Description:Field of Invention

The present disclosure relates to a process for preparing 3-octanoylthio-1-propyltriethoxysilane.

Background

3-octanoylthio-1-propyltriethoxysilane is a sulfur-containing silane coupling agent which is used extensively in rubber applications such as tires and tire components. Various processes are known for preparing 3-octanoylthio-1-propyltriethoxysilane. However, the known processes suffer from one or more disadvantages such as- low yield, undesired by-products etc. Thus, there still exists a need for a process that results in a high yield of 3-octanoylthio-1-propyltriethoxysilane while ensuring selective conversion of raw materials.

Summary

A process for preparing 3-octanoylthio-1-propyltriethoxysilane is disclosed. Said process comprises reacting an aqueous sodium hydrosulfide solution with octanoyl chloride in the presence of a phase transfer catalyst under alkaline pH to obtain an aqueous solution of sodium thiooctanoate, followed by reacting the obtained sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane in the presence of the phase transfer catalyst to form a reaction mixture containing 3-octanoylthio-1-propyltriethoxysilane.

Detailed Description

Reference will now be made in detail to embodiments of the present disclosure. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner, simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several features, no single one of which is solely responsible for its desirable attributes, or which is essential to practicing the inventions herein described.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

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.

Likewise, the terms “having” and “including”, and their grammatical variants are intended to be non-limiting, such that recitations of said items in a list are not to the exclusion of other items that can be substituted or added to the listed items.

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. All publications mentioned herein are incorporated herein by reference.

The present disclosure relates to a process for preparing 3-octanoylthio-1-propyltriethoxysilane. Said process comprises the steps of:
- reacting an aqueous sodium hydrosulfide solution with octanoyl chloride in the presence of a phase transfer catalyst under alkaline pH to obtain sodium thiooctanoate; and
- reacting the obtained sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane in the presence of the phase transfer catalyst to obtain a reaction mixture containing 3-octanoylthio-1-propyltriethoxysilane.

In an embodiment, sodium hydrosulfide is reacted with octanoyl chloride in a molar ratio in the range of 1:1 to 2.6:1. In some embodiments, sodium hydrosulfide is reacted with octanoyl chloride reacted in the molar ratio of 2:1 to 2.6:1.

In the first step, octanoyl chloride is added to the aqueous sodium hydrosulfide solution slowly, to safely handle the exotherm of the reaction. In an embodiment, octanoyl chloride is added dropwise to the aqueous sodium hydrosulfide solution. In another embodiment, the aqueous sodium hydrosulfide solution is added dropwise to octanoyl chloride.

In an embodiment, to carry out the reaction of sodium hydrosulfide with octanoyl chloride, octanoyl chloride is added to the aqueous sodium hydrosulfide solution at a temperature in the range of 0 to 10°C. In an embodiment, after the addition of octanoyl chloride, the reaction of hydrosulfide with octanoyl chloride is carried out at a temperature in the range of 0 to 30°C, under atmospheric pressure. In some embodiments, the reaction of sodium hydrosulfide with octanoyl chloride is carried out at the temperature in the range of 0 to 10°C. In an embodiment, the reaction of sodium hydrosulfide with octanoyl chloride is carried out for a time-period of 30 minutes to 2 hours. In some embodiments, the reaction of sodium hydrosulfide with octanoyl chloride is carried out for a time-period of 1 hour.

In an embodiment, the reaction of sodium hydrosulfide with octanoyl chloride is carried out under alkaline pH ranging between 10-12. In an embodiment, the alkaline pH is achieved by adding an alkali selected from the group consisting of sodium hydroxide, sodium carbonate, and potassium tert-butoxide. In some embodiments, the alkali is sodium hydroxide. Reaction of the hydrosulfide with octanoyl chloride under alkaline pH provides for complete conversion of raw materials to form aqueous solution of sodium thiooctanoate.

In an embodiment, the reaction mixture of aqueous sodium hydrosulfide solution and octanoyl chloride is subjected to continuous agitation till the reaction completes. At the end of the first step, the aqueous solution of sodium thiooctanoate is obtained.

In the second step of the process, the aqueous solution of sodium thiooctanoate is reacted with 3-chloropropyl-1-triethoxysilane. In an embodiment, 3-chloropropyl-1-triethoxysilane is added in an amount such that 3-chloropropyl-1-triethoxysilane and sodium hydrosulfide have a weight ratio in the range of 1.87:1 to 3.54:1. In some embodiments, 3-chloropropyl-1-triethoxysilane and sodium hydrosulfide have the weight ratio of 2.46:1 to 3.54:1. In some embodiments, 3-chloropropyl-1-triethoxysilane and sodium hydrosulfide have the weight ratio of 1.87:1. In an embodiment, 3-chloropropyl-1-triethoxysilane is added to the reaction mixture at a rate of 20 mL/minute at a temperature in the range of 70 to 110°C. In some embodiments, the addition of 3-chloropropyl-1-triethoxysilane is started at the temperature of 70°C at a flow rate of 20 mL/minute. In an embodiment, the reaction of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out at a temperature of 90 to 110°C. In some embodiments, the reaction of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out at the temperature of 90°C. In an embodiment, the reaction of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out for a time-period of 2 to 5 hours. In some embodiments, the reaction of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out for 3 hours.

In an embodiment, the phase transfer catalyst is selected from the group consisting of tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), and methyltrioctylammonium chloride (MTOCl). In some embodiments, the phase transfer catalyst is TBAB. In an embodiment, the weight of phase transfer catalyst used in the process is 1.25 to 3.5% of the weight of 3-chloropropyl-1-triethoxysilane. In an embodiment, a partial amount of the phase transfer catalyst is added in the first step of the process, and the remaining amount of the phase transfer catalyst is added during the second step of the process. In an alternate embodiment, the phase transfer catalyst is added in one step either during the first step or the second step of the process.

In an embodiment, the process further comprises subjecting the reaction mixture containing 3-octanoylthio-1-propyltriethoxysilane to a phase separation step to separate the reaction mixture into an organic phase and an aqueous phase. The organic phase contains 3-octanoylthio-1-propyltriethoxysilane and the aqueous phase contains the unreacted raw material, catalyst and by products produced during the reaction.

The organic phase is separated by the addition of a solvent to the reaction mixture. The solvent is any solvent known for the separation of organic phase. In an embodiment, the organic solvent is at least one selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, hexadecane, cyclohexane, cyclopentane, benzene, toluene, xylene, methylene chloride, chloroform, 1,2-dichloroethane, monochlorobenzene, dichlorobenzene, diethyl ether, dibutyl ether, ethyl acetate, and butyl acetate. In some embodiments, the organic solvent is n-hexane. The organic solvent is added to the reaction singly at a time, or in batches.

The organic phase is subjected to a further treatment using known means to purify the product. In an embodiment, a dehydrating agent is used to remove traces of moisture from the organic phase. Examples of dehydrating agent include but are not limited to sodium sulfate. After dehydration, the organic phase is filtered using standard filtration technique to obtain purified product.

The aqueous phase is treated using known means and processes to recover the unreacted raw material, catalyst and by products produced during the reaction.

The disclosed process is carried out in a reactor, including but not limited to continuous stirred tank reactor, plug flow reactor and any other similar reactor as is now known or in the future developed.

In one embodiment, the disclosed process is carried out in a continuous manner such that the unreacted raw material and the phase transfer catalyst is recycled to the process, after filtration from the reaction medium using known means.

The following examples illustrate certain embodiments and aspects of the present invention and not to be construed as limiting the scope thereof. All parts and percentages are by weight basis unless otherwise stated.

Example 1: Preparation of 3-octanoylthio-1-propyltriethoxysilane in accordance with an embodiment

Step 1: Preparation of sodium thiooctanoate

To a three necked round bottom flask, equipped with a stopper, stirrer and reflux condenser, 1140 grams of an aqueous sodium hydrosulfide solution (50% by weight), 192.46 grams of sodium hydroxide (flakes) and 1269 grams of distilled water were added. The overhead stirrer was used with PTFE element @ 200 RPM. After 10 minutes, the solution was cooled to 10°C using ice and salt. Then, 832 grams of octanoyl chloride was slowly added to the reaction mixture (addition time 42 minutes). To this reaction mixture, 50 grams of aqueous TBAB solution (25% by weight) was added drop wise, followed by stirring for 1 hour. During this time, the temperature of the reaction mixture was increased from 10°C to room temperature. An aqueous solution of sodium thiooctanoate was obtained at the end of reaction.

Step 2: Preparation of 3-octanoylthio-1-propyltriethoxysilane

After 1 hour, the solution in the flask was heated to 110°C. When the temperature reached 80°C, dropwise addition of 1 kg 3-chloropropyl-1-triethoxysilane was started at flow rate of 20 mL/minute. 50 grams of aqueous TBAB solution (25% by weight) was immediately added to the reaction mixture drop wise, followed by reflux of the reaction mixture at 110°C for 3 hours under constant stirring. A reaction mixture comprising 3-octanoylthio-1-propyltriethoxysilane was obtained at the end of reaction.

Step 3: Separation of 3-octanoylthio-1-propyltriethoxysilane from reaction mixture

To separate organic phase comprising 3-octanoylthio-1-propyltriethoxysilane from the reaction mixture, the temperature of the reaction mixture was reduced to 30°C. To this reaction mixture, 400 mL of n-hexane was added followed by stirring. The organic phase was separated using separating funnel at room temperature. This process was repeated with 400 mL of n-hexane. Anhydrous sodium sulphate was then added to the organic layer to remove the water. The organic phase was filtered followed by evaporation of solvent (using rotavapour) to recover the organic phase. The recovered organic phase comprises 3-octanoylthio-propyltriethoxysilane. The purity of the recovered organic phase was checked using High-Performance Liquid Chromatography (HPLC).

Results: HPLC revealed that the resulting product purity was 97%. The remaining 3% contains unreacted raw materials. No by-products were detected.
Industrial Applicability

The disclosed process results in > 95% conversion of the reactants and > 99% selectivity towards the desired organosilane, 3-octanoylthio-1-propyltriethoxysilane. Thus, the disclosed process results in no or negligible production of the by-products, while providing a product having a purity >95%.

The process is cost effective and can be carried out using existing apparatus. The process allows recycling of the phase transfer catalyst recovered from the aqueous phase, to a new cycle of the process.

3-octanoylthio-1-propyltriethoxysilane obtained in the disclosed process finds application as silane coupling agent in rubber applications.
, Claims:1. A process for preparing 3-octanoylthio-1-propyltriethoxysilane, the process comprising the steps of:
- reacting an aqueous sodium hydrosulfide solution with octanoyl chloride in the presence of a phase transfer catalyst under alkaline pH to obtain an aqueous solution of sodium thiooctanoate; and
- reacting the obtained aqueous solution of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane in the presence of the phase transfer catalyst to form a reaction mixture containing 3-octanoylthio-1-propyltriethoxysilane.

2. The process as claimed in claim 1, wherein the reaction of the aqueous sodium hydrosulfide solution with octanoyl chloride is carried out under alkaline pH ranging between 10-12.

3. The process as claimed in claim 1 or 2, wherein the alkaline pH is achieved by adding an alkali selected from the group consisting of sodium hydroxide, sodium carbonate, and potassium tert-butoxide.

4. The process as claimed in claim 1, wherein sodium hydrosulfide is reacted with octanoyl chloride in a molar ratio in the range of 1:1 to 2.6:1.

5. The process as claimed in claim 1, wherein the reaction of the aqueous sodium hydrosulfide solution with octanoyl chloride is carried out at a temperature in the range of 0 to 30°C.

6. The process as claimed in claim 1, wherein the reaction of the aqueous solution of the hydrosulfide with octanoyl chloride is carried out for a time period of 30 minutes to 2 hours.

7. The process as claimed in claim 1, wherein 3-chloropropyl-1-triethoxysilane is added in an amount such that 3-chloropropyl-1-triethoxysilane and sodium hydrosulfide have a weight ratio in the range of 1.87:1 to 3.54:1.

8. The process as claimed in claim 1, wherein the reaction of the aqueous solution of sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out at a temperature in the range of 90 to 110°C.

9. The process as claimed in claim 1, wherein the reaction of the aqueous solution of the sodium thiooctanoate with 3-chloropropyl-1-triethoxysilane is carried out for a time-period of 2 to 5 hours.

10. The process as claimed in claim 1, wherein the phase transfer catalyst is selected from the group consisting of tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), and methyltrioctylammonium chloride (MTOCl).

11. The process as claimed in claim 1, further comprising separating an organic phase comprising 3-octanoylthio-1-propyltriethoxysilane from the reaction mixture.