WO1999010457A1

WO1999010457A1 - Method for stabilising aqueous ester sulphate tensides

Info

Publication number: WO1999010457A1
Application number: PCT/EP1998/005199
Authority: WO
Inventors: Hermann Hensen; Jörg KAHRE; Hans-Christian Raths; Werner Seipel
Original assignee: Cognis Deutschland Gmbh
Priority date: 1997-08-25
Filing date: 1998-08-17
Publication date: 1999-03-04

Abstract

The invention relates to a method for stabilising aqueous ester sulphate tensides by adjusting the preparations to a pH of 5 to 8 and adding 0.1 to 1 wt. % organic carboxylic acids. In this way, said preparations are protected against hydrolysis for months.

Description

Process for the stabilization of aqueous ester sulfate surfactants

Field of the Invention

The invention is in the field of anionic surfactants and relates to a process for the permanent stabilization of aqueous preparations of surfactants with an ester sulfate structure by adding selected organic buffers.

State of the art

Surfactants that contain both a sulfate and an ester group in the molecule, such as hydroxycarboxylic acid ester sulfates, fatty acid polyglycol ester sulfates or monoglyceride (ether) sulfates, can only be used in the neutral pH range, since the sulfate group hydrolyzes in the acidic range and the ester group in the alkaline environment. The stabilization of the aqueous preparations by using conventional buffer systems, such as of the phosphate type, shows a surprisingly low effectiveness in these structures. Accordingly, the object of the present invention was to provide a process by means of which aqueous ester sulfate surfactants can be protected from undesired hydrolysis over a period of time which is as long as possible and over a wide pH range.

Description of the invention

The invention relates to a process for stabilizing aqueous ester sulfate surfactants, which is characterized in that the preparations are adjusted to a pH in the range from 5 to 8 and 0.1 to 1% by weight of organic carboxylic acids are added.

Surprisingly, it has been found that organic carboxylic acids prove to be far more effective than the known phosphate buffers in stabilizing aqueous preparations of surfactants with ester and sulfate groups. Within a pH range of 5 to 8, stabilization is achieved at use concentrations of typically 0.5% by weight, at which the WAS content (content of Active detergent) does not fall below 90% within 1 month and does not fall below 85% of the initial value within 3 months.

Hydroxycarboxylic acid ester sulfates

In a first embodiment of the invention, the method can be applied to the stabilization of hydroxycarboxylic acid ester sulfates. These are known anionic surfactants which are obtained, for example, by reacting fruit acid esters with gaseous sulfur trioxide or chlorosulfonic acid and then neutralizing them. Typical examples of suitable hydroxycarboxylic acid ester sulfates are selected from the group formed by the sulfation products of the esters of lactic acid, glycolic acid, tartaric acid, malic acid and / or citric acid with linear or branched, saturated or unsaturated primary alcohols with 6 to 32 carbon atoms in the form of their alkali, alkaline earth, ammonium, alkylammonium, alkanolammonium or glucammonium salts. The sulfation products of esters of lactic acid are preferably stabilized with fatty alcohols having 12 to 18 carbon atoms in the form of their sodium or ammonium salts.

Fatty acid polyglycol ester sulfates

In a second embodiment, the method according to the invention can be applied to anionic surfactants of the fatty acid polyglycol ester sulfate type. Fatty acid polyglycol ester sulfates follow the formula (I),

in the R ¹ CO for a linear or branched, saturated or unsaturated acyl radical having 6 to 22 carbon atoms, x for numbers from 1 to 3 on average and AO for a CH2CH2O-, CH CH (CH ₃ ) 0- and / or CH (CH ₃ ) CH ₂ 0 radical and X represents an alkali and / or alkaline earth metal, ammonium, alkylammonium, alkanolammonium or glucammonium are prepared by sulfating the corresponding fatty acid polyglycol esters. These in turn can be obtained using the relevant preparative processes in organic chemistry. For this purpose, ethylene oxide, propylene oxide or a mixture thereof - in random or block distribution - is added to the corresponding fatty acids, this reaction being acid-catalyzed, but preferably in the presence of bases, such as, for example, sodium methylate, tert. Amines or calcined hydrotalcite takes place. If a degree of alkoxylation of 1 is desired, the intermediates can also be prepared by esterifying the fatty acids with an appropriate alkylene glycol. The sulfation of the fatty acid polyglycol esters can be carried out in in a manner known per se with chlorosulfonic acid or preferably gaseous sulfur trioxide, the molar ratio between fatty acid polyglycol ester and sulfating agent being in the range from 1: 0.95 to 1: 1, 2, preferably 1: 1 to 1: 1, 1 and Reaction temperature can be 30 to 80 and preferably 50 to 60 ° C. It is also possible to undersulfate the fatty acid polyglycol esters, ie to use significantly fewer sulfating agents than would be stoichiometrically required for complete conversion. For example, if one chooses molar amounts of fatty acid polyglycol ester to sulfating agent from 1: 0.5 to 1: 0.95, mixtures of fatty acid polyglycol ester sulfates and fatty acid polyglycol esters are obtained, which are also advantageous for a whole range of applications. In order to avoid hydrolysis, it is very important to carry out the neutralization at a pH in the range from 5 to 9, preferably 7 to 8. Typical examples of suitable starting materials are the addition products of 1 to 3 moles of ethylene oxide and / or propylene oxide, but preferably the adducts with 1 mole of ethylene oxide or 1 mole of propylene oxide with caproic acid, caprylic acid, 2-ethylhexanoic acid, capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, Palmoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselinic acid, linoleic acid, linolenic acid, elaeostearic acid, arachic acid, gadoleic acid, behenic acid and erucic acid and their technical mixtures, which are then sulfated and neutralized as described above. Fatty acid polyglycol ester sulfates of the formula (I) are preferably used in which R ¹ CO stands for an acyl radical having 12 to 18 carbon atoms, x for an average of 1 or 2, AO for a CH∑CH∑O group and X for sodium or ammonium, such as for example lauric acid + 1 EO sulfate sodium salt, lauric acid + 1 EO sulfate ammonium salt, coconut fatty acid + 1 EO sulfate sodium salt, coconut fatty acid + 1 EO sulfate ammonium salt, tallow fatty acid + 1 EO sulfate sodium salt, Tallow fatty acid + 1 EO sulfate ammonium salt and their mixtures.

Monoq lyceride (ether) sulfate

Finally, monoglyceride sulfates and monoglyceride ether sulfates are also suitable as ester sulfate surfactants which can be stabilized against hydrolysis in the sense of the invention. These are known anionic surfactants with an ester structure, which can be obtained by the relevant methods of preparative organic chemistry. The usual starting point for their preparation is triglycerides, which, if appropriate, are transesterified to the monoglycerides after ethoxylation and subsequently sulfated and neutralized. It is also possible to react the partial glycerides with suitable sulfating agents, preferably gaseous sulfur trioxide or chlorosulfonic acid [cf. EP-B1 0561825, EP-B1 0561999 (Henkel)]. If desired, the neutralized substances can be subjected to ultrafiltration in order to reduce the electrolyte content to a desired level [DE-A1 4204700 (Henkel)]. Overviews of the chemistry of the monoglyceride sulfates are, for example, by AKBiswas et al. in J.Am.Oil.Chem.Soc. 37, 171 (1960) and FUAhmed J.Am.Oil. Chem.Soc. 67, 8 (1990). The monoglyceride (ether) sulfates to be used in accordance with the invention follow the formula (II)

in which R ² CO stands for a linear or branched acyl radical with 6 to 22 carbon atoms, x, y and z in total for 0 or for numbers from 1 to 30, preferably 2 to 10, and X stands for an alkali or alkaline earth metal. Typical examples of monoglyceride (ether) sulfates which are suitable for the purposes of the invention are the reaction products of lauric acid monoglyceride, coconut fatty acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, oleic acid monoglyceride and tallow acid monoglyceride and their ethylene oxide adducts or their form of sulfuric acid with sulfuric acid trioxide. Monoglyceride sulfates of the formula (II) are preferably used in which R ¹ CO is a linear acyl radical having 12 to 18 carbon atoms, x, y and z are 0 and X is sodium or ammonium.

Organic carboxylic acids

Organic carboxylic acids, which have proven particularly useful as stabilizers, have at least one hydroxyl group and / or an aromatic ring as a common structural feature. Typical examples are lactic acid, glycolic acid, malic acid, tartaric acid, citric acid, benzoic acid and salicylic acid, which can preferably be used in amounts of 0.2 to 0.7% by weight, based on the aqueous preparations of the ester sulfate surfactants.

Industrial applicability

Using the organic stabilizers, ester sulfate surfactants can be permanently protected against hydrolysis, which makes it possible to use these products outside of pH = 7 in surface-active agents such as washing, rinsing, cleaning and anti-aging agents as well as products for hair and body care . Another object of the invention therefore relates to the use of organic carboxylic acids, which have at least one hydroxyl group and / or an aromatic ring as a common structural feature, as a buffer for stabilizing aqueous ester sulfate surfactants. Examples

Examples 1 to 3, comparative examples V1 and V2. A 10% by weight aqueous solution of lactic acid dodecyl ester sulfate ammonium salt was adjusted to pH = 5.5 and then stored with or without 0.5% by weight buffer for 8 weeks at 25 ° C. in previously sterilized glass bottles. The results are summarized in Table 1:

Table 1:

Stabilization of lactic acid dodecyl ester sulfates

Examples V1 and 2 were repeated, but the samples were adjusted to pH = 5.6 and then stored at 45 ° C. over a period of 6 weeks. The non-buffered sample clouded after only 4 days, while the sample stabilized in the sense of the invention still had a pH of 5.5 after 6 weeks and was optically unchanged. The hydrolysis of the ester sulfate salts can therefore be reliably avoided by adding the organic acids.

Examples 4 to 7, comparative examples V3 to V6. Analogous to Examples 2 and V1, aqueous solutions of various lauric acid polyglycol ester sulfate salts (10% by weight of washing-active substance = 100%) were adjusted to pH = 5.5 and then with or without the addition of a buffer (0.5% by weight of benzoic acid) Stored for 3 months at 40 ° C. The results are summarized in Table 2: Table 2:

Stabilization of lauric acid polyglycol ester sulfates

Claims

claims

1. A process for the stabilization of aqueous ester sulfate surfactants, characterized in that the preparations are adjusted to a pH in the range from 5 to 8 and 0.1 to 1% by weight of organic carboxylic acids are added.

2. The method according to claim 1, characterized in that stabilizing hydroxycarboxylic acid ester sulfates which are selected from the group formed by the sulfation products of the esters of lactic acid, glycolic acid, tartaric acid, malic acid and / or citric acid with linear or branched, saturated or unsaturated primary alcohols with 6 to 32 carbon atoms in the form of their alkali, alkaline earth, ammonium, alkylammonium, alkanolammonium or glucammonium salts.

3. Process according to claims 1 or 2, characterized in that sulfation products of esters of lactic acid are stabilized with fatty alcohols having 12 to 18 carbon atoms in the form of their sodium or ammonium salts.

4. The method according to claim 1, characterized in that stabilizing fatty acid polyglycol ester sulfates of the formula (I),

RiCOO (AO) _x S0 ₃ X (I)

in which R ¹ CO is a linear or branched, saturated or unsaturated acyl radical having 6 to 22 carbon atoms, x is an average of 1 to 3 and AO is a CH2CH2O-, CH ₂ CH (CH ₃ ) 0- and / or CH ( CH ₃ ) CH ₂ 0 radical and X represents an alkali and / or alkaline earth metal, ammonium, alkylammonium, alkanolammonium or glucammonium

5. The method according to claims 1 or 4, characterized in that one stabilizes lauric acid polyglycol ester sulfates in the form of their sodium or ammonium salts.

6. The method according to claim 1, characterized in that stabilizing monoglyceride (ether) sulfates of the formula (II),

in which R ² CO stands for a linear or branched acyl radical with 6 to 22 carbon atoms, x, y and z in total for 0 or for numbers from 1 to 30 and X for an alkali or alkaline earth metal.

7. Process according to claims 1 and 6, characterized in that monoglyceride sulfates of the formula (II) are stabilized in which R ² CO is a linear acyl radical having 12 to 18 carbon atoms, x, y and z for 0 and X for sodium or Ammonium stands.

8. The method according to at least one of claims 1 to 7, characterized in that organic carboxylic acids are used which have at least one hydroxyl group and / or an aromatic ring as a common structural feature.

9. The method according to at least one of claims 1 to 8, characterized in that one uses organic carboxylic acids which are selected from the group formed by lactic acid, glycolic acid, malic acid, tartaric acid, citric acid, benzoic acid and salicylic acid.

10. Use of organic carboxylic acids which have at least one hydroxyl group and / or an aromatic ring as a common structural feature as a buffer for stabilizing aqueous ester sulfate surfactants.