The present disclosure provides a process for the preparation of
N, N-disubstituted benzothiazole-2-sulfenamides. The structural representation of N, N-disubstituted benzothiazole-2-sulfenamides is given as formula (I) below:

Formula (I)
wherein
R is selected from the group consisting of n-alkyl, iso-alkyl, aryl, cycloalkyl and aralkyl; and
R' is selected from the group consisting of n-alkyl, iso-alkyl, aryl, cycloalkyl and aralkyl
The process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides comprises the following steps:
i. chlorinating a compound selected from thiol substituted benzothiazole compound and disulphide substituted benzothiazole compound by using a chlorinating agent in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain benzothiazole-2-sulfenyl chloride;
ii. reacting benzothiazole-2-sulfenyl chloride and a secondary amine at a second predetermined temperature for a second predetermined time period to obtain a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines;
iii. neutralizing the product mass by using a base at a third predetermined temperature for a third predetermined time period to obtain a first biphasic mixture having a first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine and a first aqueous layer;
iv. separating the first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine from the first biphasic mixture to obtain a separated first organic layer and a separated first aqueous layer;
v. removing the free amine from the separated first organic layer by using an acid at a fourth predetermined temperature for a fourth predetermined time period to obtain a second biphasic mixture having a second organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a second aqueous layer; and
vi. separating the second organic layer from the second biphasic mixture to obtain a separated second organic layer and distilling the separated second organic layer to obtain N, N-disubstituted benzothiazole-2-sulfenamide.
The process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides is described in detail herein below.
Step I: Preparation of benzothiazole-2-sulfenyl chloride
A compound selected from a thiol substituted benzothiazole compound and disulphide substituted benzothiazole compound is chlorinated by using a chlorinating agent in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain benzothiazole-2-sulfenyl chloride.
In an embodiment of the present disclosure, the thiol substituted benzothiazole compound is 2-mercaptobenzothiazole and the disulphide substituted benzothiazole compound is 2, 2’-dithiobisbenzothiazole. In an exemplary embodiment of the present disclosure, the disulphide substituted benzothiazole is 2, 2’-dithiobisbenzothiazole.
In an embodiment of the present disclosure, the chlorinating agent is selected from the group consisting of chlorine gas and sulfuryl chloride. In an exemplary embodiment, the chlorinating agent is chlorine gas.
The use of chlorinating agents such as chlorine gas and sulfuryl chloride avoids the formation of chlorobenzothiazoles (de-thiochlorination) and results only in the formation of benzothiazole -2-sulfenyl chloride (thiol-chlorine addition).
In an embodiment of the present disclosure, the first fluid medium is selected from the group consisting of toluene, benzene and a chlorinated solvent.
In an embodiment of the present disclosure, the chlorinated solvent is selected from the group consisting of dichloromethane, dichloroethane, tetrachloroethylene, and carbon tetrachloride.
In an exemplary embodiment, the first fluid medium is toluene.
In an embodiment of the present disclosure, the volume to mass ratio of the first fluid medium to the benzothiazole compound is in the range of 5:1 to 25:1.
In an embodiment of the present disclosure, the volume to mass ratio of the first fluid medium to the benzothiazole compound is in the range of 8:1 to 15:1. In an exemplary embodiment, the volume to mass ratio of the first fluid medium to benzothiazole compound is 8:1. In another exemplary embodiment, the volume to mass ratio of the first fluid medium to benzothiazole compound is 15:1.
In an embodiment of the present disclosure, the first predetermined temperature is in the range of 30 °C to 70 °C. In an exemplary embodiment, the first predetermined temperature is 50 °C.
In an embodiment of the present disclosure, the mole ratio of the benzothiazole compound to the chlorinating agent is in the range of 1:1 to 1:1.15. In an exemplary embodiment, the mole ratio of the benzothiazole compound to the chlorinating agent is 1:1 .
The mole ratio of benzothiazole compound to chlorinating agent of more than 1:1 to 1:1.15 results in the formation of solids indicating the formation of –SCl2 type intermediates (or reverse reaction) thereby providing reduced purity of the product. The yield of benzothiazole sulfenyl chloride intermediates is improved by using the mole ratio of benzothiazole compound to chlorinating agent of more than 1:1 to 1:1.15. The mole ratio of benzothiazole compound to chlorinating agent below 1:1 to 1:1.15 results in unreacted benzothiazole compound.
Step II: Preparation of a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines
The so obtained Benzothiazole-2-sulfenyl chloride in step I is reacted with a secondary amine at a second predetermined temperature for a second predetermined time period to obtain a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines.
In a second step, particularly, the so obtained benzothiazole-2-sulfenyl chloride in the first fluid medium is cooled to a second predetermined temperature to obtain a cooled benzothiazole-2-sulfenyl chloride. Maintaining the second predetermined temperature, a predetermined amount of a secondary amine is slowly added to the cooled benzothiazole-2-sulfenyl chloride under stirring for a second predetermined time period to obtain a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines.
In an embodiment of the present disclosure, the secondary amine is a compound of structure of formula II

Formula II
wherein
R is selected from the group consisting of n-alkyl, iso-alkyl, aryl, cycloalkyl and aralkyl; and
R' is selected from the group consisting of n-alkyl, iso-alkyl, aryl, cycloalkyl and aralkyl.
In an embodiment of the present disclosure, the secondary amines are selected from the group consisting of N, N-dicyclohexylamine, N, N-dibenzylamine, N, N-diisopropylamine, N, N-diphenylamine, N-methyl-N-tert-butylamine, N-ethyl-N-tert-butylamine, N-methyl-N-cyclohexylamine, N-ethyl-N-cyclohexylamine, N-methyl-N-benzylamine, and N-ethyl-N-benzylamine. In an embodiment of the present disclosure, the secondary amine is selected from the group consisting of N, N-dicyclohexylamine and N, N-dibenzylamine. In an exemplary embodiment the secondary amine is N, N-dicyclohexylamine. In another exemplary embodiment, the secondary amine is N, N-dibenzylamine. In yet another exemplary embodiment, the secondary amine is N, N-dicyclohexylamine.
In an embodiment of the present disclosure, the second predetermined temperature is in the range of 5°C to 20°C. In an exemplary embodiment, the second predetermined temperature is 10°C.
In an embodiment of the present disclosure, the second predetermined time period is in the range of 60 minutes to 120 minutes. In an exemplary embodiment, the second predetermined time period is 90 minutes.
In an embodiment of the present disclosure, the mole ratio of the benzothiazole compound to the secondary amine is in the range of 1:2 to 1:6. In an exemplary embodiment, the mole ratio of the benzothiazole compound to the secondary amine is 1:4.25.
One mole benzothiazole compound, if it is disulfide, needs two moles of amine for reaction and more 2 moles for scavenging HCl generated in the condensation reaction. Therefore minimum four moles of secondary amine is required during the reaction. The mole ratio of the benzothiazole compound to the secondary amine is 1:4.25 is desirable to ensure complete reaction of sulfenyl chloride. Since unreacted sulfenyl chloride decomposes back to disulfide which will reduce the purity of the product with higher cyclohexane-insolubles (MBTS Content). Higher mole ratio i.e., more than 1:4.25 may not create problem, but that may require more acid followed by more base in amine recovery which is not economical and will increase the salt load in liquid effluent. If thiol is used as starting material, the amount of amine required is half i.e. 2.125 moles.
In an embodiment of the present disclosure, the product mass comprises N, N- disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of the corresponding secondary amines.
In an embodiment of the present disclosure, condensation of benzothiazolesulfenyl chlorides with secondary amines at lower temperatures ensures better selectivity of reaction.
Step III: Neutralizing the product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines
The product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines is neutralized by using a base at a third predetermined temperature for a third predetermined time period to obtain a first biphasic mixture comprising a first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine and a first aqueous layer.
The process of neutralization of the product mass of N, N-disubstituted benzothiazole-2-sulfenamide is detailed below.
In this third step, the product mass of N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of the corresponding amines, is heated to a third predetermined temperature followed by a slow addition of a base and stirring for a third predetermined time period followed by further allowing to settle for 30 minutes at the third predetermined temperature to obtain a first biphasic mixture comprising a first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a first aqueous layer containing salt.
In an embodiment of the present disclosure, the base is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide. In an exemplary embodiment, the base is sodium hydroxide.
The use of bases such as sodium hydroxide and potassium hydroxide aids in the formation of water soluble salts such as sodium chloride and potassium chloride respectively and excess base used is also soluble in water. The alkaline earth metal bases such as calcium hydroxide, magnesium hydroxide and the like are not suitable as the excess amount of such bases may create solubility problem in the given concentration in water and thereby creating a layer separation issue.
In an embodiment of the present disclosure, the mole ratio of the base to the benzothiazole compound is in the range of 1:1 to 3:1. In an exemplary embodiment, the mole ratio of the base to the benzothiazole compound is 2.5:1.
In accordance with the present disclosure, the amine-hydrochloride so formed after condensation needs to be neutralized to convert it back to amine which needs minimum two moles of base per mole of benzothiazole compound, if disulfide is used. Whereas, if thiol is used, one mole of base is sufficient. If the mole percentage is less than the range of 1:1, the un-neutralized portion of amine will come along the product after isolation and the free amine in the product will be more thereby making the product less pure.
In an embodiment of the present disclosure, the third predetermined temperature is in the range of 50°C to 80°C. In an exemplary embodiment, the third predetermined temperature is 65 °C.
In an embodiment of the present disclosure, the third predetermined time period can be in the range of 60 minutes to 180 minutes. In an exemplary embodiment, the third predetermined time period is 120 minutes.
The first aqueous layer containing salts (sodium chloride/potassium chloride) is separated by using a separation arrangement and discarded.
The so obtained organic layer comprises N, N disubstituted benzothiazole-2-sulfenamide and N, N-disubstituted secondary amine as a free amine.
Step IV: Separating the first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine from the first biphasic mixture to obtain a separated first organic layer and a separated first aqueous layer
In the fourth step, the first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine is separated from the first biphasic mixture to obtain a separated first organic layer and a separated first aqueous layer.
Step V: Removal of the free amine from the separated first organic layer
The first organic layer comprises N, N-disubstituted benzothiazole-2-sulfenamide and N, N-disubstituted secondary amine as a free amine. The N, N-disubstituted secondary amine is removed from the first organic layer by using an acid at a fourth predetermined temperature for a fourth predetermined time period to obtain a second biphasic mixture comprising a second organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a second aqueous layer comprising dissolved N, N-disubstituted secondary amine as its corresponding salt based on the acid used.
The process of removal of N, N-disubstituted secondary amine from the first organic layer is detailed below:
In this fifth step, the first organic layer comprising N, N-disubstituted benzothiazole-2-sulfenamide and N, N-disubstituted secondary amine is heated at a fourth predetermined temperature followed by a slow addition of an acid and stirring for a fourth predetermined time period to obtain an acid treated mixture. The third reaction mixture is allowed to settle for 30 minutes to obtain a second biphasic mixture comprising a second organic layer and a second aqueous layer.
In an embodiment of the present disclosure, the acid is selected from the group consisting of sulphuric acid and acetic acid. In an exemplary embodiment, the acid is sulphuric acid. In another exemplary embodiment, the acid is acetic acid.
The use of these specific acids are desirable due to the fact that a water soluble amine salts (amine hydrochloride salts) formed during the reaction could not not be washed off with water however that need to be recovered in the form of free amine followed by recovering them as the more water soluble sulfates or acetates.
In an embodiment of the present disclosure, the mole ratio of the acid to the benzothiazole compound is in the range of 0.5:1 to 4:1. In an exemplary embodiment, the mole ratio of sulfuric acid to the benzothiazole compound is 1.25:1. In another exemplary embodiment, the mole ratio of the sulfuric acid to the benzothiazole compound is 1.5:1. In yet another exemplary embodiment, the acid used is acetic acid and the mole ratio of the acid to the benzothiazole compound is 2.5:1.
The mole ratio of the acid to the benzothiazole compound in the range of 0.5:1 to 4:1 ensures complete neutralization. If the ratios are less, the un-neutralized portion of amine will come along with the product which will reduce purity and increase free amine content in the product. If the ratios are more, it is not economical and problems of salt load in the liquid effluent are also observed. In case of acetic acid used instead of sulphuric acid the mole ratio is required to be doubled (2.5 moles minimum).
In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 60°C to 90°C. In an exemplary embodiment, the fourth predetermined temperature is 70°C.
In an embodiment of the present disclosure, the fourth predetermined time period is in the range of 30 minutes to 80 minutes. In an exemplary embodiment, the fourth predetermined time period is 60 minutes.
In an embodiment of the present disclosure, the second biphasic mixture is separated to obtain a second organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a second aqueous layer.
In an optional embodiment of the present disclosure, the second organic layer is mixed with a first predetermined volume of water under stirring and allowed to settle for 15 minutes to 60 minutes to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer is separated and mixed with the second aqueous layer.
In an embodiment of the present disclosure, the predetermined volume (ml) of water used per mole of the benzothiazole compound for washing of the second organic layer can be in the range of 500ml to 1500ml (per mole of the benzothiazole compound).
In an embodiment of the present disclosure, the secondary amine is recovered from the combined mixture of the second aqueous layer and the third aqueous layers by treatment with sodium hydroxide in presence of the first fluid medium to recover the amine as a solution in the first fluid medium that can be recycled.
Particularly, during the recovery of the secondary amine from the aqueous layer by treating it with sodium hydroxide, the amine is freed from its sulfate salt and it can form a well-defined layer as a solution with the first fluid medium in a biphasic mixture. The solution can be dried by removing water/moisture by azeotropic distillation along with some amount of the first fluid medium (before it is recycled in the subsequent batches). This is applicable from the second batch onwards where recovered amine can be used.
In accordance with an embodiment of the present disclosure, the excess secondary amine is used as an acid scavenger. The amine hydrochloride salts obtained after the condensation reaction of 2-chlorosulfenylbenzothiazole with the secondary amines are not isolated as such for recycling by neutralization with sodium hydroxide, but are converted initially to free secondary amine by reaction with a dilute sodium hydroxide solution followed by converting the free amine into its sulfate salt by reaction with dilute sulfuric acid, separation and re-neutralization with a dilute sodium hydroxide solution. This is necessitated as the sulfate salts of secondary amines used are more soluble in water at operating temperatures. Isolation of the hydrochloride salts of the secondary amines by filtration of the reaction slurry is difficult owing to their physical nature being a very fine solid with slimy nature. In another exemplary embodiment, the amine is recovered as an acetate salt.
Step VI: Separation and distillation of the separated second organic layer to obtain N, N-disubstituted benzothiazole-2-sulfenamides.
Water is added to the second organic layer to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer is separated from the third biphasic mixture followed by combining the third aqueous layer with the second aqueous layer of step (v) to obtain a combined aqueous layer which is treated for amine recovery. The third organic layer is subjected to azeotropic distillation to separate the first fluid medium for reuse in step (i) to obtain a product mixture. The product mixture is cooled followed by filtration to obtain N, N-disubstituted benzothiazole-2-sulfenamide.
The process of distillation of the second organic layer is detailed below.
In this final step, the second organic layer is subjected to azeotropic distillation by continuous addition of a predetermined volume of water at a temperature in the range of 50°C to 60°C under a first predetermined vacuum to obtain a slurry. The slurry is cooled at a temperature in the range of 25 °C to 35 °C under stirring followed by filtration to obtain a wet cake. The wet cake after washing with water is dried at a temperature in the range of 50°C to 70°C to obtain N, N-disubstituted benzothiazole-2-sulfenamide.
In an embodiment of the present disclosure, the predetermined volume of water per mole of the benzothiazole compound is in the range of 1000 ml to 8000 ml. In an exemplary embodiment, the predetermined volume of water per mole of the benzothiazole compound is 3000 ml. In another exemplary embodiment, the predetermined volume of water per mole of the benzothiazole compound is 6000 ml. In still another exemplary embodiment, the predetermined volume of water per mole of the benzothiazole compound is 1500 ml.
In an embodiment of the present disclosure, the first predetermined vacuum is in the range 400 mm Hg to 600 mm Hg. In an exemplary embodiment, the first predetermined vacuum is 500mmHg.
In an embodiment of the present disclosure, the schematic representation of the preparation of N, N-disubstituted benzothiazole-2-sulfenamides is given below as Scheme A.

Scheme A
In an embodiment of the present disclosure, N, N disubstituted benzothiazole-2-sulfenamide has a yield greater than 90% and a purity greater than 95%.
In an embodiment of the present disclosure, the yield of N, N-disubstituted benzothiazole-2-sulfenamide is in the range of 90% to 97 %. In an exemplary embodiment, the yield of N, N-disubstituted benzothiazole-2-sulfenamide is 95.52%. In an exemplary embodiment, the yield of N, N-disubstituted benzothiazole-2-sulfenamide is 93.09 %. In another exemplary embodiment, the yield of N, N-disubstituted benzothiazole-2-sulfenamide is 96.42%.
In an embodiment of the present disclosure, 2, 2’-dithiobisbenzothiazole content in the obtained N, N-disubstituted benzothiazole-2-sulfenamide as determined by Cyclohexane insoluble is in the range of 0.005 % to 0.30 %. In an exemplary embodiment, 2, 2’-dithiobisbenzothiazole content in the obtained N, N-disubstituted benzothiazole-2-sulfenamide is 0.02 %. In still another exemplary embodiment, 2, 2’-dithiobisbenzothiazole content in the obtained N, N-disubstituted benzothiazole-2-sulfenamide is 0.01 %. In yet another exemplary embodiment, 2, 2’-dithiobisbenzothiazole content in the obtained N, N-disubstituted benzothiazole-2-sulfenamide is 0.20 %.
In accordance with an embodiment of the present disclosure, the free secondary amine content in the dried N, N-disubstituted benzothiazole-2-sulfenamide is in the range of 0.02 % to 1 %. In an exemplary embodiment, the free secondary amine content in the dried N, N-disubstituted benzothiazole-2-sulfenamide is 0.094 %. In another exemplary embodiment, the free secondary amine content in the dried N, N-disubstituted benzothiazole-2-sulfenamide is 0.047 %. In yet another exemplary embodiment, the free secondary amine content in the dried N, N-disubstituted benzothiazole-2-sulfenamide is 0.80 %.
In the process of the present disclosure, the condensation step involves essentially dry conditions and lower temperatures in inert non-polar or polar solvents, which provides enhanced yield with better quality, lower levels of impurities of the over-oxidized species and hence better storage-stable product.
Conventionally known processes for the preparation of N,N disubstituted benzothiazole sulfenamides such as oxidative condensation of amine with thiol precursors, reaction of thiol precursors with N-chloramines, in situ chlorination of amine-thiol mixtures in solvent medium and the like have some drawbacks such as low yield and low purity. Further, the primary amine based condensation-cum-recovery essentially yields bis-sulfinimides (Instead of sulfenamides) by reaction of two sulfenyl chlorides with one amine.
The process of the present disclosure uses secondary amines in the reaction that provides efficient recovery of secondary amines and solvents used in the reaction.
The separation of amines from the product in solvent solution is achieved by converting them into more water soluble salts like sulfates and acetates by reaction with respective acids so that almost complete removal of amines from the product in solvent is ensured. The hydrochloride salts of the amine formed in the reaction is not very much water soluble hence is converted to free amine with a base first and then isolated as more water soluble sulfate or acetate-salts of amines separately. The temperature, molar proportion and concentration of the base and acid used also ensure the complete removal of amine and complete solubility of the same as its salt in water in the biphasic mixture.
Still further known condensation methods for N, N-disubstituted benzothiazole sulfenamides use alcohols and acetone as a fluid medium, and recovery of any excess secondary amines used in the reaction is not convenient. The loss of products in the alcoholic solvents or solvents like acetone is higher. There are no suitable methods to isolate this lost product in the mother liquor. The amines are taken out from the alcohol/acetone filtrate after neutralization of the amine-hydrochlorides formed with a base, and the isolation is carried out by fractional distillation. This will make the solvent more dilute and recovery of moisture-free solvents would be highly energy-intensive involving heating and sub-zero cooling, whereas the method established by the present disclosure is simple by way of isolating amine by simple acid base reactions in the same solvent of the reaction which can be dried easily by azeotropic removal of water and involve no fractional distillations. Moreover, during the process of the present disclosure, amines are completely removed from the non-polar solvent containing the product before isolation of the product itself and the product is isolated finally as slurry in water after azeotropic removal of solvent under vacuum thereby avoiding the loss of product.
Furthermore, the process of the present disclosure involves condensation of isolated benzothiazolesulfenyl chlorides with secondary amines at lower temperatures which ensures better selectivity of reaction. Whereas the conventionally known processes involve the reaction of the mixture of amine and thiol precursors with chlorinating agents or reaction of mixture of amines and n-chloramines with thiol precursors which are less selective and need sensitive controls.
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 purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to the industrial scale.
EXPERIMENTAL DETAILS
EXAMPLE 1: Preparation of N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) in accordance with the process of the present disclosure:
33.2 g of 2, 2’-dithiobisbenzothiazole (0.1 mole, 97% purity) and 300 ml of toluene were charged to a reactor and heated to 110°C wherein the azeotropic distillation was done at 115°C until 35 ml toluene was distilled out to obtain a mixture. The mixture was cooled to 50 °C to obtain a first reaction mixture. To the first reaction mixture, 7.2 g of dry chlorine gas (dried using a trap-tower filled with 98% sulfuric acid) was bubbled at 50 °C for 30 minutes to obtain benzothiazole-2-sulfenyl chloride solution.
Benzothiazole-2-sulfenyl chloride solution was cooled to 10°C to obtain a cooled benzothiazole-2-sulfenyl chloride. Maintaining the temperature at 10°C, 77.0 g of N, N dicyclohexylamine (0.425 moles) was slowly added dropwise over a period of 60 minutes to the cooled benzothiazole-2-sulfenyl chloride to obtain a mass. The mass was further stirred at 10°C for 30 min to obtain a product mass comprising N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) and N, N-dicyclohexylamine hydrochloride.
The so obtained product mass comprising DCBS and dicyclohexylamine hydrochloride was heated to 65°C, followed by slowly adding dropwise 275 ml of sodium hydroxide solution (10g sodium hydroxide dissolved in 270 ml water (0.25 mole)) for 60 minutes to obtain a mixture. The mixture was further stirred for 60 minutes at 65°C to obtain a resultant mixture. The resultant mixture was kept without stirring and allowed to settle at 65°C for 30 minutes to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer. The first aqueous layer (bottom layer) was separated and discarded.
The separated top first organic layer was heated to 70°C. Maintaining the temperature at 70°C a solution of 215 ml of sulfuric acid (12.5 g of 98% sulfuric acid dissolved in 208 ml water (0.125 moles)) was slowly added in the organic layer for 30 min to obtain an acid treated mixture. The acid treated mixture was stirred for 30 minutes at 70°C and allowed to settle without stirring for 30 minutes to obtain a second biphasic mixture comprising a second organic layer and a second aqueous layer.
The second organic layer was mixed with 100 ml of water under stirring, allowed to settle for 30 minutes to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer was separated and combined with the second aqueous layer for amine recovery to obtain combined aqueous layer.
The third organic layer was then subjected to azeotropic distillation by continuous addition of 300 ml water at 55°C under a vacuum of 500 mm Hg, maintaining the temperature at 55°C till all the toluene was removed to obtain a slurry. The slurry was cooled to 30 oC (room temperature) under stirring for about 30 minutes, followed by filtration using a Buchner Funnel to obtain a wet cake. The wet cake was washed with 100 ml water, followed by drying in a hot air oven at 60°C (until a constant weight) to obtain N,N-Dicyclohexylbenzothiazole-2-sulfenamide.
The yield of N, N-dicyclohexylbenzothiazole-2-sulfenamide was 66.1 g (95.52 % yield on MBTS) as a creamy crystalline powder.
The properties of the so obtained N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) are provided below in Table-1.
Table – 1
Property Value
Melting Point (Initial) 101°C
Cyclohexane Insolubles 0.02 % (MBTS Content)
Free Amine Content 0.094 %
Purity (Titrimetric, by reduction with MBT) 98.6 %

EXAMPLE 2: Preparation of N, N-Dibenzylbenzothiazole2-sulfenamide (DBBS) in accordance with the process of the present disclosure:
33.2 g of 2, 2’-dithiobisbenzothiazole (0.1 mole, 97% purity) and 600 ml of toluene were charged to a reactor and heated to 115°C wherein the azeotropic distillation at 115°C was done until 100 ml toluene was distilled out to obtain a mixture. The mixture was cooled to 50°C to obtain a first reaction mixture. To the first reaction mixture 7.2 g of dry chlorine gas (dried using a trap-tower filled with 98% sulfuric acid) was bubbled at 50 °C for 30 min to obtain benzothiazole-2-sulfenyl chloride solution.
Benzothiazole-2-sulfenyl chloride solution was cooled to 10°C to obtain a cooled benzothiazole-2-sulfenyl chloride. Maintaining the temperature at 10°C, of 83.70 g of N, N dibenzylamine (0.425 moles) was slowly added dropwise over a period of 60 minutes to the cooled benzothiazole-2-sulfenyl chloride to obtain a mass. The mass was further stirred at 10°C for 30 min to obtain a product mass comprising N, N-dibenzylbenzothiazole-2-sulfenamide (DBBS) and dibenzylamine hydrochloride.
The so obtained product mass comprising DBBS and dibenzylamine hydrochloride was heated to 65°C, followed by slowly adding dropwise 275 ml of sodium hydroxide solution (10g sodium hydroxide dissolved in 270 ml water (0.25 mole) for 60 minutes to obtain a mixture. The mixture was further stirred for 60 minutes at 65°C to obtain a resultant mixture. The resultant mixture was kept without stirring and allowed to settle at 65°C for 30 minutes to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer. The first aqueous layer (bottom layer) was separated and discarded.
The separated top first organic layer was heated to 70 °C, Maintaining the temperature at 70 °C a solution of 215 ml of sulfuric acid (12.5 g of 98% sulfuric acid dissolved in 208 ml water (0.125 mole)) was slowly added in the organic layer for 30 min to obtain an acid treated mixture. The acid treated mixture was stirred for 30 minutes at 70 °C and was allowed to settle without stirring for 30 minutes to obtain a second biphasic mixture comprising a second organic layer and a second aqueous layer.
The second organic layer was mixed with 100 ml of water under stirring, allowed to settle for 30 minutes to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer was separated and combined with the second aqueous layer for amine recovery.
The third organic layer was then subjected to azeotropic distillation by continuous addition of 300 ml water at 55°C under a vacuum of 500 mm Hg, maintaining the temperature at 55°C till all the toluene was removed to obtain a slurry. The slurry was cooled to 30 oC (room temperature) under stirring for about 30 minutes, followed by filtration using a Buchner Funnel to obtain a wet cake. The wet cake was washed with 100 ml water, followed by drying in a hot air oven at 60°C (until a constant weight) to obtain N,N-Dibenzylbenzothiazole-2-sulfenamide. The yield of N, N-dibenzylbenzothiazole-2-sulfenamide was 67.4 g (93.09 % yield on MBTS) as off white crystals.
The properties of the so obtained DBBS are provided below in Table-2.
Table – 2
Property Value
Melting Point (Initial) 92°C
Cyclohexane Insolubles 0.20 % (MBTS Content)
Free Amine Content 0.047 %
Purity (Titrimetric, by reduction with MBT) 97.5 %

EXAMPLE 3: Preparation of N, N-dicyclohexylbenzothiazole 2-sulfenamide (DCBS) (Using excess chlorine and using acetic acid for Amine Recovery) in accordance with the process of the present disclosure:
66.4 g of 2, 2’-dithiobisbenzothiazole (0.2 mole, 97.30 % purity) and 600 ml of toluene were charged to a reactor and heated to 115°C wherein the azeotropic distillation at 115°C was done until 60 ml toluene was distilled out to obtain a mixture. The mixture was cooled to 50°C to obtain a first reaction mixture. To the first reaction mixture, 14.5 g of dry chlorine gas (dried using a trap-tower filled with 98% sulfuric acid) was bubbled for 30 minutes maintaining the temperature at 50 °C to obtain benzothiazole-2-sulfenyl chloride solution. The chlorine addition was continued for further ten minutes at the same rate of bubbling. The chlorine absorbed was 16.0g (some insoluble solid formation observed).
Benzothiazole-2-sulfenyl chloride solution was cooled to 10°C to obtain a cooled benzothiazole-2-sulfenyl chloride. Maintaining the temperature at 10°C, 154.8 g of N, N dicyclohexylamine (0.855 moles) was slowly added dropwise over a period of 60 minutes to the cooled benzothiazole-2-sulfenyl chloride to obtain a mass. The mass was further stirred at 10°C for 30 min to obtain a product mass comprising N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) and dicyclohexylamine hydrochloride in toluene.
The so obtained product mass comprising DCBS and dicyclohexylamine hydrochloride was heated to 65°C, followed by slowly adding dropwise 540 ml of sodium hydroxide solution (20 g sodium hydroxide dissolved in 540 ml water (0.50 mole) for 60 minutes to obtain a mixture. The mixture was further stirred for 60 minutes at 65°C to obtain a resultant mixture. The resultant mixture was kept without stirring and allowed to settle at 65°C for 30 minutes to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer. The first aqueous layer (bottom layer) was separated and discarded.
The separated top first organic layer was heated to 70 °C. Maintaining the temperature at 70°C a solution of 398 ml of aqueous acetic acid (30.50 g of glacial acetic acid dissolved in 370 ml water (0.508 moles)) was slowly added in the organic layer for 30 minutes to obtain an acid treated mixture. The acid treated mixture was stirred for 30 minutes at 70°C and allowed to settle without stirring for 30 minutes to obtain a second biphasic mixture comprising a second organic layer and a second aqueous layer.
The second organic layer was mixed with 200 ml of water under stirring, allowed to settle for 30 minutes to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer was separated and combined with the second aqueous layer for amine recovery.
The third organic layer was then subjected to azeotropic distillation by continuous addition of 600 ml water at 55°C under a vacuum of 400-600mm Hg, maintaining the temperature at 55°C till all the toluene was removed to obtain slurry. The slurry was cooled to 30 oC (room temperature) under stirring for about 30 minutes, followed by filtration using a Buchner Funnel to obtain a wet cake. The wet cake was washed with 400 ml water, followed by drying in a hot air oven at 60°C (until a constant weight) to obtain N,N-Dicyclohexylbenzothiazole-2-sulfenamide. The yield of N, N-dicyclohexylbenzothiazole-2-sulfenamide was 133.45 g (96.42 % yield on MBTS) as a creamy crystalline powder.
The properties of the so obtained N, N-dicyclohexylbenzothiazole 2-sulfenamide (DCBS) are provided below in Table-3.

Table – 3

Property Value
Melting Point (Initial) 98°C
Cyclohexane Insolubles 0.02 % (MBTS Content)
Free Amine 0.80%

Treatment of the product with an alcohol
3.1 The product of Example 3 (50.0 g) was mixed with 100 mL of 90 % v/v aqueous Isopropyl alcohol under stirring, filtered, washed with 50 ml of 90% v/v isopropyl alcohol to obtain a wet cake. The wet cake was dried in a hot air oven at 60°C (until a constant weight).
Dried Product obtained : 45.4 g
Recovery after washing : 90.8 %
Initial Melting Point : 101°C
Free Amine : 0.04 %

3.2 The product of Example 3 (50.0 g) was mixed with 100 mL of 90 % v/v aqueous methanol under stirring, filtered, washed with 50 ml of 90% v/v methanol to obtain a wet cake. The wet cake was dried in a hot air oven at 60°C (until a constant weight)
Dried Product obtained : 47.10 g
% Recovery after washing : 94.2 %
Initial Melting Point : 99°C
Free Amine : 0.08%

3.3 The product of Example 3 (25.0 g) was mixed with 50 mL of 50 % v/v aqueous Isopropyl alcohol under stirring, filtered, washed with 25 ml of 50% v/v isopropyl alcohol. The wet cake was dried in a hot air oven at 60°C (until a constant weight).
Dried Product obtained : 24.05 g
% Recovery after washing : 96.2 %
Initial Melting Point : 100 °C
Free Amine : 0.07 %
Amine Recovery from Example-3
About 680 ml of the combined first and second aqueous layers was heated to 65°C to obtain a mass. The mass was then treated at 65 °C with 47.66 g of 48% w/w caustic (0.571 mole) solution under stirring and then 75 ml of toluene was added. The mass was stirred at 65°C for 30 minutes and allowed to settle without stirring for 30 minutes.
The upper organic layer was separated. The bottom aqueous layer was separated and stirred again with 25 ml of toluene at 65°C and allowed to settle. The bottom aqueous layer was separated and discarded. The top organic layer was mixed with the already separated organic layer.
Volume of the Organic Layer (Total) 154 ml
Amine content in the organic layer (By titrimetric with Bromophenol Blue as indicator) 48.19% w/v
Amine Recovered 74.21 g (0.41 mole recovered from 0.45 moles excess dicyclohexylamine used in Example 3)

Example 4: Amine recovery and recycling of the recovered amine in the subsequent batch:
16.6 g of 2, 2’-dithiobisbenzothiazole (0.05 mole, 97% purity) and 150 ml of toluene were charged to a reactor and heated to 110°C wherein the azeotropic distillation was done at 115°C until 15 ml toluene was distilled out to obtain a mixture. The mixture was cooled to 50 °C to obtain a first reaction mixture. To the first reaction mixture, 3.55 g of dry chlorine gas (dried using a trap-tower filled with 98% sulfuric acid) was bubbled at 50 °C for 30 minutes to obtain benzothiazole-2-sulfenyl chloride solution.
Benzothiazole-2-sulfenyl chloride solution was cooled to 10°C to obtain a cooled benzothiazole-2-sulfenyl chloride. Maintaining the temperature at 10°C, 38.71 g of dicyclohexylamine (0.214 moles) was slowly added dropwise over a period of 60 minutes to the cooled benzothiazole-2-sulfenyl chloride to obtain a mass. The mass was further stirred at 10°C for 30 min to obtain a product mass comprising N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) and N, N-dicyclohexylamine hydrochloride.
The so obtained product mass comprising DCBS and dicyclohexylamine hydrochloride was heated to 65°C, followed by slowly adding dropwise 138 ml of sodium hydroxide solution (5 g sodium hydroxide dissolved in 135 ml water (0.125 mole)) for 60 minutes to obtain a mixture. The mixture was further stirred for 1 hour at 65°C to obtain a resultant mixture. The resultant mixture was kept without stirring and allowed to settle at 65°C for 30 minutes to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer. The first aqueous layer (bottom layer) was separated and discarded.
The separated top first organic layer was heated to 70°C. Maintaining the temperature at 70°C a solution of 129 ml of sulfuric acid (7.5 g of 98% sulfuric acid dissolved in 125 ml water (0.075 moles) was slowly added in the organic layer for 30 min to obtain an acid treated mixture. The acid treated mixture was stirred for 30 minutes at 70°C and allowed to settle without stirring for 30 minutes to obtain a second biphasic mixture comprising a second organic layer and a second aqueous layer.
The second organic layer was mixed with 100 ml of water under stirring, allowed to settle for 30 minutes to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer. The third aqueous layer was separated and combined with the second aqueous layer for amine recovery.
The combined aqueous layer and the water wash layer (245ml) was treated with 12.62 g 48 % caustic lye in the presence of 50 ml toluene at 65°C and then kept aside without stirring for layer separation. The upper layer was separated and about 17.0 ml toluene along with traces of water was removed by azeotropic distillation. The dried organic layer thus obtained after azeotropic distillation (48.14 g) was analysed for dicyclohexyl amine (DCHA) content (DCHA content is 41.48 % which is equal to 19.97 g and 0.110 mole of DCHA).
The third organic layer was then subjected to azeotropic distillation by continuous addition of 150 ml water at 55°C under a vacuum of 500 mm Hg, maintaining the temperature at 55°C till all the toluene was removed to obtain a slurry. The slurry was cooled to room temperature under stirring for about 30 minutes, followed by filtration using a Buchner Funnel to obtain a wet cake. The wet cake was washed with 100 ml water, followed by drying in a hot air oven at 60°C (until a constant weight) to obtain N,N-Dicyclohexylbenzothiazole-2-sulfenamide.
The yield of N, N-dicyclohexylbenzothiazole-2-sulfenamide was 32.9 g (95.09 % yield on MBTS) as a creamy crystalline powder.
The properties of the so obtained N, N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) are provided below in Table-1.
Table – 4
Property Value
Melting Point (Initial) 100°C
Cyclohexane Insolubles 0.01 % (MBTS Content)
Free Amine Content 0.094 %
Purity (Titrimetric,by reduction with MBT) 98.2 %

Example 5
The same procedure as in example 4 was repeated except that dicyclohexyl amine used in this example was recovered dicyclohexyl amine from the experiment 4.
The yield of N, N dicyclohexylbenzothiazole-2-sulfenamide obtained was 32.7 g (94.51 %).
Table – 5- Analysis
Property Value
Melting Point (Initial) 100°C
Cyclohexane Insolubles 0.02 % (MBTS Content)
Free Amine Content 0.096 %
Purity (Titrimetric, by reduction with MBT) 97.7 %

TECHNICAL ADVANCEMENT
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides that
• uses simple secondary amines for the preparation of N,N-disubstituted benzothiazole-2-sulfenamides, which also acts as acid scavenging agent;
• recovers excess amines by simple low energy-intensive methods and can be reused;
• recovers amines in the same solvent used in the reaction which can be dried easily by azeotropic distillation technique;
• is simple, economical and environment friendly;
• gives a higher yield and purity of N, N-disubstituted benzothiazole-2-sulfenamides in comparison to the conventional processes; and
• recovers solvent.
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:WE CLAIM:
1. A process for the preparation of N, N-disubstituted benzothiazole-2-sulfenamides, said process comprising the following steps:
i. chlorinating, a compound selected from a thiol substituted benzothiazole compound and a disulphide substituted benzothiazole compound, by using a chlorinating agent, in a first fluid medium at a first predetermined temperature, for a first predetermined time period to obtain benzothiazole-2-sulfenyl chloride;
ii. reacting benzothiazole-2-sulfenyl chloride and a secondary amine at a second predetermined temperature for a second predetermined time period to obtain a product mass comprising N, N-disubstituted benzothiazole-2-sulfenamide and hydrochloride salts of corresponding secondary amines;
iii. neutralizing said product mass by using a base at a third predetermined temperature for a third predetermined time period to obtain a first biphasic mixture having a first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine and a first aqueous layer;
iv. separating said first organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a free amine from said first biphasic mixture to obtain a separated first organic layer and a separated first aqueous layer;
v. removing said free amine from said separated first organic layer by using an acid at a fourth predetermined temperature for a fourth predetermined time period to obtain a second biphasic mixture having a second organic layer comprising N, N disubstituted benzothiazole-2-sulfenamide and a second aqueous layer; and
vi. separating said second organic layer from said second biphasic mixture to obtain a separated second organic layer and distilling said separated second organic layer to obtain N, N-disubstituted benzothiazole-2-sulfenamide.

2. The process as claimed in claim 1, wherein in step (i), said thiol substituted benzothiazole compound is 2-mercaptobenzothiazole and said disulphide substituted benzothiazole compound is 2, 2’-dithiobisbenzothiazole.

3. The process as claimed in claim 1, wherein in step (i), said chlorinating agent is selected from the group consisting of chlorine gas and sulfuryl chloride.

4. The process as claimed in claim 1, wherein in step (i), said first fluid medium is selected from the group consisting of toluene, benzene and a chlorinated solvent.

5. The process as claimed in claim 3, wherein said chlorinated solvent is selected from the group consisting of dichloromethane, dichloroethane, tetrachloroethylene and carbon tetrachloride.

6. The process as claimed in claim 1, wherein in step (i), a volume to a mass ratio of said first fluid medium to said benzothiazole compound is in the range of 5:1 to 25:1.

7. The process as claimed in claim 6, wherein in step (i), said volume to said mass ratio of said first fluid medium to said benzothiazole compound is in the range of 8:1 to 15:1.

8. The process as claimed in claim 1, wherein in step (i), said first predetermined temperature is in the range of 30 oC to 70 oC and said first predetermined time period is in the range of 20 minutes to 60 minutes.

9. The process as claimed in claim 1, wherein in step (i), the mole ratio of said benzothiazole compound to said chlorinating agent is in the range of 1:1 to 1:1.15.

10. The process as claimed in claim 1, wherein in step (ii), said secondary amine is selected from the group consisting of N, N-dicyclohexylamine, N, N-dibenzylamine, N, N-diisopropylamine, N, N-diphenylamine, N-methyl-N-tert-butylamine, N-ethyl-N-tert-butylamine, N-methyl-N-cyclohexylamine, N-ethyl-N-cyclohexylamine, N-methyl-N-benzylamine, and N-ethyl-N-benzylamine.

11. The process as claimed in claim 10, wherein in step (ii), said secondary amine is selected from the group consisting of N, N-dicyclohexylamine and N, N-dibenzylamine.

12. The process as claimed in claim 1, wherein in step (ii) said second predetermined temperature is in the range of 5 oC to 20 oC and said second predetermined time period is in the range of 60 minutes to 120 minutes.

13. The process as claimed in claim 1, wherein in step (ii), the mole ratio of said benzothiazole compound to said secondary amine is in the range of 1:2 to 1:6.

14. The process as claimed in claim 1, wherein in step (iii), said base is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.

15. The process as claimed in claim 1, wherein in step (iii), the mole ratio of said base to said benzothiazole compound is in the range of 1:1 to 3:1.

16. The process as claimed in claim 1, wherein in step (iii) said third predetermined temperature is in the range of 50 °C to 80 °C and said third predetermined time period is in the range of 60 minutes to 180 minutes.

17. The process as claimed in claim 1, wherein in step (v), said acid is at least one selected from the group consisting of sulphuric acid and acetic acid.

18. The process as claimed in claim 1, wherein in step (v) said fourth predetermined temperature is in the range of 60 °C to 90 °C and said fourth predetermined time period is in the range of 30 minutes to 80 minutes.

19. The process as claimed in claim 1, wherein the mole ratio of said acid to said benzothiazole compound is in the range of 0.5:1 to 4:1.

20. The process as claimed in claim 1, wherein in step (vi) said distillation is azeotropic distillation and is carried out at a temperature in the range of 50 oC to 60 oC under a vacuum in the range of 400 mmHg to 600 mmHg.

21. The process as claimed in claim 1, wherein step (vi) comprises the following steps:
a. adding water to said second organic layer to obtain a third biphasic mixture comprising a third organic layer and a third aqueous layer;
• separating said third aqueous layer from said third biphasic mixture followed by combining said third aqueous layer with said second aqueous layer of step (v) to obtain a combined aqueous layer which is treated for amine recovery;
• azeotropically distilling said third organic layer to separate said first fluid medium for reuse in step (i), to obtain a product mixture; and
• cooling said product mixture followed by filtering to obtain N, N disubstituted benzothiazole-2-sulfenamide.

22. The process as claimed in claim 1, wherein said N, N disubstituted benzothiazole-2-sulfenamide has a yield greater than 90% and a purity greater than 95%.

Dated this 26th day of December, 2023

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI