AU647593B2 - A process for producing a synthetic detergent soap base from N-acyl sarcosine - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Int. Class Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: *Actual Inventor(s) Joseph James Crudden C-HeM\CAL- Cj0(ZP, S EC Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA 09 S C S S S Invention Title: 00 0 A PROCE~SS FOR PRODUCING A SflNTI-TIC DETERGENT SOAP BASE FROM N-ACYL

*-'SARCOSINE

Our Ref :282185 POF Code: 90766/90766 following statement is a full description of this invention, including 0 0 he best method of perforrming it known to applicant 6006 A PROCESS FOR PRODUCING A SYNTHETIC DETERGENT SOAP BASE FROM N-ACYL SARCOSINE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process of making a synthetic detergent soap base from N-acyl sarcosine.

2. Description of the Prior Art The use of sarcosinate surfactants, and in particular, N-acyl sarcosinates in the manufacture of soap is well known. Typically, the sarcosinate is used in the form of its sodium, potassium or ammonium salt "solution. N-acyl sarcosinates are produced commercially by the Schotten-Baumann reaction of the sodium salt of i sarcosine with the appropriate fatty acid chloride under carefully controlled conditions: R-C-C1 HNCH 2 COONa NaOH--) R-C-NCH 2 COONa NaC1 H 2 0 11 I I I O CH 3 O CH 3 Si where R is typically a fatty acid of chain length C 10 to

C

18 commonly made from lauric, coconut, palmitic, myristic or oleic acid. After the reaction is complete, the crude sodium salt is acidified to liberate the free fatty sarcosinic acid which is separated from the aqueous by-products. It then is neutralized to a salt 6.

form. E ,rcosinates such as sodium lauroyl sarcosinate, sodium cocoyl sarcosinate and sodium myristoyl sarcosinate are commercially available under the trademark HAMPSOYL® from W. R. Grace Co.-Conn., as active solutions in water. To produce soap bars, much of the water is removed, which may require heating the mixture to temperatures in the vicinity of 150 0

C.

Such sarcosinates are used, for example, in the skin cleansing compositions disclosed in U.S. Patent No. 4,812,253. There it is disclosed that surfactants such as anionic acyl sarcosinates are present in the cleansing composition at a level of 20-70%, 20-50% in the case of soaps. In addition, sodium lauroyl sarcosinate is disclosed as being a preferred secondary surfactant together with sodium coco glyceryl sulfonate as a primary mild surfactant. The soap is disclosed as being made in situ from free fatty acids and a base selected from magnesium hydroxide, potassium hydroxide, sodium hydroxide and triethanolamine. Preferred fatty acids are mixtures of stearic and lauric acids having a ratio of from 2:1 to 1:1.

U.S. Patent No. 4,754,874 to Haney discloses a transparent, mild, low pH soap bar and package therefor. The soap formulation disclosed includes sodium stearate and sodium cocoyl sarcosine, but no method of formulation is taught.

U.S. Patent No. 4,954,282 to Rys et al. discloses skin cleaning compositions containing major amounts of acyl isethionates and at least one co-active surfactant, including sarcosinates.

SUMMARY OF THE INVENTION The problems of the prior art have been solved by the instant invention, which provides a process for the production of a synthetic soap base with an easily adjustable pH. Surprisingly, it has been found that N-acyl sarcosine can be used as a solvent for a fatty acid salt. Accordingly, the instant process involves neutralizing N-acyl sarcosine by dissolving a fatty acid salt in the heated acid until the desired pH is obtained. The desired pH can be retained while varying the ratio of the fatty acid salt to N-acyl sarcosine by adding acid or base.

In a second embodiment, the instant invention involves dissolving a fatty acid in the N-acyl sarcosine and neutralizing the acid mixture with caustic until the desired pH is obtained.

In each of the above embodiments, by using sarconsine acid rather than the salt, no excess water needs to be eliminated, and easy processability, easy control of pH, and decreased production costs are realized. The resulting product is non-irritating and non-drying, and exhibits apparent skin substantivity and pleasant skin feel.

DETAILED DESCRIPTION OF THE INVENTION Fatty acids and fatty acid salts having carbon chain lengths from about C 8 to about C 18 are functional in the instant invention. Preferred fatty acids are •stearic, myristic, palmitic and lauric acids, with stearic acid being especially preferred. Preferred fatty acid salts are salts of the aforementioned acids, *e with salts or stearic acid being especially preferred.

2 Suitable sali.ying ions including those selected from alkali metals and alkali earth metals, preferably sodium and potassium. For purposes of illustration, stearic acid and sodium stearate will be referred to except where specified otherwise, although it should be understood that other fatty acids and fatty acid salts are within the scope of the instant invention.

Suitable N-acyl sarcosines in the instant invention include lauroyl sarcosine, cocoyl sarcosine, myristoyl sarcosine, oleoyl sarcosine and stearoyl sarcosine, with lauroyl sarcosine being preferred.

In the first embodiment, the instant method ccfipr-:: s neutralizing the N-acyl sarcosine by dissolving the fatty acid salt in the sarcosine until the desired pH is reached. The preferred pH is from about 4.5 to about 9.5 with a pH between about 5 and about 7 being especially preferred. A pH below about is functional, but results in a bar that is very soft. A pH above about 9.5 deleteriously affects the foaming of the product. The fatty acid salt is easily dissolved in the sarcosine at an elevated temperature, such as a temperature of about 65 0 C to about 140 0

C,

preferably about 75°C to about 100 0 C. At temperatures below about 65 0 C, a solid tends to form. At =lj:L~zp:) f above about 100 0 C, decomposition of the fatty acid salt tends to occur, although the salt dissolves faster in the sarcosine. Thus, if temperatures higher than about 100 0 C are used, it is preferred that the temperature be quickly lowered upon 0 *dissolution of the salt. When the homogenous liquid is *allowed to cool to about room temperature, it solidifies to a hard soap-like material which functions adequately o: as a soap but is mild, non-drying and produces a pleasant skin feel. The material can be easily molded as it cools but also may be remelted. This surprising characteristic will allow production of soap bars on a commercial scale by the conventional press molding technique.

In the second embodiment, the instant method \vc emetp: dissolving the fatty acid in the N-acyl sarcosine that has been heated to a temperature of from about 50 0 C to about 140 0 C, preferably about 500 to about 70°C, most preferably about 55 0 C. At temperatures below

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about 50 0 C, the mixture tends to solidify. At temperatures greater than about 100 0 C, decomposition of the fatty acid tends to occur, although the acid dissolves faster in the sarcosine. Thus, if temperatures higher than about 100 0 C are used, it is preferred that the temperature be quickly lowered upon dissolution. The acid mixture is then neutralized with alkali, such as sodium hydroxide, potassium hydroxide, Ap$iirA?. isopropyl amine, monoethanol amine, etc., at a temperature sufficiently high to maintain fluidity of the neutralizing mix, until the desired pH is reached.

The preferred alkali is a 50% solution of sodium hydroxide. Preferred temperatures for the neutralization are from about 60 0 C to about 100 0

C,

preferably about 70 0 C. As with the first embodiment, the preferred pH is from about 4.5 to about 9.5, with a pH between about 5 and about 7 being especially preferred. A pH below about 4.5 is functional, but results in a bar that is very soft. A pH about about deleteriously affects the foaming ability of the S. product. When the homogenous liquid is allowed to cool, it solidifies to a hard soap-like material which functions adequately as a soap but is mile, non-drying *and produces a pleasant skin feel. The material can be 0: easily molded as it cools but also may be remelted, thereby also allowing production of soap bars on a commercial scale by the conventional press molding technique.

Other surfactants may be added to the formulations of either embodiment, such as isethionates, especially acyl isethionates including sodium cocoyl isethionate. The acyl isethionates may render the soap bar brittle. In such a case, the brittleness can be controlled by the addition of amines, such as isopropyl amine. In addition, other conventional soap additives, including but not limited to glycerols or EDTA solutions may be dissolved in the system without materially

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affecting its processability. It will be understood by those skilled in the art that other conventional additives, including perfumes, coloring agents, binders, skin feel and mildness aids, etc. may also be added.

In the embodiment involving fatty acid salts, the desired pH of the mixture can be retained while varying the ratio of the fatty acid salt to N-acyl sarcosine by 0

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*1 S S 0 00 adding acid or base. Suitable acids include sulfuric, citric, hydrochloric, lactic, lauric, etc. Suitable bases include sodium and potassium hydroxide, etc.

Those skilled in the art will recognize that the additions of an acid or base to the system results in an exothermic reaction, and will affect the temperature thereof accordingly.

The instant invention will be better understood by referring to the following specific but non-limiting example. It is understood that said invention is not limited by these procedures whicn are offered merely as illustrations; it is also understood that modifications can be made without departing from the spirit and scope of the invention.

EXAMPLE 1 grams of N-cocoyl sarcosine was heated in a beaker to a temperature between 80°C and 100 0 C on a stirrer hotplate. Sodium stearate powder (Witco Cl) was gradually added with constant stirring and allowed to dissolve. The pH of the system was periodically checked by dipping a spatula in the liquid and transferring a few drops of the liquid to a beaker of distilled water which contained a pH probe and was agitated by a magnetic stirrer. The pH of the aqueous system was monitored until a stable value was obtained. The initial pH value before addition of any stearate was approximately 2. With the addition of sodium stearate the pH gradually rose and, after the addition of approximately 48 grams, the desired pH of 6.5 was obtained. The resulting liquid was poured into a mold and allowed to set. When the temperature returned to ambient the mold was opened. The resulting product was a firm soap-like material which produced copious foam and a pleasant skin feel.

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0e EXAMPLE 2 grams of N-lauroyl sarcosine was heated as before and 20 grams of N-cocoyl isethionate was gradually added and allowed to dissolve. Approximately 48 grams of sodium stearate was added as before until a pH of about 6.5 was obtained. The clear liquid was formed into a bar by molding as in Example 1. The resulting material produced greater flash foam and was more brittle than the product of Example 1.

*EXAMPLE 3 20 grams of N-cocyl sarcosine was heated in a beaker to a temperature of about 55 0 C on a stirrer hotplate. 20 grams of stearic acid flakes was added and quickly dissolved, producing a clear homogenous liquid at 55 0 C. The temperature was raised to about 80 0 C, and about 6 grams of 50% aqueous sodium hydroxide was added 0 dropwise. The pH of the system was checked by dipping a few drops of the mix into deionized water, and was found to be approximately 6. The material solidified to a S* hard soaplike material on cooling and produced adequate foam with water.

EXAMPILEA

20 grams of N-lauroyl sarcosine was heated to about 55 0 C, and 20 grams of stearic acid was added and quickly dissolved. The temperature was raised to about 0 C and 20 grams of s-'dium cocoyl isethionate was dissolved and the system was neutralized with 5 grams of aqueous sodium hydroxide. The pH of the aqueous solution was approximately 7. The material solidified to a hard soaplike material on cooling and exhibited improved flash foam over the material of Example 3.

(Alternatively, the sodium hydroxide may be added before the addition of the isethionate).

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Claims (10)

1. A method of producing synthetic detergent soap base including neutralizing an N-acyl sarcosine selected from the group consisting of lauroyl sarcosine, cocoyl sarcosine, myristoyl sarcosine and oleoyl sarcosine with a fatty acid salt to a pH of from about 4.5 to about

2. The method of claim 1 wherein said N-acyl sarcosine is neutralized to a pH of from about 5 to about 7.

3. The method of claim 1 or claim 2 wherein said fatty acid salt is selected from the group consisting of salts of lauric, myristic, palmitic and stearic acid.

4. The method of any one of claims 1 to 3 wherein the fatty acid salt is sodium laurate. 5 5. The product produced by the method of any one of S 15 claims 1 to 4.

6. A method of producing synthetic detergent soap base including dissolving in an N-acyl sarcosine selected from the group consisting of lauroyl sarcosine, cocoyl sarcosine, myristoyl sarcosine and oleoyl sarcosine a fatty i. 20 acid at an elevated temperature sufficient to maintain fluidity, and neutralizing the resulting solution to a pH of from about 4.5 to about S7. The method of claim 6 wherein said acid mixture is neutralized to a pH of about 5 to about 7. 25 8. The method of claim 6 or claim 7 wherein said fatty acid is selected from the group consisting of lauric, myristic, palmitic and stearic acid.

9. The method of any one of claims 6 to 8 wherein said fatty acid is stearic acid.

10. The method of any one of claims 6 to 9 wherein said elevated temperature is from about 700C to about 1000C.

11. The method of any one of claims 6 to 10 wherein said temperature sufficient to maintain fluidity is about 80 0 C.

12. The product formed by the method of any one of claims 6 to 11.

13. A method according to any one of claims 1 to 5 or any one of claims 6 to 10 substantially as herein described with reference to any one of the Examples. rAI^ 14. A product according to claim 5 or claim 12 -9- substantially as herein described with reference to any one of the Examples. DATED: 11th March, 1992 PHILLIPS ORMONDE FITZPATRICK Attorneys for: "AMPe-\IR C-HtA(C-Au- COP. a a.. Ge 6 6O. J a. 00 6 Be. 6 0e OS 0 0; aBa p a. 6O *0 '*00 a. 0O S ABSTRACT A method of producing a synthetic detergent soap base, comprising neutralizing N-acyl sarcosine at an elevated temperature with a fatty acid salt to the desired pH, and allowing the mixture to cool. In a second embodiment, the method comprises dissolving in an N-acyl sarcosine at an elevated temperature a fatty acid, and neutralizing the mixture with base at a temperature sufficient to maintain fluidity to a pH of from about 4.5 to about 9.5. The resulting product is non-irritating and non-drying, and exhibits apparent skin substantivity and pleasant skin feel. *r b~ S t ID96/1-10/37-46 S a S