Claims:We Claim:

1. A method for preparing bis[3-(triethoxysilyl)propyl] disulfide comprising the steps of:
(a) preparing a solution of sodium hydroxide, elemental sulfur, and a sulfide compound having a formula M2S or MHS and incubating the solution, where M is an alkali metal;
(b) adding a quaternary ammonium cation to the solution to obtain a first mixture;
(c) adding to the first mixture, a triethoxy(propyl) silane compound having the formula (C2H5O)3-C3H7—Si—X where X is a chloro or thiol group, to obtain a reaction mixture wherein the concentration of sodium hydroxide in the reaction mixture is 15 to17% by weight of the triethoxy(propyl) silane compound;
(d) allowing the reaction mixture to react at a temperature in the range of 50 to 65oC for a time period in the range of 5 to 20 hours to obtain bis[3-(triethoxysilyl) propyl] disulfide; and
(e) separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture obtained in step (d).

2. The method as claimed in claim 1, wherein the weight/weight ratio of sodium hydroxide, elemental sulfur, and the sulfide compound is in a range of 1: 1.50: 2.10 to 1: 1.60: 3.

3. The method as claimed in claim 1, wherein the weight/weight ratio of sodium hydroxide, elemental sulfur, and the sulfide compound is 1: 1.55: 2.16.

4. The method as claimed in claim 1, wherein the triethoxy(propyl) silane compound is selected from 3-chloropropyltriethoxy silane (CPTES) or 3-mercaptopropyltriethoxy silane (MPTES).

5. The method as claimed in claim 1, wherein the weight/weight ratio of sodium hydroxide to the triethoxy(propyl) silane compound is in the range of 1:4 to 1:7.

6. The method as claimed in claim 1, wherein the quaternary ammonium cation is selected from the group consisting of tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), and (tetrabutylphosphonium bromide, tetrabutylphosphonium chloride).

7. The method as claimed in claim 1, wherein the weight/weight ratio of sodium hydroxide and the quaternary ammonium cation is in a range of 1: 0.10 to 1: 0.15

8. The method as claimed in claim 1, wherein reacting the reaction mixture is at a temperature in the range of 50oC to 60oC for a time period in the range of 6 to 18 hours.

9. The method as claimed in claim 1, wherein the alkali metal (M) in the sulfide compound having the formula M2S or MHS, is selected from Sodium (Na) or Potassium (K).

10. The method as claimed in claim 1, wherein separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture comprises:
(a) adding an organic solvent to the reaction mixture to obtain a first organic phase;
(b) filtering and separating the first organic phase;
(c) adding an anhydrous alkali sulphate or an anhydrous alkaline metal sulphate to the filtered first organic phase to obtain a second organic phase;
(d) filtering the second organic phase; and
(e) drying the filtered second organic phase to obtain bis[3-(triethoxysilyl)propyl] disulfide.

11. The method as claimed in claim 10, wherein the organic solvent is selected from the group consisting of low boiling point solvents such as hexane, ethyl acetate, toluene, xylene, benzene, heptane and octane.

12. The method as claimed in claim 10, wherein the anhydrous alkali sulphate is anhydrous sodium sulphate and the anhydrous alkaline metal sulphate is anhydrous magnesium sulphate.

Dated this 23rd day of December 2021

Essenese Obhan
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 864
, Description:FIELD OF INVENTION
The present disclosure relates to methods for preparing organosilanes in general. In particular, the present disclosure relates to a method for preparing bis[3-(triethoxysilyl)propyl] disulfide.

BACKGROUND
The importance of silica as a reinforcing filler during vulcanization of rubber mixtures has substantially increased in the last decade. The physicochemical characteristics of silica as a reinforcing filler is critical to meet the performance norms of rubber, e.g., significant increase in tensile strength and abrasion resistance. This in turn increases the longevity of rubber.
Sulfur containing organosilanes are commonly employed as coupling agents during the process of vulcanization of rubber and are required for the dispersion of precipitated silica in a rubber matrix. These play an important role in the dispersion of silica by enabling covalent binding of silica to the rubber matrix which improves performance of the reinforced rubber. They also increase the hydrophobicity of the silica surface by introducing organic groups, thereby improving processability as well as facilitating effective coupling with rubber. The number of sulfur atoms (or ‘rank’) is an important factor in influencing the properties of rubber during vulcanisation. While sulfur is required to decrease the plasticity of rubber compositions and simultaneously increase elasticity, a very high amount of sulfur in rubber hardens rubber and remains poorly dispersed in the rubber matrix.
Various processes are known in the prior art for the production of organosilicone compounds.
US6740767B1 describes a process for producing organosilicone compounds comprising (I) heating and reacting (A) a sulfide compound such as M2Sn or MHS where H is hydrogen, M is ammonium or an alkali metal, and n is 1-8; with (B) a silane compound of the formula (RO)3-mRmSi—Alk—X where X is Cl, Br or I, and m is 0, 1, or 2; and with (C) sulfur. The sulfur rank of the organosilicone compound(s) obtained by the process ranges from 3.5 to 3.77.
US6448426B1 describes a process for producing organosilicone compounds comprising (A) reacting sulfur, a phase transfer catalyst, a sulfide compound having the formula M2Sn or MHS, where H is hydrogen, M is ammonium or an alkali metal, and water to form an intermediate reaction product; (B) reacting said intermediate reaction product with a silane compound of the formula; (RO)3-mRmSi—Alk—X where X is Cl, Br or I to form a product mixture (C) separating the organosilicone compound from the product mixture. The disulfide percent obtained from the process ranges between 12% to 20%.

SUMMARY
The present application relates to a method for preparing bis[3-(triethoxysilyl)propyl] disulfide comprising the steps of (a) preparing a solution of sodium hydroxide, elemental sulfur, and a sulfide compound having a formula M2S or MHS and incubating the solution, where M is an alkali metal; (b) adding a quaternary ammonium cation to the solution to obtain a first mixture; (c) adding to the first mixture, a triethoxy(propyl) silane compound having the formula (C2H5O)3-C3H7—Si—X where X is a chloro or thiol group, to obtain a reaction mixture wherein the concentration of sodium hydroxide in the reaction mixture is 15 to17% by weight of the triethoxy(propyl) silane compound; (d) allowing the reaction mixture to react at a temperature in the range of 50 to 65oC for a time period in the range of 5 to 20 hours to obtain bis[3-(triethoxysilyl) propyl] disulfide; and (e) separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture.

DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment”, “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms “a,” “an,”, and “the” are used to refer to “one or more” (i.e. to at least one) of the grammatical object of the article.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion and are not intended to be construed as “consists of only”, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described.
The present disclosure relates to a method for preparing bis[3-(triethoxysilyl)propyl] disulfide. The method comprises the steps of: preparing a solution of sodium hydroxide, elemental sulfur, and a sulfide compound having a formula M2S or MHS where M is an alkali metal and incubating the solution; adding a quaternary ammonium cation to the solution to obtain a first mixture; adding to the first mixture, a triethoxy(propyl) silane compound having the formula (C2H5O)3-C3H7—Si—X where X is a chloro or thiol group, to obtain a reaction mixture, wherein the concentration of sodium hydroxide in the reaction mixture is 15 to17% by weight of the triethoxy(propyl) silane compound; allowing the reaction mixture to react at a temperature in the range of 50 to 65oC for a time period in the range of 5 to 20 hours to obtain bis[3-(triethoxysilyl) propyl] disulfide; and separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture.
In accordance with an embodiment, the weight/weight (w/w) ratio of the sodium hydroxide, elemental sulfur and the sulfide compound is in a range of 1:1.50: 2.10 to 1:1.60:3. In a further embodiment the weight/weight ratio of the sodium hydroxide, elemental sulfur and the sulfide compound is 1:1.55: 2.16
In accordance with an embodiment, the elemental sulfur has a purity of 99% and may be in the form of flakes or a powder. In an embodiment the weight/weight ratio of sodium hydroxide to elemental sulfur is in the range of 1.50 to1.60. In a specific embodiment, the weight/weight ratio of the sodium hydroxide to elemental sulfur is 1:1.55.
The sulfide compound has a formula M2S or MHS where H is hydrogen and M is alkali metal. In an embodiment, the alkali metal (M) of the sulfide compound is selected from sodium or potassium. In a specific embodiment, the alkali metal (M) of the sulfide compound is sodium. In accordance with an embodiment the weight/weight ratio of sodium hydroxide to the sulfide compound is 1:2.10 to 1:3. In a specific embodiment, the weight/weight ratio of sodium hydroxide to the sulfide compound is 2.16.
In accordance with an embodiment, a solution comprising 45% to 60% by weight of sodium hydroxide is used in the method described herein. In a specific embodiment, a solution comprising 50% by weight of sodium hydroxide is used in the method described herein.
In accordance with an embodiment, water is added to the solution comprising sodium hydroxide, elemental sulfur, and a sulfide compound. In some embodiments, the amount of additional water added is in a weight/weight range of 1:0.5 to 1:1 ratio of sodium hydroxide to water. In an alternative embodiment, the amount of additional water is in the weight/weight ratio of 1: 0.9 of sodium hydroxide to water.
In accordance with an embodiment, once the solution comprising sodium hydroxide, elemental sulfur, and a sulfide compound is prepared, a quaternary ammonium cation is added to said solution after a time period of 5 to 15 min. In an alternative embodiment, the quaternary ammonium cation is added after a time period of 10 min.
In accordance with an embodiment, the weight/weight ratio of sodium hydroxide to the quaternary ammonium cation is 1: 0.10 to 1: 0.15. In a further embodiment, the weight/weight ratio of sodium hydroxide to the quaternary ammonium cation is 1:0.13. In accordance with an embodiment, the quaternary ammonium cation is selected from the group consisting of tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), (tetrabutylphosphonium bromide, tetrabutylphosphonium chloride. In a specific embodiment, the quaternary ammonium cation is tetrabutylammonium bromide (TBAB). The quaternary ammonium cation is added drop-wise to the solution comprising sodium hydroxide, elemental sulfur, and the sulfide compound until said solution turns an orange-red colour to obtain the first mixture.
The triethoxy(propyl) silane compound having the formula (C2H5O)3-C3H7—Si—X where X is a chloro or thiol group is added to the first mixture. In accordance with an embodiment, the triethoxy(propyl) silane compound is added to the first mixture in a weight/weight ratio of 1:4 to 1:7 of sodium hydroxide to the triethoxy(propyl) silane compound. In accordance with an embodiment, the triethoxy(propyl) silane compound is 3-chloropropyltriethoxy silane (CPTES), and is represented by the formula (C2H5O)3-C3H7—Si—Cl. In a specific embodiment, the ratio of sodium hydroxide to CPTES is 1:6.12. In an alternative embodiment, the triethoxy(propyl) silane compound is 3-mercaptopropyltriethoxy silane (MPTES) and is represented by the formula (C2H5O)3-C3H7—Si—SH.
Once the triethoxy(propyl) silane compound is added to the first mixture, a reaction mixture is obtained. In accordance with an embodiment the concentration of sodium hydroxide to the triethoxy(propyl) silane compound is in the range of 15% to 17%. In a specific embodiment, the concentration of sodium hydroxide to CPTES is 16.3%.
In accordance with an embodiment, the reaction mixture is reacted at a temperature in the range of 50oC to 65oC for a time-period in the range of 5 to 20 hours. In a further embodiment, the reaction mixture is reacted at a temperature in the range of 50oC to 60oC for a time-period in the range of 6 to 18 hours. In a specific embodiment, the reaction mixture is reacted at a temperature of 50oC for a time period of 18 hours when the triethoxy(propyl) silane compound is CPTES. In another embodiment, the reaction mixture is reacted at a temperature of 60oC for a time period of 6 hours, when the triethoxy(propyl) silane compound is CPTES. In an alternative embodiment, the reaction mixture is reacted for a time period of 0.5 hours at a temperature of 15oC, when the triethoxy(propyl) silane compound is MPTES.
The bis[3-(triethoxysilyl) propyl] disulfide obtained after reacting the reaction mixture is then separated. In an embodiment, separating bis[3-(triethoxysilyl) propyl] disulfide comprises adding an organic solvent to the reaction mixture to obtain a first organic phase; filtering and separating the first organic phase; adding an anhydrous alkali sulphate or an anhydrous alkaline metal sulphate to the filtered first organic phase to obtain a second organic phase; filtering the second organic phase; and drying the filtered second organic phase to obtain bis[3-(triethoxysilyl)propyl] disulfide.
In accordance with an embodiment, the organic solvent is selected from the group consisting of low boiling point solvents. Examples of such low boiling point solvents include but are not limited to hexane, ethyl acetate, toluene, xylene, benzene, heptane and octane. In a specific embodiment, the organic solvent is hexane.
In accordance with an embodiment, after the organic solvent is added in the first step to separate bis[3-(triethoxysilyl)propyl] disulfide, a first aqueous phase and the first organic phase is obtained. The first organic phase is first filtered to remove impurities and insoluble solid components and is then separated from the first aqueous phase. The anhydrous alkali sulphate or anhydrous alkaline metal sulphate is then added to the filtered and separated first organic phase. In an embodiment, the anhydrous alkali sulphate is selected from anhydrous sodium sulphate and the anhydrous alkaline sulphate is anhydrous magnesium sulphate. In accordance with an embodiment, once the anhydrous alkali sulphate or anhydrous alkaline metal sulphate is added to the first organic phase, the traces of water are removed from the first organic phase and a second organic phase is obtained. The second organic phase is then filtered to remove the unreacted anhydrous alkali sulphate or anhydrous alkaline metal sulphate. The filtered second organic phase is then dried to remove the organic solvent. In some embodiments, the filtered second organic phase is dried under rotary evaporation to remove the remaining organic solvent to obtain the purified bis[3-(triethoxysilyl)propyl] disulfide.
In accordance with an embodiment, the sulfur rank of the product obtained from the method described herein is in the range of 2.1 to 2.3. In a specific embodiment, the sulfur rank obtained is 2.15.
In accordance with an embodiment, the bis[3-(triethoxysilyl)propyl] disulfide content in the product is in the range of 75 to 90% and the bis[3-(triethoxysilyl)propyl] tetrasulfide content in the product is in the range of 1 to 5%. In an alternative embodiment, the bis[3-(triethoxysilyl)propyl] disulfide content in the product is in the range of 80 to 90% and no bis[3-(triethoxysilyl)propyl] tetrasulfide is formed. In a specific embodiment, the bis[3-(triethoxysilyl)propyl] disulfide content in the product is in the range of 83 to 85% and no bis[3-(triethoxysilyl)propyl] tetrasulfide is formed.
In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and the exact compositions, methods of preparation and embodiments shown are not limiting of the invention, and any obvious modifications will be apparent to one skilled in the art.

EXAMPLES
Example 1: Process for preparing bis (triethoxysilyl)propyl] disulfide (TESPD)
14.14 g water, 24.34 g sulfur (99% purity), 93.02 g NaHS solution (50% by weight, 73% purity), and 31.40 g sodium hydroxide solution (50% by weight, 99.8% purity) was added to a 1 Litre Shott Duran Beaker with a lid. The solution so obtained was stirred with a PTFE element at 300 RPM. After 10 min, 8.16 g TBAB (25% by weight, 99.9% purity) solution was added drop-wise until the solution turned orange in colour. Once the colour appeared, 100 g CPTES (96% purity) solution was added drop-wise for 10 to 15 min. The solution was then incubated to allow the components to react at a temperature maintained between 50oC to 60oC for a time-period ranging from 6 hours to 18 hours.
Once the reaction was complete, the temperature of the solution was reduced to 30oC. 100ml of hexane was added to the reaction mixture and the mixture was stirred to separate the mixture into an aqueous phase and a first organic phase. The first organic phase was separated at room temperature using a funnel. Anhydrous sodium sulphate was added to the first organic phase to separate out the aqueous phase and a second organic phase. This second organic phase was then filtered to remove any impurities and was then evaporated using a rotavapour to evaporate the solvent.
The sulphur rank and the disulphide content of the compound obtained from the disclosed method was analysed by HPLC with the following parameters: Agilent C18 Eclipse Column (4.6 mm x 250 mm), mobile phase of acetonitrile (95%) and tetrahydrofuran (5%); at a flow rate of 0.5 mL/min, 30oC, 10µl injection volume. Sample detection was measured at 254nm.

The sulphur rank of the compound obtained from Example 1 was analysed as described in Tables 1 and 2:

Peak No. Sulphur Chain Length RT Batch No. P47 1367 ppm Weight Sulphur Rank
(min) (Area) (Area %) (%)
1 S2 11.0 1619820 57.03 83.1 2.18
2 S3 12.9 1084145 38.17 15.8
3 S4 15.1 136336 4.8 1.1

Table 1: HPLC Analysis of Sulphur Rank obtained from reaction carried out 50 0C for 18 hours using CPTES as a precursor

Peak No. Sulphur Chain Length RT Batch No. P84 1409 ppm Weight Sulphur Rank
(min) (Area) (Area %) (%)
1 S2 11.1 1571606 58.15 83.7 2.17
2 S3 13.1 1012377 37.46 15.3
3 S4 15.4 118670 4.39 0.99

Table 2: HPLC Analysis of Sulphur Rank obtained from reaction carried out at 60 0C for 6 hours using CPTES as a precursor

The disulphide content of the compound obtained from Example 1 is described in Table 2 below:
S.No NaOH (50%)
(g) CPTES (g)
NaHS (50%)
(g)
Elemental
Sulphur (g) TBAB
(25%)
(g) Time (h) Temp.
(°C) Disulphide Content
Purity 99% 96% 73% 99% 99.8%
1 4.62 14.72 13.68 3.58 1.2 18 50 84%
2 4.62 14.72 13.68 3.58 1.2 6 60 85%

Table 3: Disulfide content obtained from the method of Example 1

The weight/weight ratio of the components in the above processes are given in Table 2 below:

S.No NaOH CPTES NaHS Elemental
Sulphur
TBAB

Weight of compound in Process 1 & 2 (above) 2.31 14.72 6.84 3.58 0.3
Weight corrected for purity 2.31 14.13 4.99 3.58 0.3
weight/weight ratio 1 6.12 2.16 1.55 0.13

Observation: As demonstrated in Table 1 to 4, it is possible to obtain a compound with a sulphur rank of 2.17 to 2.18, and with a high disulphide content from the method of the present disclosure. For instance the reaction for 6 hours at 60oC yields 85 % of bis[3-(triethoxysilyl)propyl] disulfide, while only 1to 2 % of bis[3-(triethoxysilyl)propyl] tetrasulfide is obtained.

Example 2: Effect of NaOH concentration and reaction temperatures on the disulphide content
The process of Example 1 was repeated while varying the concentration of NaOH used in the reaction process and the results obtained were analysed by HPLC. The results of the experiments are summarized in Table 5 below.

Batch
Details CPTES
(g) NaHS (50% aq. solution) (g) Element-al
Sulphur
(g) TBAB (25% aq. solution)
(g)
NaOH (50% aq. solution)
(g) Time (h) Temp. (°C) Disulphi-de content
Purity 96% 73% 99% 99.8% 99%
Preferred Process 14.72 13.68 3.58 1.2 4.62 18 50 85%
Batch 1 14.72 13.68 3.58 1.2 0 18 50 11.1%
Batch 2 14.72 13.68 3.58 1.2 2.31 18 50 27.2%
Batch 3 14.72 13.68 3.58 1.2 3.46 18 50 52.9%

Table 5: Results obtained by varying the NaOH concentration in the reaction mixture

Observation: As can be seen from Table 5, the concentration of NaOH has a significant effect in the amount of disulphide obtained from the reaction process. Unexpectedly, the weight/weight percentage of 15 to 17 wt % of NaOH to CPTES (preferred process in Table 5) ensures that the optimum amount of disulphide is obtained. Varying this percentage results in a considerable reduction in the disulfide content obtained from the reaction mixture and also results in a reduced disulphide to tetra-sulphide content. For instance, while Batch 3 resulted in a disulphide content of 52.9 %, however the tetra-sulphide content was 9.2 % which is undesirable.
In addition to varying the NaOH content, the parameters of the reaction temperature and reaction time were also varied. The results of the experiment are provided in Table 4 below.

Batch
Details CPTES (g) NaHS (50%) (g) Elemental
Sulphur (g) TBAB (25%) (g) NaOH (50%) (g) Time (h) Temp. (°C) Disulphide Content
Purity 96% 73% 99% 99.8% 99%
50oC
Reaction Temperature 14.72 13.68 3.58 1.2 4.62 18 50 84%
60oC
Reaction Temperature 14.72 13.68 3.58 1.2 4.62 6 60 85%
70 oC
Reaction Temperature 14.72 13.68 3.58 1.2 4.62 6 70 0 % disulphide formed

Table 5: Effect of reaction temperature and reaction time on final disulphide content
Observation: As can be seen from the results of Table 5, while the reaction temperature in the range of 50oC to 60oC resulted in a high disulphide content in the reaction, unexpectedly, increasing the temperature to 70oC resulted in no disulphide production even though the other process parameters remained the same. This shows that the reaction temperature plays a crucial role in determining the final disulphide content in the reaction mixture.

Specific Embodiments
Specific embodiments are herein described below:
A method for preparing bis[3-(triethoxysilyl)propyl] disulfide is disclosed. The method comprises the steps of: (a) preparing a solution of sodium hydroxide, elemental sulfur, and a sulfide compound having a formula M2S or MHS and incubating the solution, where M is an alkali metal; (b) adding a quaternary ammonium cation to the solution to obtain a first mixture; (c) adding to the first mixture, a triethoxy(propyl) silane compound having the formula (C2H5O)3-C3H7—Si—X where X is a chloro or thiol group, to obtain a reaction mixture wherein the concentration of sodium hydroxide in the reaction mixture is 15 to17% by weight of the triethoxy(propyl) silane compound; (d) allowing the reaction mixture to react at a temperature in the range of 50 to 65oC for a time period in the range of 5 to 20 hours to obtain bis[3-(triethoxysilyl) propyl] disulfide; and (e) separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture obtained in step (d).
The method(s) wherein the weight/weight ratio of sodium hydroxide, elemental sulfur, and the sulfide compound is in a range of 1: 1.50:2.10 to 1: 1.60: 3.
The method(s) wherein the weight/weight ratio of sodium hydroxide, elemental sulfur, and the sulfide compound is 1: 1.55: 2.16.
The method(s) wherein the triethoxy(propyl) silane compound is selected from 3-chloropropyltriethoxy silane (CPTES) or 3-mercaptopropyltriethoxy silane (MPTES).
The method(s) wherein the weight/weight ratio of sodium hydroxide to the triethoxy(propyl) silane compound is in the range of 1:4 to 1:7.
The method(s) wherein the quaternary ammonium cation is selected from the group consisting of tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), and (tetrabutylphosphonium bromide, tetrabutylphosphonium chloride).
The method(s) wherein the weight/weight ratio of sodium hydroxide and the quaternary ammonium cation is in a range of 1: 0.10 to 1: 0.15
The method(s) wherein reacting the reaction mixture is at a temperature in the range of 50oC to 60oC for a time period in the range of 6 to 18 hours.
The method(s) wherein the alkali metal (M) in the sulfide compound having the formula M2S or MHS, is selected from Sodium (Na) or Potassium (K).
The method(s) wherein separating the bis[3-(triethoxysilyl)propyl] disulfide from the reaction mixture comprises: (a) adding an organic solvent to the reaction mixture to obtain a first organic phase; (b) filtering and separating the first organic phase; (c) adding an anhydrous alkali sulphate or an anhydrous alkaline metal sulphate to the filtered first organic phase to obtain a second organic phase; (d) filtering the second organic phase; and (d) drying the filtered second organic phase to obtain bis[3-(triethoxysilyl)propyl] disulfide.
The method(s) wherein the organic solvent is selected from the group consisting of low boiling point solvents such as hexane, ethyl acetate, toluene, xylene, benzene, heptane and octane.
The method(s) wherein the anhydrous alkali sulphate is anhydrous sodium sulphate and the anhydrous alkaline metal sulphate is anhydrous magnesium sulphate.

INDUSTRIAL APPLICATION
The method of the present disclosure is simple to perform and provides high yields of of bis[3-(triethoxysilyl)propyl] disulfide. The final product obtained from the disclosed method has a high bis[3-(triethoxysilyl)propyl] disulfide content, while the bis[3-(triethoxysilyl)propyl] tetrasulfide content is significantly low. Therefore, the purity of the bis[3-(triethoxysilyl)propyl] disulfide is also high with less contamination from other polysulfides.
The bis[3-(triethoxysilyl)propyl] disulfide obtained from this method is particularly useful as a coupling agent during rubber compounding, which in turn is utilized in the preparation of a wide range of rubber products, such as tyres for automobile industry.