CLIAMS:We claim

1. A solvent-free, one pot process for preparing high active, substantially salt-free guanidinium salts of N-acyl sarcosinates of Formula I,

Formula I
wherein, R is selected from C7 to C17 alkyl group;
said process comprising steps of
i) reacting fatty acid chloride RCOCl with salt of sarcosine in aqueous media, under typical Schotten-Baumann conditions, wherein total water used in the reaction is not more than 2.2 times of the fatty acid chloride (weight basis), to get 34% - 35% active alkali metal salt of N-acyl sarcosinates of Formula II;

Formula II
wherein X is selected from Na+ or K+;
ii) acidifying the product of step i) at 75-850C followed by phase separation, to give compound of Formula III

Formula III

wherein no additional water is added;

iii) neutralizing the compound of Formula III with guanidine carbonate at temperature of 30- 500C;
wherein the water used during the entire process is not more than 2.8 times of the product, Formula I (active basis) and the content of inorganic salt is not more than 0.2%.

2. The process as claimed in claim 1 wherein free fatty acid is not more than 1%.

3. The process as claimed in claim 1 wherein the viscosity is less than 500 cps at 250C.

4. The process as claimed in Claim 1 wherein the acidification is carried out with strong inorganic acids such as sulfuric acid or hydrochloric acid.

5. The process as claimed in claim 1 wherein the activity of guanidinium salts of N-acyl sarcosinates is 40-41%.

6. High active, aqueous composition of guanidinium salt of N-acyl sarcosinates prepared by the process as claimed in claim 1, containing
a. 40-41% guanidinium salt of N-acyl sarcosinate;
b. free fatty acid not more than 1%;
c. total inorganic salts not more than 0.2%;
d. free sarcosine less than 0.1%;
e. balance water.
,TagSPECI:FIELD OF INVENTION

The present invention relates to a sustainable process for preparing guanidinium salts of N-acyl sarcosinates which find application in personal care products.

More particularly, the present invention relates to a process for the preparation of guanidinium salt of N-acyl sarcosinates with high active content and low salt content.

BACKGROUND OF INVENTION
N-acyl sarcosinates are mild anionic surfactants derived from amino acid sarcosine and fatty acid. They have been used for many years and are recognized as safe and effective surfactants. Due to their strong and gentle cleaning action, combined with their ability to produce stable lather even in the presence of sebum and sodium chloride, the sarcosinates have been used in the manufacture of soap and for various personal care formulations such as shampoo, shower gels, skin cleansers, bath additives. They also find application in corrosion inhibition, industrial emulsification and detergents (Surfactant Science series, volume 100, 2001).

Typically, the sarcosinate is used in the form of its sodium, potassium or ammonium salt solution. Sodium N-acyl sarcosinates are commercially available as 30% aqueous solutions. (Hamposyl from Dow Chemicals, Perlastan® from Struktol, Beautymild SC/SL from Univar, Crodasinic LS30 from Croda).

US patent 5386043 highlights the difficulties in preparing high active acyl sarcosinates due to the problem of gel phase leading to high viscosity. It states that above 30% concentrations, at any pH, the solutions become highly viscous to handle and that is the reason why acyl sarcosinates are available commercially as 30% solutions. The patent provides a process of producing concentrated sarcosinate solutions by doing non-aqueous neutralization of N-acyl sarcosines using anhydrous hydroxides or hydroxides with low water content. The acyl sarcosine and hydroxide are both reacted under high shear, in solid form at high temperature followed by rapid cooling to solidify the product. The process is industrially not viable as the neutralization is carried out between the solid reactants at high temperature and when alkali is added to the solid N-acyl sarcosine an increase in the temperature of the order of 50-600C is observed due to exothermicity of the reaction.

Guanidine soap solutions have surface tension properties comparable to those of alkali metal soaps. The excellent ability of guanidine soaps to disperse soil and superior emulsifying power is reported and established in prior art (Ind. Eng. Chem., 40 (2), 335–337, 1948).

Guanidinium salts of N-acyl amino acids are disclosed for the first time in US patent 2778773 (1953). This patent discloses that guanidinium salts of N-acyl amino acids possess various beneficial properties and find utility in many fields of application. They may be employed in admixture with a carrier or vehicle of any suitable form, such as solid, liquid or semi-solid carrier. These compounds exhibit a high degree of stability in solution even at moderately elevated temperature in comparison to the corresponding ammonium derivatives. These compounds possess marked anti-microbial property and exhibit a significant inhibiting effect on the production of acid from fermentable carbohydrates by the micro-organisms found in saliva. Further, these guanidinium salts of N-acyl amino acid exhibit the property of getting adsorbed and released by proteinaceous material and thus exert a long term anti-bacterial activity in such applications where it comes in contact with suitable proteinaceous material.

In addition to their application as anti-microbial agents, the patent US2778773 reports that guanidine addition compounds also possess significant detersive, foaming, softening and other surface-active properties in solution and therefore find application in personal care products such as in toothpastes, dental creams, mouthwashes, soaps, shaving creams, skin creams or lotions and in home care products such as detergents.

The guanidine salts of N-acyl amino acid are compatible with other anionic and non-ionic surfactants and can be mixed with them in any suitable manner.

US patent 2778773 discusses composition and preparation of the guanidinium salts whereby it discloses a method of preparation by reacting N-aliphatic acyl amino acid with a basic guanidine compound at reflux temperature and further separating the compound by precipitation, solvent extraction and final purification by recrystallization from an organic solvent. The patent emphasizes the use of organic solvent to get a product of high yield and purity; however there is no data on the yield and purity. Further, the major drawback of the process is the use of large quantities of organic solvent which adds a heavy load to the effluent.

With the increase in environmental awareness and sustainability, processes which avoid organic solvents and employ aqueous processes are desirable. In case of aqueous processes too, the use of water should be minimized so that the load of effluent is minimum.

The inventors of the present invention have developed an efficient, environment-friendly, aqueous process for preparation of high active guanidinium salt of N-acyl sarcosinates with a low effluent load.

OBJECT OF INVENTION

i) It is an objective of the present invention to provide a process for the manufacture of high active guanidinium salt of N-acyl sarcosinates.

ii) It is an objective of the present invention to provide a green, cost-effective and industrial process for the manufacture of high active guanidinium salt of N-acyl sarcosinate based surfactants.

iii) It is yet another object of the present invention to provide a process for the manufacture of the guanidinium salt of N- acyl sarcosinates with low effluent load.

iv) It is yet another object of the present invention to provide a process for the manufacture of the guanidinium salt of N- acyl sarcosinates with low content of inorganic salts.

v) It is yet another object of the present invention to develop a process for the preparation of guanidinium salt of N-acyl sarcosinates which is free of guanidine salt (guanidine hydrochloride).

SUMMARY OF INVENTION
The present invention relates to a solvent-free, one pot process for preparing high active, substantially salt-free guanidinium salt of N-acyl sarcosinates of Formula I,

Formula I
wherein, R is selected from C7 to C17 alkyl group;
said process comprising steps of
i) reacting fatty acid chloride RCOCl with salt of sarcosine in aqueous media, under typical Schotten-Baumann conditions, wherein total water used in the reaction is not more than 2.2 times of the fatty acid chloride (weight basis), to get 34% - 35% active alkali metal salts of N-acyl sarcosinate of Formula II;

Formula II
wherein X is selected from Na+ or K+;
ii) acidifying the product of step i) at 75-850C followed by phase separation, to give compound of Formula III

Formula III
wherein no additional water is added;

iii) neutralizing the compound of Formula III with guanidine carbonate at temperature of 30- 500C;
wherein the water used during the entire process is not more than 2.8 times of the product, Formula I (active basis) and the content of inorganic salt is not more than 0.2%.

The process of the present invention is solvent free. The term ‘solvent-free’ herein means ‘free of organic solvent, protic or aprotic’.

The guanidinium salts of N-acyl sarcosinates (Formula I) of the present invention find application in personal and home care products.

DETAILED DESCRIPTION OF INVENTION

The present invention relates to a sustainable, commercially viable process for the preparation of guanidinium salts of N-acyl sarcosinates of Formula I,

Formula I
In an aspect of the present invention there is provided a solvent-free, one pot process for preparing high active, substantially salt-free guanidinium salts of N-acyl sarcosinates of Formula I,

Formula I
wherein, R is selected from C7 to C17 alkyl group;
said process comprising steps of
i) reacting fatty acid chloride RCOCl with salt of sarcosine in aqueous media, under typical Schotten-Baumann conditions, wherein total water used in the reaction is not more than 2.2 times of the fatty acid chloride (weight basis), to get 34%- 35% active alkali metal salts of N-acyl sarcosinate of Formula II;

Formula II
wherein X is selected from Na+ or K+;
ii) acidifying the product of step i) at 75-850C followed by phase separation, to give compound of Formula III

Formula III
wherein no additional water is added;

iii) neutralizing the compound of Formula III with guanidine carbonate at temperature of 30- 500C;
wherein the water used during the entire process is not more than 2.8 times of the product, Formula I (active basis) and the content of inorganic salt is not more than 0.2%.

The free fatty acid content of the composition containing guanidinium salts of N-acyl sarcosinates is not more than 1% and the viscosity is less than 500 cps at 250C.

Guanidinium salt of N-acyl sarcosinates of Formula-I can also be prepared directly by reacting acid chloride with sarcosine in presence of guanidine carbonate. However, such a process leads to formation of guanidine salt (guanidine hydrochloride) as side product. Guanidine hydrochloride is very irritating to skin and eyes and also causes severe dryness of skin and eyes. Hence, its presence in the product is not desirable.

The inventors of the present invention have developed a simple, aqueous process for preparing guanidinium salts of N-acyl sarcosinates. By means of the method according to the invention, high active solutions of guanidinium salts of N-acyl sarcosinates with a low content of byproducts (such as fatty acid salt, chlorides and sulfates) can be prepared, which have low viscosity and are easy to handle and cost-effective. Further, these compositions are free of guanidine salt (guanidine hydrochloride).

The process of the present invention for preparation of guanidinium salts of N-acyl sarcosinates of Formula I is shown in the Scheme I

The fatty acid chlorides used in step one are prepared by the eco-friendly catalytic process reported by Koshti et al. in their recently filed patent application (WO2014030038).
The process
The process of manufacture of guanidinium salt of N-acyl sarcosinates of this patent application involves
i) Reacting fatty acid chloride RCOCl with an aqueous solution of sarcosine in the presence of base and stirring at a temperature of 10-400C, maintaining pH of 9.5-11.5 to get alkali metal salts of N-acyl sarcosinates of Formula-II.

The pH and temperature of the reaction plays an important role in controlling the free fatty acid content of the final product (Formula I). At reaction conditions wherein the pH is less than 9.5 or more than 11.5 and for temperatures above 400C, the rate of hydrolysis is high leading to a higher free fatty acid content which further leads to an increase in the viscosity of the product. Therefore, restricting the free fatty acid content to less than 1% leads to low viscous product (Formula I).

The total water used in the reaction is not more than 2.2 times of the fatty acid chloride (weight basis) thereby leading to low effluent load.

ii) The aqueous solution of compounds of Formula-II, obtained in step i) is acidified and heated at 75-850C for phase separation and no additional water is added during this step. The upper phase is fatty N-acyl sarcosine (Formula-III).

Acidification and heating at 75-85 0C results in phase separation- an upper organic phase which is molten compound of Formula III and lower aqueous phase. The aqueous phase contains free sarcosine and inorganic salt such as sodium chloride.

iii) The organic layer containing N-acyl sarcosine (Formula-III) is diluted with water and then neutralized with guanidine carbonate at a temperature of 30- 500C to give aqueous composition of guanidinium salt of N-acyl sarcosinates of Formula-I.

According to an embodiment, the pH of step i) is maintained by using a base selected from hydroxides or carbonates of potassium or sodium, preferably sodium hydroxide.
According to an embodiment of the present invention, the acid used in step ii) is sulfuric acid or hydrochloric acid.

The amount of acid is preferably 0.5-0.6 mole per mole of alkali metal salts of acyl amino acid of Formula II (active basis).

According to an embodiment of the present invention, the amount of guanidine carbonate used in step iii) is 0.5 mole per mole of alkali metal salts of acyl amino acid of Formula II (active basis).

According to an embodiment of the present invention, guanidinium salts of N-acyl sarcosinates (Formula-I) have activity of 40%-41%.

In an embodiment, water used during the entire process is not more than 2.8 times of the product, Formula I (active basis).

In an embodiment, effluent generated during the entire process is not more than 0.8 times of the product, Formula I (weight basis).

The inventors attempted synthesis of high active guanidinium salts of glycinates, however it was observed that in case of glycinates, up to 27% active (31% solid content) can be synthesized (Example 4 ) and the activity cannot be increased beyond it due to the gel formation.

Advantages of the invention
1. The process of preparation of guanidinium salts of N-acyl sarcosinates is a green process since water used in the process is minimum and therefore the load of effluent generated is insignificant.

2. The present invention provides a simple process for preparation of aqueous solution of guanidinium salts of N-acyl sarcosinates which can be directly incorporated into the final formulations thereby obviating the need of dissolution.

3. The guanidinium salts of N-acyl sarcosinates prepared by the process of the present invention are high active and have low salt content (sodium chloride & sodium sulfate).

4. The guanidinium salts of N-acyl sarcosinates prepared by the process of the present invention are free of guanidine salt (guanidine hydrochloride).

5. The process of the present invention gives good conversion (free fatty acid content not more than 1%) of guanidinium salts of N-acyl sarcosinates.

6. The aqueous solution of guanidinium salts of N-acyl amino acid are stable and can be stored at room temperature for prolonged period of 24 months without any significant degradation.

EXAMPLES
The details of the invention provided in the following examples are given by the way of illustration only and should not be construed to limit the scope of the present invention.

Example 1
Synthesis of high active sodium N-lauroyl sarcosinate
To a stirred solution of sodium sarcosinate (660 g, 2.379 mol, 40% solution) in water (614 g) at 20-250C was added lauroyl chloride (500 g, 2.265 mol, 99% pure) and sodium hydroxide (189 g, 2.265 mol, 48 % aqueous solution) simultaneously while maintaining the pH between 10.4 to 10.8 over 2 hours. The reaction was continued for additional 4 hours maintaining the pH range of 10.4 -10.8 and temperature 20-250C to get aqueous solution of sodium N-lauroyl sarcosinate (1963 g).
The analysis of sodium N-lauroyl sarcosinate obtained was as follows
Analysis
Test Results
pH 10.52
Total Solids, % by mass 43.09
NaCl, % by mass 6.8
Free Fatty acid, % by mass 0.57
Free Sarcosine, % by mass 0.77
Sodium N-lauroyl sarcosinate, % by mass 34.7
Viscosity (cps) 2600

Example-2
Synthesis of N-Lauroyl Sarcosine
Sodium N-lauroyl sarcosinate of example 1 (1963 g of 43 % aqueous solution, 34.7 % active with 6.8 % sodium chloride) was acidified with sulfuric acid (128 g, 1.28 mol). The reaction mass was heated at 75-850C followed by phase separation. The aqueous layer (1394 g) was removed. The organic layer (683 g) contains N-lauroyl sarcosine.

Analysis
Test Results
Total Solids, % w/w 88.4
NaCl, % w/w 0.14
Acid value 185.4
Water , % w/w 11.6

Example-3
Synthesis of high active guanidinium N-lauroyl sarcosinate
N-lauroyl sarcosine of Example-2 (683 g) was diluted with water (898 g) and neutralized with guanidine carbonate (190 g) at 30-500C to get 40.2% active guanidinium N-lauroyl sarcosinate (1771 g).
Analysis
Test Results
Appearance Clear, pale yellow liquid
Colour on APHA 60-65
Total Solids, % by mass 41.25
Active matter, % by mass 40.2
Free fatty acid content, % by mass 0.65
NaCl, % by mass 0.1
Na2SO4 , % by mass 0.1
pH 8.4
Viscosity (cps) 160

Example-4
Comparative Example
Synthesis of guanidinium N-cocoyl glycinate
Sodium N-cocoyl glycinate (521 g of 30 % aqueous solution, 23 % active with 5 % sodium chloride, 0.442 mol) was acidified with sulfuric acid (23 g, 0.23 mol). The reaction mass was heated at 90-950C followed by phase separation. The aqueous layer was removed (292 g). The organic layer (220 g) contains N-cocoyl glycine which was diluted with water (285 g) and neutralized with guanidine carbonate (39 g) at 30-500C to get 27.61 % active guanidinium N-cocoyl glycinate (544 g).
Analysis
Test Results
Appearance Clear, pale yellow liquid
Colour on APHA 70-85
Total Solids, % by mass 30.47
Active matter, % by mass 27.61
Free fatty acid content, % by mass 1.68
NaCl, % by mass 1.13
Na2SO4 , % by mass 1.4
pH 8.74
Viscosity (cps) 460

We claim

1. A solvent-free, one pot process for preparing high active, substantially salt-free guanidinium salts of N-acyl sarcosinates of Formula I,

Formula I
wherein, R is selected from C7 to C17 alkyl group;
said process comprising steps of
i) reacting fatty acid chloride RCOCl with salt of sarcosine in aqueous media, under typical Schotten-Baumann conditions, wherein total water used in the reaction is not more than 2.2 times of the fatty acid chloride (weight basis), to get 34% - 35% active alkali metal salt of N-acyl sarcosinates of Formula II;

Formula II
wherein X is selected from Na+ or K+;
ii) acidifying the product of step i) at 75-850C followed by phase separation, to give compound of Formula III

Formula III

wherein no additional water is added;

iii) neutralizing the compound of Formula III with guanidine carbonate at temperature of 30- 500C;
wherein the water used during the entire process is not more than 2.8 times of the product, Formula I (active basis) and the content of inorganic salt is not more than 0.2%.

2. The process as claimed in claim 1 wherein free fatty acid is not more than 1%.

3. The process as claimed in claim 1 wherein the viscosity is less than 500 cps at 250C.

4. The process as claimed in Claim 1 wherein the acidification is carried out with strong inorganic acids such as sulfuric acid or hydrochloric acid.

5. The process as claimed in claim 1 wherein the activity of guanidinium salts of N-acyl sarcosinates is 40-41%.

6. High active, aqueous composition of guanidinium salt of N-acyl sarcosinates prepared by the process as claimed in claim 1, containing
a. 40-41% guanidinium salt of N-acyl sarcosinate;
b. free fatty acid not more than 1%;
c. total inorganic salts not more than 0.2%;
d. free sarcosine less than 0.1%;
e. balance water.