FIELD OF INVENTION

The present disclosure relates to a process for preparing 4-hydroxy pentadecyl benzene sulfonic acid and its alkali metal salts in general. In particular, the present disclosure relates to a solvent free process for preparing 4-hydroxy pentadecyl benzene sulfonic acid and its alkali metal salts.

BACKGROUND

Surfactants have widespread use in different industries including pharmaceuticals, cosmetics, and toiletries among others. Most of the commonly used surfactants are primarily manufactured using petrochemical products and therefore their synthetic nature poses environmental concerns including reliance on petroleum resources and resistance to microbial degradation.

Renewable sources are increasingly being explored to produce surfactants as an alternative to using fossil fuels and to manufacture environment friendly surfactants. Such renewable sources include but are not limited to wood, proteins, cellulose, lignin, tannins, starch, vegetable oils, animal resources like chitin and chitosan. A promising surfactant that can be obtained from a renewal source is 4- hydroxy pentadecyl benzene sulfonic acid, which has excellent surfactant properties and is used in commercial detergent compositions. 4-hydroxy pentadecyl benzene sulfonic acid is typically obtained by the sulphonation of cardanol, which is obtained from sources such as Cashew nut shell liquid (CNSL).

In the sulphonation reaction, cardanol is reacted with a sulfonation reagent to obtain 4-hydroxy pentadecyl benzene sulfonic acid which is then converted into its salt by reacting with an alkali metal hydroxide. Typically, in methods of sulphonation known in art, cardanol is first dissolved in solvents such as methanol, ethanol, isopropyl alcohol, toluene, and methylene chloride, for instance, before the reaction with the sulfonation reagent is carried out. Since these processes use solvents, they are costly and cannot be considered as green processes. Known processes also have disadvantages such as long reaction time of 3 to 5 hours. In addition, in most of the known processes the yield of 4-hydroxy pentadecyl benzene sulfonic acid is around 80% to 85%.

SUMMARY

The present application relates to a process for preparing a salt of 4-hydroxy pentadecyl benzene sulfonic acid. The process comprises reacting 3-N- Pentadecylphenol with sulphuric acid in a molar ratio in a range of 1:1 to 1:1.9 at a temperature in a range of 100°C to 150°C to obtain 4-hydroxy pentadecyl benzene sulfonic acid; and neutralizing the 4-hydroxy pentadecyl benzene sulfonic acid with an alkali to obtain the salt of 4-hydroxy pentadecyl benzene sulfonic acid.

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.

In order that this disclosure 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 disclosure.

The present disclosure relates to a process for preparing a salt of 4-hydroxy pentadecyl benzene sulfonic acid. The process comprises reacting 3-N- Pentadecylphenol with sulphuric acid in a molar ratio in a range of 1:1 to 1:1.9 at a temperature in a range of 100°C to 150°C to obtain 4-hydroxy pentadecyl benzene sulfonic acid; and neutralizing the 4-hydroxy pentadecyl benzene sulfonic acid with an alkali to obtain the salt of 4-hydroxy pentadecyl benzene sulfonic acid.

The present process uses 3-N-Pentadecylphenol, also known as hydrogenated cardanol having the formula:

Formula I

3-N-Pentadecylphenol may be obtained from any methods known in the art. Suitable methods for hydrogenation of cardanol are described in V. Madhusudhan, M. A. Sivasamban, R. Vaidyeswaran, and M. Bhagawantha Rao. Kinetics of hydrogenation of cardanol Industrial & Engineering Chemistry Process Design and Development 1981 20 (4), 625-629; Sylvain Caillol. Cardanol: A promising building block for biobased polymers and additives. Current opinion in green and sustainable chemistry, Elsevier, 2018, 14, pp.26-32. ffl0.1016/j.cogsc.2018.05.002.hal-01803769-, and US2284369A, herein incorporated by reference.

The process comprises reacting 3-N-Pentadecylphenol with sulphuric acid in a molar ratio in the range of 1:1 to 1:1.9. In an embodiment, 3-N- Pentadecylphenol is reacted with sulphuric acid in a molar ratio in the range of 1 : 1.4 to 1:1.9. In another embodiment, 3-N-Pentadecylphenol is reacted with sulphuric acid in a molar ratio in the range of 1 : 1.5 to 1:1.7.

The 3-N-Pentadecylphenol is reacted with sulphuric acid at a temperature in the range of 100°C to 150°C. In accordance with an embodiment, 3-N- Pentadecylphenol is reacted with sulphuric acid at a temperature in the range of 120°C to 140°C. In a specific embodiment, 3-N-Pentadecylphenol is reacted with sulphuric acid at a temperature of 120°C to 130°C.

In an alternative embodiment, the process comprises heating 3-N- Pentadecylphenol to a temperature in the range of 100°C to 150°C. The heated 3- N-Pentadecylphenol is then reacted with sulphuric acid at a molar ratio in the range of 1:1 to 1:1.9. In an embodiment, 3-N-Pentadecylphenol is heated at a temperature in the range of 120°C to 140°C and then reacted with sulphuric acid.

In accordance with an embodiment, the sulphuric acid has a concentration in the range of 95% to 99%. In accordance with a specific embodiment, the sulphuric acid has a concentration of 98%.

In accordance with an embodiment, the process comprises reacting 3-N- pentadecylphenol with sulphuric acid for a time period of 15 to 90 minutes. In some embodiments, 3-N-pentadecylphenol is reacted with sulphuric acid for a time period of 30 to 60 minutes. In a specific embodiment, 3-N-pentadecylphenol is reacted with sulphuric acid for 45 minutes.

The step of reacting 3-N-pentadecylphenol with sulphuric acid is carried out without the addition of an external solvent thereby making said process a solvent- free process. Examples of such external solvents include, but are not limited to methanol, ethanol, isopropyl alcohol, toluene, methylene chloride. Since the process does not require the use of any external solvent, itis both economical as well as environmentally friendly.

Once 3-N-pentadecylphenol is reacted with sulphuric acid in a molar ratio in the range of 1:1 to 1:1.9 at a temperature in the range of 100°C to 150°C, 4- hydroxy pentadecyl benzene sulfonic acid is obtained at the end of the reaction. 4- hydroxy pentadecyl benzene sulfonic acid, also known as cardanol sulphonic acid, is represented by Formula II below:

Formula II

The 4-hydroxy pentadecyl benzene sulfonic acid so obtained is neutralized with an alkali at a pH of 7 to 10 to obtain a salt of 4-hydroxy pentadecyl benzene sulfonic acid having the formula:

Formula III wherein X is selected from the group consisting of Na, K, Ei In accordance with an embodiment, the alkali is selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, lithium bicarbonate. In a specific embodiment, the alkali is sodium hydroxide.

In accordance with some embodiments, prior to neutralizing, an aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid is prepared. The aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid is prepared by mixing 10% to 30% by weight of the 4-hydroxy pentadecyl benzene sulfonic acid in water. In another embodiment, the aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid is prepared by mixing the 4-hydroxy pentadecyl benzene sulfonic acid in water until clear solution of 4-hydroxy pentadecyl benzene sulfonic acid in water is obtained. The obtained aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid is then neutralized with the alkali to a pH of 7 to 10.

In an alternative embodiment, the 4-hydroxy pentadecyl benzene sulfonic acid is cooled prior to preparing the aqueous solution. In some embodiments, the 4- hydroxy pentadecyl benzene sulfonic acid is cooled to a temperature in a range of 60°C to 90°C. In some embodiments, an aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid is prepared without the prior step of cooling the 4-hydroxy pentadecyl benzene sulfonic acid.

In accordance with an embodiment, after neutralizing, the salt of 4-hydroxy pentadecyl benzene sulfonic acid is dried to obtain a powder form of the salt of 4- hydroxy pentadecyl benzene sulfonic acid. In accordance with an embodiment, the salt of sulphonic acid is dried using techniques known in the art, including but not limited to spray drying, tray drying, flash drying, fluidized bed drying, spin flash drying, and rotary drum drying. The drying operation can be conducted either under vacuum or without vacuum. In accordance with an embodiment, the percentage yield of the salt of 4- hydroxy pentadecyl benzene sulfonic acid obtained by the process described herein is at least 95%. In accordance with a further embodiment, the percentage yield of the salt of 4-hydroxy pentadecyl benzene sulfonic acid is in a range of 95% to 97%.

EXAMPLES:

Example 1: Process for preparation of sodium salt of 4-hydroxy pentadecyl benzene sulfonic acid

100 gm of 3-N-Pentadecylphenol was heated in a reaction vessel at a temperature between 100°C to 140°C, with constant stirring. 48g of sulphuric acid was added to the heated 3-N-Pentadecylphenol. Mixing of sulphuric acid with 3-N- Pentadecylphenol was done with constant stirring to ensure homogeneous and thorough mixing, under controlled the temperature conditions at 120±10°C.

Once the sulphuric acid was thoroughly mixed with 3-N-Pentadecylphenol, the reaction mixture so obtained was incubated for 45 to 55 minutes under constant temperature with constant stirring. At the completion of the reaction, 4-hydroxy pentadecyl benzene sulfonic acid was obtained in the reaction mixture. The reaction mixture containing the 4-hydroxy pentadecyl benzene sulfonic acid was then cooled to a temperature of 70°C to 80°C. An aqueous solution of 4-hydroxy pentadecyl benzene sulfonic acid was then prepared by mixing the 4-hydroxy pentadecyl benzene sulfonic acid so obtained with water until a clear solution was obtained i.e. approximately 10% to 30% by weight of the 4-hydroxy pentadecyl benzene sulfonic acid was utilized for preparing said aqueous solution. This aqueous solution was then neutralized with an alkali to obtain a salt solution of 4-hydroxy pentadecyl benzene sulfonic acid. In this instance, sodium hydroxide (NaOH) was added and the salt solution of 4-hydroxy pentadecyl benzene sulfonic acid was maintained at a pH between 7 to 10 units. The salt solution of 4-hydroxy pentadecyl benzene sulfonic acid was then dried using techniques such as spray drying to obtain the salt of 4-hydroxy pentadecyl benzene sulfonic acid in a dried powder form. As the yield of 4-hydroxy pentadecyl benzene sulfonic acid is directly proportional to the yield of the salt form of the 4-hydroxy pentadecyl benzene sulfonic acid after neutralization, hereinafter, 4-hydroxy pentadecyl benzene sulfonic acid and the salt form of the 4-hydroxy pentadecyl benzene sulfonic acid are used interchangeably.

The active content is also measured as percentage Active Surfactant Matter. The active content was measured using IS 4955: 2001, Annex B method. To determine the active content, 1 g solution (500 ml) of surfactant is prepared in water. 25ml Methylene blue indicator solution, 15 ml chloroform and 10 ml of surfactant solution is taken in a measuring cylinder. Titration is done against Hyamine (0.004 M) with vigorous shaking in a biphasic titration to achieve same colour in both layers to calculate the active content.

Example 2: Effect of temperature on the process for preparation of 4-hydroxy pentadecyl benzene sulfonic acid

The process as described in Example 1 was repeated, however, this time the temperature at which the reaction mixture of 3-N-Pentadecylphenol and sulphuric acid was incubated was varied. The percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid obtained was then compared as shown in Table 1 below. The percentage Active Surfactant Matter obtained was also compared as shown in Table 1 below. Table 1: Effect of temperature on percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid Results and Observations: As seen from the results of Table 1, a higher percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid is obtained when the reaction mixture of 3-N-Pentadecylphenol and sulphuric acid is incubated at temperatures above 100°C. From Table 1, it is clear that at a temperature of 110°C onwards the percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid is above 95% with a maximum of 96.2% yield at 140°C. It is also observed that a higher percentage Active Surfactant Matter is achieved when the reaction mixture of of 3-N-Pentadecylphenol and sulphuric acid is incubated at temperatures above 100°C. Therefore, the temperature range of 100°C to 140°C provides a very high yield percentage of 95% and above of 4-hydroxy pentadecyl benzene sulfonic acid. Example 3: Effect of the molar ratio of 3-N-Pentadecylphenol and sulphuric acid on the process for preparation of 4-hydroxy pentadecyl benzene sulfonic acid

The process as described in Example 1 was repeated, however, this time the molar ratio of 3-N-Pentadecylphenol and sulphuric acid in the reaction mixture was varied and the reaction mixtures were incubated for 45 to 55 minutes at 120°C. The percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid obtained from these reaction mixtures were then compared as shown in Table 2 below. The percentage Active Surfactant Matter obtained from these reaction mixtures were also compared as shown in Table 2 below.

Table 2: Effect of the molar ratio of 3-N-Pentadecylphenol and sulphuric acid on the percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid.

Results and Observations: As seen from the results of Table 2, a higher percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid is obtained when molar ratio of 3-N-Pentadecylphenol and sulphuric acid in the reaction mixture is between 1.5 to 1.7. From Table 2, it is clear that the molar ratio of 1.5 yields a high percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid at 95%. This percentage yield increases when the molar ratio is 1.7. However, at molar ratios below 1.5, the percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid is significantly reduced. It is also observed that the percentage active surfactant matter is observed highest when the molar ratio of 3-N-Pentadecylphenol and sulphuric acid in the reaction mixture is 1:1.5.

Therefore, a very high yield percentage of 95% and above of 4-hydroxy pentadecyl benzene sulfonic acid is obtained when the molar ratio between 3-N- Pentadecylphenol and sulphuric acid is 1.5 and above.

Example 4: Effect of incubation time on the process for preparation of 4- hydroxy pentadecyl benzene sulfonic acid

The process as described in Example 1 was repeated, however, the time period at which -N-Pentadecylphenol and sulphuric acid were reacted was varied while keeping the temperature at a constant 120°C. The percentage yield of 4- hydroxy pentadecyl benzene sulfonic acid obtained was then compared as shown in Table 3 below.

Table 3: Effect of incubation time on percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid

Results and Observations: As seen from the results of Table 3, a higher percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid is obtained when the reaction mixture of 3-N-Pentadecylphenol and sulphuric acid is incubated for 30 minutes or longer. From Table 2, it is seen that at upon incubation for 30 minutes, a percentage yield of 4-hydroxy pentadecyl benzene sulfonic acid of 95% is obtained from the reaction mixture. At 45 minutes, the maximum yield is obtained at 96% and this does not increase if the reaction mixture is incubated for longer time periods.

Therefore, an incubation time period between 45- 55 minutes is sufficient to obtain a high yield percentage of 95% of 4-hydroxy pentadecyl benzene sulfonic acid.

Industrial Application

The present process is an efficient and environmentally friendly process for preparing a salt of 4-hydroxy pentadecyl benzene sulfonic acid. The process requires short reaction times and provides a high percentage yield of the salt of 4- hydroxy pentadecyl benzene sulfonic acid. In addition, the process eliminates the use of solvents making the process safe, non-hazardous, sustainable and effluent free. With excellent yield and high productivity the process utilizes less raw material per Kg of product, consumes less energy, and is solvent free, making the process greener, safer, less hazardous.