US2345307A - Detergent composition - Google Patents

Description

Patented Mar. 28, 1944 2,345,307 DETERGENT COMPOSITION Emil A. Vitaiis, East Port Chester, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application March 19, 1943, Serial No. 479,783

4Claims. (01452-121) I This invention relates to a soap composition and more particularly to a detergent composition containing soap together with a mild aciditying agent and a dispersing agent capable of maintaining the detergency of the soap at low pH values.

Ordinary soap (by which term is meant the alkali metal salts of higher fatty acids-such as stearic, palmitic, oleic acid and the like) is strongly alkaline when in aqueous solution, since it is a salt of a weak organic acid with a strong base. Thus, for example, even high grade toilet soaps exhibit a pH of about 10.0-10.5 in water solution. It has long been recognized that this degree of alkalinity has a harmful and irritating action on the skin, and recently it has been shown that severe cases of dermatitis are traceable to this cause. It is a principal object of the present invention to provide a soap composition in which the natural alkalinity of the soap is reduced to a range wherein these undesirable properties are avoided.

It is a well known fact that soap loses its detergency upon the addition of water-soluble acids or acidic materials, even when it is only partially neutralized. Thus, for example, acidlflcation to a pH of only 8.5 will result in a complete loss of wetting and detergent properties, and at a pH of 8.0 the soap loses about 10-20% of its fatty acids content. When the acidification is continued to pH values of 7.2 to 7.4 about 50-60% of the fatty acids of the soap are liberated. These fatty acids possess no detergent properties and will separate out as a scum on the sides of the vessel and upon objects being washed. It is evident, therefore, that the admixture of ordinary soap with even relatively small quantities of an acidic material in an effort to reduce its natural alkalinity will only result in rapid deterioration and eventually in complete loss-of detergency of the soap.

My present invention is based on the discovery that mildly acidic materials such as boric acid. tartaric acid, sodium or potassium acid tartrate, sodium acid phosphate and the like can be added to soap in quantities sufiicient to reduce the alkalinity of the soap to a pH value of about 7.2-8.0 without destroying the wetting and detergent properties of the composition, .providing certain quantities of surface-active agent containing a single l0ng aliphatic chain of 8 or more carbon atoms are added to the composition. This discovery provides a soap composition which is only mildly alkaline and therefore has no deleterious action on the skin, but which has wetting, sudsing and detergent properties equal and in some cases better than those of ordinary soap.

I have discovered that certain surface-active agents characterized by the presence of a single long aliphatic chain of 8-20 or more carbon atoms in the hydrophobic portion thereof are extremely effective dispersing agents in soap compositions containing acidifying agents. It is well known that surface-active or wetting agents are organic compounds containing hydrophobic or oil-solubilizing groups together with hydrophilic or water-solubilizing groups, these two groups being balanced in such a manner that the molecules of the compound possess the property of orienting themselves at an oil-water interface. I have found that those compounds of this class which contain one (but not more than one). relatively long aliphatic radical of at least 8 carbon atoms possess the important property of dispersing or solubilizing free soap-forming fatty acids, and that they will cause soap to maintain its detergent power within the pH range of 7.2-8.0 when added thereto in the proper quantities.

The range of surface-active or wetting agents used in practicing the invention is not limited by the type or types of hydrophilic groups that may be present. In the great majority of commercial wetting agents the hydrophilic portion of themolecule consists of or contains a sulfuric acid derivative such as a sulfonic acid or sulfuric ester group, preferably neutralized with sodium,

' potassium or other salt-forming base which forms of a long aliphatic radical of 8-20 or more carbon atoms.

I believe that the efficiency of the above-described class of surface-active agents in maintaining the detergency of soap at the relatively low pH values of 7.2-8.0 is due principally to the long alkyl chains which they contain. It is a well-recognized fact that the detergency of soap is due to the formation of micelles, or

minute bundles of parallel rod-like soap molecules orientated at the interface between the water and the object to be washed, which possess the property of carrying grease, soot and other similar water-insoluble materials into solution. These micelles are ordinarily destroyed when the soap is even partially acidified. I believe, however, that dispersing agents containing a long alkyl chain have a natural afllnity for free fatty acids and will function'to retain these micelles intact under acid conditions.

That this property is a function of a single long alkyl radical and is not inherent in wetting agents generally is shown by the fact that a wide variety of well-known wetting agents have little or no dispersing action on soap in the pH range of 7.2-8.0 and will not prevent its loss of detergency in this range. Thus, for example, sodium, isopropyl and butyl naphthalene sulfonates, which possess only short' alkyl groups, and such highly active wetting agents as sodium dioctyl sulfosuccinate (sold commercially as "Aerosol T), tri(2-ethyl butyl) sodium sulfotricarballylate (sold as "Nekal NS) and higher secondary alcohol sulfates (sold as Tergitol"), which contain two relatively long alkyl groups,

' are ineffective for the purposes of the present invention. On the other hand the following classes of compounds, all of which contain ,a

single long allwl chain, are very effective for this All:

MOzS

I wherein M is a salt-forming base which forms a water-soluble sulfonic acid salt, such as alkali metal, ammonium and the like, Y is hydrogen or hydroxyl, X is hydrogen or a phenyl group and Alk is an alkyl radical of 8-20 carbon atoms. This alkyl radical may be connected with the phenyl radical directly by a carbon to carbon bond or.by means of an ether group, at any suitable point. Representative compounds of this type are available commercially under the trade names Nocconol NR, Keminol, Santomerse, "Triton NE" and Ultrawet. Nacconol NR." is the sodium salt of an alkylated benzene sulfonic acid obtained by condensing a chlorinated kerosene with benzene and sulfuric acid followed by neutralization with caustic soda. Keminol is a compound of the same general type in which phenol is substituted for the benbon atoms, but this material is sold as a product and therefore contains no added salt.

II. Esters of sulfonated carboxylic acids with a single higher aliphatic alcohol and esters of a single higher fatty acid with short-chain sulfonated alcohols. Typical examples and their tradenames are the following:

Disodium monolaurylsulfosuccinate, Aerosol NAL" Disodium monooleyl sulfosuccinate,

NAO

Sodium lauryl sulfoacetate, Nocconol LAL Sodium stearyl sulfopropionate, Igepon AP Trisodium monostearyl sulfotricarballylate III. Sulfonated higher primary aliphatic alco- Aerosol hols of 8-20 carbon atoms and sulfonated higher V. Unsuifonated amides and esters of higher fatty acids with polyamines and polyhydroxy polyamines, e. g. Ninol 737," which is a mixed fatty acid alkylol amine condensation product wherein the fatty acid contains 12 carbon atoms.

In preparing the detergent compositions of the invention I add to ordinary soap 8. sufllcient quantity of a mild acidifying agent to reduce the alkalinity of the soap to the desired pH of 7.2-8.0.

About 18-20% of boric acid, based on the weight of the soap, or equivalent quantities of monosodium dihydrogen phosphate, citric acid, monoor disodium citrate or sodium acid tartrate may be used for this purpose. The proper quantities of dispersing agent may be incorporated into the composition either before or after the acid is added in amounts dependent upon the activity of the particular dispersing agent used. Thus, for example, most of the higher alkyl-aryl sulfonates -of group I are used in amounts of 4-20% of the active dispersing agent, based on the weight of the soap and irrespective of additional quantities of sodium sulfate or other water-soluble salts that may have been included when the commercial product is used. However, I prefer to employ up to 50% of the product "Ultrawet since this is a a less powerful dispersing. agent. About 4-20% or more of the alkyl sulfonates and alcohol sulfates of group III should be employed while 5-30% of the sulfo acid esters of group II and of the sulfonated amides of group IV represent the proper quantities. In all cases the best results are obtained when quantities approaching the upper limits are employed. The compound "Igepon T is sold commercially as a 40% material, and 15-100% by weight of this material should be used, based on the weight of the soap, to obtain the best results. The sulfosuccinamates, on the other hand, are extremely active dispersing agents 'agent such as di(methyl amyl) sulfo-succinate on the order of -10%, based on the entire weight of the composition, may be employed. Perfumes, plasticizers and other similar ingredients may also be added if desired. The soap, acidifying agent, dispersant and auxiliary material are preferably blinded by mixing with a small amount of water, or by melting 'the soap and mixing in the other ingredients, after which the product may be molded into cakes in the usual manner. In this form it is well suited for general use as a toilet soap, particularly for those persons whose skins are sensitive to alkali. When larger quantities of water are added the product is an excellent shaving cream of the type ordinarily sold in tubes.

What I claim is:

l. A detergent composition comprising a major proportion of soap consisting essentially of alkali metal salts of fat acids, together with a quantity of an acidifying. agent sufficient to reduce the alkalinity of the soap to a pH of 7.2-8 and about 3-30%, based on the weight of the soap, of a surface-active agent containing a hydrophobic portion together with a hydrophilic portion, said hydrophobic portion containing a single long aliphatic radical of at least 8 carbon atoms.

2. A detergent composition comprising a major proportion of soap consisting essentially of alkali metal salts of fat acids together with a quantity of an acidifying agent sufilcient to reduce the alkalinity of the soap to a pH of 7.2-8 and 3-30%, based on the weight of the soap, of a surfaceactive agent selected from the group consisting of sulfonated amides of fatty acids containing at least 8 carbon atoms and monoamides of sulfonated carboxylic acids containing at least 8 carbons in the amide radical.

3. A detergent composition comprising a major proportion of soap consisting essentially of alkali metal salts of fat acids together with a quantity of an acidifying agent suflicient to reduce the alkalinity of the soap to a pH of 7.2-8 and 13-30%. based on the weight of the soap, of a surfaceactive agent of the formula MOzS -Alk alkalinity of the soap to a pH of 7.2-8 and 3-30%,

based on the weight of the soap, of a surfaceactive agent of the formula MO3S.R, wherein M is a salt-forming base which forms water-soluble sulfuric ester and sulfonic acid salts and R is a member of the group consisting of alkyl and oxyalkyl radicals containing at least 8 carbon atoms attached to sulfur near the end thereof.

EMIL A. VITALIS.