I N D U S T R I A L -4 S D ELVGINEERINGCHE.MISTRY
July, 1929
685
Ethanolamine Soaps‘ Ralf B. Trusler2 & f E L L O l i I N S T I T U T E OF I X D V S T R I A L
RESEARCH, U N I V E R S I T Y OF
HE soaps obtained from the ethanolamines promise to
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become outstanding among the organic base soaps, because of the peculiar properties of the ethanolamine fatty mid compound, as well as the striking and unusual character of these hydroxyalkylamines themselves. The ethanolamines, from which ethanolamine soaps are made, are three in number-viz., mono-, di-, and triethmolamines. These compounds are synthesized from ammonia and fundamentally are substituted ammonia compounds, in which one or /H more of the hydrogen atoms of the compound S-H have \H ethanol group HO--C!H2-CHz’ Hence, by ”le reOf One hydrogen in there monoethanolamine, WO-CH,-CHs.
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which is chemically classifiedasa hydroxyalkylalnine’ Since each Of the hydrogen a t o m can be replaced by an ethanol group, three ethanolamines are obtain-
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Soaps have been m a d e f r o m f a t t y acids a n d t h e ethanolamines. These soaps have diversified properties which may bring t h e m i n t o technical importance. Among t h e prospective uses are t h e following: (1) They are excellent emulsifiers for vegetable, animal, a n d mineral oils; ( 2 ) they are thickeners for lubricating oils; (3) incorporated i n special compositions, they have detergent a n d cleaning utility; (4) t h e oleates are efficient dry-cleaning soaps, d u e t o their solubility i n organic solvents a n d t o their specific detergent a c t i o n ; (5) will cations.
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amines. including pH values, will be determined and reported in the future. The ethanolamines are basic compounds, as shown by their structural formulas. When dissolved in water, they are strongly alkaline to phenolphthalein. Titration wkth standard hydrochloric acid has shown that 1 mol of any one of the ethanolamines is equivalent to 1 mol of sodium hydroxide in combining Jyith an acid. Similarly, ethanolamines combine with fatty acids t o form soaps provided that the fatty acids belong to the soap-producing class. The reaction is strictly the formation of a soap and not an esterification, the latter case being possible only under certain dehydrating conditions.
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PITTSBURGH, PITTSBURGH,
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In the course of his researches Koganei (a)* found that monoethanolamine (or p-aminoethanol) was sufficiently basic to react with stearic and oleic acids to produce compounds having decided soap-like properties. This work was done w h e n monoethanolamirle was p r e p a r e d by tedious academic means. A few years later, the ethanolamines were approaching c o m m e r c i a 1 availability
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INDUSTRIAL A S D E-VGINEERING CHEMISTRY
approxima,tely correct quantities of both ethanolamine and the fatty acid could be run into the reaction kettle, and then the final necessary amount of either ingredient could be added to bring about a neutral product, as shown by testing portions of it by an indicator. This method so far has proved t o be unreliable, because even with methyl red in alcohol the color change from red to yellow occurs so slowly that uncertain results are had. The liquid fatty acids, such as oleic acid, permit the easy preparation of ethanolamine soaps. For example, let us consider the preparation of ethanolamine oleate from the technical oleic acid, which may be of either the ‘‘saponified” or the “distilled” variety. Analyses of distilled oleic acid have shown it to have usually an acidity of 97.5 per cent in terms of oleic acid, and the ethanolamine has been found to have such alkalinity that 100 grams will combine with 215 grams of pure oleic acid. (While the molecular weight of oleic acid is about 282.27, and that of triethanolamine is about 149.16, it has been mentioned that technical ethanolamine contains some of the lighter molecular weight ethanolamines, which increase the ratio of oleic acid to ethanolamine above the molecular proportions of 282.27 to 149.16.) Then, for every 100 kg. of ethanolamine there must be added 215/97.5, or about 220.511 kg., of oleic acid. The oleic acid is run into the container, which should be provided with a strong and slowly revolving stirrer. The entire amount of ethanolamine can be run in before stirring is begun. When stirring is finally started and the two ingredients are brought intointimate contact, reaction occurs with sufficient heat to keep the contents mobile during stirring. External heat does not promote the combination. Inasmuch as neither of the components appreciably vaporizes, there is no loss during the reaction. Water increases the viscosity of these soaps, and hence the ethanolamine should not contain over 10 per cent moisture, and preferably should be nearly anhydrous; otherwise stirring the reaction mixture will become more difficult. Combining solid fatty acids, such as stearic acid, with the ethanolamines requires slightly different treatment. Tn order to mix intimately a solid fatty acid with an ethanolamine to bring about complete reaction, two different procedures are availahle, namely: (1) The solid fatty acid may be melted and heated to about 60” C., and into it is stirred the correct quantity of ethanolamine, which has also been warmed to about 60” C. This preheating plus the heat of reaction will keep the soap sufficiently soft t o allow thorough stirring, otherwise the viscous product will solidify. (2) The stearic acid, or other fatty acid, may be dissolved in a solvent, such as denatured alcohol, to which the ethanolamine is then added with stirring. The soap may be recovered by evaporating the solvent. Physical Properties
The consistency of any one of the ethanolamine soaps, when anhydrous or nearly anhydrous, depends more upon the nature of the fatty acid employed than upon the particular ethanolamine. The oleate of monoethanolamine has the consistency of petroleum jelly, while the oleates of di- and triethanolamine are only slightly more viscid. Compared with these, monoethanolamine stearate is a hard, waxlike solid. Ethanolamine soaps are pale yellow t o reddish brown, depending upon the purity and color of the fatty acids employed, and, generally speaking, all these compounds have an agreeable, soapy odor. Those made from the higher fatty acids, such as oleic and stearic acids, are soluble in a great variety of organic solvents, which is one of their unusual and outstanding properties. They are dissolved readily by benzene, toluene, and similar compounds. Turpentine, alcohols, glycols, glycerol, ketones, and many aldehydes are excellent solvents for these soaps. It is surprising to note that even heavy petro-
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leum products, such as lubricating oils and petrolatum, will dissolve quite appreciable amounts. This is particularIy true of the oleate. In most cases, excepting the heaby oils, the ethanolamine soaps are soluble in the solvents in all proportions, yielding transparent solutions. Dilute water solutions of the ethanolamine soaps are opalescent and in some cases milky, somewhat resembling sodium soaps. The oleate in water solution froths readily and maintains its soapy character upon standing, but the stearate and, to a less extent, the palmitate hydrolyze, with subsequent partial separation of the fatty acid. Ethanolamine oleate is capable of taking up a considerable amount of water and still remaining jelly-like. The addition of water first causes an increase in the consistency of the soap, this effect continuing until the weight of the water absorbed is about equal to the weight of the soap. Further addition of water renders the soap more plastic and somewhat creamy. Ethanolamine stearate absorbs water in a somewhat similar manner, first becoming a translucent gel, and then with further hydration being converted into a viscous liquid. Applications
The study of the applications of the ethanolamine soaps has chiefly dealt with the oleates because of their ease of handling. These oleates are nearly liquid soaps and have comparatively high stability in the presence of water. The two classes of soaps-those from liquid fatty acids and those from solid fatty acids-are not interchangeable in their applications, each one having rather well defined adaptations. ETHAKOLAMINE OLE.4TE AS AN E~uLsrFrER-Ethanolamine oleate possesses striking emulsifying ability in promoting oil-in-water emulsions. These emulsions can be made in any one of the known technical ways, two simple methods being as follows: (1) The soap may be dissolved in oil, into which water may later be added with stirring to make the desired emulsion. The amount of soap required depends largely upon the nature of the oil involved. Some fatty oils-as, for example, linseed oil-emulsify with ease as compared with others and therefore require less soap. This same difference has been observed in the case of mineral oils. Ethanolamine oleate in the proper concentration will frequently produce excellent emulsifying action; however, in instances where the necessary amount of soap required t o render the oil emulsifiable is too great for economy or for other reasons, it will be found advantageous to incorporate rosin soap with the ethanolamine oleate. I n a general way, however, it may be said that from 6 to 10 per cent of soap on the basis of the oil is sufficient for making a good emulsion. It should be mentioned t h a t many fatty oils contain varying amounts of free fatty acids due t o the decomposition of their original glycerides. This fatty acid content can be converted into soap by stirring in the correct amount of anhydrous ethanolamine. The soap resulting from the neutralization of the free fatty acid by the ethanolamine will be soluble in the oil. Excessive moisture and an excess of the base tends t o make the soap insoluble in both fatty and mineral oil and to cause it t o precipitate out. The remainder of the soluble soap necessary to make the oil emulsifiable may then be added. There are instances where the incorporation of some other water-soluble ingredient, such as glycerol or alcohol, enhances the emulsifiability of an oil. Usually 6 to 10 parts of soap per 100 parts of oil should be dissolved in the oil during warming and stirring. A transparent or nearly transparent solution of soap in oil results, which may be stored for a stock from which emulsions may be prepared as needed. In order to prepare an emulsion from one of these compositions, it is only necessary t o add the desired amount of water, which should be stirred in slowly at first until the weight of water used is approximately 15 per cent of the weight of the oil. At this stage a creamy paste or a mayonnaise-like emulsion should result, and care should be taken that this mixing is complete because the success of the final emulsion depends largely upon the thoroughness of this operation. The dilution may then be completed by the further addition of water. Fatty-oiI emulsions of this nature appear to have many applications for non-edible purposes and excellent emulsions for textile oiling and fiber lubrication have been prepared.
July, 1929
IA'DUXTRIAL/ AA'D ESGI,VEERI.YG C H E X I S T R Y
Mineral oils may be similarly emulsified. Usually a little more soap is required than for fatty oils, but the necessary amount can be readily found by experimentation. A small amount of a fatty oil dissolved in a mineral oil will often enhance its emulsifiability. Linseed, cottonseed, soy bean, and lard oils have been found efficacious for this application, and doubtless there are many others. Since rosin soaps are soluble in ethanolamine oleate, this compound will be found an efficient carrier or mutual solvent, and will be particularly useful in compositions where comparatively large amounts of rosin and rosin soap are required in oil. hlineral-oil emulsions of this nature have shown some desirable features for cutting and grinding purposes. A universal formula for making emulsifiable oils cannot be given, unless one disregards the quantity of soap involved, because of the wide differences in the character of various oils, as well as the different purposes for which emulsions are required. It will be necessary for the experimenter to develop a formula for his own particular need. (2) . The other method for making emulsions from both fatty and mineral oils involves less soap than the foregoing procedure. To emulsify 100 grams of oil, first thoroughly mix 4 to 8 grams of ethanolamine oleate with 7 t o 12 cc. of water and when this has been reduced to a uniform, sticky consistency stir in the oil slowly and completely. This should produce a sort of mayonnaise-like emulsion, which probably will be unstable until additional water is incorporated. Usually an excellent, creamy emulsion will be obtained when 50 t o 100 cc. of water have been stirred into the oil a t this stage. The emulsification of fatty oils can be materially assisted by the addition of a small percentage of ethanolamine to the soap and water mixture before any oil is incorporated. In the case of mineral oils assistance may be gained by incorporating a small amount of fatty oil in the mineral oil before emulsifying it.
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prediction that the soap will be technically valuable. The fact that ethanolamine oleate is readily soluble in naphtha over a wide range of concentrations is a feature that makes it especially important, as it is easily adaptable t o special drycleaning formulas. I t is not necessary to employ an excess of the fatty acid to keep the soap in solution as is the practice for sodium, potassium, and ammonium soap compositions generally used for dry-cleaning purposes. This implies a corresponding decrease in the development of rancid odors in garments after cleaning, since there is no excess fatty acid to be rinsed out. The soap remains in solution in naphtha in the presence of appreciable amounts of water, which is a desirable feature for dry-cleaning soaps ( 1 ) . Alcohol
