The Ethanolamines CHESTER B. K R E M E R The City College, The College of the City of New York, New York City
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THE ethanolamines, the chemist h d s another example of chemical substances which, just laboratory specimens a t first, are today of great practical importance. So diversified and numerous are the uses of these materials that it would take many pages fully to outline all their applications. This article will touch only upon comparatively few of the more common or interesting uses. The ethanolamines are the simplest members of that group of organic compounds known as amino alcohols. They were lirst synthesized (1) in 1862 when a German scientist reacted ethylene oxide with ammonia under pressure and, after fractionation of the resulting liquid, obtained a few grams of a strongly alkaline, water-white liquid, somewhat ammoniacal in odor. Analysis proved it to have the formula NHzCHzCHzOH and it was given the name "colamine." From the reaction mixture two more distinct compounds were obtained, one boiling a t 268'C. and the other a t 195'C. (under 10 mm. pressure). The chemical reactions of these two products showed them to he closely related to colamine and their structures were soon proved to be:
is a salt formed by the combination of a base (usually sodium or potassium hydroxide) with a fatty acid (such as stearic or palmitic acids). Using triethanolamine as the reacting hase, instead of potassiam or sodium hydroxide, results in the formation of a triethanolamine soap.' These soaps are soluble in ordinary dry cleaning solvents such as xylene or naphtha. A dry cleaning solvent incorporating such a soap exhibits, in addition to its usual solvent action, the emulsifying action of the organic soap. Thus the volume of solvent required in a given cleaning is materially reduced and a corresponding saving is effected. The use of simple componnds derived from the ethanolamines is widespread in the field of cosmetics ( 4 , 5 , 6 ) . In the main, these compounds are used as emulsifiers. Practically all cold, cleansing, and vanishing creams are emulsions of oil or oily materials in water. However, in order to prepare emulsions of this type, a third substance must he present to keep the emulsion from separating. Separation occurs when the tiny droplets of dispersed material come together to form increasingly larger and larger drops until finally the oil separates completely and floats on top of the water. To prevent this separation an emulsifying agent, such as an CH2CH20H ethanolamine soap, is added to the starting materials. / H-N Triethanolamine soaps are ideal emulsifying agents for \ cosmetic preparations because of their complete lack of alkaline irritation effect. Moreover they aid in the absorption of various oils by the skin and are external Since the three substances differed from one another in antiseptics. A typical cleansing cream is one made of the number of ethanol (-CH1CH20H) residues, they stearic acid, lanolin, mineral oil, triethanolamine, became known as monoethanolamine (formerly called water, and terpineol. The latter is added to mask the colamine), diethanolamine (I), and triethanolamine odor of lanolin. Perfumes and agents to retain the (11). As a group, they are today called the ethanol- moisture of the emulsion are invariably added. amines. Not only certain derivatives of the ethanolamines, Since the ethanolamines are alcohols as well as but the ethanolamines themselves find valuable use in amines, their adaptability is based upon the properties the cosmetic industry. Thus, materials used in the of both classes of compounds. When to these are added permanent waving of women's hair contain monothe specific properties of each molecular substance, it ethanolamine. The latter is used here chiefly as a is not difficultto understand their versatility. source of ammonia. Ordinary ammonia in solution is Perhaps one of the most common uses of the etha- diilicnlt to employ because it is so easily lost when the nolamines in industry is their use as gas absorbers (2); solution is heated. Monoethanolamine, however, gives in this instance, advantage is taken of their basic prop- off ammonia slowly when heated, due to decomposition erties. Either the mono-, di-, or triethanolamine can of the molecule. This slow process assures the presbe employed; all are capable of absorbing large quan- ence of the latter ingredient during the entire operatities of an acidic gas. Carbon dioxide, for example, is tion. readily taken up and any non-acidic gas contaminated Of passing interest is the use of the ethanolamines in with COz can be freed of this constituent merely by depilatories. Their function here is that of a solvent, bubbling the mixture of gases through the ethanol- it having been established that the sulfur componnds amine. On heating the solution, the carbon dioxide is employed in depilatories are much more soluble in a freed from combination and the amino alcohol can then hase cream incorporating the amino alcohol. be used again to absorb fresh quantities of gas. In the dry cleaning industry, triethanolamine soaps 1 wateris not split out in the formation of the triethanolamine are of great practical importance (3). Ordinary soap soap.
Perhaps the three most interesting uses of these ethanolamine derivative, diethyl aminoethyl alcohol. amino alcohols are their applications in the production Novocaine is prepared by treating this latter substance of dyes, drugs, and explosives. When cellulose acetate with p-nitrobenzoyl chloride, thus forming diethyl and cellulose nitrate silks began to attain the impor- aminoethyl p-nitrobenzoate. This is then reduced to tance they now hold in the textile world, i t was evident Rive d i c t y l arninoethyl p-aminobcnzoate. The hythat a new branch of dye chemistry would have to be drochloride of the latter is known as norocaine. evolved. Many of the dyes previously developed for the dyeing of natural silk were found to be useless when GH5>N-CH,CHz-O-CCIHs Hsl applied to acetate or nitrate silk. Research soon developed new dyes for these silks, in the synthesis of Novocaine which- the ethanolamines played a prominent role While novocaine is widely used, it is far from the (7, 8). A valuable cellulose acetate dye, for example, is synthesized from 2,4-dichloronitrobenzeneand mono- ideal anesthetic because of its lack of pressor action. ethanolamine as follows: For this reason, novocaine is often mixed with adrenalin before injection, the latter acting as a vasoconNO* H NO. H . strictor. A tremendous amount of research has been H;-&-CH~CH~OH camed out in an effort to produce a local anesthetic which, in the same molecule, will exhibit both anesthetic and pressor action. Recently some success has been attained and once again the ethanolamines play a This dye, 2-(5-chloro-2-nitroani1ino)-ethanol, in which leading part (10, 11). From monoethanolamine, a the only chromophore group is the nitro group on the derivative with a mono alkyl substitution on the amine benzene ring, imparts a yellow color to cellulose ace- nitrogen was synthesized, and this was then condensed tate silks. An entire series of these compounds, dif- with p-nitrobenzoyl chloride and the resulting product fering in substituted groups, have been synthesized reduced as in the production of novocaine. This comand have found application as dyes. pound, iso-butylaminoethyl p-aminobenzoate, exhibits The use of monoethauolamine in the synthesis of not only pronounced anesthetic properties, but pressor certain explosives is of increased interest due to war action as well. The formula of this compound is: conditions existing today. The best known explosive CH, CHs of this type is called "Pentryl" (9), an appreciably \ / more powerful explosive than TNT (trinitrotoluene). C-H I Its chemical name is sym-trinitrophenylnitraminoethyl nitrate. The product is synthesized in two stages. First, 2,4-diuitrochlorobenzeneis condensed with monoethanolamine to give 2 - (2,5-diuitroanilino) -ethanol: Thus today it is not suprising to find the ethanolamines highly valued for commercial use. New uses for these compounds and their derivatives are constantly being found. Few chemicals have, in such a short time, attained as general a use as the ethanolamines which, from their start in test tubes, now are shipped across country in tank cars. Then this product is nitrated with nitric acid to give Pentryl: LITERATURE CITED (1) WURTZ, "Ueber die Oxyathylenbasen," Ann., 121, 226 W-N-CHnCHsON02
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In the field of physiologically active compounds, the ethanolamines well as-many amino alcohols) play a most important role. Here, however, i t is not the simple amino alcohol, but rather a derivative of this substance that is of importance. In this short article, only two of many important illustrations will be givenboth in the field of local anesthetics. The most widely used of all local anesthetics is the compound novocaine, which is synthesized from an
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(2) FRYDLANDBR, "The ethanolamines and their industrial use," Reu. plod. chim., 33.3337 (1930). (3) HARVEY,"Triethanolamine," Am. Dyestuff Reph., 19, 1 9 K - 7 110'2nl ,A"-",. (4) WILSON,"Triethanolamine emulsions," J. I d . Eng. Chem., 22, 143-6 (1930). (5) JANL~TYN, "Use of triethanolamine and its derivatives in cosmetics," Chimie el Indudrie. 28, 134 (1932). (6) DE NAYARRE, "Triethanalamine emulsions." Am. Perfumer, 27, 650-2 (1933). (7) British Patent 403,118, "The coloration of materials made of or containing cellulose esters or ethers" (1932). (8) French Patent 781.430, "Fabrication de colorants" (1935). (9) CLARK."Analogs of tetryl I. Trinitrophenylnitraminoethyl nitrate (Pentryl);' J. Id. Eng. Chem., 25,1385-90 (1933). (10) GOLDBERG AND WEITMORE,"Preparation of para-aminobenzoic esters of monoalkylaminoalcohols." J.Am. Chem. Soc., 59,2zsO (1937). (11) British Patent 482,886, "Loeal anesthetic bases" (1936). AU"
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