Title:  Thickened aqueous surfactant solutions

United States Patent:  6,300,508

Assignee:  Henkel Kommanditgesellschaft auf Aktien (Duesseldorf, DE)

Filed:  June 30, 1998

Fatty acid esters of alkylene glycols corresponding to the formula R¹ COO(AlkO)_n H are thickeners for aqueous surfactant solutions, particularly for personal care products.

DESCRIPTION OF THE INVENTION

Accordingly, the present invention relates to thickened aqueous surfactant solutions which are characterized in that they contain as organic thickeners fatty acid esters of alkylene glycols corresponding to formula (I):

R¹ COO(AlkO)_n H (I)

in which R¹ CO is a linear or branched, aliphatic, saturated and/or unsaturated acyl group containing 6 to 22 carbon atoms, Alk stands for --CH₂ CH₂ --, --CH₂ CH₂ CH₂ -- and/or --CH₂ CH(CH₃)-- and n is a number of 0.5 to 5.

In the context of the present invention, the expression "thickened" means that the thickened surfactant solutions have a demonstrably higher viscosity than the unthickened surfactant solutions, as determined by physicochemical methods, more particularly with a Brookfield viscometer. In addition, the terms "thickener" and "thickening agent" are used synonymously.

The fatty acid esters of alkylene glycols are products of the addition of ethylene oxide and/or propylene oxide to fatty acids with the formula R¹ COOH, where R¹ CO is as defined above. Typical examples are caproic acid, caprylic acid, 2-ethyl hexanoic acid, capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenic acid, elaeostearic acid, arachic acid, gadoleic acid, behenic acid and erucic acid and the technical mixtures thereof obtained, for example, in the pressure hydrolysis of natural fats and oils, in the reduction of aldehydes from Roelen's oxosynthesis or in the dimerization of unsaturated fatty acids. Technical fatty acids containing 12 to 18 carbon atoms, for example, cocofatty acid, palm oil fatty acid, palm kernel oil fatty acid or tallow fatty acid, are preferred.

Ethoxylated, propoxylated or ethoxylated and propoxylated fatty acids with a degree of alkoxylation n of 1 to 2 are particularly preferred. The fatty acids in question may be exclusively propoxylated fatty acids, exclusively ethoxylated fatty acids or both ethoxylated and propoxylated fatty acids, the ethoxylated/propoxylated fatty acids being both random and block compounds.

The ethoxylated and/or propoxylated fatty acids, which are also known as fatty acid esters of alkylene glycols, are known compounds. They may be prepared, for example, by reaction of carboxylic acids with alkylene oxides in the presence of amines as catalysts as described in U.S. Pat. No. 3,884,946, the entire contents of which are incorporated herein by reference. Better yields can be obtained for low-ethoxylated fatty acids by the process described in copending patent application Ser. No. 08/767,123, filed Dec. 9, 1996, the entire contents of which are incorporated herein by reference. In this process, the ethoxylation is carried out in the presence of alkanolamines as catalysts and gives distinctly higher yields. In the development of the present invention, it was found that the propoxylation or propoxylation/ethoxylation of the fatty acids can also be carried out in the presence of alkanolamines. Accordingly, the present invention also relates to a process for the production of fatty acid esters of propylene glycol corresponding to formula (II):

R¹ COO(PO)_n H (II)

in which R¹ CO has the same meaning as defined for formula (I), PO stands for --CH₂ CH₂ CH₂ O-- and/or --CH₂ CH(CH₃)O-- and n is a number of 0.5 to 5, and fatty acid esters of ethylene propylene glycols corresponding to formula (III):

R¹ COO(EO)_x (PO)_y (EO)_z H (III)

in which R¹ CO has the same meaning as defined for formula (I), EO stands for --CH₂ CH₂ O--, PO stands for --CH₂ CH₂ CH₂ O-- and/or --CH₂ CH(CH₃)O-- and x=0-5, y=0.1-5 and z=0-5, the sum of x and z being greater than 0 and the sum of x, y and z being in the range from 0.5 to 5, by propoxylation or propoxylation/ethoxylation of fatty acids, characterized in that the propoxylation or ethoxylation/propoxylation reaction is carried out in the presence of alkanolamines as catalysts.

Typical examples of alkanolamines suitable for use as basic catalysts are monoethanolamine, diethanolamine and preferably triethanolamine. The alkanolamines are normally used in quantities of 0.1 to 5% by weight and preferably in quantities of 0.5 to 3.0% by weight, based on the fatty acids.

The propoxylation and/or ethoxylation/propoxylation reaction may be carried out in known manner. The fatty acid and the catalyst are normally introduced into a stirred autoclave which is freed from traces of water before the reaction by alternate evacuation and purging with nitrogen. The fatty acid is then reacted with the propylene oxide or with the ethylene oxide/propylene oxide mixture in a molar ratio of 1:0.5 to 1:5 which may be introduced into the autoclave in portions through a siphon after heating. The fatty acids are preferably reacted with 1 to 2 moles of propylene oxide or with 1 to 2 moles of the mixture of ethylene and propylene oxide. The reaction may be carried out at temperatures of 80 to 180^oC. and preferably 100 to 120^oC. under autogenous pressures of 1 to 5 bar and preferably 2 to 3 bar. After the reaction, it is advisable to stir the reaction mixture for a certain time (15-90 mins.) at the reaction temperature in order to complete the reaction. The autoclave is then cooled, vented and, if desired, acids, for example, lactic acid or phosphoric acid, are added to the product to neutralize the basic catalyst.

The fatty acid esters of alkylene glycol of the type described above are normally present in the thickened aqueous surfactant solutions according to the invention in quantities of 0.2 to 5% by weight, based on surfactant solution. The surfactant solutions additionally contain 3 to 30% by weight of surfactants and 0 to 10% by weight of water-soluble inorganic and/or organic electrolyte salts. The balance to 100% by weight of the surfactant solution is water.

The surfactants may be ionic surfactants, nonionic surfactants or mixtures of ionic and nonionic surfactants.

Anionic, zwitterionic and cationic surfactants may be present as the ionic surfactants. Suitable ionic surfactants are distinguished by a lipophilic, preferably linear alkyl or alkylene group containing 8 to 18 carbon atoms and an ionic group dissociating in water preferably attached terminally thereto. The anionic group may be, for example, a sulfate, sulfonate, phosphate or carboxylate group. The cationic group may be, for example, a quaternary ammonium group. The ionic surfactants are preferably anionic surfactants. Typical examples of anionic surfactants are alkyl benzene sulfonates, alkane sulfonates, olefin sulfonates, alkyl ether sulfonates, glycerol ether sulfonates, .alpha.-methyl ester sulfonates, sulfofatty acids, alkyl sulfates, monoglyceride (ether) sulfates, fatty acid amide (ether) sulfates, mono- and dialkyl sulfosuccinates, mono- and dialkyl sulfosuccinamates, sulfotriglycerides, amide soaps, ether carboxylic acids and salts thereof, fatty acid isethionates, fatty acid sarcosinates, fatty acid taurides, acyl lactylates, acyl tartrates, acyl glutamates, acyl aspartates, alkyl oligoglucoside sulfates, protein fatty acid condensates (more particularly wheat-based vegetable products) and alkyl (ether) phosphates. If the anionic surfactants contain polyglycol ether chains, they may have a conventional homolog distribution although they preferably have a narrow homolog distribution. Preferred anionic surfactants are alkyl sulfates, fatty alcohol ether sulfates, alkane sulfonates and/or ether carboxylic acids, fatty alcohol ether sulfates being particularly preferred.

Instead of the anionic surfactants, cationic surfactants may also be present. Typical examples of cationic surfactants are quaternary ammonium compounds and esterquats, more particularly quaternized fatty acid trialkanolamine ester salts.

Zwitterionic surfactants may also be present either on their own or in admixture with another ionic surfactant providing there are no troublesome interactions. Typical examples of amphoteric or zwitterionic surfactants are alkyl betaines, alkyl amidobetaines, aminopropionates, aminoglycinates, imidazolinium betaines and sulfobetaines. Within this group, alkyl betaines and alkyl amidobetaines are particularly preferred. Alkyl betaines are known surfactants which are mainly produced by carboxyalkylation, preferably carboxymethylation of aminic compounds. Typical examples are the carboxymethylation products of hexyl methyl amine, hexyl dimethyl amine, octyl dimethyl amine, decyl dimethyl amine, dodecyl methyl amine, dodecyl dimethyl amine, dodecyl ethyl methyl amine, C_12/14 cocoalkyl dimethyl amine, myristyl dimethyl amine, cetyl dimethyl amine, stearyl dimethyl amine, stearyl ethyl methyl amine, oleyl dimethyl amine, C_16/18 tallow alkyl dimethyl amine and technical mixtures thereof.

Alkyl amidobetaines which represent carboxyalkylation products of amidoamines are also suitable. Typical examples are reaction products of fatty acids containing 6 to 22 carbon atoms, namely caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenic acid, elaeostearic acid, arachic acid, gadoleic acid, behenic acid and erucic acid and technical mixtures thereof, with N,N-dimethylaminoethyl amine, N,N-dimethylaminoproply amine, N,N-diethylaminoethyl amine and N,N-diethylaminoproply amine which are condensed with sodium chloroacetate. The condensation product of C_8/18 cocofatty acid-N,N-dimethylaminopropyl amide with sodium chloroacetate is preferably used.

In addition, nonionic surfactants may be present either on their own or in admixture with the ionic surfactants. Typical examples of nonionic surfactants are fatty alcohol polyglycol ethers, alkylphenol polyglycol ethers, fatty acid polyglycol esters, fatty acid amide polyglycol ethers, fatty amine polyglycol ethers, alkoxylated triglycerides, alk(en)yl oligoglucosides, fatty acid-N-alkyl glucamides, protein hydrolyzates (more particularly soya-based vegetable products), polyol fatty acid esters, sugar esters, sorbitan esters and polysorbates. If the nonionic surfactants contain polyglycol ether chains, they may have a conventional homolog distribution although they preferably have a narrow homolog distribution. Particularly preferred nonionic surfactants are alkyl and/or alkenyl oligoglycosides.

Alkyl and alkenyl oligoglycosides are known nonionic surfactants corresponding to formula (IV):

R² O--[G]_p (IV)

in which R² is an alkyl and/or alkenyl group containing 4 to 22 carbon atoms, G is a sugar unit containing 5 or 6 carbon atoms and p is a number of 1 to 10. They may be obtained by the relevant methods of preparative organic chemistry.

The alkyl and/or alkenyl oligoglycosides may be derived from aldoses or ketoses containing 5 or 6 carbon atoms, preferably from glucose. Accordingly, the preferred alkyl and/or alkenyl oligoglycosides are alkyl and/or alkenyl oligoglucosides.

The index p in general formula (IV) indicates the degree of oligomerization (DP degree), i.e., the distribution of monoglycosides and oligoglycosides, and is a number of 1 to 10. Whereas p in a given compound must always be an integer and, above all, may assume a value of 1 to 6, the value p for a certain alkyl oligoglycoside is an analytically determined calculated quantity which is generally a broken number. Alkyl and/or alkenyl oligoglycosides with an average degree of oligomerization p of 1.1 to 3.0 are preferably used. From the performance point of view, alkyl and/or alkenyl oligoglycosides with a degree of oligomerization below 1.7 and, more particularly, between 1.2 and 1.4 are preferably used.

The alkyl or alkenyl group R² may be derived from primary alcohols containing 4 to 11 and preferably 8 to 10 carbon atoms. Typical examples are butanol, caproic alcohol, caprylic alcohol, capric alcohol and undecyl alcohol and the technical mixtures thereof obtained, for example, in the hydrogenation of technical fatty acid methyl esters or in the hydrogenation of aldehydes from Roelen's oxosynthesis. Alkyl oligoglucosides with a chain length of C₈ to C₁₀ (DP=1.1 to 3), which are obtained as first runnings in the separation of technical C_8/18 cocofatty alcohol by distillation and which may contain less than 6% by weight of C₁₂ alcohol as an impurity, and alkyl oligoglucosides based on technical C_9/11 oxoalcohols (DP=1 to 3) are preferred.

In addition, the alkyl or alkenyl group R² may also be derived from primary alcohols containing 12 to 22 and preferably 12 to 14 carbon atoms. Typical examples are lauryl alcohol, myristyl alcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol, brassidyl alcohol and the technical mixtures thereof obtained as described above. Alkyl oligoglucosides based on hydrogenated C_12/14 cocoalcohol with a DP of 1.1 to 3 are preferred.

In a particularly preferred embodiment of the invention, the surfactants to be thickened are mixtures of anionic surfactants, preferably alkyl ether sulfates, and zwitterionic surfactants, preferably alkyl amidobetaines, and nonionic surfactants, preferably alkyl (alkylene) oligoglucosides, the ratio by weight of the mixtures preferably being from 1:1:1 to 10:1:1.

Suitable inorganic electrolyte salts are any water-soluble alkali metal, ammonium and/or alkaline earth metal salts, such as the fluorides, chlorides, bromides, sulfates, phosphates and nitrates providing they are soluble in water at 20^oC. in a quantity of at least 1% by weight. The chlorides or sulfates of an alkali metal, ammonium or magnesium are preferably used. Sodium chloride (common salt) and magnesium chloride are particularly preferred.

Suitable organic electrolyte salts are, in particular, any water-soluble alkali metal, ammonium and alkaline earth metal salts of mono-, di- and tricarboxylic acids. Carboxylic acids with a molecular weight of less than 200 g/mole are preferred.

In addition, the aqueous formulations according to the invention may contain other components which make them suitable for the particular application envisaged. For example, they may contain small amounts of fragrances, dyes, opacifiers and pearlescers, antimicrobial agents, preservatives, active skin-care substances, plant extracts, protein hydrolyzates, buffers, complexing agents and other known auxiliaries and additives typically present in shampoos, bath additives, shower baths, liquid skin-cleansing preparations, liquid hair shampoos and in liquid laundry and dishwashing detergents and liquid domestic cleaners based on ionic surfactants.

Increasing the viscosity of aqueous solutions of the described type with a comparatively small amount of organic thickeners and inorganic thickening electrolyte salts is of particular interest from the applicational point of view. By using the described fatty acid esters of alkylene glycols, the thickening effect of the inorganic electrolyte salts is enhanced, above all synergistically, so that the quantity of inorganic electrolyte salts used can be reduced for the same viscosity.

Finally, the present invention also relates to the use of the fatty acid esters of alkylene glycols corresponding to formula (I) as organic thickeners for aqueous surfactant solutions.

Claim 1 of 20 Claims

What is claimed is:

1. A process for the production of a fatty acid ester of an ethylene-propylene glycol of the formula (III):

R¹ COO(EO)_x (PO)_y (EO)_z H (III)

wherein R¹ CO is a linear aliphatic, saturated or unsaturated acyl group, or a combination thereof, having from about 6 to about 22 carbon atoms, EO is --CH₂ CH₂ --, PO is --CH₂ CH(CH₃)O-- or --CH₂ CH₂ CH₂ O-- or a combination thereof, and x=0 to about 5, y=about 0.1 to about 5 and z=0 to about 5, such that the sum of x and z is greater than 0 and the sum of x, y and z is in the range from about 0.5 to about 5, comprising reacting a fatty acid having from about 6 to about 22 carbon atoms with an alkylene oxide selected from the group consisting of propylene oxide, ethylene oxide or a combination thereof, in the presence of an alkanolamine.

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